Advanced Techniques for Testing of Cement-Based Materials by Marijana Serdar & Ivan Gabrijel & Dirk Schlicke & Stéphanie Staquet & Miguel Azenha

Author:Marijana Serdar & Ivan Gabrijel & Dirk Schlicke & Stéphanie Staquet & Miguel Azenha
Language: eng
Format: epub
ISBN: 9783030397388
Publisher: Springer International Publishing

4.4.2.3 Bleeding

In case of concrete with high water content or with a lack of fines particles in the mix, bleeding can occur. The water-to-cement ratio is higher on the top of the sample and consequently a lower stiffness is expected on the top of the sample. The effect of bleeding on the measurement system depends on the situation of the sample. With the BTJASPE, the sample is tested on the vertical direction. The piston has the particularity to have holes which allows the bleed water to pass through so the upper bearing is always in contact with the solid phase of the concrete. Through these holes, the amount of drying is negligible so that the sealed conditions are obtained. Thus it is assumed, if there is bleed water, that this water is removed from the sample through the hole of the upper bearing when the load is applied. Then the water is still available and can be reabsorbed by the cement paste during the whole test. It is also assumed that if a small weak layer of concrete exists during the test on the top of the sample, this layer is very small and has no real impact on the measurement of the elastic and creep strain. With the TSTM, the sample is tested on the horizontal direction. If there is bleeding at a moment, bleed water would be firstly on the top of the sample and will have no effect on the horizontal stiffness of the concrete and no effect will appear on the measurement. During the test, bleed water could be reabsorbed by the concrete and create a swelling of the concrete on the upper part of the sample and will lead to a bending of the sample. However, it is assumed that the potential swelling will represent a very small layer, will not create a significant bending effect and therefore will not influence the measurement of the elastic and creep strain. With the vertical testing device developed at ULB and TUWIEN, the sample is tested few hours after setting and the upper part of the sample is removed in order to assure the flatness of the sample. In consequence, no effect of bleeding is expected with these devices. In order to assure that no damage, irreversibility or effect of bleeding occurs during the test, classical extensometry can also be performed in parallel to the repeated minute-scale-duration loadings test.

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