Flexural Behavior of Reinforced Concrete Beams with Horizontal Cold Joints at Variable Levels
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Date
2024-05-29
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Abstract
Flexural behavior of reinforced concrete beam specimens containing horizontal cold joints at variable levels was discussed in this study. Cold joints in reinforced concrete elements can be formed due to many reasons. Lack of concrete quantity delivered to the site, accidents or problems happened while pouring the concrete, massive infrastructures that are very difficult to be poured continuously, rejecting “out-of-specifications” concrete patches, etc. all can consequently cause the formation of cold joints.
To achieve the goals of the study, sixteen rectangular reinforced beams with overall dimensions of 1200 mm in total length and a rectangular cross- section of 160 mm × 100 mm were cast and tested as simply supported beams under two-point loading. The beams have been designed to ensure that flexural failure is the mode of failure. Sixteen RC beams were divided into four groups and examined according to the time of cold joint ,location of cold join , compaction process and use steel fiber to strength : Thirteen beams , divided into three categories: one control beam (without cold joint , without steel fiber)and twelve divided into three group, each group contains four beams according to the difference in the time elapsed between pouring the two layers: two with horizontal cold join at compression fiber ,two with horizontal cold joint at tension fiber and whether the first pour had been compacted before pouring the second patch have been investigated as well. The second pour in the first group (G1) has been done after 1.5 hour after the first pour. Similarly, the second pour in groups (G2 and G3) have been done after 3.0 and 4.5 hours after the first pour, respectively., Furthermore three beams were cast by choosing the least failure load and strengthening the joint interface with steel fiber of 1.0% volume ratio as a trial to enhance the behavior of joint interface.II
The main parameters of this study are the effect of time elapsed between the first pour and the second pour, the effects of location of the joint, the effect of compaction of the first RC layer and addition of steel fiber.
The experimental results showed that a longer time delay between the first and second pours may result in a larger decrease in the total capacity, it can also be noted from these results that compacting the first layer prior to pouring the second layer in the first two samples has provided for a better behavior than leaving the first layer uncompacted. The location of the cold joint, on the other hand, has also influenced the load carrying capacity and midspan deflection. A significant reduction in the flexural loading capacity has been reported when the joint is located at the compression zone of the beam’s cross section (i.e., at 0.7h), especially when the first pour had been left uncompacted.
It was found that the presence of cold joints has decreased the ultimate load and ultimate deflection, ductility, stiffness and toughness in comparison to reference beam. The decrease in the ultimate load and ultimate deflection were by about 40.91% and 43.4% when the time between pours has been changed from 1.5 to 4.5 hours, when the cold joint located at the compression fiber and when the first layer had not been compacted.
The test result also showed that adding 1.0% hooked-ends steel fiber of aspect ratio equals to 50 for beams with horizontal cold joint it can provide for better bonding between concrete layers, and therefore, increase, or restore, the lost flexural capacity of the beams with cold joints.