Modeling of Aggregate Stiffness and Its Effect on Shrinkage of Concrete

Somnuk Tangtermsirikul and Siwal Tatong

ABSTRACT: This paper is aimed to propose a model for simulating aggregate phase stiffness and its effect on concrete shrinkage based on the concept of concrete as a two-phase material (paste phase and aggregate phase). Regarding the effect of aggregate phase, concrete shrinkage is found to be affected by the aggregate content, strain of the aggregate phase and the proportion between coarse aggregates and fine aggregates. The aggregate particles are considered to be uniformly distributed in the concrete and in contact with one another at various contact angles. As a result, the stress of the aggregate phase can be obtained from the summation of stresses of all contact angles. A two-dimensional constitutive model is used for computing the stiffness of the aggregate phase of concrete. The stiffness of the aggregate particle system is then derived from the ratio between stress and strain. Because of concrete shrinkage is restrained by aggregates, the effect of aggregate stiffness on concrete shrinkage is proposed based on the concrete shrinkage model by Tangtermsirikul and Nimityongskul.¹ Verification tests on fine aggregates are conducted on mortar specimens while coarse aggregates and binary mixture of aggregates are conducted on concrete specimens. The verification indicated that the model is effective for deriving the stiffness of aggregate phase and predicting the shrinkage of concrete as well. From the test and analysis results, high aggregate contents induce great stiffness. As a result, it will have effect on small shrinkage.

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Department of Civil Engineering and Environmental Technology, Sirindhorn International Institute of Technology, Thammasat University, Pathumthani, 12121, Thailand.

Received 13 Aug 2000, Accepted 20 Apr 2001