Experimental Study On Early-Strength Polycarboxylate Superplasticizer For Precast Concrete

With the acceleration of housing industrialization and the increase of infrastructure construction,the demand for prefabricated concrete products is increasing,and the early strength of concrete has higher requirements to meet the rapid turnover of formwork.In order to achieve the purpose of improving production efficiency.Polycarboxylic acid superplasticizer?PC?is the most widely used high performance water-reducing agent in concrete production at present.However,due to its own structural characteristics,common polycarboxylic acid water reducer has a certain retarding property.Therefore,the development of prefabricated concrete early-strength polycarboxylic acid water-reducing agent has a great market prospects.In this paper,a long side chain ether type macromonomer was used.At the same time,an early amphoteric polycarboxylic acid superplasticizer ZQ-3 was synthesized by introducing 2-acrylamide-2-methylpropylsulfonic acid?AMPS?and the cationic monomer methacryloxy ethyl trimethylammonium chloride?DMC?in the redox initiator system.Performance testing of mud and concrete,Compared with the other three early strength polycarboxylic acid superplasticizers,the early strength mechanism was studied by XRD analysis.The main contents and results are as follows:?1?The polycarboxylic acid water reducer with different acid/ether ratio and side chain length was synthesized by changing the molar ratio of acrylic acid?AA?to modified alcohol ether?HPEG?and changing the length of side chain.The dispersion,retention,setting time and mechanical properties of cement paste were studied.The results show that the synthetic polycarboxylic acid superplasticizer has excellent comprehensive properties when the ratio of acid to ether is 3.5:1 and the molecular weight of side chain is 4000.?2?AMPS and DMC were introduced into the molecular synthesis of polycarboxylic acid superplasticizer.Some functional groups in the molecular structure of the superplasticizer were confirmed by FT-IR test.The influence of AMPS and DMC on the properties of cement paste and concrete and the adaptability of the amphoteric early-strength polycarboxylic acid superplasticizer to cement were studied.The results show that the maximum compressive strength of 1 day concrete is 10.9MPA when the content of AMPS is 1.6%?mass of macromonomer?and the loss rate of flowability of 0.5 h,1 h is the lowest.When the amount of cationic monomer DMC was 2%of the mass of macromonomer,the adsorption capacity of Amphoteric early-strength polycarboxylic acid superplasticizer ZQ-3 on the surface of cement particles was the largest 1.19 mg.g^-1,and the macroscopical performance was that the fluidity of cement paste was the largest.The concrete has good adaptability to cement,and the compressive strength of concrete is obviously improved under the same water-cement ratio and slump.?3?The properties of ZQ-3 and other early strength polycarboxylic acid superplasticizers were compared and tested by XRD.The results showed that:ZQ-3had good dispersity and dispersibility,and could not affect the normal setting time of concrete.It can effectively improve the early strength of concrete.The XRD analysis results of cement hydration products show that the Ca?OH?₂ peak value of hydration product of hardened cement paste mixed with ZQ-3 water reducer is the highest for 8 h,which indicates that the hydration rate is the fastest and the hydration product is the most.