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In this paper, the fatigue failure of engineered cementitious composites (ECC) and concrete laminated structure was investigated by using a model based on the peridynamics (PD) method. The model enhances efficiency by incorporating "residual life" and "cyclic blocks," utilizing the fully discrete method for ECC interfaces and the energy-based PD model for bimaterial interfaces. Its effectiveness, accuracy, and versatility have been validated through various numerical examples. Furthermore, the study examines crack propagation in ECC pavement overlays under four-point bending and investigates the impact of ECC layer thickness and fiber content on the fatigue characteristics of laminated structures. • A fully discrete fatigue model of ECC is constructed based on PD. • The energy-based PD model for the interfaces in ECC-concrete laminated structures was built. • The established model simulated the fatigue failure of ECC-concrete laminated structures. [ABSTRACT FROM AUTHOR]

Based on the characteristics of alkali-activated materials (AAMs) in energy saving and emission reduction, as well as giving full play to the complementary advantages of multi-component solid waste. In this study, a new type of AAMs was prepared from oil shale residue (OSR), ground granulated blast furnace slag (GGBFS), and fly ash (FA). Compressive and flexural strength tests, fluidity experiments, setting time, heat of hydration, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Thermo-gravimetric analysis (DTG-TG) were used to analyse the mechanical properties, workability, mineral composition, microstructure, and hydration products of the AAMs. The results showed that the microstructure of AAMs was dense, with high early strength, good mechanical and working properties, and no tendency for retrogressive strength with an increase in the age of maintenance. Under the action of NaOH/Na 2 SiO 3 , there is a synergistic hydration of the water-hard and volcanic ash materials, and the three raw materials have synergistic hydration properties and indispensable coupling mechanisms. Meanwhile, the effect of the activator content on AAMs is bidirectional. The OSR, GGBFS, and FA in the AAMs exhibited faster hydration reactions under the action of NaOH/Na 2 SiO 3 and abundant hydration products, which mainly included C-S-H, C-A-S-H, N-A-S-H, and small amounts of CaCO 3 , hydrotalcite (HT), and Ettringite (AFt). The specimens all met the requirements of the 42.5-grade composite silicate cement, and some specimens reached the strength requirements of the 62.5-grade silicate cement or above. OSR has great potential as a silicate-aluminate material, and this study provides a solid foundation for its further development and utilisation. • Oil shale residue was added into to blended slag/fly ash alkali activated binder system. • There is a synergistic effect of OSR-GGBFS-FA. • All specimens are comparable with Portland cement 42.5, even to Portland cement 62.5. • The hydration products are C-S-H, C-A-S-H, N-A-S-H gels, calcite, hydrotalcite, and AFt. [ABSTRACT FROM AUTHOR]

Highlights • The synthetic of novel SAC-MKPC clinker under low-temperature was proposed. • The mechanical properties of SAC-MKPC mortar was discussed. • The mineral composition and microstructure of SAC-MKPC were investigated. Abstract Although the novel sulphoaluminate-magnesium potassium phosphate cementitious composite (SAC-MKPC) has the advantages of rapid setting, high early strength, and excellent water resistance, MKPC factories traditionally use dead burnt magnesite as raw material, which requires a high consumption of primary energy sources. This research was mainly focused on investigating the feasibility of using magnesium sulphate, calcium oxide, and aluminium oxide in the preparation of the SAC-MKPC composite clinker at low-temperature. Two different CaO:Al 2 O 3 :MgSO 4 molar ratios, namely 4:3:37.7 and 4:3:16.15, were calcined at temperatures ranging from 1200 to 1350 °C, with a spacing of 50 °C. The results showed that the composite clinker was successfully obtained by calcining a mixture of magnesium sulphate, calcium oxide, and aluminium oxide at 1250–1350 °C, which is 150–250 °C lower than the temperature used in the dead burnt magnesite production. In the clinker system, yeelimite, periclase, and anhydrite were the main mineral phases and the hydration products consisted mainly of K-struvite, ettringite, residual periclase, and yeelimite. The CaO:Al 2 O 3 :MgSO 4 molar ratio yielding the best mechanical properties was 4:3:37.7. The compressive strength of the hydration products reached 31 and 70 MPa after 2 h and 1 day, respectively. The scanning electron micrographs of the hydration products showed a relatively dense structure, covered by 'amorphous materials' generated during the preparation process. The elemental composition of the amorphous materials included O, Mg, Al, P, S, K and Ca, and derived mostly from the cementation of MKPC and AFt. [ABSTRACT FROM AUTHOR]

Sulfoaluminate cement exhibits a good dimensional stability, an early strength, a high strength, a high resistance to chemical attack (from seawater, sulfates and chlorides), a low energy consumption and low carbon-dioxide emissions during production. However, sulfoaluminate cement factories traditionally use limestone, bauxite and gypsum as materials, which places significant pressure on these natural resources. This study aimed to investigate the feasibility of substituting traditional raw materials with industrial solid wastes in sulfoaluminate clinker production. It was achieved by sintering a mixture of industrial solid wastes (coal gangue: 8%–15%, flue gas desulfurization gypsum: 25%–35%, aluminum slag: 30%–35%, carbide slag: 30%–35%) at 1150–1300 °C. The mineralogical composition of the clinker was C 4 A 3 S ‾ , C 2 S and C 4 AF. The compressive strength of hydrated specimens reached as high as 75 MPa after a 28 d curing. This research provides a feasible and promising way to produce high-value products using industrial solid wastes and may promote their large-scale utilization. [ABSTRACT FROM AUTHOR]

• Innovative preparation of CSA cement entirely with FGD gypsum providing the CaO. • Decomposition characteristics of FGD gypsum in CSA clinker preparation were elaborated. • Properties of CSA cement made from FGD gypsum were investigated. Flue gas desulfurization (FGD) gypsum is an industrial by-product of the desulfurization process. The gross product of FGD gypsum has reached 550 million tons in China by 2016 and quite a portion was discarded. The purpose of this study is to investigate the feasibility of an innovative concept of producing the CSA cement based on sulfur recovery and entirely made of the FGD gypsum to replace natural gypsum and limestone as CaO and SO 3 sources. A mixture of industrial solid waste was calcined under different calcination conditions to study the decomposition behavior of FGD gypsum and properties of CSA cement made from the FGD gypsum. Experimental results show that it is feasible to use the FGD gypsum to entirely supply the CaO and SO 3 of this cement, the optimized calcination temperature is between 1270 and 1310 °C, and the suitable retention time is 60–100 min. The highest compressive strengths of 63.3, 85.3, 102.8 MPa were attained at 1, 3, and 28 d, respectively when the temperature was kept at 1310 °C for 60 min. Results also indicate that the FGD gypsum decomposition, which is mainly influenced by calcination temperature, retention time and alumina–silica ratio, has a significant impact on the clinker mineral phase formation. The novel technical idea developed in this research can greatly improve the utilization of FGD gypsum and may reduce about 50% of CO 2 emission in routine production. [ABSTRACT FROM AUTHOR]

The preparation of gypsum-based self-leveling mortar (GSLM) from solid waste-derived sulfoaluminate cement-modified hemihydrate gypsum is an effective path to enhance its mechanical properties. However, the phosphorus impurities in phosphogypsum (PG) still pose a challenge to the hemihydrate gypsum & sulfoaluminate cement composite system. To evaluate the impact of phosphorus impurities and develop targeted removal strategies, this study first assessed the effects of different types of phosphorus impurities on the mechanical properties and hydration characteristics of the GSLM. Then, a method of pretreating PG with carbide slag (CS) was proposed, and the removal efficiency and mechanism of phosphorus were examined by ICP-OES and XPS testing. The results indicated that the soluble phosphorus impurities severely inhibit the hydration of both CŜH 0.5 and C 4 A 3 Ŝ, leading to a most notable reduced mechanical performance. The sequence of inhibitory action was as follows: H 3 PO 4 >> Ca(H 2 PO 4) 2 ·H 2 O > CaHPO 4 ·2H 2 O > Ca 3 (PO 4) 2. CS could effectively immobilize the soluble phosphorus in PG. The pretreatment by CS notably enhanced the hydration degree of the GSLM by converting soluble phosphorus into Ca 3 (PO 4) 2 beforehand. In addition, the alkaline environment provided by CS promoted the ettringite formation. When the CS content approaches 3%, a PG-based GSLM with good performances meeting the G20 standard requirements of GSLM can be prepared. • The negative influence degree: H 3 PO 4 >> Ca(H 2 PO 4) 2 ·H 2 O > CaHPO 4 ·2 H 2 O > Ca 3 (PO 4) 2. • PG pretreatment by CS reduces soluble phosphorus and promotes ettringite formation. • GSLM meeting G20 standard was successfully prepared with CS-pretreated PG. [ABSTRACT FROM AUTHOR]

The traditional additives are constrained by issues such as energy intensity and pollutant emissions. As being cost-effectiveness and renewability, bio-additives have significant potential for application in cement industry. In this study, the byproduct of applewood pyrolysis, pyroligneous acid (PA), was utilized as a novel bio-additive. The results indicated that PA, as a cement strength enhancer, could markedly enhance the compressive strength of both calcium sulfoaluminate cement and ordinary Portland cement at low dosages (0–2 %), with the maximum increase reaching 26.13 % and 27.11 %, respectively. Additionally, PA retarded the setting time of both types of cement, with a more pronounced effect as PA dosage increased, with maximum delay times of 40 minutes and 188 minutes for calcium sulfoaluminate cement and ordinary Portland cement, respectively. Furthermore, owing to the abundance of organic functional groups in PA, its incorporation into cement improved the morphology of hydration products, accelerating the generation of hydration products and forming a dense structure. Consequently, in addition to broadening the application of PA, this study proposed a novel bio-additive that effectively addressed the pollution and energy issues associated with traditional additives, improving cement eco-efficiency and performance. [Display omitted] • PA's abundant hydroxyl and carboxyl make it a novel bio-additive in two typical cements. • As a strength enhancer, PA increases the compressive strength of both cements by more than 25 %. • As a retarder, PA can extend the setting time of both cements by several times. • Low-dose PA aids hydration product nucleation and growth, improving microstructure. [ABSTRACT FROM AUTHOR]

The utilization of municipal solid waste incineration fly ash (MSWI-FA) is environmentally significant. In this study, MSWI-FA was pretreated using organic acid solution and CO 2 microbubble carbonation washing. The pretreated MSWI-FAs were then used to produce Iron-rich calcium sulfoaluminate (IR-CSA) cement at different substitution rates (C FA) for various raw materials. The evolution of iron phase distribution, mineral composition, and hydration of IR-CSA cement were investigated, alongside heavy metal migration. The results showed that the MSWI-FA-based IR-CSA clinker had suitable mineralogical phases. However, gehlenite in MSWI-FA reduced CaO availability in the clinker formation reaction, hindering the involvement of Fe 2 O 3 in the ye'elimite formation reaction. The calcination temperature was increased to facilitate clinker and iron phase formation in the case of high C FA levels. CO 2 microbubble carbonation washing pretreatment of MSWI-FA, with which the IR-CSA clinker achieved suitable pH values and alkali content, facilitated the early growth and chained evolution of ettringite, resulting in a denser microstructure and lower cumulative hydration heat. Consequently, the compressive strength of MSWI-FA-based IR-CSA cement increased, with a maximum gain of 43.65 MPa. Chromium content in the residual form increased, and heavy metal leaching was well below standard limits. This approach provides a new perspective for the purification treatment of MSWI-FA and its high-value, large-scale recycling in low-carbon cement. [Display omitted] • Gehlenite in MSWI-FA negatively affects ye'elimite formation. • Raising firing temperature enhances MSWI-FA's usability and iron phase distribution. • Pretreatment variations in MSWI-FA alter IR-CSA cement hydration. • Suitable pH and alkali levels enhance AFt's early growth and intertwined development. • In hydration, other chromium distillates primarily transform into residual forms. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) is a solid waste generated during the wet process of phosphoric acid, the utilization of which is hindered by impurities. Herein, natural gypsum and limestone were replaced by PG as the only source of CaO for the production of sulfoaluminate cement (SAC). The effects of fluoride impurities such as NaF, CaF 2 , and Na 2 SiF 6 on the mineral formation and hydration of SAC were investigated. Results show that with increasing fluoride content, the decomposition of CaSO 4 initially decreased and then increased. An increase in the NaF content facilitated mineral formation in the clinkers, whereas an increase of over 1.0 wt% in the contents of CaF 2 and Na 2 SiF 6 each resulted in a positive impact. The fluoride impurities helped convert o-C 4 A 3 S̅ to c-C 4 A 3 S̅ and α'-C 2 S to β-C 2 S as well as influenced the hydration behavior of SAC. They reduced the 1-day compressive strength of SAC while enhancing its 3- and 28- day strengths. Moreover, a quantitative analysis of the distribution of F in the clinkers revealed that F from NaF and Na 2 SiF 6 was uniformly distributed in all clinker minerals, whereas F from CaF 2 was more concentrated in C 4 A 3 S̅ and C 2 S. Na mainly existed as Na 2 SO 4 , which coexisted with CaSO 4. Furthermore, F was immobilized by Ca in the clinker minerals to form CaF 2. This study will promote the use of PG in SAC preparation. • Effect of NaF, CaF 2 , and Na 2 SiF 6 on preparation and hydration of SAC was studied. • Distribution characteristics of F in the clinkers was quantitatively revealed. • SAC was prepared using PG as the only CaO source. [ABSTRACT FROM AUTHOR]

• Sulfoaluminate high-activity material entirely stemmed from solid waste was used for construction 3D Printing (C3DP). • Coordinated adjustment of material properties for C3DP was conducted by employing double additives. • Suitable setting time, good flowability, and high compressive strength were simultaneously realized. • The optimized material was tested in practical C3DP and performed well. Construction 3D printing (C3DP), as a green building concept, yields savings in terms of time, material, and labor costs and, hence, has become increasingly popular in recent years. The potential printing materials should have the characteristics of low cost, quick-setting, good flowability, and high mechanical strength. However, these properties are difficult to be obtained simultaneously in material adjustment. In the present study, the coordinated adjustment and optimization of setting time, flowability, and mechanical strength for a sulfoaluminate high-activity material (SHAM) were achieved, and the material was proved to be suitable for C3DP. This material was entirely prepared from industrial solid waste ingredients and thus cost-effective when used in C3DP. Optimal initial setting time (42 min), flowability (180.7 mm), and compressive strength (19.2 MPa and 97.5 MPa for 2-h and 28-d, respectively) were realized. The coordinated adjustment of these three properties was realized through cross changing the ratios of boric acid as a retarder and flowability enhancer and lithium carbonate as an accelerator. Moreover, 3D structures with different shapes were successfully printed using optimized material. This work has opened the way for the use of solid waste to prepare high value-added products and promote green building construction. [ABSTRACT FROM AUTHOR]

Blends of high belite sulfoaluminate cement (HBSAC) and iron-rich sulfoaluminate cement (IRSAC) can leverage the advantages of both materials and adapt to different application requirements (e.g., hydration heat adjustment, mechanical strength enhancement, dimensional stability maintenance etc.). In this study, the physicochemical properties and hydration characteristics of solid waste-based HBSAC and IRSAC blends with different blending ratios (100–0, 75–25, 50–50, 25–75, and 0–100) were investigated. Attributed to the higher amount of AFt produced by the hydration of active C 4 A 3- x F x S ̅ , the compressive and early flexural strengths of the blends increase with increasing IRSAC proportion, and there shows a high correlation between the compressive strengths and the AFt content. However, the late-stage flexural strength increases with the rising proportion of IRSAC before it reaches to 50%, and afterwards, the flexural strength shows a declining trend, which is closely related to the change in porosity. The needle-like AFt formed by HBSAC and rod-like AFt formed by IRSAC in the blends contribute to a crystal spatial interlock, resulting in the formation of a denser microstructure. Thus, the blend is more favourable for the development of late-stage flexural strength than the single microstructural form of AFt in HBSAC or IRSAC. This study holds significant guiding implications for directing the rational blending of HBSAC and IRSAC, thereby enhancing the performance of the cement. • Blends of HBSAC and IRSAC improve the stability of cementitious materials. • Blend of 50–50 ratio exhibits the highest late-stage flexural strength. • Densification of blend benefits from interlocking of different forms of AFt. [ABSTRACT FROM AUTHOR]

Preparing beta-hemihydrate gypsum and then using it for gypsum-based self-leveling mortar (GSLM) in building engineering is one of the promising approaches to consume by-product gypsum such as flue gas desulfurization gypsum and phosphogypsum. In order to overcome the deficiencies of low mechanical strengths and large fluidity loss of beta-hemihydrate gypsum, solid wastes-derived sulfoaluminate cement (WSAC) was used to modify beta-hemihydrate gypsum and prepare GSLM in this work. The effects of various additives on the fluidity and setting characteristics of GSLM prepared using WSAC-modified beta-hemihydrate flue gas desulfurization gypsum was firstly studied, and an optimal formula was obtained. The WSAC-enhanced GSLM had good mechanical performance due to the well-connected structure of the hydration products gypsum and ettringite. However, the hydration speed and degree of GSLM prepared using WSAC-modified beta-hemihydrate phosphogypsum were seriously weakened by phosphorus impurities, which resulted in poor mechanical performance. PO 4 3- would react with Ca2+ and Al3+ dissolved from ye'elimite in WSAC to form CaHPO 4 ·2H 2 O and AlPO 4 precipitates, which seriously inhibited ettringite formation. This negative effect was found mainly acting on the hydration of WSAC and could last until later hydration. [Display omitted] • WSAC-modified GSLM has good mechanical performance. • Ettringite bridging between gypsum enhanced compactness and strength of GSLM. • H 3 PO 4 in phosphogypsum weakened GSLM mainly by severely inhibiting its hydration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Comprehensive review of recent advances in incorporating wastes into foamed concrete. • Utilization of various wastes as binder, aggregate, and modifier replacements. • Effect of physicochemical properties of wastes on foamed concrete were analyzed. • The challenge and development direction of waste-based foam concrete were discussed. Globally, various solid wastes are produced and stockpiled in large quantities, causing serious environmental, social, and economic problems. Foamed concrete has attracted worldwide attention because of its excellent functional properties. Incorporating recycled waste and byproducts into foamed concrete is considered a win–win strategy for sustainable waste management and green transformation of foamed concrete. However, the reviews of alternative forms of different wastes/byproducts and their effects on foamed concrete are limited, which has hindered the promotion of this concept. Therefore, this paper compiles and reviews the reuse potential of various types of waste and byproducts as cementitious materials, aggregates, and modifier replacements. Together with the chemical and physical properties of the waste byproducts, the effects of different waste/by-product substitution pathways on the properties, pore structure, hydration products, and carbon emission reduction of foamed concrete were comprehensively evaluated. Our findings are important for guiding the rational introduction of wastes/byproducts and optimizing the combination of the inherent characteristics of waste byproducts and the requirements of foamed concrete. Furthermore, this review also discusses the challenges and development directions of waste-based foam concrete. This study provides an important basis and guidance for sustainable waste management, and low-carbon foamed concrete manufacturing. [ABSTRACT FROM AUTHOR]

• Nano-TiO 2 played a catalytic role in the early hydration process of C 2 S, C 3 S, C 4 A 3 S ‾ . • Nano-TiO 2 limited the mechanical properties of C 4 A 3 S ‾ at the later stage of hydration. • Nano-TiO 2 reduced the reaction activation energy of C 2 S, C 3 S and C 4 A 3 S ‾ , but did not affect the hydration control process. To clarify the details of hydration between nanomaterials and single minerals in cement, C 2 S, C 3 S and C 4 A 3 S ‾ were prepared by chemical synthesis, and the effects of nano-TiO 2 on the hydration properties of C 2 S, C 3 S and C 4 A 3 S ‾ were explored to reveal the mechanism of different hydration stages from the perspective of hydration kinetics. The results suggested that nano-TiO 2 did not essentially change the type of hydration products of C 2 S, C 3 S and C 4 A 3 S ‾ , but mainly acted as seeds to promote the nucleation and crystal growth of hydration products, and as fillers to form denser microstructures and higher strength. However, for C 4 A 3 S ‾ , the crystal growth of AFt at the late stage of hydration was further promoted by nano-TiO 2 , resulting in microcracks due to volume expansion of the hydrated matrix. Meanwhile, the relatively insufficient amount of alumina gel caused that the AFt could not being effectively cross-linked into a monolith, so the compressive strength decreased by 29.21% and 37.8% at 14d and 28d. The hydration kinetics shows that the acceleration period of C 2 S, C 3 S and C 4 A 3 S ‾ appeared earlier by reducing the activation energy required for the reaction by nano-TiO 2. However, the hydration kinetic processes of C 2 S and C 3 S (NG-I-D) and C 4 A 3 S ‾ (NG-D) were not disturbed by nano-TiO 2 , but significantly increased the hydration rates of the corresponding stages and advanced the turning point of the control stage. This demonstrated that nucleation and crystal growth of hydration products of these minerals are promoted by nano-TiO 2 , and the difficulty of phase boundary reactions and diffusion was also weakened. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multi-shell CLAs was innovatively prepared by synergistically using RM and FGD. • The synergistic effect between RM and FGD as well as the multi-shell structure design mechanism were illustrated. • The viable CLAs with high CS of 7.3 MPa, LBD of 940 kg/m3 and 1 h WB of 6.91 % were obtained. • The sustainable concrete with lower carbon emission and cost was prepared by using the CLAs as aggregates. In this study, novel multi-shell CLAs were prepared by synergistically using red mud (RM) and flue gas desulfurization gypsum (FGD). The performance optimization, mineral compositions, microstructures, and pore size distributions of the CLAs were investigated in detail. The results indicated that the synergistic using of RM and FGD significantly improved the strength of the CLAs, and that the multi-shell structure design by encapsulating, incorporating, and coating EPS, EPP, and hydrophobic shell effectively reduced the density and water absorption of the CLAs. Based on the synergistic effect between RM and FGD, the ettringite, C(N)-A-S-H and U-phase were the main minerals of the CLAs, which jointly contributed to the strength development of the CLAs. The multi-shell structure including lightweight core, intermediate shell and the hydrophobic outer shell further reduced the density and water absorption of the CLAs. Hence, viable CLAs with loose bulk density of 940 kg/m3, compressive strength of 7.3 MPa and 1 h water absorption of 6.91 % were obtained. The environmental impact and durability of the CLAs were evaluated acceptable. Furthermore, the prepared CLAs were employed as aggregates for lightweight aggregate concrete (LWC) preparation. The workability and mechanical strength of the LWC were investigated, and the LWC with density of 1880–2100 kg/m3, compressive strength of 39.8–54.5 MPa, and splitting tensile strength of 2.44–2.95 MPa was obtained. Finally, the carbon emissions and cost of the LWC were calculated as 288.5 kgCO 2 /m3 and 335.31Yuan/m3 (¥), respectively, which were 36.2 % and 23.1 % lower than those of traditional concrete. Overall, this research may provide a green approach for converting RM and FGD into value-added CLAs, with a potential application in sustainable concrete. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-TiO 2 modified the pore structure and increased the adsorption pressure of CO 2. • Nano-TiO 2 improved ettringite crystallization and crystallization region of C S H. • 1% nano-TiO 2 led to the formation of concave hexahedrons of ettringite. Calcium sulphoaluminate cement from solid waste (WCSA) has a relatively lower sintering temperature and low CO 2 emission, meanwhile, the low cost of WCSA and the good CO 2 absorption capacity make it one of the current hot topics of research. In this work, based on the optimal water-cement ratio, the effect of titanium oxide (TiO 2) on the pore structure and the hydration process of WCSA were explored. The hydration process and microscopic evolution were studied by compressive strength test, carbonization test, Brunauer-Emmet-Teller measurement (BET), X-ray diffraction (XRD), the heat of hydration, thermogravimetric analysis (TG), and scanning electron microscope (SEM). The effect of nano-TiO 2 on the carbon sequestration behavior of WCSA was also analyzed. The results show that WCSA with a water-cement ratio of 0.4 is the optimal carbonization substrate and nano-TiO 2 will make the pore structure more uniform and dense, simultaneously increasing the adsorption pressure for the CO 2. Meanwhile, the nano-TiO 2 can effectively promote and regulate the crystallization, nucleation, and growth of ettringite crystals. It can be found that the WCSA containing 1% nano-TiO 2 has the highest carbon capture ability among all the contents, and the ettringite crystal is concave hexahedron. The research considered that the concave surface with large specific surface energy can effectively increase the contact area between CO 2 and ettringite, which greatly improved the CO 2 absorption of ettringite. Overall, WCSA containing nano-TiO 2 may provide some new opportunities for efficient carbon capture. [ABSTRACT FROM AUTHOR]

[Display omitted] • ASAM was innovatively prepared using LCM, RM and SG as raw materials. • The strength development mechanism and Na+ solidification role of ASAM was illustrated. • A viable ASAM based CBLA with a high CS of 11.6 MPa, LBD of 1180 kg/m3 and WB of 5 % was obtained. • Hundred percent of solid waste could be recycled in the produced AASM and CBLA. In this study, a novel alkali and sulfate coactivated ternary cementitious matrix (ASAM) was produced using sulfur-aluminum low-carbon cementitious material (LCM), red mud (RM), and blast furnace slag (SG). The mechanical properties, mineral components, hydration characteristics, microstructures and pore size distributions of ASAM were systematically investigated, and the results indicated that the compressive strength of ASAM was apparently higher than that of the LCM–RM binary matrix. Based on the alkali and sulfate coactivation effect, the ettringite formed by sulfate-activated SG and the C(N)–A–S–H generated by alkali-activated SG, as well as the U-phase products were the main mineral components of ASAM, which jointly contributed to the compressive strength of ASAM. The maximum compressive strength of ASAM was 34.5 MPa at a curing age of 56 d, when the mass ratio of SCM:RM:SG was 3:5:2. Furthermore, the leaching behaviors and solidification mechanism of Na+ in ASAM were analyzed. The results illustrated that the Na+ could be effectively solidified by C(N)–A–S–H and U-phase, through physical encapsulation and chemical adsorption. The maximum solidification ratio of Na+ was up to 44.3%, when the mass ratio of LCM:RM:SG was 3:5:2. Finally, the optimal ASAM was employed to prepare cold bonded lightweight aggregates (CBLA), and high-strength CBLA with a crushing strength of 11.6 MPa, loose bulk density of 1180 kg/m3 and water absorption of 5% were obtained. Hence, this work provides a new approach for the preparation of a novel ASAM using 100% solid waste, and also verified its potential application in CBLA production. [ABSTRACT FROM AUTHOR]

[Display omitted] • GO and TGO can play a catalytic role in the hydration process of CSA. • Fewer carboxyl groups and the steric hindrance effect of TGO result in better dispersion in CSA. • The greater water storage capacity of TGO can facilitate the later hydration of CSA. To meet the urgent demand of ultra-early strength cementitious materials for modern infrastructure, this work explored the preparation of ultra-early strength cementitious materials based on calcium sulfoaluminate cement (CSA) from solid waste with 3% graphene oxide (GO) (named G3 sample) and 3% triethanolamine (TEOA) modified GO (TGO) (named TG3 sample). The results show that CSA doped with TGO has more potential to prepare ultra-early strength cementitious materials, which originated from the better dispersion of TGO in CSA paste, caused by the fewer –COOH group and more –OH group branched chains in TGO with an enhanced steric hindrance effect. Compared with the blank group, the initial setting times of G3 and TG3 were decreased by 11.90% and 26.19%, respectively, while for the compressive strength at 3 h and 28d, the G3 sample was increased by 253.4% and 6%, respectively, while for TG3 it was 294.9% and 23.38%. This is due to the better dispersion of TGO in the CSA paste and better storage capacity of water molecules, which results in a significant catalytic effect on the early hydration as well as the later continuous hydration of CSA. Meanwhile, the ability of TGO to effectively refine the pores and micro-cracks in the cement matrix also contributes to its strength. In addition, the hydration kinetics of TG3 at different reaction stages demonstrated that the activation energy needed for each order reaction section of hydration was obviously reduced, resultantly, the hydration reaction occurred easily. [ABSTRACT FROM AUTHOR]

[Display omitted] • A HSPC for permeable pavements was prepared by two-stage utilization of coal gangue. • The prepared WSAC meeting Chinese standard for 52.5 N ordinary Portland cement. • The HSPC has both high strength and high-water permeability. • The HSPC prepared with WSAC and coal gangue is an environmentally friendly product. As the most discharged solid waste in China; coal gangue (CG) occupies a considerable amount of land and severely pollutes the environment. Large-scale production, low added value of products, and lack of innovative disposal methods have lead to the difficult situation of effective utilization of CG. Therefore, it is very important to develop new ways to utilize CG on a large scale and with high-valued. This paper proposes a new method for reducing the environmental burden and realizing a high-value utilization of CG. The study was based on a two-stage utilization approach. Raw CG was first used to prepare solid-waste-based sulfoaluminate cement (WSAC). Then the prepared WSAC combined with self-ignited coal gangue (SCG) was used to prepare a high-strength pervious concrete (HSPC). The mechanical properties, mineral composition, and microstructure of the prepared WSAC clinker were analyzed. The results show that mortar from the prepared WSAC clinker had a reasonable mineral composition, well-developed crystals, and a compressive strength of 55.2 MPa at three days, which meets the standard for 52.5 N ordinary Portland cement. Furthermore, the influence of the water-binder (W/B) ratio, a ggregate-binder (A/B) ratio, and different SCG content on the performance of HSPC was studied. It was observed that the optimal HSPC was prepared when the W/B ratio and the A/B ratio were 0.22 and 4.0, respectively. Compared with traditional pervious concrete, the prepared HSPC has both high strength and high water permeability, and the obtained compressive strength is 34.8 MPa, a connected porosity of 19.80%, a water permeability of 7.95 mm/s, and a hardening density of 1930.8 kg/m3. An SCG content of 10%–20% was considered to the best dosage range for the preparation of HSPC. Furthermore, the freeze–thaw cycle analysis and abrasion resistance test indicated that HSPC with 10% SCG content has acceptable durability. Finally, the environmental impact of HSPC was evaluated through heavy-metal leaching tests, revealing that HSPC has a good curing ability on heavy metals and the leaching index was lower than the limit specified by the regulations, which reflects the environmental friendliness. Thus, this paper presents a low-cost and promising method for the resourceful utilization of CG and production of a sustainable pavement material. In addition, further research is needed before the application of this material to explore its durability and practicality in a specific environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • CBLAs were prepared using RM and SCM via synchronous palletization and foaming. • Up to 80 % of RM could be recycled in the produced CBLAs. • Viable CBLAs with low LBD of 680 kg/m3, CS of 3.1 MPa and WB of 8.7 % was obtained. • Mechanism of the formation of hierarchical porous structure in CBLAs was illustrated. • Durability and environmental impact of the CBLAs were evaluated acceptable. Here, solid-waste-based cementitious material (SCM) and red mud (RM) were innovatively applied to produce cold bonded lightweight aggregate (CBLAs) via synchronous pelletizing and foaming process. To integrally demonstrate the feasibility of developing the acceptable CBLAs, the following were investigated: (1) the effects of the production parameters on the pelletizing efficiency of CBLAs was investigated, and the results showed that SCM and RM exhibited the best compatibilities for CBLAs with a pelletizing efficiency of 91.9 %; (2) the effects of SCM and the addition of a novel hydrogen peroxide (HP, a foaming agent) on the properties of CBLAs was investigated, and the results revealed that the coordination of SCM with HP promoted synchronous pelletizing and foaming, thereby generating unified hierarchical pores on CBLAs and significantly decreasing their density. Viable CBLAs with low loose bulk density of 680 kg/m3, crushing strength of 3.1 MPa and water absorption of 20.7 % were obtained; (3) two surface modification methods of organosilicon waterproofing agent (OWA) spraying and SCM coating were carried out to further reduce water absorption of the prepared CBLAs, and the results indicated that the spraying of an OWA can effectively reduce the water absorption to 8.7 %. Additionally, the durability and environmental impact of CBLAs were evaluated acceptable employing the frost resistance and leaching tests. This work offers a new method for producing CBLAs from 100 % solid wastes and is a promising approach for the large-scale recycling of RM. [ABSTRACT FROM AUTHOR]

• GO is the potential to promote the growth of ettringite crystals. • Addition of GO can improve the ability of WSAC to immobilize heavy metals. • The mechanism of solidification of heavy metals by WSAC and GO-WSAC was analyzed. Heavy metal pollution is one of the most severe issues facing the environment for its persistent and stable physicochemical property. This research demonstrated that, ettringite crystal phase -- main hydration product of solid waste source sulphoaluminate cement (WSAC), has a highly efficient heavy metal removal via cation exchange. Meanwhile, due to large specific surface area, rich functional groups, good adsorption performance for heavy metals and ability to promote the growth of ettringite crystal, graphene oxide (GO) was selected to further improve the solidification effect of WSAC towards heavy metals. The heavy metal ion adsorption effects on the WSAC, including to theadsorbent dosage, solution pH, adsorption time, initial Cr(III) concentration, adsorption temperature, and competitive adsorption for multiple heavy metal ions, were systematically investigated. The experimental results revealed that with 0.03% GO addition, the compressive strength of WSAC after curing 1d, 3d, 28d increased by 24.1%, 18.6% and 21.5% compared to control sample, respectively, originating from promoting the hydration process and ettringite crystal growth in WSAC by GO. The heavy metal ion Cr(III)-exchanged by the Al(III) in ettringite crystal follows the Langmuir model with high exchange capacities, q m , 108.46 mg/g for GO-WSAC and 105.73 mg/g for WSAC. The GO-WSAC retains more excellent heavy metal ion removal capacity (95.2 mg/g, initial adsorbent dosage of 0.4 g) in very high concentration (400 mg/L), and the adsorption equilibrium could be reached basically within 10 min. When multiple ions coexist (Zn(II), Cu(II), Cr(III) and Cd(II)), WSAC and GO-WSAC still exhibit excellent removal efficiency, as high as 95.9% and 96.7%, respectively, apart from Cd(II) (only 75.03% and 89.3%, respectively). The findings in our research make WSAC as a new, environmentally friendly and cost-effective adsorbent for heavy metal ions removal from wastewater. [ABSTRACT FROM AUTHOR]

• Iron-rich CSA cement was produced using gypsum as CaO and SO 3 sources. • Effect of iron on phase composition and hydration of IR-CSA cement was shown. • Incorporation of iron in ye'elimite, belite and ferrous phase was studied. Iron-rich calcium sulfoaluminate (IR-CSA) cement is a low-carbon cement that contains small amount of aluminum. In this study, IR-CSA cement preparation method using gypsum as the source of calcium oxide was developed. The effects of iron on the decomposition of gypsum, formation of phases, microstructure of the clinker, and hydration of cement paste were investigated. The results indicated that the decomposition of gypsum and the formation of the target phase were first slightly promoted and then hindered when the iron content in the raw material increased. The presence of iron enhanced the growth of crystal grains and densification of the microstructure in the clinker. The early hydration behavior of IR-CSA cement mainly depended on the hydration of the iron-bearing ye'elimite and ferrous phases. Furthermore, the incorporation of iron into mineral phases was studied. The maximum incorporation content of Fe 2 O 3 in ye'elimite and belite phase reached 19.36 wt%, expressed as C 4 A 2.61 F 0.39 S - , and 2.83 wt%, respectively. The chemical composition of the ferrous phase was similar to that of C 4 AF, and its mineral phases were C 2 F, C 6 AF 2 , C 4 AF, and C 6 A 2 F from the center to the edge. Finally, the feasibility of preparing IR-CSA cement using phosphogypsum as the sole calcium oxide source was evaluated for engineering applications. This unique preparation method reduces the use of aluminum in raw materials and thus promotes recycling of iron-containing or low-aluminum-containing industrial solid waste materials. [ABSTRACT FROM AUTHOR]

• Foamed concrete with high compressive strength was produced using 100% industrial solid wastes. • A 3-D bubble-wall self-extension hole-forming method was defined. • The stabilization mechanism of hydroxypropyl methylcellulose in RLFC was analyzed. • A low-cost approach for ready-to-use low-density foamed concrete preparation was proposed. Foamed concrete is widely used as a highly energy-efficient building material. However, low-density foamed concrete requires increased amounts of Portland cement or steam curing to meet engineering requirements. This is due to inadequate compressive strength and long setting time of Portland cement. In this study, we investigate a method for preparing green, high strength, low-density foamed concrete, which is ready to use without the application of heat or pressure. First, a sulfoaluminate high-activity material (SHAM) was prepared using red mud, aluminum dust, flue gas desulfurization-gypsum, and carbide slag. The SHAM was used to produce ready-to-use low-density foamed concrete (RLFC). RLFC with a dry density of 615 kg/m3 had a compressive strength of 4.11 MPa and a thermal conductivity of 0.1638 W/m·K. Addition of 0.2 wt% hydroxypropyl methylcellulose (HPMC) as foam stabilizer, increased the compressive strength by 27.22% to 5.22 MPa, which was 3.48 times the compressive strength specified by the relevant Chinese standard (1.5 MPa). To further enhance the practicality, other solid wastes (limestone tailings and gold tailings) were blended with SHAM to prepare the RLFC. RLFC prepared from SHAM, limestone tailings, gold tailings, and HPMC in the match ratio of 54:6:40:0.11 (wt%) delivered dry density, compressive strength and thermal conductivity values of 612 kg/m3, 2.37 MPa and 0.1556 W/m·K, respectively. This study provides a low-cost and highly promising method for preparing low-density foamed concrete, which not only consumes a large amount of industrial solid waste but also avoids depletion of resources and generates profits. [ABSTRACT FROM AUTHOR]

• It is feasible to use water repellents reduce the water absorption of LPC based on SW-CSA cement. • The effect of water repellents on the properties of SW-CSA cement paste was presented. • Using calcium stearate as the water repellent doesn't affect the hydration of SW-CSA cement. Solid waste-based calcium sulfoaluminate (SW-CSA) cement is a type of low carbon cement that uses solid waste as raw material. It is usually used to prepare lightweight porous concrete (LPC) due to its short setting time. However, high water absorption of LPC based on SW-CSA cement limits its extensive application. Water repellent can be mixed into binder material to reduce the water absorption of LPC, but it may affect the hydration properties of SW-CSA cement paste, which influences the performance of LPC correspondingly. Calcium stearate (CS), sodium oleate (SO) and sodium methyl siliconate (SMS) are three familiar commercial water repellents. To find the suitable internal mixing water repellent for LPC based on SW-CSA cement, the effects of three CS, SO and SMS on the water absorption, hydration, compressive strength, fluidity, and setting time of SW-CSA cement paste were explored. Besides, the properties of LPC with CS and SO added were also studied. The results indicated that using CS as the water repellent could reduce the 1 day water absorption of SW-CSA cement paste by 45.9% and the water absorption of LPC by 33.0%. It also reduced the setting time of SW-CSA cement paste and increased the final compressive strength of LPC, which was conducive to the preferred rapid setting and high compressive strength of LPC. The hydrophobicity of SW-CSA cement paste with SO was better than that of SW-CSA cement paste with CS. But using SO and SMS as the water repellent retarded the early hydration of SW-CSA cement and prolonged the setting time of SW-CSA cement and reduced the final compressive strength of SW-CSA cement paste. Therefore, SO and SMS can't be used as the internal mixing water repellent of LPC based on SW-CSA cement, while CS is a promising internal mixing water repellent of SW-CSA cement to prepare LPC. [ABSTRACT FROM AUTHOR]

• CaO content in raw materials influences the phase composition of the FR-CSA clinker. • Lower CaO content in raw mixture promotes the incorporation of Fe 2 O 3 into ye'elimite. • A method to optimize the phase composition of FR-CSA clinker is provided. Ferric-rich calcium sulfoaluminate (FR-CSA) cement is an eco-friendly cement. Fe 2 O 3 exists in different minerals of FR-CSA clinker, e.g., Ca 4 Al 2 Fe 2 O 10 (C 4 AF), Ca 2 Fe 2 O 5 (C 2 F), and Ca 4 Al 6-2 x Fe 2 x SO 16 (C 4 A 3- x F x S -). The mineral composition depends on the chemical composition of the raw materials and significantly determines the reactivity of FR-CSA cement. To optimize the phase composition of the FR-CSA clinker, chemical reagent raw mixtures with different amounts of CaO were used to prepare the FR-CSA clinker. X-ray diffraction (XRD) analysis, Rietveld quantitative phase analysis (RQPA), Fourier Transform Infrared spectroscopy (FT-IR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) were used to identify the mineralogical conditions of the FR-CSA clinker. The results indicated that the amounts of CaO in raw materials greatly affected the iron-bearing phase formation in the FR-CSA clinker. With decreasing CaO content involved in calcination reaction, the amounts of Fe 2 O 3 incorporated in C 4 A 3- x F x S - increased up to 17.72 wt% (where x = 0.36). The findings make it possible to optimize the mineral composition of the FR-CSA clinker by changing the CaO content in raw materials. Furthermore, low CaO content in the raw material is beneficial to the formation of C 4 A 3- x F x S - , which enables the use of solid wastes containing low calcium for producing FR-CSA cement. [ABSTRACT FROM AUTHOR]

• Nano-pores introduced by silica fume affected thermal conductivity and strength. • Effects of amorphous phase on thermal conductivity of bricks were analyzed. • Effects of pore structure and continuous dense phase were quantified. • Thermal insulation properties and strength performance were enhanced simultaneously. As the inevitable by-product of sewage treatment, millions of tons of municipal sewage sludge (MSS) are increasingly stockpiled every year around the globe, creating enormous pressure on the environment and society. The preparation of porous insulation bricks based on MSS is put forward to realize environment protection and waste reclamation. However, the excessive amount of MSS will lead to the deterioration of strength and durability in the bricks. In this paper, the pore structure and crystalline phase of bricks were adjusted by the introduction of the ultra-fine amorphous phase, to improve the thermal insulation performance as well as the compressive strength. The thermal conductivity of the bricks could reach the lowest value of 0.194 W/(m·K) with the compressive strength of 10.2 MPa. Under the requirement of the mechanical strength, adding 3% of borax into bricks can increase the compressive strength to 18.8 MPa. The effects of the continuous dense phase and pore structure on thermal conductivity and compressive strength of bricks were investigated in reference to Bauer and Gibson model, respectively. The results provide a development direction for the preparation of thermal insulation bricks with high content MSS and alleviating the pressure of the shortage of clay. [ABSTRACT FROM AUTHOR]

• A promising method to reduce the Al 2 O 3 content in FR-CSA cement was presented. • The effect of CaSO 4 on the phase composition of the FR-CSA clinker was shown. • A method for calculating the incorporated level of Fe 2 O 3 in C 4 A 3-x F x S was provided • The effective utilizations of Al 2 O 3 and Fe 2 O 3 in FR-CSA clinker were improved. Ferric-rich calcium sulfoaluminate (FR-CSA) cement is a type of low-carbon cement. Common CSA needs to consume a large number of bauxite during the preparation process. In FR-CSA, Fe 2 O 3 can act as an alternative for Al 2 O 3 by shaping some iron-bearing minerals (Ca 4 Al 2 Fe 2 O 10 (C 4 AF), Ca 2 Fe 2 O 5 (C 2 F), and Ca 4 Al 6−2 x Fe 2x SO 16 (C 4 A 3 - x F x S -)). In order to reduce the use of Al 2 O 3 and optimize the iron-bearing mineral compositions in the FR-CSA clinker, this study investigated the effect of CaSO 4 batching in raw material on the formation of C 4 AF and C 4 A 3 - x F x S - at 1250 °C. It was proved that CaSO 4 plays an important role and the maximum incorporation amount of Fe 2 O 3 could be 16.18 wt% in C 4 A 3 - x F x S - , thereof x in the subscripts being 0.33. With the CaSO 4 contents in the targeted clinker increasing from 0 to 10 wt%, the effective utilization rates of both Al 2 O 3 and Fe 2 O 3 significantly increased. When the excess amount of CaSO 4 was >10 wt%, the effective utilization rate of Fe 2 O 3 increased but that of Al 2 O 3 decreased. The findings in this research can contribute to the mineral optimization of FR-CSA cement clinker and the improvement of effective utilization of Al 2 O 3 and Fe 2 O 3. The production of high-performance FR-CSA cement becomes possible by the substitution of solid wastes containing relatively low Al 2 O 3 content for bauxite. [ABSTRACT FROM AUTHOR]

• Solid wastes were used as raw material to prepare green calcium sulphoaluminate cement. • The prepared standard green calcium sulphoaluminate mortar meets the current commercial standard for 52.5 N cement. • Blinds of ordinary Portland cement and green calcium sulphoaluminate cement are used produce foamed concrete for the use of road embankment. • Both fresh and hardened state properties measurements show that the proposed mixture design allows for the application of cast-in-situ foamed concrete for road embankment. This paper aims at using green calcium sulphoaluminate (GCSA) cement to prepare foamed concrete for the use of road embankment. Solid wastes were used as raw material to prepare the GCSA cement. X-ray diffractometer (XRD) analysis shows that ye'elimite, gehlenite and belite are the main mineral phases in the produced GCSA clinkers, which is in accordance with the sulphoalumiate cement (CSA). Afterwards, the GCSA cement was blended with ordinary Portland cement (OPC) as binder to make the foamed concrete. The dosage of GCSA cement in the blinds was first optimized by comparing the 3-d and 28-d compressive strengths of mixes having different amount of GCSA cement. The optimized blinds (with 25% GCSA cement) was used to design foamed concrete mixes with wet density of 700 kg/m3, 800 kg/m3 and 900 kg/m3 using different amount of foam. Stability and consistency measurements were conducted at the fresh state. Mechanical measurements including compressive strength, flexural strength, splitting strength, elastic modulus and California bearing ratio were conducted at the hardened state. The measurements show that the proposed mixes have good spread ability and stability and high strength, elastic modulus and bearing capacity, indicating that the proposed mixtures can be accepted in industry practice for the in-situ foam concrete road embankment. [ABSTRACT FROM AUTHOR]