Effect Of Polycarboxylate Superplasticizer On The Hydration And Hardening Performance Of Sulphoaluminate Cement

The sulphoaluminate cement(SAC)have lots of advantages such as high early strength,frost resistance,impermeability,and corrosion resistance.However,its rapid hydration speed causes a large loss of slurry easily.So retarder is needed to meet the basic construction requirements.As a new type of high performance water-reducing agent,polycarboxylate superplasticizer(PCE)has good water-reducing and retarding effects in ordinary Portland cement,and there are many related researches.The mineral composition of SAC is different from that of ordinary portland cement.A small amount of research results indicate that PCE can improve the fluidity without affecting the strength of SAC at present effectively,but the PCE has retarding effect usually.If the PCE can play the role of water-reducing and retarding at the same time in the SAC,it will solve the problem of short construction time in the engineering application.The effect of the PCE on the setting time,initial fluidity,loss over time,viscosity,and compressive and flexural strength performance of SAC paste was studied in this paper.At the same time,the temperature rise process of cement hydration and hydration products were also tested from the microscopic level.The results show that the optimum dosage of PCE in SAC paste is 0.4%,and the water reduction rate can reach over 33%.The initial fluidity of the paste can reach more than 375 mm,and the initial and final setting time of SAC paste were extended from 24 min and 36 min to 117 min and 129 min respectively.The setting time between initial and final had no significant changes and remained around 10 minutes.The 7d compressive strength of the SAC reached 102 MPa,and the flexural strength reached 11.6 MPa.Compared with the control group,the 7d compressive strength increased by 41.8% and the flexural strength increased by 20.8%.The study found that the PCE can increase the fluidity of the SAC paste significantly,and reduce the loss of the paste,and improve the rheological properties of the cement effectively.PCE mainly plays a role in water-reducing in the SAC paste under the optimum PCE dosage,and there is a certain delay in the setting time.When exceed the optimum PCE dosage,the effect of water-reducing is saturated and mainly causes the retarding effect.PCE played a role in water-reducing and retarding in the SAC in the same time.Therefore the 4h strength had retarded,but it played a positive role in promoting the later strength.In addition,the effect of different composition and PCE content on the compressive strength,flexural strength and bond strength of SAC mortar was studied in this paper.The results showed when the cement:water:sand:PCE =1:1:0.26:0.4%,the compressive strength in 4h reached 20.51 MPa,and the compressive strength in 7d reached 74.83 MPa,and the flexural bond strength was up to 3.63 MPa,and the maximum bond strength reached 0.54 MPa.So it can meet the needs of general engineering competely.If the fluidity of SAC mortar was 170 mm,when the cement: sand: PCE = 1:3:0.2%,the mortar saturated water-cement ratio is 0.36.And when the cement: sand: PCE =1:1:0.4%,the saturated water-cement ratio of the mortar drops to 0.195.PCE can reduce the water consumption of the SAC mortar,and improve the slurry workability,and facilitate the mechanical properties of the SAC significantly.Based on the above studies,the proper PCE dosage can improve the early the hydration and hardening performance of SAC effectively.The loss of SAC paste was reduced,and the strength was improved gradually,so the workability was ensured.PCE played a role in water-reducing and retarding in the SAC paste at the same time.