Strength and microstructure analysis of concrete containing rice husk ash under seawater attack by wetting and drying cycles

Concrete containing rice husk ash (RHA), subjected to seawater under wetting and drying cycles, was studied through an investigation of the compressive strength and microstructure of various types of blended cement paste. Five levels of cement replacement (0%, 10%, 20%, 30% and 40% by weight) were studied. The total cementitious content used was 420 kg/m(3): A water/binder ratio of 0.49 was used to produce concrete with a target strength of 40 MPa at age 28 days. The performance of blended cement concrete was evaluated based on compressive strength and chloride ion permeability. Microstructural changes in the specimens were determined by differential thermal analysis, X-ray diffraction and scanning electron microscopy. The addition of RHA was found to decrease calcium hydroxide formation by hydration and, consequently, gypsum and ettringite were reduced during seawater attack. RHA at 40% cement replacement improved resistance to seawater attack and effectively decreased ettringite and gypsum formations.