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An empirical equation was proposed to predict compression index (Cc) of saturated reconstituted contaminated clays. Experimental data from 464 oedometer tests from literature were analyzed, aiding to develop a method for predicting the Cc of saturated reconstituted contaminated clays. The predictive capacity of three existing empirical equations of Cc with either liquid limit (wL), plasticity index (PI) or initial porosity (n0) was assessed. It was found that these equations previously used for clean soils roughly predict the Cc value of saturated reconstituted contaminated clays. To better predict the Cc, a series of empirical equations were established by regression analysis of the experimental data. Finally, the “best” equation was determined by an assessment of goodness of fit.

Moisture transport has a great impact on concrete durability. In this study, a hard-pulse one-dimensional frequency coding sequence of low-field nuclear magnetic resonance (LF-NMR) imaging was applied to investigate moisture transport in cement-based materials (CBMs) considering the influences of the water/binder (w/b) ratio, sand/cement (s/c) ratio and contents of silica fume (SF) and super-absorbent polymer (SAP). A weighing method was also applied and the results were compared with the LF-NMR imaging measurements. The results showed that the moisture distribution curves can be divided into three stages by height. In addition, it was found that the moisture absorption height (h) increased with time and the growth rate of water absorption proceeded from fast to slow. Additionally, as the w/b ratio of the sample was increased, h increased. The value of h decreased with increasing s/c ratio and increased with an increase in SF content. When SAP was mixed into the CBMs, the values of h increased with 0·15% SAP addition but decreased with the addition of 0·30% SAP. The LF-NMR imaging measurements were in agreement with the results of the weighing method.

The current scheme of building climate zones in China generally assumes that building climate zones of island cities are identical to adjacent land stations. Consequently, building design strategies for island buildings usually refer to those developed for inland cities. This approach has to some extent hindered the energy–saving design and green development of island buildings in China.This research takes a first step on this issue by defining the building climate zones of 36 marine islands over China marine area using two-stage zoning methodology adopted by current building climate zoning standard (GB50178-1993). The meteorological data used for analysis was obtained from the National Climate Center of China over the 30-year period from 1985 to 2014. As comparison, 40 coastal stations which are adjacent to the investigated marine islands were also included in this study. Subsequently a more objective technique—cluster analysis was operated as an effective supplement to discover the climate characteristics among different observations. The results of both methodologies consistently show that among the 36 islands investigated, the majority of islands located in northern and eastern marine area belong to the same climate zones as their adjacent coastal cities. However, island cities in southern marine area cannot be assigned to any current climate zone, which was demonstrated by its distinctive climate features different from any other sites investigated through cluster analysis as well as different energy use patterns. Thus a new zone was defined to supplement the current building climate zoning scheme to cover marine area of China.

The effect of polycarboxylate superplasticiser (PCS) architecture in terms of a flexible or rigid backbone and repartition of side-chains along the backbone on the hydrodynamic radius, adsorption properties, flow behaviour and rheological behaviour was systematically evaluated. PCSs with different architectures were found to affect the flow behaviour of cement paste differently, mainly due to difference in PCS surface coverage area on cement particle surfaces. The PCS surface coverage area on cement particle surfaces was determined by the adsorption layer thickness of a single PCS molecule and the adsorption amount. The adsorption layer thickness of a single PCS molecule is correlated with the hydrodynamic radius in solution. The PCS with a rigid structure in the main chain had a more coiled conformation, with an inevitably smaller hydrodynamic radius and thus a thinner adsorption layer. The adsorption amount is closely related to the exposed density of carboxylic groups. A more extended solution conformation facilitates the exposure of carboxylic groups, which is beneficial for the adsorption of PCS onto cement particle surfaces. As a consequence, the thicker the adsorption layer thickness of a single PCS molecule and a larger adsorption amount results in larger PCS surface coverage area on cement particle surfaces, producing better workability of cement paste.

The restrained volume expansion of expansive agents during hydration is often used to offset strains caused by the shrinkage of cement-based materials (CBMs). The hydration and expansion process of a laboratory-prepared calcium-oxide (CaO)-type expansive agent (CEA) in CBMs and modelling of the same are discussed in this paper. Based on isothermal calorimetry and thermogravimetry/differential thermal analysis, the hydration behaviour of the CEA in cement paste was examined, based on which the hydration kinetics were analysed and the apparent hydration activation energy of the CEA was calculated. Based on the degree of hydration, a chemo-mechanical model of the expansion of the CEA in CBMs was developed and analysed by comparison with experimental data obtained by the dual-ring restraint test method. Based on this model, it is possible to predict the expansion performance and crack resistance of concrete containing CEA agent.

A transpired solar-collector is a device, which is attached to building walls, that uses solar energy to provide preheated fresh outdoor-air before it is drawn into the building through the ventilation system. A transpired collector consists of a heat-collection plate with infiltration holes, an air layer, an air outlet, and other auxiliary components. A transpired solar collector with non-uniform holes is investigated in this paper, and a physical model for it is developed. The model is then simplified to enable effective simulation and subsequently verified by experiments to evaluate the reliability of the simulation results. Furthermore, a multi-factor sensitivity analysis of a transpired solar collector, with respect to airflow and thermal characteristics, is performed using a numerical simulation. In addition, the application of the device is combined with the thermal requirements of the actual building. The results show that the air-layer thickness has the strongest effect on the heat-collection efficiency, which can be increased to 93% when thickness is 30 mm and height ratio is 0.30. This effect is obvious only in the case of non-uniform perforation. Although a high air-velocity can increase the daily heat-exchange by 595.2 W, the average daily air-supply temperature decreases by 34.2 °C. Even though the temperature-target may not be reached when more fresh air is introduced, the reduction of the fresh air heating-load is substantial.

Ultrahigh-strength concrete (UHSC) is a promising material for engineering applications, owing to the rapid increase of compressive strength at early ages. In this study, the creep behaviour of UHSC with an ultralow water/binder ratio (= 0·16) under loading at early ages was investigated. The influence factors of loading age (1, 2, 3 and 7 d), normal coarse aggregate and steel fibre content (0, 1 and 2%) were taken into consideration. Experiment results showed that the addition of coarse aggregates and ultrafine steel fibres were obviously effective in decreasing the creep deformation of UHSC but that the specific creep of UHSC with 2% steel fibres was higher than that of UHSC with 1% steel fibres. Specimens loaded at earlier ages had higher creep. At a microscopic level, it could be seen that the creep of UHSC was influenced by hydration products and concrete internal defects. From a macroscopic perspective, it could be seen that this was the result of a combination of strength and elastic modulus development factors. By introducing a coordination factor for the development of strength and elastic modulus, a modified creep model was proposed to predict the creep of UHSC.

Autogenous shrinkage of cementitious materials is a key factor leading to early-age cracking of concrete. Based on the micromechanics, the underlying multiscale framework and capillary pressure theory, a multiscale model of autogenous shrinkage is presented for cementitious materials with a homogenization method. By comparing the predictive values from models with the experimental data in the literature, the HYMOSTRUC relative humidity model and Shimomura and Maekawa pore size distribution model are recommended for use in the proposed autogenous shrinkage multiscale model. Combined with the HYMOSTRUC chemical shrinkage model, the simulated results of the autogenous shrinkage multiscale model proposed in this paper match well with the experimental data in the literature and the predictive capability is successfully validated.

Volatile organic compounds (VOCs) emitted from decorative building materials are the main source of indoor air pollution, which endangers human health. Source control is the most direct method to reduce the amount of harmful substances emitted from a material. In view of the excellent adsorption performance and effective fixation of the adsorbent on VOC molecules, small amounts of adsorbents can be blended into the raw materials used in the production of building materials, which results in the manufacture of modified building materials with low VOC emissions. According to the type and ratio of additional adsorbents, the VOC emission characteristics of the modified building materials vary. Based on the analysis of the multi-component and multi-scale mass transfer mechanism, a prediction system for the VOC emission characteristics of modified building materials was proposed. Four types of adsorbents, namely, wood-based activated carbon (WAC), shell activated carbon (SAC), coconut shell activated carbon (CSAC), and potassium permanganate impregnated alumina (PIA) were used to manufacture the modified medium density fiberboards. Moreover, pore structure characterization tests and environmental chamber tests were conducted to verify the accuracy of the theoretical prediction system. The results revealed that an absorbent with a high partition coefficient has a more significant source suppression effect. The proposed VOC emission characteristic prediction system for modified building materials can optimize the type and ratio of adsorbents for engineering applications and therefore, provide a basis for the selection of effective VOC source control strategies.

Sulfonate graphene nanosheet (SGN), as a new chemical admixture obtained by sulfonation of graphene, has been used to investigate the effects on tricalcium silicate (C3S – Conventional cement chemistry notation is often used in this article to specify the composition of solid phase, whereby C = CaO, S = SiO2, F = Fe2O3 and H = H2O) hydration. Results show that SGN can prolong the dissolution period and induction period during C3S hydration owing to its adsorption behavior. In situ X-ray diffraction analysis demonstrated that the crystal growth on 001 planes of Calcium hydroxide (CH) will be enforced by addition of SGN, which is probably by the following steps: 1) Ca2+ released by C3S more likely diffused to the surface of SGN prior to nucleation of CH; 2) the nanosheets provide a template for aligned growth of the CH especially on the 001 planes. Meanwhile, scanning electron microscope photos directly show that the growth of CH is layer by layer on the 001 plane when SGN was added. Hopefully, the mechanism of C3S hydration cooperating with SGN proposed in this paper can make a guidance for the application of SGN in cement based materials.

This paper presents an experimental study on the flexural behavior of an innovative CA-UHPC (ultrahigh-performance concrete containing coarse aggregate) slab with high and low reinforcement ratios. A total of eighteen CA-UHPC slabs were tested to failure under the parameters of longitudinal reinforcement ratio, curing method, and maximum aggregate size. Test results indicated that sufficient longitudinal reinforcement should be embedded to prevent the brittle failure and disastrous damage. High ductile failure mode was observed for specimens with high reinforcement ratio compared with specimens with low reinforcement ratio. Instead of extensively crushing as normal strength concrete, delamination failure appeared in the compression zone of the CA-UHPC slabs owing to the fibers’ bridging effect, the yielding of longitudinal reinforcement, and the large expansion of flexural cracks which led to the final failure. The reinforced CA-UHPC slabs demonstrated excellent deformability, and ultimate ratio of deflection to span increased from 1/281 to 1/12 when the reinforcement ratio raised from 0% to 3.45%. Stiffness of the reinforced specimens at the flexural cracking state was about 88% and only approximately 6% at the ultimate state, but nearly 50% of the initial stiffness remained when the longitudinal reinforcements yielded, which indicated superior load resistance ability and excellent postcracking deformability. A new ductility index was proposed to evaluate the postcracking ductility of the CA-UHPC specimens. Finally, test results were compared with the flexural strength predictions of CECS 38-2004, ACI 544.4R, and BS EN 1992.

Buildings on tropical islands in the South China Sea are facing an overheating challenge. High-water-absorbency unglazed porous ceramic (UPC) materials could counteract heat gain by evaporation. Salty humid air and seawater in the marine environment lead to evaporative cooling differences from inland conditions. This research replicated a salty humid atmosphere with a stable concentration similar to the actual environment in a dynamic hot-humid climate wind tunnel (DHWT). The influence of salt in gas-liquid media on evaporative cooling is discussed. The results showed that the salt concentration of humid air in the wind tunnel can be controlled by adjusting the atomization rate and the concentration of the atomized liquid. Humid air and liquid with salt reduced the evaporation rate of the UPC tiles. The influence of salty humid air was generally less than that of seawater. In 6 mg/m3 salty air, the total evaporative cooling effect decreased by 2.63% and 40.44% when saturated with fresh water and a 3.5% sodium chloride solution, respectively, relative to saturation with fresh water and evaporation in humid air without salt. In conclusion, sea salt in humid air and in the liquid phase reduced but did not eliminate the evaporative cooling effect of UPC materials. Seawater source utilization showed a significant benefit in cooling and water conservation aspects in coastal areas.

In this study, the interaction between the major phase of cement clinker, C3S, and GO was explored to investigate its effect on the microstructures of G3S/GO composites at different GO dosages in a range of 0–0.05 wt%. The compressive strength of C3S/GO composites was tested and their microstructural developments were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TG), nitrogen adsorption and 29Si solid-state nuclear magnetic resonance (NMR) techniques. The results show that the addition of GO can improve the compressive strength of C3S/GO paste up to 32.5% at 1 day. In addition, the incorporation of GO provided an increasing number of nucleation sites to form denser microstructure and refined the pore structure by reducing the total porosity and increasing the gel pores. In particular, the hydration degree was increased by approximately 20% at the age of 7 days when the GO dosage was in the range of 0.03–0.05 wt% as evidenced by TG and NMR results. The ratio of Q2/Q1 in C-S-H gel decreased slightly with the increased GO content, which was further corresponding to the decreased mean chain length of C-S-H gel. Therefore, the introduction of GO exerts a positive effect on the hydration of C3S, which provides essential supports to the hydration mechanism of GO in Portland cement matrix.

High-performance concrete easily generates early-age cracks due to its sharp and large temperature and relative humidity (RH) changes. The temperature and RH with and without axial compress...

Accelerated bridge construction (ABC) is becoming progressively popular in China due to its advantages in sustainable development. However, some challenges still prevent it from being furt...

A design scheme of multi-element sensor which included electrical resistivity probes, multiple Cl&minus, selective electrodes, and a steel corrosion monitoring system was proposed in this work. Embedding this multi-element sensor in concrete enables the real-time and non-destructive monitoring of internal electrical resistivity, free Cl&minus, (Clf) contents in the concrete pore solution at different depths, and steel corrosion parameters. Based on the monitoring data obtained by the multi-element sensor, the freezing-thawing (F-T) damage degree, the Clf diffusion coefficient, the quantitative relation between F-T damage degree and Clf diffusion coefficient, the initiation period of steel corrosion, and the critical content related to steel corrosion are determined. To conclude, the multi-element sensor provides key durability parameters for the establishment of the Clf diffusion model, the assessment of health condition, and the prediction of service life of concrete under the coexistence of the F-T cycle and Cl&minus

The present study aims to examine the mechanism influencing the expansion characteristics of expansive cement paste in presence of different dosages of Temperature Rising Inhibitor (TRI). The expansion of cement pastes showed a higher expansion strain of the OPC-EA mixture with 0.2% and 0.4% TRI in comparison to the reference sample and a decreased shrinkage of cement pastes containing expansive agent (OPC-EA). Meanwhile, dynamic elastic modulus, hydration kinetics, mineral phase compositions and microstructure characterization of hydration products were also investigated by ultrasonic method, isothermal calorimetry, quantitative X-ray diffraction and scanning electron microscope, respectively. The delayed hydration process of expansive agent increases the amount of expansive agent available to react after the setting of cement pastes, resulting in the increased expansion strain of OPC-EA-0.2%TRI sample. The higher expansion strain of OPC-EA-0.4%TRI sample can be attributed to the lower stiffness of cement paste affected by TRI. The results showed that the addition of TRI is the main force in delaying the hydration process of ye’elimite in expansive agent by acting on the formation and morphology of ettringite. The delayed ye’elimite hydration process can be explained by inhibition of the precipitation or/and growth of ettringite.

The high absorption of recycled fine aggregate (RFA) directly affects the effective W/C ((W/C)eff) of paste in cement-based materials, giving poor fresh state consistency and affecting the mechanical behavior in the hardened state. A novel method was proposed to determine the water absorption of RFA in fresh paste (WAp) at plastic stage in this paper, which was calculated by the difference of total water content of paste between the mixture incorporating the RFA and the reference cement paste. Three series of mortars were prepared respectively for investigating the influence factors on the WAp, considering the absorption capacity of RFA in water at 24 h (WA24h), W/C (0.35, 0.45, 0.55) of fresh paste and A/C (1, 2, 3) of the proportions. The results show that the water absorption of RFA in paste and its evolution is lower than that in water, being up to 44.38%–80.18% of WA24h at 1 h. In the first 5 min, the WAp reaches quickly to the 36.34%–57.61% of WA24h. And it decreases when using RFA with smaller WA24h, and in the mixture proportions with a lower W/C and higher A/C. Based on the relationship between the WAp and these factors, the (W/C)eff of mortar with dry RFA can be estimated in different mixtures. Conversely, the additional water for a better workability can be also calculated with the proposed W/C, which has been verified by the testing results for total water content of paste in various mortars. The corresponding reduction of water absorption in paste should be taken into account during the mixture design with RFA.

The particulate matters (PM10 and PM2.5) inside urban subway stations greatly influence indoor air quality and passenger comfort. This study aims to analyze and interpret the concentrations of PM10 and PM2.5, measured in several subway stations from October 9th to 22nd, 2016 in Beijing, China. The overall methodology was based on the Statistical Package for Social Science (SPSS) software while General linear model (GLM) and correlation analysis were further applied to examine the sensitivities of different variables to the particle concentrations. The data analysis showed the average overall mass ratio of PM concentrations inside subway station is about 68.7%, much lower than outdoor condition (79.6%). In the areas of the station hall and platform, the real-time PM10 and PM2.5 concentrations varied periodically. In working and operation offices, all rooms had much higher PM concentrations than the outdoor environment when its pollution level was level 3, in which the facility room reached the highest level, while the closed meeting room had the lowest. Correlation analysis results indicated that PM10 and PM2.5 concentrations were mutually correlated (average R2 = 0.854), and a strong linear correlation (R2 = 0.897) of the subway-station PM concentrations to the outdoor PM conditions, regardless of the outdoor atmospheric PM concentrations pollution level was. Nevertheless, the impact of passenger number and temperature & humidity on the station PM concentrations was less, when compared to the outdoor environment. This paper is expected to provide useful information for further research and design of effective prevention measures on PM in local subway stations, towards a more sustainable and healthier built environment in the city underground.

Formaldehyde emissions of building materials are greatly influenced by the indoor air temperature. An accurate evaluation of the influence of formaldehyde emissions on indoor air quality requires an investigation of the emission characteristic parameters at different temperatures. Based on the adsorption potential theory, this paper derived the correlation between the initial emittable concentration (C0) and the partition coefficient (K) of formaldehyde emissions from building materials. On account of the characteristics of a high equilibrium concentration of formaldehyde emissions under high temperatures in an airtight environment, a step temperature rising emission (STRE) method to simultaneously determine the characteristic parameters of formaldehyde emissions at multiple temperatures was proposed. This innovative method was validated by theoretical models in the literature and via independent experiments. In addition, an optimization method for determining the appropriate volumetric air/material phase ratio was discussed and analyzed to improve the accuracy and reliability of the STRE method. This method aims to improve the measurement efficiency of the emission characteristic parameters and provides inspiration for evaluating the hazard posed by formaldehyde emissions from furniture and building materials.

A novel polymer-type shrinkage-reducing admixture (SRA) with promising shrinkage-reducing and water-reducing functions was developed recently. However, its effects on the early age properties of cement pastes which determine the long term durability of concrete structure still remain unclear. This study aims to investigate its effects on the early age microstructure evolution and transport properties of cement paste. Comparative studies between this novel SRA and traditional SRA were carried out in terms of their influence on the early age hydration, capillary pressure, electrical resistivity and the strength of the cement pastes. The results show that with the presence of the novel SRA, hydration and microstructure development were slowed down together with an increase of the transport-related properties while the mechanical properties were declined slightly due to the higher capillary porosity compared to the traditional SRA. Larger Kelvin's radium in the novel SRA system was found, which would cause faster water evaporation after exposing to dry conditions, suggesting that special care needs to be taken in the early curing.

This paper proposes an optimal parking site selection scheme to alleviate CO2 emissions of the traffic flows for green urban road networks. Through the creative dynamic traffic zone programming, a constrained optimization model is set up to assess the impact of potential public parking locations on road traffic emissions. In each scenario, Thiessen Polygon based zoning method is applied to investigate the distributions of road traffics. The main contribution of this study is as follows. Firstly, this proposed model takes the CO2 emission of the whole traffic network of sustainable city development as the optimization goal, instead of the traditionally discussed travel distance or cost efficiency. Secondly, a Thiessen polygon based public parking zoning method is developed and implemented realistically. This zoning method provides a precise approach to traffic distribution and parking demand estimation. Rather than the quadrilateral or radial zoning, this method pays more attention to the parking supply demand and its impact on parking congestion. Thirdly, the genetic algorithm (GA) is used to find the optimal public parking location (PPL) sets. GA has a great application value in speeding up stochastic search for global optimization. It is especially suitable to simulate complex and large capacity problems concerning the realistic solutions. By implementing the dynamic zoning and modelling method into intelligent transportation system (ITS), the efficiency of parking induction and dynamic optimization of traffic distribution could be ensured for the future smart mobility. Therefore, this model not only serves as a novel method for public parking allocations, but hold potential to support intelligent parking guidance, as a part of the intelligent traffic system for smart city development.

Cement additives and concrete admixtures are construction chemicals that reliably improve the sustainability of a broad range of cement-based systems. This improvement can be derived from enhancing durability and strength through water reduction, and catalyzing the cement hydration process to enable replacement of clinker with supplementary cementitious materials. Through current best practices, incorporation of these potent chemicals at a fraction of a percent of the entire concrete mix affords a clinker replacement of about 20% by weight. This replacement amount can be more than doubled with correct mix proportioning. Innovative technologies such as pre-test tools and smart concrete management systems further improve the effectiveness of admixtures applied in both current and new cementitious materials. Provided longer set times, a consequence of SCM incorporations, can be tolerated, further reduction in CO2 emissions can be attained. Making trade-offs such as this will be essential to optimizing the sustainability of cement-based materials.

The effects of graphene oxide (GO) on the hydration kinetics, pore structure, mechanical properties, and the structure of calcium silicate hydrate (C-S-H) gels were systematically investigated by combinatorial techniques. GO can accelerate the cement hydration, refine the pore structure and increase the polymerization degree of C-S-H gels due to the nucleation effects of GO. The specific surface area of cement paste and the number of gel pores were reduced with the addition of GO. A 3D network structure of GO modified C-S-H gels was originally proposed based on the obtained results that GO could intercalate into the interlayer space of C-S-H gels through ionic bonding with Ca2+ and fill in the gel pores. A small fraction of GO (0.022 wt%) increased the 28 d compressive strength by 16.31%–25.60% at a various water to cement ratios, indicating that GO is a potential nano-reinforcing material for cement composites. The results would provide a well understanding of the reinforcing mechanisms of GO in cement composites and pave a pathway for the design of high-performance cement composites.

High-volume fly ash is normally used as a partial replacement for cement to improve the workability, durability, and economic properties of concrete. The pore structure is an important factor affecting the performance of concrete. In this study, the influence of water-binder ratio (w/b) and fly ash content on the pore structure of early-age cement paste was determined using low-field nuclear magnetic resonance spectroscopy. Experimental results show that the most probable pore diameter increases with fly ash content and w/b and decreases with age. The porosity increases with w/b and decreases with age. A modified pore structure model, which is based on the existing models and the Weiball distribution, is proposed for high-volume fly ash cement-based materials.

Building envelopes integrating with phase change materials (PCMs) can achieve excellent thermal storage performance, which would benefit the establishment of comfortable indoor thermal environment and the reduction of building energy consumption. In the present paper, the thermal performance of PCMs-based lightweight wallboards integrating PCMs with insulation materials are investigated by comparative experiments. By using two reduce-scale test cells, the experiments are conducted in an artificial climate chamber which is controlled by harmonic and linearly rising/falling temperature changing processes. The comparisons of different PCM layer arrangements and layout areas on the wallboard thermal performance are conducted. Experimental results depict that the PCMs-based lightweight wallboard with PCM layer arrange on interior surface can reduce 32.4% of the temperature fluctuation amplitude and delay the lag time from 2.9 h to 4.1 h compared with the arrangement on exterior surface. To provide a convenient approach for engineers and architects to estimate the thermal performance of PCM envelopes in early design stage, a simple thermal design method is proposed based on harmonic response method and equivalent specific heat capacity principle. The calculation results of interior surface temperature agree well with the experimental results with an 7.7% relative error. The present work could provide validation data for simulation investigations of PCM envelopes and provide references for PCM envelopes thermal design.

This study examines the effect of Temperature Rising Inhibitor (TRI) on Portland cement hydration process and analyzes the mechanism. The investigation of the impact of TRI on cement dissolution, C-S-H nucleation and growth process shows that TRI has little influence on the dissolution kinetics of cement and crystal-solution interfacial energy of C-S-H. In contrast, the modification of C-S-H grain size in solution and the C-S-H growth rate in cement suspensions are observed. Experiments involving TRI and synthesized C-S-H confirm that TRI will preferentially adsorb on the C-S-H surface and inhibit growth of C-S-H.

Significant improvements to modern concrete have emerged in recent years, primarily due to application of various polycarboxylate dispersant with designed structure. However, self-compacting or high strength concrete characterized by a low water-to-cement ratio (w/c) pose challenges for their viscosity and pumpability. Here we propose a strategy so called in situ redox polymerization method to synthesis hyperbranched polycarboxylate superplasticizers. By adopting a unique monomer Dimethylaminoethyl Methacrylate, acting as monomer as well as initiator, hyper-branched structure are obtained through this one-pot synthesis procedure. In contrast to their conventional counterparts, that is, comb-like polycarboxylate, hyperbranched structure is shown to cut down the viscosity of pore solution and alleviate the shear thickening behavior of cement paste, leading to a 30% reduction in viscosity of paste. Moreover, owing to the ease of industrial manufacture, our approach, in situ redox polymerization method, show broad prospects and great potential for development.

In order to improve the fluidity retention performance of cement, monomers containing ester groups were introduced into slow-release polycarboxylate superplasticisers (PCEs). Four slow-release PCEs with different molecular weights (Mw) were synthesised through aqueous free radical polymerisation. The effect of the molecular weight of slow-release PCEs on the dispersion performance, hydrolysis reaction ratio, adsorption process and hydration of cement was investigated systematically. Due to the hydrolysis reaction, the amount of adsorbed groups continued to increase over time. The adsorption amount of PCEs on the cement particles increased with increasing Mw, indicating that Mw was the main factor affecting adsorption. The retardation of cement hydration was weakened with increased Mw, due to a reduction in the number of molecules adsorbed on the surface of the cement particles. Among the four PCEs, the PCE with medium Mw displayed excellent initial dispersion. The PCE with the highest Mw exhibited the worst dispersion retention, the strongest adsorption capacity and the most cement hydration acceleration. The PCE with the lowest Mw showed outstanding dispersion retention and the maximum delay in cement hydration. According to fluidity retention requirements, an appropriate Mw may be thus selected, which provides a reference for the synthesis and performance of slow-release PCEs.

This study proposes a novel heated bed that can heat the whole room in the daytime and heat the surroundings of the bed at night. The conditions of conversion between the daytime and nighttime are achieved by the opening and closing of the fan and vents. The simplified calculation method of heat dissipation of the bed was obtained via the flow and heat transfer process analysis in two heating modes. Numerical simulations of heat dissipation and indoor thermal environment under different conditions in the daytime and nighttime were performed using computational fluid dynamics (CFD) to master the indoor temperature distribution characteristics. The simulation results were compared with the experimental results and show good agreement. The results show that the maximum of heat dissipation can reach 1300 W in the daytime and the indoor thermal environment can meet the human thermal comfort requirement. At night, the bed can create a high-temperature circle around it, which can ensure the sleep thermal comfort of the human body at a cooler indoor thermal environment, whose temperature can be 5°C lower than normal conditions. The heated bed can achieve the time-sharing district heating of room and reduce the heating energy consumption significantly. This study can provide the design and selection basis for the heated bed.

In this paper, the effect of a new starch-based chemical admixture (SA) on cement hydration is investigated and its preliminary action mechanism is discussed. The results from isothermal calorimeter and semi-adiabatic calorimetry test show that SA could decrease the maximum heat flow from the 2.6 mW/g to 1.5 mW/g and the peak temperature from 35.9 °C to 24.9 °C when the SA dosage increased from 0% to 0.6% (weight ratio of SA/cement). The effect of SA with different dosage on cement hydration has also been investigated by electrical resistance test and X-ray diffraction analysis. Though the cement hydration rate is decreased at early stage, it has no influence on the final total heat release and no influence on concrete compress strength at 28 d. Such results show that it might have great sense to control thermal crack in mass concrete in practical application which is normal problem in mass concrete.

A recent microstructural model for simulating external sulfate attack on cement paste is used to calculate the driving force for local expansive growth of AFt phase in terms of crystallization pressure, and the strain and stress fields are tracked within the microstructure with micrometer-scale resolution using a linear elastic finite element model. Damage induced by expansion modifies both the local effective transport properties and linear elastic properties of each microstructure at different depths, and thereby potentially alters the rates of sulfate ingress and expansion. Simulations give insight about sulfate attack mechanisms, which are investigated in more detail by separating the individual influences of sulfate concentration and pH of the pore solution. Especially when soluble carbonates are present, reductions in the pore solution pH, which often accompany ingress of sulfates, significantly destabilizes calcium monosulfoaluminate and accelerates AFt growth. In fact, within a narrow pH range some calcium monosulfoaluminate can spontaneously transform to AFt without any additional sulfate addition. Therefore, the progress of phase transformations and expansion from the surface to the interior of the porous material is dictated by the rate of ingress of concentration fronts of both sulfate ions and pH, which do not necessarily coincide.

The ultra-high performance concrete (UHPC) mixed with normal coarse aggregate is a promising material due to its excellent mechanics, durability performance and relatively lower cost. To verify the applicability of the current creep prediction models on this concrete with ultra-high strength grade, the creep behaviors of the specimens with different steel fiber contents of 0%, 1% and 2% and two water-to-binder ratios of 0.16 and 0.22 were examined. The results show that the creep coefficient with 1% and 2% ultra-fine steel fibers exhibits remarkably decline of 25.4% and 13.4% after 180 days of loading in comparison to that without steel fibers. The rise of W/B has a negative effect on creep behavior of UHPC. While the specimens with similar compressive strength have different creep coefficients. The test results are compared with the values simulated by the common prediction models (fib MC2010, ACI 209-08, B4 and simplified B4, GB 50010-2010 and JTG D62-2004 models). By substituting the experimental compressive strength with the calculated compressive strength derived from the elastic modulus of UHPC, the modified creep prediction model based on fib MC2010 functions is applicable for the concrete with higher strength grade and more complicated components. In the meanwhile, the creep mechanism of UHPC was discussed based on the mesoscopic and microscopic analyses determined by X-ray computer tomography (CT) and scanning electron microscope (SEM) techniques.

The compensation of thermal shrinkage with the delayed expansion of MgO expansive agent has been used not only in mass concrete, but also in some underground sidewall in subway stations in China. This study investigated the expansion behaviors and crack resistance of three kinds of MgO with different reactivity values (90 s, 150 s and 250 s) in concrete based on a comprehensive test system including the length test using the differential strain gauge, a dual-ring test and the environment simulation test chamber. The results showed that the expansion behavior of MgO expansive agent was closely related to its reactivity value and the temperature history of concrete. MgO with lower reactivity value (90 s, 150 s) showed larger expansion in concrete than MgO with higher reactivity value (250 s) under the temperature history of low temperature rise and high cooling rate, while MgO with higher reactivity value showed larger expansion at temperature fall stage and better crack resistance under the temperature history of high temperature rise, low cooling rate and long cooling period. The results indicate that the reactivity value of MgO expansive agent should be properly selected according to the characteristics of temperature histories of different concrete structures to give full play of its shrinkage compensating efficiency.

In this study, an ultra-stable foam used for foamed concrete was fabricated by modifying the gas–liquid interface by coupling the effects of an organic surfactant and nanoparticles. A serial of techniques was employed to study the products and microstructure development of foam and foamed concrete, respectively. The results show that nano-silica and hydroxypropyl methylcellulose can slow the coalescence and disproportionation of the bubbles by adsorbing at the air bubble surface and increasing the viscosity of cell wall paste, thus preventing gas transfer and hindering physical drainage between the gaseous and liquid phases. Also, a more homogeneous and finer pore structure is generated with the inclusion of the organic surfactant and nanoparticles. The pozzolanic reaction between the nano-silica and Ca(OH)2 results in an increased C-S-H content and the densification of the cell wall structure. In addition, the stability of foamed concrete with modification and relevant stabilization mechanisms were also investigated.

This paper focuses on the optimum design of low-binder Self-Compacting Concrete (SCC) based on particle packing theories. It is first demonstrated that a multi-scales approach can be considered and the mortar with particle sizes smaller than 0.60 mm can be regarded as the matrix of the concrete mixtures. It is also shown that in order to design a low-binder SCC, it is necessary to consider the thresholds of the inclusion volume fraction, the relative matrix thickness and the yield stress of the matrix that respectively relating to flowability, passing ability and stability of the concrete mixtures. Finally, in order to simplify the mix design of the low-binder SCC, recommendations of the values of the distribution modulus (q) in the optimum packing curves are proposed for both the aggregate mixtures and the total particle mixtures (including powders) in SCC, respectively.

Presently, self-compacting concrete (SCC) has been widely used and has many incomparable advantages compared to the traditional vibrated concrete. While it also has many disadvantages among which the robustness of SCC seems to be a serious problem at the production stage. In this study, both the fresh and hardened properties of a low binder content SCC were studied in the cases of the quantity variations of components. Meanwhile, a new robustness assessment method based on the concepts of linear algebra (using norm analysis of vectors) was proposed in order to define and evaluate the robustness of SCC. The results show that the robustness of the hardened properties is higher than that of the fresh-related properties. Additionally, by adopting the proposed method, the robustness of the SCC mixtures can be described and evaluated in a more intuitive way and both the variations of moisture content and aggregate quantities, such as the volume fraction and the gradation, strongly affect the fresh properties of the low-binder SCC. Finally, a good consistency was found between the proposed method and a previous robustness evaluation method thus proving that the proposed methods can be regarded as a concise and effective tool to define and evaluate the robustness of the SCC mixtures.

Graphene oxide (GO) is an attractive candidate for use as a nano-reinforcement in cement composites. However, a prerequisite for GO to fulfill its function is the uniform dispersion of GO throughout the cement matrix. In this paper, the dispersion behavior of GO modified by lignosulfonate (LS), polycondensate of β-naphthalene sulfonate formaldehyde (PNS), and polycarboxylate superplasticizer (PC) in cement pore solution was investigated by a combination of visual observation, optical microscopy and transmission electron microscopy (TEM). Results show that GO modified by PC exhibited better dispersion in cement pore solution than LS and PNS. Zeta potential analysis demonstrated that LS and PNS failed to adsorb onto the GO surface when pH > 11, while successful attachment of PC to GO was achieved even in the alkaline environment. The dispersion mechanisms of PC modified GO were thought to be a combination of covering the surface of GO, lowering the free Ca2+ concentration and impeding the cross-linking of Ca2+ due to steric hindrance effect of PC. With the addition of PC modified GO, the fluidity and mechanical strength of cement composites were improved significantly, indicating that this dispersion route can be successfully used for the preparation of GO reinforced cement composites.

Cement-asphalt (CA) mortar, a grouting material consisting of Portland cement (PC), asphalt emulsion, sand, water and other related admixtures, has been widely used as a cushion layer material in the construction of High-Speed Railways (HSR) during the past decade in China due to its excellent damping property. The fresh and hardened properties of CA mortar are closely related to the PC hydration in the presence of asphalt emulsion. However, the retardation effect introduced by the anionic asphalt emulsion on the hydration process of PC has not been fully understood. In this paper, the effect of an anionic asphalt emulsion on the early hydration process of CA paste was first investigated by setting time test, isothermal conduction calorimeter and electrical resistivity. The MIP and SEM were then employed to characterize the microstructure evolution of the CA paste. Based on the data and observation obtained from the experimental study, three possible retardation mechanisms introduced by the anionic asphalt emulsion on the PC hydration were then assessed in this paper, including (i) selective adsorption by anionic emulsifier via electrostatic attraction, (ii) coating formed by the demulsification of anionic asphalt emulsion, and (iii) reduced reactivity of water molecules in anionic asphalt emulsion.

The heat and moisture states of building floors without impermeable boundary construction, which affect the indoor thermal and moist environment, are determined by the heat and moisture distribution features and coupled transfer process of the under-soil and groundwater level. Previous studies based mainly on mathematical models only considered heat transfer or simplified the boundary conditions as adiabatic and impermeable, which resulted in limitations in application, specifically greater errors in shallow groundwater areas. In this paper, a scale model experiment that combined the floor, soil and groundwater was conducted to study the affected degree of the thermal and wet conditions of the floor in terms of the combined effect of soil heat and moisture transfer and indoor thermal and moist environment. The results showed that under the influence of the latent heat of vaporization, groundwater increases the floor temperature in the short term, and under the influence of water vapor pressure, groundwater decreases the relative humidity of the floor in the short term. The influence range of underground moisture source, analysis of building energy consumption effected by underground moisture source, process of ground surface hot and humid states reaching equilibrium, were discussed by numerical calculations.

Accurate determination of the absorbed water content of recycled fine aggregates (RFAs) is necessary for proper proportion cement-based mixtures. However, some current standard methods are time consuming and have high operator error. In this paper, we propose an alternative method to control the absorbed water content of RFAs by centrifugation. The rotation speed, centrifugation time, and initial water content are considered as parameters. Ten commercially available RFAs were tested by a single operator with multiple measurements by the centrifugation method, and the results were compared with those obtained by the cone and volumetric flask methods. In addition, the fluidity of the mortar with RFAs and manufactured sand were compared to evaluate the additional water required for saturation. The experimental results indicate that the pre-wetted RFAs can reach the saturated-surface-dry condition after centrifugation at 2000 rpm for 10 min when the centrifugal radius is 6–10 cm, at which the water content can be defined as absorbed water. By comparing the standard deviations with other methods, the absorbed water content can be more accurately and repeatedly controlled by the centrifugation method. The fluidity of the mortar with RFAs including additional water by centrifugation shows a good relationship with that of manufactured sand. Therefore, the centrifugation method can be used to control the absorbed water content of RFAs and applied to mixture design.

This study presents an ultra-high strength and ultra-high ductility cementitious composites (UHS-UHDCC) with a compressive strength higher than 160 ​MPa and an uniaxial tensile ductility exceeding 6%. When the mixture ratio is 0.4SF ​+ ​W0.19 ​+ ​PE, the UHS-UHDCC's compressive strength, compression elastic modulus , uniaxial tensile ductility, four-point bending mid-span deflection is 163 ​MPa, 54 ​GPa, more than 6% and 29.72 ​mm, respectively. The toughness at the ultimate mid-span deflection accurately reflects the energy absorption capacity of UHS-UHDCC. Compared with high-strength matrix without fiber, the flexural strength of USH-UHDCC grows 53.21%, its compressive strength only grows 8.24%, the effect of fiber on the flexural strength is more pronounced, and it shows a residual compressive strength of 40%, residual flexural strength of 50%, a good compression deformation capacity and compression toughness. The combination of high fiber dispersion , high matrix density, appropriate interfacial bonding strength, and high tensile strength and high elastic modulus of PE fiber achieves the ultra-high strength and ultra-high ductility of UHS-UHDCC.

For PCM utilization in building component, energy storage structure is expected to improve the ability to extract heat from heat source and dissipate heat to the room at the same time. This paper presents a ring-shaped energy storage structure with combination of an outer casing pipe and an inner coil pipe in heating terminal. To better understand thermal performance and integration strategy of the terminal, effects of thermal parameters of PCM and structural parameters of casing pipe are analysed by numerical model. Root mean square deviation (RMSD) are 0.3% and 2.1% with experiments conducted to validate numerical model. Compared with conventional PCM and traditional heating terminal, casing tube PCM heating terminal have highest stability coefficient index at 0.983, which shows its thermal constancy and comfort level. Results show both thermal conductivity and heat of fusion of PCM have lifting limit at 0.2 W/m2·K and 350 J/g for enhancing the heating terminal thermal performance. PCM melting temperature have matching point at 293 K for high concrete layer surface average temperature and low temperature amplitude. Changing the ratio of casing and coil pipe diameter from 1.5 to 2 could reduce 12.3 K temperature fluctuation on floor surface. The above research provides a heating terminal which can simultaneously enhance heat absorption from heat source and emission to indoor room, while a basic reference for the terminal design and selection is investigated.

This paper examines the mechanisms of desorption within cement pastes for superabsorbent polymers (SAP) with different sorption kinetics: retentive and non-retentive (self-releasing). Despite the different behavior in solution, both SAP types mitigated the autogenous shrinkage of cement pastes. 1H NMR and X-ray tomography showed that the cavities formed by both SAP types were saturated until 9–11 h after mixing, while the entrained water in the cavities redistributed to the cement matrix afterwards. In particular, the non-retentive SAP might have rapidly released the absorbed water, but the released water stayed in the original cavities. Therefore, the behavior of the SAP in the pore solution may not completely determine their internal curing performance in cement pastes. In particular, the initial absorption that forms the solution-filled cavities might be more important than whether the SAP are able to retain the solution for extended periods of time or not.

Owing to both shrinkage-reducing and water-reducing functions, shrinkage-reducing polycarboxylate admixture (SRPCA) has great advantages to mitigate shrinkage cracking of the low water-to-cement ratio cementitious materials. In this paper, cracking behavior of ultra-high strength mortar (UHSM) containing SRPCA and shrinkage reducing admixture (SRA) was evaluated by the temperature stress testing machine (TSTM) tests. To analyze the cracking reduction mechanism of SRPCA, mechanical properties, autogenous shrinkage, tensile creep and elastic modulus of UHSM with SRPCA and SRA were studied. Furthermore, the effect of SRPCA on the mechanical properties, autogenous shrinkage, tensile creep and elastic modulus was discussed by analyzing surface tension, hydration progress, portlandite content, pore structure and relative humidity. The results show that the addition of SRPCA significantly reduces autogenous shrinkage of UHSM mainly due to internal relative humidity reduction. The surface tension reduction and hydration regulation are key for the RH decrease. In addition, SRPCA can increase tensile creep and decrease elastic modulus of UHSM. As a result, incorporating SRPCA can improve cracking resistance of UHSM.

This paper introduces an untreated flue gas desulfurization (FGD) gypsum-based high-strength building materials prepared using the uncalcined desulfurization gypsum. The chemical compositions, physical properties and particle micromorphology of the untreated FGD gypsum were analyzed. The influence of digestion time on the mechanical properties of untreated FGD gypsum-based high-strength building materials was studied, therefor the optimal digestion time was determined to be 18 h. The mechanical properties, water resistance, frost resistance and shrinkage property of the building materials were tested. The hydration reaction mechanism, hydration process, hydration products, pore structure, micromorphology of the building materials were researched by means of XRD (X-ray diffraction), MIP (Mercury Intrusion Porosimeter) and SEM (scanning electron microscope). Non-evaporable water content was used to represent the hydration degree. The results show that the untreated FGD gypsum-based high-strength building materials has good mechanical properties, water resistance, frost resistance and low shrinkage ratio, high hydration degree, dense microstructure. And its Ca/Si atom ratio is low. This study provides a new approach for the more effective use of untreated FGD gypsum, which effectively saves the natural resources.

Multiple Supplementary Cementitious Materials (SCM) in large quantities have been used in quasi-mass concrete to minimize the crack risk. Yet the hydration process of concrete with high volume addition of SCM, especially effect of temperature on the early stage hydration, has been rarely investigated. In this paper, early age hydration progress and mechanical properties of concrete with high volume GGBS and FA were studied under different curing temperatures. The results show that high volume GGBS and FA accelerate the cement hydration in early age due to the dilution and filler effects. However, the hydration was slowed down when the addition of FA is up to 55% and 70%. Compared to binders with GGBS, the hydration process of binders with FA are more sensitive to temperature. The results also imply the necessity of the introduction of a range factor of hydration degree for effective estimation of Ea for binders with high volume of SCM. The equivalent age equation effectively predicts the early age strength development of high volume SCM concrete curing under changing temperature in an actual structure and what needed to do is to modify the activation energy by considering the hydration progress of binder with high volume SCM.

In this paper, the influence and underlying mechanism of superplasticizers (SP) dosage on the viscosity of cement pastes with four water-binder ratio (w/b) were investigated. The results showed that apparent viscosity of the pastes with w/b of 0.24 and 0.32 decreased with SP dosage. Whereas, it is reverse for cement paste with w/b of 0.20 and 0.16. The addition of SP increased the packing density and the water film thickness of pastes with a w/b of 0.32 and 0.24. However, the increase of SP dosage had little effect on the packing density and the water film thickness of pastes with a very low w/b (0.16). For the cement pastes with a very low w/b (e.g., 0.16), the small spaces between the binder particles and the high concentration of the un-adsorbed SP in the interstitial solution may be the primary factors responsible for the increase in viscosity of the pastes.

As a potential matrix of inorganic coating, aluminosilicate geopolymer has excellent properties of low Volatile Organic Compounds (VOC) emission, anticorrosion and long life. However, little concern has been devoted to basic parameters of the aluminosilicate geopolymer coating. The present paper investigated the influence of water to solid ratio on the property and microstructure of the coating. Results showed that as the water to solid ratio of geopolymer coating increased from 0.8 to 1.0, the hardening process was delayed significantly. The variation of autogenous shrinkage differed from that of drying shrinkage. The overall porosity measured by Mercury Intrusion Porosimetry (MIP) decreased, while a dramatic increased volume of pores with the size of 30–50 nm was detected. Besides, the Fourier Transform Infrared Spectroscopy (FTIR) results indicated that polycondensation degree was affected in an inverse manner at early and late ages of geopolymer hardening.

The benefits of internal curing (IC) have been confirmed by extensive laboratory studies under constant room temperature. In practical engineering, sidewall concrete undergoes a variable temperature evolution, which involves significant physical, chemical, and thermal changes during the hydration process at the early age and a high cracking risk at the temperature drop stage. Expansive agent (EA) has always been used to mitigate early-age cracking, but it has limited efficacy in the temperature drop stage and low mechanical properties. This study examines the efficacy of IC through pre-soaked lightweight aggregate (SLWA) and the combined use of SLWA and EA in mitigating shrinkage deformation under constant and variable temperature conditions. Results indicate that SLWA shows a higher efficacy than EA in mitigating shrinkage deformation during the temperature drop stage and can provide continuous expansion at the later stage. The combined use of SLWA and EA exhibits high efficacy in mitigating shrinkage deformation under constant and variable temperature conditions and can limit the reduction of mechanical properties caused by a single EA.