The Feasibility of Re Mixing Concrete (original) (raw)
Delays may occur after the completion of the mixing process for several reasons beyond the existing ability on the site. This study was conducted to determine the feasibility of re-mix concrete (mechanical mixing), after leaving it in the open air. The concrete mixtures were left after completion of mixing process in room temperature (25 o C) for different periods of times 0, 15, 30, 45, 60 and 75 minutes then returned the mixing process then, placed in its moulds. Results were compared to those samples cast within the mould immediately after mixing. A number of 144 standard cubes were cast to measure the concrete compressive strengths at 7, 28 days. To improve the properties of concrete after re-mixing different additives were used. The used additives were water or cement mortar or workability additive compared to mixing without any additions to improve the mixing process. The most important results of the study confirm that the compressive strength of the samples increases when the mix left then re-mixed after 15 minutes. The mix could be also re-mixed after leaving in the fresh air for periods of up to 75 minutes. The results also showed that the values of compressive strength were lower than that recorded for control, but it could be used with loss of strength by about 18% of the maximum compressive strength. For re-mixing concrete it was preferred to use cement mortar to provide best results.
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