Study On Corrosion Expansion Cracking Of Protective Layer Of Admixture Concrete Under Sulfate Attack

Reinforced concrete structure will suffer a lot of sulfate attack under the environment of coastal waters and saline soil.Although sulfate itself is not corrosive to rebar in concrete,it can erode concrete out of rebar and cause concrete crack,so as to accelerate the corrosion of steel.So the sulfate erosion problems have gradually become the focus of attention of many scholars.In this paper,the research object is admixture concrete,the main line of study is steel corrosion.By combining theoretical analysis and experimental research,the influence of admixtures,water-binder ratio,concentration of sulfate and magnesium ions,chloride ions,the ratio of thickness of concrete cover to the rebar diameter were deeply discussed to explore the influence of corrosion rate of steel when admixture concrete cover cracked due to corrosion and got the formulas for calculating the corrosion rate.The results show that decreasing water-binder ratio,increasing single fly ash content,the ratio of thickness of concrete cover to the rebar diameter and decreasing the concentration of sulfate can increase the corrosion rate of steel when admixture concrete cover cracked due to corrosion.Magnesium ion and chloride ion in the solution has a certain effect on the corrosion rate of admixture concrete,the presence of magnesium ion decreased the steel corrosion rate,while the presence of chloride ions improves the corrosion rate of steel.In addition,the crack calculation model considering the concrete compressive strength,types and dosage of admixture,concentrations and types of erosion solutions,reinforcement type,the ratio of thickness of concrete cover to the rebar diameter was proposed by non-linear regression according to the test data under 20 times of dry-wet cycle,the calculation results can well coincide with the experimental results.