Study On Preparation And Impermeability Of Cement-based Composite Material With In-Situ Slow Release Initiated Polymerization Plugging

The impermeability of cement-based composite materials would be declined due to the cracking caused by improper curing and auto-shrinkage.In this study,a slow-release initiator with a coated structure was designed and synthesized to improve the impermeability.The breaking time of the coated structure of the prepared slow-release initiator in an alkaline environm ent is later than that of cement hydration and hardening,so that the cement hydration and hardening reaction precedes the polymerization reaction of the slow-release initiator.Therefore,the cement-based composite material would firstly complete the hydration and hardening reaction and have sufficient strength,then the slow-release initiator inside the system begins to break the wall and initiate the polymerization product to form the plugging structure in the cement-based composite material,which would further improves the impermeability of the cement-based composite material.This research provides a new material structure system and method for improving the impermeability of cement-based composites.In this paper,the potassium persulfate(KPS)and benzoyl peroxide(BPO)were chosen as the core,and the polypyrrole/glycerin was chosen as the coating layer,then the slow-release initiator KPS(abbreviated as KPS/Ppy)and BPO(abbreviated as BPO/Ppy)were prepared and screened by the emulsion polymerization;In an alkaline environment(simulating the cement hydration environment),the methacrylic acid/hydroxyethyl methacrylate type polycarboxylate Acid(P(MAA/HEMA)),acrylic acid and acrylamidewere polymerized with KPS/Ppy to initiate polymerization of binary copolymer products and ternary copolymer products,and the synthesis parameters were optimized;In the optimized copolymerization system,by adding the cement gel material,the in-situ polymerization plugging cement-based composite material was prepared,by controlling the in-situ reaction time of the ternary copolymerization initiated by the cement hydration,hardening reaction and the slow-release initiator,thus.Through analysis techniques such as FT-IR,SEM,XPS,XRD,laser particle size analysis and electrical conductivity analysis,the effect of pyrrole monomer/glycerin addition amount,synthesis time and other preparation process factors on the microscopic morphology and structure of the sustained-release initiator were investigated and screened;the microscopic morphology,structural composition,and polymerization of binary or ternary copolymer products under two influencing factors(P(MAA/HEMA)and KPS/Ppy),were measured and analyzed;The reaction time and water absorption performance were tested and characterized,and the synthesis parameters were optimized;The mechanism of the cross-sectional morphology,water absorption performance,water loss performance and mechanical properties of the in-situ slow-release initiation polymerization plugging cement-based composite material were explored.The main conclusions of this article are as follows:1.KPS/Ppy prepared by the emulsion polymerization has better sustained-release effect compared with BPO/Ppy.When the optimum content of pyrrole/glycerol is 1.46 wt%and the optimum synthesis time is 6h,KPS is successfully coated by the polypyrrole.It has good dispersion performance in water system,and the distribution of surface micropores is relatively uniform,which is conducive to the release of KPS.The average particle size fo KPS/Ppy is 200?m,and the initiator is continuously released within 24h,and the conductivity reaches 6650s/cm,which can meet the slow release experiment.2.Compared with the binary copolymerization of acrylic acid,acrylamide,etc.,the ternary copolymerization of shows better perfomances.the water absorption rate of the ternary copolymerization prepared by the P(MAA/HEMA),acrylic acid,acrylamide,etc.is 21.5%larger than that of the binary copolymerization.The optimal KPS/Ppy addition amount of the ternary copolymerization product is 0.16 g,and the optimal reaction temperature is 60?;In the ternary copolymerization system initiated by KPS/Ppy,the polymerization reaction starts at 12h,that is,the polymerization reaction time of KPS/Ppy is later than the hydration and hardening time of cement(10 h).The breaking time of KPS/Ppy in alkaline environment is coupled with its material structure.3.The best KPS/Ppy content for preparing in-situ slow-release initiation polymerization plugging cement-based composites is 6 wt%.The 7 d water absorption rate and water loss rate are 6.3%and 3.04%,respectively.The 28d water absorption rate and water loss rate are 6.32%and 2.52%,respectively.The 7 d compressive strength loss is small,and the 28 d impermeability strength is 15.7%higher than that of the cement with only P(MAA/HEMA)polycarboxylic acid added.