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This study proposes a novel thermal energy storage composite (TESC) with an alumina ceramic-based form-stable phase change material (FSPCM) as the phase-change aggregate and alkali-activated slag as the matrix material. FSPCM was prepared with alumina hollow sphere as the supporting material and paraffin as the phase change material (PCM). A series of tests were conducted to investigate the thermo-mechanical properties of the TESC. The results show that the phase transition peak temperature of FSPCM is 23.6 °C, the latent heat value is 69.8 J/g, and the paraffin adsorption mass fraction with respect to the alumina hollow sphere can be as high as 82.33%. As the mass fraction of FSPCM increases from 0% to 80%, the latent heat value increases from 0 J/g to 19.18 J/g, while the compressive strength can still be maintained above 24.04 MPa. The effective thermal penetration depth and the thermal energy storage performance of the TESC were mathematically analysed and experimentally tested. Meanwhile, the influence of FSPCM dosage on the mechanical strength of the TESC and the microstructure characteristics of the interface transition zone between FSPCM and the matrix were investigated. A mathematical model with a maximum relative error of 12.08% was established for predicting the 28-day compressive strength of TESC.

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.

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.

Efficient use of solar energy by thermal energy storage composites and utilizing environmentally friendly cementitious materials are important trends for sustainable building composite materials. In this study, a paraffin/low density polyethylene (LDPE) composite shape-stabilized phase change material (SSPCM) was prepared and incorporated into a sulphoaluminate cement (SAC) mortar to prepare thermal energy storage mortar. The thermal and mechanical properties of SSPCM and a SAC-based thermal energy storage material (SCTESM) were investigated. The result of differential scanning calorimeter (DSC) analysis indicates that the latent heat of SCTESM is as high as 99.99 J/g. Thermogravimetric analysis demonstrates that the SCTESM does not show significant decomposition below 145 °C. The volume stability test shows the volume shrinkage percentage of the SCTESM is less than that of pure SAC mortar and far less than that of ordinary Portland cement mortar. The SCTESM has high early strength so that the compressive strength at 1-, 3-, and 7-day curing age is up to that at 28-day curing age of 67.5%, 78.3%, and 86.7%, respectively. Furthermore, a mathematical prediction model of the SCTESM compressive strength was proposed. The investigation of latent heat storage characteristics and the thermoregulating performance reveals that SCTESMs have the excellent capacity of heat storage and thermoregulating.

Building energy consumption is influenced evidently by solar radiation. To achieve a stable indoor temperature by minimizing the heat fluctuations resulted from solar radiation, latent heat thermal energy storage systems with phase change materials (PCMs) in building envelope have been studied. Though inorganic PCMs have promising potential applications among all kinds of PCMs, the supercooling and segregation are the major issues which have restricted their practical applications. The purpose of this study is to lessen the supercooling degree of an industrial grade PCM (CaCl2·6H2O) by using a nucleating agent - flake graphite. A super absorbent polymer (SAP) was also used as a thickener to prevent segregation of CaCl2·6H2O during phase transition. The combined method of thermogravimetric analysis/differential thermal analysis (TGA-DTA) was firstly proposed to evaluate the segregation of inorganic PCM innovatively. The results showed that using 0.5 wt% flake graphite not only eliminated the supercooling of CaCl2·6H2O, but also improved its thermal conductivity for better thermal performance. The results of Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) demonstrated that the flake graphite did play an important role on the crystallization of CaCl2·6H2O. Numerical simulation demonstrated that using modified CaCl2·6H2O within walls of buildings in Hong Kong and Changsha are economically feasible with the payback periods of 18.3 years and 8.4 years respectively.

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.

In this paper an investigation on TGRM cementitious special grouting materials performance of setting time, fluidity, expansion ratio, elastic modulus, strength of compression and bending with different water-cement ratio is presented. Experimental results show that the material has the performance of rapid setting, high fluidity, low elasticitymodulus, higher strength of compression and tensile, furthermore the influence of water-cement ratio to the material is obvious. This material may modify the water-cement ratio in order to adjust the practical engineering, as well as meet requirements of engineering.