ASR expansion behavior in reinforced concrete : experimentation and numerical modeling for practical application




Wald, David Michael

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Most practicing structural engineers are not well-equipped with the knowledge or tools necessary to adequately address the problem of alkali-silica reaction (ASR). While the mechanisms and consequences of ASR in plain, unloaded concrete are fairly well-understood, such a statement cannot be made about ASR-affected reinforced concrete (RC). Central to the problem is that the expansion behavior of ASR-affected RC behavior as influenced by restraint in the form of embedded reinforcing bars and sustained applied loads is unclear. It is these ASR-induced expansions in concrete that lead to cracking, possible strength and stiffness degradation of the material, and the introduction of unanticipated material stresses that may impair the durability, serviceability, functionality, and integrity of affected structures.

In an effort to transition from a materials science perspective on ASR toward a practical structural engineering approach for addressing ASR in RC, experimental and analytical research was conducted with the goals of: 1) generating more insight into the mechanism of ASR expansion in RC and better assessing how a variety of structural details influence expansion behavior, 2) enlarging the database of information on ASR expansion behavior in RC within the literature, and 3) developing a new tool that could be used to reliably estimate life-cycle expansions for subsequent use in quantifying current and future load-carrying response of existing ASR-affected structures.

Expansion monitoring studies were carried out at the Ferguson Structural Engineering Laboratory on a large-scale, biaxially reinforced concrete beam and large-scale, multi-axially reinforced concrete cubes affected by ASR. The multi-directional expansion behaviors of these elements were measured over time and with volumetric expansion development to evaluate the influences of different reinforcing schemes (e.g., amounts, directions, and layouts of reinforcement) on overall behavior.

Using principles of mechanics, a new ASR expansion model, the Distributed Volumetric Expansion Pressure (DVEP) model, was developed to estimate the multi-directional distribution of volumetric expansions developing in RC structures. The DVEP model was designed as a non-incremental analysis tool accounting for constitutive relationships and utilizing simple, structural detailing inputs (e.g., reinforcement ratios and material properties) for rapid and accurate assessment of global RC expansion behavior by hand or within the framework of finite element analysis programs employing secant stiffness solution algorithms. The modeling approach was extensively validated and shown to be robust and capable of being implemented with limited subjective application.

The results obtained from the numerical modeling of expansion behavior were used to preliminarily examine the consequences of expansion on RC load-deformation behavior. Finally, several recommendations for future work were provided.


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