项目名称: 高延性低收缩纤维增强水泥基复合材料设计及形成机理
项目编号: No.50878119
项目类型: 面上项目
立项/批准年度: 2009
项目学科: 金属学与金属工艺
项目作者: 张君
作者单位: 清华大学
项目金额: 35万元
中文摘要: 研究以项目申请者近年来的先期工作为基础,基于细观与断裂力学原理,设计开发了能够实现微细开裂的高延性水泥基复合材料,通常称为之为通过设计的水泥基复合材料(ECC)。研究中通过对传统水泥基材进行改型,新型的高延性复合材料基材干燥收缩应变达到、甚至低于普通混凝土的干燥收缩水平,典型基材的28天干燥收缩是200微应变左右(该值低于传统相同等级的普通混凝土),是传统高延性材料所用基材收缩量的0.12-0.20。由于基材收缩性能大幅度降低,使得纤维与基材粘接强度降低,纤维桥接效率提高,多点开裂时单条裂纹宽度降低,目前最低可达30微米。同时保留了该材料应变硬化与多点微细开裂的特性。所研发的低缩延性材料养护20天时的极限抗拉应变达2.5%,抗拉强度可达4-5MPa;同时材料的抗压也表现良好的延性,其极限抗压应变(与抗压强度相对应)与普通混凝土比也获得较大幅度的提高。此外,研究还通过三点弯曲试验,对纤维桥接应力与裂纹宽度本构关系进行了求解,应用断裂力学模型,实现了材料轴拉行为的数值模拟,为基于性能要求的材料设计提供了分析手段。最后,对所研发的材料的应用进行了研究,例如无切缝水泥混凝土路面等。
中文关键词: 纤维增强水泥基复合材料;收缩;应变硬化;抗拉应变;开裂
英文摘要: Based on related research work carried by applicant, present project focus on development of cementitious fiber reinforced composite with characteristics of tensile strain hardening and multiple cracking performance, normally be called Engineered Cementitious Composite (ECC), meanwhile the drying shrinkage behavior can be significant reduced, to achieve the shrinkage level of plain concrete. Through modifications on cement matrix, a new kind of cement matrix with drying shrinkage as low as 200 micro strain at 28 days was developed in the present project. While the drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain in 28 days is only 0.12 to 0.20 of shrinkage of the traditional ECC. Due to the reduction on drying shrinkage of the matrix, the bond strength between fiber and matrix is reduced and then leads more fiber be pullout instead of breakage. The efficiency of crack bridging of fibers is enhanced and the crack width of individual crack is reduced, the crack width of one of the samples has achieved as low as 30 micro meter. The average tensile strain capacity after 28 days curing can achieve 2.5% of the LSECC with tensile strength of 4-5MPa. The experimental results also show that the composite with compressive strength ranging from 20 to 60 MPa can be obtained by varying w/c from 0.55 to 0.25. A significant plasticity, like yielding of metal, is found under compressive load after peak stress. Meanwhile, through three point bending test, the stress crack opening relationship of the LSECC are obtained by inverse analyses, such relations can be used to guide the design of composite. Finally, the potential applications of LSECC are investigated, including ductile strips in concrete pavement, ductile connections for bridge slabs and joints for concrete column and beam。
英文关键词: fiber reinforced cementitious composite; shrinkage; strain hardening; tensile stran; cracking