This paper briefly discusses the setting, form, problem type, treatment method and control of concrete construction joints.

Keywords: concrete; Treatment of construction joints: causes of problems: control

In the process of project implementation, due to the design, construction technology and construction organization,

If the whole structure cannot be continuously poured, and the intermittent time exceeds the allowable duration of concrete transportation and pouring, the joint surface of continuously poured concrete is called construction joint. The setting and treatment quality of construction joints directly affects the overall quality and safety of building structures, so the quality of construction joints must be strictly controlled. This paper briefly discusses the setting, form, problem types and treatment methods of construction joints.

First, the setting of concrete construction joints

Hydraulic concrete should be poured continuously, leaving few construction joints. When it is really necessary to leave construction joints during design or construction, the following provisions shall be observed:

(a) Floor and roof should not leave construction joints; Bottom arch and top arch should not leave longitudinal construction joints.

(2) the wall should not leave vertical construction joints. Horizontal construction joints should not be left at the place with the maximum shear force and bending moment or at the junction of bottom plate and side wall, but on the wall not less than 300mm above the bottom plate surface. 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, and the horizontal construction joint combined with the arch wall should be left below the joint line of the arch (slab) wall 150 mm ~ 300 mm, and the construction joint of the back wall of the arch can be left at the bulging line, but attention must be paid to strengthening waterproof measures. The water surface of the joint should be affixed with waterproof water stop, and coated with waterproof coating and mortar.

(3) Under the action of power, no construction joints should be left on the equipment foundation.

Second, the form of construction joints

The joint forms of construction joints include high-low joint, convex-concave joint and flat joint. High and low joints should not be used at the root of the wall. The biggest disadvantage of concave-convex joint is that the construction is difficult and the quality is difficult to guarantee. When the concrete in the construction joint is chiseled, it is easy to knock off the protruding stare blankly, and it is difficult to clean the cement mortar powder in the groove, so that after the new concrete is poured, a slag inclusion layer is formed in the groove, which affects the bonding quality of new and old concrete. Flat seam is more convenient and widely used.

Third, the construction joint surface treatment method

(1) Manual shearing: the labor intensity is high and the efficiency is low, which easily affects the construction period;

(2) high-pressure water scouring: the scouring water pressure reaches 25 ~ 50mpa, with high efficiency, and the intermittent time exceeds 2 weeks, with poor scouring effect;

(3) Low-pressure water scouring: After the concrete is finally set, the surface concrete may be washed away by 2 ~ 3 cm thick with water pressure of 0.3~0.6 MPa;

(4) Sand blasting: It is effective for long-age concrete blasting, but it is labor-consuming, time-consuming and material-consuming, and the construction interference is great;

(5) Wire brush mechanical bristles: high efficiency, good effect and high cost, but the corners are not in place;

(6) Spraying retarder: it can promote the retarding of concrete surface and prolong the scouring time, which is more economical.

Four, construction joint treatment problems and reasons

(A) the problems and phenomena in the treatment of construction joints

The problems in the construction of construction joints are mainly manifested in the following phenomena: the concrete aggregate at the construction joints is concentrated, the concrete is crisp, the old and new concrete are obviously grafted, and water leaks along the cracks.

(B) the reasons for the problems in the treatment of construction joints

1, the concrete surface is not chiseled and the residue is not washed away, so that the new and old concrete cannot be firmly combined.

2, in the process of shuttering and steel binding, sawdust, adhesive tape, sawdust, nails and other debris fell into the seam and not removed in time. After pouring the upper concrete, an interlayer is formed between the old and new concrete.

3. When pouring the upper concrete, a layer of cement mortar was not laid at the construction joint in advance, and the upper and lower concrete could not be firmly bonded.

4. The water stop is not installed at the construction joint.

5, improper blanking method, aggregate concentrated in the construction joints, affect the quality of concrete.

6, concrete wall is thin, because the steel bar is too dense, tamping vibration is difficult, resulting in concrete tamping vibration is not dense.

7. Shrinkage-compensating concrete is not used, resulting in shrinkage cracks at planting sites in summer.

8. Improper selection of joint forms of construction joints.

(3) Control of concrete pouring after construction joint treatment

1, the compressive strength of the poured concrete should not be less than 1.2 MPa.

2. On the hardened concrete surface, cement film, loose stones and weak concrete layer should be removed, fully wetted and rinsed, and no water can accumulate. To remove the milk skin, slightly exposed coarse sand, rough surface.

3. Before pouring, the horizontal construction joints shall be paved with a layer of cement mortar with the thickness of 10 mm ~ 15 mm, and the mixture ratio is the same as that of the mortar in concrete.

4, concrete should be compacted, shall not leak vibration, to ensure the close combination of new and old concrete.

5, steel binding and wall shuttering. The convenience of construction should be considered. It is easy to ensure the construction quality.

6. Walls with a height of more than 2 meters. It is advisable to use string drum or vibrating chute for blanking, and vibrate in layers.

The treatment of concrete construction joints is an important link that can not be ignored in water conservancy construction. We need to know the causes and types of problems, take necessary measures, strictly control the quality of construction joints and ensure the structural safety of the project. As long as the construction joints are retained and treated according to the requirements of construction specifications, and the construction is carefully organized, the concrete strength at the construction joints will not be lower than the design strength requirements, and the quality of the construction joints can be well controlled and guaranteed.

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