This paper investigates the effect of microsilica (MS), water proofer (WP) and MS-WP contents on the durability of concrete to phosphoric acid attack. Three MS replacement levels and three WP mixes were considered in the study: 10%, 15% and 20% by weight of cement for MS and mixes of 0.4, 0.6 and 0.8 L for WP. The water to cement ratio was considered to be constant. The workability, durability of concrete to freezing thawing after 300 cycles, durability of concrete to phosphoric acid attack after 15 cycles of wetting and drying in phosphoric acid solution, compressive strength and modulus of rupture after 28 days were investigated. The degree of acid attack was evaluated by measuring the loss in weight. The study showed that the combined effect of MS-WP improved the durability of concrete to freezing thawing and to phosphoric acid attack without significantly reducing the compressive strength or modulus of rupture of the concrete. The optimum mix was 10% of MS replacement and 0.8 L of WP
