16 - Concrete construction for liquid-retaining structures

Abstract

This chapter discusses the special requirements for reinforced concrete liquid-retaining structures. Such structures are required to be watertight but not vapour proof. Containment vessels are normally tested for liquid retention during construction and some initial short-term seepage may be tolerated at this stage. According to the recommendation, the concrete should have low permeability. This is important not only for its direct bearing on watertightness but also because of its influence on durability and the protection from corrosion of embedded steel. Maximum cement contents are restricted in order to minimize cracking due to thermal contraction and drying shrinkage. In BS 8007 the limits for reinforced concrete are 400 kg/m3 for Portland cement and Portland-slag cement and 450 kg/m3 for Portland-fly ash cement. Values of 500 kg/m3 and 550 kg/m3 respectively are allowed for concrete that is to be pre stressed, on the basis that any cracking would be counteracted by the pre stress. In BS 8007 it is stated that for normal use the target mean proportion of ground granulated blast furnace slag should not exceed 50%. Methods of test are specified and maximum admissible concentrations for the aqueous leaching of metals, and tests on readymixed concrete are carried out at the Water Research Centre. It was concluded that the concentrations of metals found in the tests were not a cause for concern, and that the actual testing of admixture-free concretes to obtain an authorization for use should not be necessary.