Study On The Volume Stability Of Limestone Powder-Slag-Fly Ash Concrete And Hydration Heat Of Composite Cementitious Materials

In recent years,with the vigorous development of the national construction industry,the demand for commercial concrete has increased significantly,and new requirements have been put forward for the performance of concrete.The mixing of limestone powder,slag and fly ash in concrete can not only improve the performance of concrete,but also promote the sustainable develop;ment of the concrete industry.In this paper,limestone powder,slag and fly ash have been used as objects.Physical testing and theoretical analysis have been combined to study the volume stability of limestone powder-slag-fly ash concrete and the hydration heat of limestone powder-slag-fly-cement composite binder with water-binder ratios of 0.35,0.40,and 0.49.The analysis of the feasibility and economic benefit of limestone powder-slag-fly ash concrete was carried out.The aim is to provide theoretical guidance for the practical application of limestone powder-slag-fly ash concrete.The main conclusions and innovations of this paper are as follows:1.The autogenous shrinkage rate and creep degree of limestone powder-slag-fly ash concrete are all lower than those of reference Portland cement concrete,and the drying shrinkage rate is slightly higher than that of reference Portland cement concrete.The wet expansion rate of limestone powder-slag-fly ash concrete is less than the reference Portland cement concrete in the early stage,and the latter is higher than that of Portland cement concrete.The autogenous shrinkage rate has decreased by 19.2%,the creep degree has decreased by 31.5%,the dry shrinkage rate has increased by 3.2%,and the wet expansion rate has increased by 20%.With the increase of water-binder ratio,the drying shrinkage rate and creep degree of limestone powder-slag-fly ash concrete and reference Portland cement concrete increase,and the autogenous shrinkage rate and wet expansion rate decrease.2.A trivariate function calculation model for the autogenous shrinkage,drying shrinkage,wet expansion rate and creep of limestone powder-slag-fly ash concrete and reference Portland cement concrete with age and water-binder ratio has been proposed.The creep law and mechanism of lime stone powder-slag-fly ash concrete have been revealed from the macro and micro level.The secondary hydration products of mineral admixtures in limestone powder-slag-fly ash concrete improve the pore structure and are tightly integrated with the cement slurry to ensure the normal operation of the micro-aggregate effect.3.The cement mortar with admixture not only has reduced the hydration heat in all ages,but also has delayed the emergence of the second exothermic peak and has reduced the peak of the exothermic rate.With the growth of hydration age,the hydration heat of mineral admixture-cement mortar continues to increase,and the growth rate gradually slows down.The hydration heat of 7 days first increases and then decreases with the increase of water binder ratio.The reference Portland cement mortar has showed the same pattern.Limestone powder-slag fly-ash cement mortar is better than slag-fly ash cement mortar in reducing the heat of cement hydration;With the increase of the specific surface area of limestone powder,the hydration heat and exothermic rate increase slightly,but the effect is not obvious.4.Under the normal ground conditions,it is technically feasible to use limestone powder,slag,fly ash and cement as composite cementitious materials in concrete,and the cost of lime stone powder-fly ash concrete with 1 cubic meters of strength of C30,C40 and C50 is 16%,15.5% and 16.2% lower than that of ordinary Portland cement concrete.