Research On The Effect Of Water-cement Ratio And Water Reducer On The Self-healing Properties Of Concrete

In order to explore the law of intrinsic self-healing of concrete and its significance to engineering practice,it aims to improve the theoretical guidance for the self-healing of engineering structures.This paper mainly studies the feasibility of experimental verification of the self-healing mechanical properties of concrete after damage to the concrete by different methods.Five different water-cement ratios and naphthalene,aliphatic,and polycarboxylic acids are studied.With three different water-reducing agents,the strength of concrete before and after self-healing changes;the effect of five different water ash and three different water-reducing agents on the self-healing properties of concrete was studied.Through crack opening microscopic observation,ultrasonic pulse velocity test and ultrasonic shape analysis,the self-healing ability of concrete cracks with different water-cement ratio and water reducer was evaluated.By thermogravimetric analysis and scanning electron microscopy,the differences of hydration products on the inner surface of cement matrix cracks with different water-cement ratios and water-reducing agents and the differences between self-healing products were compared.The mercury intrusion method was used to test the difference in porosity of different water-cement ratios and water-reducing agent substrates,and to predict the reasons for promoting calcium carbonate precipitation.The research results are as follows:（1）Select the method of pre-compression loss to characterize the change of mechanical properties of concrete self-healing,and use the force of 90%of the compressive strength of concrete as the pre-compression loss value.0.25,0.30,0.35,0.40 and 0.45 of the five different water-cement ratio concrete strength recovery rates are 58%,62%,68%,75%and78%,respectively.The strength healing effect of the samples gradually becomes better.It is preliminarily inferred that the increased water-cement ratio is more beneficial to the impact.The strength of the damaged concrete is restored,the better the self-healing effect.The concrete recovery samples of the three water-reducing agents have strength recovery rates of81%,79%,and 65%,respectively.The greater the recovery rate,the better the strength recovery effect of the sample.It is preliminarily inferred that the strength of the naphthalene system is self-healing.Preferably,the aliphatic is slightly worse,but the strength healing effect of polycarboxylic acid is not ideal.（2）On the basis of meeting the strength and durability requirements of concrete.As the water-cement ratio continues to increase,the effect of self-healing gradually improves.The higher the water-cement ratio,the denser the internal structure of the concrete after self-healing,and the amount of self-healing products is continuously increasing.When the water-cement ratio is low,the healing products consist of a large number of needle-like products（ettringite or C-S-H gel）intertwined into a loose network structure,and a small amount of Ca CO₃is generated.For the high water-cement ratio healing products,continued hydration cannot be observed.The product,the healing product is completely covered by Ca CO₃crystalline particles,and the accumulation is relatively tight.With the increase of the water-cement ratio,the higher the total porosity of the cement matrix,the greater the amount of macropores,the deeper the methyl orange staining depth,the more effective areas of self-healing increase,and the more favorable the migration of Ca²⁺is;The degree of hydration is deepened and the content of Ca（OH）₂is increased.From the analysis of crack self-healing products,it can be seen that the greater the water-cement ratio,the more self-healing products,and the amount of Ca CO₃gradually increases,the better the self-healing effect.Therefore,the formation of Ca CO₃crystals plays a more important role in the self-healing of concrete,and the effect of hydration products is weaker.（3）On the basis of meeting the strength and durability requirements of concrete.The self-healing effect of naphthalene and aliphatic concrete is better,the internal structure of concrete after self-healing is denser,and the effect of polycarboxylic acid is poorer.The amount of self-healing products at the cracks of the naphthalene-based and aliphatic concrete samples was similar,and the cracks were almost completely filled with the healing products,while the amount of self-healing products at the cracks of the polycarboxylic acid concrete was small,and obvious cracks could still be observed Porosity.