Abstract
Creep of concrete is a complex phenomenon that has proven difficult to model. Nevertheless, for many reinforced and prestressed concrete applications, a reasonably accurate prediction of the magnitude and rate of creep strain is an important requirement of the design process. Although laboratory tests may be undertaken to determine the deformation properties of materials, these are time consuming, often expensive and generally not a practical option. In addition, this is not often an option at the design stage of a project when decisions about the actual concrete to be used have not yet been taken. National design codes therefore rely on empirical prediction models to estimate the magnitude and development of the creep strain. This paper considers the suitability of nine ‘design code type’ creep prediction models when compared with the actual strains measured on a range of concretes under laboratory control conditions. The concretes tested incorporate three aggregate types and two strength grades for each aggregate type. The results are compared with the predictions of creep using models contained in BS 8110 (1985), SABS 0100 (1992), SABS 0100 (1992) modified, ACI 209 (1992), AS 3600 (1988), CEB-FIP (1970, 1978 & 1990), the RILEM Model B3 (1995) methods. The results indicate that the CEB-FIP (1970) and BS 8110 (1985) methods provide suitably accurate predictions over all the concretes tested. These methods yielded overall coefficients of variation of approximately 18 % and 24 %, respectively. The least accurate method was the CEB-FIP (1978) which yielded a coefficient of variation of approximately 96 %. The results of this investigation led to recommending the BS 8110 (1985) model for South African conditions.