A Comparative Assessment of the Accuracy of the Hong Kong (HKBD) and Japanese (JSCE) Code Concrete Shrinkage Prediction Models

The magnitude of concrete shrinkage is an important design consideration, as shrinkage may result in cracking, warping and deflection (and even loss of serviceability) of concrete structures. Ideally laboratory tests may be undertaken to quantify the shrinkage of concrete proposed for a structure. However, these are generally not a practical option as they are time consuming. Hence, empirical code-type prediction models are relied upon to predict total shrinkage strain with time. This investigation assessed the accuracy of the Hong Kong Code of Practice Model (HKBD, 2013) and the two Japanese Code of Practice Models (JSCE, 2007), the one applicable to normal strength concretes (referred to as JSCE) and the subsequently introduced model which is applicable to high strength concretes (> 55 MPa), referred to as JSCE HS. The models were evaluated when compared with actual shrinkage strains, measured over a period of approximately six months, on a range of concretes under laboratory-controlled conditions, for six mixes (comprising three aggregate types and two water cement ratios). The HKBD was the most accurate model in the case of all the mixes, with an overall coefficient of variation (ωall) of 43.1%. This model generally over-predicted shrinkage in the relatively lower strength mixes and over-predicted in the relatively higher strength mixes. Both the JSCE models over-predicted shrinkage, at all ages, in the case of all the mixes. The JSCE HS model was more accurate (with a ωall of 109.7%) than the JSCE model (with a ωall of 123.2%).