常温养护的纤维增强高与超高强水泥基复合材料收缩调控与延性设计研究

Considering the practical needs, present research focuses on the development of normally-cured high strength fiber reinforced engineered cementitious composite (HS-ECC). Low-shrinkage and high-ductility should be the two key problems to be solved for the present research. Along with the two key problems, first, the impact of newly developed admixture for shrinkage reduction of cement-based materials, especially for high strength ECC matrix should be tested in order to evaluate the efficiency on shrinkage reduction. Based on above experimental study, the optimal mixture proportion of high strength ECC matrix with the characteristic of low shrinkage should be proposed. Second, the bond performance of different fibers in the developed high strength-low shrinkage cement matrix should be obtained through fiber pull-out tests. The fiber bridging stress model of different fiber/matrix system should be developed based on above bond properties between fiber and matrix. The model will be verified through experimental determined fiber bridging stress obtains from independent three points bending test on the composite beam. After that, a fracture mechanics model to simulate tensile performance of fiber reinforced cementitious composite based on fiber bridging model should be developed. The contribution of different fibers to strength and ductility will be evaluated through the model. The condition of strain-hardening and strain-softening should be provided by the model calculation. In such, to realize the research targets that to develop the composite with characteristics of high-strength, low-shrinkage and high-ductility.

针对工程实际与相关基础研究需求，本项目拟研究常温养护的高与超高强纤维增强延性水泥基复合材料,其中高强度水泥基材的收缩调控与强度提高后的延性保留是本项目的量大关键问题。本项目将围绕这两个关键问题开展研究，首先将在先期研究结果基础上，系统研究新型降缩材料对高强度水泥基材自身与干燥收缩的影响，获得高强度低收缩基材配合比；其次，通过系统研究高模量纤维、低模量纤维与高强度低收缩水泥基材的界面粘接性能，建立各类纤维在基材中的纤维桥接应力模型，通过三点弯曲试验对上述模型进行验证、修正；第三，利用基于纤维桥接应力的纤维增强水泥基复合材料抗拉模型，优化纤维组合，实现纤维增强高强复合材料拉伸应变硬化与高延性。

纤维增强延性水泥基复合材料（ECC）抗拉性能优异且具有良好的裂纹控制能力，在土木工程领域得到广泛关注。随着工程应用的推广，对ECC材料的强度、延性、收缩等性能提出了更高要求。但提高ECC的强度，会使其延性降低，同时收缩增大，限制了进一步推广应用。本项目旨在对高与超高强纤维增强水泥基延性材料进行性能优化，研发具有低收缩、高强度、高延性特征的ECC产品。首先，研究以提升内养护效率并保证强度为目标，通过提高沸石掺量，改变沸石-水泥替代率，对基材配合比进行优化，得到了硫铝酸盐水泥高强与超高强系列、普通硅酸盐水泥高强与超高强系列不同沸石掺量的优化基材配合比。设计的复合材料抗压强度范围为72.1-115.4 MPa，抗拉强度、极限拉应变分别在5.56-8.65 MPa和0.66%-1.27%之间，与抗拉强度对应的平均裂纹宽度在18-43 μm之间。其次，通过对基于优化基材的复合材料在直拉过程中的裂纹开展状况进行跟踪，得到了多缝开裂破坏模式下的平均裂纹间距与裂缝数量、平均裂纹宽度之间的关系。根据裂纹间纤维的拔出原理，对多缝开裂模式下纤维的有效锚固长度进行修正，并据此对传统桥接应力模型进行改进，改进后复合材料桥接应力模型峰值与单轴拉伸试验结果吻合良好。另外，对基于优化基材的复合材料在密封与干燥条件下的收缩与内部相对湿度的变化规律进行了研究，通过钢环约束试验对其抗裂性进行评价。结果显示，随着沸石掺量的增加，材料的收缩逐渐降低，内部相对湿度逐渐提高，抗开裂性提高，基于收缩试验数据与环约束试验数据，对材料湿度饱和期与湿度下降期两个阶段的徐变系数进行了拟合。本项目所获结果与模型可用于ECC收缩调控与开裂分析，所研发的高强度低收缩ECC产品具有广阔的应用前景。