Abstract

In the present work, concrete affected by alkali-silica reaction (ASR) is represented as a two-phase material made of a solid skeleton and an expanding gel, which exerts a pressure capable of severely damaging concrete. As suggested by the experimental results, degradation due to ASR is considered to be localized around the reactive sites and it is described through an isotropic chemical damage variable. Another internal variable is introduced to describe the mechanical damage induced by the external loads. The chemical damage evolution depends on the reaction extent and it is calibrated using the value of the gel pressure, estimated by applying the electrical double-layer theory to the experimental values of the surface charge density obtained from ASR gel specimens. The model is then employed to simulate compression and flexure tests results reported in the literature.

Highlights

  • The alkali-silica reaction (ASR) occurs in concrete between some forms of amorphous silica contained in the aggregates and the alkali in the cement paste

  • A different behavior is observed in concrete structures affected by the reaction: there is a severe damage in the neighborhood of the reactive sites while the overall mechanical properties reduction is limited

  • In the framework of the mechanics of porous materials ([10], [11]), concrete affected by ASR is interpreted as a two-phase heterogeneous material constituted by the homogenized concrete skeleton (s), that includes the cement paste, the aggregates and the non-connected porosity, and the homogenized wet gel, which consists of the gel produced by the chemical reaction, the adsorbed water and the gas phases see Figure 3a

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Summary

INTRODUCTION

The alkali-silica reaction (ASR) occurs in concrete between some forms of amorphous silica contained in the aggregates and the alkali in the cement paste. In the literature ([4], [5], [6]) poro-mechanical models have been proposed and successfully used in order to describe the structural effects due to ASR With these existing models good results in terms of expansion can only be obtained with values of the gel pressure one order of magnitude higher the experimental ones. A different behavior is observed in concrete structures affected by the reaction: there is a severe damage in the neighborhood of the reactive sites while the overall mechanical properties reduction is limited Starting from these experimental evidences, the main objective of the present work is the combination of a phenomenological approach of poro-mechanics with the experimental information at the micro-scale, elaborated through the double-layer theory. The model is validated by simulating the experimental tests on reacted concrete cylindrical specimens axially loaded and confined with steel rings reported in [7] and the compression tests and the three point bending tests reported in [8]

COMPUTATION OF THE ASR GEL PRESSURE
CHEMICAL AND MECHANICAL DAMAGE MODEL
MODEL VALIDATION
CONCLUSIONS
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