Experimental Study On The Early-Age Shrinkage And Cracking Of Sea-sand Concrete

The ocean is a huge treasure trove of resources.Taking greater measures to utilize its resources and advancing the project of coastal island reef construction have been a common consensus.Because the island reef is far from inland and the raw material of concrete are scarce.Thus,using the sea sand to supersede part of river sand as the raw material of concrete is an effective means to solve the shortage of raw material.The volume stability of concrete has an important influence on its permeability resistance and mechanical properties,but the complex marine environment has strict requirements on the mechanical properties and durability of concrete which used in island reef construction.At present,the research on seasand concrete is limited to the anti-penetration and anti-corrosion aspects,and there are few studies on its volume stability.Therefore,the purpose of this paper is to study the volume stability of sea sand concrete in order to provide reference for large-scale engineering application in the future.In this thesis,two different series of concrete are set up as series A and series B.The series A uses the traditional high-strength mix ratio designing method,and the concentration gradient of chloride ions are 0?0.12%?0.24%?0.36%.The series B uses the most compact mix ratio method with concentration of chloride ions 0 and 0.12%which margin coefficients were 1.1?1.2?1.3.Though the experiments of compressive and splitting tensile strength?drying shrinkage?crack resistance?pore structure to study the law of concentration of chloride ions and early stability of sea-sand concrete,and compare the stability of sea-sand concrete of series A and series B.The results of mechanical properties experiments indicate that with the increase of the concentration of internal chloride ions,the 7d compressive strength and splitting tensile strength of sea-sand concrete increased,while have no influence on the same performance of 28d basically.In addition,the compressive strength of the series B is higher than that of the series A when the concentration of chloride ion is 0 or 0.12%.The results of volume stability test show that the higher chloride ions concentration,the larger drying shrinkage and autogenous shrinkage of sea-sand concrete,the earlier cracking time point,the larger cracking width and the worse anti-cracking resistance.When the concentration of chloride ions is 0 or 0.12%,the autogenous shrinkage and drying shrinkage of series B are less than series A,with the better anti-cracking resistance property.The results of mercury intrusion experiment shows that as the chloride ions concentration increases,the pore structure is refined,and the ratio of harmless pores to less harmful pores increases.When the chloride ion concentration is 0 or 0.12%,the porosity and total pore volume of the series B concrete is smaller than that of series A concrete.