【作者】 王鹏刚；

【导师】 赵铁军； F.H.Wittmann；

【作者基本信息】 青岛理工大学 ， 结构工程， 2014， 博士

【摘要】 应变硬化水泥基复合材料(Strain Hardening Cement—based Composite,简称SHCC)在拉伸荷载作用下具有应变硬化特性和多缝开裂特性,其极限拉伸应变可达到4%以上。因此SHCC在控制结构裂缝以及提高结构抗震性能等方面有广阔的应用前景。目前,SHCC的设计理论、基本力学性能、耐久性能等方面的成果较多。但大多数研究是针对未收损伤构件进行的,这与实际工程有一定的差别。所以,本文针对上述问题研究SHCC的开裂损伤机理以及开裂后的耐久性,主要结论如下：(1)采用数字图像处理的方法研究了拉伸荷载作用下SHCC试件成型面和底面的裂缝开展过程,并用数理统计和概率的方法对其进行分析。发现试件底面的裂缝密度低于试件成型面,其平均裂缝宽度大于成型面,裂缝密度、平均裂缝宽度等裂缝宽度统计参数均与拉伸应变呈三次多项式关系,并且通过分析发现拉伸荷载作用下SHCC的裂缝宽度分布可以用Gamma分布进行描述。在此基础上进行毛细吸水试验和氯离子侵蚀试验,研究不同拉伸应变下SHCC的耐久性,同时研究了硅烷浸渍防水处理对开裂SHCC的防护效果。发现随着拉伸应变的增加,SHCC试件的吸水速度增快,吸水量增大,毛细吸收系数随拉伸应变线性增加,氯离子侵入深度和侵入量增大。而硅烷防水处理可以有效地延缓开裂SHCC中水分和氯离子的侵入。最后基于上述研究结果给出了裂缝特征与SHCC渗透性的关系,用于开裂SHCC的耐久性评价。(2)应用中子成像技术,突破SHCC的非透明局限,实现了对SHCC材料在未开裂以及多缝开裂情况下水分侵入过程的可视化成像追踪和定量计算。研究发现：SHCC在无裂缝时,水分侵入量很少；但当多缝开裂且裂缝宽度较大时,水分迅速沿裂缝侵入试件内部,并为裂缝两侧基体提供水源,甚至通过纤维与水泥基体之间的微孔道大量渗透而侵入整个开裂区域。但采用内掺硅烷乳液方法制备的整体防水SHCC在开裂后表现出良好的耐久性。(3)从引起干缩的本质原因——湿度扩散着手,针对应变硬化水泥基材料湿度扩散和干燥收缩提出了一种湿度扩散系数和干缩应力的反演分析方法。在迭代计算过程中引入了遗传算法进行优化。由反演分析法计算得到的SHCC及其基体的失水曲线和收缩曲线与试验曲线基本吻合。表明文中采用的反演算法反演值可信度较好,计算精度较高。同时也表明反演算法具有良好的适应性,可达到多参数反演分析的目的。从试验结果来看：随着环境湿度的减小,SHCC及其基体的失水率和干缩率均增大；所有试件前期失水速度和干缩速度快,后期逐渐减小；SHCC的气态水湿度扩散系数D,小于其基体的D,。随着干燥龄期的增长,试件内部靠近试件表面处由于湿度梯度的作用逐步受拉,甚至达到其抗拉强度,从而引起开裂；当干缩应力达到材料的抗拉强度时,由于该种材料特有的应变硬化特性,其应力并没有软化降低,而是保持该抗拉强度值；随着干燥龄期的增长,试件的干燥前锋逐步向试件内部推进；当试件某位置达到其抗拉强度时,其内部的应力先由抗拉逐步降低并逐步过渡到受压,呈梯度分布。非常直观的呈现了SHCC在干燥收缩过程中的损伤全过程。(4)通过快速冻融试验,研究了不同冻融循环次数下SHCC的相对动弹性模量变化、质量损失率、SHCC棱柱体弯曲韧性、毛细吸水特性、抗氯离子侵蚀性能、碳化性能以及SHCC与钢筋的粘结滑移性能。SHCC经300次冻融循环后相对动弹性模量损失仅4%,质量损失不到2%。纤维的掺入有效的提高了SHCC的抗冻性。随着冻融循环次数的增加,由于PVA纤维与基体界面之间粘结强度的降低,PVA纤维在拉伸作用下的拔出数量增多,而拔断数量减少,从而使得SHCC棱柱体试件的弯曲抗拉强度有一定幅度的下降,但试件跨中挠度增大。冻融前后SHCC试件的毛细吸水试验、抗氯离子侵蚀试验以及碳化试验均表明,冻融作用对其耐久性能影响不大。随着冻融循环次数的增加,钢筋与普通混凝土极限粘结强度近似线性降低。试件发生劈裂破坏。而SHCC粘结试件随着冻融循环次数的增加,钢筋与SHCC极限粘结强度逐渐下降,但降低幅度不大。试件发生拔出破坏。更多还原

【Abstract】 Strain Hardening Cement—based Composite(SHCC) is featured with its tensile strain-hardening characteristic and multi-crack characteristic. It ultimate tensile strain can reach4%.So It can be applied into crack controlling structure, enhancing the seismic resistance of structures and so on. There are a lot of papers on design theory, basic mechanical performance and durability performance of SHCC up till now. But most of these results are based the undamaged SHCC. This is different for real saturation of SHCC in practice. Based on the above problem, this thesis will focus on the cracking mechanism and its influence on durability of SHCC. The detailed contend of this thesis are as follows:(1) Digital image process was used to investigate the crack pattern of SHCC both on finished surface and formed surface under direct tension load. Then statistical and potential methods were used to deal with the crack width distribution. Results indicate that the crack density of formed surface is lower than finished surface. But the average crack width of formed surface is bigger than finished surface. And the crack width parameters such as crack density, average crack width follows polynomial equation with the order of3. Also it was established that the Gamma distribution is the most accurate statistical distribution to describe the distribution of crack widths of SHCC at different tensile strains. Based on this, capillary absorption of and chloride penetration into SHCC under different strain level were performed. At the same time silane impregnation was used to protect the cracked SHCC. From the results, we can get that with the increase of strain level, water was absorbed quicker, more water was absorbed and the coefficient of capillary absorption will increase linearly with strain level. And for chloride penetration, the depth and amount of chloride increased with strain level too. But silane impregnation can reduce the penetration of water and chloride into SHCC. Finally, three evaluation methods of the influence of crack pattern on permeability were performed. This can be used to evaluate the durability of cracked SHCC.(2) Neutron radiography has been successfully applied to visualize the process of water penetration into cracked SHCC and to quantify the corresponding time-dependent moisture distributions in cracked SHCC. Results indicate that in un-cracked SHCC, less water can be found. But for cracked SHCC especially for the specimens with big crack, water will penetration into the specimens along the crack immediately and then water migrated further into the surrounding matrix from water filled cracks. Later water moved into the matrix adjacent to the cracks which was mechanically damaged by direct tension. But for integral water repellent SHCC, little water can penetrate into it.(3) Based on moisture diffusion, a method of inverse analysis has been proposed to calculate the moisture diffusion coefficient and shrinkage stress of SHCC. Evolutionary algorithm was selected during optimization process. A quite good fit of analysis results to the experimental data could be achieved. This indicates that the accuracy of the calculated results by the proposed inverse analysis method is very high. This method can solve the feedback problem of milti-parameter. From the experimental results, we can get that with the decrease of RH, the weight loss and shrinkage rate of SHCC and its matrix will increase. And at the beginning of exposure time, all of the specimens will loss water quick and also the speed of shrinkage is quick. But with the increase of exposure time, the speed of water losing and shrinkage will go down. At the same time, the vapor diffusion coefficient of SHCC is smaller than its matrix. Because of the moisture gradient, the surface layer of SHCC was tensioned. And the tension stress can reach the ultimate tension stress, and then crack will happen. But strain softening will not happen, the stress will remain the sameo With the increase of drying time, the drying front kept moving into deeper layer step by step. So from the surface layer to dapper layer of SHCC, the stress gradient exist, it will change from tensile stress to compressive stress. From the stress distribution, the whole deterioration process is very clear.(4) Accelerated freeze-thaw test on SHCC has been conducted, and change of relative dynamic elastic modulus, mass loss, bend property, water capillary absorption, chloride penetration, carbonation and bond behavior are gained. After300freeze-thaw cycles, the reduction of dynamic elastic modulus is just4%and the weight loss is just2%. So the adding of PVA fiber increases the frost property. With the increase of freeze-thaw cycles, the bond strength between PVA fiber and matrix will decrease, then more fiber will be pulled out and less fiber will be destroyed under tensile stress. In this way, the bending strength will go down for the prism of SHCC under4-point bending, but the deformation of the prism will increase. From the results of water capillary absorption test, chloride penetration test and carbonation test of SHCC before and after frost damage, the influence of frost damage is very little. From the results of pull out test, the bond strength between steel bar and normal concrete decreases linear with increase of freeze-thaw cycles. And all of concrete specimens fail in a split way. But for SHCC, the bond strength between steel bar and SHCC decreases with the increase of freeze-thaw cycles a little. Pull-out failure happened for all SHCC specimens.更多还原