Effect Of Alkali And Limestone Powder On Rheology And Hydration Characteristics Of Cement-superplasticizer System

The excellent workability of concrete is not only required for modern mechanized construction,but also the guarantee of good mechanical properties and durability of concrete.In projects,the workability of concrete is generally improved by adding superplasticizers and admixtures?such as fly ash,limestone powder,silica fume?.The alkali in the cement is one of the important factors that affect the compatibility of the cement and superplasticizer.And compared with other admixtures,limestone powder has good economic and environmental benefits.Therefore,in this paper,the influences of alkali and limestone powder on the rheological and hydration characteristics of cement-superplasticizer system were studied by measuring the fluidity,fluidity loss over time,rheological behavior,Zeta potential,hydration heat,electrical resistivity and compressive strength of cement-superplasticizer system.The results show:?1?With the increase of alkali(Na₂O_eq)content,the initial fluidity decreases,the fluidity loss increases with time,the yield stress and plastic viscosity increase,the first exothermic peak increases,the induction period shortens,and the peak of the second exothermic peak shifts forward and the peak value increases,the total heat release decreases,the 1d compressive strength increases,and the 28d compressive strength decreases of the system.?2?With the same alkali content,the Na₂CO₃ group has the largest loss of fluidity over time,and the NaOH group and Na₂SO₄ group have less loss over time.The order of the yield stress values is:Na₂SO₄ group>NaOH group>Na₂CO₃ group.The effects of alkali species on the shortening of the induction period and the role of promoting the forward shift of the second exothermic peak are:NaOH group>Na₂CO₃ group>Na₂SO₄group.The compressive strength values of 1d and 28d are the largest in the Na₂SO₄group.?3?With the increase of limestone powder content,both the initial fluidity and the loss of fluidity increase,both the yield stress and the plastic viscosity decrease,the first exothermic peak increases,the induction period shortens,and the peak of the second exothermic peak shifts forward,the peak value of the second exothermic peak and the total heat release decrease,and both the 1d and 28d compressive strength values decrease of the system.?4?With the increase of limestone powder fineness,the initial fluidity decreases,the fluidity loss increases with time,the yield stress and plastic viscosity increase,the peaks of the first and second exothermic peaks shift forward,the peaks value increase,the induction period shorten,and the total heat release increase of the system,the 1d compressive strength increases,and the 28d compressive strength decreases of the system.?5?Under the coupling of alkali and limestone powder,with the increase of content or fineness of limestone powder,the yield stress and plastic viscosity increase,the degree of shear thickening decreases,the induction period shorten,the second exothermic peaks shift forward.The peak value of the second exothermic peak and the total heat release decrease with the increase of limestone powder content,and increase with the increase of limestone powder fineness.With the increase of alkali(Na₂O_eq)content,the yield stress and the degree of shear thickening decrease,the plastic viscosity increases,the induction period shorten,the peak of the second exothermic peak shifts forward and the peak value increases,but the total heat release decreases of the system.