New evidences on the effect of the internal relative humidity on the creep and relaxation behaviour of a cement paste by micro-indentation techniques

A recent survey has revealed that the deflection of concrete bridges increases incessantly over a period of more than 20 years and can exceed by far the predictions of current design recommendations. This work applies microindentation techniques, which allow quickly assessing the long term rate, to investigate the effect of relative humidities on both the viscous behaviour of a cement paste. A large campaign of microindentation tests was carried out at different relative humidities, loading histories, curing times, and load levels for both creep and relaxation testing. The correlations between creep rate, relaxation rate, and relative humidity were investigated. The results showed that the increase of the relative humidity reduces the indentation modulus and hardness, but increases the long term creep rate of a cement paste. The effect of the relative humidity on the creep rate was possibly explained by local forces acting on Calcium-Silicate-Hydrates sheets or by microcracking drying effects. (C) 2016 Elsevier Ltd. All rights reserved.