【Daily Topic】【Civil Engineering Version 20160913】

Processing: 1. Pouring can continue only after its compressive strength reaches 1.2 Mpa. 2. Remove water films and loose stones or weak ready-mixed concrete layers. It should be thoroughly moistened and rinsed clean, with no water accumulation allowed. 3. Before pouring, lay a layer of cement slurry 10–15 mm thick, or a layer of cement mortar with the same composition as that of the ready-mixed concrete, at the construction joint.

After the concrete of the construction joint has been poured, and after it has begun to set but before it has fully set, a layer of citric acid is sprayed onto it to prevent the 1 cm thick layer of concrete on the surface from setting. Afterwards, high-pressure water is used to roughen the surface and remove any excess slurry. When pouring the upper layer of concrete, a layer of cement mortar with the same grade and a thickness of about 2–3 cm is applied first; for vertical joints, a layer of pure cement paste is applied first to ensure good bonding between the old and new concrete. The concrete at the interface between the old and new concrete should be compacted carefully. Some construction joints are treated by manual chiseling.

Treatment of construction joints: After the concrete for the construction joint has been poured, and after it has begun to set but before it has fully set, a layer of citric acid is sprayed onto its surface to prevent the concrete within 1 cm of that surface from setting. Afterwards, the surface is roughened using high-pressure water to remove any excess cement slurry. When pouring the new layer of concrete, a layer of cement mortar with the same grade and a thickness of about 2–3 cm is applied first; for vertical joints, a layer of pure cement paste is applied first to ensure good bonding between the old and new concrete. The concrete at the interface between the old and new concrete should be compacted carefully. Some construction joints are treated by manual chiseling.

The location of construction joints should be chosen in areas where the structure is subject to less shear force and where construction is easier; furthermore, the following rules must be followed: horizontal joints should be used for columns, while vertical joints should be used for beams, slabs, and walls. (1) Construction joints should be placed on the top surface of the foundation, below the beams or the brackets of the crane beam, above the crane beam, and below the column caps of floor slabs without beams. (2) For large-section beams that are integrated with the floor slabs, construction joints should be placed 20 mm to 30 mm below the bottom surface of the slab. When there is a beam support under the slab, it is placed below the beam support. (3) For one-way slabs, construction joints should be placed at any position parallel to the short side of the slab. (4) For floor slabs with primary and secondary beams, pouring should be carried out in the direction of the secondary beams, and construction joints should be placed within 1/3 of the span of the secondary beams. (5) Construction joints on the wall should be placed within 1/3 of the span of the lintel above the door opening, or they can also be located at the junction of vertical and horizontal walls. (6) The construction joint on the stairs should be located at 1/3 of the tread height. (7) The construction joint in the pool wall should be located on the vertical wall at a height of 200 mm to 500 mm above the surface of the bottom slab. (8) For floor slabs subjected to bidirectional loads, mass concrete, arches, shells, silos, equipment foundations, multi-story rigid frames, and other complex structures, the locations of construction joints shall be determined in accordance with the design requirements. After the concrete has fully set, the retaining plates are removed, and the surface is roughened using an axe or steel rod; loose stones are cleared away. At this stage, the concrete’s strength is very low, so it is easy to roughen the surface by 20–30 MM. When pouring concrete a second time, the joint surfaces should be cleaned thoroughly with pressurized water in advance, and a layer of plain cement slurry should be applied while pouring to enhance the adhesion between the materials

1. Before pouring concrete, it is advisable to apply a layer of cement slurry at the construction joint (with an appropriate amount of interface agent added), or lay a layer of cement mortar with the same composition as that used in the concrete； 2. If the concrete at the construction joint has already hardened prior to simulated pouring, the cement film, loose gravel, and weak concrete layers must be removed; the area should be thoroughly moistened and rinsed clean, with no water accumulation allowed ； 3. The poured concrete should be carefully compacted to ensure tight bonding between the old and new concrete ；

Clean the dust away, then pour in high-grade cement

Before pouring concrete at the construction joint, the concrete surface should be roughened, debris removed, cleaned and moistened. Then a layer of 2–3 cm thick cement mortar (i.e., the original mix without stones) or concrete with reduced stone content using the same mix ratio should be applied. The height of the first pour should be 40 cm; subsequent pours should be 50–60 cm in height each. Pouring must be carried out strictly in the sequence specified in the construction plan. Concrete should not fall freely from a height of more than 2m; if the height exceeds 3m, buckets or chutes should be used for its descent.

The construction joints in concrete should be treated as follows during pouring: 1. Before pouring the concrete, it is advisable to apply a layer of cement slurry at the construction joint (with an appropriate amount of interface agent added), or lay a layer of cement mortar with the same composition as that used in the concrete； 2. If the concrete at the construction joint has already hardened prior to simulated pouring, the cement film, loose gravel, and weak concrete layers must be removed; the area should be thoroughly moistened and rinsed clean, with no water accumulation allowed ； 3. The poured concrete should be carefully compacted to ensure tight bonding between the old and new concrete ； 4. Note that when pouring concrete at construction joints, its compressive strength should not be less than 1.2 N/mm2.

Before pouring concrete at the construction joint, the concrete surface should be roughened, debris removed, cleaned and moistened. Then a layer of 2–3 cm thick cement mortar (i.e., the original mix without stones) or concrete with reduced stone content using the same mix ratio should be applied. The height of the first pour should be 40 cm; subsequent pours should be 50–60 cm in height each. Pouring must be carried out strictly in the sequence specified in the construction plan. The free fall distance of concrete from a height should not exceed 2m; if the height is more than 3m, buckets or chutes should be used for delivery

1. Before pouring concrete, it is advisable to apply a layer of cement slurry at the construction joint (with an appropriate amount of interface agent added), or lay a layer of cement mortar with the same composition as that used in the concrete； 2. If the concrete at the construction joint has already hardened prior to pouring, the cement film, loose gravel, and weak concrete layers must be removed; the area should be thoroughly moistened and rinsed clean, with no water accumulation allowed ； 3. The poured concrete should be carefully compacted to ensure tight bonding between the old and new concrete ； 4. Note that when pouring concrete at construction joints, its compressive strength should not be less than 1.2 N/mm2.