Study On Free Shrinkage Factors And Model Prediction Of PVA-ECC

Polyvinyl alcohol fiber-reinforced engineered cementitious composite(PVA-ECC)is a kind of composite material with high tenacity,light weight and high durability.It shows a characteristics of strain-hardening and multiple-cracking under direct tensile load and has been used in many projects.It cannot entirely replace concrete for its higher cost relatively,therefore,it mainly used in restoration projects,the positions demand higher toughness and crack control abilities.In these applications,the difference inevitably exist between the shringkage of concrete and PVA-ECC when PVA-ECC as repair or connection material work with new or old concrete.Face with these problems,the main work is as follows:1.Designed 18 single factor mixture ratios,and turned out that the dry shrinkage strain of the PVA-ECC increases with the increasing of W/C,decreases with increasing of S/C,and decreases with the increasing of the dosage of fly ash,and decreases with the increasing of expansion agent and shrinkage-reducing agent,the dosage of fiber’s effect on shrinkage strain is non-significant,but on the crack resistance is significant.As a result,PVA-ECC has small shrinkage strain,good tensile strength,high compressive strength and ultimate tensile strain when W/C is in the range of 0.25~0.33,S/C is in the range of 0.33~0.45 and the dosage of fly ash is about 65%.2.A five factors,five levels of orthogonal experiment was carried out as the each factor divide into five levels in the optimum range based on single factor experiment.Through the single index analysis of the test results,primary and secondary order,the optimal combination can be carry out.Considering interaction,the formula about shrinkage strain of 28 dwas regression analysed.Also the comprehensive primary and secondary order and the optimal combination can be obtain by the multi-index analysed.3.The time-shrinkage strain model considered coupled action of multiple factors was designed by using Origin software based on the shrinkage strain regression formula of 28 d.And the optimal mixture ratio which has minimum shrinkage correspondwith different compressive strength grade of PVA-ECC was found out.According to the shrinkage model of PVA-ECC and concrete,the reasonable casting time interval between concrete and PVA-ECC at the same strength grade can be calculated.