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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.

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.

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.

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.

Many industrial solid wastes are rich in silica (SiO2) which can be used as supplementary cementitious material (SCM) to replace part of Portland cement. Existing studies mainly focus on the impact of solid waste on tricalcium silicate (C3S) hydration. Since tricalcium aluminate (C3A) is the most reactive component of the Portland cement, it is of great interest t to investigate the effect of solid waste containing SiO2 on the hydration process of C3A. In this study, different amounts of nano-silica (nano-SiO2) were mixed with C3A and the hydration products after 72 h of hydration were analyzed by means of X-ray diffraction (XRD), Fourier Transform Infrared analyzer (FT-IR), Environment Scanning Electronic Microscope - Energy Dispersive Spectrometer (ESEM-EDS), X-ray Photoelectron Spectroscopy (XPS) and Solid-state Nuclear Magnetic Resonance (NMR). The results showed that nano-SiO2 can promote the hydration of C3A and stabilize the hydration products of C3A in the form of crystalline hydrogarnet (C3AH6). The formation of Si-O-Al bonds was also found in the hydration products. ESEM results revealed that the surface of the crystalline hydration products (C3AH6 particles) was covered by gel-like products. The results from the XPS and NMR analyses further confirmed that the negatively charged nano-SiO2 and the silicate anions can literally interact with C3A to produce calcium silicoaluminate hydrate (C-A-S-H) gel, whereas the formation of C-A-S-H is attributed to the substitution reaction of Al in the Si-O-Si network occurring on the surface of C3A. In addition to the reactive silica-aluminum component reacting with Ca(OH)2 to form additional calcium silicate hydrate (C-S-H) and C-A-S-H gels, the reactive silicon in solid waste can also undergo pozzolanic reaction with C3A to form C-A-S-H gel.

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 paper, the enthalpy method is used to simulate the influence of phase change materials (PCM) with different thermos-physical parameters on the indoor thermal temperature of solar greenhouses in Xi’an, China. The simulation results show that the temperature adjustment effect of PCM on solar greenhouses is significantly greater than common heat storage materials such as rammed soil, gravel and water. The lowest indoor temperature in the solar greenhouse increases first and then decreases with the increase of the phase transition temperature. The influence of PCM with different latent heat values on the average indoor temperature of the solar greenhouse increases first and then stabilizes. Increasing the thermal conductivity of PCM can reduce the temperature range of the solar greenhouse, but the increase in thermal conductivity has little effect on the indoor temperature when the thermal conductivity is greater than 0.4 W/(m⋅°C). For the Xi'an area, the best thermos-physical parameters of PCM used in solar greenhouses are: phase change temperature of 11 °C, latent heat value of 140kJ/kg, thermal conductivity greater than 0.4 W/(m⋅°C). This article provides a reference for the practical application of PCM in solar greenhouses.

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.

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.

This study describes the experimental testing of the hygrothermal properties of the earth brick and the numerical analysis of the hygrothermal behaviour of a residential building in a desert climate in order to evaluate the effect of the earth brick on the indoor environment. The hygrothermal properties, i.e. thermal conductivity, specific heat capacity, equilibrium moisture content and water vapour permeability, were characterized to be used in the following numerical simulation of indoor environment. The numerical analysis was conducted by whole building simulations using EnergyPlus which can be used to simulate the indoor climate in buildings. An existing residential building was monitored for two days in summer in order to validate the accuracy of the model. The simulated results showed that compared with the fired brick, the earth walls reduce the amplitude of both indoor air temperature and relative humidity fluctuations, especially the maximum of relative humidity, due to both thermal inertia and moisture capacity of the earth bricks. Besides, the heating energy consumption results of the earth brick rooms were significantly lower than the fired brick rooms during the heating period.

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.

Reducing energy consumption and creating a comfortable thermal indoor environment in rural residential buildings can play a key role in fighting global warming in China. As a result of economic development, rural residents are building new houses and modernizing existing buildings. This paper investigated and analyzed a typical rural residential building in the Ningxia Hui Autonomous Region in Northwest China through field measurements and numerical simulation. The results showed that making full use of solar energy resources is an important way to improve the indoor temperature. Reasonable building layout and good thermal performance of the building envelope can reduce wind velocities and convective heat loss. Insulation materials and double-glazed windows should be used to reduce energy loss in new buildings, although it is an evolution process in creating thermally efficient buildings in rural China. This research provides a reference for the design and construction of rural residential buildings in Northwest China and similar areas for addressing energy poverty.

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 order to study the status of the indoor thermal environment of the northwest rural dwellings in winter, the thermal performance and the residents' adaptability are investigated and the indoor and outdoor thermal environment parameters are measured in Zhongwei region of Ningxia, the indoor thermal environment is analyzed and evaluated by the operating temperature. The results show that the northwest rural residents have strong adaptability to the cold indoor thermal environment in winter. In this area, the cold and daily temperature difference in winter is large, but the solar energy is rich, and it has the geographical advantage of developing passive solar building. The thermal performance of existing rural dwellings is poor and the indoor thermal environment is not ideal. It is necessary to enhance the thermal performance of building's heat collection, thermal storage and enclosure structure.

The investigation and testing of the rural building in Ningxia found that the indoor thermal environment of existing residential buildings was not enough to meet the requirement of local residents. Taking Zhongwei city of Ningxia province as study area, the energy saving construction system for solar energy heat utilization is studied by analyzing the factors of indoor thermal environment. Analysis results show that by using non-uniform wall construction of energy saving design and combined with the improvement design for direct-gain solar heat collecting system, improving the indoor thermal environment quality of local rustic residence effectively. The conclusions of this paper can provide reference for the optimization design of the rural residential buildings in the similar region.

The areas of Qinba Mountain locate between Qinling and Daba mountains, it’s not hot in summer, but very clammy in winter. Focusing on the typical rural architecture, the paper analyzed the consumption of architecture heating affected by the parameters of heat transmission coefficient of envelope, also carried out optimal design for the architecture thermal performance. The results show that through the optimal design of envelope, the consumption value of heat transmission on the roof decreases from 36.45W/m2 to 6.29W/m2, therefore, reduce the architecture heat consumption and improve the indoor thermal comfort of the rural architecture in winter in the region. The research method and conclusions in the paper can be used to guide the development of rural architecture in the region. Keywords-Qinba mountain areas; rural architecture; heat consumption; energy saving construction; thermal performance analysis

Two typical civilian dwellings, the earth dwelling and the brick and concrete dwelling, in northwestern areas of China were investigated, on-site measurement on winter outdoor meteorological parameters, indoor air temperature and relative humidity were conducted. The paper analyzed space arrangement, construction design, indoor thermal environment and situations of civilian dwellings, the results show that the resources of solar energy in winter in these areas are abundant, however, the indoor thermal environment of the dwelling is not satisfactory. Based on the analysis of indoor and outdoor thermal environment, with the consideration of local natural resources and climate situations, the paper proposes a design plan of energy saving for the traditional dwellings and provides recommendations for the healthy development of local civilian dwellings. Keywords-northwestern areas of China; rural civilian dwelling; indoor thermal environment; passive solar energy heating

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.