Effect of delaying addition time of SMF superplasticizer on the physico-mechanical properties and durability of cement pastes

This research aimed to investigate the influence of delaying addition time of laboratory prepared sulphonate melamine formaldehyde (SMF) superplasticizer on the physico-mechanical characteristics and durability of cement pastes subjected to elevated temperature up to 800 °C, or immersed in 4% MgSO4 and 4% MgCl2. The compressive strength increases with delayed addition time at 7.5 min up to 90 days. The cement pastes containing 1.0 mass% SMF superplasticizer, with delayed addition time at 7.5 min, has highest compressive strength, bulk density and lower total porosity. The presence of SMF superplasticizer with delaying addition time process of mixing increases the compressive strength, bulk density and decreases the total porosity. These work together to produce a compact structure, inhibiting the chloride and sulphate ions penetration, hence the total sulphate and chloride contents decrease.

► Delaying addition time increases the compressive strength, whereas decreases the total porosity.
► The optimum mix contains 1.0 mass% superplasticizer, with delayed addition time at 7.5 min.
► Superplasticizer improves the microstructure by precipitated additional C–S–H in the open pores.
► Formation of compact structure decreases the accessibility of SO42- and Cl− into the pore system.