A Study On Environmental Impact Assessment,shrinkage And Creep Of Sea Water Sea-sand Self-compacting Concrete

Self-compacting concrete(SCC),with excellent flowability and good mechanical durability,is currently widely used in the construction of high-rise buildings and coastal infrastructure.Fly ash,an important component of SCC,comes from the primary solid waste generated by thermal power plants.As an environmentally friendly cementitious material that replaces cement,it can effectively reduce energy consumption and greenhouse gas emissions during concrete production.However,it should not be overlooked that the addition of fly ash has a significant impact on the strength and shrinkage creep of concrete.Shrinkage creep,as an important characteristic for evaluating the long-term performance of concrete,affects the durability and safety of concrete structures.Against this background,this paper attempts to introduce green and environmentally friendly materials such as sea sand and fly ash in the production process of SCC,to reduce costs,reduce environmental pollution,and use reasonable proportion design to predict foreseeable shrinkage creep deformation,thereby promoting wider engineering applications.In addition,in order to completely solve the problem of chloride ion corrosion of steel bars in seawater and sea sand,this paper combines it with fiber-reinforced composite rebars(FRP)in an effort to expand its reasonable use in coastal engineering.The paper mainly carries out experimental testing and theoretical analysis on the short-term tensile and compressive mechanical properties,long-term shrinkage creep,and environmental impact of seawater sea sand self-compacting concrete.Specifically,the research content and main conclusions of this paper are as follows:(1)Conduct research on the short-term mechanical properties and environmental impact of SWSS-SCC: By producing 264 100 mm cube specimens,the workability and mechanical properties of SWSS-SCC with different water-cement ratios and fly ash contents were tested,and prediction formulas for compressive and split-tensile strength of SWSS-SCC were established,considering the effects of various parameters.In addition,based on the userdeveloped life cycle assessment model(LCA)and the latest concrete production technology in China,the environmental benefits of using SWSS-SCC in Dongguan City,Guangdong Province were explored.Sea sand has a limited impact on the mechanical properties of SCC,but fly ash has an adverse effect on its early mechanical properties.The use of seawater and sea sand instead of freshwater and natural sand in Humen Town only slightly reduces the environmental impact of SCC production.When producing SWSS-SCC,using electricity generated from clean energy sources can reduce energy consumption and equivalent CO2 emissions.(2)By verifying the LCA model,the impact of a series of common factors such as watercement ratio,power grid structure,kiln fuel type,fly ash content,curing temperature,and transportation distance on energy and CO2 equivalent emissions in concrete production was thoroughly explored.When producing SWSS-SCC,using electricity generated from clean fuel can reduce energy consumption and CO2 emissions,but reducing cement consumption or increasing the replacement amount of fly ash through high-temperature curing is not environmentally friendly.In practical engineering,the energy consumption and CO2 equivalent emissions from concrete production are related to the distance from the batching plant.(3)The shrinkage and creep properties of SWSS-SCC were studied.Long-term SWCCSCC shrinkage and creep tests were conducted to investigate the effects of water-cement ratio,seawater and sea sand usage,and fly ash content on the autogenous and drying shrinkage of SWCC-SCC.Microstructure testing was also performed to demonstrate the changes in the microstructure of self-consolidating concrete due to the use of seawater,sea sand and fly ash,and to reveal the mechanism of the research variables on shrinkage.Based on the test results,a calculation model was revised and established to accurately predict the development of SWCCSCC shrinkage and creep.Relevant influence coefficients were determined based on the effects of dosage on strength and shrinkage strain ultimate values,as well as the experimental results.The revised shrinkage and creep prediction model and the test results showed good consistency.(4)Study on the long-term creep properties of FRP-reinforced SWSS-SCC beams: By making 10 beams,the significant effects of fly ash content,water-cement ratio,chloride ions,etc.on the development of bending creep of FRP-reinforced SWSS-SCC beams were investigated.At the loading period of 90 days,the deformation of GFRP-reinforced sea sand self-consolidating concrete beams still remained in the rapid deformation stage during long-term load-bearing.However,the increase of chloride ions and water-cement ratio had adverse effects on the shrinkage creep of the beams,while fly ash could to some extent inhibit the increase of mid-span deflection of the beams.