Experimental Study On The Mechanical Properties,water Resistance And Shrinkage Of Basic Magnesium Sulphate Cement Based-RPC

Reactive Powder Concrete（RPC）is a new breed of cement-based material created as a means to improve the particle compactness and the pozzolanic reaction of concrete and also decrease the water to cement ratio.it has ultra-high strength,high toughness,high durability.It has been used in roads,bridges,etc.Basic magnesium sulfate cement（BMSC）is a modified ternary system cementing material fabricated by light burnt magnesia powder,magnesium sulfate heptahydrate,water and a modifier.Its main hydration product is the 5·1·7 Phase.The use of BMSC in the production of RPC has certain advantages over RPC produced with Portland cement.To assist alleviate environmental impacts linked with cement manufacturing,including such high energy consumption and consequent air pollution issues,like the releasing of greenhouse gases,and to lower expenses,the use of CFBC ash can not only reduce cost of BMSC but also protect environment.The problem of low water resistance can also be curbed by the use of additives.This paper envisages the use of admixtures and steel fibres to improve the mechanical properties,water resistance,fluidity,strength,and explored the effect of different conservation regimes[Ambient Temperature curing（ATC）,Water Curing（WC）,Standard curing（SC）,Thermal Curing（TC）on BMSC based-RPC.Two separate samples were prepared,thus samples with fibre and samples without fibre addition.The results show that,5%CFBC ash and 0.75%water reducer dosage was the best and is suitable for BMSC Based-RPC preparation taking into consideration its mechanical properties,water resistance and fluidity.The 28 days compressive strength of BMSC based-RPC reached maximum which was99.18 MPa with 0.75%water reducer dosage whiles the highest value of flexural strength for 28 days recorded was 23.2 MPa for 5%CFBC ash and 0.75%water reducer dosage both without steel fibres.Based on the characteristics of steel fibre reinforced ordinary cement RPC,also it was analyzed the effect of steel fibre on the flowability and mechanical parameters of BMSC based-RPC.The flowability reduced as the steel fibre concentration rises,according to the findings,but the mechanical properties were continuously improved.When the steel fibre content was 2%,the 28-day flexural strength was 25.3 MPa and 28-day compressive strength was119.1 MPa,and the fluidity was 189.7 mm.The water resistance of BMSC based-RPC was tested by comparing the compressive strength and softening coefficient variations after immersion in water.To investigate the mechanism,XRD and SEM were used to examine the microstructure before and after immersion.Based on additions in BMSC Based-RPC it restricts the hydration of hard burned Mg O to sheet-like Mg（OH）₂ and decrease crystallization,BMSC Based-RPC showed good water resistance with softening co-efficient of 0.88for no fibre and 0.95 for 2%fibre.The best curing system for BMSC based-RPC:first ATC 7 days,then 70℃TC 7 days,final SC 14 days,its flexural strength was 22Mpa and compressive strength was 108.76Mpa.