High performance concretes are increasingly gaining in importance in the concrete industry. Due to their enhanced performance, concrete products can be designed and manufactured with greater span lengths, thinner cross-sections and less weight. They also contribute to improving product durability. However, the rheological characteristics of these extremely compact construction materials also favour the entrapment of air bubbles in the course of individual production stages (mixing, spreading concrete in formwork). A major part of the air bubbles remain in the matrix even after compacting. These entrapped air bubbles (whose size ranges between one and several millimetres) are the cause of a reduction in the product’s performance values. Lower mechanical strength, less aesthetical facing concrete qualities, greater susceptibility to contamination, and decreasing durability are the results. The research work carried out at CERIB was primarily concerned with understanding the mechanisms causing air bubble formation in the cement matrix. The experimental study consisted in determining the definitive parameters at the time of air bubble formation in high performance concrete both in relation to the material (concrete admixture, properties of fines, etc.) and also in terms of the manufacturing process (mixing, spreading the concrete, compaction, oil, formwork properties).
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