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To increase the mechanical strength and thermal energy storage/release efficiency, fine steel fibers and graphite-modified shape stabilized phase change materials (GM-SSPCM) were added into sulphoaluminate cement mortar. Paraffin, low density polyethylene and flake graphite were heating mixed to produce GM-SSPCM. Fine steel fibers were used to reinforce sulphoaluminate cement-based thermal energy storage composite (STESC) for improving mechanical strength and thermal conductivity. The thermophysical and microstructure of GM-SSPCM, and the thermal and mechanical properties of steel fiber reinforced sulphoaluminate cement-based thermal energy storage composite (SF-STESC) were investigated. The results indicated that about 50% paraffin could be effectively encapsulated in GM-SSPCM with multi-level space network structure. And, the steel fiber can increase the mechanical and thermal properties of SF-STESC. When a 3.5 vol% steel fiber was added, the 28-day compressive strength and flexural strength of the SF-STESC were increased by 7.3% and 40.6%, also the compressive/flexural strength ratio was decreased by 21.6%. The three-dimensional reinforcement of steel fibers reduced the volume shrinkage of the composites. In addition, the thermal conductivity of SF-STESC increases with the increase in volume fraction of the steel fibers. When the steel fiber volume fraction increases from 0 to 3.5%, the thermal conductivity of SF-STESC is increased by 51.3% while the inner paraffin is in solid state and 84.5% while the inner paraffin is in liquid state. The results of thermal energy storage/release performance tested using a self-designed setup showed that the steel fiber reinforced STESC leads to a high thermal energy storage/release rate.

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 KNO3, 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. KNO3 shows the greatest initial fluidity increase. When 0.2% Ba(NO3)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 KNO3 respectively mixed with 0.2% Ba(NO3)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 KNO3 respectively blended with 0.2% Ba(NO3)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.

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.

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.

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.

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 SiO4 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.

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.