Effect Of The Additive With Sulphoaluminate Cement On Early Strength Of Concrete

In the rapid development of industrialization of buildings,there is a higher requirement for the early strength of precast concrete products.Now factories usually use thermal curing to improve the early strength of concrete,but thermal curing has a negative effect on durability and long-term strength of concrete,and it increases the economic cost.Therefore,the use of normal techniques to prepare high-early-strength concrete is of important significance to the industrialization of building.In this paper,a small amount of sulphoaluminate cement(SAC)was used to modify ordinary Portland cement(OPC),and super early strength concrete was prepared at 20°C±2°C.The workability,mechanical properties and volumetric deformation of SAC modified OPC cement were systematically studied.The mechanism of early strength was studied by XRD,TG-DSC and non-evaporable water test,C50 super early strength concrete was prepared by using modified OPC cement,the influence of SAC on the early performance of concrete was discussed.The results show that the SAC which dosage is within 10%can greatly shorten the setting time and promote the early strength development.The composite gelling system with SAC cement can be measured the strength at 6h,while the pure OPC cannot be demolded in 6h.SAC will reduce the workability.The addition of proper amount of fly ash can ensure the early strength and improve the workability.The improvement of the workability of slag is better than fly ash.But slag will reduce early strength.The long-term shrinkage is less than that of the pure OPC.The later expansion of the ettringite produced by the hydration of the SAC cement will reduce the shrinkage,and the incorporation of fly ash and slag can further reduce the shrinkage of composite cementitious material.The incorporation of SAC into OPC can introduce calcium sulphoaluminate.Microscopic studies have shown that early rapid hydration produces more ettringite,which makes the early strength develop rapidly.OPC and SAC can promote hydration and improve early hydration.At the same time,ensure that the 28d strength does not shrink.C50 high early strength concrete was prepared by SAC modified OPC cement.The water-cement ratio is 0.28,and the composite cementing material is 450kg/m~3.The sand ratio is 41%,and 7%SAC cement is used in the omposite cementing material.At the same time,20%fly ash is used instead of OPC to reduce the cement dosage and improve the workability of concrete.The high early strength concrete slump is 121mm,the 8h compressive strength is 8.7MPa,the 10h compressive strength is 15.2MPa,reach the demoulding strength,28d compressive strength can reach 70MPa,28d flexural strength14.3MPa,this concrete can meet the requirements of workability and mechanical properties of high early strength concrete.The concrete prepared by the SAC modified OPC cement obtained can ensure the early strength development without using heat curing,which can help realize rapid turnover of the mold,improve production efficiency and economic benefit.