Influence of delayed addition time of sodium sulfanilate phenol formaldehyde condensate on the hydration characteristics of sulfate resisting cement pastes containing silica fume

The water–silica fume–cement system is highly sensitive to the effect of superplasticizers. This work aimed to study the individual effects of the dosage and delayed addition time of laboratory synthesized sodium sulfanilate phenol formaldehyde condensate (SSFP) on the hydration characteristics of sulfate resisting cement (SRC) pastes incorporating 10 mass% SF and hydrated up to 90 days. Initial and final setting times, compressive strength, bulk density, total porosity and hydration kinetics were determined. Some selected specimens were analyzed using IR spectroscopy. The results showed that the fluidity of cement pastes increases with SSFP dosage and delayed addition time up to 10 min this is due to the electrostatic repulsion between cement particles and the decrease of C3A content that is minimized by hydration until the dormant period (10–15 min). The values of combined water, compressive strength and bulk density increase with polymer content up to 1.5 mass% with delayed addition time up to 10 min; this is intrinsically associated with the reduction of W/C ratio with polymer content as well as the improvement of superplasticizing effect of SSFP with delayed addition. IR spectra are in a good agreement with the results of physico-chemical and mechanical properties. The synthesized SSFP condensate could improve the fluidity, bulk density and compressive strength of the investigated cement pastes.

► Delaying addition time enhances fluidity of cement pastes.
► Delaying addition time leads to increase the compressive strength and bulk density of cement pastes.
► Whereas it decreases the total porosity of cement pastes up to 90 days.
► Optimum composition is obtained with 1.5 mass% at 10 min delayed addition time.