In ground concrete durability

Durability analysis is often a difficult part of the design for structures subject to severe exposures. Project specifications often quote national standards as a minimum requirement and require a specified design life be achieved. This paper shows how national standards can be conflicting and may be inadequate with regard to design for concrete in contact with ground. This places the responsibility on the contractor to ensure that state of the art durability designs will provide the serviceability required over the design life.

The paper specifically considers in-ground deterioration applicable to loaders, linings, railways, slabs and ports. Deterioration mechanisms considered include cracking, corrosion, and chemical attack (including acid sulphate soil issues). The rate of decay is dependent on the access and penetration of contaminants and their subsequent reaction with the concrete and steel. The paper reviews these processes to give a logical approach to design. The importance of cement systems to provide chemical resistance, mix design to provide impermeable paste and aggregate selection to avoid integral problems are discussed.

Even so, the best design will fail if construction is not adequate. The paper also outlines specific concrete properties (e.g. bleed, setting time, slump loss, heat of hydration, shrinkage) that the Contractor needs to understand and use in planning concrete pours so that construction defects do not compromise durability objectives and lead to expensive repairs.

Authors’ note: Throughout this paper, we employ the use of capitalised text to denote the various roles and elements that contribute to a major project’s success, in particular for durability management.