Superplasticizer effects on setting and structuration mechanisms of ultrahigh-performance concrete

The effect of superplasticizer addition on chemical and mechanical kinetics of ultrahigh-performance concrete realization is studied by ultrasonic spectroscopy, calorimetry, and autogenous shrinkage determination. Different percentages of superplasticizer have been used. We have firstly been able to identify the role of the superplasticizer on the early mechanisms of settlement of the solid particles in the mix. and the influence of entrapped air. The delay in the chemical activity brought by the superplasticizer has been analyzed according to the results of the three experimental methods. The continuous information upon the state of organization of the concrete and the structuration of the material is given by ultrasonics for any stage of the chemical reaction. A desynchronization of the shrinkage intense period versus the peak of released power and the material structuration is analyzed in terms of fissuration healing capability and material damaging. (C) 2001 Elsevier Science Ltd. All rights reserved.