(a) Concretes are sometimes placed in environments where they are in contact with solutions of sulfates. Discuss three ways that the sulfate resistance of the concrete may be improved.
(b) Discuss the good work practices that should be employed in relation to the delivery and storage of cement, both in bags and bulk deliveries.
(c) List three types of admixtures used in concrete and discuss why they are used, and how they modify the properties of the fresh concrete and in some cases the hardened concrete.
(d) Discuss the properties of CEM I R 52.5 and outline two situations where you would recommend the use of this cement in concrete.
Sulfate attack is another possible deterioration mechanism of concrete. It can have endogenous origin (developing without any contribution from the environment) or exogenous origins (such as sulfates contained in the soils or in liquids) (Germain, 2008; Neville, 2004). In both cases, the consequence is some volume expansion owing to the delayed formation of ettringite, which is an expansive component. The internal sulfate attack is characterized by a delayed mobilization of cement sulfates, and it leads to the generalized deterioration of the concrete. The main cause is a high elevation of the temperature, which can be encountered in the case of massive structures (see Section 3.2.2) or during precasting while using steam curing. The word ‘delayed’ indicates that ettringite could not form (as is the usual process) during the cement hydration, because of an overly elevated temperature (ettringite is destroyed over 70 °C). It then appears several weeks, months or years after the casting.