Evaluating mechanical, microstructural and durability performance of seawater sea sand concrete modified with silica fume

The study investigates the effects of cement replacement with varying silica fume (SF) percentages on the material properties of seawater sea sand concrete (SWSSC). Five different mixes comprising normal concrete (NC), SWSSC, and modified SWSSC with 5%, 7.5%, and 10% SF were subjected to compressive strength, water absorption, water penetration, rapid chloride permeability and microstructural evaluation tests. It revealed that modified SWSSC exhibits comparatively higher strength and low permeability. The optimum cement replacement of 7.5% with SF showed denser microstructure which can be associated with the binding of silica with unreacted portlandite that leads to the formation of calcium silicate hydrates (C–S–H). The microstructural results of Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), and Differential Thermogravimetric Analysis (DTGA) also suggest the higher polymerization of C–S–H in SWSSC alone and SWSSC with 7.5% SF than NC. The improved performance of SWSSC and its modified mixes is attributed to the formation of Friedel's salt observed in the XRD analysis.