Abstract

The internal relative humidity (RH) and humidity gradients in concrete at early ages have significant influence upon the properties of concrete, where exists, great discrepancy among the test results under different methods. By comparing and analyzing the common measuring methods of the RH in concrete, a newly developed measuring method will be introduced in this study, which could measure the internal RH in cement-based materials accurately, conveniently and digitally. The changing laws of the internal RH in concrete at early ages were discussed. And the numerical simulation of the internal RH was carried out, using the calculated parameters appropriately. The results indicate that the measuring results under the newly developed system was more accurate than that by the predrilled-hole method, while the external environment does not have any effect on the measured results obtained by using the new measurement system. There exist obvious humidity gradients in concrete. In concrete with low water/cement ratio, self-desiccation considerably influence on internal RH distribution. The finite element analysis results from moisture diffusion theory were in good agreement with experimental results.

Key words: Concrete, low water-cement ratio, admixtures, early ages, internal relative humidity, a new measurement system, self-desiccation, finite element analysis.