foundation system of burj al arab

Behavior of Microcracking Under Loading (Part-2)

We were on cracking through mortar. When loading increased to (70 to 90) percent of ultimate strength of concrete, cracks make their way through the mortar. A new pattern of cracking in concrete in continuous form is developed which release the bond between fine aggregate and cement paste.

The cracking state discussed above is fast propagation stage. As discussed in last post, reaching stable stage depends on water to cement ratio. Here, in this fast propagation cracking stage, the starting point depends on strength i.e. initiation of this stage is higher in higher strength concrete and lower in normal strength concrete.

Microcracking under uniaxial compression in unconfined state
Higher strength concrete shows better performance than normal strength concrete in both stages i.e. the number, width and length of cracks, in all respects, high strength concrete performs well. Cumulative length of cracking of such types is measured using the neutron radiography. The high strength concrete possesses lower values in cumulative length of microcracks as usual.

The commencement of fast propagation stage of cracking corresponds to discontinuity in volumetric strain. We will discuss about volumetric plotting in determining poisson’s ratio elaborately in our upcoming post. Here we are providing a basic idea about this. We all know about stress-strain graph; when volumetric strain is counted as strain and steady but rapid increasing of loading is applied, above particular stress level, poisson’s ratio shows rapid increment, due to formation of extensive vertical cracks. When stress level is increased further the volumetric strain variations changes sign; we are talking about this point.
Volumetric strain in concrete cylinder (increasing loading)
What would be under sustained loading? Under sustain load failure is matter time. Both high strength and normal strength concrete fails under this sustained loading. Dear reader we are finishing this topic here. For learning about measuring crack length graphically and consequently microcracking under cyclic loading; please stay with us to have such nice and useful information.

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