Abstract
A timely knowledge of concrete and ultra-high-performance concrete (UHPC) strength is possible through the so-called strength-equivalent time (Et) curves. A timely knowledge of concrete strength is useful, for instance, to precisely determine when the shores of a hardening structural element can be safely removed. At the present time, the preparation of the strength-Et curves requires time-consuming and labor-intensive testing prior to the beginning of construction operations. This paper proposes an innovative method to derive the strength-Et and total heat-Et curves for both normal strength and UHPC. Results confirmed that the proposed method is fast, inexpensive, self-calibrating, accurate and can detect any variation of the concrete mix proportions or components quality. In addition, the quality of predictions of strength–maturity curves can be constantly improved as the specimens’ population increases. Finally, results obtained with the proposed method were compared with those obtained using standard methods, showing a good agreement.
Highlights
In this paper research is presented whose objective is to provide an accurate method to predict the strength of commercial concretes at any time
The method is still not suitable for concrete, due to the poor electrode contact and non-uniformity caused by the presence of coarse aggregate
The crossover refers to a lower final strength of a concrete curing at high temperatures during the early hydration age compared with the same concrete curing at lower early age temperatures
Summary
In this paper research is presented whose objective is to provide an accurate method to predict the strength of commercial concretes at any time. The laws accounting for the effect of both temperature and time on the hydration speed are not generally linear, and they do not apply to temperatures that are too low or too high This limitation might be overcome by adopting a different method governed by a resistivity model based on Winner bounds. This method can determine the equivalent time of concrete by measuring the electrical resistivity of concrete, for wider curing temperature ranges. The method is still not suitable for concrete, due to the poor electrode contact and non-uniformity caused by the presence of coarse aggregate For this reason, the strength prediction methods based on the maturity indexes are still the most suitable for commercial concretes
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