Serviceability Performance Evaluation of RC Flexural Members Improved by Using Low-Shrinkage High-Strength Concrete

M. Tanimura, R. Sato and Y. Hiramatsu Journal of Advanced Concrete Technology, 5(2) 149-160, 2007 This paper focuses to show the importance of autogenous shrinkage on serviceability performance of reinforced high-strength concrete (HSC) flexural beams, and also the effectiveness of low-shrinkage HSCs (LS-HSC) that made by using expansive additive and/or shrinkage-reducing chemical agent and/or Belite-rich low heat Portland cement with regards to the improvement of flexural serviceability performances of the beams. In addition, this paper, from the design equation point of view, proposes a new concept for evaluating flexural crack width and deformation of RC beams, considering the early age deformation of concrete before loading. The experimental results show that autogenous shrinkage of HSC affect the increase in crack width and deformation of the RC beams significantly, while LS-HSCs markedly improve its serviceability performances. The present concept, taking into account strain change in tension reinforcement and curvature change at cracked section before and after loading, is effective in explaining the effects of shrinkage and expansion of concrete before loading on maximum crack width and flexural deformation of the RC beams. JSCE (Japan Society of Civil Engineers) code equations for predicting maximum crack width and flexural deformation into which the present concept is incorporated, improve the prediction accuracy compared with conventinal ones and show fairly good agreement with experimental results.

Autogenous shrinkage is not taken into consideration in an appropriate way in most design procedures. Therefore serviceability often is reduced and early damage is observed. This paper points out clearly the implied risk and proposes ways to avoid damage. (Prof. Folker H. Wittmann, Aedificat Institute, Germany) The use of additives and chemical agents in minimising autogenous shrinkage of high-strength concrete is demonstrated in this paper. This leads to improved flexural serviceability performance of such beams, for which the authors proposed a approach to evaluate the flexural crack width and deflection taking into consideration the early-age deformation of concrete before loading. The information is useful for implementation in codes. (Prof. Kiang Hwee Tan, Department of Civil Engineering, National University of Singapore, Singapore)