The main objective of the proposed study is to obtain insight in phenomena leading to loss of stiffness of cementitious composites under mechanical and environmental load. Degradation of glass fibre textile reinforced cementitious composites occurs due to a complex mix of chemical attack and propagation with time of nano- and microdefects under mechanical load. These effects have major influence on the macro-mechanical constitutive behaviour and therefore also on design under serviceability limit states. These combined and complex effects can only be studied systematically and thoroughly when co-operation in several disciplines is assured: mechanics of materials, constructions, chemical analysis, non-destructive testing, etc.
Damage mechanisms occur at different length-scales. Therefore experiments will be carried out at these different scales. The effects, which will be studied in detail, are:
- on nano-scale and micro-scale: analysis of chemical elements leaching from glass fibres due to high alkalinity, and of formation of hydration products at the matrix-fibre interface
- on meso-scale: matrix - fibre bundle interaction and introduction and propagation of matrix cracks
- on macro-scale: composite stress-strain behaviour
In reality a virtually infinite number of combinations of mechanical load and environmental loading can act on constructions. The proposed project will be limited to three relevant cases of loading: (1) the study of accelerated ageing of cementitious composites under elevated temperature and humidity (classical accelerated ageing), (2) degradation under combination of a constant mechanical load and accelerated ageing and (3) subsequent freezing-thawing and mechanical loading cycles