聚丙烯纤维对水泥砂浆塑性收缩行为的影响

Effect of Polypropylene Fiber on the Plastic Shrinkage Stress and Plastic Shrinkage Ratio of Mortar

采用自行研制的水泥砂浆塑性收缩应力测试装置和非接触式测长装置,分别研究了低掺量的聚丙烯纤维对水泥砂浆塑性收缩应力和塑性收缩率的影响.结果表明:水泥砂浆的最大塑性收缩力约为28.5 N,最大塑性收缩开裂应力约为0.003 2 MPa;未经改性处理的聚丙烯纤维对水泥砂浆塑性收缩应力影响较小,塑性减裂作用较小,而改性聚丙烯纤维可使其塑性减裂作用明显增加;水泥砂浆的塑性收缩率约为3 600微应变,该数值明显大于水泥基材料硬化后的干燥收缩率;PP纤维对混凝土坍落度及力学性能影响不大,在使用时可主要关注其对水泥基材料的塑性减裂作用.

The effects of polypropylene fiber on the plastic shrinkage stress and plastic shrinkage ratio of the mortars were investigated by use of a self-designed measuring device. The research results show that the maximum plastic shrinkage force and plastic shrinkage stress of plain cement mortar are 28.5 N and 0.003 2 MPa respectively. The plastic shrinkage ratio of plain cement mortar is 3 600με,which is much bigger than the drying shrinkage ratio of hardened cement mortar. The plastic shrinkage of cement mortar can be reduced by the addition of PP fiber. The modifica- tion of PP fiber has more effect on the improvement of plastic shrinkage of cement mortar than normal PP fiber. The test results also show that PP fibers have no obvious effect on the slump and mechanical properties of cement mortars. So it is suggested that the significance of PP fiber on the reduction of plastic shrinkage of cement mortar should .be paid more attention.