Research On Property And Mechanism Of Polymer Modified Rapid Cement-based Repaired Material

Cement-based repair mortar has been widely used in repairing civil engineering.However,the traditional cement-based repairing mortars exist the defects of brittleness and low bonding strength,which limits its engineering applications.In this paper,the sulphoaluminate cement（CSA）and Portland cement/calcium aluminate cement/gypsum ternary bonding composite system（TBS）were taken as the modified cement-based repair material,and the styrene acrylic copolymer emulsion（SA）and ethylene/vinyl acetate copolymer emulsion（EVA）were adopted respectively to modify them,which formed new composite systems.Then we study the rule of strength development and micro-structure change of the systems to make the polymer modified cement based-material can be used in practical rapid repair engineering.Firstly,SA emulsion and EVA emulsion with different dosages were added to CSA and TBS in composites,and four different polymer-modified cement based repair systems were formed,namely SA-CSA,EVA-CSA,SA-TBS and EVA-TBS.The effects of polymer emulsion dosages on setting time,compressive strength,flexural strength,bonding strength and water absorption of CSA and TBS were studied,and the optimal proportion of modified mortar system with the best mechanical properties were obtained.Secondly,the effects of different curing systems on the properties of different systems were studied,and the optimal curing system of polymer modified mortar was proposed.Finally,the kinds of hydration products,the hydration rate,polymer film-forming condition and microstructure characteristics of polymer modified cement mortar were studied.And the modification mechanism of polymer-modified cement based material was studied further.The results show:（1）The hydration rate is delayed by SA emulsion and EVA emulsion and the setting time can be prolonged.When the dosage is 3%¹2%,the initial setting time and final setting time of SA-CSA are 10.8 min²8.3 min and 15.1 min³6.5 min respectively;the initial setting time and final setting time of EVA-CSA are 11.5 min¹4.6 min and 14.1min²2.5 min respectively.However,compared with the CSA system,the hydration of TBS is accelerated by SA and EVA,and the setting time of TBS can be shorted.In the SA-TBS and EVA-TBS systems,the setting time is prolonged with the increase of emulsion dosage.（2）When the dosage of SA emulsion is above 3%,the flexural strength of CSA and TBS systems can be improved with the increase of dosage,but the compressive strength of that is reduced.When the curing age is 28d,the flexural strength of SA-CSA containing12%SA and SA-TBS containing 15%SA increased by about 50%and 133%,but the compressive strength and flexural strength of CSA and TBS systems both are reduced by EVA emulsion.Meanwhile,the bonding strength and the bonding performance of CSA and TBS also can be improved by SA emulsion and EVA emulsion greatly.When the curing age is 28d,the bonding strength of SA-CSA containing 12%SA,EVA-CSA containing 12%SA,SA-TBS containing 15%SA and EVA-TBS containing 15%EVA increased by about 105%,272%,293%and 89%respectively.（3）The combination of early wet curing condition and later dry curing condition is the best curing system for the polymer modified cement-based repair materials.The water absorption of CSA and TBS mortar can be reduced by SA emulsion and EVA emulsion,and the hole structure of the mortars are improved.However,the improving effect of EVA emulsion is not stable and is affected by the external environment.（4）The effect of polymer on polymer modified cement-based repair materials mainly through adsorption effect,filling effect,bridge effect of polymer and the effect of film forming.Additionally,the cement hydration reaction and the microstructure of polymer-cement matrix are influenced by the bonding effect between carboxyl group and Ca²⁺.That influences the mechanical performance of polymer modified cement-based material.