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To prevent the sulphate attack on concrete, we must understand the factors which affect the sulphate attack. Prevention of Sulphate Attack on Concrete Microscopical Examination of Sulphate Attack
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Spalling of concrete due to sulphate attack.It is not only a cosmetic problem, but it is the visible displaying of possible chemical and microstructural problems within the concrete matrix.īoth chemical and physical phenomena observed as sulphate attack, and their separation is inappropriate.physical sulphate attack, often evidenced by bloom (the presence of sodium sulphates Na2SO4 and/or Na2SO4.10H2O) at exposed concrete surfaces.The complex physicochemical process of "sulphate attack" are interdependent as is the resulting damage.Composition of cement paste in concrete.Concentration and source of sulphate ions.MgSO4 + Ca(OH)2 + 2H2O = CaSO4.2H2O + Mg(OH)2 Two forms of chemical reaction occurs depending on: The sulphate ion + hydrated calcium aluminate and/or the calcium hydroxide components of hardened cement paste + water = gypsum (calcium sulphate hydrate) The sulphate ion + hydrated calcium aluminate and/or the calcium hydroxide components of hardened cement paste + water = ettringite (calcium sulphoaluminate hydrate) Sulphate attack process decrease the durability of concrete by changing the chemical nature of the cement paste, and of the mechanical properties of the concrete. Reactions of Sulphate Attack on Concrete Nature of reaction: Chemical and physical reactions Ground water be transported to the concrete foundations, retaining walls, and other underground structures.Soil may contain excessive amounts of gypsum or other sulphate.Admixtures also can contain small amounts of sulphates.Įxternal sources of sulphate are more common and usually are a result of high-sulphate soils and ground waters, or can be the result of atmospheric or industrial water pollution.presence of natural gypsum in the aggregate.
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Portland cement might be over-sulphated.This is more rare but, originates from such concrete-making materials as hydraulic cements, fly ash, aggregate, and admixtures. These new crystals occupy empty space, and as they continue to form, they cause the paste to crack, further damaging the concrete.įollowing are the sources of sulphates which are responsible for sulphate attack:.As sulphate dries, new compounds are formed, often called ettringite. It combines with the C-S-H, or concrete paste, and begins destroying the paste that holds the concrete together.What happens when sulphates get into concrete? The atmospheric environment which the concrete is exposed to.Sulphate attack on concrete might show itself in different forms depending on: Main factors affecting sulphate attack are:.Prevention of Sulphate Attack on Concrete.Microscopical Examination of Sulphate Attack.Diagnosis of Sulphate Attack on Concrete.Reactions of Sulphate Attack on Concrete.What happens when sulphates get into concrete?.