Tvbm - 3126 Self - Desiccation and Its Importance in Concrete Technology

The premise of this paper is that low water-to-cement ratio (w/c), higher strength concrete may undergo substantial volume changes, especially at early ages (< 24 hours), and the prevention of these volume changes can lead to invisible micro-cracking as well as visible through-cracking. This paper compares the predicted response of concrete undergoing autogenous shrinkage using two different models. The first model considers the concrete as a homogeneous material with effective elastic properties. The second model considers the concrete as a heterogeneous two-phase composite. The paper begins with an overview of common effective elastic property computations. These effective properties are then used to compute residual stresses when external restraint is provided. Heterogeneous system simulations were performed to quantify the effect of both internal and external restraint on shrinkage. Internal restraint may be caused by aggregate particles while the structure surrounding the concrete composite may produce external restraint. These simulations considered a series of ‘model systems’ ranging from a single aggregate particle, to an assembly of hexagonal unit cells containing aggregate particles, to a more realistic system consisting of various sizes and shapes of aggregate particles. The finite element analysis (FEA) simulations illustrate how localized stresses develop, how effective equivalent properties can be determined for heterogeneous composites, and how localized stresses can lead to cracking. 1. Research approach and motivation This paper provides an overview of a research program that is currently being conducted at Purdue University. The objective of the overall program is to develop procedures to enable information from sensors placed in a concrete structure or pavement to be utilized efficiently as real-time feedback for updating performance simulation models [1]. While this project has many facets, one aspect of this work is to better understand how an embedded stress sensor may be used to quantify residual stresses in concrete. Toward this end, a series of preliminary computations have been performed to better understand the residual stresses that develop in a heterogeneous composite system when one phase (the paste phase) shrinks and the other phase (the aggregate phase) does not. Subsequent computations have been performed to investigate stresses that develop when both phases experience differential movement, though they will not be discussed in this paper.