纤维-内养护轻集料复合增强高性能混凝土的收缩与抗裂性能研究

Study on Shrinkage and Crack Resistance of High-performance Concrete Reinforced by Fiber Internal Curing Lightweight Aggregate Composite Materials

为缓解高性能混凝土的高收缩、易开裂等体积稳定性不足问题,基于纤维-内养护材料的复合作用,采用非接触式自收缩仪和平板法对不同轻集料内养护剂替代率(10%~20%)、纤维组合(钢纤维、聚丙烯纤维、混杂纤维)条件下的高性能混凝土自收缩性能和抗裂性能进行分析。结果表明:1)轻集料的替代率对降低早期自收缩效果显著,可将3 d、28 d自收缩率分别降低42.8%~62.6%、14.5%~32.8%,但也会增加自收缩率在28 d后的增长速率;2)纤维与轻集料的组合作用可进一步将28 d自收缩率最大降低45.8%,且可将28 d后的自收缩增长率降低60%(1.2μm/d~1.44μm/d);3)轻集料和纤维的掺入对减少裂缝面积、裂缝条数和最大裂缝宽度、长度具有显著效果,3种纤维对裂缝面积削减效果依次为钢纤维<聚丙烯纤维<混杂纤维,且混杂纤维还可进一步减少后期裂缝面积的发展速率;4)纤维与20%轻集料替代率组合作用下,产生的相对抗裂指数为94.7%~98.7%,同时可将最大裂缝长度和宽度分别削减92.7%和90%;5)纤维-内养护材料的复合作用可显著提升高性能混凝土的收缩和抗裂性能,可在工程实践中予以推广。

To alleviate high shrinkage,easy cracking and other volume stability insufficiency problems of high performance concrete,based on the composite effect of fiber-inner curing materials,the self-shrinkage performance and anti-cracking performance of high performance concrete under the conditions of different lightweight aggregate-inner curing agent substitution rate(10%~20%) and fiber combinations(steel fibers,polypropylene fibers,and blended fibers) were analyzed by non-contact self-shrinkage meter and plate method.The results show that:1) The substitution rate of lightweight aggregate has a significant effect on reducing the early self-shrinkage,which can not only reduce the 3 d and 28 d self-shrinkage by 42.8%-62.6% and 14.5%-32.8%,respectively,but also can increase the growth rate of self-shrinkage in the late 28 d period;2) The combination of fibers and lightweight aggregates further reduces the maximum self-shrinkage rate of 28 d by 45.8% and reduces the self-shrinkage rate of 28 d by 60%(1.2%,1.2%).The growth rate can be reduced by 60%(1.2~1.44 μm/d) after 28 d;3) The incorporation of lightweight aggregates and fibers has a significant effect on the reduction of crack area,the number of cracks and the maximum crack width and length,and the three kinds of fibers have a significant effect on the reduction of crack area,in the following order:steel fibers<polypropylene fibers<mixed fibers and mixed fibers can further reduce the rate of the development of the crack area in the late stage;4) Under the combination of fiber and 20% lightweight aggregate substitution rate,the relative anti-cracking index is 94.7%-98.7%,and the maximum crack length and width can be reduced by 92.7% and 90% at the same time;5) The composite effect of fiber-inside curing materials can significantly improve the shrinkage and crack resistance of high-performance concrete,which can be promoted in engineering practice.