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Magnesium oxychloride cement (MOC) is an eco-friendly cementitious material with a fine prospect in construction and protection engineering. A full understanding of the time-dependent rheological behavior of MOC paste is crucial to many applications. In this study, the shear flow curves of MOC pastes with various H 2 O/MgCl 2 molar ratios were tested at different reaction times. The setting process of MOC paste was characterized by the time evolution of storage modulus (G′). Results indicate that the rise of the H 2 O/MgCl 2 molar ratio reduces the dynamic yield stress and plastic viscosity while leading to a more prominent shear-thinning behavior. The formation of crystalline 5-phase greatly accelerates the development of rheological parameters. The evolution of G′ reveals that the setting process of MOC paste includes five stages, which are governed by the gradual rigidification of 5-phase linkages among particles and the dynamic evolvement of electrostatic repulsion induced by the ionic composition changes of interstitial solution. Moreover, the rise of the H 2 O/MgCl 2 molar ratio is found to weaken the mechanical efficiency of 5-phase in the setting process. • The impact of 5-phase crystallization on the rheological properties of MOC paste was investigated. • The setting process of MOC paste was characterized by the growth of storage modulus. • The evolution of storage modulus derives from the 5-phase linkage formation and the changing electrostatic repulsion. • The rise of H 2 O/MgCl 2 molar ratio weakens the mechanical efficiency of 5-phase during setting. [ABSTRACT FROM AUTHOR]

The artificial aggregates prepared with high crystalline wet quarry sludge (WQS) by cold-bonded process suffer from low mechanical strength and poor solidification effect. Inspired by the shell, polymer chains were incorporated to enhance the connection among WQS particles. However, traditional polymer modification faces many limitations such as high cost and hydration inhibition. In this work, calcium oxide (CaO) and polyacrylamide (PAM) were co-used to address the above limitations and improve the properties of artificial aggregates. The compressive strength, hydration products and microstructure of modified WQS-aggregates were monitored. The main findings prove that the co-use of CaO and PAM effectively improves the mechanical performance of WQS-aggregates. The compressive strength of aggregates modified by CaO and PAM reach 11.85 MPa, exceeding the control by approximately 46.3 %. This approach mitigates issues like crack generation and poor cement hydration, which will occur when they are added separately. Through metal coordination and promoted carbonation behaviors, the introduction of CaO and PAM promotes the formation of a 3D organic-inorganic network and induces a denser microstructure. The porosities of aggregates reduce from 27.48 % to 24.83 %. The incorporation of CaO and PAM enhances the solidification of heavy metals. The prepared WQS-aggregates meet the requirements of environmental security. It is believed that this work will provide a new solution for the preparation of low carbon artificial construction products with low activity solid wastes. [Display omitted] • High crystalline wet quarry sludge was used to prepare cold-bonded artificial aggregates. • CaO and PAM can optimize the properties of cold-bonded artificial aggregates. • The CaO and PAM promotes the formation of 3D organic-inorganic network. [ABSTRACT FROM AUTHOR]

The interaction mechanism behind concrete damage induced by the combined effects of freeze-thaw cycles and fatigue load (FTF) remains insufficiently understood. This study aims to shed light on this mechanism by employing three sets of specimens, each subjected to different conditions: freeze-thaw cycles alone, low-stress impact fatigue (LIF) load alone, and FTF coupled action. Macro performance and microstructural changes of these specimens were measured after each testing round to analyze the evolution of concrete damage. Additionally, the influence of load duration on the damage under the coupled action was also explored. Results indicated that under FTF action, when LIF loading is applied for a short duration, freeze-thaw cycles play a dominant role in concrete damage, while the influence of LIF loading is minimal. However, when LIF loading is sustained for an extended period coupled with freeze-thaw cycles, it can accelerate concrete degradation. This can be attributed to the accumulation of micro-cracks during longer loading duration, eventually manifesting as visible cracks. These cracks link adjacent pores and increase the number of interconnected pores. This, coupled with freeze-thaw damage increasing the probability of crack forming, results in accelerated deterioration of concrete. The mechanism underlying this concrete deterioration was also analyzed from an energy dissipation prospect. • A setup was designed to simultaneously implement low-stress impact fatigue and freeze-thaw cycle. • The mechanisms of concrete damage under FTF action were discussed from the perspectives of pore structure and energy dissipation. • the influence of load duration on the concrete damage under the coupled action was explored. • The evolution of macro performance and microstructure properties were explored. [ABSTRACT FROM AUTHOR]

The water transport behaviors of cement-based materials are altered after hydrophobic modification. The influence of hydrophobic modification on the water transport behaviors of mortar was investigated through 1H NMR and the absorption test. The results indicate that the incorporation of paraffin significantly reduces both the capillary and moisture absorption masses of mortar. The ratio of moisture absorption mass to capillary absorption mass increases with higher hydrophobicity, attributed to the paraffin coverage around the pores and the subsequent increase in contact angle. When incorporating 10 wt% paraffin, the increase in capillary absorption mass of mortar is mainly attributed to vapor diffusion and capillary condensation, accounting for 90.3 %. And the content of interlayer water, gel water, and inter-hydrate water in the two mentioned specimens is approximately equal, attributed to increased resistance to the ingress of liquid water. The reinforcement corrosion protection performance improves by one to two orders of magnitude due to the alteration of water transport behaviors. • Hydrophobic modification alters the proportion of various water transport behaviors. • 1H NMR is employed to characterize the distribution of water content in different water absorption environments. • When the hydrophobicity of the mortar increases, the capillary and moisture absorption specimens exhibit similar mass increments and absorption rates. [ABSTRACT FROM AUTHOR]

The water status within concrete under low air pressure (AP) condition has been reported to affect the long-term properties of concrete in plateau regions, however, the underlying mechanism for the microstructural changes is not fully understood yet. In this paper, the confined water statuses within cement pastes curing at 98% RH and different APs (i.e. 101 kPa, 60 kPa, and 20 kPa) were first demonstrated and then correlated to the nanomechanical property changes of calcium-silicate-hydrates (C-S-H) phase by means of the 1H NMR relaxometry and nanoindentation techniques. The results show that low AP conditions increase the evaporable water content and drive the water movement from interlayer spaces to gel pores during wetting at 98% RH. According to the nanoindentation investigations, low AP conditions increase the volume fraction of high-density (HD) C-S-H and improve the nanomechanical and creep characteristics and bending strength of hardened cement pastes, which is attributed to the water redistribution within C-S-H phase. • Water statuses within cement pastes were identified by 1H NMR relaxometry. • Low air pressures drove water redistribution from interlayer space to gel pores. • Low air pressures changed nanomechanical characteristics of cement pastes. • Nanomechanical characteristics changed with water statuses of cement pastes. [ABSTRACT FROM AUTHOR]

• The strength development and drying shrinkage of SBR-SAC compositeswith different ratios were studied. • The pore size distributions and microstructure change of the SBR-SAC composites were monitored. • The brittleness-ductility transition of the SAC-SBR composite was highlighted. The composite of sulphoaluminate cement (SAC) and styrene-butadiene rubber (SBR) latex is expected to possess rapid strength development and adjustable elastic modulus, mainly used in rush repair engineering. This paper investigates the mechanical strength and drying shrinkage of SBR-SAC composites with different proportions. The change of pore structure, phase composition, and microtopography behind the composites was further revealed. Results indicate that, when the SBR/SAC ratio increases from 0/10 to 3/10, the flexural strength of the composite is increased by 343% and its compressive strength is increased by 14.7%, the drying shrinkage is almost not considered, below 0.1%. Besides, at the SBR/SAC ratio of 5/10, the composite loses brittleness, with no obvious peak value of load–displacement curves, and the drying shrinkage of composite at 23 d is 1.496%. This is because dehydrated polymer occupies the location of SAC hydrates, and the polymer film gradually and continuously covers the surface of the cement and becomes thickened. With the increasing SBR/SAC ratio, the continuous phase of composite probably transforms from inorganic cement phase to organic polymer phase. [ABSTRACT FROM AUTHOR]

• The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. • Three distinct zones in term of local calcium content in the direction of radius of the specimen were found. • Compressive behavior was modelled by the combination of compression damage model degradation damage model. Calcium leaching is an important durability problem for cement asphalt (CA) mortar used in ballastless slab track. In this paper, calcium leaching in CA mortar was accelerated by immersing in 6 mol/L ammonium nitrate solution. The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. Results showed that calcium leaching followed the Fick's law. The calcium leaching led to the formation of three distinct zones in term of local calcium content in the direction of radius of the specimen. Due to the leaching of calcium hydroxide and the progressive decalcification of C S H, the three zones had different chemical compositions. The compressive mechanical behavior was modeled by a compression damage model derived from Weibull distribution. The degradation damage model was established on the distribution of local elastic modulus. The combination of these two models can well predict the compressive behavior of partially leached CA mortar. [ABSTRACT FROM AUTHOR]

Highlights • Rheological properties have a good relation with the absorption of SAP. • The thixotropy shows the effect of SAP absorption behavior compared with plastic viscosity and maximum shear stress. • Large SAP's particles led to a high absorption rate and a long absorption time. Abstract Superabsorbent polymer (SAP) is an important internal curing agent for concrete with low or ultra-low water-to-binder ratio (w/b). When SAP is added, it will absorb water from fresh concrete fast. Thus, water absorption of SAP will affect the rheological properties of cement-based materials, especially at low w/b. Moreover, SAP with different particle size has a different absorption rate which will also affect the rheological properties. In this paper, two SAPs with different particle size are used to investigate its effects on the maximum shear stress, yield stress, plastic viscosity and thixotropy of cement-based materials within 80 min. Basic w/b of 0.18 was specified as reference values. Rheological results show that the absorption of SAP changed the evolution of yield stress, plastic viscosity and thixotropy of fresh mortar with time. Large SAP's particles led to a high absorption rate and a long absorption time which increased the yield stress and plastic viscosity. The above effects of SAP are closely related to the availability of water near SAP in cement mortar which causes to be a nonlinear relationship between the amounts of SAP and extra water required. In addition, the amount of extra water should be adjusted according to particle size of SAP and the addition level of SAP. [ABSTRACT FROM AUTHOR]

Structural build-up is of great importance in many concrete applications, such as formwork pressure, multi-layers casting, slip form paving, stability, and 3D printing. In this paper, the growth of static yield stress (τ s ) and thixotropic area were used to characterize the structural build-up of cement paste. The effects of different mineral admixtures, i.e. silica fume (SF), ground slag (GS), fly ash (FA), attapulgite (AG), nano calcium carbonate (NC), and nano silica (NS) on the structural build-up of cement pastes were studied. Calorimetric curves, zeta potential and conductivity of the pastes were also measured. Results showed that thixotropic behavior characterized by the growth of τ s and thixotropic area gave different ranking on cement pastes with various mineral admixtures. NS, AG, NC and SF increased the growth of τ s over 120 min, and NS was the most effective one. FA and GS decreased the growth of τ s over 120 min. Hydration of cement played a dominant role in the structural build-up of cement paste. However, high hydration rate didn’t always lead to high structural build-up rate. [ABSTRACT FROM AUTHOR]

Cement asphalt composite is a porous material with various connected and closed pores, and pore structure is the major factor affecting its strength. In this paper, the pore structure of cement asphalt composites with different asphalt contents were analyzed by the combination of Nuclear Magnetic Resonance (NMR) and modified image analysis methods. The former one mainly detects the smaller and open pores, and the latter one mainly measures the larger and spherical closed pores. The total porosity is the sum of open and closed porosities. A model, based on Griffith theory and complete pore structure, was developed to predict the compressive strength of cement asphalt composites with high and low asphalt contents. It is demonstrated that the proposed models predict the compressive strength of cement and asphalt composite quite well. [ABSTRACT FROM AUTHOR]

• The influence of time intervals and curing ages on the bonding strength of the composite specimens was studied. • The failure mode and microstructure of the composite specimens were analyzed. • The bond strength prediction model was proposed and verified. The issue of concrete vibration in the continuous beam 0# block is resolved by using a combination of self-compacting concrete (SCC) and ordinary concrete (OC). As a consequence of the multi-layer casting technique, SCC-OC structures consist of two layers and a bonding interlayer, so the bonding performance is crucial to guarantee the reliability of the structure. This paper studies the bonding performance between distinct layers of SCC and OC and attempts to establish the relationship between the two parameters (i.e., casting time interval and curing age) and the bonding strength (i.e., spitting strength and shearing strength). The results indicate that the casting time interval between SCC and OC has a stronger effect on the failure mode than that of curing age, and the shearing test can better characterize the weakly bonded interface than the splitting test. A shorter casting time interval and a longer curing age lead to higher bonding strength. Based on the bonding micro-mechanism and failure modes of SCC-OC interfaces, a mechanical model is proposed to predict the shear strength of the SCC-OC composite. The innovative approach of combining SCC and OC is promising to solve the problem of concrete vibration in the continuous beam 0# block at a low cost. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel stranded steel (SS) fiber was first proposed and realized by simply cutting the commercial steel strands. • The SS fiber had a superior anchoring capacity than the hooked-end and straight fibers. • Cementitious composites reinforced by SS fiber demonstrated remarkably superior mechanical performance as any other types of steel fiber. Reinforced materials with helically twisted geometries have been successfully applied in the concrete structures, owing to their superior mechanical properties and anchoring capabilities. Helically twisted types materials with diameters less than 1.0 mm might be an ideal type of fiber for cement-based materials reinforcing. In this article, a novel stranded steel (SS) fiber was first proposed and realized by simply cutting the commercial steel strands. The fiber–matrix interfacial properties and mechanical performance of steel fiber reinforced cementitious composites (SFRCC) were investigated. It was found that the SS fiber-cement matrix interface demonstrated superior interfacial bonding performance, as compared to those for the interface between hooked-end/straight fibers and cement matrix. For the mechanical properties of SFRCC, cementitious composites reinforced by SS fiber exhibited strikingly outstanding mechanical property as any other types of steel fiber with the same fiber amount. In conclusion, SS fiber may be more suitable for cementitious composite reinforcement than hooked-end and straight fibers. [ABSTRACT FROM AUTHOR]

Cement asphalt (CA) mortar, a porous and organic-inorganic composite, has been widely used in high-speed rail. Since the high content of asphalt and its low strength, mercury intrusion porosity (MIP) may not be applicable to measure the complete pore structure of cement asphalt (CA) mortar. In this paper, nuclear magnetic resonance (NMR) relaxometry method was used to measure the pore structure of CA mortar with various water-to-cement (W/C) ratio and asphalt to cement (A/C) ratio. The porosity obtained by MIP under the pressure of 0–0.4 MPa was used to infer the surface relaxivity which is a key parameter for the calculation of pore size in NMR relaxometry method. Results showed that a value of 40 μm/s can be adopted as the surface relaxivity of CA mortar. Pore size distribution of CA mortars presented three peaks. The peaks did not shift with w/c ratios, but got higher with the increase in W/C ratios. Low A/C ratio leads to coarser pore structure of CA mortar. [ABSTRACT FROM AUTHOR]

In this paper, the effects of asphalt-to-cement ratio (A/C) and water-to-cement ratio (W/C) on the elastic modulus E c of cement asphalt (CA) binder were studied through measuring the stress-strain curves and phase volume fractions of various CA binder specimens. The results illustrate that the CA binder with high asphalt content (A/C ⩾ 0.6) is a two-phase composite with complicated microstructure formed by both cement hydrates and asphalt agglomerates. The elastic modulus of CA binder decreases with the increase of A/C and W/C, especially A/C. A composite model that describes the CA binder in terms of the properties of asphalt and volume fractions of cement phases is suggested, and E c of CA binder can be predicted by this model according to A/C, W/C and properties of asphalt. [ABSTRACT FROM AUTHOR]

Sealed-space-filling self-compacting concrete (SSFSCC) is used in China Rail Track System (CRTS) III ballastless slab track of high-speed rail, which has been originally developed in China recently. In this track system, SSFSCC needs to be grouted into a flat, narrow, and sealed space (90 mm × 2500 mm × 5600 mm) which is enclosed by above prefabricated slab and bottom base plate. Good bonding between SSFSCC filling layer and above prefabricated slab has to be secured since these two layers are required to work as a composite plate. SSFSCC presents some special characteristics in comparison with normal SCC. This paper elaborated the property requirements of SSFSCC and the structural characteristics of SSFSCC layer of CRTS III ballastless slab track of high-speed rail. The compositions and mix proportioning of SSFSCC as well as construction technology were briefly introduced. The challenges of the application of this special SCC were also addressed. [ABSTRACT FROM AUTHOR]

• Estimated the temperature and stress development of the early-age concrete in base plate. • Predicted the early-age cracking risk of base plate concrete. • Introduced various measures to mitigate the early-age cracking risk of base plate concrete. Early-age cracking of base plate may result in safety and durability problems for slab ballastless track. However, very limited studies are available on the mechanisms of early cracking of the base plate of the CRTS III slab ballastless track which is quite common in practice. In this study, a thermal–mechanical model was developed to investigate the cracking behavior of early-age concrete in base plate. The influences of curing method, demolding age, demolding temperature, the diameter of the steel bar, and the longitudinal continuous length were taken into account. It was found that the most unfavorable stress conditions in the early-age base plate were located at the corners between base plate and position-limitation recess, and the stress level at the middle point is the highest at longitudinal directions. This has been validated by field experiences. Furthermore, various measures were introduced to mitigate the early-age cracking risk. [ABSTRACT FROM AUTHOR]

• The early properties of cement pastes modified by anionic, cationic and nonionic PAM were contrastively studied. • The absorption and hydration of cement pastes with different ionic PAMs were investigated. Polyacrylamide (PAM) has been widely applied as a viscosity modifier to optimize the workability of cement-based materials, but PAMs with different ionic types may show various effects, which is often ignored in practical engineering. In this paper, the early properties including the rheology, flowability, and setting of cement pastes modified by three ionic PAMs (anionic APAM, cationic CPAM, and nonionic NPAM) were contrastively studied. The absorption and hydration of cement pastes with different ionic PAMs were further investigated. Moreover, the contributions of physical flocculation and chemical hydration on the structural build-up of cement pastes were quantified by combining the static yield stress and heat release at the same time scale. The results indicated that three ionic PAMs showed different effects on the structural build-up, fluidity and setting of fresh cement pastes, which were dominated by the different physical flocculation and hydration retardation effects of three ionic PAMs on the cement pastes. The order of flocculation and hydration retardation effects of these three ionic PAMs was APAM ≫ NPAM > CPAM, which was concentration-dependence and evolved over times. The reason is mainly due to the distinct molecular structures and physicochemical properties of three ionic PAMs and their different adsorption behaviors with cements particles. [ABSTRACT FROM AUTHOR]

• The variation of internal temperature field of shotcrete in high ground thermal tunnel. • The phase distribution of shotcrete in high ground thermal tunnel. • Hydration and morphology of hydration products of shotcretein high ground thermal tunnel. • The mechanical properties and pore structure of shotcrete in high ground thermal tunnel. Geothermal tunnel creates one-dimensional heat conduction field which may have an uneven effect on the hydration, microstructures, and mechanical properties of shotcrete for the first lining layer. In this study, the evolution of the internal temperature gradient of shotcrete specimens subjected to the simulated geothermal environment was measured, and its effects on the heterogeneous distribution of internal microstructures, hydration products, and mechanical properties were characterized. Results showed that there was an obvious temperature gradient in the shotcrete exposed to the geothermal environment, which dramatically changes within 24 h of contact and then remains stable afterward. For the properties of shotcrete at an early age (within 24 h), the compressive and flexural strength of specimens exposed to a geothermal environment is significantly higher than that of specimens cured in standard conditions, due to the accelerating effect on hydration by the elevated temperature. The phase assemblage, hydration degree, and mechanical property in the specimens at an early age show a gradient distribution, and more hydration degree and lower porosity were formed in the internal regions with a higher temperature, resulting in a higher compressive and flexural strength. [ABSTRACT FROM AUTHOR]

• The use of different materials in ultra-high-performance concrete (UHPC) were reviewed to lower its cost. • These materials include fly ash, ground granulated blast furnace slag, glass powder, rice husk ash, limestone powder, fine and coarse aggregate. • Total cost (cost/m3) and strength-normalized cost (cost/MPa/m3) with these materials were computed. • The workability, mechanical properties, shrinkage and durability of UHPC with these materials were reviewed. Ultra-high-performance concrete (UHPC) is a new type of cement-based material. It has excellent different properties such as high workability, superior mechanical properties and durability. It has been proved to be a promising material for building, structural rehabilitation and retrofitting, and bridge engineering. However, despite its many benefits, its wide applicability is hindered due to its high cost. The high cost of UHPC is mainly associated with the high cost of its constituents such as cement, silica fume (SF), quartz powder (QP), quartz sand, superplasticizer (SP), and fibers. In this review paper, the use of different materials such as fly ash (FA), ground granulated blast furnace slag (GGBS), glass powder (GP), rice husk ash (RHA), limestone powder (LP), natural fine and coarse aggregate to reduce the content of cement, SF, QP, quartz sand, and SP and the corresponding decrease in the cost of UHPC have been reviewed. The total cost (USD/m3) and strength-normalized cost (USD/MPa/m3) were calculated when these materials were used in UHPC as partial/full replacement of cement/SF/QP/quartz sand. In addition, the effects of FA, GGBS, GP, RHA, LP, fine and coarse aggregate on workability, mechanical properties (compressive strength, splitting tensile strength, flexural strength and elastic modulus), drying and autogenous shrinkage, and durability characteristics were reviewed. In the end, a future research need was summarized. [ABSTRACT FROM AUTHOR]

• The rheological properties of LHC pastes with MEA and SRA were studied. • The variations of dynamic yield stress and plastic viscosity were estimated by response surface methodology. • The roles of MEA and SRA on the static yield stress development of LHC pastes were investigated. The combined use of low heat Portland cement (LHC), MgO-based expansive agent (MEA) and shrinkage reducing admixture (SRA) is beneficial to reduce the cracking risk of concrete. In this study, the effects of MEA and SRA on the rheological behaviour of LHC paste were investigated using dynamic and static shearing tests. The response surface methodology was used to estimate the effects of MEA, SRA, and superplasticizer on dynamic rheological parameters, while the zeta potential, calorimetric, and solid phases tests were conducted to explore the mechanisms of time-dependent rheological behaviour. Results indicate that MEA contributes to higher dynamic yield stress and plastic viscosity, while the effect of SRA is dependent on its dosage. MEA promotes the static yield stress development for accelerating the hydration of blends and the formation of Mg(OH) 2. SRA retards the hydration of LHC and blended paste and reduces the number of main hydration products. However, the static yield stress is further increased by SRA, showing a consistent changing trend with the surface area of hydrated particles. [ABSTRACT FROM AUTHOR]

• Resistivity evolution of fresh HSC were measured to characterize the early age hydration process in HSC. • Influence of pumping on early age hydration in HSC were evaluated. • Changes in dynamic yield stress of HSC after pumping were related to corresponding changes in hydration process. The pumping process exerts high pressure and strong shearing on fresh concrete, which may affect the hydration process and rheological behavior of concrete. In this paper, full-scale pumping circuits with lengths of 348-, 600-, and 924-m were established to evaluate the effect of pumping on hydration and rheology of concrete. Electrical resistivity measurement was employed to indirectly evaluate the hydration process of concrete. Ten high-strength concrete (HSC) mixtures with slump flow of 680 ± 50 mm and strength grades of C60-C100 were pumped, and HSC mixtures were sampled before and after pumping for rheological properties and electrical resistivity measurements. Findings indicated that the hydration process, determined by the electrical resistivity evolution, was accelerated after pumping. The end of the dormant period of fresh concrete was decreased by 10.3%-27.3%, and the end of the setting period was shortened by 15.6%-28.4% after pumping. The reduction in the dormant period can be well correlated with the drop in slump flow or increase in dynamic yield stress after pumping. [ABSTRACT FROM AUTHOR]

This study systematically investigated the influence of varying carbon dioxide (CO 2) dosages and steel slag (SS) replacement rates on the fresh and hardened properties of concrete through the injection of CO 2 gas during the mixing process. The composition of hydration products, degree of hydration, and the evolution of microstructural characteristics within the CO 2 -SS-cement system were analyzed. The results showed that CO 2 addition during the mixing process enhanced early strength in SS concrete. For concrete with a 10 wt% SS replacement rate, the incorporation of CO 2 ranging from 0.4 wt% to 1.2 wt% of the total mass of cementitious materials resulted in notable compressive strength increases of 1.26%–12.47%, 0.64%–6.14%, and 11.79%–18.24% at ages of 1 d, 3 d, and 7 d, respectively. CO 2 rapidly reacted with SS to form calcite-type CaCO 3 and promoted the generation of C-S-H through synergistic hydration with cement. However, a high CO 2 dosage (1.2 wt%) led to issues such as microcrack propagation and interface loosening due to CaCO 3 deposition, which could be mitigated to some extent by appropriately increasing the SS content. • CO 2 -mixing and steel slag synergistically improve early strength of concrete. • Increasing steel slag content alleviates adverse effects of high CO 2 dosage. • CO 2 -mixing enhanced the early cement hydration. [ABSTRACT FROM AUTHOR]

To investigate the synergistic effects of steel slag (SS) and granulated blast furnace slag (GBFS) on cementitious systems during carbon dioxide (CO 2) mineralization curing. Ternary paste specimens containing SS, GBFS, and Portland cement (PC) were prepared to analyze the influence of drying pre-treatment time and SS–GBFS mixing ratios on mechanical properties, CO 2 fixation rate, and microstructure evolution. Results emphasize the significance of appropriate drying pre-treatment in enhancing mineralization degree and compressive strength. At 60 °C drying pre-treatment temperature, extending drying pre-treatment time up to 12 h enhances both compressive strength and CO 2 fixation rate. However, beyond 12 h, a decline is observed in both parameters. Moreover, under the optimal drying pre-treatment time, the compressive strength of ternary paste specimens post-mineralization increases with higher SS content, with SS exerting a more pronounced positive effect on CO 2 fixation rate and compressive strength compared to GBFS. After 4 h of mineralization curing, specimens with 50% SS and 10% GBFS demonstrate a 13.16% increase in compressive strength and a 9.16% increase in CO 2 fixation rate compared to specimens with 10% SS and 50% GBFS. Microscopic test results reveal that the primary crystalline product in ternary paste specimens after mineralization is calcite, with traces of aragonite. The SS–GBFS mixing ratio has minimal effect on the type of reaction products but has a predominant influence on the total content and crystallinity of calcarea carbonica. • The increase of steel slag content can improve the degree of mineralization curing. • Increasing blast furnace slag reduces calcite crystallinity. • Steel slag boosts carbon fixation more than blast furnace slag. [ABSTRACT FROM AUTHOR]

• Effects of raw materials, processing factors and environment on air entrainment in fresh concrete are reviewed. • The testing methods of air void system in concrete at fresh and hardened states are summarized. • Effects of air entrainment on properties of concrete at fresh and hardened states are reviewed. The presence of the stable and adequate air-void system in fresh and hardened concretes are crucial to many properties, such as resistance against freeze and thaw cycle, workability/rheology, pumpability, strength, and fire resistance of concrete. This paper presents a critical review of the air-void system in fresh and hardened concretes and its effects on various properties. The air entrainment mechanisms and testing methods for air void system were first reviewed. Although the air void system can be measured by different methods, the measurement of the air void system in fresh concrete is still challenging. The influence of air void parameters on the workability and rheology of concrete was then discussed. In the hardened state, the effect of air entrainment on compressive strength, freeze-thaw resistance, and fire resistance was illustrated. Moreover, the effect of binder, chemical admixture, mixing time, vibration, pumping, temperature, and low atmospheric pressure on the parameters of the air-void system were reviewed in detail. In the end, the future researches on this topic are also recommended. [ABSTRACT FROM AUTHOR]

• The early-age deformation behaviors of CA mortar with AP and/or UEA were studied. • Deformation results from the graduated flask method and the buoyancy method were compared. • Four deformation stages of CA mortar were found and the underlying mechanisms were discussed. Early-age deformation of cement emulsified asphalt mortar (CA mortar) is a key parameter for its application in the CRTS I and CRTS II slab ballastless tracks of China. In this paper, the buoyancy method was used to measure the early-age deformation behaviors of CA mortars with aluminum powder (AP) and/or U-type expansive agent (UEA). The results indicate that the buoyancy method accurately and stably reflects the early-age deformation of CA mortar. The deformations of CA mortars with AP and/or UEA are composed of four stages: slight shrinkage stage, fast expansion stage, gradual shrinkage stage, and stable stage. Further analyses of relative expansions of samples reveal that different mechanisms of AP and UEA take effect at the gradual shrinkage stage of CA mortar deformation. Thermal effect induced by internal heat accumulation increases the air pressure in voids entrained by AP in CA mortar, thereby increasing the peak deformation values. Then the deformation tends to decrease with heat dissipation at the gradual shrinkage stage. Similar shrinkage stage is also observed in field tests. The buoyancy method can reflect the entire early-age deformation process of CA mortar with AP. This method is more suitable for engineering applications than the graduated flask method which is standardized in the specifications of China. [ABSTRACT FROM AUTHOR]

• The hydration, structural build-up and strength development of cement pates with different accelerators were investigated. • Accelerators increase the structural build-up rate by different mechanisms. • Mechanical efficiency of C-S-H may give wrong ranking on the efficiency of C-S-H. Fast structural build-up and strength development of fresh/hardened cement-based materials are always desired in many scenarios, where accelerators are often used. In this paper, the hydration, structural build-up and strength development of cement pates with different accelerators were investigated. The growth of static yield stress was used to characterize the structural build-up of fresh cement paste with 1% nano silica. Calorimetric curves, zeta potential and conductivity of pastes and strength development of mortars were also measured. Results showed that accelerators promote the reaction of C 3 S or C 3 A at different stages and in different mechanisms. Mechanical efficiency of C-S-H determined by growth of elastic modulus or yield stress over cumulated hydration heat may give wrong ranking on the efficiency of C-S-H. Apart from formation of C-S-H gel, structural build-up may originate from other sources. [ABSTRACT FROM AUTHOR]

• Buildability of 3D printing mortar was evaluated by the deformation of stacking layers. • A deformation monitoring device was designed to monitor the deformation of printing layer. • An equation between the optimal interval time and structural build-up rate was proposed. The buildability of fresh concrete is of great importance to 3D printing technology. In this paper, the buildability of 3D printing mortar was evaluated from the perspective of deformation of fresh mortar during the process of printing. A deformation monitoring device was designed to monitor the change of deformation of printing layer with stacking. The physical and chemical effects on the evolution of structural build-up were evaluated by the growth rate of static yield stress and penetration resistance. Results showed that the chemical effect was more effective than the physical effect, and the combination of physical and chemical effects was the most effective one. The growth of penetration resistance had a linear relationship with the growth of static yield stress, and both of them can be used to characterize the structural build-up of fresh mortar. The deformation value and optimal printing interval time could be obtained by simulating the printing process using the deformation monitoring device. An equation between the optimal interval time and the growth rate of static yield stress was established. [ABSTRACT FROM AUTHOR]

• Time-dependent rheological behavior after continuously shearing was investigated. • A parameter describing the disappearance of shear thinning at down curve was proposed. • Physical and chemical properties affect the evolutions of rheological properties with shearing. Shear history exerts a great impact on the rheological properties, and thus the consolidation and construction quality of concrete. This study experimentally investigated the time-dependent rheological behavior of cementitious pastes under continuously shear mixing. A parameter describing the disappearance of shear thinning at the decelerating curve was proposed. Results indicate that continuous shear mixing could not effectively hinder the development and evolution of thixotropy and yield stress of cementitious pastes over time. After continuously shear mixing for a while, the critical shear rate corresponding to the disappearance of shear thinning increased. Cementitious pastes tended to exhibit shear thinning behavior at relatively lower shear rate ranges. At higher shear rates, the rheological behavior of cementitious pastes after continuously shearing was strongly dependent on the composition of cementitious materials. The evolutions of rheological properties after continuously shearing were associated with the physical nature and chemical hydration of cementitious pastes. [ABSTRACT FROM AUTHOR]

• The influence of coarse aggregate on the printability of 3DPC was revealed. • The relationship between the printability and mechanical properties of 3DPC with coarse aggregate was studied. • Water-retention agent is employed to improve the printability of 3DPC with coarse aggregate. Increasing the dosage of the coarse aggregate is always desirable for 3D printed concrete (3DPC), which is essential for promoting the practical application of 3DPC. This study investigated the effect of coarse aggregate on the printability and the mechanical properties of 3DPC. The internal pore distribution of 3DPC with different coarse aggregate dosages was characterized using X-ray computed tomography (X-CT). It was observed that the mechanical properties of 3DPC with coarse aggregate are closely related to printability. The change in printability caused by the incorporation of the coarse aggregate can effectively improve the mechanical strength of the interfaces between the vertical and horizontal filaments, and attenuate the mechanical anisotropy phenomenon in 3DPC, but does not enhance the overall compressive strength. Water-retention agent is crucial for fabricating uniform 3DPC with coarse aggregate. This research advances the capabilities of understanding the printing technology for 3DPC and designing 3DPC with coarse aggregate. [ABSTRACT FROM AUTHOR]

Highlights • Effects of rotational shearing on rheology of mortars with glass fiber are investigated. • The shear-induced behavior of mortar with glass fiber depends on the matrix composition. • Fresh mortars with glass fibers easily exhibit shear-thickening behavior. Abstract Shear stresses are always applied to fresh concrete during mixing and transporting processes, which have significant influences on the dispersion and agglomeration of cement particles. In this study, the effects of rotational shear mixing on rheological properties of fresh short glass fiber reinforced mortars with different mineral admixtures (containing fly ash and silica fume) were experimentally investigated. The shear rates of 50 s−1, 100 s−1 and 150 s−1 were selected as the rotational shearing rates. The Herschel-Bulkley model was used to characterize the rheological behavior of fresh glass fiber reinforced mortar. Results showed that the shear-thickening intensity increased with the increase of glass fiber volume fraction for the cement-fly ash binary mortar, while the addition of glass fiber resulted in the rheological behavior of cement-silica fume binary mortar changed from shear-thickening to shear-thinning response. After subjecting to rotational shear mixing, the measured shear stress was significantly increased and the fresh mortars with glass fibers easily showed shear-thickening behavior. [ABSTRACT FROM AUTHOR]

Highlights • The effect of temperature on the structural buildup of cement pastes with various mineral admixtures was studied. • The hydration kinetics of cement paste was studied by boundary nucleation and growth model. • The relation between hydration kinetics and structural buildup was analyzed. Abstract The temperature dependence of structural build-up is of great importance to some new concrete technologies, such as 3D printing and slip-form casting concrete. In this paper, the structural build-up of cement paste with various mineral admixtures, characterized by the growth of static yield stress, were measured at 10, 20 and 40 °C. They were related with the calorimetric curves of cement paste at various temperatures. Nucleation kinetic (K N) and growth kinetic (K G) were introduced to analyze the hydration dynamics. The results showed that the addition of fly ash and slag were unfavorable for the structural build-up of cement paste at 10 and 20 °C, however, a favorable phenomenon was observed at 40 °C. The additions of nano-CaCO 3 or nano-SiO 2 had positive effect on structural build-up at all temperatures. The incorporation of silica fume had negative effect on structural build-up at 10 °C, while positive effect at 20 and 40 °C. Both the K N and K G played important roles on the structural build-up rate of cement paste. K G contributed more to the temperature dependence of structural build-up than K N. [ABSTRACT FROM AUTHOR]

Highlights • The rheological behavior of cement paste under continuous mixing was investigated. • High-rate shear mixing or adding fly ash slowed down the evolution of thixotropy. • An effective way to hinder the evolution of flocculation structure was proposed. Abstract The shear rate experienced by the cement pastes inside fresh concrete depends on the placing operations and the nature of concrete, and it plays an important role in the evolution of rheological properties and stability of fresh concrete over time. In this study, the effects of continuous shear mixing and fly ash on thixotropy, apparent viscosity, and shear-thickening behavior of cement pastes were experimentally investigated. Various shear rates of 1 s−1, 15 s−1 and 30 s−1 were selected to continuously shear the cement pastes. Results showed that the action of high-rate shear mixing slowed down the evolution of thixotropy, but the efficiency of reduction was gradually limited. Under the state of continuous shear mixing, the apparent viscosity of reference paste was significantly increased and the shear-thickening intensity at higher shear rate range was decreased. However, for the cement pastes containing fly ash, only slight increase in apparent viscosity was observed and the shear-thickening intensity also exhibited a slight increase behavior. It would be an effective way to hinder the evolution of flocculation structure by exerting a continuous shear mixing at an appropriate shearing rate and adding fly ash. [ABSTRACT FROM AUTHOR]

• The rheological properties of AAS pastes have been improved by low surface free energy mineral admixtures. • The surface free energy properties of low surface free energy mineral admixtures have been determined by IGC method. • The interparticle forces were calculated to reveal the mechanism for rheological improvement. This study investigates the effect of low surface free energy mineral admixtures (CaF 2 -dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars. [ABSTRACT FROM AUTHOR]

• The performance of calcined CSMR as a new SCM was corroborated. • Fresh and hardened properties of blended cement-based materials were examined. • Calcined CSMR exhibited higher reactivity than siliceous fly ash. • Cement composites with 20% calcined CSMR showed desired engineering performances. • Adding calcined CSMR reduced the environmental footprints of the final products. Supplementary cementitious materials (SCMs) have been widely used in modern concrete technology to improve the sustainability and performance of concrete, but the concern over the decreasing supply of conventional SCMs in the future raises a need to explore their alternatives. This study aims to corroborate the performance of a calcined solid waste, i.e., cutter soil mixing residue (CSMR), as a new SCM in sustainable cementitious materials. The rheological behaviors, hydration kinetics, pore structures, physico-mechanical properties, and durability of cement paste and mortar blended with calcined CSMR were experimentally investigated. Results showed that the calcined CSMR powders with a lower specific surface area than the cement particles could improve the flowability of the cement paste. The calcined CSMR exhibited higher reactivity than the coal fly ash and could accelerate the cement hydration, create additional hydrates, and refine pore structures. Adding 20% calcined CSMR in the cement mortar had negligible adverse effects on the compressive strength, dry shrinkage resistance, electrical resistivity, and sulfate attack resistance. Meanwhile, the incorporation of 15–30% calcined CSMR reduced the embodied energy and carbon emissions of the cement mortar by around 13–25%. Overall, this research demonstrated the possibility of using calcined CSMR as a new SCM to develop greener cementitious materials without compromising the engineering properties. [ABSTRACT FROM AUTHOR]

• Effects of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on chloride binding behaviour of seawater cement paste (SCP) are investigated. • Influence of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on the porosity and pore size distribution of SCP is revealed by the 1H Nuclear magnetic resonance (NMR) measurement. • The risk of steel corrosion in SCP with different w/b ratios is evaluated by the [Cl−]/[OH−] ratio. • The relationship between chloride binding ratio, porosity and [Cl−]/[OH−] ratio has been explored. This work investigates the effects of water-to-binder (w/b) ratio and supplementary cementitious materials (SCMs) including silica fume (SF) and metakaolin (MK) on chloride binding of seawater cement paste (SCP) by using a water extraction method. The chloride binding capacity, contents of chloride bound in Friedel's salt and chloride adsorbed by C S H gel are quantified. The resistance to steel corrosion is evaluated by [Cl−]/[OH−] ratio. The results show that the chloride binding ratio (content of bound to free chloride) gradually increases with the w/b ratio decreasing from 0.4 to 0.2. In addition, the chloride ions adsorbed by C S H gel in SCP with w/b ratio 0.2 contributes more largely to chloride binding capacity than SCP with w/b ratio 0.4. Moreover, the incorporation of MK improves the chloride binding capacity of SCP while the utilization of SF doesn't make much difference. In addition, the [Cl−]/[OH−] ratio in SCP keeps at a very low level during the whole experimental process, and decreases with the reduction of w/b ratio, the increase of content of MK and curing ages. The correlation of chloride binding ratio with [Cl−]/[OH−] ratio can be described by an exponential decay model while a linear relationship is observed between chloride binding ratio and the volume of macropores larger than 200 nm in diameter. [ABSTRACT FROM AUTHOR]

Polyurethane solidified ballasted track (PSBT) offers a novel solution to the frequent maintenance requirements of ballasted track, delivering a high-quality track infrastructure. In this study, laboratory tests were carried out on polyurethane solidified ballast (PSB) specimens under compression, tensile and shear conditions to obtain stress-strain curves and deformation characteristics. The numerical model of the PSB specimens was developed based on the discrete element method (DEM). The effects of the parameters related to the bond elongation on the tensile and compressive properties of the PSB specimens were analysed, and the parameters were calibrated by the test results. The results showed that the compressive, tensile and shear strengths of the specimens increased with increasing polyurethane foam density. During uniaxial and split loading, the stress-strain curves of the PSB specimens gradually entered the stress softening stage after an elastic phase. The compressive-tensile strength ratio of the specimens was around 1.55. From the perspective of deformation, the PSB specimen is primarily strained by the highly compressible polyurethane materials, and the specimen generates a considerable residual strain at the initial stage of cyclic loading. Thus, it is necessary to pre-compress the PSB to achieve an optimal load-bearing condition. DEM simulations show that there is a strong correlation between the mesoscale bond elongation of particles and the macroscopic tensile and compressive strengths of the specimens. It is therefore possible to utilise a high value of bond elongation to simulate bonded granular materials with low compressive-tensile strength ratios. The results obtained from the simulation of the numerical method used in this study are in high agreement with the test, which provides a new idea for revealing the meso- and macro- mechanical properties of PSB and its application in PSBT. • The mechnical propertiesof polyurethane solidified ballast (PSB) were conducted systematically. • The stress-strain curves, ultimate strength, and deformation characteristics of PSB were obtained. • A numerical model of the PSB was established and calibrated based on DEM using the soft bond model. • Reveal the influence of meso-scale bond elongation on macroscopic mechanical properties. [ABSTRACT FROM AUTHOR]

Double-block ballastless tracks are affected by environmental loading during their service life. The damage evolution of track slab concrete under cyclic air temperature fluctuations and solar radiation is not well understood. In this study, a new numerical simulation framework was introduced to analyze the long-term damage characteristics of ballastless tracks under cyclic environmental loading, considering the thermal properties of the track and the nonlinearity of concrete. The findings indicate that ballastless tracks are prone to cracking under solar radiation. Tensile damage in the track slab concrete increases with prolonged exposure duration. Especially, at corners of concrete sleeper, as the exposure time increased from 1 year to 10 years and 100 years, the tensile damages of concrete increased from 0.384 to 0.479 and 0.565 respectively. To minimize long-term damage in track slab concrete, it is effective to reduce the short-wave absorption rate on the track surface and increase concrete thermal conductivity. Furthermore, it was observed that both thermal effects and long-term tensile damage in a ballastless track increase with longitudinal-continuous length. [Display omitted] • A novel numerical method has been suggested to study the service properties of ballastless tracks under solar radiation cycles. • Ballastless tracks are prone to cracking under solar radiation, damage of track slab concrete increases with exposure ages. • Several solutions were suggested for minimizing the long-term thermal damage of ballastless track. [ABSTRACT FROM AUTHOR]

Given the crucial role of cement-styrene butadiene rubber (SBR) composites in the application of damping structural materials, their long-term damping performance needs to incorporate a focused examination of organic phase aging. This study investigated the changes in the dynamic mechanical properties of these composites subjected to thermo-oxidative and ultraviolet aging, and explored the damping degradation mechanisms specific to SBR. The results demonstrated a significant reduction in the damping capability of the composites under aging, exceeding 19.5 %, 33.9 %, and 46.0 % after 1, 2, and 4 years of service, respectively. The decrease is attributed to the alteration in the molecular structure of SBR, which includes the oxidation of the α-H double bond to a hydroxyl group, followed by a dehydrogenation reaction leading to the formation of aldehyde. Furthermore, the study utilized a three-element standard solid model to elucidate the frequency-dependent dynamic mechanical properties of the cement-SBR composites. • The dynamic mechanical properties of cement-SBR composites were monitored under aging processes. • The aging mechanism of SBR polymer was investigated under aging processes. • A three-element standard solid model was proposed to elucidate the dynamic mechanical properties of the cement-SBR composites. [ABSTRACT FROM AUTHOR]

• Mechanical properties of PVA-FRCCs with calcined CSMR were investigated. • Binder chemistry, matrix properties, and fiber bridging behaviors were studied. • Calcined CSMR can significantly improve the tensile strain-hardening properties. • Enhanced fiber–matrix interface by calcined CSMR was demonstrated. In this paper, a cutter soil mixing residue (CSMR), which is a soil–cement solid waste, was calcined and then used as a partial cement replacement in polyvinyl alcohol fiber reinforced cement composites (PVA-FRCCs). The binder chemistry was characterized using XRD, TGA and FTIR. The fiber–matrix interfacial properties were examined with SEM. The composite mechanical properties, including compressive strength, flexural properties and tensile behaviors and fiber bridging stress-crack opening relationships, were investigated. Results showed that the calcined CSMR can produce additional hydrates to aid the strength gain and densify the fiber–matrix interface. With a cement replacement level up to 40%, the tensile strength was not compromised, while the tensile strain capacity significantly increased to a maximum value of 3.2%. The micromechanical analysis revealed that the improved strain capacity is mainly attributed to the optimized fiber–matrix interface yielding enhanced pseudo strain-hardening indices. The results obtained in this study indicate that calcined CSMR is an attractive novel supplementary cementitious material for developing greener strain-hardening cementitious composites. [ABSTRACT FROM AUTHOR]

• The effect of roughness on bonding performance between old OPC concrete and new MPC concrete was studied. • Fractal dimension was used to define the roughness of the bonding surface. • Roughness has significant influence on the bonding strength and microstructure of interface between new and old concretes. This paper investigated the bonding performance between magnesium phosphate cement concrete (MPC) and ordinary portland cement concrete (OPC) with different roughness. The bonding interface was characterized using fractal dimension, backscattered electronic microscopy, and microhardness. The optimal mixture proportion of MPC is selected with the mass ratio of MgO-KH 2 PO 4 (M/P) by 3:1 and Na 2 B 4 O 7 ·10H 2 O-MgO (B/M) by 40%, which has the compressive strength of 52.8 MPa and the initial setting time of 24 min 20 s. It is found that the roughness indicated by fractal dimension has a positive correlation to rough depth and the bonding performance. The bonding interface can be categorized into two forms that either MPC paste bonds to OPC paste or bonds to the aggregate. Micro-analysis shows that the former has denser hydration products and lower porosity, providing better chemical bonding and the latter contributes to the mechanical interlocking which is the major form of the bonding force. MPC is a potential material for the field application of wet joints of the floating slab tracks. [ABSTRACT FROM AUTHOR]

Aging of Portland cement, due to its reaction with moisture and atmospheric CO 2 prior to regular use, has the potential to severely impair its hydration reactivity. The effectiveness of using metakaolin to improve the properties of aged Portland cement exposed to a laboratory conditions (RH=65 %, 20 °C) as well as the associated mechanism are studied. The incorporation of 5–10 % metakaolin changes the early-stage hydration kinetics of aged cement obviously by enhancing reactions of both C 3 S and C 3 A through the filler effect at the early hydration stage, thereby mitigating detrimental influences of aging on setting time and early-age strength development (up to 7 days). Metakaolin exhibits significant effectiveness on enhancing 28-day strength of aged cement, and the enhancement arises from the synergic reaction between metakaolin and CaCO 3 , which converts CaCO 3 resulting from aging into carboaluminate phases and produces secondary C-S-H. The incorporation of 5 % metakaolin increases the 28-day compressive strength of the sample with cement aged for one month to a comparable level as that of fresh cement. • Aging leads to relaxation and reconstruction of the cement surface can hinder the activity of the cement. • The filler effect caused by metakaolin promotes the reaction of C 3 S and C 3 A in aged cement. • The synergistic reaction between metakaolin and CaCO 3 formed in aged cement improves the mechanical property. [ABSTRACT FROM AUTHOR]

• The limited fractal behavior in cement paste is discussed. • Two modules of ordinary and multiscale fractal are adopted. • Pore structure in cement paste is well reconstructed. The fractal nature of cement paste has been discussed a lot in recent decades. Most of studies are concentrated on ordinary fractal dimension of a complete fractality, while an incomplete or limited fractality is exhibited in fact. This paper presents some results towards a comprehensive understanding about the limited fractal behavior in cement paste upon the mercury intrusion porosimetry test. To that end, two modules of analysis are adopted, i.e., the ordinary fractal and the multiscale fractal. Moreover, ordinary and multiscale fractal models are introduced to simulate pore structure, and pore size distributions are compared among ordinary fractal model, multiscale fractal model and test. Results indicate that multiscale fractal provides a much richer and preciser way than ordinary fractal to describe the limited fractal behavior in cement paste even it may deviate far from perfect fractaltiy. [ABSTRACT FROM AUTHOR]

The influence of pumping on the rheological properties of self-consolidating concrete (SCC) is widely recognized, but there is still limited understanding of its behavior within the pipeline. In this study, we propose a novel approach using equilibrium distances to investigate the evolution of rheological properties along the pipeline. Full-scale horizontal pumping circuits spanning 328 m were established to assess the axial development of SCC's rheological properties. Thirteen mixtures, with water-to-cement (w/c) ratios ranging from 0.22 to 0.27, were pumped at discharge rates varying from 5.77 to 12.69 L/s. Our findings show that for pumping setups and material studied, both the w/c ratio of SCC and the discharge rate significantly affected the influence of rheological equilibrium distances on pressure loss gradient changes. In all tested samples, viscosity values required the entire length of the pipeline to reach post-pumping levels, while yield stress values rapidly achieved their fully developed state upon entering the pipeline. Importantly, the predicted pressure loss displayed a strong correlation with experimental measurements, with an accuracy of 89.42% across all tested mixtures. Our predictive model showed an average improvement of 4.6% in accuracy compared to the linear approach, with the most significant enhancement observed in samples with higher w/c ratios. This research sheds new light on the behavior of SCC during pumping and provides valuable insights for optimizing the pumping process. • The equilibrium distance of rheology is introduced to describe SCC flow behavior along the pipeline. • Horizontal pumping circuits spanning 328 m is used. • Factors affecting the equilibrium distance of rheology are discussed. • The prediction accuracy of the model is validated. [ABSTRACT FROM AUTHOR]

• The bonding behaviors of the new-old mortar interface were studied. • The deterioration of the new-old mortar interface after coupled cycles was studied. • The microstructures of the new-old mortar interface were characterized. A well-bonded interface between concrete substrate and repair materials is of great significance for the durable repaired concrete. In this paper, the performance of the new-old mortar interface and deteriorations after wet-dry or heat-cool cycles were investigated by mechanical tests and microstructural analyses. Slant shear test, four-point bending strength test, back scattering electron microscopy (BSEM), microhardness test and thermogravimetric analysis (TGA) were carried out to characterize the interface deterioration. The results show that the slant shear test is suitable for evaluating the new-old mortar bond strength. The constituents of repair mortars affect the bond strength, but have little impact on the bending strength of composite beams. After cycled treatments, coupled effect of wet-dry and heat-cool cycles result in severer deteriorations of new-old mortar interface than heat-cool cycles do. Effect of heat-cool cycles is mainly attributed to reduction of interlocking point, while reductions in both interlocking point and chemical bond force are responsible for the interface deterioration after coupled cycles. The microstructural analyses further reveal the characterization of the new-old interface zone. [ABSTRACT FROM AUTHOR]

• Analytical solution to Couette inverse problem of Herschel-Bulkley fluid was derived. • The transformation equation was validated by both computer synthesized and experimental data. • Comparison between the analytical equation and the approximation equation was conducted. The Herschel-Bulkley model is one of the most commonly used rheological models for Non-Newtonian fluids, and it has been applied to describe the non-linear rheological behavior of fresh concrete. However, because it is difficult to transform the measured rotating speed and torque data into fundamental rheological units for coaxial cylinder rheometers, only an approximate approach has been proposed for this model. In order to improve the accuracy of the solution, a new integral equation describing the torque-rotation speed of Herschel-Bulkley model was derived in this paper, and 40 sets of simulated data were used for the comparison between the two methods. The equation introduced in this study was further validated by the experimental data of SCC. The results indicated that the established solution yielded more accurate results than the approximate one. [ABSTRACT FROM AUTHOR]

• Carbonation of steel slag results in the formation of CaCO 3 barrier which blocks the reaction of silica gel. • The incorporation of metakaolin enhances the reactivity of steel slag by promoting the reaction of CaCO 3 and formed silica gel. • The coupled substitution of carbonated steel slag and metakaolin leads to significant improvement of strength and water absorption. This study aims to promote the reactivity of basic oxygen furnace slag (BOFS) through accelerated carbonation and the combined use of metakaolin (MK). Influences of the incorporation of the combination of carbonated BOFS and MK at various cement substitution levels on strength development, water absorption, phase composition, and microstructure are investigated. It is revealed that the coupled substitution with carbonated BOFS and MK improved the formation of carboaluminate phases and stabilized ettringite owing to the synergic reaction between metakaolin and CaCO 3 derived from the carbonation of BOFS; and the consumption of CaCO 3 facilitates the pozzolanic reaction of the amorphous SiO 2 gel formed during carbonation, generating more hydration products. All these reactions contribute to improved impermeability and enhanced strength development; 45% of ordinary Portland cement (OPC) can be replaced while achieving a comparable strength to sample consisting of 100% OPC. In addition, compared to the sample incorporated with uncarbonated BOFS and MK, the compressive strength of the sample blended with 30% carbonated BOFS and 15% MK was improved by 32.5% at the age of 56d; meanwhile, the water absorption during 72 h was lowered by 67.7%. In terms of the environmental impact, the CO 2 emission and intensity for sample incorporated with 30% carbonated BOFS and 15% MK only account for 59% and 62% of those in sample comprised of 100% OPC. The study proposes an approach to improve the reactivity of BOFS efficiently and sequestrate a significant amount of CO 2 simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] • The role of CGS on the workability of cement paste with and without PCE was investigated. • The decrease of interparticle force leads to the improvement of fluidity when added CGS. • The aggregation of PCE in pore solution leads to its efficiency decrease in the cement pastes blended with CGS. Coal gasification slag (CGS) is the main by-product of coal gasification technology, and the utilization of CGS as mineral admixture is environmentally sound. In this paper, the effect and mechanisms of CGS on the workability (i.e., fluidity and rheological behaviors) of ordinary Portland cement (OPC) paste with and without polycarboxylate superplasticizer (PCE) were studied. The zeta potential and surface free energies of OPC and CGS were tested to calculate the electrostatic force and Van der Waals force variations due to the addition of CGS particles. The results revealed that CGS mainly decreases the van der Waals attraction force between binder particles, enhancing the fluidity and reducing cement pastes' yield stress and plastic viscosity. When blended with PCE, the dissolution of CGS mainly increased the ionic concentrations of Si(OH) x (4-x), which promoted the aggregation of PCE and decreased its adsorption, thus decreasing the fluidity and increasing the rheological parameters. [ABSTRACT FROM AUTHOR]

• Mortar bar incorporated with 30% glass powder exhibits good volume stability during external sulfate attack (ESA) test. • The pozzolanic reaction of glass powder significantly elevates the Na concentration and pH. • Elevated alkalinity of pore solution in sample with 30% glass powder leads to the dissolution of monosulfate. • The Pitzer model could give a reasonable estimation of the dissolution and/or precipitation trend of products formed during ESA test. Due to the presence of high alkali content, it is inferred that the improvement of sulfate attack resistance for blend with glass powder should not be solely ascribed to the refinement of microstructure. This study aims to explore the effect of glass powder on the pore solution and its relationship with the chemical sulfate attack process. Paste samples blended with 30 % wt. glass powder and quartz powder were prepared and subjected to a simulated external sulfate attack (ESA) test. To eliminate the effect of microstructure on sulfate ingress and alkali leaching, the pressed paste grains (after pore solution extraction) were immersed in test solution consisting of 5 % Na 2 SO 4 and extracted pore solutions during the ESA test. The evolution of the chemical composition of test solution and phase assemblage of pressed paste grains during the ESA test were quantitatively characterized. Results indicate that the improvement of sulfate attack resistance is related to the increase in alkalinity of pore solution. The high alkalinity of pore solution leads to the dissolution of monosulfate, which suppresses the formation of ettringite. The maintained high alkalinity reduces the saturation degree of ettringite, monosulfate and gypsum with respect to the pore solution, preventing it from precipitating even at a high sulfate ions concentration up to 0.5 M. This study highlights the effect of glass powder on alkalinity of pore solution and its relationship with stability of ESA products. [ABSTRACT FROM AUTHOR]

• Application of steel slag in cementitious materials based on dense packing can achieve high utilization efficiency of both steel slag and cement. • Early age hydration kinetics, fluidity of blends, and properties including strength and water absorption are investigated on paste specimens. • The appropriate amount of gypsum addition can enhance long-term strength through improving the early-age hydration kinetics SS-SPC cementitious systems. • The findings of this research help to valorize steel slag utilization in cement-based materials without sacrificing mechanical property and durability. Steel slag is an industrial solid waste with latent hydration nature, possessing a high potential use in cement and concrete but has not been fully utilized yet. This study reveals an implication approach based on dense packing to achieve high utilization efficiency of both steel slag and cement. Steel slag-based reverse filling approach utilizes higher volume of relatively coarser steel slag particles as micro fillers and a smaller quantity of fine cement grains as the major binding component. Thus, giving an initial compact packing structure and an enhanced strength of the resulting materials. Based on the packing density of various mixes, steel slag-based reverse filling cementitious materials are formulated. Early age hydration kinetics, fluidity of fresh pastes, and properties including mechanical strength and water absorption are further investigated on paste specimens. Results indicated that a maximum packing density of 0.6956 was attained for the blend containing 85 % steel slag with 15 % superfine Portland cement. The compressive strength of formulated mixes reached 96.4 MPa, 105.6 MPa and 123.8 MPa at 180 days for pastes containing 15 %, 25 % and 35 % of superfine Portland cement, respectively. The addition of appropriate amount of gypsum can enhance long-term strength by 8 ∼ 18 MPa through improving the early-age hydration kinetics of the steel slag based cementitious systems. The findings of this research help to valorize steel slag utilization in cement-based materials without sacrificing mechanical property and durability. [ABSTRACT FROM AUTHOR]

The stress relaxation behavior of cement and asphalt mortar (CA mortar) under different initial strain levels was investigated. Results show that the stress relaxation of CA mortar can be divided into two parts: the attenuation stress relaxation stage and stable stress relaxation stage. With the increasing strain levels, the relaxed stress, stress relaxation rate, stress relaxation modulus and specific stress relaxation of CA mortar increase gradually. Under the same initial strain level, the relaxed stress of type I CA mortar and type II CA mortar are little different, whereas the specific stress relaxation of type I CA mortar is much greater than that of type II CA mortar. In the strain range of 0.32–0.80%, the isochronous stress-strain relation of type I CA mortar is linear. When the strain is greater than 0.80%, the isochronous stress-strain relationship concaves to the strain axis gradually. The isochronous stress-strain relationship of type II CA mortar show linear increase in the strain range of 0.47–1.42%. A stress relaxation model based on thermodynamic theory was established, which agrees very well with the experimental results. [ABSTRACT FROM AUTHOR]