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2 -Plastic shrinkage cracking in concrete.

2 -Plastic shrinkage cracking in concrete.

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Early-age (up to 24 hours after casting) cracking may become problematic in concrete. It can have a negative influence on the aesthetics of the structure, as well as decreasing the durability and serviceability, by facilitating the ingress of harmful materials into the concrete bulk. Moreover, these cracks may expand gradually during the member's s...

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... opposite effect was observed when the SP content was increased to 1.0% of cement weight in SP1. On the other hand, decreasing the SP content, caused higher capillary pressure build-up rate, see Figure 12. However, the pressure value in all the specimens started to increase almost simultaneously, regardless the SP dosage. ...
Context 2
... amount of SP also affected the hydration rate, where SP0.6 and SP1, respectively, shortened and prolonged the dormant period, compared to the REF mix. Figure 12 -Influence of SP dosage on the internal temperature and capillary pressure (time after starting the measurement). Table 4 gives the length of the dormant period (from the time of mixing), in addition to the rate and the onset time of the capillary pressure build-up, for all mixtures. ...
Context 3
... prolongation of the dormant period in SP1 (see Figure 12), can be attributed to the retarding effect of the polycarboxylate ether based SP [37]. The slower hydration, facilitates more upwards transportation of the pore water, which in turn results in a higher cumulative evaporation, see Figure 11. ...
Context 4
... it can be seen in Figure 12, the capillary pressure build-up rate decreased by raising the SP dosage. The trend can be explained based on the impact of SP on the concrete porosity, i.e. intrinsic permeability. ...

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... The susceptibility of concrete for plastic shrinkage induced cracking was investigated inside a climate chamber to maintain stable environmental conditions throughout the experiment. A rectangular mould with the internal dimensions of 560 mm × 355 mm × 100 mm was fabricated with a stress riser (i.e., which acts as the crack inducer) at the middle that complies with the standard ASTM C1579 [59]. Two metal inserts were provided next to the stress riser to accommodate the internal restraints of concrete during shrinkage. ...
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... However, based on some investigations it was identified that the provision of these two metal inserts alone was not sufficient to restrain the concrete shrinking. 55,56 Hence, the specimen suggested by ASTM C1579 52 was modified by providing additional six 10 mm diameter corrosion-free end bolts and nuts at both shorter spans of the mold. Similar modifications were also used in the studies made by Sayahi 55 and Sivakumar and Santhanam. ...
... 55,56 Hence, the specimen suggested by ASTM C1579 52 was modified by providing additional six 10 mm diameter corrosion-free end bolts and nuts at both shorter spans of the mold. Similar modifications were also used in the studies made by Sayahi 55 and Sivakumar and Santhanam. 56 After the design slump achieved, fresh concrete was introduced into mold as a single layer to avoid compaction. ...
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... The only mixture that falls way out of this range has a w/c ratio of 0.55. This particular mixture is still in the optimum crack reducing w/c ratio range, defined by (Sayahi, 2019), i.e. 0.45 < w/c < 0.55, and thus, does not affect the cracking tendency. (Sayahi et al., 2019) Maritz (2012) investigated the plastic shrinkage cracking of VC by focusing on evaporation and bleeding. ...
... This particular mixture is still in the optimum crack reducing w/c ratio range, defined by (Sayahi, 2019), i.e. 0.45 < w/c < 0.55, and thus, does not affect the cracking tendency. (Sayahi et al., 2019) Maritz (2012) investigated the plastic shrinkage cracking of VC by focusing on evaporation and bleeding. He also used a mold manufactured according to (ASTM C 1579(ASTM C , 2013. ...
... However, there seem to be some contradictions in the literature. Some studies reported that fibres tend to reduce the quantity of bleeding water by reducing segregation, which succeeds at lower water evaporation rates [12,17,22]. On the contrary, other studies reported higher water evaporation rates that were attributed to the development of so-called bleeding channels along the fibres [3,[23][24][25][26]. ...
... Metallic fibres are most commonly produced as macro fibres with hooked ends or other deformed shapes to improve the fibre-to-matrix bonding [22][23][24][25]35]. Naaman et al. [2] found that relatively fine metallic fibres (d = 0.175 mm, L = 15 mm) almost eliminated the total crack area when added at volume fractions of 0.4%. ...
... It was found that these composites with hybrid fibre additions performed well in controlling the crack formation, while other beneficial mechanical properties were obtained with the addition of steel fibres. Steel fibres extracted from recycled tyres were studied by Sayahi [22] who found that the recycled steel fibres performed almost as good as commercially available steel fibres with hooked ends. ...
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... Although discrepancies between theoretically determined and measured deformations can be observed for humidity range below 70%, capillary tension theory can explain the key factors for a majority of natural conditions in a simple and robust way. The relation between humidity and pressure can be written as an equilibrium between Young-Laplace (1) [3]. ...
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... The absolute pressure value is dependent on the location, owing to different degrees of air penetration into the pore network, and therefore it cannot be considered as a material property (Sayahi, 2019;Slowik and Schmidt, 2010). However, assuming constant drying conditions at a given depth, the rate at which the capillary pressure increases is the same, regardless of the location Slowik et al., 2008), see Figure 1, and thus can be used instead of the absolute pressure value for estimating the level of the tensile stresses in the concrete mass (Sayahi, 2019). ...
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