Finding a means of quantifying the structural deterioration suffered by concrete buildings, bridges and dams is a high priority for studies of Alkali Aggregate Reaction (AAR). In this paper we are primarily interested in linking the change in the deformation properties to a damage index. First, a simple mode1 is built, relating the initial elastic stiffness of a nominally undamaged cementitious system with its phase proportions, degree of hydration and aggregate modulus. Comparisons are made between the model predictions and earlier data. New results on the measured stiffness of damaged and undamaged concrete, cored from existing AAR affected structures, are then presented and an interpretation made using the model. The work attempts to provide a connection between the fabric of the material, the internal mechanisms and the macro-continuum response. The technique has potential for evaluating damage to concrete from other sources of deterioration.
1. INITIAL STATE
CONCRETE in its various forms is the most widely used construction material and one of the most complex. It is essentially a composite consisting of randomly distributed mineral inclusions embedded in a continuous, comparatively soft, viscous, porous hydrated cement matrix. Realistic constitutive models for this material, and an understanding of the fundamental mechanisms, are important to the calculation of the integrity of deteriorating structures and forecasting their future life. It will be shown that the longitudinal deformation moduli form convenient continuum measures of damage.
The elastic moduli of structural concretes (more particularly the Young's modulus) are typically estimated from empirical expressions based on the cylinder or cube crushing strength, and possibly the mass density of the mix. For example: E, (GPa) = 1.36(r)'.'(f,)O.'
(5 <fc < 40: AC1 31%83[1])