Study On Shrinkage And Chloride Resistance Of Internally-cured Engineering Cementing Composites

Fiber reinforced cement matrix composite(ECC)has been used more and more in engineering due to its super toughness and excellent crack resistance.Among them,PVA-ECC(PVA-ECC)has higher tensile strength,elastic modulus and excellent hydrophilicity.In addition to the excellent mechanical properties and economic cost of ECC materials,the longterm performance and durability are the important factors affecting the use and promotion of ECC materials.The shrinkage property of the material is closely related to the durability of the structure,while the shrinkage value of ECC material is several times larger than that of ordinary concrete due to the large amount of cementing material and small water-binder ratio.Based on this,this paper determined through quality content is 0.05%,0.1% of the dry mix SAP,pre bibulous high absorbent resin(SAP),and the volume content of 10%,20% of the full water crude lightweight aggregate(LWA)after curing.ECC material shrinkage performance within 60 d,7 d and 28 d compressive strength,the flexural strength of 7 d and 28 d and 28 d of the chloride ion permeability were tested and compared with the conventional ECC material.The main research contents and conclusions of this paper are written as follows:(1)Keeping the total water-binder ratio unchanged,the dry-mix SAP internal curing method has an obvious shrinkage reduction effect on the self-shrinkage and total shrinkage of ECC material in the same age period.Besides,the method can improve the chloride ion permeability and compressive strength.At the dosage of 0.1% and age of 60 d,the shrinkage rate of self-shrinkage is 58.3%,while the total shrinkage rate of shrinkage can reach 29.2% at the highest,and the dry shrinkage is slightly reduced by about 5%.The compressive strength of 28 d increased by 16.1%,but there was no significant change in the Flexural Strength.The multipoint cracking and strain hardening properties changed little.The chlorine permeability of 28 d decreased by 25.6%.The performance of ECC internally-cured using SAP improved obviously with the growth of age.(2)Keep the effective water-cement ratio unchanged,and the SAP internal curing method of pre-absorption has an obvious shrinkage reduction effect on the self-shrinkage and total shrinkage of ECC material.The maximum shrinkage reduction rate and the total shrinkage reduction rate of 60 d were 83% and 25.6%.At 60 d,the maximum self-shrinkage and total shrinkage reduction rates of ECC internally-cured using pre-absorbent SAP were 83% and 25.6%,respectively,and the self-shrinkage reduction rates were higher than ECC internally-cured using SAP,but the total shrinkage reduction rates were lower than ECC internally-cured using SAP.The main reason is that the internal curing water increases the drying shrinkage of the material.The material's 7d compressive strength,7d flexural strength and 28 d chloride penetration resistance showed obvious deterioration,with the highest degree of deterioration being 13.98%,11.8% and 45.2%,respectively.The main reason was that SAP increased the water-cement ratio and the early free water content in the cement.The compressive strength and flexural strength of 28 d did not change much,and the improvement of hydration degree was the main reason for the strength compensation.(3)The maximum shrinkage reduction efficiency of self-shrinkage and total shrinkage reduction of ECC material can be as high as 51.2% and 30.5% at 60 d,and the shrinkage reduction effect becomes more obvious with the increase of LWA content.However,the degradation of the 7d and 28 d compressive strength(the maximum reduction is 10.2%),the flexural strength(the maximum reduction is 17.9%),and the resistance to chloride ion penetration(the maximum reduction is 31.9%)of ECC material is obvious.In particular,the weakening of the multi-point cracking and strain hardening properties has serious adverse effects on the ECC material.(4)Hyperbolic function,logarithmic function and exponential function have a goo d fitting effect on the contraction curve of ECC material.Among them,the residual s um of squares of the exponential function is the smallest and the fitting effect is the best.