Rapid freeze-thaw (F-T) tests were conducted to study the frost resistance of desert sand concrete (DSC) at different stress levels (SL), desert sand replacement rate (DSRR) and the number of F-T cycles. The impact of the SL, DSRR, and number of F-T cycles on the mass loss rate, ultrasonic wave velocity, and stress-strain curve of DSC was investigated through uniaxial compression tests. Scanning electron microscope (SEM) was used to examine the microstructure of DSC. The constitutive relationship was established considering the influence of the SL and number of F-T cycles. The results indicated that the frost resistance and uniaxial compressive mechanical properties of DSC could be effectively enhanced when desert sand was added at 40%. The peak strain initially decreased and then increased as the DSRR increased. In contrast, the peak stress first increased and reached a maximum value as the DSRR increasing to 40%, followed by a gradual decrease. The F-T cycles gradually deteriorated the macroscopic properties of DSC. The proposed constitutive model of DSC was established by combining the two classical models as the ascending and descending sections, respectively. The model prediction results matched well with the experimental results, which can provide a theoretical basis for the engineering application of DSC under F-T cycles and loading environments.

In order to investigate the effects of loading and high temperature on the uniaxial compressive properties of desert sand concrete （DSC）， the uniaxial compression experiment of DSC subjected to different loading and temperatures were carried out to obtain the stress-strain curves. The influences of loading level， temperature and cooling methods on the mass loss rate， ultrasonic velocity and axial compressive properties of DSC were analyzed. Experimental results showed that the mass loss rate of DSC gradually increased with the temperature. The uniaxial compressive strength and modulus of elasticity of DSC declined， peak strain increased greatly， and the stress-strain curve gradually became flat. The "pseudoplastic plateau" near uniaxial compressive strength of DSC stress-strain curve became more obvious. Taking into account of temperature and loading level， the stress-strain model was established to simulate the mechanical properties of DSC on the basis of two-stage constitutive model， which provided technical support for performance evaluation of DSC after high temperature.

采用不同替代率沙漠砂制备沙漠砂混凝土,研究其高温后经二次养护抗压性能.通过高温后沙漠砂混凝土抗压强度试验,分析试件质量损失变化及温度、沙漠砂替代率对抗压强度影响;通过二次养护后抗压强度及SEM试验,分析二次养护龄期和方式对沙漠砂混凝土抗压强度和微观结构影响.试验结果表明:随温度升高,沙漠砂混凝土质量损失率逐渐增大,抗压强度逐渐减小;随沙漠砂替代率增加,抗压强度呈先增大后减小趋势;高温后沙漠砂混凝土内部孔洞、微裂缝数量增多,微观结构劣化严重.高温后沙漠砂混凝土经过二次养护,随养护龄期增加,抗压强度恢复率呈先增大,到达峰值后呈下降或持平趋势.

To study the influence of freeze-thaw cycles on the mechanical properties of concrete, compression strength experiments of concrete mixed with desert sand and fly ash（DSC） after freezing and thawing cycles at different low temperatures（-20 ℃,-30 ℃ and-40 ℃） were carried out. The influence of desert sand replacement rate（DSRR）, temperature and number of freezethaw cycles on DSC compressive strength and ultrasonic velocity was analyzed. The regression models between DSC compressive strength, ultrasonic velocity and temperature, DSRR and number of freeze-thaw cycles were established. The results show that as the number of freeze-thaw cycles increases, the DSC compressive strength and ultrasonic velocity decrease. When the temperature decreases, the DSC compressive strength and ultrasonic velocity decrease. With the increase in DSRR, DSC compressive strength firstly increase and then decrease. When the DSRR is 40%, its compressive strength reaches the maximum.

为了研究沙漠砂混凝土动态力学性能,利用落锤冲击试验机进行了沙漠砂混凝土动态抗折性能试验,分析沙漠砂替代率对沙漠砂混凝土动态抗折强度影响.研究表明:沙漠砂混凝土具有明显率相关性,沙漠砂混凝土动态抗折性能随沙漠砂替代率增加呈现先增大后减小趋势.沙漠砂替代率40％时,沙漠砂混凝土动态抗折强度最大.

The shortage of sand resources and high-rise building fires are becoming increasingly prominent. Desert sand (DS) with smaller particles can effectively fill the concrete voids and further improve its working performance; it is used as a fine aggregate to produce concrete. This article studied the performance of desert sand concrete (DSC) against fire resistance by using mathematical modeling for simulation. The stress-strain curves of desert sand mortar (DSM) after elevated temperatures were tested, and the constitutive model was established. By comparing the experiment and simulation results, it was verified that the model is suitable to be adopted in this study. Data from experiment and past literature can serve as parameters for the subsequent simulation. The destruction process of DSC under uniaxial compression after elevated temperature was simulated by using ANSYS. The simulation results indicated that, after elevated temperature, compressive strength reduced with increase of interface thickness. The compressive strength of DSC had a substantially linear increase as the interface compressive strength increased. For two-grade coarse aggregate, the optimum volume content was 45%, and particle size of it showed a significant effect on the compressive strength of DSC. The DSM constitutive model and simulation results can provide a sound theoretical basis and technical support for DSC engineering applications.

Demand for medium sand has increased greatly with increasing infrastructure construction items. The shortage of construction sand resources has become a serious problem in many districts. It not only increases the engineering cost, and the overexploitation of river sand and mountain as medium sand also brings a series of serious environment problems. There are abundant desert sand (DS) resources in western China. If DS resources can be used to substitute medium sand to produce desert sand concrete (DSC), which was suitable for engineering practice, the environment can be improved and engineering cost can be reduced. Although many researchers had focused on the mechanical performance of DSC, there were few documents on the frost resistance of DSC. Frost resistance experiments of DSC with 50% desert sand replacement ratio (DSRR) and ordinary concrete (OC) were performed in this paper. Influence of freeze-thaw cycles on the mechanical properties of OC and DSC was analyzed. Experimental results showed that, with increasing freeze-thaw cycles, the damage, peak strain, and porosity increased, while elastic modulus, Poisson's ratio, and peak stress declined, the stress-strain curves tended to be flat. Under the same condition of freeze-thaw cycles, the frost resistance of DSC with 50% DSRR was higher than that of OC. Constitutive model of DSC after different freeze-thaw cycles was formulated. The results predicted by constitutive model agreed well with experimental results, which can provide technical support for DSC engineering practice.

Building fires and shortage of medium sand resources have become two major issues in building domain. Desert sand was used to produce desert sand concrete (DSC), which was suitable for engineering utility. The mechanical properties tests of DSC with different desert sand replacement ratio (DSRR) were carried out after elevated temperature. The effects of elevated temperature and DSRR on DSC mechanical properties were analyzed. DSC microstructure was investigated by SEM and XRD. Research studies’ results showed that the relative compressive strength increased gradually with increasing temperature. The maximum value appeared at 200°C–300°C, and it began to decrease at 500°C. Compared with room temperature, the compressive strength at 700°C was about 70% of that at room temperature. Relative splitting tensile strength increased first and then decreased, and the value reached the maximum at 100°C. DSC relative flexural strength decreased with the temperature. Relative compressive strength, splitting tensile strength, and flexural strength of DSC enhanced first and then decreased with DSRR, and the maximum values were obtained with 40% DSRR. Based on the regressive analysis, the relative compressive strength was a quadratic polynomial with relative porosity. Relative splitting tensile strength and relative flexural strength were linear with relative porosity. Research results can provide the technical support for DSC engineering application and postfire assessment.

通过进行单掺粉煤灰、单掺沙漠砂、双掺粉煤灰和沙漠砂混凝土抗压强度、电通量和RCM试验,揭示沙漠砂替代率和粉煤灰掺量对沙漠砂混凝土抗氯离子渗透性能和抗压强度的影响规律,分析电通量和氯离子扩散系数的相关性.研究表明:单掺粉煤灰混凝土抗氯离子渗透性能随着粉煤灰掺量增加而增强;单掺沙漠砂混凝土抗氯离子渗透性能随着沙漠砂替代率增加呈先增强后减弱趋势,沙漠砂替代率60％时混凝土抗氯离子渗透性能最好;粉煤灰掺量30％、沙漠砂替代率60％时,双掺粉煤灰和沙漠砂混凝土抗氯离子渗透性能最好;电通量和氯离子扩散系数相关性良好.

为了对沙漠砂混凝土高温后力学性能进行研究,通过不同沙漠砂替代率的沙漠砂混凝土高温试验,分析温度、沙漠砂替代率和冷却方式对沙漠砂混凝土高温后抗压强度的影响规律,建立沙漠砂混凝土高温后抗压强度的衰减模型.结果表明,与普通混凝土相似,随着温度升高,沙漠砂混凝土试件表面颜色逐渐变浅;随温度升高,沙漠砂混凝土抗压强度呈先增大后减小趋势;随着沙漠砂替代率增加,沙漠砂混凝土高温后抗压强度呈先增大后减小趋势,沙漠砂替代率40％时,沙漠砂混凝土高温后抗压强度达到最大.

The carbonation resistance tests of concrete with single fly ash,single desert sand and compound of fly ash and desert sand at 3 d,7 d,14 d,28 d and 56 d were carried out. The influences of fly ash dosage and desert sand replacement ratio on the carbonation resistance property of concrete were analyzed. The regression model among the carbonation depth of concrete at 28 d and fly ash dosage and desert sand replacement ratio was established. Experimental results show that the carbonation depth of concrete increases with fly ash dosage. The carbonation depth of concrete with single fly ash at early age increases faster than the latter. With the enhancement of desert sand replacement ratio,the carbonation depth of concrete with single desert sand decreases firstly,and then increases. When desert sand replacement ratio is equal to 20%,the carbonation depth of concrete with single desert sand reaches minimum value. When fly ash and desert sand are mixed into concrete simultaneously,the carbonation depth of concrete with the compound of fly ash and desert sand reaches the minimum value on the condition that the fly ash dosage is 10% and desert sand replacement ratio is 20%.

采用直锥变截面式Φ74mm分离式霍普金森压杆,对不同替代率沙漠砂混凝土进行冲击压缩实验,得到了不同替代率沙漠砂混凝土在不同应变率下的应力应变曲线.分析应变率对沙漠砂混凝土峰值应力、峰值应变和比能量影响,揭示了沙漠砂替代率对沙漠砂混凝土峰值应力影响规律,并对沙漠砂混凝土动态破坏模式进行研究.研究表明:随着应变率增加,沙漠砂混凝土峰值应力、强度增强因子、比能量和峰值应变逐渐增大;在同一应变率下,随着替代率增加,沙漠砂混凝土峰值应力逐渐减小.本文研究结果可为沙漠砂在工程中的应用提供指导和借鉴.

通过单因素实验,在水胶比、砂率和外加剂掺量不变的情况下,研究不同沙地砂替代率对高强混凝土抗压强度的影响规律,并利用其应力-应变曲线进一步研究沙地砂替代率对高强混凝土抵抗变形能力和韧性的影响.研究结果表明,沙地砂替代建筑用砂配制高强混凝土是可行的,沙地砂高强混凝土中沙地砂的最优替代率为0％～40％.

设计正交试验,研究水胶比、粉煤灰掺量、砂率和沙漠砂替代率对沙漠砂混凝土7d、28 d、56 d抗压强度和28 d劈裂拉伸强度的影响,通过极差分析和方差分析确定了沙漠砂混凝土的最优配合比.研究结果表明:用沙漠砂替代中砂配制混凝土是可行的;综合考虑沙漠砂混凝土7d、28 d、56 d抗压强度和28 d劈裂拉伸强度,沙漠砂混凝土的最优配合比为水胶比0.34、粉煤灰掺量10％、砂率30％、沙漠砂取代率30％,为沙漠砂在工程中的应用提供指导和借鉴.

The orthogonal experiment is carried out to analyze the influence of water-binder ratio,fly ash dosage,sand ratio and desert sand replacement ratio on the 7 d,28 d,56 d compressive strength and 28 d splitting tensile strength of desert sand concrete. On the basis of the optimal mixture ratio from orthogonal experiment,the regulation on the influence of fly ash dosage and desert sand replacement ratio on the 28 d compressive strength and splitting tensile strength of desert sand concrete was further analyzed. Experimental results show that with the increase of desert sand replacement ratio,the 28 d compressive strength and splitting tensile strength of desert sand concrete increases firstly,then declines. When desert sand replacement ratio amounts to 20%,the 28 d compressive strength and splitting tensile strength of desert sand concrete reaches maximum. With the enhancement of fly ash dosage,the 28 d compressive strength and splitting tensile strength of desert sand concrete also increases firstly,then declines. When fly ash dosage amounts to 10%,the 28 d com-pressive strength and splitting tensile strength of desert sand concrete reaches maximum,which provides guidance for the engineering ap-plication of desert sand.

The orthogonal experiment is designed to analyze the influence of water-binder ratio,fly ash dosage,sand ratio and desert sand replacement ratio on the compressive strength of high strength concrete at different age.On the basis of the result from the orthogonal experiment,single factor experiment is further carried out to study the influence of desert sand replacement ratio on the compressive strength of desert sand high strength concrete. Experimental result shows that it is practical to use the desert sand from Muus desert to mix high strength concrete. Taking into account of the results from the orthogonal experiment and single factor experiment,the optimum desert sand replacement ratio of desert sand high strength concrete is 20%.

The orthogonal experiment is carried out to analyze the influence of water-binder ratio,fly ash content,sand ratio and desert sand replacement ratio on the 7,28 d compressive strength and 28 d splitting tensile strength of desert sand high strength concrete.The opti-mum mix ratio of desert sand high strength concrete is also given out.On the basis of the optimal mixture ratio from orthogonal experi-ment,single factor experiment is carried out to study the influence of concrete compressive strength under different desert sand replace-ment ratio.Experimental result showed that it was practical to use the desert sand from Mu Us desert to mix desert sand high strength con-crete.The optimum desert sand replacement ratio of desert sand high strength concrete was from 0 to 40%.

Based on the damage and Ottosen failure criterion, a dynamic constitutive model is proposed to investigate the mechanical behavior of concrete subjected to impact loading. The model predictions fit well with experimental results. So it can be used to simulate dynamic mechanical behavior of concrete

The dynamic compression tests of reinforced concrete with different reinforcement ratios are carried out by split Hopkinson pressure bar (SHPB). Reinforced steel bar is placed along longitudinal and transverse direction. Experimental results show that reinforced concrete is non-linear and rate-dependent. With the enhancement of strain rate, the peak stress of reinforced concrete increases correspondingly.

The dynamic compression experiments of reinforced concrete are carried out by one-stage light gas gun apparatus which subjects the reinforced concrete to deformation at strain rates of the order of 104/s with confining pressures of 1~1.5GPa. The stress-strain curves of reinforced concrete with different impact velocities are obtained using Lagrangian analysis method. Experimental results indicate that reinforced concrete is non-linear, rate-sensitive and pressure-dependent.