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Most previous studies introduce high dose CO 2 (＞0.05 %) into fresh cement paste during mixing (CO 2 -mixing) to sequester CO 2. However, this strategy results in poor workability and lower long-term strength. This study attempts to use a lower CO 2 -mixing dose (0.017–0.083 wt.‰) to improve the performance of fresh and hardened cement pastes. The planar distribution, morphology, and evolution of the reaction products over time were investigated. The results showed that all the lower CO 2 -mixing fresh pastes displayed a good workability, and the compressive strength was increased by 0.3–21.7 % at 1–28 days. The enhancement in compressive strength was attributed to the formation of monocarbonate (Mc), deriving from the reaction of nano-CaCO 3 covering the clinkers with the aluminum phase, which strengthened the interface bond between the clinker and the new hydration product. Moreover, the generated nano-CaCO 3 also resulted in local high supersaturation on the clinker surface and promoted the formation of nano-Ca(OH) 2 embedded in the calcium silicate hydrate (C-S-H). As a result, the compactness of the hydration products was enhanced. The refinement in the microstructures of the low-dose CO 2 -mixed samples was translated into enhanced mechanical properties. [Display omitted] • Extremely low CO 2 -mixing dose yields better workability and mechanical properties. • Intimate nanoscale mixture of C-S-H and nano-CH/CaCO 3 reduces porosity. • Formation of monocarbonate strengthens interface bond force. • Nucleation effect of nano-CaCO 3 induces formation of thicker and ordered C-S-H rim. [ABSTRACT FROM AUTHOR]

Basalt fiber is widely used in pavement engineering for its strong mechanical properties, while its smooth surface can cause it to slip within the asphalt mixture, weakening the overall structure. In addressing this issue, this study explores the application of a titanate coupling agent (TCA) for surface treatment of the fibers. The aim was to enhance the interfacial adhesion between the fiber and the asphalt, consequently improving the crack resistance of the fiber-asphalt mixture. This study delves into the modification mechanism and chemical grafting process of TCA, employing scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Furthermore, digital image correlation (DIC) was utilized to dynamically monitor the semicircular bending test (SCB) specimens under full loading conditions, facilitating a comprehensive evaluation of the damage evolution process. Through comparative analyses of load-displacement profiles, full-field strain, displacement, and crack development, alongside the characterization of the fracture process zone (FPZ), a multi-scale quantitative assessment was conducted on the cracking characteristics of the asphalt mixtures. Throughout the damage evolution process, the toughening and crack-blocking effects of the modified fibers were extensively evaluated. Concurrently, SEM was employed to observe the fiber distribution and microscopic morphology of the fracture surface, shedding light on the mechanism of action of TBF (Treated basalt fiber) from a microscopic perspective. The augmentation of TBFAM (Treated basalt fiber Asphalt Mixture) is systematically elucidated, demonstrating that, in comparison with the other two asphalt mixtures, TBFAM exhibits prolonged microcrack formation time and a slower rate of crack propagation. The strain at the crack initiation point increased by 1.45 %, with a concurrent 2.49 % increase in the high strain area, indicative of its superior crack resistance. TCA facilitates the generation of a biomimetic coating via chemical grafting, thereby enhancing the surface structure of basalt fibers and fortifying the fiber-asphalt interface bonding ability. The favorable surface structure of TBF fosters a three-dimensional network within the asphalt mixture system, offering functionalities such as bridging, adsorption, toughening, and crack prevention. This impedes crack development and further bolsters the stability of TBFAM. [Display omitted] • The titanate coupling agent can be firmly attached to the fiber surface，forming octopus-like bionic coating structure. • The fracture of asphalt mixture was divided into four stages, and the toughening and crack resistance effect of TBF was quantitatively analyzed. • The spatial structure, crack resistance, bridging, toughening and adsorption of TBF in the system were analyzed and discussed from the microscopic point of view by SEM analysis. [ABSTRACT FROM AUTHOR]

Given the low reactivity and difficulty in large-scale utilization of lithium slag (LS), this study successfully synthesized highly reactive alkali-fused LS(ALS) through NaOH treatment and thermal activation, and analyzed the mechanism behind its enhanced reactivity. The results indicate that, under alkali erosion and high-temperature conditions, the Si-O and Al-O bonds within the LS become more susceptible to breaking. The non-bridging oxygen content increased from 37.8 % to 47.1 %, and the amorphous phase content rose from 15.9 % to 54.3 %. Consequently, more Si4+ and Al3+ can dissolve in an alkaline environment, enhancing reactivity. Based on this, a one-part geopolymer (OPG) was prepared for the first time by gradually replacing slag with ALS. The results showed that the incorporation of ALS extended the setting time of the OPG but reduced its compressive strength. At a 60 % substitution level, the initial setting time of the OPG was 81 minutes, and the compressive strength after 28 days of curing reached 50.6 MPa. Through XRD, SEM, and TG analysis, it was evident that the primary product of the OPG is N(C)-A-S-H gel. Since the reactivity of ALS remains lower than that of slag, increasing the proportion of ALS in the geopolymer system consumed more alkali while reducing the formation of N(C)-A-S-H gel, thus decreasing the compressive strength of the OPG. However, the slight incorporation of ALS did not significantly reduce the strength of OPG and effectively improved the setting time of the geopolymer. This reduction in slag consumption while promoting the resource utilization of LS in cementitious materials is beneficial. • The amorphous phase content of alkali-fused lithium slag increased to 54.2 %. • Alkali fusion facilitated the leaching of Si4+ and Al3+ from lithium slag. • The geopolymer prepared with alkali-fused lithium slag achieved a strength of 50.6 MPa. [ABSTRACT FROM AUTHOR]

In the process of service, the coating is vulnerable to ultraviolet radiation, which leads to aging failure. The metakaolin base geopolymer coating studied in this paper has excellent mechanical and anti-corrosion properties through the previous mix ratio study. However, the UV aging resistance of the coating is unknown. In response to this issue, the present study devised UV aging experiments for metakaolin based geopolymer coatings. Employing UV irradiation in conjunction with EIS tests, the aging resistance of the geopolymer coatings was assessed through electrochemical fitting and analyses such as SEM. The study delves into the structural evolution of metakaolin based geopolymer coatings under UV aging conditions. After 500 h of ultraviolet irradiation, the resistance of the geopolymer coating is enhanced, its water diffusion coefficient is reduced, two orders of magnitude increase the resistance of the coating, and the protection performance of the geopolymer coating is enhanced. In the control group, the waterproof performance of epoxy resin decreased significantly, the impedance decreased, and the resistance decreased by three orders of magnitude. SEM results show that the post-curing of the coating under UV irradiation continuously generates NASH gels, and the coating microstructure is dense. The results show that geopolymer has strong aging resistance. • This experiment investigates the mechanism of UV ageing resistance of metakaolin base geopolymer coatings. • Comparison with epoxy resin coatings concludes that the geopolymer coatings have very good UV aging resistance. • The system of evaluating the water resistance and porosity of the coatings by capacitance method based on Fick's law of diffusion is applicable to the geopolymer coatings. • UV irradiation induces a post-curing reaction of the geopolymer coatings. [ABSTRACT FROM AUTHOR]

This study investigated the feasibility of applying defect-containing recycled aggregates (RA) in ultra-high-performance concrete (UHPC) and studied the effect of nanosilica (NS) and steel fiber (SF)) together on its modification. The effects of RA substitution rate, SF content and NS content on the flexural behavior and microstructure of RA-UHPC were analyzed by four-point bending test. The experimental results showed that the specimens without added SF exhibited a linear elastic growth on the load-deflection curve, with a sharp decrease in load after the peak without a significant falling segment. In contrast, the specimens with added SF showed a typical three-phase characteristic with a smoother and flatter descending phase. The cross-distributed SF improves the ductility of the specimens after the peak by bridging effect and changes the damage behavior from quasi-brittle to ductile. Increasing the SF content significantly improved the flexural strength and toughness of the specimens, while increasing the RA substitution rate and NS content slightly decreased the flexural strength. The trends of the residual strengths calculated by the two methods were basically the same, while the specimens with brittle failure had almost no residual strengths. In addition, crack locations could be predicted prior to peak loading using digital image correlation techniques, while SEM analysis revealed the pore space between the cement matrix, interfacial transition zones, and fibers, as well as the ameliorating effects of SF and NS on micro- and macro-scales. These findings are valuable for understanding the flexural mechanism of fiber-nanocomposite concrete. ● RA-UHPC was prepared by incorporating RA in UHPC and co-modified with NS and SF. ● SF improves the flexural strength and toughness of RA-UHPC and transforms its brittleness into ductile failure. ● DIC measurements captured the initiation and evolution patterns of cracks. ● NS filled material's pores and improved ITZ structure between SF and the matrix. [ABSTRACT FROM AUTHOR]

• The synergistic modification of RAC with nano-silica and hybrid fibers were investigated. • The workability, strength, and microstructure of RAC with different parameters. • DIC measurement effectively displays crack propagation. • 3D-CT scanning characterizes NS particles changing specific pore spaces. The present study was conducted to meet the demand of the construction schedule for emergency repair and construction in special projects by using the recycled aggregates produced by mechanically crushing the demolished materials on-site. The study aims to modify recycled aggregate concrete (RAC) by incorporating silica nanoparticles (NS) and mixed fibers together to meet the needs of the above special project. Here, the properties of 21 kinds of concrete with different NS contents and mixed proportions of fibers were tested, including their fresh properties, hardening properties and microstructure. Their working properties in the fresh state were studied by measuring slump and unit weight; while the mechanical properties after hardening were mainly evaluated in terms of compressive strength, splitting tensile strength, modulus of elasticity and flexural strength, and here the flexural toughness as well as the residual strength of the specimens were calculated using two methods. In addition, the effects of different NS contents, steel fibers and polyvinyl alcohol (PVA) fibers on crack development and water absorption were investigated in the microstructure. The pores between the cement matrix, interfacial transition zone (ITZ) and fibers and how they are alteredby NS were characterized by SEM and 3D-CT scans. All these results indicate that NS content has a significant effect on both the workability and mechanical properties of RAC, that steel fibers are beneficial to improve the overall mechanical index of RAC, while PVA fibers have a limited enhancement effect, and that NS particles in the microstructure help to fill the pores of 0.001–0.01 mm3 volume in the cement matrix and improve the performance of the ITZ. [ABSTRACT FROM AUTHOR]

• Pressurized carbonation with presoaking process was used to improve RCA. • The fracture property of RCAC with RCA treated by carbonization was evaluated. • The microstructure changes of carbonated RCA and RCAC were discussed. Carbonation is effective in enhancing recycled coarse aggregate, but the shortage of carbonizable Ca2+ in recycled coarse aggregate and the low permeability efficiency of CO 2 at ambient pressure limit the carbonation efficiency and industrial application. To solve these issues, the Ca2+ content in recycled coarse aggregate and the carbonation effectiveness were increased by presoaking recycled coarse aggregate in calcium hydroxide and enhancing the carbonation pressure, respectively. The optimal carbonation condition was obtained based on the physical properties of the recycled coarse aggregate and the strength of recycled coarse aggregate concrete: the carbonation pressure was 4 bar, and the concentration of the calcium hydroxide solution was 0.04 mol/kg. The fracture behaviour and microstructure of the recycled coarse aggregate concrete under different carbonation conditions were evaluated. The recycled coarse aggregate concrete after pressurized carbonation with presoaking in calcium hydroxide solution (RCAC-C0.04-P4) has higher toughness and a more stable crack propagation process than untreated recycled coarse aggregate concrete. Pressurized carbonation with presoaking in calcium hydroxide solution significantly increased the initial cracking load, peak load, Young's modulus, initial toughness, unstable toughness, and fracture energy of the recycled coarse aggregate concrete by 67.35%, 2.83%, 12.19%, 60.77%, 2.31%, and 5.38%, respectively, and reduced the critical crack mouth (CMOD c) and tip opening displacement (CTOD c) by 9.13% and 10.96%. Simple pressurized carbonation made the toughness of the specimens worse than that of untreated recycled coarse aggregate concrete. Compared with untreated recycled coarse aggregate concrete, although the initial toughness, unstable toughness, and fracture energy of recycled coarse aggregate concrete after simple pressurized carbonation (RCAC-P4) were increased by 16.02%, 1.86%, and 0.28%, respectively, the Young's modulus was slightly reduced by 1.35%, and the CMOD c and CTOD c were increased by 5.37%. In addition, a microstructural analysis showed that the contents of Ca(OH) 2 and CaCO 3 of RCAC-C0.04-P4 were increased by 50.56% and 37.62% compared to untreated recycled coarse aggregate concrete, respectively, and the average indentation modulus of the old aggregate and old mortar interface of RCAC-C0.04-P4 was increased by 24.37% compared to untreated recycled coarse aggregate concrete, which confirmed that pressurized carbonation with presoaking in a calcium hydroxide solution made CaCO 3 fill the cracks in the interface and improved the macroperformance. These results can promote the application of recycled coarse aggregate in engineering. [ABSTRACT FROM AUTHOR]

Anisotropic mechanical characteristics are crucial to the application of the printed structure. This study is aimed to investigate the effects of interval time and interfacial agents on the anisotropic mechanical strength of ultra-high toughness cementitious composite under 3D-printed technology. The bending capacity of ultra-high toughness cementitious composite under 3D-printed technology was compared with mould-casting ultra-high toughness cementitious composite. The compressive strength, flexural strength and splitting tensile strength were measured to represent mechanical properties in different directions and the microstructure of ultra-high toughness cementitious composite under 3D-printed technology with different interval time and interfacial agents were characterized using nanoindentation, scanning electron microscopy, and X-ray computed tomography. The experimental results indicated that the ultimate bending strength and bending toughness of ultra-high toughness cementitious composite under 3D-printed technology were 13.6% and 3.3% to 13.3% higher than those of mould-casting ultra-high toughness cementitious composite at 28 d, respectively. As the interval time increased, the mechanical properties showed differential development patterns. Specifically, compressive strength and splitting tensile strength had a higher rate of decline in the X direction (parallel to the printing path) than in the Y and Z directions but flexural strength was the opposite. A 3-h interval time reduced the 28-d compressive strength and splitting tensile strength in the X direction by 24.02% and 49.64% but the strength only decreased by 10.57% and 26.59% in the Z-direction. The addition of interfacial agents reduced anisotropy in compressive strength and splitting tensile strength but increased the anisotropy of flexural strength. When the interval time was 3 h, the increase rate of the 28-d flexural strength in the X direction, in which the flexural strength was weakest, was 22%–29% lower than that in the Y and Z directions under the effects of interfacial agents. A microstructure analysis showed that the filling effect and high moisture content of interfacial agents counteracted the negative impact of interval time on the width of the interface between layers and the porosity of ultra-high toughness cementitious composite under 3D-printed technology, which can enhance the interlayer bonding. These results can promote the application of ultra-high toughness cementitious composite under 3D-printed technology in additive manufacturing. [ABSTRACT FROM AUTHOR]

• The multi-scale characteristics of normal concrete and UHPC interface are evaluated by both experimental and molecular dynamics simulation methods. • Revealing the effects of moisture and bonding adhesive agents on the bonding behavior of NC-UHPC. • Comparison of macro bonding properties of NC-UHPC and the nano mechanism of calcium silicate hydrate and epoxy interfaces. In this paper, moisture conditions and epoxy bonding agents on interfacial behavior between normal concrete (NC) and ultrahigh performance concrete (UHPC) were investigated by both experiment and molecular dynamics (MD) simulation methods. The NC was exposed to different moisture conditions and bonding agents prior to UHPC reparation. The bonding strength was studied by slant shear and splitting tensile tests. A quantitative analysis of backscattered electron images as well as X-ray diffraction were applied to study the microstructure of the overlay transition zone (OTZ) between NC-UHPC. In addition, molecular dynamics (MD) simulation was combined with the macro experiments to explore the bonding mechanism between calcium silicate hydrate (C-S-H) and epoxy adhesive agents. The results show that UHPC is a promising repair material for concrete structure reinforcement/reparation with excellent bonding strength. The splitting tensile strength increases with a higher area ratio of NC to UHPC under the same substrate conditions, but varies when different adhesive agents are applied. Waterborne epoxy resin (WEP) can improve the bonding property of an imperfect NC substrate, while this improvement effect decrease with a smooth NC substrate. On the other hand, bisphenol-A-type epoxy resin (E51) has a negative effect on the bonding property. Finally, NC substrate moisture has no significant influence on the microstructure of OTZ and bonding strength. The MD results show, the growth of bonding strength between C-S-H and epoxy by adhesive agent is negligible while toughness can be improved to a certain extent. This work provides multi-scale new insight for understanding the bonding mechanism on NC-UHPC. [ABSTRACT FROM AUTHOR]

• Fast-hardening early-strength geopolymers fabricated at ambient temperature. • The product of geopolymer made with UMK has only the NASH phase. • With the increase of sodium hydroxide concentration, the internal macropores of UMK geopolymer gradually evolved into mesopores. • The time for UMK geopolymer to reach optimum strength is related to sodium hydroxide concentration. Geopolymer is a new type of green gelling and environmental protection material, but the curing temperature limits the application of geopolymer in the construction industry. In this paper, the effects of NaOH on the pore structure and mechanical properties of ultrafine metakaolin (UMK) geopolymers under room temperature curing conditions were investigated. In this experiment, different concentrations of alkaline activators were prepared by changing the concentration of NaOH in the composite alkaline activator, and geopolymers were prepared with different alkaline activators and UMK. Different UMK geopolymers have been extensively analyzed to characterize their pore distribution, pore structure, and mechanical properties. The relationship between NASH gel and NaOH concentration was quantified by simultaneous thermal analysis (TG-DTG) and X-ray diffraction (XRD). The evolution of pore distribution and pore structure of UMK geopolymers with NaOH concentration was characterized by scanning electron microscopy (SEM) and proton nuclear magnetic resonance spectroscopy (1H NMR). The results show that UMK only generates the NASH phase in the geopolymerization reaction. With the increase of sodium hydroxide concentration, the formation of NASH gel increases, and the crystallinity of the sample increases. SEM and 1H NMR results show that the UMK geopolymer prepared with a high concentration of NaOH is fully hydrated and has a dense structure. Through comparative analysis of UMK geopolymer pore distribution and pore structure characteristics, it was found that the porosity of UMK geopolymer decreased with the increase of sodium hydroxide concentration. The proportion of small pores did not change much, while the large pores gradually evolved into mesopores. In addition to this, curing time was found to have no significant effect on geopolymer microstructure and strength development. This research provides a theoretical basis for the practical engineering application of UMK. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO 2 -mixing dose decreased the flowability but enhanced the early cement hydration. • The presence of fly ash can offset the flowability loss. • Low CO 2 -mixing dose (<0.6 %) slightly improved the early compressive strength. • Micro cracks formed in CO 2 -mixing pastes degraded the 28 days strength. Injecting CO 2 in the fresh cement-based mixture during mixing could considerably lower the workability. In this study, fly ash (FA) was used as a cement replacement at 10, 15, and 20 wt.% to overcome the CO 2 -injecting caused negative impact. The effects of CO 2 -mixing dose (injected during fresh stage) on the fresh, mechanical and microstructural performances of cement pastes were examined. The experimental results showed that FA resulted in a lower hydration heat and improved the blended cement paste workability. At a fixed FA content of 20 % and with the presence of a relatively lower CO 2 -mixing dose (0.3 and 0.6 %), the formation of CaCO 3 on the clinkers can act as a nucleation site to promote the hydration of cement and fill the pores in the matrix to reduce the pores, resulting in a 3.3–8.2 % improvement of the early compressive strength at 1 and 3 days. However, at a relatively higher CO 2 -mixing dose (0.9 and 1.2 %), prolonging the curing ages to 7–28 days resulted in a slightly decrease in the compressive strength due to the excessive CaCO 3 covering on the clinker surface and the formation of micro-pores and cracks between the clinker and the new hydration products. It can be concluded that below 0.3 % CO 2 dose can be mixed in the FA blended cement pastes for the production of environmentally-friendly CO 2 -sequestrating construction materials. [ABSTRACT FROM AUTHOR]

• Glass-ceramic was prepared using granite powder and waste marble by melting-sintering method. • The addition of MgO changes the main crystalline phase of the glass–ceramic from wollastonite to augite. • The acid resistance of glass-ceramics is weakened with the increase of basic oxide content in the chemical composition. • The glass–ceramic with flexural strength of 146.95 MPa and Vickers hardness of 10.24 GPa can be achieved. A large amount of solid waste is generated during the stone processing, and a serious environmental issues has arisen from the accumulation of these wastes. In this work, granite powder and waste marble are used to prepare architectural glass–ceramic. The mechanical properties, microstructure, and acid resistance of glass-ceramics designed with different compositions were investigated. With the increase of waste marble content, the main crystalline phase of glass–ceramic changed from anorthite to wollastonite, and the flexural strength of glass–ceramic was also enhanced. When the mass ratio of granite powder to waste marble is 40:60, a CaO-Al 2 O 3 -SiO 2 (CAS) glass–ceramic with a flexural strength of 109.33 MPa and a Vickers hardness of 6.61 GPa is obtained. After the addition of MgO, the main crystalline phase of the glass–ceramic is augite. Under the addition of 5 wt% MgO, the flexural strength and Vickers hardness of CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) glass–ceramic reached the maximum, which are 146.95 MPa and 10.24 GPa, respectively. The mechanical properties of these two types of glass-ceramics developed from granite powder and waste marble can meet the requirements of building materials. From the acid resistance test results, it was found that the higher the content of MgO and CaO in the chemical composition of glass–ceramic, the worse the acid resistance. Therefore, the basic oxide content should be carefully controlled in the composition design of glass–ceramic. This technology of converting granite powder and waste marble into value-added glass–ceramic provides a promising method for the utilization of solid waste from stone processing, which can greatly improve the sustainability of the stone industry. [ABSTRACT FROM AUTHOR]

• Sodium-montmorillonite (sMT) is functionalized with a non-ionic surfactant. • The interlayer structure of sMT is modified with improved vapor and water sorption. • Improved pozzolanic reactivity and dispersion in the cement matrix are abtained. • Improved cement hydration degree with more C-S-H and Al-rich phases are obtained. • With functioalized sMT, cement microstructure is densified with improved strength. This study investigates the hydration behavior and phase evolution of portland cement composites containing montmorillonite (MT) with an objective to address the poor dispersion and improve physical features and chemical reactivity of MT through functionalization with a non-ionic surfactant (polyethylene glycol ether). After functionalization, the MT exhibited an enlarged layer spacing (122%), organic chemical bonds intercalated, improved dispersion in concrete pore solutions, reduced moisture sorption capacity. The cement composites containing the functionalized MT showed enhanced cement hydration, less portlandite, more calcium silicate hydrates (C-S-H) and aluminum-containing hydrates, a more densified microstructure, and higher strength than the composites with raw MT. [ABSTRACT FROM AUTHOR]

• GO i mpacts on strength, water absorption and ASR durability of mortar are studied. • GO is positive to anti-penetration of mortar at long-term rather than initial stage. • GO is valid in control ASR expansion of mortar, and more valid with more glass bead. Alkali-silica reaction (ASR) is a slowly occurring reaction in concrete between alkaline pore solution and reactive non-crystalline silica in aggregates, which is a challenge to physical property and durability of concrete. The oxygen-containing functional groups coupled with large surface area of graphene oxide (GO) nanomaterial renders highly reactive interaction with cement-based composite. Here, the physical properties and ASR expansion test of cement mortars modified with varied loadings of GO (w GO) or/and Pyrex glass (GOPM) were implemented after optimizing GO dispersion efficiency in water. The water absorption and microstructures of GOPM were observed to figure out the mechanism of GO's effect on mechanical strength, permeability, and ASR expansion of GOPM. Results show, 15 kJ is the optimal sonication energy for the dispersion of 300 mL pristine GO-water suspension with 0.04% w GO ; the effect of GO on improving the flexural and compressive strength of GOPM is remarkable, the maximal amplitude is up to 24.16%, 43.03% compared with the baseline, respectively; GO has great influence on long-term anti-permeability and controlling expansion, the nano-nucleation and interlocking effect of GO render the expansion rate of GOPM be well below 0.1% threshold. [ABSTRACT FROM AUTHOR]

This study proposes to premixing CO 2 with 10 % of cement and water before blending it with the remaining 90 % of cement powder, aiming to address the substantial workability loss caused by CO 2 -mixing at the fresh stage and promote a higher amount of CO 2 uptake. Four different CO 2 dosages (0.06, 0.6, 6, and 12 % by weight of 10 % cement) were systematically examined. The results reveal that the carbonated 10 % cement slurry exhibits a remarkable 4.78 % CaCO 3 content, accompanied by the formation of needle-like and flocculent reaction products on the surface of carbonated particles. This led to an increase in the particles' specific surface area and interparticle frictional force, subsequently resulting in a reduced sedimentation rate and a minor decrease in pH. However, no workability loss was noticed. In the early curing stages (1–7 days), all CO 2 -mixed samples manifest a noteworthy 7–18 % increase in compressive strength. However, this increment shows a slight reduction with extended curing times up to 28 days. This trend may be attributed to the formation of numerous microcracks in the matrix, particularly evident in samples with higher CO 2 concentrations (0.6 % and 1.2 %). [Display omitted] • Surface of carbonated cement particles is covered by numerous reaction products. • CO 2 -mixed cement pastes possessed comparable workability to control sample. • Higher strength compared to control sample is obtained with high CO 2 dosage. • The hydration of cement pastes is promoted at low CO 2 dosages. • Excessive CO 2 induces micro cracks on the surface of samples at later stages. [ABSTRACT FROM AUTHOR]

• Sonication is more efficient than manual stirring for the dispersion of nanoparticles. • Better dispersed nanoparticles can bring additional benefits to the strength of geopolymer. • Nanosilica particles accelerate the reaction at the early stage, especially with better dispersion. • Nanosilica increases micro elastic modulus of gel by 15.18% and 29.93% for different samples. • Dispersion can make the particles play a better filling effect and have a more uniform distribution. Nanosilica-geopolymer composites with different dispersion levels of nanoparticles were investigated on the physical properties and gel properties. The results indicated that compared with the nanosilica-geopolymer composites without ultrasonic dispersion, the 20 and 120 min of sonication brought 3.88% and 13.59% of additional strength enhancement, respectively. For the micromechanical properties of N-A-S-H gel, the better dispersed samples exhibited higher elastic modulus. In comparison to the reference sample, the elastic modulus was increased by 15.18% and 29.93% respectively for samples with 20 and 120 min of sonication. The better dispersed nanoparticles exhibited smaller sizes and increased the physical filling effect which could result in densified microstructures, better bonding behaviors and the both improved micro and macro mechanical properties. [ABSTRACT FROM AUTHOR]

• A lithium-slag-based one-part geopolymer is prepared. • Amount of lithium slag and the activator moduli affect mechanical and microstructure properties. • Reasonable compressive strength of up to 32.5 MPa is achieved at 28 days. Lithium is an important yet scarce energy material with great significance to the national economy and defense industry. However, a large amount of lithium slag (LS) is discharged in the production process. This paper proposed a high-volume and efficient utilization method of LS to synthesize LS geopolymer cement through a one-part mixing method. The effects of LS on the workability and mechanical properties of the LS-based geopolymer were investigated. The hydration process, products, and microstructures of LS-based geopolymers were studied. The results showed that LS had a negative effect on the fluidity of the geopolymer, yet hydration heat of LS geopolymer was lowered. The optimal 28d compressive strength of geopolymer reached 32.5 MPa in case of 50% LS used, which could be used as low-quality construction material in the producing place of LS. [ABSTRACT FROM AUTHOR]

• High-volume iron tailing powder (HVITP) concrete has lower total temperature rise. • Properties of HVITP concrete are poor compared with high-volume fly ash concrete. • Later-age properties of HVITP concrete are adversely affected by high temperature. • Reducing water/binder ratio or adding slag improves the properties of HVITP concrete. • The use of HVITP concrete in massive concrete engineering should pay more attention. The mechanical properties, microstructure and permeability of high-volume iron tailing powder (HVITP) concrete and high-volume fly ash (HVFA) concrete were comparatively investigated by measuring the adiabatic temperature rise, rate of temperature rise, compressive strength, splitting tensile strength and chloride permeability grade of concrete and determining the pore structure, bound water content and morphology of paste. The total adiabatic temperature rise of HVITP concrete are lower than that of HVFA concrete. But the early higher rate of temperature rise of HVITP concrete is obtained. The HVITP concrete shows low compressive strength and splitting tensile strength, coarse pore structure, loose microstructure and high chloride permeability compared with HVFA concrete with the same water/binder ratio. The early temperature matching curing (TMC) adversely affects the later-age properties development of HVITP concrete, but it promotes the properties development of HVFA concrete. The decrease in water/binder ratio or the partial replacement of ITP with slag improves the properties of HVITP concrete, especially for the early properties under TMC condition. But these two means still lead to properties difference between HVITP concrete and HVFA concrete due to the low reactivity of ITP. [ABSTRACT FROM AUTHOR]

The direct use of stainless steel slag in cement presents potential weaknesses in terms of strength and the risk of cracking, which limits its large-scale utilization. Therefore, it was crucial to explore the use of stainless steel slag in clinker cement. In this study, the hydration characteristics of stainless steel slag cement (SS) and ordinary Portland cement (OPC) were compared and analyzed using isothermal calorimetry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), and heavy metal leaching tests. The study investigated the hydration heat, compressive strength at curing ages of 1d, 3d, 5d, 7d, and 28d, hydration products, and safety aspects of SS and OPC. Results showed that the optimum calcination temperature of stainless steel slag cement (SC) and Portland cement (PC) are 1350℃ and the holding time is 2 h. The clinker composition of the two is similar. The main minerals are dicalcium silicate (C 2 S), tricalcium silicate (C 3 S), tricalcium aluminate (C 3 A) and aluminum ferrite tetracalcium (C 4 AF). Compared with OPC, SS shows a delayed heat release peak during hydration. SS exhibited a delayed exothermic peak in the heat release during hydration compared to OPC. Furthermore, during the stable hydration period, SS produced more calcium aluminate-type solid solution, tightly encapsulating the crystal surface, and exhibited lower heat release. With an increase in curing age, the contents of acicular ettringite (AFt), C-S-H gel, and hexagonal calcium hydroxide (CH) gradually increased in both SS and OPC. Due to higher contents of C 4 AF, C 3 S, and C 2 S in SS, it produced more AFt and C-S-H than OPC. The compressive strength of both SS and OPC increased with curing age, reaching 55.4 MPa and 42.4 MPa at 28 days, meeting the requirements of the national standard (GB/T 21372-2008) in terms of initial and final setting times and f -CaO content. Additionally, heavy metal leaching and soluble Cr6+ tests indicated that their use is safe. • The hydration mechanism of cement was investigated by comparison and multi-means experiment. • Stainless steel slag cement has low heat release and reduces the risk of cracking. • The hydration products of stainless steel slag cement have more flocculent C-S-H, acicular AFt, and hexagonal Ca (OH) 2. • Using 15% stainless steel slag instead of limestone calcined cement is feasible, 13 MPa higher than Portland cement, and is conducive to carbon reduction. [ABSTRACT FROM AUTHOR]

• For the fresh mortar with WGP, Modified Bingham model is more suitable for estimating the yield stress (τ 0) and H-B model is more appropriated to interpret the plastic viscosity. • The flow index (n) remains relatively minor scatter and change slightly, ranging from 0.6 to 0.88; the plastic viscosity varied with a little fluctuation with the scope of 4.0 Pa·s to 5.94 Pa·s. • The contents of the WGP had great influences on the autogenous shrinkage of the mortar, the tremendously change mainly taken placed in the rapidly increase stage. • The addition of WGP can further reduce the heat of hydration of the hardened cement paste, and the rate of hydration heat peaked at about 20 h, there is no reaction occurred for 49.38 μm WGP with calcium hydroxide (CH). To achieve a much better utilization the medium and small particle size of WGP, this study investigated the effect of WGP with different particle sizes (6.63 μm, 18.33 μm, 30.15 μm and 49.38 μm) and replacement ratios (3.0 %, 6.0 %, 9.0 %, 12.0 % and 15.0 %), as the supplementary cementitious materials, on the performance of the mortar. First, the rheological properties of the fresh mortar was evaluated by using Bingham model, Modified Bingham model, and H-B model; Second, the autogenous shrinkage and dry-wet cycling deformation of the hardened mortar were monitored; Finally, the micromorphology, weight loss and crystalline structure of hydration products were analyzed by SEM, TG and XRD. The results show that, for the fresh mortar with WGP, Modified Bingham model is more suitable for estimating the yield stress (τ 0) and H-B model is more appropriated to interpret the plastic viscosity. As the averaged diameter of WGP increased, the yield stress (τ 0) emerged a reversed S-shaped variation tendency; the flow index (n) remains relatively minor scatter and change slightly, ranging from 0.6 to 0.88; the plastic viscosity varied with a little fluctuation with the scope of 4.0 Pa·s to 5.94 Pa·s. The contents of the WGP had great influences on the autogenous shrinkage of the mortar, the tremendously change mainly taken placed in the rapidly increase stage; with the condition of same WGP content, the particle size of the WGP has a minimal impact on the autogenous shrinkage; under the drying and wetting cycle environment from 28 days to 140 days, the deformation rate changed in a way of sinusoidal wave. The addition of WGP can further reduce the heat of hydration of the hardened cement paste, and the rate of hydration heat peaked at about 20 h, there is no reaction occurred for 49.38 μm WGP with calcium hydroxide (CH). [ABSTRACT FROM AUTHOR]

• Quarry sludge can be used as a siliceous material for autoclaved bricks preparation. • Ca(OH) 2 is an ideal calcium source for producing press-moulding quarry sludge-based autoclaved bricks. • The dissolution of SiO 2 in quarry sludge can be optimized by adjusting autoclaved parameters. • The optimum parameters are 200 °C of curing temperature, theoretical Ca/Si ratio of 0.83, and 15 h of exposing time. Quarry sludge (QS) is a common by-product of quarry mining and the subsequent aggregate washing process, but its utilization in construction materials was limited by fine particle size and high crystallization. This paper assesses the feasibility of reusing QS as siliceous materials to prepare a novel eco-friendly brick via press moulding and autoclave treatment. Three types of calcium sources including CaO, Ca(OH) 2 , and CaCO 3 were employed to evaluate the binding efficiency with QS by using X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC) and scanning electron microscopy (SEM). The effect of curing temperature, Ca/Si ratio and exposing time on the reaction activity of QS were estimated, and their roles on the microstructure and compressive strength of QS-based bricks were evaluated. Results demonstrate that the activity of QS can be effectively activated by Ca(OH) 2. The morphology of the curing phases is determined by the dosage of QS. Moderating curing temperature (160 °C to 200 °C) and exposing time (≤15 h) contribute to higher reaction activity of QS and favor the generation of plate-like tobermorite and C-S-H, which induced a denser structure of QS-based autoclaved bricks and further promoted the strength development. In addition, 24 h of exposing time induced the transformation from tobermorite to xonotlite, prejudicing the strength of QS-based autoclaved bricks. Considering the performance and energy consumption, the optimum manufacturing parameters of QS-based autoclaved bricks are curing at 200 °C for 15 h, with a Ca/Si ratio of 0.83. Under this treatment, the compressive strength of QS-based autoclaved brick is as high as 49.9 MPa with a QS dosage of 63.5%. In addition, an assessment of the mobility of heavy metals associated with QS-prepared bricks reveals that autoclaved treatment can solidify heavy metals and QS-based autoclaved bricks can be regarded as an environmentally friendly building product. This research provides a foundational framework for the efficient utilization of QS through hydrothermal activation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We studied static tensile, fatigue property and moisture absorption of CFRP plates with DW, AS, NI invasion for 2 years. • We got 3 prediction formula by S - N curve, Whitney's, and Sendeckyj's method. • We studied fatigue failure mechanism of CFRP with DW, AS invasion by microstructure and thermal behavior. Abstract Moisture absorption rate (M t), static tensile strength (f u), fatigue life (N), stiffness degradation curves of unidirectional pultruded CFRP plates during two years distilled water (DW), alkaline solution (AS), and non-immersion (NI) were comprehensively studied along with their thermal behavior, microstructure and fatigue failure mechanism; Their stress level (S)- N curves were further fitted and predicted by three methods. Results reveal, the N of the pultruded CFRP plate with AS is much lower than those with DW and NI. The corresponding microstructure deteriorations with AS are more serious, and the resin ripples under higher S and AS are much more and bigger than with DW and NI. When the N reaches 2 million, the allowable S in S - N prediction curves is 69.28% f u , 68.72% f u and 60.75% f u with NI, DW and AS for 2 years, respectively. The corresponding allowable S in Whitney's method and Sendeckyj's method with a reliability of 95% is 73.39% f u , 72.72% f u , 68.55% f u and 65.00% f u , 65.93% f u , 54.41% f u , respectively. [ABSTRACT FROM AUTHOR]

• The effects of BF on the mechanical properties of CAC at different curing ages are studied. • Detailed chloride contents brought by coral aggregates of BFRCAC are recorded, including total and free chloride content. • Water absorption and sorptivity properties of BFRCAC are investigated. • TG-DTG and FE-SEM are used to study microstructure of BFRCAC. With the development of marine technology, the potential of coral aggregate concrete (CAC) for use in the construction of reefs has been identified. However, the shape, surface structure, high porosity, and chloride-ion-carrying properties of coral aggregates yield special microstructures and affect the mechanical properties and durability of CAC. This study investigates the effect of basalt fiber (BF) on the mechanical properties, chloride content carried in coral aggregates, and water absorption of CAC. The results indicate that with the increase in fiber content, the mechanical properties and water absorption resistance of basalt fiber reinforced coral aggregate concrete present an increasing trend then followed decreasing trend. Furthermore, 0.05% BF yields the highest improving effect on the mechanical properties and water absorption resistance at 28 days. Compared with the reference concrete, the compressive strength and splitting tensile strength of CAC with 0.05% BF increase by 9.87% and 1.36% at 28 days, respectively. When the fiber content continues to increase, the strengthening effect decreases, and cause adverse effects. The dissolution of chloride in coral aggregates was accelerated by 0.05% BF, while the chloride dissolution was inhibited by 0.1%–0.2% BF. Moreover, the microstructure of CAC is investigated to elucidate the enhancement mechanism of BF in terms of thermogravimetric analysis, theoretical total pore volume, fiber bonding performance, and fiber-matrix interfacial characteristics. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of nano-TiO 2 addition on properties of fluidized bed fly ash based geopolymer. Compressive strength, drying shrinkage, carbonation and microstructure of fluidized bed fly ash based geopolymer incorporating nano-TiO 2 were reported. Geopolymer specimens were prepared by alkali activation of fluidized bed fly ash in sodium silicate and sodium hydroxide solutions and were cured in microwave radiation environment plus a heat curing period. Properties for geopolymer with and without nano-TiO 2 were assessed and compared. The experimental results reveal that the addition of TiO 2 enhances both the early and later age compressive strength of geopolymer with the increasing content of nano-TiO 2 . The strength enhancement effect of nano-TiO 2 on geopolymer is more obviously when 5% nano-TiO 2 is introduced at 28-day. Microstructure analysis uncovers that the addition of nano-TiO 2 promotes the formation of geopolymer and results in compact microstructure with less cracks. The incorporation of nano-TiO 2 particles improves the carbonation resistance and reduces the drying shrinkage of geopolymer. [ABSTRACT FROM AUTHOR]

Shotcrete is extensively used in underground engineering and other fields. In cold regions, the initial shotcrete lining of tunnels is repeatedly frozen and melted several times in a single year when temperatures alternately change. Thus, the freeze-proof durability of shotcrete is significantly impacted by the freeze–thaw cycle. Computed tomography (CT), a non-destructive scanning method, was adopted to demonstrate the process of shotcrete microstructural damage in a freeze–thaw environment. CT scanning results showed that looseness and slippage of the cement mortar became increasingly apparent and that the number of internal micro-pores significantly decreased with increasing number of freeze–thaw cycles. In addition, the axial compressive strengths of the shotcrete prism specimens significantly decreased. After 300 freeze–thaw cycles, the total number of micro-pores in specimens DR1-1 and DR1-2 decreased by 50.32% and 34.20%, respectively, and the axial compressive strength loss reached 63.78%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gap-graded blended cement pastes presented comparable chemical shrinkage with Portland cement paste. [•] Most of chemical shrinkage occurred after the formation of skeleton structure, leading to reduced autogenous shrinkage. [•] The microstructure of gap-graded blended cement paste was dense and homogeneous. [•] Shrinkage stress was small and uniformly distributed in gap-graded blended cement paste. [•] Gap-graded blended cement paste presented smaller volumetric deformation and superior resistance to cracking. [Copyright &y& Elsevier]

Mining and beneficiation processes are accompanied by the discharge of large quantities of tailings, which occupy large areas of land and cause environmental pollution, which is a significant concern. This study prepared an environmentally friendly geopolymer using sulfur tailings and granulated blast furnace slag (GBFS) and characterized its performance and mechanism analysis. A low-cost and efficient CaO-Na 2 SiO 3 composite activator and comprehensive utilization method for sulfur tailings have been proposed. The experimental results showed that the CaO-Na 2 SiO 3 composite activator can improve the strength of STBG, especially the early strength. The highest 28d compressive strength of STBG can reach 32.2 MPa when the CaO content in the composite activators was 10%. However, when the CaO content in the activators was greater than 10%, the cumulative pore volume and harmful pore volumes of the STBG increased to 0.17 mg/L and 0.07 mg/L respectively, and the compressive strength developed slowly in the later period. In addition, the highest immobilization efficiency of STBG for Cu, Pb, and Mn can reach 99.9%, 93.9%, 91.6% respectively. The STBG can effectively immobilize heavy metals. • CaO-Na 2 SiO 3 composite activator can improve the early strength of sulfur-tailings-based geopolymer (STBG). • The maximum 28 d compressive strength of STBG can reach 32.2 MPa. • The addition of hybrid solid activator calcium oxide can promote the formation of C-A-S-H/N-A-S-H gel. • STBG can effectively solidify heavy metal elements such as Cu, Pb, and Mn. [ABSTRACT FROM AUTHOR]

• Performance of RPC with different fibre dosages after high temperature is discussed. • After 300 ℃, the strengths of all RPC begin to drop as temperatures rise. • RPC showed increasing mass loss and water absorption when temperature increases. • RPC with with 2% steel fibre and 0.15% PP fibre showed the best performance. • Equations between the residual strengths and the temperatures are established. This research was aimed to evaluate the performance of reactive powder concrete (RPC) mixed with steel fibre and polypropylene (PP) fibre after exposure to 20 ℃–800 ℃. The volume contents of steel fibre and PP fibre are (2%, 0%), (2%, 0.1%), (2%, 0.15%) and (2%, 0.2%), respectively. Residual mechanical properties of cubic compressive strength and split-tensile strength were measured. Besides, physical parameters such as mass loss and appearance change after different temperatures have also been determined. The thermal deterioration of RPC is assessed by water absorption and sorptivity. Results show that the residual strength increased from ordinary temperature to 300 ℃. However, it's decreased gradually as temperatures rise. RPC with 2% steel fibre and 0.15% PP fibre showed the best performance regarding spalling resistance and mechanical characteristics compared to the others. In addition, all specimens showed increasing in mass loss and water absorption with the increasing temperature. Based on the experimental results, equations to express the relationships of the strength with the heating temperatures are established. Distinct changes in the microstructure of RPC reveal mechanical properties from a macroperspective. [ABSTRACT FROM AUTHOR]

• PCE-type GA was synthesized by grafting acylamino groups and hydroxyl groups. • PCE-type GA led to shorter grinding duration with homogenized particle morphology. • Cement ground by PCE-type GA showed higher fluidity and mechanical strength. Modified polycarboxylate-type (PCE-type) grinding aid (GA) by grafting acylamino group and hydroxyl group into the backbone of PCE polymer was synthesized, and its possibility to be adopted as cement GA was estimated in this research. The grindability of PCE-type GA was measured in terms of grinding duration as well as particle size distribution, and the grindability of PCE-type GA was systematically compared with that of triethanolamine (TEA) and ordinary PCE-type superplasticizer. The cement hydration kinetics, the microstructure, and the physical–mechanical properties of ground cement samples in the function of PCE-based GA were analyzed. The results indicated that PCE-type GA was more effective in cement grinding process than TEA as well as PCE-type superplasticizer, exhibiting shortened grinding duration, optimized particle size distribution, and homogenized particle morphology. And cement ground by PCE-type GA was characterized with lower water demand, higher fluidity property, and increased mechanical strength, ascribed to the dispersion capability of PCE polymer as well as the unified cement particle size distribution. The application of PCE-type GA could slightly prolong the induction period of the ground cement, but gently enhance the hydration degree. Lower porosity and denser microstructure with higher density of cement hydration products uniformly distributing in the hardened matrix could be achieved with PCE-type GA adopted in the ground cement. [ABSTRACT FROM AUTHOR]

This study investigated the interfacial bond performances between ordinary Portland cement concrete (OPCC) and self-compacting geopolymer concrete (SCGC). The studied factors include nano-SiO 2 , repair material type, curing time, casting direction, and interface pretreatment method. The interfacial bond performances were assessed by Bi-surface shear and drying shrinkage tests. The evolutions in elemental compositions, hydration products, and microstructure in the matrix and interface were verified by BSE/EDS, XRD, and FTIR tests, respectively. ANOVA analysis was conducted to quantitatively analyze the influences of each factor from a statistical approach. The results demonstrated that the bond strength of SCGC increased by 24.5% to 31.7% compared to conventional OPCC. Meanwhile, geopolymers exhibited more compact microstructures but higher drying shrinkage (ε sh,u =891 µε). While nanofillers significantly amplified the cracking potential of geopolymers, which was attributed to the higher early-stage autogenous shrinkage instead of drying shrinkage. The SCGC showed a high enrichment degree of calcium at the interface, indicating that more calcium-rich products were formed. In contrast, the use of nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions, which provided extra nucleation sites for the polymerization of (C, N)-A-S-H gels. The nano-SiO 2 enhanced the intensity of the hydroxide ion and Si-O-T band and promoted the formation of (C, N)-A-S-H gels. The ANOVA analysis proved that the repair material, nano-SiO 2 , and interface treatment were significant factors to affect the interfacial bond strength. In addition, geopolymer-based repair materials were less sensitive to the casting direction, which differed from the conventional self-compacting OPCC. [Display omitted] • Geopolymer concrete at the same strength grade has 25-30% higher bond strength than conventional OPCC. • Nanofillers amplified the cracking potential of geopolymers due to higher early-stage autogenous shrinkage. • nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions. • geopolymer-based repair materials were less sensitive to the casting direction. [ABSTRACT FROM AUTHOR]

The widespread use of magnesium oxychloride cement (MOC) can effectively solve the waste problem in the potash industry. However, its poor water resistance limits its practical application. Electrolytic Manganese Residue (EMR), as a solid waste from manganese metal smelting, requires an effective utilization method. In this work, we have attempted to incorporate EMR into MOC after its treatment in order to improve the water resistance of MOC and increase the utilization rate of EMR. The addition of EMR to MOC increased the density of MOC. The incorporation of EMR did not significantly reduce the strength of the MOC samples. The incorporation of EMR reduced the relative content of magnesium oxide in the specimens and EMR can be used as a source of soluble Al, Si and Fe to produce insoluble amorphous gels. The combined effect resulted in an effective improvement in the water resistance of the samples. The 28-day water immersion strength of the EMR100 can reach 38.3 MPa, and its water resistance coefficient was 82.10%. The appropriate doping of EMR can improve the pore structure of the specimens, reduce the porosity and refine the pore size distribution. Carbon emission per unit compressive strength and cost per unit compressive strength were used as evaluation indices of environmental and economic benefits. A high dosage of EMR-incorporated MOC resulted in low cost and carbon emission, especially the strength of the specimen after water immersion as a strength index. Taking into account the strength after 14 days of air curing and 28 days of water immersion, the advantages of cost per unit compressive strength and carbon emission per unit compressive strength of EMR100 were further extended and reduced by 86.23% and 22.15% respectively compared to the benchmark group. The heavy metal curing of EMR was evaluated by ion leaching test, and the result showed that MOC effectively cured the heavy metal ions in EMR and reduced the environmental risk of EMR. The good performance of EMR in MOC systems not only provides an effective breakthrough for the efficient utilization of EMR and its heavy metal curing, but also effectively improves the performance of MOC and reduces the production cost. [Display omitted] • The incorporation of EMR did not significantly reduce the compressive strength of MOC. • EMR improved the water resistance of the specimens. • MOC can effectively solidify heavy metals in EMR. • EMR is used in MOC, which effectively reduces the production cost and is expected to solve the buildup problem of EMR. [ABSTRACT FROM AUTHOR]

• The effects of three kinds of admixtures (silica fume, nano-SiO 2 , nano-CaCO 3) on properties and microstructure of sulphoaluminate cement mortar at −10 °C were studied. • The hydration of sulphoaluminate cement can continue at −10 °C. At the age of 1 d, ettringite is yielded in the mortar. • The pore structure of mortar at the age of 1 d has the fractal characteristics. With the optimum content of three kinds of admixtures, the fractal dimension of pore structure of mortar with 0.5% nano-SiO 2 is the minimum. The traditional cement-based cementitious materials cannot hydrate at −10 °C, and the sulfoaluminate cement can hydrate, but the cement slurry has poor properties and low strength. Three kinds of nano admixtures (silica fume, nano-SiO 2 , nano-CaCO 3) were selected as modified materials, and the effect of nano admixtures on the fluidity, strength, internal temperature, micro-morphology, mineral composition and pore structure of sulphoaluminate cement mortar were studied under the condition of mixing and curing of cooled materials at −10 °C. The results show that the fluidity, compressive strength and flexural strength of mortar increase first and then decrease with admixture content. When the content of silica fume, nano-SiO 2 and nano-CaCO 3 is 3 %, 0.5 % and 0.5 % respectively, the fluidity and strength of mortar are the maximum. With the optimum content of three kinds of nano admixtures, nano-SiO 2 has the best improvement on the strength and internal temperature of mortar. The hydration of sulphoaluminate cement can continue at −10 °C. At the age of 1 d, ettringite is yielded in the mortar. After the addition of nano admixtures, the amount, characteristic diffraction peak and diffraction intensity of ettringite in mortar increase. The nano admixtures can optimize the pore structure of mortar with the age of 1 d. The fractal dimension of pore structure of mortar with 0.5% nano-SiO 2 is the minimum. [ABSTRACT FROM AUTHOR]

Highlights • Capillary tension theory used to predict the concrete shrinkage restrained by bar. • The reinforcement bar changed the pore structure size of concrete. • Shrinkage strain and capillary stress decreased with reinforcement ratio increase. • Experimental values applied to validate prediction results of concrete shrinkage. Abstract In this study, we proposed a method for predicting early shrinkage of concrete restrained by reinforcement bar based on capillary tension theory and microstructure pore of concrete. Concrete specimens with two different strength grades and four different reinforcement ratios were prepared. The pore structure, shrinkage, and physical properties of concrete were investigated at ages of 3, 7, and 28 days. Experimental results show that the reinforcement bar changed the pore structure of the concrete. The pore structure size of the concrete increased linearly with increase in the reinforcement ratio. Concrete shrinkage restrained by reinforcement bar decreased. It was because of the co-deformation between concrete and reinforcement bar and restrictions on capillary stress. The predicted values of shrinkage of concrete restrained by reinforcement bar were in good agreement with measured values. [ABSTRACT FROM AUTHOR]

Highlights • Montmorillonite layers in paste can refine capillary voids to form nanopores. • The nanopore volume in paste increases with increasing pre-statured bentonite. • A bentonite-to-water ratio of 1:5 has slight influence on the stability of paste. • Thermal insulation property of paste can be enhanced by increasing nanopores content. Abstract Nanopore-rich lightweight cement pastes (NLCPs) were successfully prepared by adding pre-swelled bentonite to cement paste. The pore structure, thermal conductivity, and compressive strength of these pastes were investigated. The results indicated that montmorillonite layers in paste can subdivide and refine capillary voids, thereby forming nanopores. When the volume percentage of bentonite in cement paste was increased from 0% to 80%, the nanopore volume increased gradually from 0.093 cc/g to 0.654 cc/g, while the corresponding volume percentage increased from 82.1% to 90.7% and then decreased to 57.7%. More importantly, nanopores contribute to a reduction in the thermal conductivity. Adding pre-saturated bentonite to cement paste yielded NLCPs with a dry density, compressive strength, and thermal conductivity of 510 kg/m3–1873 kg/m3, 2.9 MPa–88.4 MPa, and 0.093 W/(m·K)–0.554 W/(m·K), respectively. [ABSTRACT FROM AUTHOR]

• RCBP and GGBFS were used as SCMs to prepare a novel low-carbon concrete. • RCBP-GGBFS makes up for the excessive strength loss of concrete with high volume RCBP. • RCBP-GGBFS has an excellent combined effect on optimizing the microstructure. • RCBP and GGBFS can effectively reduce the energy intensity, CO 2 emission and cost. This study focuses on a novel low-carbon concrete containing recycled clay brick powder (RCBP) and ground granulated blast furnace slag (GGBFS). The effects of RCBP and GGBFS on hydration process and microstructure of the novel low-carbon concrete with different replacement levels ranging from 0 to 40% have been studied by testing workability, compressive strength, hydration heat, hydration products and pore structure. The incorporation of blended GGBFS and RCBP makes up for the excessive strength loss of concretes with high volume RCBP. Furthermore, RCBP and GGBFS can reduce the cumulative hydration heat and accelerate Portland cement hydration. Samples with RCBP and GGBFS have a lower portlandite content and a high hydration degree at 90 d. Meanwhile, RCBP-GGBFS has an excellent combined effect on optimizing the microstructure. Ultimately, the CO 2 emission and cost of mixtures with RCBP and GGBFS are significantly reduced. This study is expected to help enhance the utilization efficiency of RCBP to produce the low-carbon building materials. [ABSTRACT FROM AUTHOR]

• Geopolymers are prepared by thermal-mechanical activated aluminum sulfate residue. • The effects of design factors on the performance of TMASR geopolymer are evaluated. • The main products of efflorescence in TMASR geopolymer are sodium sulfate crystals. In this study, geopolymer prepared from thermal-mechanical activated aluminum sulfate residue (TMASR) and alkali activator was studied. This work aims to investigate the effects of different design factors on the workability, compressive strength, and efflorescence of TMASR-based geopolymer. The reaction products and structures of the geopolymer binders made from TMASR were tested by FTIR, XRD, and SEM. The results showed that the type, dosage, silicate modulus of the activator, and the water to binder ratio can significantly affect the fresh and hardened properties of TMASR-based geopolymer. A mixture with optimal compressive strength, workability, and efflorescence characteristics can be obtained by using Na 2 SiO 3 solid content of 30%, the water to binder ratios of 0.6–0.65, and the modules of sodium silicate of 1.2–1.6. The main hydration products of TMASR-based geopolymer were amorphous geopolymeric materials. The efflorescence product compositions in TMASR-based geopolymer were Na 2 SO 4 , Na 2 SO 4 ·10H 2 O, Na 2 CO 3 , and Na 2 CO 3 ·nH 2 O. The results obtained in this study can promote the utilization of waste acidic aluminum sulfate residue for the production of sustainable construction materials. [ABSTRACT FROM AUTHOR]

• The composite improvement method (CIM) is used to improve loess mechanical properties. • The CIM increases the mechanical strength of loess by changing the microstructure. • The CIM decreased the total number and fractal dimension of particles and pores. • The CIM can stimulate mutual activity between the improved materials. • The composite improvement mechanism of CIM is further revealed. Loess has poor engineering geological properties due to its loose and porous soil structure. To meet the engineering requirements of bearing capacity of foundations in loess areas, various stabilizers have been added to the loess during construction. Currently, cement, fly ash, fibers (natural and synthetic) and ionic curing agents have been widely used as stabilizers worldwide. In this study, the Composite Improvement Method (CIM) was used to improve the loess mechanical properties. A series of experimental tests with three factors and five-level orthogonal were conducted on loess samples with the inclusion of cement, curing agent and polypropylene fiber, to investigate the relative strength in terms of direct shear tests and unconfined compression tests. The test results were analyzed by range and variance analysis to quantify the significance of the improved materials, and the optimal improvement scheme was obtained. The results show that cement content has the greatest influence on shear strength, especially on unconfined compressive strength (UCS), followed by polypropylene fiber content and curing agent content. To reveal the internal mechanism of loess improvement by CIM, the quantitative microstructural information of the improved soil was extracted, and the microscopic geometric parameters such as apparent porosity and fractal dimension were calculated and analyzed as well. Based on the qualitative and quantitative analysis of microscopic images, it is observed that CIM increased the roundness of soil particles, decreased the total number of soil particles, and reduced the fractal dimension of particles and pores. Additionally, the composite improvement mechanism of CIM is further revealed. CIM can stimulate the activity of each other between the improved materials and work together to improve the engineering geological properties of the soil. [ABSTRACT FROM AUTHOR]

• The hydration superposition effect of SSCP was clarified. • The microstructure of SSCP hydration products was analyzed. • The hydration mechanism of SSCP was revealed. Steel slag has great potential as a supplementary cementitious material, and often shows good effects when used in combination with granulated blast furnace slag (GBFS). In order to reveal the interaction law of steel slag and GBFS, the hydration superposition effect and mechanism were studied in this paper in terms of ion dissolution, hydration heat, hydration products, hydration degree, microstructure and mechanical properties. The results show that steel slag and GBFS have a significant hydration superposition effect, and the strength of the paste when the two are used in combination is much higher. The mechanical properties at the early and later ages are the best (16.5 MPa at 7 days and 31 MPa at 28 days) when the steel slag-to-GBFS ratio is 1:1 and 2:3, respectively. Steel slag-slag composite powder (SSCP) has three exothermic peaks, which are the dissolution peak, hydration peak of steel slag and pozzolanic ash reaction peak of GBFS (after 85 h), respectively. The fibrous and amorphous C-S-H gels and plate Ca(OH) 2 appear in the SSCP pastes at 3 days. Furthermore, the microstructure of hydration products consists of a number of fiber-like and particle-like C-S-H gels with widths ranging from 15 nm to 20 nm and lengths ranging from 50 nm to hundreds of nanometers. The C-S-H gels wrap the unhydrated mineral phase (UMP) to form a nucleus(UMP) - membrane (C-S-H) structure. The early hydration of steel slag would increase the pH and conductivity of the pore solution, promoting the dissolution of aluminosilicate glass in GBFS and pozzolanic ash reaction, at the same time, the consumption of Ca(OH) 2 by the pozzolanic ash reaction would promote the further hydration of steel slag. The synergistic hydration effect of SSCP would promote hydration and generate more hydration products to fill the pore structure, resulting in good hardening properties. [ABSTRACT FROM AUTHOR]

• MGO applied as the early strength agents in the low temperature. • MGO effectively compensate the early mechanical strength. • Nucleation effect of MGO accelerated the hydration reaction. The mechanical strength of cement mortar is normally decreased in a low-temperature environment, which is mainly due to the slow cement hydration reaction rate and an increase in the total pore volume, especially the harmful pore volume. With the modification of nano-materials, the early mechanical strength of cement-based materials can be effectively compensated. In this study, the effect of multilayer graphene oxide (MGO) on the early mechanical properties and microstructure of cement mortar at low temperatures of 0 °C, 5 °C, and 10 °C is studied by measuring the fluidity, setting time, mechanical property, scanning electron microscope (SEM), thermogravimetric (TG), and nitrogen adsorption/desorption test. Compared with the mechanical strength of control mortar with curing temperature of 20 °C, the mortars with the addition of MGO curing at low temperature present higher mechanical strength and denser microstructure. And the mechanism of the interaction between cement particles and MGO nano particles at low temperatures (0 °C, 5 °C, and 10 °C) is further discussed. The initial hydration reaction of MGO mortar is accelerated, which is mainly due to the nucleation effect of MGO and chemical reactions between –COOH on the edge of MGO nanosheets and the Ca2+ of Ca(OH) 2. The promotion of the initial hydration refined the pore diameter of samples by reducing the pore size and total porosity, thus making the microstructure of samples denser and enhancing the strength of specimens. [ABSTRACT FROM AUTHOR]

• The effects of the electrical field and different liquid media on hydration products were studied. • The portlandite had been proved to be affected by the electrical field. • The pure water affected the stability of C S H gel under the electrical field. • The fractal model was used to analyze the pore structure and morphology of hydration products. Electrical fields accelerate the sulfate attack, which induces detrimental effects on the durability of cement-based materials. However, the role of the electrical field and aggressive liquid media in the degradation process is still unclear. Investigation of the role of the electrical field and aggressive liquid media during the degradation allows a better understanding of the mechanism of accelerated technique. Four different liquid media were used in this work to study the effect of the electrical field and liquid media in terms of the stability of hydration products. The evolution of hydration products was experimentally identified using multiple techniques, including X-ray diffraction (XRD), thermogravimetric analysis (TG), transmission electron microscopy (TEM), nitrogen adsorption/desorption (NAD), pH and CaO content measurements. The results indicated that the C S H structure was stable under the electrical field and saturated Ca(OH) 2 solution. The calcium loss under the electrical field was more likely to leach out from portlandite even though the mixed Ca(OH) 2 -Na 2 SO 4 solution was present. A severe degradation occurred under the electrical field and low-pH liquid media (pure water, Na 2 SO 4 -MgSO 4 solutions). The Ca/Si ratio significantly decreased from 1.34 to 0.82 under the coupling effect of the electrical field and Na 2 SO 4 -MgSO 4 solutions. Based on the fractal dimension results derived from NAD and TEM, the variations of pore structure and C S H gel morphology were quantitatively characterized. The coupled electrical field and low-pH liquid media dramatically altered the microstructure of hydration products, resulting in coarser pore networks and a shift to the disordered C S H gel. [ABSTRACT FROM AUTHOR]

• The low CG content can improve the mechanical properties of foam concrete. • The content of CG is the key factor affecting the porosity of foam concrete. • SEM was used to verify the effect of coal gangue on the microstructure of sample. Coal seam fires are a significant disaster in coal mine production. In order to prevent spontaneous coal combustion, it is necessary to build airtight walls in areas such as mined-out areas or working face roadways. Coal gangue (CG) is a solid waste produced in coal mine production, causing ecological damage and resource waste. So in this paper, a coal gangue lightweight foam concrete is developed for confined filling in coal mines. The effect of water-binder ratio(w/b), CG content, fly ash(FA) content, and foam content on the compressive strength, dry density, water absorption, and porosity of coal gangue foam concrete was analyzed in the single-factor and orthogonal experiment. It was found that the w/b and foam content were the two factors with a more significant effect on the mechanical properties of the specimens. For the porosity of the specimens, the amount of CG content is the critical factor that affects them. A scanning electron microscope (SEM) analyzed the specimen's microstructure and observed its pore structure. It was found that the amount of CG content would significantly affect the specimen's microstructure. When the CG content was 30%, the specimen had the best performance index of pores and poor connectivity between pores. This study shows that the foam concrete mixed with CG can have good mechanical properties and pore structure, making a valuable reference for the coal gangue foam concrete for the confinement filling treatment in mined-out areas or working face roadways mines. [ABSTRACT FROM AUTHOR]

• Nanoindentation (Ni) was used to characterize cement-elastomer composites. • Big data Ni (BDNi) can characterize cross-scale mechanical properties. • Emulsion and particulate elastomers play different roles in microstructure. • Hematite can counteract the influence of elastomers. • Multiple functioning phases contribute to the overall behavior of composites. Intensive big data nanoindentation (BDNi) characterization was performed to reveal the cross-scale mechanical properties of, and hence distinguish the different phases in, inorganic–organic hybrid oilwell cement-elastomer composites, hydrothermally cured at 160 °C and 20 MPa for 28 days. Totally-three emulsified and particulate elastomers, including styrene-butadiene latex (SBL) emulsion (6, 12, and 14 wt.%), polypropylene (PP) powder (12 wt.%), and nitrile rubber (NR) powder (6 wt.%), and a weighting agent, hematite (50 wt.%), were used as additives to finely adjust the mechanical properties and microstructure of the hybrid composites, which were respectively examined by the BDNi and mercury intrusion porosimetry and scanning electron microscopy. BDNi data were statistically deconvoluted by the Gaussian mixture modeling (GMM) to discern mechanically distinct phases and their Young's moduli and hardness at the micro/nano scale and the bulk composites' properties at the macro scale. Results show that the SBL emulsion can be more homogeneously dispersed into the cement matrix, due to its emulsified soft consistency and hydrophilicity, resulting in the formation of soft coatings on, and softer infills intermixed with, the cement hydration products (CHPs). In contrast, the two hydrophobic, inert, particulate elastomers, PP and NR powders, only act as isolated soft inclusions embedded in the hydrated cement matrix. The NR melts at high temperatures and permeates into the pores of the cement matrix, leading to the formation of complex intervened micromorphology and hence functions better than the PP. All elastomers can effectively reduce the composites' Young's moduli: with increasing the elastomer contents, while the modulus of a BDNi-identified major CHP phase decreases from 20.9 to 11.3 GPa, the bulk composites' counterpart from 17.3 to 10.7 GPa. The BDNi enables the identification of multiple mechanically distinct phases in the hybrid composites and quantification of the property changes of these phases. [ABSTRACT FROM AUTHOR]

• ZnO/layered silicate composite with three different carriers is synthesized. • Adding EVMT can significantly weaken agglomeration effects of ZnO particles. • Introducing ZnO particles can enhance UV absorption ability of layered silicates. • Exfoliated phase structure is formed in ZnO/MMT or ZnO/EVMT modified asphalt. • EVMT and REC are preferable to form composite and improve asphalt aging resistance. With the use of nanocomposite synthesis operations, the produced zinc oxide/expanded vermiculite (ZnO/EVMT) composite, a combination of ZnO particles and EVMT, has ZnO particles of the weakened agglomeration effects and can comprehensively improve the resistance of asphalt to thermo-oxidative and ultraviolet (UV) aging. However, the effects of different carriers for ZnO particles on the microstructure of ZnO/layered silicate composite and aging resistance of the composite modified asphalt are still unknown. In this research, three ZnO carriers, montmorillonite (MMT), expanded vermiculite (EVMT) and rectorite (REC), were employed to support ZnO particles (named ZnO/MMT, ZnO/EVMT and ZnO/REC, respectively). Then, the microstructure of different ZnO/layered silicate composites was investigated by field emission scanning microscope (FESEM), X-ray diffractometer (XRD) and UV–visible spectrometer (UV–vis) tests. Finally, the effects of different carriers on the morphology, phase structure, storage stability, physical properties and aging resistance of ZnO/layered silicate composite modified asphalt were discussed. Results showed that with the unique layered structure and its integrity, the three carriers are feasible to synthesize ZnO/layered silicate composite, and ZnO particles are supported or embedded on the surface of layered silicate sheets and have weaker agglomeration effects. Except for ZnO/MMT composite, the other two composites have sufficient composition connection strength. The exfoliated phase structure is formed in the ZnO/MMT or ZnO/EVMT composite modified asphalt systems. Additionally, the three ZnO/layered silicate composites have good asphalt compatibility and storage stability in asphalt, especially for ZnO/REC composite. The addition of ZnO/layered silicate composites into asphalt slightly influences physical properties of asphalt. Incorporating ZnO/layered silicate composites, regardless of the types, into asphalt could comprehensively enhance the resistance of asphalt to thermo-oxidative and UV aging. Comparatively, EVMT and REC are preferable to support ZnO particles and generate ZnO/layered silicate composite and comprehensively improve the aging resistance of asphalt. [ABSTRACT FROM AUTHOR]

The damage process of plain and blended cement mortars subjected to sulfate attack under electrical field was investigated in this paper. The deterioration of mortars was investigated by measuring the loss of compressive strength. To identify the changes of microstructure and mineral phases after the test, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis were performed on the selected samples. The results indicated that compared with sulfate attack alone, the combination of sulfate attack and electrical field accelerated the damage process of mortars, which can be explained through two different mechanisms. On the one hand, Ca 2+ ions directionally moved and then leached out from mortars under the electrical field, leading to the dissolution of portlandite as well as the decomposition of C–S–H gel at the later stage. On the other hand, the electrical field accelerated the migration of sulfate ions and then they reacted with hydration products to form massive ettringite and gypsum, which resulted in the microcracks and strength loss of mortars. Moreover, the deterioration of the mortar blended with fly ash was still visible in spite of its better chemical resistance. The strength loss of limestone powder incorporated mortar increased in comparison with Portland cement mortar as a result of an increase in porosity. [ABSTRACT FROM AUTHOR]

This work aims to verify the feasibility of utilizing sawdust in geopolymer to make reinforced composites and broaden application of sawdust in geopolymer. Fresh properties including workability and setting time, density, nailing ability, drying shrinkage, mechanical strength and microstructure of fly ash geopolymer activated by sodium silicate and sodium hydroxide solutions blended with 0–20% of sawdust by mass with an interval of 5% were investigated. The experimental results uncover that sawdust addition influences the workability of geopolymer. The sawdust content is inversely proportional to the setting time and a good linear relation is found between density and sawdust content. Sawdust is beneficial for the resistance to cracking and drying shrinkage especially the later ages. Sawdust exhibits little effect on compressive strength before 14 days of curing and it possesses positive effect after 28 days. 5% of sawdust addition exhibits little effect on flexural strength regardless of days of curing. The flexural strength increases with increasing content of sawdust. With the increasing addition levels of sawdust, the porosity decreases and compact matrix can be observed. Sawdust addition leads to the formation of an optimal microstructure. The results from mechanical properties and microstructure observation are compatible. [ABSTRACT FROM AUTHOR]

Given the different hydration processes of ordinary concrete, shotcrete with low-alkali accelerator not only has short final setting time and high early age mechanical properties but also different hydration products. Shotcrete microstructure was studied at different curing ages by X-ray diffraction, thermogravimetry–differential scanning calorimetry, and scanning electron microscopy to investigate its hydration process. The pore structure and permeability of shotcrete were also tested. The mechanical properties of shotcrete were then studied. Results showed that under the effect of accelerator, the retarded action of gypsum disappeared in the cement–accelerator–water system. C 3 A hydrated quickly to form calcium aluminate hydrate (CAH) crystals, and a mesh structure was formed by ettringite, albite, and CAH. A large amount of hydration heat improved the hydration rate of the cement clinker mineral and the density, thus leading to high mechanical properties at the early curing age. The setting time of pastes increased with increasing water–binder ratio and fly ash (FA) dosage. Thus, the hydration process and the microstructure and morphology of the hydration products changed. Excessive water and FA increased the percentage of pores in shotcrete, which directly caused poor permeability. The permeability and compressive strength were poor when the FA dosage was 30% compared with that of 20%. Based on the investigation, a simple 0.5 power relationship between compressive strength and splitting tensile strength of mixture S2, meanwhile, there was an exponential relationship between mechanical performance and permeability or porosity, respectively. [ABSTRACT FROM AUTHOR]

• The pore solution pH and chloride concentration of BPHFRC after salt spray erosion were studied. • A calculation model of apparent chloride diffusion coefficient was proposed. • The addition of fibers could inhibit the deterioration of pore structure in the process of erosion. • With the increase of erosion time, the bond strength between fibers and concrete matrix decreased. The chloride diffusion performances of basalt-polypropylene hybrid fiber reinforced concrete (BPHFRC) in salt spray environment were investigated. The effects of concrete strength, fiber addition form and content on the pore solution pH and chloride concentration were evaluated. The results showed that the stable depth of pore solution pH of BPHFRC increased with the increase of exposure time. The greater the strength of concrete, the slower the decrease rate of pore solution pH with exposure time. The effects of addition form and content of basalt fiber (BF) and polypropylene fiber (PF) on chloride concentration were different. When the fiber content was 0.1%, the addition of BF, PF or hybrid BF-PF could improve the chloride corrosion resistance of concrete. However, addition of 0.2% hybrid BF-PF increased the chloride concentration in the concrete. The apparent chloride diffusion coefficient of BPHFRC decreased with an increase of salt spray erosion time, and exhibited a power function with erosion time. The calculation model of BPHFRC apparent chloride diffusion coefficient was established, and its effectiveness was verified. In addition, the pore structure, phase composition and micromorphology of BPHFRC before and after erosion were performed using RapidAir-457 porosity analyzer, X-ray diffraction and field emission scanning electron microscope, and the influence rules of BF and PF on chloride diffusion properties of concrete was discussed. [ABSTRACT FROM AUTHOR]

• Interfacial zone in recycled aggregate asphalt mixture was classified into Natural aggregate and Cement mortar interfaces. • Microstructural characteristics of recycled aggregate (RA) and interface transition zone (ITZ) were investigated. • The influence of RA on interfacial zone failure under high temperature deformation was quantified. • Energy and maximum principal stress during fracture were evaluated using FEM with cohesive zone elements of ITZ. Construction and demolition wastes (CDW) is a complex mixture containing cement mortar and mineral aggregate, recycled aggregates (RA) are further prepared by CDW after the crushing process. Investigating the effect of RA on interfacial zone failure of asphalt mixture is beneficial to promote the utilization of CDW in pavement engineering. Firstly, RA without strengthening treatment was used to prepare recycled aggregate asphalt mixture (RAAM), then the physical and mechanical properties of RA and RAAM were studied using microstructure analysis and performance tests. To comprehensively understand the influence of RA percentage on interface damage, the interfacial zone in RAAM was classified into cement mortar interface and natural aggregate interface. Results show that the attached cement mortar of RA is a porous material and leads to a weak interface adhesion with asphalt mortar. The cement mortar interface presents greater porosity and lesser modulus compared with the natural aggregate interface. Increasing RA percentage causes more interface failure during deformation, and the damage of cement mortar and its interface with asphalt mortar are the primary resources of failure. According to numerical simulation for fracture processing, the influence of replacing natural aggregate with RA on energy consumption is obvious, and it increases the average stress value of the interface. This study shows that RA can be used as an effective alternative for natural aggregate after enhancing its attached cement mortar. [ABSTRACT FROM AUTHOR]

• The hydration process of HPG in alkaline environment were analyzed by a muti-technique approach. • Both the dissolution of hemihydrate and crystallization of gypsum were frustrated in alkaline environment. • As an increase in pH, HPG plaster sets slow with a fall in strength. • The morphology of gypsum crystal in hydrated HPG plaster were modified contributing to loose microstructure. The hydration of hemihydrate phosphogypsum in the alkaline environment was investigated aiming to recycle phosphogypsum-a promising gypsum resource in gypsum-based materials that generally incorporated alkaline binders. Isothermal conduction calorimetry and transmission electron microscopy showed that the hydration reaction of hemihydrate phosphogypsum was significantly changed by alkali. Both the dissolution of hemihydrate particles and crystallization of gypsum were impeded, as a result of phosphate precipitation from neutralization reaction. Consequently, the setting times decreased with the increase of pH and the time span of heat liberation was extended. The impurities in hemihydrate phosphogypsum, especially phosphate, served as setting retarders and crystal modifiers in alkaline environment, contributing to loose crystal microstructure with lower strength. This important finding called for the extra attention to the utilization of hemihydrate phosphogypsum in an alkaline environment. [ABSTRACT FROM AUTHOR]