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Mixing polyethylene glycol (PEG) solution and ordinary Portland cement (OPC) to prepare cement-based phase change composite (CPCC) is an emerging paradigm that has attracted much attention. However, the non-setting problem of CPCC at high PEG content limits the improvement of its heat storage capacity. In this study, the setting process of CPCC was promoted by the modification of calcium aluminate cement (CAC), furthermore, its phase evolution, microstructure and thermo-mechanical properties were investigated by Rietveld quantization, SEM, DSC and conductometer. The results show that monocalcium aluminate from CAC reacts with gypsum from OPC to accelerate the formation of ettringite, thus shortening the setting time of CPCC. Alternatively, the excess aluminum ions inhibit the hydration of alite, thereby reducing the compactness of CPCC. A looser microstructure means a larger pore diameter and porosity, the former reducing the confining effect of pores on PEG, resulting in an increase in latent heat, but the latter increases the thermal conduction path, resulting in a decrease in thermal conductivity. Nevertheless, the mechanical strength of CPCC increases with the increase of CAC content, which is inferred to be due to the increased content of high-strength AFm and strätlingite. When the CAC content is increased from 0 wt% to 40 wt%, the setting time of CPCC is shortened by 86.0 %, the latent heat and 28d compressive strength are increased by 71.3 % and 50.2 %, respectively. This study provides a methodological and theoretical reference for improving the paradigm of CPCC. • Mixing PEG solution and OPC prepare cement-based phase change composite (CPCC). • The hydration process and microstructure of CPCC doped with CAC are studied. • The setting progress of CPCC is analyzed based on its phase evolution. • The thermo-mechanical properties of CPCC are discussed based on its microstructure. [ABSTRACT FROM AUTHOR]

The cement-based composite phase change material (CCPCM) prepared by blending polyethylene glycol (PEG) solution and sulphoaluminate cement (CSA) have been proved to have excellent heat storage capacity, but the interaction mechanism between PEG and CSA, which is related to the thermo-mechanical properties of CCPCM, has not been thoroughly studied. In this work, thermal gravimetric analyzer (TG), thermoporometry (TPM), differential scanning calorimeter (DSC) and mechanical strength test were used to study and analyze the hydration degree, pore structure of cement matrix in CCPCM and thermo-mechanical properties of CCPCM. The results show that PEG can decrease the hydration degree of the matrix, and then increase its pore size and porosity. The increase of the matrix pore size weakens its confinement effect on PEG and enhances the heat storage capacity of CCPCM. However, the increase of matrix porosity weakens the mechanical properties of CCPCM. When the content of PEG is 80 wt%, the latent heat of CCPCM can reach 35.7 J/g, while the 28d flexure and compressive strength of CCPCM are 64.1% and 90.6% lower than those of S0 at the same age. In addition, when studying the pore size distribution of the matrix, it was found that PEG may insert into the middle pore channel of the ettringite crystal to increase its characteristic pore radius from 11 to 13 nm to 13–15 nm. This study provides theoretical support for further improving the thermo-mechanical properties of CCPCM. • Cement-based composite PCM (CCPCM) were prepared by blending PEG solution and CSA. • The hydration and pore structure of cement matrix were determined and analyzed. • The thermo-mechanical properties of CCPCM were analyzed based on matrix pore structure. [ABSTRACT FROM AUTHOR]

Polymer ethylene vinyl acetate copolymer (EVA) modified high porosity (>90%) cement-based foam materials (HPECFM) were prepared by mechanical mixing air-entraining method. The influence of EVA on the mechanical properties of HPECFM was studied. The results showed that there was a direct correlation between the mechanical properties and EVA content. The maximum compressive strength 248 kPa was obtained when the ratio of EVA polymer to cement by weight (P/C) was 0.1. The impact toughness of EVA modified foam materials was increased with the rising of P/C. The impact toughness would be increased by 142.3% from 6.64 to 16.09 N m when the P/C varied from 0 to 0.33. The formed EVA polymeric film in the foam materials was observed by scanning electron microscopy (SEM). With the formation of EVA polymeric film, the matrix character of the foam materials would be changed from being brittle to flexible. Thus, the cement-based foam materials with excellent property of dissipating impact energy was obtained. This materials should be explored because of its simple fabrication process and good impact resistance properties. [ABSTRACT FROM AUTHOR]

High porosity cement-based foam materials were prepared through physical air-entraining method and the pore structure and the properties of materials were characterized. The results show that water–cement ratio and Hydroxypropyl Methyl Cellulose (HPMC) content have crucial influence on material properties. When the water–cement ratio was 0.9 and the content of HPMC was 0.4%, the cement-based foam material with the porosity of 94.33% and thermal conductivity value of 0.049 W/(m K) could be obtained. The formation mechanism of pore structure was analyzed that water–cement ratio and HPMC content affect the bubble film toughness which influence on material properties. [ABSTRACT FROM AUTHOR]

• Shape-stabilized phase change material (SSPCM) was prepared with paraffin and ceramsite. • A novel alkali-activated slag-based thermal energy storage composite (ASTESC) was developed. • The thermo-physical properties of SSPCM and ASTESC were determined and analyzed. • Based on experimental test data, the thermo-mechanical properties of ASTESC are mathematically modeled. • The microstructure of ASTESC were investigated. In this paper, a novel alkali-activated slag-based thermal energy storage composite (ASTESC) was developed, which uses alkali-activated slag cementitious material as matrix to incorporate paraffin/ceramsite shape-stabilized phase change material (SSPCM)prepared by vacuum impregnation method. A series of tests were conducted to investigate the thermo-physical properties of SSPCM and ASTESC. The results indicated that the paraffin mass fraction of SSPCM can reach as high as 55.93%, and the peak phase change temperature and latent heat value of SSPCM is 29.0 °C and 56.13 J/g respectively. Compared with the ASTESC without SSPCM, after incorporating SSPCM, its thermal conductivity decreased by 25.17% to the maximum extent, and there was a significant linear relationship between the thermal conductivity of ASTESC and the mass fraction of SSPCM. Infrared thermal image analysis results show that ASTESC combined with SSPCM has good heat storage performance and temperature regulation ability. The mechanical strength test shows that ASTESC has excellent mechanical properties. Although the increase of SSPCM content will reduce the compressive strength of ASTESC, the results show that even when the mass fraction of SSPCM is as high as 60%, the 28-day compressive strength of ASTESC can still reach 47.3 MPa, which can meet the compressive strength requirements of general structural applications. From the investigation, it can be inferred that the ASTESC developed by this work is a promising thermal energy storage composite with structural and functional integration. [ABSTRACT FROM AUTHOR]

Alkali-Activated Slag Cement (AASC) activated by weak alkaline components has good workability and safety. Sodium carbonate (Na 2 CO 3 , SC), sodium sulfate (Na 2 SO 4 , SS), reactive magnesium oxide (R-MgO), and calcium hydroxide (Ca(OH) 2 , CH) were used to prepare the AASC. The hydration process, phase composition and hydration kinetics of AASC were studied. The results showed that the pH value of AASC slurry activated by weak alkaline components ranging from 10.8 to 13.2. CH could significantly affect the pH of AASC slurry. When the dosage reached more than 5%, the pH value of AASC slurry reached more than 12.0. The hydration heat release of AASC activated by weak alkaline components was mainly concentrated in 1 day. Two hydration heat release peaks appeared. The initial hydration peak appeared within 0.5 h-1 h, and the acceleration hydration peak appeared within 1 h-8 h. When the content of CH was 5%, and the content of SS and SC was 7% and 4%, the acceleration peak of AASC was much higher than that of others. At the same time, the Krstulovic-Dabic model was used to study the hydration kinetics of AASC. The increase of SS content prolonged the NG-I and I-D processes. CH accelerated the hydration rate of AASC and shortened the hydration process of AASC. The main hydration products of AASC activated by weakly alkaline components were C-(A)-S-H gel, calcite, ettringite, hydrotalcite and gaylussite. R-MgO was favorable for the formation of hydrotalcite, while SS was favorable for the formation of ettringite. • Weakly alkaline salt can make Alkali-Activated Slag Cement (AASC) have a good alkaline environment. • The nucleation and crystal growth (NG)- phase boundary reaction (I) - diffusion (D) process of AASC is affected by weak alkaline salt. • There are more crystals in hydration products. [ABSTRACT FROM AUTHOR]

• The addition of PVA is helpful to improve the workability and mechanical property of SCARM. • The incorporation of PVA and PP can improve the mechanical property, toughness and adhesive property of SCARM, especially when mixed together. • PVA increases the compactness of SCARM. • PVA can enhance the interface combination of PP and SCARM. Alkali-activated slag (AAS) cement shows the characteristics of fast hardening and high early strength, which is particularly suitable for repair materials. However, its high brittleness, poor toughness and poor workability hinder its application. The effects of polyvinyl alcohol (PVA) latex powder and polypropylene (PP) fiber on the fluidity, mechanical properties including toughness and adhesive property of self-compacting alkali-activated slag repair mortar (SCARM) were studied. Their effects on the microstructure of SCARM were also studied. The results show that the addition of PVA is helpful to improve the workability. With the increase of PVA content, the 30 min fluidity increases greatly. The addition of PP reduces the fluidity of SCARM. The incorporation of PVA and PP can improve the mechanical property, toughness and adhesive property, especially when mixed together. PVA increases the compactness of SCARM. In addition, it also enhances the interface combination of PP and SCARM. The addition of PVA does not change the hydration products of AAS cement, but slightly increases the hydration degree. [ABSTRACT FROM AUTHOR]

• Multi-component CFA can significantly improve the stability of foam. • High alkaline environment has a negative effect on foam stability. • AAS are suitable to prepare foamed concrete with high foam content. • AAS foamed concrete has better pore distribution than OPC foamed concrete. The multi-component composite foaming agent (CFA) with excellent properties was prepared by sodium α-alkenyl sulfonate (AOS), sodium dodecyl sulfate (K12), coconut oil (CO), and rosin liquid (RL), and three foam stabilizers, namely hydroxypropyl methylcellulose ether (HPMC), xanthan gum and sucrose. The foam stability and the foam stability in an alkaline environment and slurry were studied. The results show that the optimal composition of the multi-component CFA is 0.4% AOS, 0.1 % K12, 0.2% RL, 0.3% CO, 0.08% HPMC, 0.6% xanthan gum and 0.6% sucrose. When the CFA is used to prepare foam, the foaming multiple (FM) is 41, and the 1-hour settlement distance (SD) and the 1-hour bleeding ratio (BR) are zero. Moreover, the foam can maintain excellent stability within 2 h. Under an alkaline environment, when the pH is higher than 12.4, the foam stability will be adversely affected. The effective foam ratio (EFR) of foamed concrete increases first and then decreases with the increase of foam content. When foam content is less than 2.8 L/kg, the foam stability in ordinary Portland cement (OPC) paste is better than that of alkali-activated slag (AAS) paste. When the foam content is higher than 2.8 L/kg, the foam stability of the latter is better than the former. When foam content is 2.8 L/kg, the apparent density OPC and AAS system is 698 kg/m3 and 623 kg/m3, respectively. Compared with OPC foamed concrete, AAS foamed concrete presents more small pores, smaller average pore size and better roundness. [ABSTRACT FROM AUTHOR]

• Potential phase change materials (PCMs) for the buildings were summarized. • Preparation methods of shape-stabilized PCMs (SSPCMs) were reviewed. • Effects of incorporating SSPCMs into cementitious materials were identified. • The application of thermal energy storage cementitious materials was revealed. Phase change materials (PCMs) have attracted considerable attention as potential energy storage media for improving the energy storage densities of building envelopes. Therefore, researchers have committed to introducing PCMs into cementitious materials to develop structural–functional integrated thermal energy storage cementitious materials (TESCMs). Nevertheless, TESCMs have not been widely applied in large-scale engineering and remain in a trial or test stage. This review provides an overview of TESCMs for passive buildings to keep researchers abreast of the latest research trends and technological advances. Among the different types of PCMs, inorganic PCMs with low cost and high thermal conductivity have the most potential for application in buildings; however, their supercooling and phase separation must be addressed before use. Vacuum impregnation and micro-encapsulated and macro-encapsulated techniques are the main methods to encapsulate PCMs for preparing shape-stabilized PCMs (SSPCMs) and preventing PCM leakage from TESCMs. The inclusion of SSPCMs was found to have a negative effect on the workability, mechanical strength, and thermal conductivity of cementitious materials. However, thermal energy storage buildings (TESBs) composed of TESCMs can regulate the indoor temperature within the thermal comfort range, significantly decreasing energy consumption. This is because the effectiveness of TESBs depends highly on such factors as PCM dosages, climatic conditions, and the phase change temperature of PCMs; thus, a multi-objective optimization design is required to design TESB layouts. [ABSTRACT FROM AUTHOR]

• The negative hydration of inorganic salt ions is used to regulate the properties. • The inorganic salt improves the fluidity and setting time of AAS paste. • The inorganic salt makes the ζ-potential of AAS suspension more negative. • The inorganic salt deceases the yield stress and plastic viscosity of AAS paste. Alkali-activated slag (AAS) cement is a low-carbon environmentally friendly cementitious material. Water glass (WG) activated slag cement has excellent physical and mechanical properties, but it is not conducive to the construction due to its rapid setting and hardening, easy loss of fluidity. Negative hydration ions can reduce the viscosity of aqueous solution. So, in the present paper, inorganic salt composed of negative hydration ions were used to adjust the fluidity and setting time of AAS paste. The results show that with the increase of NaCl, KCl, KBr and KNO 3 , the initial fluidity of AAS paste increases slightly, and the 30 min fluidity increases a lot, while the fluidity at 60 min is greatly affected by the amount of inorganic salt. KNO 3 shows the greatest initial fluidity increase. When 0.2% Ba(NO 3) 2 is added with other four inorganic salts, the fluidity retention is significantly improved, especially the fluidity of 60 min. When 5% NaCl, KCl, KBr and KNO 3 respectively mixed with 0.2% Ba(NO 3) 2 are added, the fluidity retention of AAS paste at 60 min are 97.4%, 92.7%, 100%, 82.5% respectively. Compared with the AAS paste without inorganic salt, when 5% NaCl, KCl, KBr and KNO 3 respectively blended with 0.2% Ba(NO 3) 2 are added, the initial setting time increase by 228.6%, 285.7% 307.1% and 239.3%, while the final setting time increase by 175.6%, 222.0%, 231.7% and 178.0% respectively. With the inorganic salt, the ζ-potential of the originally negative AAS cement suspension become more negative, both yield stress and plastic viscosity coefficient decease, especially the plastic viscosity coefficient greatly reduces. This may be the reason for the change of fluidity and setting time of AAS paste. [ABSTRACT FROM AUTHOR]

• HL enhances the strength development of AAS cement, especially that at early age. • HL increases the autogenous shrinkage and reduces the drying shrinkage of AAS system. • HL increases the crystal-like hydration products and reduces the pore amount. Alkali-activated slag (AAS) cement activated by water glass (WG) has a high compressive strength, however, its high shrinkage restricts its popularization and application. In the present paper, hydrated lime (HL) was added to the AAS cement activated by WG. The influence of HL content on the mechanical properties, autogenous shrinkage and drying shrinkage was studied. The influence mechanism was discussed based on the results of hydration percentage, pore structure and microstructure of AAS paste by chemical binding water content measurement, nitrogen sorption, XRD, SEM and thermogravimetric analyses. The results show that the incorporation of HL affects the mechanical properties and increases the autogenous shrinkage, especially the early development in mechanical properties and autogenous shrinkage, while it reduces the drying shrinkage of AAS system. With the increase of HL content from 0 to 12%, the mechanical strength of AAS mortar first increase, then decrease, and reach the maximum value when the HL content is 5%. Compared with the specimen without HL, the flexural strength and compressive strength of the specimen with 5% HL at 3 days increase by 21.0% and 31.3%, respectively. With the increase of HL content from 0 to 12%, the autogenous shrinkage of AAS paste gradually increases. Compared with the specimen without HL, the autogenous shrinkage of the specimen with 12% HL increase by 58.0% and 41.4% at 1 day and 7 days respectively. This can be attributed to the fact that the addition of HL promotes the hydration of AAS cement, especially the hydration within 1 day. With the increase of HL content from 0 to 10%, the drying shrinkage decreases more. Compared with the specimen without HL, the drying shrinkage of the specimen with 10% HL decreases by 43.0% and 28.5% at the age of 28 days and 180 days respectively. This is due to the formation of more crystal-like hydration products and the reduction in the number of pores, especially the mesopores. [ABSTRACT FROM AUTHOR]

• Mixing sequence would greatly change the hydration kinetics of AAS. • Dynamic equilibrium of silicate species would determine the hydration kinetics of AAS. • Pseudo depolymerization degree can be used to predict the hydration kinetics of AAS. In this study, the interaction mechanism between two types of blast furnace slags (named S1 and S2) with distinct chemical compositions and activators with various alkali and silicate concentrations were investigated. Based on the calorimetric results, it was found that the mixing sequence of alkali silicate solutions greatly changed the hydration kinetics of the alkali-activated slags (AAS), which indicates highly dynamic silicate structures in the activator. Although S1 with a higher specific surface area and basicity was less reactive than S2 in the presence of silicate anions, the influence of silicate anions on the hydration kinetics of alkali activated S1 and S2 was divergent. To solve the issues, NBO/T (the number of Non-Bridging-Oxygen per SiO 4 Tetrahedral unit) ratio for the depolymerization degree of glass structure was innovatively introduced into AAS study by taking both precursor and alkali activator into consideration. The results show NBO/T has a strong capacity to predict hydration kinetics and compressive strength of AAS at early age. However, a dynamic equilibrium of the silicate species between the slag and water glass determined the hydration kinetics of the water glass-activated slag. This study provides a worthwhile exploration direction for clarifying the AAS hydration kinetics based on combination of quantitative glass structure index and isothermal calorimetrical analysis. [ABSTRACT FROM AUTHOR]