Stresses attributed to moisture change

The concrete slab tends to expand as moisture content in its mass increases otherwise, it contracts. Thus, tensile or compressive stresses are developed. The development of such stresses, attributed to non-uniform moisture distribution, causes slab warping, as in the case of warping owing to temperature gradient. 

It could be said that the stresses that developed as a result of moisture change actually oppose the stresses that developed owing to thermal contraction/expansion. This happens because during the summer, the moisture of the concrete slab is reduced, resulting in the development of compressive stresses, whereas at the same time, because of high temperature, tensile stresses are developed. 

Moisture-induced stresses are more important at the early stage of curing and in hot regions with wet and dry seasons. 

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An equally important function of the concrete layer is to withstand the thermal stresses attributed to expansion, contraction or warping the friction stresses that developed with the underlying layer and the stresses attributed to moisture changes of the concrete. 

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