Discuss the causes and control engineering papers on the treatment of concrete construction joints
Abstract: This article briefly discusses the settings, forms, problem types, processing methods, and control of concrete construction joints.
Keywords: concrete; construction joint treatment: problem cause: control
During the project implementation process, due to poor design, construction technology and construction organization, etc. The reason is that the entire structure cannot be poured continuously, and the intermittent time exceeds the allowed duration of concrete transportation and pouring. The joint surfaces of concrete poured successively are called construction joints. The setting and treatment quality of construction joints directly affect the overall quality and safety of the building structure, so the quality of construction joints must be strictly controlled. Now we will briefly discuss the construction joint settings, forms, problem types, and treatment methods.
1. Setting of concrete construction joints
Hydraulic concrete should be poured continuously and fewer construction joints should be left. When it is necessary to leave construction joints in design or construction, the following regulations should be observed:
(1) There should be no construction joints in the bottom plate and top plate; there should be no longitudinal construction joints in the bottom arch and top arch.
(2) There should be no vertical construction joints in the wall. Horizontal construction joints should not be left at the point where the shear force and bending moment are maximum or at the intersection between the base plate and the side wall. They should be left on the wall no less than 300mm above the surface of the base plate. When there is a hole in the wall, the distance between the construction joint and the edge of the hole should not be less than 300 m. The horizontal construction joint between the arch wall and the arch wall should be left 150 mm to 300 mm below the joint line of the arch (slab) wall. Construction of the arch first and then the wall The seam can be left at the arch line, but attention must be paid to strengthening waterproofing measures. On the facing surface of the joint, waterproof waterstop tape should be applied externally, and waterproof coating and mortar should be applied externally.
(3) Construction joints should not be left in the equipment foundation that is subject to dynamic action.
2. Forms of construction joints
There are many types of construction joints, including high and low joints, convex and concave joints, flat joints, etc. High and low joints should not be used at the root of the wall. The biggest disadvantage of convex-concave joints is that the construction is difficult and the quality is difficult to ensure. When the concrete at the construction joints is roughened, the convex ribs are easily knocked off, and the cement mortar powder in the grooves is also difficult to clean. After pouring new concrete, A slag layer is formed in the groove, which affects the bonding quality of new and old concrete. Flat seams are more convenient and widely used.
3. Construction joint surface treatment methods
(1) Artificial chiseling: labor intensity is high, efficiency is low, and it is easy to affect the construction period;
(2 ) High-pressure water flushing: The flushing water pressure reaches 25-50MPa, the efficiency is high, and the intermittent period exceeds 2 weeks, the flushing effect is poor:
(3) Low-pressure water flushing: after the final setting of the concrete , using 0.3 to 0.6 MPa water pressure to flush away the 2 to 3cm thick surface concrete;
(4) Use an air blast gun to flush out the roughened concrete: It is effective, but it is labor-intensive, time-consuming and material-intensive, and the construction interferes greatly;
(5) Mechanical wire brush bristles: high efficiency, good effect, high cost, but the corners are not in place;
< p> (6) Spraying retarder: It can promote the retarding of the concrete surface and extend the flushing time, which is more economical.4. Problems and causes of construction joint processing
(1) Problems and phenomena in construction joint processing
Problems that occur in the construction process of construction joints The main manifestations are the following phenomena: the concentration of concrete aggregates at construction joints, loose concrete, obvious stubble between old and new concrete, water leakage along the gaps, etc.
(2) Causes of problems in construction joint treatment
1. The concrete surface was not roughened, and the residue was not rinsed and removed, resulting in the old and new concrete not being firmly combined.
2. During the process of setting up the formwork and tying the steel bars, sawdust, tape, wood chips, nails and other debris fell into the joints and were not removed in time. After the upper layer of concrete was poured, a sandwich was formed between the old and new concrete.
3. When pouring the upper layer of concrete, a layer of cement mortar was not laid at the construction joint in advance, and the upper and lower layers of concrete could not be firmly bonded.
4. No waterstops are installed on the construction joints.
5. Improper cutting method and aggregate concentration at the construction joints affect the quality of concrete.
6. The concrete wall is thin, and due to the dense steel bars, it is difficult to ram, resulting in the concrete not being tamped densely.
7. Shrinkage-compensating concrete was not used, causing shrinkage cracks at the joints.
8. The joint form of construction joints is improperly selected.
(3) Concrete pouring control after treatment of construction joints
1. The compressive strength of poured concrete should not be less than 1.2 MPa.
2. On the hardened concrete surface, the cement film, loose stones and weak concrete layer should be removed, fully moistened and rinsed, and no water should accumulate. To the extent that the milk skin is removed, the coarse sand is slightly exposed, and the surface is rough.
3. Before pouring, the horizontal construction joints should be laid with a layer of 10mm to 15mm thick cement mortar, the mix ratio of which is the same as the mortar composition in the concrete.
4. The concrete should be vibrated densely without leakage or vibration to ensure the close combination of new and old concrete.
5. Bundling of steel bars and wall formwork. Convenience of construction should be considered. Easy to ensure construction quality.
6. Walls with a height greater than 2m. It is advisable to use a string tube or vibrating chute to unload materials and vibrate in layers.
The treatment of concrete construction joints is an important link that cannot be ignored in the construction of water conservancy projects. We need to understand the causes and types of problems, take some necessary measures, and strictly control the quality of construction joints to ensure the safety of the project. Structural safety. As long as the construction joints are left and treated in accordance with the requirements of the construction specifications and the construction is carefully organized, the strength of the concrete at the construction joints will not be lower than the design strength requirements, and the quality of the construction joints can also be better controlled and guaranteed. ;