Study On Shrinkage Properties Of Windcumulated Sand Reinforced Polyvinyl Alcohol Fiber Cement Matrix Composites

Compared with ordinary concrete,polyvinyl alcohol fiber reinforced cementitious composite(PVA-FRCC)has the characteristics of high toughness and good crack resistance,which can effectively improve the ductility and durability of structural members.PVAFRCC materials usually use quartz sand or natural river sand as fine aggregate.However,with the wide application of cement-based materials such as concrete,the excessive exploitation of natural sand not only has a serious impact on the environment,but also makes the sand resources increasingly scarce and the project cost increases.There are abundant aeolian sand resources in the central and western regions of Inner Mongolia.If it is used to replace natural sand for the preparation of cement-based materials,it can achieve the effect of using local materials and turning waste into treasure.The utilization of aeolian sand can not only alleviate the shortage of sand resources,but also be conducive to environmental protection and reduce the project cost.At present,it has been proved that the mechanical properties of cement-based materials can meet the general engineering requirements by properly adding aeolian sand instead of natural sand.However,aeolian sand has small particle size,smooth surface and strong water absorption.It is generally prepared with a small water-binder ratio,which makes the chemical shrinkage and autogenous shrinkage of aeolian sand cement-based materials larger,resulting in premature shrinkage cracks of components,affecting the applicability and durability of structural components,and even causing safety problems in severe cases.Based on this,considers the factors such as the replacement rate of aeolian sand(0%,30%,60%),water-binder ratio(0.25,0.35,0.45),fiber volume ratio(0%,0.5%,1.0%,1.5%)and sand-binder ratio(0.35,0.45,0.55)to study the shrinkage performance of aeolian sand PVA-FRCC.The main research contents and conclusions are as follows:(1)The working performance was studied by fluidity test.At a water-binder ratio of0.25,the appropriate aeolian sand replacement rate(30%)increases the fluidity;when the replacement rate of aeolian sand is too high(60%),the fluidity decreases;with the increase of water-binder ratio,the fluidity increases.The larger the fiber volume fraction,the smaller the fluidity;the fluidity of 0.45 sand-binder ratio material is slightly better than that of 0.35sand-binder ratio material,and the fluidity is at a low level at 0.55 sand-binder ratio.(2)The mechanical properties were studied by compression test.When other conditions are constant,with the increase of aeolian sand replacement rate,the compressive strength of PVA-FRCC increases first and then decreases.With the increase of water-binder ratio,the compressive strength of the specimen decreases sharply.With the increase of PVA fiber volume fraction,the compressive strength of the specimen increases gradually.With the increase of sand-binder ratio,the compressive strength of the specimens showed an upward trend.For the specimens without fiber,the mortar spalling is obvious and the brittleness is large.The specimen mixed with fiber showed a ’ bad but not scattered ’ state,and the integrity was good.(3)The mechanical properties were studied by tensile test.In the water-binder ratio of0.25,0.35 and 0.45,the ultimate tensile strength and ultimate tensile strain of PVA-FRCC with 30 % aeolian sand replacement rate are generally at a better level.With the increase of water-binder ratio,the ultimate tensile strength of the specimen decreases,and the ultimate tensile strain increases first and then decreases.The ultimate tensile strength and ultimate tensile strain increase with the increase of PVA fiber volume fraction.(4)The shrinkage performance was studied by shrinkage test and mass loss rate test.When other conditions are certain,in the dry environment and ordinary indoor environment,with the increase of aeolian sand replacement rate,the shrinkage and mass loss rate of aeolian sand PVA-FRCC increase;with the increase of PVA fiber volume fraction,the shrinkage and mass loss rate decreased slightly.With the increase of water-binder ratio,the shrinkage and mass loss rate increased.With the increase of sand-binder ratio,shrinkage and mass loss rate increase.With the increase of water-binder ratio,the influence of aeolian sand replacement rate on shrinkage and mass loss rate gradually decreases.In the three groups of environmental conditions,the shrinkage strain of PVA-FRCC in dry and ordinary indoor environment is about 3 times that under standard curing conditions,indicating that standard curing conditions can greatly reduce the shrinkage value of cement-based materials.At the same time,the final shrinkage value(28d)of PVA-FRCC in indoor environment was higher than that in dry environment.(5)Through the regression analysis of the experimental data,the CEB-FIP model is modified,and a shrinkage estimation model suitable for the PVA-FRCC material of aeolian sand is proposed.The model has high calculation accuracy,and the experimental value is in good agreement with the model calculation value.