Effect Of Mineral Admixture On High Alumina Cement Foam Concrete

High-alumina cement is famous for high early strength,high temperature resistance and resistance to sulfate attack,but its late strength is easy to shrink,which limits the application range of high-alumina cement.Foam concrete as a kind of light,heat preservation and heat insulation of porous material is widely used in recent year,but the problem of its high porosity and easy drying shrinkage is worthy of attention.Mineral admixtures are used in high-alumina cement to make foam concrete,which can not merely improve the high alumina cement poor stability of later strength,but also make the concrete safe and green to realize energy conservation and emission reduction.In this article,the influence of limestone,gypsum,fly cash,slag on the physical and mechanical properties of high alumina-cement was studied by performance test and microscopic analysis.And the foam concrete of mechanics performance,thermal insulation performance were study under the best content.Afterwards,the following conclusions can be drawn:(1)High-alumina cement later strength reduction was improved by the four kinds of admixtures.(2)The best dosage of limestone,gypsum,fly ash and slag was 10%,15%,5%and 5%,respectively.In this dosage,the strength of high-alumina cement was improved by incorporating limestone,gypsum and fly ash.(3)When the content was 10%,the early rate of hydration high-alumina cement was accelerated by limestone,gypsum,fly ash and slag.(4)Under the premise of w/c=0.5 and 0.02 percent mass polypropylene fibers,10%limestone was used to make high-alumina foam concrete,and its strength and thermal conductivity were increased,but the water absorption and drying shrinkage were reduced,due to the reaction of limestone and hydration products of high-alumina cement to produce stable C3A·CaCO3·11H2O.When the dry density of foam concrete was 500Kg/m3,the compressive strength and flexural strength of 7d,28d were 1.57MPa,1.80MPa and 1.01MPa,1.49MPa.The drying shrinkage was 1190 ×10-6,1280 ×10-6 of 7d,28d,the thermal conductivity was 0.1390 W/(m · K).(5)The strength and thermal conductivity of foam concrete with 15%gypsum were increased,but water absorption and drying shrinkage decreased as the gypsum changed the hydration path of high-alumina cement to produce the stable ettringite(Aft).When the dry density of foam concrete was 500Kg/m3,the compressive strength and flexural strength of 7d,28d were 1.56MPa,1.98MPa and 0.99MPa,1.54MPa.The drying shrinkage was 1160 ×10-6,1270 ×10-6 of 7d,28d,the thermal conductivity was 0.1393 W/(m · K).(6)The filling effect,the pozzolanic activity of fly ash,and the C2ASHg formed by reaction of the C-H-S gel and the hydration product of high alumina cement increased the strength but decreased water absorption and dry shrinkage of foam concrete with 5%fly ash.When the dry density of foam concrete was 500Kg/m3,the compressive strength and flexural strength of 28d were 1.90MPa,and 1.51 MPa.The drying shrinkage was 1280 ×10-6,1370 ×10-6 of 7d,28d.