[Engineering Version] Daily Question 20180618
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Which of the following statements regarding the placement and treatment of construction joints is correct? ( ) A. Construction joints should be placed in areas of the structure where shear forces are low and where construction is easier. B. Horizontal joints should be used for columns, while vertical joints should be used for beams and slabs. C. When pouring concrete at a construction joint, it is necessary to wait until the compressive strength of the previously poured concrete reaches at least 1.2 MPa, in order to resist the disturbances caused by the additional concrete being poured. D. When dealing with construction joints, a layer of cement paste with a thickness of 20–50 mm, or cement mortar with the same water-cement ratio as the concrete, must be applied before continuing with the pouring of concrete. E. When pouring concrete at a construction joint, the surface of the concrete must be roughened, cleaned, and any cement paste film or loose stones or weak layers of concrete must be removed. Answer: ABCE 【Explanation】The location of construction joints should be determined in advance; they should be placed in areas of the structure where shear forces are low and where construction is feasible. Horizontal joints should be left in columns, while vertical joints should be left in beams, slabs, and walls. Treatment of construction joints: When continuing to pour concrete at a construction joint, it is necessary to wait until the compressive strength of the concrete to be poured reaches at least 1.2 MPa before proceeding, in order to resist the disturbances caused by the further pouring of concrete. Moreover, the construction joints need to be treated. Generally, the concrete surface is roughened, cleaned, of any cement slurry film removed, and any loose stones or weak layers of concrete are removed. After that, a layer of cement slurry 10–15 mm thick, or cement mortar with the same water-cement ratio as the concrete, is applied before concrete can be poured again. The concrete at the construction joint should be compacted carefully to ensure a tight bond between the old and new concrete.
A. Construction joints should be placed in areas of the structure where shear forces are low and where construction is easier
The location of the construction joints left by ABCE should be determined in advance; these joints should be placed in the 40% of the structure where shear forces are low and where construction is easier. To effectively protect the rebar and prevent water from reaching it, the thickness of the rebar protection layer in the water-facing waterproof concrete must not be less than 50 mm. During pouring, it is necessary to carry out pouring in strict layers continuously; the thickness of each layer should not exceed 300–400 mm, and mechanical vibration should be used to compact the mixture. Wall structures generally allow only horizontal construction joints, which should be located at a height on the wall of at least 500 mm above the top surface of the base slab. If vertical construction joints must be used, they should be placed at the deformation joints in the structure.
A. Construction joints should be placed in areas of the structure where shear forces are low and where construction is easier. B. Horizontal joints should be used for columns, while vertical joints should be used for beams and slabs. C. When pouring concrete at a construction joint, it is necessary to wait until the compressive strength of the previously poured concrete reaches at least 1.2 MPa, in order to withstand the disturbances caused by the additional concrete being poured. E. When pouring concrete at a construction joint, the surface of the concrete must be roughened, cleaned, and any cement paste or loose stones or weak layers of concrete removed. The location of construction joints should be determined in advance; they should be placed in areas of the structure where shear forces are low and where construction is feasible. Horizontal joints should be left in columns, while vertical joints should be left in beams, slabs, and walls. Treatment of construction joints: When continuing to pour concrete at a construction joint, it is necessary to wait until the compressive strength of the concrete to be poured reaches at least 1.2 MPa before proceeding, in order to resist the disturbances caused by the further pouring of concrete. Moreover, the construction joints need to be treated. Generally, the concrete surface is chiseled, cleaned, of the cement slurry film as well as any loose stones or weak concrete layers are removed. Then, a layer of cement slurry 10–15 mm thick, or cement mortar with the same water-cement ratio as the concrete, is applied before concrete pouring can proceed. The concrete at the construction joint should be carefully compacted to ensure a strong bond between the old and new concrete.