Crown corrosion of concrete pipe and its subsequent repair is a topic much discussed in recent years. Present protective methods have not worked effectively. Due to its properties and its low cost, fly ash was used as a cement replacement of mortar to investigate its sulfuric acid resistance.

Different types and different percentages of fly ashes were mixed with and without admixtures including microsilica, and superplasticizer. The main parameters investigated included the chemical compounds, the fineness and the volume of fly ash. 2"x2" cubes were immersed in a 10% sulfuric acid pond. The weight of each cube was determined continuously up to 28 days. The results indicated that fly ash can be used effectively to improve sulfuric acid resistance of mortar in term of weight loss when using the finest fly ash in the optimum percentage, 50%. However the strength of these samples under the same conditions was significantly deteriorated. Microsilica and superplasticizer cannot inhibit the strength deterioration when mixed with fly ash mortar.