Improved Superplasticized Precast Concrete Tiles

Concrete tiles were produced according to a new technology based on a vacuum treatment combined with a vibro-compacting placement of superplasticized mixture. Three concrete mixtures (all vibro-compacted according to this technique) were manufactured with different water-cement ratio (0.50 or 0.32) and in the absence or in the presence of the vacuum treatment. Measurements of flexural strength, dimensional stability, SEM, image analysis and particle size distribution of anhydrous cement in concrete tiles were carried out. The vacuum treatment, which removed entrapped air voids from the fresh mixture during the vibro-compacting placement, increased flexural strength but did not change the dimensional stability. The reduction in the W/C from 0.50 to 0.32 significantly increased flexural strength. It is also improved the dimensional stability in terms of a lower curling effect caused by different humidity exposures of the two opposite faces of the concrete tile. The combination of vacuum treatment with low W/C produces a macro-defect free and low micro-porosity cement matrix which is responsible for the high strength and low curling effect of these concrete tiles.