Study On Early Shrinkage And Cracking Behavior Of PVA-FRCC Plates In Aeolian Sand

The concrete floor has a large surface area.In practical engineering,the early sealing water retention and wet curing measures are simple,and the time dimension is short,which makes the shrinkage larger and may cause cracking in severe cases.In addition,the wind in spring and summer in the central and western regions of Inner Mongolia is strong,and the sunshine intensity is high,which aggravates the shrinkage cracking of the plate.In recent years,polyvinyl alcohol fiber reinforced cementitious composite(PVAFRCC)has excellent crack resistance,impermeability,impact toughness,frost resistance and corrosion resistance.Using it to make floor can improve the crack resistance of floor and improve its performance.Quartz sand or river sand is generally used in PVA-FRCC materials,but with the increasing amount of cement-based materials such as concrete,the excessive exploitation of natural sand has a serious impact on the environment;the increasing shortage of sand resources has also led to the increase of project cost.Aeolian sand is widely distributed in the central and western regions of Inner Mongolia,Ningxia and Xinjiang,and the reserves of aeolian sand are considerable.If the aeolian sand resources in the region are fully utilized in cement-based materials such as concrete,it can not only reduce the project cost,but also alleviate the sand damage,which is conducive to environmental protection.However,the small particle size and large specific surface area of aeolian sand make the shrinkage of aeolian sand cement-based materials greater than that of ordinary cement-based materials.Therefore,the problem of early shrinkage cracking must be solved when using aeolian sand PVA-FRCC to make slab and bridge deck in the central and western regions of Inner Mongolia.Based on this,this paper considers the factors such as the replacement rate of aeolian sand(0 %,30 %,60 %),fiber volume ratio(0 %,0.5 %,1 %)and water-binder ratio(0.25,0.35),and simulates the environmental conditions of strong sunshine and strong wind in spring and summer in the central and western regions of Inner Mongolia.The early shrinkage cracking performance of the PVA-FRCC quadrilateral restraint plate was studied.The main research contents and conclusions are as follows :1.Work performance research.The fluidity of mortar can be improved by replacing part of quartz sand with aeolian sand,and the fluidity of substrate will decrease when the replacement rate of aeolian sand is too high(60 %).In this experiment,the mortar with 30 %aeolian sand replacement rate has the best fluidity.2.Study on compressive properties.When other variables 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 PVA-FRCC showed a downward trend.With the increase of fiber volume fraction,the compressive strength of PVA-FRCC showed a gradually increasing trend.The specimen mixed with fiber is better when it is destroyed under compression,and the specimen without fiber is destroyed when the base material is peeled off in a large area.With the change of research variables,the elastic modulus and compressive strength have similar variation rules.3.Study on tensile properties.When other variables are constant,the ultimate tensile strength and ultimate tensile strain of PVA-FRCC increase first and then decrease with the increase of aeolian sand replacement rate.With the increase of water-binder ratio,the ultimate tensile strength of PVA-FRCC showed a downward trend,and the ultimate tensile strain showed an upward trend.With the increase of fiber volume fraction,the ultimate tensile strength of PVA-FRCC increases first and then decreases,and the ultimate tensile strain increases gradually.4.Study on free shrinkage performance.The free shrinkage and mass loss rate of eolian sand PVA-FRCC increased with the increase of eolian sand substitution rate and water-binder ratio,and decreased with the increase of fiber volume rate.The addition of fiber will significantly reduce the shrinkage of the material,but the increase of shrinkage reduction effect decreases with the increase of content.5.Study on restrained shrinkage cracking performance and mechanism.(1)With the change of fiber volume fraction,aeolian sand replacement rate and waterbinder ratio,the change rule of confined shrinkage of aeolian sand PVA-FRCC plate is basically the same as that of free shrinkage.The closer to the constraint end,the smaller the shrinkage;the higher the humidity of the external environment,the lower the humidity,the greater the shrinkage of the plate.(2)At the same age,at the same position inside the plate,the higher the replacement rate of aeolian sand,the lower the internal relative humidity;the higher the fiber volume fraction,the higher the internal relative humidity.The higher the ambient temperature,the smaller the humidity,the lower the internal humidity.By fitting,the functional relationship between shrinkage strain and relative humidity inside the plate is established.The two are nonlinear,and the calculated values are in good agreement with the experimental results.(3)After the incorporation of fibers,the crack resistance grade of each group of plates is second and above.When the replacement rate of aeolian sand is 30 %,the number of cracks is the largest,and the cracks are fine and dense.The addition of fibers effectively improves the crack resistance of the plate.With the increase of fiber volume fraction,the total area and maximum width of cracks decrease.When the humidity of the external environment is higher and the temperature is lower,the total area of the plate cracks,the maximum crack width and the number of cracks are reduced.(4)Through the analysis of grey relational entropy,it can be seen that the main factors affecting the 7d free shrinkage and constrained shrinkage are water-binder ratio.(5)Comprehensive analysis of the research results shows that the use of 0.35 waterbinder ratio,30 % aeolian sand replacement rate,and incorporation of 0.5 % volume rate of PVA fiber,and strengthening constraints and improving maintenance quality will effectively reduce the early cracking risk of aeolian sand PVA-FRCC board.6.Establishment of shrinkage estimation model.Based on the existing constraint shrinkage prediction model,the constraint shrinkage prediction model of aeolian sand PVAFRCC plate is established by regression analysis of experimental data.The model has high calculation accuracy,and the experimental value is in good agreement with the model calculation value.