Properties And Microstructure Of PB-g-PS Latex-Modified Cement Mortars

The paper synthesized polybutadiene-graft-polystyrene (PB-g-PS) latexes and polybutadiene-graft-polystyrene epoxypropyl methacrylate (PB-g-PSG), and be used to modify cement mortar. The properties and microstructure of modified mortar were investigated. The effect of PB-g-PS latex, silica fume and coupling agent on cement hydration were researched by FTIR、DSC、TG and XRD, the main works as follows:Graft copolymers of styrene (St) onto polybutadiene (PB) were prepared via semiconscious seeded emulsion grafting copolymerization method using a redox initiator system. The effect of initiator, reaction temperature, qualitys ratio of PB/PS, and monomer dropping time on the graft copolymerization were investigated. The results show that the grafting efficiency (GE) and degree of grafting (DG) increase with increase reaction temperature and decrease quality ratio of PB/PS.The GE and DG is increased with increase initiator content for low content, and then begin to decrease of higher content of initiator. The GE is increased with increase monomer dropping time. The DG is increased first, and then decreased with increase monomer dropping time. The synthesized PB-g-PS was confirmed by FTIR and1H NMR. The morphology and diameter of PB-g-PS latex particle were studied by TEM and laser diameter analyzer. The study show that PB-g-PS latex particle is ball-like, and have a core-shell shaped structure.The PB-g-PS latex with the mass ratios of70/30,50/50to30/70were used to modify cement mortar. In the fixed flow of175±5mm and a constant water-cement ratio(W/C) of0.5,and two curing methods(mixed curing methods:6d immersed in20℃water followed by21d at20℃,RH65%air; wet curing methods:27d immersed in20℃water).This study examines the effect of mass ratios of PB/PS on physical and mechanical properties of PB-g-PS latex-modified cement mortars, and compared with performance of the carboxyl SBR latex-modified cement mortar at fixed flow of175±5mm and mixed curing condition. The experimental results show that the three kinds of latex-modified mortars has a good workability, can decrease W/C, and improve water reduction rate, it exceeded56%. Its can improve the performance of mortar water retention during a certain range of P/C, and the maximum of water retention ratio are99%.The PB-g-PS latex can markedly reduce capillary water absorption rate, it reaches0.156Kg/m2at the P/C of20%and24h.The bulk density is decreased firstly, and increased with increase P/C,or is increased firstly, and then decreased.PB-g-PS latex can marked in influences much on the mechanical properties of modified mortars. The compressive and the flexural strength of the polymer modified mortar are fluctuated with increase P/C. By contrast, the properties of mass ratio of50/50latex modified mortar are best, and is almost with SD623carboxyl SBR latex-modified cement mortar.The polymer modified mortar structure was studied by SEM. The microstructure analysis showed that mortar constituents in PMMs are compactly joined with each other, and the structure is close. Polymer film has already formed in the polymer-modified cement mortars, which exist in cave, hydrates, and between hydrates and aggregate.The polymer film may acquire different structures. They may appear as branch-like, band-like, and dense network structure. The structure was improved because of addition of polymer to cement mortars. The development of little crackle was effective prevented, and the holes and chink were packed and closed. Hence, the performance of the mortar has been improved.In the constant water-cement ratio of0.45and using water curing methods. PB-g-PS latex with a mass ratio of50/50was used to modify cement mortar. This study examines the effects of silica fume and coupling agent content on properties and structure of latex modified cement mortar. The experimental results show that silica fume can marked in influences much on the properties of modified mortars. The suitable silica fume content can improve properties and structure of mortars. The flowability of mortar is bad at silica fume content of15%, and water-reducing agent not be added. Hence, the silica fume is aggregated, resulting in reducing performance. The suitable silica fume content is cement mass of10%; the coupling agent can also marked in influences much on the properties and structure of modified mortars. The flow of fresh mortar is bigger at coupling agent content of1.0%, which leaded in more caves and chink in PMMs. The suitable coupling agent content is cement mass of0.6%; the properties of modified mortar increase with increase silica fume and coupling agent content when its were added into PB-g-PS latex-modified mortars. The modified mortar structure was studied by SEM. The microstructure analysis showed that the structure is close.The tree structure and hexagonal sheet crystal structure of Ca(OH)2was seen.The effect of PB-g-PS latex, silica fume and coupling agent on cement hydration were researched by FTIR、DSC、TG and XRD. The experiments results show that the cement hydration increase with an increase of P/C for low P/C, and then begin to decrease of higher P/C, it reached a maximum at P/C of10%; with an increase silica fume content up to5%are accompanied by a significant increase in cement hydration, beyond this content, the cement hydration decrease markedly; it increase as the coupling agent content increase,the cement hydration increase and reaches a maximum at the content0.6%; at a constant silica fume content of15%, it can seen that as coupling agent content increase there is decrease in the cement hydration, at content of0.2%, it reaches a maximum value; at a fixed coupling agent content of0.6%,with an increase silica fume content, it causes an increase in the cement hydration, when the silica fume content was higher10%,the cement hydration decreased.The PB-g-PSG were synthesized at the best process conditions of PB-g-PS, and the quality ratios of polybutadiene to styrene and epoxypropyl methacrylate ranged from50/50/0,50/49/1to50/46/4. The PB-g-PSG be confirmed by FTIR, and was used to modify cement mortar in the constant water-cement ratio of0.4and mixed curing.This study examines the effects of GMA content and the P/C ratios on properties of PB-g-PSG latex modified cement mortar, and compared with performance of the carboxyl SBR latex-modified cement mortar. The study show that the flow of modified mortar is increased with increasing polymer-cement ratios, and is almost change with increasing GMA content. The four kinds of latex can markedly reduce capillary water absorption rate, and can marked in influences much on the mechanical properties of modified mortars. The compressive strength of PB-g-PSG are decreased with increasing P/C, and are lower than control mortar, and flexural strength of polymer modified mortars are increased with increasing P/C at P/C lower than10%, and are higher than control mortar. The maximum of flexural strength of polymer-modified mortar are9.65MPa. The effect of polymer on cement hydration was explored by FTIR and DSC, the analysis results showed that the cement hydration was influenced by GMA content and P/C. Polymer modified mortar structure was studied by SEM. The microstructure analysis showed that the mortar constituents of polymer-modified cement mortars are compactly joined, have ultimate improved properties. The hexagonal sheet crystal structure of Ca(OH)2was seen.