Durability Evaluation Of Seawater/Sea Sand Cement-based Composites Under Sulfate Attack

The rational development of marine resources to alleviate the shortage of raw materials in construction projects is not only an important part of China’s marine power strategy,but also a research hotspot that more and more scholars pay attention to.At present,most of the research results of seawater and sea sand cement-based materials focus on the mechanical properties and how to avoid the corrosion of steel bars.The addition of seawater and sea sand has an impact on the durability of cement-based materials,especially sulfate attack in the marine environment.From the above,this paper studies the effects of seawater and sea sand on the mechanical properties and hydration process of cement-based materials.Explores the deterioration rules of specimens with time at four different erosion ages,including macro indicators,such as strength,surface degradation degree,quality changes,dimensional changes,and pore structure changes during erosion,the generation and morphology of corrosion products,and microscopic changes For example,the distribution law of erosion ions;from the perspective of practical engineering,discuss the impact of maintenance on the corrosion resistance of seawater and sea sand cement-based materials to sulfate corrosion.The following research results have been achieved:(1)Seawater and sea sand have the effect of improving the compressive strength.At the same time,the pore structure of the cement matrix is also changed.The total porosity decreases and the pore distribution is refined.Under the premise that seawater is incorporated into the test piece,the effect of sea sand on the compressive strength is negative.This may be due to the shell particles in the sea sand affecting the integrity of the hydration product.Combining XRD patterns and thermogravimetric analysis curves,it can be found that seawater and sea sand change the material composition and proportion of hydration products and produce Friedel ’s salt.By affecting the content and solubility of calcium hydroxide,it promotes the hydration process,promotes the increase in the amount of C-S-H produced,and has a positive effect on strength.(2)In terms of sulfate resistance,seawater and sea sand have a negative impact on the durability of cement-based materials.The specimen showed greater dimensional change and mass increase and more obvious external surface degradation.The pore refinement process with time was observed to be more significant through the mercury intrusion test,and a large number of short-needle bar Ettringite with strong expansion appeared in the electron micrograph.From the point of view of sulfate ion concentration,both the ion concentration at the same depth and the ion penetration depth are higher than those of pure water standard sand specimens.The ability of sea sand to accelerate the deterioration of the test piece is weaker than seawater.(3)The specimens without standard curing will suffer more severe attack,which is mainly reflected in three aspects: appearance peeling is more serious;the amount of erosion products is increased;the surface area has a higher sulfate ion content at the same depth.Microscopic analysis found that the development of compressive strength and calcium hydroxide content is similar.The curing condition affects the accelerated period of sulfate attack,and the specimens without standard curing enter the declining stage of compressive strength earlier.