Because concrete is widely used for industrial buildings, warehouses, sewage plants, auto repair shops, and other structures that experience intimate contact with corrosive liquids and other aggressive agents, it is called upon to stand up to rigorous conditions. Liquids spilled on floors, sewage stored in tanks, ensilage fermenting is silos, walls, or metals embedded in slabs are examples of materials that can attack concrete. This article deals basically with the effect of such substances on hardened, not plastic, concrete of ordinary makeup, that is, not containing special cements or aggregates and lists suitable protective measures including liquid treatments, coatings and jacketing materials.
Acids are requisite to many industrial processes; and other liquids, including many of those in food processing, can become transformed into acids. These can pose a serious threat to concrete, especially to floors on which they are spilled. Acids typically combine with the calcium compounds in the hydrated cement matrix to form soluble materials that are readily leached out of the concrete mass. The resulting deterioration of the concrete may be rapid and complete. Some common inorganic acids that rapidly attack and disintegrate concrete are sulfuric, sulfurous, hydrochloric, nitric, hydrobromic, and hydrofluoric.
Not all mineral acid solutions are dangerous (boric acid is an eye wash). The major factors that determine the extent of attack are the kind of acid, the concentration and the pH value. High concentrations generally mean more extensive attack, though some inorganic acids will attack concrete even in solutions of less than one percent. The lower the pH value, the more likely and more rapidly is an acid apt to attack concrete. Organic acids such as lactic, humic, tannic and acetic are not as aggressive as the inorganics but in time they, too, can cause extensive damage to concrete.