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A fairly well-defined reaction front can often be observed in thin sections; ahead of the front the concrete is normal, or near normal. Behind the reaction front, the composition and the microstructure of concrete are modified. These changes may vary in type or severity but commonly include: Extensive cracking; Expansion
The curing of concrete when it continues to harden after its initial setting and progressively develops its mechanical strength is a critical phase to avoid unwanted cracks in concrete. Depending on the temperature (summer or winter conditions) and thus on the cement hydration kinetics controlling the setting and hardening rate of concrete ...
When a reinforced concrete member is put in tension, after cracking, the member elongates by widening of cracks and by formation of new cracks. Figure 1 Formation of internal cracks Ignoring the small elastic strain in the concrete between the cracks, we can relate the crack width to the strain of the member by:
The mechanical stresses induced by the thermal cycles create micro-cracks in the concrete matrix and so facilitate the accessibility to water of the reactive mineral phases in the treated samples. [48] The concrete microbar test was proposed by Grattan-Bellew et al. (2003) as a universal accelerated test for alkali-aggregate reaction. [49]
Changes of pore water content due to drying or wetting processes cause significant volume changes of concrete in load-free specimens. They are called the shrinkage (typically causing strains between 0.0002 and 0.0005, and in low strength concretes even 0.0012) or swelling (< 0.00005 in normal concretes, < 0.00020 in high strength concretes).
Typically concrete slabs perform better than implied by their R-value. [5] The R-value does not consider thermal mass, since it is tested under constant temperature conditions. Thus, when a concrete slab is subjected to fluctuating temperatures, it will respond more slowly to these changes and in many cases increase the efficiency of a building ...
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