A Basis for Material Selection for Large-Volume Applications of Offshore Grout and Concrete

Abstract

Concrete and grout, when placed in large volumes, generate significant amounts of heat as the hydration process develops. On cooling, temperature gradients within the material lead to the formation of tensile strains which if greater than the co-existent strength of the material will cause it to crack. The paper describes an analytical technique developed to provide guidance on the selection of suitable grout and concrete mixes for use in large volume applications. The technique was developed from consideration of the use of grout and concrete in offshore applications such as pile plugs, grouted connections with thick grout annuli and concrete bell foundations. The analytical assessment comprises calculation of temperature variations with time; calculation of thermal stresses and strains induced during the thermal cycle and prediction of thermal cracking using a nonlinear constitutive model that allows for cracking and crushing; and subsequent load analysis including the effects of residual thermal strains. The technique can be applied to all situations where the effects of thermal strains are likely to significantly affect load carrying capacity, such as grouted pile plugs, localised member reinforcement, pile sleeve and insert connections with thick grout annuli and concrete bell foundations. The results of analysis on the concrete bell foundation proposed for the North Rankin 'A' foundation improvements are presented and compared with measurements made on full scale tests carried out to assess their thermal performance. The technique permits selection of suitable grout and concrete mixes in thermally sensitive applications and allows assessment of the reduction in strength possible due to the effects of thermal strains. See also following Abstract.