Research On Synthesis And Performance Of Early-strength Polycarboxylate Superplasticizer

Polycarboxylate superplasticizers have become the most widely used high performance water reducing agent in concrete production at the present stage owing to their excellent performances.However,the early strength of the concrete is required to be higher due to acceleration of construction speed and the development of prefabricated concrete in the construction industry.And the traditional polycarboxylate superplasticizers couldn't meet this requirement because of their retardation.Therefore,it is imperative to development of early-strength polycarboxylate superplasticizers are.Based on molecular structure design of this paper,the early-strength polycarboxylate superplasticizers were synthesized by the method of changing the backbone length of polycarboxylate superplasticizers and introducing the cationic group.The effect of early-strength polycarboxylate superplasticizers on the properties of cement paste,mortar and concrete were studied under the condition of standard-curing and steam-curing.The mechanism of early-strength was analyzed by hydration temperature,XRD,FT-IR and TG.The main contents and results were followed:Firstly,polycarboxylate superplasticizers with different backbone length were synthesized by changing the dose of the chain transfer agent sodium methacrylate sulfonate(SMAS).The performance of dispersion,hydration and mechanical properties of cement paste and mortar with different backbone length of polycarboxylate superplasticizers were tested.The results indicated that polycarboxylate superplasticizer with longer backbone length had obvious early-strength performance when the dose of SMAS was 1.0%.Compared with other polycarboxylate superplasticizers with differentbackbone length,the initial and final setting time was shorter,the hydration temperature peak was higher,and the time of temperature peak could be shortened to 4h.The synthesized polycarboxylate superplasticizer with 1.5% SMAS had better dispersibility,but the early-strength was not obvious,and the adsorption capacity of this polycarboxylate superplasticizer on cement was up to 0.92 mg.g-1.Secondly,the amphoteric polycarboxylate superplasticizers were synthesized by grafting the cationic monomer methacryloyloxyethyl trimethyl ammonium chloride(DMC)in the molecule of polycarboxylate superplasticizers.The influnce of this superplasticizer on the setting time of cement paste,and the compressive strength of mortar and concrete was studied.And the mechanism of early-strength was analyzed through hydration temperature,XRD,FT-IR and TG.The results indicated that amphoteric polycarboxylate superplasticizers shortened the setting time of cement paste and enhance time of the hydration temperature peak.In addition,the strength(early-strength,post-strength)of mortar and concrete with incorporated the amphoteric polycarboxylate superplasticizer,were both improved.The early-strength performance of amphoteric polycarboxylate superplasticizer was more excellent when the dose of DMC was 12%.And initial and final setting time had reducement of 58 min and 65 min,respectively,the time hydration temperature peak could be shortened to 3h,the compressive strengths of concrete of 1d,3d and 28 d with same ratio of water-cement were increased by 49.6%,35.6%,and 23.4%,respectively.XRD and TG results showed that the early-strength of amphoteric polycarboxylate superplasticizer resulted in promoting the early hydration of C3 S and generating more C-S-H.Finally,the early-strength effect of the amphoteric polycarboxylate superplasticizers on the concrete was studied under the condition of steam-curing.The results indicated that the early-strength performance of amphoteric polycarboxylate superplasticizer with the dose of DMC 12% was more excellent,and the compressive strength of concrete with same ratio of water-cement at 1d was increased by 10.1% and13.8%,respectively compared with naphthalene superplasticizer and anionic polycarboxylate superplasticizer.