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• A multi-phase concrete creep model considering the real surface topography and geometric shapes of aggregate were developed. • The sensitivity of Burgers model parameters was conducted. • A contact-force-based method was proposed to quantitatively assess the effect of ITZ on creep. • Contact network, force-chain probability distribution, and meso-fabric anisotropy were assessed to explain the creep mechanism of concrete. Studying creep behaviors of concrete materials at a mesoscale level is crucial to understanding their mechanism. Discrete element method (DEM) could provide an effective numerical tool to explain the mesoscale mechanism of concrete materials. In this study, the creep characteristics of concrete are analyzed by combining DEM and Burgers model. Firstly, a multi-phase concrete numerical model consisting of matrix, aggregate, and interfacial transition zone (ITZ) was developed. Then, the sensitivity of the Burgers model parameters was conducted. Finally, to investigate concrete creep behaviors at a mesoscale level, a series of numerical simulations were carried out. Simulation results show that Burgers model can reflect the creep behavior of concrete well. The porosity gradually decreased as the loading duration increase, and deceleration became stable at the later stage. The creep contribution of ITZ decreases with the increase of the ratio of ITZ strength to matrix strength. Force-chain strength in ITZ was greater than that in matrix, and viscoelastic sliding or squeezing occurs at Burger contact. Meanwhile, the direction distribution of force-chain strength in the matrix is regular and the main direction of the contact distribution is about 90° or 270°. In addition, the probability function of contact force is exponential, and the strength probability distribution of matrix and ITZ contact reached the peak at 0.7 f / f ¯ and then decreased, and the proportion of strong contact and weak contact in matrix and ITZ was about 70% and 30%, respectively. The current study can bridge the gap between simulation and experimental research. [ABSTRACT FROM AUTHOR]

• Specimens made on-site using the same raw materials and processes. • Bubble defect areas were divided into 13 classifications. • Correlation between the distribution of bubble defects and the splitting tensile strength. In this research, the bonding performance of the interlayer interface was investigated via the two main factors of the size and number of bubble defects in combination with field tests. The mechanical index of the splitting tensile strength was used to characterize the bonding performance of the interlayer interface. The bubble defect areas of the specimens were divided into 13 classes. Via the statistical analysis of the bubble defects, the probability of the occurrence of small bubble defects was found to be greater than that of large bubble defects. For the same or a similar area ratio of bubble defects, the splitting tensile strengths of specimens with different bubble sizes were found to be different. The bond strength near the perfusion hole area was found to be relatively weak. The splitting tensile strength was also found to be larger at locations farther away from the perfusion hole area. This work provides an effective reference for the scientific evaluation of the pouring quality of the self-compacting concrete filling layer. [ABSTRACT FROM AUTHOR]

The tensile strength is one of the main parameters in the design of concrete structures and has an important influence on the cracking performance and durability of concrete materials. As the weak region in concrete, the strength of the interface transition zone (ITZ) directly affects the dynamic mechanical response of concrete. Meanwhile, considering that the tensile performance of concrete is far weaker than its compressive performance, the study of the strength of ITZ is of great significance to the dynamic tensile fracture characteristics and mechanical properties of concrete. In this paper, a method combining 3D scanning technology and Clump-Cluster was proposed to generate a real geometry shape model of crushable aggregate. On this basis, the 3D discrete element model (DEM) of high-strength concrete was constructed using the Flat-Joint Model (FJM). The effects of the ITZ strength on the failure mode, number of microcracks, tensile strength and strain rate effect of high-strength concrete under strain rates from 0.01/s to 100/s were studied by splitting tensile test. The simulation results indicate that the number of microcracks generated decreases with the increase of ITZ strength, and the proportion of ITZ cracks decreases obviously. When the ITZ strength exceeds the critical value of 0.8 times that of mortar, the tensile strength is almost not affected by ITZ strength. In addition, based on the numerical simulation results, a modified formula that can reflect the functional relationship between the ITZ strength and the dynamic increasing factor of the concrete tensile strength (TDIF) is proposed, and the rationality of the TDIF modified formula is verified. • Crushable aggregates with the real geometry shape are generated by using clump-cluster method. • Flat-Joint Model is adopted as the constitutive law. • The tensile strength is almost not affected by ITZ strength when its strength exceeds 0.8 times that of mortar. • A modified formula that can reflect the functional relationship between the ITZ strength and the TDIF is proposed. [ABSTRACT FROM AUTHOR]

• Aggregates with the real geometry shape was generated by using clump module. • Flat-Joint Model is adopted as the constitutive law. • The damage evolution process of concrete is analyzed from microscopic point of view. • Effects of aggregate surface texture on the mechanical behaviors of concrete are studied. As the main component of concrete, aggregate has an important influence on the performance of concrete. In this study, the influence of coarse aggregate content and surface characteristics on the compressive mechanical properties and the damage evolution process of high-strength concrete were studied by using a 3D discrete element method (DEM). In order to improve the reliability of simulation results of concrete, a more accurate numerical simulation method was proposed. First, clumped-particle modules from the real aggregate geometry obtained by 3D Scanning were generated and then randomly distributed in the concrete model according to the specified aggregate content. Then the Flat-Joint Model (FJM) which can represent the micro-structure characteristics of concrete more reasonably was used to define the contact mechanical characteristics between different components. Based on this, the compressive strength, number of microcracks and damage evolution process of concrete with different aggregate surface texture factor (STF) and volume ratio were analyzed. The simulation results showed that aggregate surface texture and volume ratio were closely related to the compressive strength of concrete, and both have an exponential correlation with the compressive strength. The STF and volume ratio of aggregate have a significant effect on the proportion of tensile microcracks, and the concrete with large aggregates STF has more uniform stress distribution and wider damage range. [ABSTRACT FROM AUTHOR]

• Electric curing is proposed for the rapid curing of cement at room temperature. • Suitable electrical curing regime can effectively improve the early strength of cement. • Joule heat is the key to accelerate the hydration of cement. • Electric curing consumes much less energy than steam curing. To understand the effects of direct electric curing condition on the mechanical strength and microstructure of cement paste, a series of experiments were carried out to investigate the effects of alternative current voltages and frequency on compressive strength of samples. And the corresponding microstructure of samples were also analyzed by several measurements including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porometer. The results show that alternative current electric voltage and frequency can greatly influence the early compressive strength of a cement paste. And a suitable electric curing condition can make hardened cement paste keep a steady growth of compressive strength and excellent microstructure. The Joule heat of direct electric curing on cement paste is the main reason that accelerates the hydration and improve the early strength development of sample. This study will provide an important technical support for exploring low carbon rapid electric curing method to produce green high early strength cement concrete prefabricated element. [ABSTRACT FROM AUTHOR]

• The effect of plastic viscosity of SCC mixtures on mechanical properties is studied between SCC layer and steam-cured concrete. • Fractal dimension is used to characterize the characteristics of bonding surface. • The microstructure characteristics of the bonding interface are obtained. • The bonding interface zone model is established and the optimal value of plastic viscosity is obtained. In CRTSIII ballastless track structure, the bonding interface between self-compacting concrete (SCC) filling layer and steam-cured concrete track slab not only affected the interaction between filling layer and track slab, but also affected the effect and bond stiffness of connecting reinforcement, which was one of the key links of the whole track structure. Quality control of rheological properties of SCC mixture was proving to be critical for the success of the bond between steam-cured concrete and SCC layer concrete. In this research, the fractal dimension was calculated to characterize the bonding interface characteristics with different plastic viscosities. Moreover, the effect of plastic viscosity on mechanical properties was studied between SCC layer and steam-cured concrete. The bonding interface zone between SCC layer and steam-cured concrete was defined by microhardness and BSE tests. The experimental results indicated that the fractal dimension can better characterize the characteristics of bond surface and had a negative correlation with splitting tensile strength. Mechanical properties and bonding interface structure between steam-cured concrete and SCC layer improved with increasing the plastic viscosity of SCC mixture, especially when the viscosity was greater than 100 pa.s. The bonding interface zone model was established to explain the mechanism of the bond between steam-cured concrete and SCC layer. [ABSTRACT FROM AUTHOR]

• Using the SVM-PSO algorithm to predict the splitting tensile strength. • An effective classification method for the bubble defect area of the bonding interface. • Every training sample set or every test sample set has a 14-dimensional feature vector. The bonding performance of the interface between two concrete layers is of great importance for China Rail Track System III (CRTS III) slab ballastless track structure. While the bonding performance is close to the distribution and amounts of defects such as the bubble or the void on the bonding interface. In this paper, combining the Support Vector Machine (SVM) with the Particle Swarm Optimization (PSO) algorithm, named SVM-PSO algorithm is used to predict the splitting tensile strength of the bonding interface based on the distribution of defects. And the influence of different parameters in the SVM-PSO algorithm on the prediction ability is discussed. Results indicate that the relative error between the average strength value of every 100 predictions and the experimental strength value is less than 5%. The achievements will provide an effective method for predicting the splitting tensile strength of the bonding interface between two concrete layers like CRTS III slab ballastless track structure in practice. [ABSTRACT FROM AUTHOR]

This paper systematically investigated the effects of alkali activator modulus (AM), alkali dosage (AD), and water-fly ash ratio (W/FA) on the pore volume, pore size distribution, pore volume fractal dimension (D v), and pore surface fractal dimension (D s) of fly ash-based geopolymer (FABGs) by orthogonal test and mercury intrusion porosimetry test. D v and D s of FABG can be calculated by the Menger sponge model and Zhang and Li's models, respectively. The relationship between multiple synthesis parameters and pore characteristics of FABGs was detailedly studied through range analysis and correlation detection analysis, which provides a basic understanding of the influence of multiple parameters on the pore characteristics of FABG, as well as the relationship between pore characteristics and mechanical properties. The results show that AM has the greatest effect on the volume proportion of gel pores and transition pores, and AD and W/FA have the greatest effect on the volume proportion of capillary pores and large pores, respectively. W/FA has the greatest effect on the porosity, and the porosity and the most probable aperture increase with the increment of W/FA and decrease with a rise in AD. It is worth noting that AM, AD, and W/FA have little effect on the D v of larger pores, but have a greater on the D v of smaller pores, with the influence order of AD-W/FA-AM. D s of the large pores and capillary pores range between 2.70–2.90, and the D s of the transition pores and gel pores are mostly greater than 3.00, which suggests that there may be more ink-bottle pores in transition pores and gel pores. In addition, there was a strong linear relationship between the porosity and compressive strength of FABGs, and the compressive strength of FABGs showed a decreasing trend with the increase of porosity. Compared with D v , there is a stronger correlation between D s and compressive strength, indicating that the roughness of the pore surface and the pore size distribution have a greater influence on the compressive strength of FABGs. • The influence order of synthesis parameters on the porosity of FABGs was W/FA-AD-AM. • AM, AD and W/FA have the greatest effect on the volume proportion of gel and transition pore, capillary pore and large pore. • The pore surface fractal dimensions of the large pores and capillary pores range between 2.70-2.90. • There was a strong linear relationship between the porosity and compressive strength of FABGs. [ABSTRACT FROM AUTHOR]

To investigate the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste, various admixtures such as fly ash, metakaolin, super-absorbent polymer, and expansion agent were selected for the above-mentioned experiments. The effects of mixing two admixtures on the drying shrinkage deformation and crack resistance performance of the limestone powder-cement paste was studied. Additionally, hydration exotherm, hydration products, microscopic morphology of samples were analyzed to understand the underlying mechanisms. Based on the hydration process, the addition of fly ash and metakaolin can promote the formation of carbon aluminate in the reaction system, thereby reducing the porosity. Fly ash is more beneficial for the hydration heat peak value of cement paste, effectively eliminating temperature strain. The results indicate that effects of mixing two admixtures on the improvement of drying shrinkage and crack resistance of limestone powder cement paste are much better than using a single admixture. Among them, the combination of metakaolin and expansion agent shows the best overall mitigating effect on the drying shrinkage and crack resistance of limestone powder cement paste. This compound admixtures reduces the drying shrinkage of the paste by approximately 30% and delays the cracking time of the specimens by 34.4 h. • The utilization of limestone powder in limestone powder cement paste can be effectively enhanced by mixing two admixtures. • Using a smaller ring size for the ring test to monitor the cracking resistance of cement paste. • The application of linear fitting revealed that the moisture loss characteristics of cement paste manifest in two stages. • Analyzing the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste. [ABSTRACT FROM AUTHOR]

Traditional cement-based materials are quasi-brittle materials characterized by their low flexural toughness and susceptibility to cracking. In recent years, numerous endeavors have been devoted to this challenge, and also plentiful fruits have been evidenced. In this work, the comprehensive review is dedicated to exploring enhancement technologies for the toughness of cement-based materials. Emphasis is placed on current advancements in the area of toughening materials and manufacturing processes. The reviewed toughening materials are systematically categorized according to their scales, including nano, micro, and macro scales. The combination of toughening materials at multi-scales has also been illustrated. Moreover, the manufacturing processes are examined, with a focus on homogenization mixing and precision molding. The effects of these technologies and the corresponding mechanisms behind them are compared and revealed, respectively. Eventually, this work concludes the existing findings and provides insights into future research directions for the toughening of cement-based materials. • Toughening effects and mechanisms of materials on nano-, micro- and macro-scales are compared and revealed, respectively. • Advanced manufacturing processes for improving the toughness of cement-based materials are reviewed. • The future research directions on toughness enhancement of cement-based materials are provided. [ABSTRACT FROM AUTHOR]

Enhancing the interfacial deformability of UHPC positively impacts its toughness and durability. In this work, a novel interfacial toughening strategy was proposed and employed for UHPC, in which the aggregates were treated with polyacrylate emulsion (PL) or PL modified by silica fume or carbon nanotubes to form an interfacial flexible layer (FL). The flexural characteristics of the prepared UHPC were comprehensively investigated, with attention to the damage evolution based on acoustic emission. Meanwhile, the corresponding toughening mechanism was discussed. The results showed that the FL modified by carbon nanotubes effectively enhanced the flexural deformation capacity, energy absorption capacity, and toughness of UHPC, while maintaining flexural strength. Introducing FL reduced ringing count and acoustic emission energy and mitigated damage rate of UHPC. The FL altered the flexural damage mode of UHPC by alleviating stress concentration to prevent sudden matrix cracking and fiber debonding. During the elastic stage, FL and the UHPC matrix jointly sustained tensile cracks, enhancing the matrix's energy absorption capacity, which correlated positively with the percentage of tensile cracks. In the softening stage, this capacity correlated positively with the percentage of shear cracks. Moreover, FL reduced the probability of microcracks at the interface. Although the FL reduced the average microhardness at the interface, it stabilized the performance of hydration products and increased their maximum microhardness. The FL promoted interfacial energy dissipation and synergistically bridged microcracks with steel fibers, ultimately enhancing the flexural toughness of UHPC. • A novel interfacial toughening strategy for UHPC was proposed. • The flexural characteristics of UHPC with flexible layer were investigated. • The flexible layer promoted the flexural deformability and toughness of UHPC. [ABSTRACT FROM AUTHOR]

Damping cementitious materials have been widely used in engineering structures for vibration control. However, achieving a balance between the mechanical strength and damping capacity of cementitious materials remains a challenge. Herein, we utilized an initiator (APS) to initiate the self-crosslinking reaction of PVA molecules in C 3 S paste, then successfully introduced the viscoelastic PVA membranes into C-S-H gel to enhance its energy dissipation capacity. Results showed that the self-crosslinking PVA (scPVA) increased the loss modulus (E ′ ′) of C-S-H gel by about 158 %, increased loss tangent (tan δ) by 85 % and increased the compressive strength by 24 %. Nano-microscopic tests and molecular dynamics (MD) simulation confirmed that scPVA was introduced into C-S-H gel via the hydrogen-bonding interaction, and then formed the viscoelastic PVA membranes, which promoted C 3 S hydration, reduced the pore size of C-S-H gel and increased the mean chain length (MCL) of C-S-H gel. This study proposes a novel approach for designing high-damping cementitious materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of Green Ultra-High Performance Concrete (GUHPC) is one of the primary approaches to combat global warming in the construction industry and has received widespread attention. Accurately quantifying the physical and chemical filling effects of binder materials can aid in the development of more efficient design methods for GUHPC. The hydration and microstructure development of GUHPC were investigated by a combination of the isothermal calorimetry, mercury intrusion porosimetry (MIP), thermogravimetry (TG), X-ray diffraction (XRD) and backscattered electron microscopy (BSEM). The physical and chemical filling effects of each binder material on the porosity of paste were quantified. The results indicated that both the physical and chemical filling effects of the binder materials made essential contributions to the porosity. Compared with in UHPC, supplementary cementitious materials (SCMs) play a better chemical and physical filling role in GUHPC. More attention needs to be paid to the chemical filling effect of mineral admixtures in the design of GUHPC. Reasons for limiting the ability of binder materials in GUHPC to achieve better chemical filling effects were discussed. • The hydration degree of each binder material in GUHPC were investigated. • The physical and chemical filling effects of binder materials were quantified. • The chemical filling effect of mineral admixture becomes more pronounced in GUHPC. • The link between chemical and physical effects on pore structure was established. [ABSTRACT FROM AUTHOR]

• Investigate the fatigue performance of slab track filling layer. • The fatigue damage law and fatigue life of the slab track filling layer are significantly affected by environmental factors such as rainfall and acid rain. • The mechanical behavior of the filling layer is observed by combining ABAQUS/CAE and Extend Finite Element Method (XFEM). • The stress intensity factor (SIF) combined with stress and strain is used to analyze the evolution of the stress field and displacement field of the FLC crack tip. The filling layer concrete (FLC) is the crucial component materials in the CRTS III slab track structure. In order to investigate the properties evolution of FLC under the coupling action of environment and fatigue load, a three-dimensional finite element model of the CRTS III slab track structure system was established, and extended finite element method (XFEM) was used to calculate the stress intensity factor (SIF) of the crack tip under different conditions through the domain interaction. Results show the fatigue load significantly decreases stiffness of FLC. Coupling actions of water-saturated and fatigue load, acid-rain and fatigue load accelerate the deterioration of FLC. The decrease of stiffness leads to stress redistribution in FLC. With the increase of fatigue load, the stress of FLC decreases, but the stress of steel in the FLC increases. Positions of fatigue load on FLC take on significant influence on the evolution of properties. The deterioration rate of FLC at the end of the slab is greater than that of the middle FLC. Under the coupling of fatigue load and environment, FLC at the end of the slab is more likely to crack and propagation, and the cracks are most likely to appear from the bottom of the FLC. Due to the influence of the stress field and displacement field at the crack tip, with the fatigue load increasing, the SIF at the external crack of FLC has an exponential decrease. The coupling action of environment and fatigue load accelerates the deterioration of FLC, and also leads to the rapid reduction of SIF. In this study, the coupling of acid-rain and fatigue reduces the properties of FLC most obviously. [ABSTRACT FROM AUTHOR]

• The physical effect of intense UV radiation accelerates the mass loss of the cement mortar. • The chemical effect of the intense UV radiation exacerbates the carbonation of the cement mortar. • FA and GGBS have the effect of reducing drying shrinkage under conditions of intense UV radiation. • The incorporation of FA and GGBS weakens the carbonation resistance of the cement mortar. The intense UV irradiation factor in the plateau area is easy to ignore, but it may have adverse effects on the microstructure and properties of concrete. Theredore, to clarify the evolution characteristics and the corresponding mechanism of the drying shrinkage of cement-based materials under intense UV irradiation environments at high altitudes cement mortars incorporating three types of mineral admixture were prepared to investigate the drying shrinkage, mass loss and microstructure, respectively. The hydration process and microstructure of samples were discussed in detail by microscopic experiments including TG-DTG, MIP, XRD, and IR patterns analysis. The results show that the mass loss and drying shrinkage of the cement-mineral admixture mortar exposed to intense UV irradiation were higher than those under the standard environment. Under intense UV radiation environment, the total porosity, mesoporosity (<50 nm), and carbonization degree of each group of samples increased. However, UV irradiation did not change the phase composition, chemical bond type, and polymerization degree of the C S H gel of the cement-based material. The incorporation of fly ash and slag resulted in the reduction of drying shrinkage of mortars, an increase in carbonation degree, and decreasing the hydration degree. [ABSTRACT FROM AUTHOR]

In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and double-layer board with gradient structure. The physical, mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with appropriate mixture design exhibited almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3 MPa and 1 MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and disclose the mechanism of sound absorption and insulation in the material. [ABSTRACT FROM AUTHOR]

The impulse response method, as a mechanical impedance analysis method with high-impact energy, can provide a rapid assessment of structural integrity. For this reason, the impulse response method is applied to subway slab ballastless tracks, and the theory behind this method, as well as the applicability of detecting the voids within the self-compacting concrete (SCC) filling layer, are deeply studied. The theoretical derivation of the mobility function of subway slab ballastless track under impact load is performed. The finite element model is established and the propagation of elastic waves in the process of impulse response method is simulated. The study also investigates the sensitivity of various characteristic parameters and the frequency analysis range to void identification in the SCC filling layer. Furthermore, the characteristic parameters for defect identification in the SCC filling layer are constructed and subsequently validated through a full-scale test. The results reveal that the impulse response method is capable of generating elastic waves with higher energy and longer wavelengths within the structure. This characteristic is advantageous for the detection of concealed defects in the multi-layer structure. The mobility spectrum of subway slab ballastless track exhibits multi-frequency peak characteristics, and the calculated cut-off frequency of the peak-mean mobility ratio should be extended to more than 1600 Hz. Among the three characteristic parameters of peak mobility, dynamic stiffness, and peak-mean mobility ratio, the peak-mean mobility ratio has the advantage of accurately identifying the void position and providing a more precise range. • The propagation of elastic waves was simulated. • Characteristic parameters were reconstructed. • Verified through full-scale tests with preset defects. [ABSTRACT FROM AUTHOR]

• Higher calcination temperature reduced the dissolved degree of Al in sludge ash. • S600 ash promoted the formation of Al-bearing products but inhibited the C 3 S hydration significantly. • The reaction of S800 ash with cement contributed to more hydration heat and hydration products. Sewage sludge ash has potential to be used as supplementary cementitious material in the production of building materials. The chemical effect of sewage sludge ash on early-age hydration of cement was investigated in this study. Two types of sludge ash calcined at 600 °C (S600) and 800 °C (S800) were blended with cement for analysis of hydration heat evolution, solid phase assemblage and aqueous composition. The aluminate dissolution of S600 ash promoted the formation of ettringite and consumption of gypsum, resulting in a high initial hydration heat. However, high concentrations of Al and Si caused by continuous dissolution of aluminate and silicate in S600 ash inhibited significantly the C 3 S dissolution. Interestingly, S800 ash had slight effect on early cement hydration since higher calcination temperature decreased the activity of aluminate. As compared with the reference, cumulative hydration heat of blended paste with 30% S800 ash at 7 days was increased by 18.72% indicating the occurrence of reaction between sludge ash and cement. Further study is recommended to focus on the long-term performance of cement-based materials blended with sludge ash. [ABSTRACT FROM AUTHOR]

• Physicochemical properties and pozzolanic activity of sludge ashes were investigated. • The sludge ash calcined at 800 ℃ presented high pozzolanic activity. • Sludge ash addition enhanced the formation of Al-bearing hydrates. • No leaching risk was detected for the use of sludge ash in building material. The application of aluminum-based flocculant in wastewater treatment results in a large amount of aluminum-rich sewage sludge. This work investigated the influence of calcination process on physicochemical characteristics and pozzolanic activity of aluminum (Al)-rich sludge ash and studied the effect of sludge ash on cement hydration. The results showed that higher calcination temperature from 600 ℃ to 900 ℃ increased the amorphous content in sludge ash. The pozzolanic activity of sludge ash calcined at 800 ℃ and 900 ℃ was confirmed by Frattini test. In view of strength activity index of blended mortar and energy conservation, the optimal calcination condition of sewage sludge ash was calcined at 800 ℃ with air-cooling. The addition of sludge ash promoted the transformation of ettringite to monosulfate phase in cement paste. However, the high Al concentration dissolved from S6 and S7 ash inhibited significantly the cement hydration and resulted in low compressive strength values of the blended mortars. The pozzolanic reaction of S8 and S9 ash produced more hydration heat and additional Al-bearing products such as katoite and monosulfate which contributed to the strength development of mortars. Furthermore, the heavy metals in sewage sludge can be immobilized in ash structure during calcination process and the structure of hydration products, which ensures the environmental security of sludge ash utilization in construction materials. [ABSTRACT FROM AUTHOR]

A recently developed type of metaconcrete consists of engineered resonant steel cells exhibiting superior wave attenuation and energy dissipation capacity. Nonetheless, it has always been a challenging task to prepare affordable and environmentally friendly metaconcrete. In this study, we employed recycled rubber powder (RP) to coat coarse aggregate (crushed stone) as a resonant aggregate (RA). The RA was then incorporated into the metaconcrete using conventional mechanical mixing techniques. The results demonstrated a significant 175% increase in the damping ratio of the metaconcrete, primarily attributable to the superior energy dissipation of the RA. Furthermore, the RP coating eliminated the interface transition zone (ITZ) in the concrete, thereby enhancing its impermeability and freeze-thaw resistance. This research presents an innovative approach to developing environmentally friendly cementitious materials with high damping properties. [Display omitted] • The resonant aggregates were produced by coating rubber powder onto coarse aggregates. • A novel high-damping metaconcrete was prepared by using designed resonant aggregates. • The compressive strength and durability of the metaconcrete were investigated. [ABSTRACT FROM AUTHOR]

Geopolymeric recycled aggregate concrete (GRAC) has been treated as an environmentally friendly construction material by recycling construction and demolition waste and utilizing sustainable binders. For the first time, the flexural fatigue performance of GRAC based on fly ash/ground granulated blast furnace slag was studied, in which three slag contents (i.e., 0%, 15%, and 40% of the mass of the total binder) was employed. GRAC specimens with 100×100×400 mm3 were prepared, and tested under different stress levels and the constant-amplitude cyclic loading conditions. Based on the results, the fatigue life, fatigue strength, and damage process of GRAC were analyzed and also compared with that of geopolymeric natural aggregate concrete. The results show the fatigue life distributions of GRAC were in good agreement with the two-parameter Weibull distribution. Furthermore, the fatigue equation based on a double logarithmic relationship was determined for the flexural fatigue strength of GRAC corresponding to different survival probabilities. It was revealed that the flexural fatigue strength of GRAC was decreased after the recycled aggregate replacement but was improved after the slag incorporation. Also, the fatigue flexural strengths at two million cycles at 95% survival probability were 0.577–0.708 of its static flexural strength, which is identical to ultra-high performance concrete. • Flexural fatigue performance of GRAC has been investigated. • Flexural fatigue life of GRAC conforms to a two-parameter Weibull distribution. • Fatigue equations of GRAC were established. • Fatigue limit strength of GRAC was determined. • Faitgue reliability based on the Miner model was performed to illustrate the damage process of GRAC. [ABSTRACT FROM AUTHOR]

• C-S-H seeds and sulphoaluminate cement were used to prepared RH-UHPC. • The flexural load–deflection response of RH-UHPC was studied by AE technology. • The flexural failure pattern, strength, energy absorption capacity, and toughness index of RH-UHPC were investigated. • Micromorphology, phase composition, and pore structure of RH-UHPC were studied. With the increasing requirements for emergency repair projects, there is a pressing need for high-quality repair materials. In this work, a series of rapid hardening ultra-high performance concrete (RH-UHPC) were prepared by using C-S-H seeds and SAC as early-strength agents. The effects of these early-strength agents on RH-UHPC's flexural behaviors, including failure pattern, strength, energy absorption capacity, and toughness index, were investigated. Also, the variations of acoustic emission signals and microstructure were studied to provide a thorough insight into the influence of early-strength agents on RH-UHPC. The results show that C-S-H seeds and SAC exhibited a good effect on improving the 1-day flexural strength of RH-UHPC, but increased the risk of shear failure at 28 days. The flexural strength, energy absorption capacity, and toughness of RH-UHPC at 28 days were reduced by adding C-S-H seeds. However, combining C-S-H seeds with SAC alleviated this reduction. Moreover, incorporating early-strength agents enhanced the ringing counts, AE energy, damage rate, and the proportion of shear cracks. The noticeable increase in r value (i.e., RA/AF) judged the damage stage of RH-UHPC more reliably. Micro-analysis revealed that introducing C-S-H seeds increased the internal cracks and the Ca/Si ratio of C-S-H gel, but the hybrid of C-S-H seeds and SAC partially mitigated above problem. The incorporation of SAC notably increased the AFt content and decreased the CH content. C-S-H seeds presented little effect on the hydration degree of RH-UHPC, but roughened the pore size and enlarged the average pore size. [ABSTRACT FROM AUTHOR]

Steam curing is a crucial stage for the strength development of steam-cured concrete. This study comprehensively investigated the hydration kinetics, mechanical properties, and autogenous shrinkage (AS) of cement pastes during steam curing. A hydration-dependent analytical method was proposed to analyze the mechanisms governing the development of mechanical properties and AS of steam-cured cement pastes (SCPs). Results revealed that in this investigated curing regimes, the peak hydration rate of SCPs was approximately 7 times higher than that of standard-cured pastes (NCPs). SCPs exhibited faster time-dependent mechanical property development but slower hydration-dependent mechanical property development than NCPs. This difference was primarily attributed to variations in initial structure establishment and free water content. Moreover, an elevated curing temperature reduced the growth rate of hydration-dependent AS due to large capillary pores and low surface tension, which suggested that AS should not be considered as a cause of heat damage to SCPs. [ABSTRACT FROM AUTHOR]

• Increasing the recycled aggregate replacement ratio increases the mass loss rate. • Sensitivity of drying shrinkage increases with higher recycled aggregate replacement. • The drying shrinkage strain of GRACs develops rapidly in the early stage. • Higher slag content and curing temperature reduce drying shrinkage of GRACs. In this work, the drying shrinkage behavior of geopolymeric recycled aggregate concrete (GRAC) was studied with attention devoted to the mass loss, drying shrinkage strain, and sensitivity of drying shrinkage to water loss. The GRACs were prepared based on different fly ash/slag ratios and various dosages of recycled aggregate. Also, two types of curing regimes were employed, including ambient and heat curing. Additionally, the drying shrinkage strain development of GRACs was fast in the first 28 days and then slowed down with time. Recycled aggregate dosage increased the dry shrinkage strain while increasing the slag content and curing temperature reduced the drying shrinkage strain. Analogously, the sensitivity of drying shrinkage to the mass loss was raised under high recycled aggregate replacement ratios, whereas decreased when the slag content increased or heat curing was employed. Based on the test results, a prediction model was established for the drying shrinkage of GRACs, in which the factors of recycled aggregate replacement ratio, slag content, and curing regime were involved. [ABSTRACT FROM AUTHOR]

[Display omitted] • The BSE-IA and EDS analysis were employed for characterize the ITZs of RAC. • Aggregate enhancements could take obviously strengthening effect on ITZs. • Soaking RCA in CEM-SF slurries had a better improvement effect on ITZs. • The Ca/Si atomic ratio of ITZs was reduced after enhancement of RCA. Recycled concrete aggregate (RCA) enhancement is an important method to improve the performance of recycled aggregate concrete (RAC). However, the quantitative studies on the change of microstructure of interfacial transition zones (ITZs) were few and far, especially after enhancement of RCA with different methods. This paper investigated the influence of carbonation enhancement (carbonation time, soaking in CH saturated solution and then carbonation) and chemical enhancement (respectively soaking in Na 2 SiO 3 saturated solution and cement-silica fume (CEM-SF) slurries) of RCA on the change of microstructure of ITZs (including the ITZ between old aggregate-new paste (ITZ 1) and ITZ between old paste-new paste (ITZ 2)) in RAC. The porosity, the un-hydrated cement particles (UH) content, the volume fraction of hydration products (VFHP) in ITZs and the width of ITZs were obtained by backscattered electron imaging analysis (BSE-IA) and energy dispersive spectrometer (EDS) analysis. Results showed that the carbonation enhancement of RCA could not effectively strengthen ITZ 1. However, soaking RCA in Na 2 SiO 3 saturated solution and CEM-SF slurries could decrease the porosity and the UH content, develop the VFHP, and reduce the width of ITZ 1 , then strengthening ITZ 1. Both carbonation and chemical enhancement could take obviously improvement on ITZ 2. Additional calcium sources could be added to RCA by soaking in CH saturated solution, improving the effect of carbonation enhancement of RCA. Soaking in CEM-SF slurries had a better improvement effect on ITZs. After RCA was soaked in CEM-SF slurries, the porosity in ITZ 1 and ITZ 2 decreased by 36.8% and 44.0%, the UH content of ITZ 1 and ITZ 2 decreased by 22.6% and 53.6%, the VFHP of ITZ 1 and ITZ 2 increased by 22.6% and 20.9%, and the width of ITZ 1 and ITZ 2 decreased by 42.9% and 50%. EDS analysis showed that the Ca/Si atomic ratio of ITZs was reduced after RCA enhancement, which generated more hydration products and then decreased the porosity and the width of ITZs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sewage sludge ash (SSA) was utilized to produce sustainable Portland cement. • Slag and fly ash compensate for the shortage of sewage sludge ash. • High cement replacement as 30 wt% demonstrated great performance. • The synergy of admixtures refined the pore structure of cement-based materials. Substituting cement with sewage sludge ash greatly benefits the environment and the economy, but the improved methods of the performance of sludge ash cementitious materials should be further studied. Systematic experiments were designed to investigate the effects of typical municipal sewage sludge ash (SSA) in combination with slag and fly ash on cementitious material properties, including workability, mechanical strength, water absorption, chloride penetration, and drying shrinkage. Furthermore, the hydration and microstructure of the cement pastes were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption and desorption (NAD) tests to better understand the properties of sludge ash cementitious materials. The results demonstrate that, 30 wt% SSA resulted in 18.6 % fluidity loss, 16.01 % lower compressive strength, and higher water absorption coefficient and chloride migration coefficient (D RCM) at 28 days compared with the reference specimen. However, the performance of the sludge ash mortar was improved with the combination of SSA, slag, and fly ash. The optimum combination proportion was found to be 10 wt% SSA, 10 wt% fly ash, and 10 wt% slag, and the corresponding mortar demonstrated ideal strength and resistance to water absorption and chloride migration. Additionally, the mortar with 30 wt% SSA had more than 30 % reduced drying shrinkage compared to the reference cement mortar at 90 days. The slag converted monosulfate into hemi/monocarboaluminate, thus increasing the abundance of hydrates, and the incorporation of slag and fly ash promoted pozzolanic reactions and refined the pore structure of the blended pastes. This study proposes a reliable and practical method to promote the utilization of sludge ash. [ABSTRACT FROM AUTHOR]

Developing an eco-friendly UHPC with Belite cement (BC) is a great challenge because the mechanical strength of concrete with BC develops much more slowly than Ordinary Portland cement (alite-rich cement, OPC). However, BC has a lower CO 2 footprint than OPC due to a lower calcined temperature and less limestone demand, making it green cement. Besides, concrete with BC has better long-age performance. In this study, the utilization of BC in UHPC was compared to that of OPC. Three curing regimes were used for the designed UHPC. The compressive and flexural strengths of UHPC-BC are lower than of UHPC-OPC at one day but higher after 28 and 90 days of standard curing. After heat curing, the mechanical strength development of UHPC-BC improves noticeably and exceeds UHPC-OPC. UHPC-BC has a higher flexural strength to compressive strength ratio (f f /f cu), and there are more C–S–H, less CH and lower pore coarsening of UHPC-BC paste than UHPC-OPC, especially after heat curing. UHPC-BC has lower environmental impact indices at long age than UHPC-OPC. At 90 days of autoclaved curing, the compressive of UHPC-BC reaches up to 197.5 MPa with the embodied carbon content of 934.37 kg/m3, which is much lower than most UHPCs. [ABSTRACT FROM AUTHOR]

This paper elucidated the temperature dependence of cement setting by comparing the storage modulus (Gʹ) evolutions under different temperatures ranging from 10 to 55 °C. The temperature-induced changes in cement hydration and colloidal interaction were also explored to reveal the underlying physio-chemical effects. It was found that the increase in temperature significantly accelerates the growth of Gʹ in all the stages of setting process, which mainly arises from the promotion of forming "calcium silicate hydrates (C–S–H) bridges" and compressing the electrical double layer of particles. For the same hydration degree, the rise of temperature leads to a greater Gʹ of cement paste. It was attributed to the diminution of the electrostatic repulsive force between particles caused by not only the direct effect of rising temperature but also the higher SO 4 2-/Ca2+ concentration ratio of interstitial solution in the paste cured at the higher temperature. [ABSTRACT FROM AUTHOR]

Gypsum has been known to regulate cement setting since more than 100 years, whereas the understanding of the physio-chemical mechanism remains incomplete. Here, we investigated the influence of gypsum on elasticity evolution of fresh tricalcium silicate (C 3 S) paste through small amplitude oscillation shear method. Isothermal calorimetry, X-ray diffraction, 1H nuclear magnetic resonance, and zeta potential measurements were performed to explore the corresponding changes in hydration, microstructure, and colloidal interaction. It was found that incorporating gypsum is beneficial for inter-particle agglomeration by significantly weakening electrostatic repulsion force between particles, which accelerates elasticity development in the early period of setting. Although the retardation effect of gypsum on C 3 S hydration hinders the further development of elasticity in the later period, the more divergent needle-like calcium silicate hydrate (C-S-H) and the stronger cohesion of the C 3 S particle network in presence of gypsum lead to a higher elasticity at the same hydration degree. [ABSTRACT FROM AUTHOR]

The global cement industry is facing severe pressure to reduce emissions, it is of great importance for developing low-carbon cement-based materials. Natural hydraulic lime (NHL), as an environmentally friendly binder, can be used to prepare green concrete instead of cement. In this paper, a thermodynamic simulation method was employed to analyze the hydration products of the NHL-mineral admixture system. The strength of mortars with NHL-mineral admixtures was tested. The environmental impacts of different NHL-mineral admixtures were analyzed based on the embodied CO 2 (EC) indicators. The relationships between the main hydration product (CSH gel) in the NHL-mineral admixture system, the mechanical strength, and EC were established. In addition, considering the best mechanical properties and low carbon emissions, the optimal composition of the system was discussed. The results showed that in the NHL-mineral admixture system, different composition ratios of mineral admixture and NHL had significant effects on CSH gel content and EC. The optimal compositions of binary and ternary systems of different NHL-mineral admixtures were analyzed. Among them, the NHL-GGBS-SF ternary system is the best, in which the CSH gel content is greater than 80%, and the EC is only one-third of Portland cement and one-half of pure NHL systems, respectively. This achievement will provide important technical support for the development of sustainable cement-based materials. [ABSTRACT FROM AUTHOR]

Steam-cured concrete is widely used in precast element production due to its high early strength and efficiency, but its long-term performance is often poor. Integrating phase change materials (PCMs) into steam-cured samples is a potential solution. The influences of six PCMs on the fluidity, mechanical strength, toughness, water absorption, and pore structure of steam-cured mortars are investigated by a series of experiments. PCMs employed are paraffin (P-45 and P-58), fatty acids (lauric acid, LA and myristic acid, MA), and polyethylene glycol (PEG1500 and PEG4000). The results show that PEG powder can improve the fluidity of fresh mortar, while the fluidity reduces as the amount of LA or MA increases. The addition of appropriate PCMs slightly reduces the strength of steam-cured mortar but effectively improves the toughness. Incorporating proper PCMs significantly decreases the capillary water absorption of the steam-cured mortar due to the modification of the surface characteristics of pore walls by paraffin and fatty acids. Compared with specimens containing PEG and fatty acids in this study, mortar containing paraffin have higher strength, especially for the one-day early strength. Employing an appropriate amount (not more than 5%) of paraffin is an excellent way to develop high-performance steam-cured cement-based materials, which extend the service life and reduce an environmental load of steam-cured cement-based materials. • Except for LA or MA, the addition of paraffin or PEG does not adversely affect the fluidity of fresh mortar. • Compared with fatty acids and PEG, the mortar with paraffin has higher mechanical properties. • The impermeability of mortar is improved due to the surface modification of pore walls by paraffin or fatty acids. • Employing an appropriate amount of paraffin is an excellent way to improve the durability of steam-cured mortar. [ABSTRACT FROM AUTHOR]

• Calcium laurate is synthesized and proves the presence of carboxylate in LA-samples. • The addition of LA and PEG4000 promotes the formation of carboxylate in specimens. • The carboxylate can be decomposed into carbonate phase at high temperature. • PCMs have almost no influence on the phase compositions of cement pastes. The application of phase change materials (PCMs) in steam-cured cement-based materials is very interesting, and a good improvement effect has been achieved in the water resistance of specimens. However, there are few studies on the interaction between PCMs and steam-cured cement-based materials. The influence of PCM, including lauric acid (LA), polyethylene glycol (PEG4000) and paraffin (P-58) on the hydration products of steam-cured cement paste were explored in this study. Calcium laurate is synthesized from lauric acid and calcium hydroxide in atmospheric water medium without additives to facilitate analysis the impact of LA on hydration products. The physical and chemical interactions occurring in the PCMs modified cement pastes were investigated using thermal gravimetric analyzer (TG) and Fourier transform infrared spectrometer (FTIR). The type and morphology of hydration products were studied using X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that pure calcium laurate is synthesized, and calcium laurate has only low calcium content and free acid. The P-58 evaporates during the thermal decomposition of samples. The addition of P-58 delayed the decomposition of calcium hydroxide. There is no new product formed in the steam-cured cement pastes containing P-58. The addition of LA and PEG4000 into the steam-cured cement pastes promotes the formation of organic salt-carboxylate. The carboxylate can be decomposed into carbonate phase at high temperature. In the current investigated area, the addition of LA, PEG4000 or P-58 has almost no influence on the quantity of cement hydration products and phase compositions of steam-cured cement pastes. [ABSTRACT FROM AUTHOR]

AC impedance spectroscopy (ACIS) is a promising technique for monitoring the microstructure evolution of fresh cement paste in real-time. This paper compared the change of bulk electric resistivity (ρ bulk) obtained from ACIS with the developments of storage modulus (G′) and the mean transverse relaxation times (T 2) of fresh Portland cement pastes within 5 h. It was found that the three different phases (Phase I, II, and III) on the microstructural build-up process of fresh paste can be accurately distinguished by analyzing ρ bulk , as well as G′ and T 2. The use of ρ bulk fails to characterize the microstructural changes in Phase I due to the great sensitivity on the electrical conductivity of the interstitial solution. However, it can successfully reflect the developing features of microstructure in Phases II and III, and reliably evaluate the impacts of water to cement ratio, superplasticizer, and supplementary cementitious materials on the microstructural development. [ABSTRACT FROM AUTHOR]

• Green UHPC based on optimization of the physical and chemical effects of binders is proposed. • Nanomaterials and chemical activator proven to improve the properties of green UHPC. • The designed green UHPC shows a better performance and environmental impact. The development of Green Ultra-High Performance Concrete (GUHPC) has become a hotspot of concern in the construction industry. GUHPC with very low cement content can be prepared based on the combined optimization of the physical and chemical effects of the binder materials. On this basis, this paper proposes to prepare a new GUHPC by further enhancing chemical effects of the binder materials through the addition of nanomaterials and chemical activator. Series of experiments are designed to investigate the mechanical properties and environmental impact in respect to embodied CO 2 -emissions of GUHPC. The hydration characteristics and the pore structure of GUHPC are evaluated by employing thermogravimetry analysis and mercury intrusion porosimetry. The results show that GUHPC with good mechanical performance and very low environmental impact can be prepared with very low cement content (no more than 370 kg/m3). The high initial packing density of GUHPC can be achieved by application of multi-scale particles system, especially in the presence of nano-scale particles. Chemical activator can effectively improve the reactivity of binder materials and promote the hydration of GUHPC. The GUHPC has lower porosity and finer pore size than UHPC. [ABSTRACT FROM AUTHOR]

Generally, tunnel waste is stacked in the slag field nearby for landfilling, which is harmful to sustainable development. The broken rocks and rock powder among the tunnel waste can be recycled to produce machine-made sand, producing many by-products calling rock powder. Based on the practical project, three types of waste basalt powder (BP), from tunnel excavation waste and by-products (rock powder) of machine-made sand producing from tunnel excavation waste in Sichuan-Tibet railway construction sites, was used to prepare an eco-friendly UHPC. The BP is used to replace the cement and is included in the design UHPC based on Modified Andreasen &Andersen particle packing model (MAA). Moreover, the chemical and physical behaviors and ecological evaluation of the designed UHPC and UHPC pasted were discussed. The results showed that when BP (Specific surface area 4.6582 m2/g) replaces up to 15%, the highest compressive strength of designed UHPC (220 MPa) was obtained. Compared with quartz powder, the pozzolanic activity of BP was generally low and increased with the increase of reaction temperature. However, the presence of BP and its fineness in UHPC pastes increased the values of the total autogenous shrinkage and decreased the total heat release at an early age of designed UHPC pastes, this effect is more pronounced with temperature increasing. Based on a quartering method with embodied carbon dioxide emissions and the compressive strength, UHPC with waste BP reduced embodied carbon dioxide and possessed higher compressive strength and lower environmental impact than the control samples of UHPC. [ABSTRACT FROM AUTHOR]

• The influences of FA and SL on the nucleation and growth of cement paste were studied. • FA retards the early hydration of cement at 20℃ due to its hindering nucleation. • SL has stronger seeding effect than FA because it produces more additional C-S-H gel. In this study, isothermal calorimetry and the boundary nucleation and growth model (BNG model) were adopted to investigate the influence of fly ash (FA) and slag (SL) on the nucleation and growth of cement hydrates at early-stage. Afterwards, the mechanism was discussed by analyses of instantaneous activation energy and microtopography. The results show that the hinderance of FA on the early hydration at 20℃ is possibly contributed by the inhibition of nucleation, while SL promotes nucleation at both 20℃ and 60℃. Moreover, it is found that the paste containing FA has the lowest activation energy at early-stage, while the paste containing SL has the highest activation energy, which further indicate that the nucleation of the paste containing FA is more difficult. Besides, the surface microtopography analysis of particles confirm that SL has higher reactivity than FA in paste to generates more additional C-S-H gel to provide stronger seeding effect for producing C-S-H. [ABSTRACT FROM AUTHOR]

[Display omitted] • The temperature and humidity gradient during steam curing process is closely related to its long-term performance. • Surface covering can significantly reduce surface porosity and damage of steam-cured concrete. • The effects of steam-curing regime and surface covering method on the permeability of concrete were evaluated. • The high temperature-humidity gradient during steam curing is detrimental to the development of concrete microstructure. Steam curing has an adverse effect on the long-term performance of concrete, which is inseparable from the early hygro-thermal coupling action. The temperature-humidity field and performance of steam-cured concrete with different surface covering methods were characterized under the treatment temperature ranging from 45 to 75 ℃ by water permeability along with hydration characteristics, porosity, microhardness, and microstructure. The results show that steam-curing regimes directly affect the long-term performance of steam-cured concrete by changing internal temperature-humidity field. During the steam curing process, a higher treatment temperature often corresponds to a more complex temperature-humidity gradient, so that the steam-cured concrete exhibits low compactness and high permeability. In addition, the surface covering methods can reduce the surface porosity and interface transition zone width of steam-cured concrete. Meanwhile, with the increase of treatment temperature, the improvement effect of the surface covering methods on the impermeability of steam-cured concrete is more obvious. [ABSTRACT FROM AUTHOR]

• Small amount of CPCM can accelerate the early hydration of steam-cured cement paste. • Both paraffin and carriers in CPCMs jointly promote the hydration of cement. • The combination of two carriers promotes cement hydration better than single carrier. • The phase compositions of steam-cured cement paste are almost not affected. The application of phase change materials (PCMs) in building materials has attracted more and more attention. However, there is little information on the interactions between PCMs and cementitious material during hydration process. This study investigates the influence of PCMs on cement hydration behavior under steam curing condition. Three kinds of composite phase change material (CPCM) are synthesized, denoted by D/P, EG/P and D/EG/P, respectively. The thermal stability and crystalline phase of PCMs are characterized. The effects of above PCMs on hydration process of cement are evaluated by several testing methods, including isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Results indicate that CPCMs exhibit good thermal stability compared with single paraffin when the operating range is less than 200 °C. The time to reach the heat release rate peak of binders containing paraffin, D/P, EG/P and D/EG/P is 20 min, 20 min, 20 min and 30 min earlier than the cement pastes without PCM at 60 °C isothermal condition, respectively. The addition of a small amount of CPCM can accelerate the early hydration of steam-cured cement paste due to the combined action of paraffin and carriers with high surface area that can provide nucleation sites. Moreover, the combination of two carriers promotes cement hydration better than the single carrier. However, the number of hydration products and phase compositions of steam-cured cement paste are almost not affected by the addition of CPCM. [ABSTRACT FROM AUTHOR]

• Study the relationship between mechanical properties and composition of CA mortar. • A mechanical model of CA mortar from four different levels was proposed based on experimental results and theoris. • The asphalt has a limited contribution to the static compressive strength f and elastic modulus E CA of the CA mortar. As an organic–inorganic composite material, the mechanical properties of cement asphalt mortar (CA mortar) are closely related to its composition. In order to studying the relationship between mechanical properties and composition of CA mortar, a mechanical model of CA mortar from four different levels (i.e.,cement hydration products, cement gel skeleton, cement-asphalt composite system and CA mortar) was proposed based on the microscopic experimental results, the gel-space ratio theory and the Hashin composite ball model. The mathematical relationships among the elastic modulus of CA mortar, compressive strength f and composition parameters were derived. The results shown: The volume fraction of cement hydrates is an important parameter affecting the CA mortar elastic modulus E CA and the compressive strength f. When the asphalt is regarded as a pore or a low modulus phase, the static elastic modulus of the CA mortar E CA and the volume fraction of cement hydrates V CH , the compressive strength f and gel-space ratio x all have a power function relationship, and R 2 > 0.7. The cement hydrates in the CA mortar are still a continuous phase and constitutes the composite gel skeleton, asphalt interspersing among them, and the contribution of asphalt to the CA mortar strength and elastic modulus is relatively limited. [ABSTRACT FROM AUTHOR]

• An innovative design approach of binder system of eco-efficient ultra high performance concrete is proposed. • The design principles of binder system are based on physical packing and chemical effect optimization. • The chemical effect is ensured by optimizing the oxide composition and reaction degree index. • The designed eco-efficient ultra high performance concrete shows a better performance and environmental impact. This research presents an innovative design approach of binder system for eco-efficient UHPC (EUHPC) to achieve a densely compacted hardened paste by optimizing the physical packing and chemical effect of binder system. The influences of binder system composition on the compressive and environment impact of UHPC under different curing regime were studied. The hydration and microstructure of the designed EUHPC was investigated. The results show that the initial packing density and CaO/SiO 2 ratio of the binder system have remarkable impact on the environmental impact and mechanical performance of UHPC. The optimal range of CaO/SiO 2 ratio and packing density of binder system for eco-efficient UHPC is 0.9 to 1.2 and 0.7 to 0.73, respectively. According to this design method, the EUHPC with a very low carbon dioxide index (about 3.4 kg/MPa‧m3) and compressive strength of 150 to 200 MPa is successfully prepared. [ABSTRACT FROM AUTHOR]

Rheological curves of cement-fly ash (C-FA) paste incorporating nanomaterials including nano-SiO 2 (NS), nano-CaCO 3 (NC) and nano-Al 2 O 3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel-Bulkley (H-B) model, and the influences of these nanomaterials on rheological properties of C-FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C-FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C-FA paste. When the content of NS and NA were 2 wt%, the rheological index of C-FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C-FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m 2 /g) and NA (120 m 2 /g) are much larger than that of NC (40 m 2 /g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.