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The application of ultra-light cement-based foam composites (ULCF) in buildings has been verified as an effective way to achieve energy conservation in the building sector. However, the production process of ULCF is difficult to complete at the ideal constant temperature during practical industrial production due to cost control and other factors. The sun exposure and residual heat from the machines will cause the initial casting temperature of ULCF to be raised in the preparation process, which will inevitably have an impact on the macroscopic properties of ULCF. In this study, a series of tests were conducted to explore the effect of initial casting temperature (30–55 °C) on the macroscopic properties and microstructure of ULCF for the first time. The results indicated that the 28-day compressive strength of ULCF exhibited a tendency to first increase and then decrease with the increase of initial casting temperature, which was attributed to the variation of its internal pore structure. The thermal conductivity test shows that the thermal conductivity of ULCF existed a minimum value of 0.0651 Wm−1 K−1 when the initial casting temperature reached 40 °C. Meanwhile, SEM and XRD were employed to examine the microstructure and hydration products of ULCF with different initial casting temperatures. Furthermore, the internal pore structure parameters of ULCF were quantitatively analyzed through Image-Pro Plus software, and the results demonstrated that there is a critical value for the initial casting temperature of ULCF, which allows the internal pore structure of ULCF to have characteristics of small size and approximate spherical shape. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) embedded in the building contributes to enhancing indoor thermal comfort and reducing the heating load in winter by absorbing/releasing solar energy. The application effects of PCM incorporated into a single-space passive solar building with the auxiliary heating system (AHS) were investigated numerically in the six representative regions of western China. In the calculation and analysis by the enthalpy model, it was found that the effectiveness of PCM greatly depended on local climate conditions, thickness, and location of PCM. The results indicated that it was necessary to adopt the AHS for winter heating of the passive solar building. On this basis of using AHS, it showed a favorable thermal energy storage effect after the application of PCM resulting in the minimum indoor air temperature being maintained above 15°C within the comfort range stably. The integrated discomfort degree in each region was decreased by more than 96% compared to the original building, and the average temperature in Lhasa was 2°C higher than that in Urumqi. Furthermore, the highest rate of energy saving and carbon dioxide emission saving in the six regions was 19.7% and 17.4% in Lhasa, and the lowest were 4.3% and 4.2% in Urumqi, while other regions were relatively close, respectively. As a result, it can be stated that for a passive solar building using the AHS during the heating period, PCM was the most suitable for application in Lhasa, unsuitable in Urumqi, and generally suitable in other regions. [ABSTRACT FROM AUTHOR]

The mechanical and thermal properties of thermal energy storage mortar usually have the characteristics of mutual restrictions and are difficult to synergistically improve. In this study, steel fibers (SFs) and carbon fibers (CFs) with high thermal conductivity were innovatively used to enhance the thermal and mechanical properties of sulphoaluminate cement-based composites for thermal energy storage (SCCTES). The influence of SFs and CFs on the thermal and mechanical properties of SCCTES were comparatively analyzed through the experimental tests. The test results demonstrated that the influence of SFs and CFs on the thermal and mechanical properties of SCCTES are different, which is due to the difference of surface roughness and dispersion between the two fibers. The thermal conductivity, flexural strength and compressive strength of SFs modified SCCTES (SCCTES-SF) all show an increasing rule when the content of SFs increases from 0% to 3.5vol%. However, when the content of CFs increases from 0% to 0.47vol%, the flexural strength and thermal conductivity of the CFs modified SCCTES (SCCTES-CF) show a non-linear change rule that first increases and then decreases. In addition, adding an appropriate dosage of SFs or CFs can improve the shrinkage characteristics of SCCTES, but the influence of SFs on the shrinkage characteristics of SCCTES is better than that of CFs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pervious planting concrete (PPC) is in line with the concept of ecological environmental protection. However, due to its own porous structure, it is difficult to obtain excellent mechanical properties and water permeability at the same time, which hinders its promotion and application. In this paper, natural gravel (NG), ordinary Portland cement (OPC), polyvinyl alcohol latex powder (PVAP) and polycarboxylate superplasticizer (PS) were used to prepare the PPC, and its mechanical properties and water permeability were studied. Three kinds of plants were planted in the PPC and their planting properties were studied. At the same time, the effect of Bacillus on the planting properties was studied. The results show that when the water–binder ratio (W/B) was 0.28 and the PVAP content was 0.8%, both the mechanical properties and water permeability of the PPC were optimal. The compressive strength and permeability coefficient were 14.2 MPa and 14.48 mm/s, respectively. The mechanical properties and water permeability of PPC prepared with 10~20 mm NG were better than those prepared with 5~10 mm NG. Among the three plants, the germination rate and growth of Elymus dahuricus Turcz (EDT) were the best. The incorporation of Bacillus can optimize its planting properties and promote the effective combination between plants and the PPC substrate. [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]

Highlights • A novel fine steel fiber reinforced cement-based thermal energy storage composite was developed. • GM-SSPCM was fabricated by heating mixing of paraffin, low density polyethylene and flake graphite. • Mechanical strength of STESC is improved with the reinforcement of steel fibers. • The thermal conductivity of SF-STESC at different temperatures was measured and analyzed. • Heat storage/release performances of STESCs are enhanced with fine steel fibers. Abstract 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. [ABSTRACT FROM AUTHOR]

Water glass (WG) is generally considered to be the most effective activator to prepare alkali-activated slag (AAS) cement in terms of strength and durability. However, the rapid setting and hardening of WG activated slag results in rapid loss of fluidity of AAS concrete mixture, which limits its engineering application. In the paper, the effect of blended inorganic salts containing negative hydration ions on the fluidity, setting time and mechanical strength of AAS cement was studied. The hydration process and hydration products were used to explore the action mechanism. Ba(NO 3) 2 greatly delayed the hydration of AAS cement. The four inorganic salts (KCl, KNO 3 , KBr and NaCl) blended with a small amount of Ba(NO 3) 2 can improve both the initial fluidity and fluidity retention, and a wide setting time range can be obtained to meet engineering requirements. The compressive strength decreased with the increase of inorganic salts. The incorporation of inorganic salt did not change the composition of the main hydration products. Considering the fluidity required by construction, mechanical properties and the durability of structure, it is recommended to add 4%–5% KBr or KNO 3 blended with no more than 0.2% Ba(NO 3) 2 into AAS cement. [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]

Sodium sulfate (Na2SO4) and sodium carbonate (Na2CO3) are weakly alkaline activators. Alkali-activated slag (AAS) cement prepared with them shows the special advantages of long setting time and low shrinkage, but it shows slow development of mechanical properties. In the paper, Na2SO4 and Na2CO3 were used as activators and compounded with reactive magnesium oxide (MgO) and calcium hydroxide (Ca(OH)2) to optimize the setting time and mechanical properties. The hydration products and microscopic morphology were also studied using XRD, SEM, and EDS. Furthermore, the production cost and environmental benefits were compared and analyzed. The results show that Ca(OH)2 is the main influencing factor for setting time. It reacts preferentially with Na2CO3 to form CaCO3, which makes AAS paste lose plasticity rapidly and shortens the setting time, and then produces strength. Na2SO4 and Na2CO3 are the main influencing factors for flexural and compressive strength, respectively. Suitably high content is beneficial to promote the development of mechanical strength. The interaction of Na2CO3 and Ca(OH)2 shows a great effect on the initial setting time. High content of reactive MgO can shorten the setting time and increase the mechanical strength at 28 days. There are more crystal phases in hydration products. Considering the setting time and mechanical properties, the composition of activators are: 7% Na2SO4, 4% Na2CO3, 3–5% Ca(OH)2, and 2–4% reactive MgO. Compared with ordinary Portland cement (OPC) and AAS cement activated by sodium hydroxide (NaOH, NH) and water glass (WG) with the same alkali equivalent, the production cost and energy consumption are greatly reduced. Compared with P·O 42.5 of OPC, CO2 emission is reduced by 78.1%. AAS cement activated by weakly alkaline activators shows excellent environmental and economic benefits and good mechanical properties. [ABSTRACT FROM AUTHOR]

This study describes the numerical analyses of the indoor air temperature of the earth building located in dry-hot and dry-cold area in order to evaluate the effects of the passive design parameters on the indoor environment and then determine the optimal values of the design parameters. Firstly, a short-term monitoring was performed in an existing earth building, aiming to validate the numerical building model developed by using an advanced simulation software EnergyPlus. Then a series of regional studies on the effect of building parameters on indoor environment of the earth building were investigated and the simulated results indicated that four design parameters, i.e. building orientation, window to wall area ratio, projection factor of window shading and external wall thickness, exhibit the distinctly impacts on the indoor thermal environment in winter and summer. Next, a back propagation (BP) neural network model with ten neurons in the hidden layer was established using Matlab R2016a to predict the indoor environment, and the degree discomfort hours (DDH) in winter and summer were calculated as the output data. Finally, the itemized intensive scanning technique was used to successively select the values of the passive parameters in their range and the predicted results indicated that the optimal passive parameters are 6°east of south, 18.20 %, 0.66 and 643 mm, respectively. [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]

Near-neutral salt activated slag cement has better performance in environmental protection and shrinkage behavior than common sodium silicate -activated slag (AAS) cement. However, the growth of mechanical performance is too slow, which limits its application. Reactive MgO can improve early mechanical properties, while it may have different effects on the shrinkage due to changes in alkali-activators. Two near-neutral salts, sodium carbonate (SC) and sodium sulfate (SS), were selected to prepare AAS cement. The influence of reactive MgO on autogenous and drying shrinkages was studied. The hydration process and pore structure were assessed with hydration heat and nitrogen adsorption, respectively. The phase composition was evaluated by thermogravimetry (TG/DTG) and X-ray diffraction (XRD). The results indicate that the addition of reactive MgO increases the autogenous shrinkage of SC and SS activated slag. This is mainly due to accelerated reaction by reactive MgO. The drying shrinkage of AAS mortars activated with SC increases first and then decreases with the increase in reactive MgO. For SS activated slag, the more the reactive MgO used, the lower the drying shrinkage is observed. This is related to the effect of reactive MgO on pore structure and hydration products. When reactive MgO increases from 2% to 10%, the mesopore in SC activated slag increases at first and then decreases, while the SS activated slag group shows a constant decrease. Reactive MgO promotes the formation of hydrotalcite in SC activated slag, while AFt is found in SS activated slag. Hydrotalcite and AFt are crystalline products, which are beneficial to inhibit drying shrinkage. [ABSTRACT FROM AUTHOR]

This paper aims to perform a techno-economic evaluation for the sensible heat, latent heat, and combined sensible-latent heat storage systems applied in concentrated solar power (CSP) plants. An analytical model that integrates the uncertainty of input variables is developed to observe the probability distribution of the levelized cost of electricity (LCOE) for various energy storage systems using a combination of Monte Carlo methods and economic indicators. Uncertainty quantification reveals that the combined sensible-latent heat storage system has the least uncertainty. The sensible-latent heat storage system has certainty equivalents of 0.1852 $/kWh and 0.1321 $/kWh for both the Blue Map and Roadmap scenarios, which is approximately 29% less than the two-tank molten salt energy storage system. Under emission trading, the environmental and social benefits of carbon reduction in energy storage systems can reduce the LCOE for CSP plants. This study can provide decision makers with more comprehensive information in determining the economic viability of different energy storage systems. • Techno-economic assessment of thermal energy storage (TES) systems was analyzed. • A probabilistic model for the assessment of levelized cost of electricity (LCOE) was proposed. • A scenario with integrating carbon pricing into the calculation of LCOE was evaluated. • The feasibility for the sensible-latent heat energy storage system was higher than for other TES systems. • The certainty equivalent of LCOE for C-PCM2 system was 0.1852$/kWh and 0.1321$/kWh under the Blue Map and Roadmap scenarios. [ABSTRACT FROM AUTHOR]

How to create a healthy and comfortable indoor environment without causing a substantial increase in energy consumption has become a strategic problem that the development of all countries must face and solve. According to the climatic conditions of Qinba Mountains in China, combined with the characteristics of local rural residential buildings and residents' living habits, the field survey and theoretical analysis were used to study the thermal environment status and the heating energy consumption condition of local rural residential buildings. The thermal design method of walls for the local rural energy-saving buildings based on the indoor uniform radiation field was explored by using the outdoor comprehensive temperature function expressed by the fourth-order harmonic Fourier series as the boundary condition of the wall thermal analysis. ANSYS CFX was adopted to study the suitability of the energy-saving wall structure designed by the above method. The results show that the indoor thermal environment of local rural residential buildings in winter is not ideal and the heating energy consumption is high, but this area has the geographical advantage to develop solar energy buildings. It is proposed that the indoor thermal comfort temperature of local rural residential buildings in winter should not be lower than 14°C. When the internal surface temperature of the external walls in different orientations are equally based on the design principle of uniform radiation field, the heat transfer coefficient of the east wall, the west wall, and the north wall of the local rural residential buildings is 1.13 times, 1.06 times, and 1.14 times of the south wall heat transfer coefficient, respectively. The energy-saving structural wall with KPI porous brick as the main material and the south wall heat transfer coefficient of 0.9 W/(m2·K) is the most suitable energy-saving wall for local rural residential buildings. [ABSTRACT FROM AUTHOR]

In this paper, the effects of carbon nanotubes (CNTs) on properties of alkali activated slag (AAS), including rheology, strength and shrinkage were studied and the resulting mechanisms were investigated by microstructure tests and heat of hydration test. In the presence of CNTs, the viscosity of AAS-CNTs composites paste was dramatically increased. At an optimal dosage of CNTs (0.1 wt%), the compressive and flexural strength of the composite increased by 7.18% and 37.69%, respectively, while the shrinkage decreased by 12.31%, compared with that of the control sample. The reinforcement mechanism was then investigated by Isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Though the hydration of AAS was retarded in the first few hours as indicated by the heat of hydration, negligible difference on the hydration products at 28-day was found for samples with and without CNTs. The XPS results further revealed that there was no chemical shift occurred between the samples with and without CNTs. Only minor modification on the calcium aluminosilicate gels by the CNTs was evidenced by the 29Si NMR measurements. The SEM and MIP results demonstrated that CNTs acted as nano-filler in the composite and reduced the porosity of the matrix up to 14.16%. Based on these findings, it can be suggested that CNTs reinforced the AAS composite primarily by means of their physical effects. • The addition of the CNTs increased the apparent viscosity of AAS remarkedly. • The stability of the CNTs dispersion in sodium silicate solution was reduced, even with the aid of carboxyl function groups. • CNTs hindered the hydration of ASS in the diffusion stage and its role as nucleation sites was not supported. • The dispersion of single CNT in the composite was limited as the dosage of the CNTs was above 0.1 wt%. [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]

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. [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]

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 (CaCl 2 ·6H 2 O) by using a nucleating agent - flake graphite. A super absorbent polymer (SAP) was also used as a thickener to prevent segregation of CaCl 2 ·6H 2 O 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 CaCl 2 ·6H 2 O, 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 CaCl 2 ·6H 2 O. Numerical simulation demonstrated that using modified CaCl 2 ·6H 2 O 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. Image 1 • The supercooling degree of CaCl 2 ·6H 2 O can be reduced to less than 1 °C with the addition of 0.5 wt% flake graphite. • The addition of 25 wt% SAP can eliminate the segregation of CaCl 2 ·6H 2 O. • The combined method of TGA-DTA can evaluate the segregation of CaCl 2 ·6H 2 O effectively. • Using modified CaCl 2 ·6H 2 O in buildings is economically feasible with the payback period of 15 years. [ABSTRACT FROM AUTHOR]