In order to better solve the problem of electromagnetic pollution in the civil building cement, to improve the absorption capacity of magnesium oxysulfide cement based materials, and to better use sulfur oxide magnesium cement foamed sheet for improvement of electromagnetic industry, this paper uses the excellent microwave absorbing properties of ferrite and the modified sulfur oxide magnesium cement foam board, and discusses the microwave absorbing performance, aiming at improving the electromagnetic pollution in daily life. The effects of ferrite and silicon carbide doping on microwave absorption properties of modified magnesium oxysulfate cement were studied. At the same time, the wave absorbing properties of the corresponding samples were detected by bow method, and the causes of the corresponding phenomena were analyzed by scanning electron microscopy (SEM). The results show that the lowest reflectance of the material is −17.9 dB at 34.1 GHz and the average reflectance of the whole band is −15.9 dB under the target frequency band of 26.5–40 GHz. Under the action of external magnetic field, the absorbing particles are affected by magnetization force, magnetic dipole and resistance coupling, and play the absorbing effect in the cement base solidified completely in the electromagnetic field environment. The lowest reflectance is −17.3dB at 36.4GHz and the average reflectance is −14.3dB for the whole band.
A coupling model of fatigue damage evolution and cohesive zone equations was developed to simulate the damage behaviors of tile-mortar interface under various temperature loadings. The effects of temperature variation amplitudes, cyclic times and mortar thickness on the interface damage were analyzed. Results show that the proposed fatigue cohesive zone model is feasible for the simulation of damage behaviors of tile-mortar interface under temperature cycles. The interface damage is mainly caused by the shear movements between the tile and mortar. The effect of cooling is much greater than that of heating on the interface damage. With increasing temperature cycles, the interface damage initiates at the edge of tile, and extends to the middle of tile in a decreasing growth rate. Increases of temperature variation amplitudes and a sudden thickening of mortar will accelerate the initiation and evolution of interface damage. The damage generating by the sudden thickening of mortar mainly appears in the thicker side.
为解决机制砂生产过程产生的废弃石粉(WSP)处置难题,本文提出了将废弃石粉用作混凝土矿物掺合料的利用新途径,研究了废弃石粉的特征及其对混凝土抗压强度与孔结构的影响,并基于生命周期评价方法分析了利用废弃石粉带来的碳减排效益.结果表明:废弃石粉虽较磨细石粉(GSP)具有更高的亚甲蓝值,但对砂浆流动度的影响较小;相比于磨细石粉和粉煤灰,废弃石粉会降低低强度等级混凝土的抗压强度,但对高强度等级混凝土的抗压强度影响较小;废弃石粉作为矿物掺合料可有效降低混凝土的生产碳排放,内掺20%废弃石粉的混凝土碳排放总量降低了近20%.
通过抗折强度、抗压强度、界面弯拉强度、体积变形以及红外光谱测试,研究了苎麻纤维(RF)掺量对硫铝酸盐水泥基材料力学性能与体积变形的影响.结果表明:随着RF掺量(体积分数,下同)的增加,硫铝酸盐水泥净浆的抗折强度和抗压强度均呈现先增加后减小的趋势,并且在纤维掺量为0.50%时同时达到峰值;在约束条件下,掺入RF对硫铝酸盐水泥净浆界面弯拉强度的提升幅度较大,纤维掺量为0.75%试样的28 d界面弯拉强度较无约束条件下提高了31.82%;RF的掺入显著增加了硫铝酸盐水泥净浆的膨胀量,其自生变形和干燥变形均随着RF掺量的增加逐渐增大;改性后的RF可以在硫铝酸盐水泥基材料的碱性环境中稳定发挥作用,提高试样的整体强度.
基于压入法原理,提出了1种混凝土超早期弹性模量的测试方法.采用数值分析方法设计试件尺寸,选用30°球锥形压头作为混凝土超早期弹性模量的测试压头,优化压入深度为5 mm.通过改变混凝土的水胶比和粉煤灰掺量,并与超声波法相对比,对该方法进行验证.以初凝时刻的弹性模量0值为起点,传统应力-应变方法最早测得的弹性模量为终点,用这2点之间的连线预测混凝土超早期弹性模量.该预测法与压入法试验结果相比,误差均在30%以内.
研究了"灯芯效应"下珊瑚骨料混凝土在Mg2+、SO2-4 共同作用下Cl-的传输规律,建立了"灯芯效应"下珊瑚骨料混凝土Cl-传输模型.结果表明:Cl-沿半浸泡混凝土高度方向由下而上传输的同时也由表层向中心传输,其在混凝土内部的含量呈类抛物面分布;SO2-4 的存在会加快Cl-在混凝土中的传输,而Mg2+的加入会抑制Cl-的传输,导致混凝土在相同高度及深度处的Cl-含量小于SO2-4与Cl-共同作用下的Cl-含量;本文建立的"灯芯效应"下珊瑚骨料混凝土氯离子传输模型计算结果与实测结果吻合良好.
利用CO2气体碳化处理再生微粉替代水泥制备砂浆试样,探究了不同替代率下再生微粉对砂浆水化和性能的影响规律.结果表明:当替代率为20%时,与未经处理的再生微粉相比,碳化再生微粉砂浆的1、3 d抗压强度分别提高了66.7%、17.6%;碳化再生微粉主要成分是CaCO3 和无定形硅胶,二者在水泥水化早期可与水泥水化产物反应从而发挥火山灰效应,再生微粉中的微细石英砂粉则发挥成核效应,均加速水泥的早期水化进程,显著提升其早期力学性能;在加速碳化处理过程中,再生微粉的固碳量可达自身质量的10.0%;制备砂浆后,其平均单位抗压强度最高可减少18%的CO2排放.
采用超高性能混凝土(UHPC)修复普通混凝土(NSC)基体时可以获得优异的界面黏结强度,其值甚至高于基体强度,导致界面性能测试时容易发生基体失效,从而不能准确评价界面性能及其影响因素.针对上述问题,提出了基体约束加强的方法,将失效位置控制在修复界面,测得了真实的UHPC-NSC界面黏结强度,分析了基体强度和修复面粗糙度对界面性能的影响与机理,克服了传统测试方法的评价结果过于保守且难以反映粗糙度等影响因素的不足.UHPC-NSC界面较NSC-NSC界面更加致密,界面过渡区的钙硅比更低,宽度和孔隙率分别降低了91%和70%.
系统研究了以NaOH、水玻璃以及NaOH复掺Na2CO3为激发剂,激发矿渣、粉煤灰、矿渣/粉煤灰和矿渣/水泥4种胶凝体系的凝结时间和7 d抗压强度变化规律,获得了凝结时间与掺量变化公式及早期抗压强度预测公式.结果表明:单一NaOH或水玻璃激发矿渣条件下,掺入少量粉煤灰、水泥对改善复掺体系凝结时间的效果不显著,并且均会降低早期抗压强度;采用NaOH/Na2CO3复合激发剂后,能够有效延长体系凝结时间,在一定程度上提高体系抗压强度.针对NaOH/Na2CO3复掺激发矿渣/水泥体系凝结时间和抗压强度出现"不增却减"的现象,深入讨论了掺NaOH/Na2CO3复合激发剂的作用机理.
基于新疆若羌盐渍土环境,对水胶比为0.32、0.35和0.38的混凝土试件,进行硫酸盐溶液浸泡腐蚀(标准养护 28 d)、盐渍土腐蚀(标准养护 28 d)、盐渍土腐蚀(标准养护 3 d)这 3种腐蚀制度下的耐久性试验,分析腐蚀制度与水胶比交互作用下混凝土动弹性模量经时演变规律与作用机制.并基于混凝土动弹性模量动态变化过程,通过Wiener过程理论,建立了盐渍土环境下混凝土服役寿命预测模型,以定量表征混凝土损伤劣化规律.结果表明:在各腐蚀制度下,随腐蚀龄期增加,混凝土损伤度均出现先减小后增大的规律;在腐蚀终期,混凝土水胶比与其损伤度呈负相关;在相同水胶比下,硫酸盐溶液浸泡腐蚀(标准养护28 d)、盐渍土腐蚀(标准养护28 d)、盐渍土腐蚀(标准养护 3 d)对混凝土损伤程度的影响依次增加;由Wiener过程理论建立的混凝土服役寿命预测模型可知,混凝土预测寿命退化呈3阶段变化趋势,其趋势与试验中混凝土劣化过程保持一致.
采用试验和三维随机骨料细观模型,研究了全珊瑚海水混凝土(CASC)在高温前后的静动态力学性能、抗侵彻和防爆性能.结果表明:添加剑麻纤维能有效改善CASC的脆性;随着温度的提高,CASC的残余抗压强度先增后减;经历高温后CASC的静动态力学性能明显降低,温度越高,高温弱化效应越明显.提出了描述CASC高温后受压应力-应变关系的两段式方程.建立了一种适用于CASC的三维随机骨料细观模型,数值模拟结果与试验结果较为吻合.
从全球碳中和与可持续混凝土发展角度阐述了低碳混凝土的基本概念及全生命周期的减碳与碳汇核心技术理念.从原材料、混凝土设计、制备、施工、服役及再生利用等全生命周期过程提出了低碳混凝土的三大技术途径——直接减碳、间接减碳及碳汇技术,并分析了每个技术途径下的具体减碳技术路线.综述了混凝土的碳排放评价方法和准则,阐释了混凝土碳排放的生命周期评价方法.提出了低碳混凝土未来的重点研究方向——开发新型胶凝材料以及碳汇技术.
通过混凝土抗冻性快冻法试验,研究了氧化石墨烯再生粗骨料混凝土(GO-RAC)在冻融循环与氯盐侵蚀耦合作用下的耐久性能,测试分析了GO-RAC的相对动弹性模量、质量损失率、抗压强度及氯离子侵蚀情况.结果表明:冻融循环与氯盐侵蚀的耦合作用加速了再生粗骨料混凝土(RAC)的劣化损伤,经历72次冻融循环后不同GO掺量GO-RAC的相对动弹性模量均降至其初始值的60%以下,宏观劣化程度较普通RAC有不同程度的降低;由于耦合初期侵蚀产物的填充致密效应,GO-RAC的抗压强度呈现先增大后减小的趋势;GO-RAC在冻融循环与氯盐侵蚀耦合作用下的Cl⁻分布符合Fick第二定律,表面的Cl⁻质量比随着耦合次数的增加呈指数形式增大,扩散系数随着耦合次数的增加先减小后增大.
基于纤维改性沥青混凝土路用性能强化提升需求,提出了采用木质素纤维(CF)/玻璃纤维(GF)复合改性沥青混凝土路用性能的方法,研究了复合纤维组成对沥青混凝土路用性能的影响机理.结果表明:CF/GF复合改性有效提升了沥青混凝土的高温稳定性,并具有良好的水稳定性和低温性能;当CF/GF以质量比1∶3掺入时,沥青混凝土动稳定度为单掺CF组的2.2倍;试件低温破坏时,最大弯拉应变提升13.3%.复合纤维具有吸附、加筋及阻滞裂纹的作用,强化了沥青混凝土在温度变化、水损及应力作用下的稳定性,从而提高了其路用耐久性能.
为提高混凝土的抗冻性及促进工业废料的应用,利用快冻法对混凝土试件进行冻融试验,测试冻融前后试件的相对动弹性模量(Er)和抗压强度,研究单掺玄武岩纤维束(BMF)、双掺短切玄武岩纤维(CBF)和BMF以及在双掺的较优配比基础上继续掺加硫酸钙晶须(CSW)对高强混凝土抗冻性能的影响.结果表明:素高强混凝土(PC)在经历150次冻融循环后的Er值为52.4%,视为冻融破坏;单掺、双掺和三掺均提高了高强混凝土的抗冻性,三掺的效果最好;当BMF体积分数为0.30%、CBF掺量为0.15%、CSW掺量为水泥质量的3%时,高强混凝土试件(CSW3CBF0.15BMF0.3)的抗冻性最佳,经历300次冻融循环后的Er值为86.6%,仍未冻融破坏;试件CSW3CBF0.15BMF0.3在经历150次冻融循环后的抗压强度损失率仅为2.5%,远低于PC(30.9%);CSW、CBF和BMF发挥混掺效应,多尺度阻止了高强混凝土的冻胀开裂.
In order to comprehensively consider the influence of low-temperature performance of asphalt on low-temperature performance of asphalt mixture， and predict low-temperature performance of asphalt mixture based on low-temperature performance of asphalt and mixture. The low temperature evaluation indexes of five kinds of asphalt and mixture were determined by bending beam rheological test， conventional low temperature test and TSRST. They were carried out grey correlation analysis， and were established fractional grey prediction model. The results show that the low temperature continuous classification temperature， glass transition temperature， brittle point， creep rate and dissipation energy ratio at four temperatures have great influence on the low temperature performance of asphalt mixture. The error of FGM （1，4） model for freezing temperature and turning point temperature is 1.83% and 3.71% respectively， indicating that the accuracy is excellent and the prediction result is reasonable.
10 concrete filled steel tube （CFST） specimens with different strength grades and sizes were cured under pressure by self-designed hydraulic device. The effects of curing pressure and its duration on uniaxial compressive strength， stress-strain variation and failure characteristic of CFST specimens were studied. Microscopic test methods were used to study the development and formation of pore structure and hydration products. The results show that， the particles in the mixture were squeezed close to each other under pressure curing， and the formation and development of microcracks were inhibited， which lead to the higher compactness of core concrete; Moreover， the crystallization process of hydration products were promoted， and the pore structure can be fully filled by the hydration products， which improved the strength of core concrete. In addition， the pressure caused the circumferential tensile strain of steel tube， which provided pre-compressive stress on core concrete after final setting time. Therefore， the uniaxial compressive properties of the CFST were improved.
The anti-clogging performance of novel recycled pervious concrete （NRPC） was studied by designing storm and clogging test， and the influence of pore diameter of NRPC and particle size of clogging material on clogging structure， permeability coefficient， clogging depth and clogging material passing rate was analyzed. The results show that the clogging structure of NRPC is determined by the ratio of pore diameter to clogging material diameter （d/r）. The clogging structure can be divided into single particle surface clogging， single particle pore channel clogging and multi-particle channel clogging after rainstorms. The decrease of permeability coefficient mainly occurs in the first rainstorm clogging cycle. Multi-particle clogging caused by small particle size clogging material （r＜1.18 mm） is the main reason for the decrease of NRPC permeability coefficient. With the increase of d/r， the stability of multi-particle pore clogging structure decreases. When d＞r， the smaller d/r is， the deeper the NRPC pore channel is clogging. With the increase of d/r， the passing rate of clogging material increases， and the screening effect of pore channels decreases.
对不同冻融损伤程度的混凝土圆环体试件进行了试验研究.结果表明:当相对冻融深度小于临界值时,混凝土的峰值应力、峰值应变均呈线性退化,超过临界值后则保持稳定;当冻融循环次数由100次增加到200次时,相对冻融深度临界值由0.5增大到0.8;基于应变等价性假说和统计损伤理论,建立了不同冻融损伤程度下承压混凝土的应力-应变关系模型.
To objectively evaluate the whole process of transport-reaction-damage of concrete under sulfate attack， a transport model considering porosity， tortuosity and critical damage degree is established based on the theory of crystallization pressure， volume expansion theory and Fick’s second law. Meanwhile， the variable coefficient of sulfate transport is solved by alternating implicit difference method. Results show that the prediction results are basically consistent with the experiment. The model can better predict the diffusion law of sulfate ions in concrete， with a maximum error of 28.6%. The influence factors analysis shows that the concentration of sulfate attack and the critical damage degree present a great influence on the spalling thickness of concrete cover. Under the same critical damage degree， the spalling speed increases with the sulfate concentration. It shows that the spalling speed in 5% sodium sulfate solution is 133.0% faster than that in 1% sodium sulfate solution. Under the same concentration of sodium sulfate solution， the spalling thickness decreases with the critical damage degree. When the critical damage degree increases from 0.8 to 0.95， the spalling thickness decreases by 42.9%.
