Treatment method of concrete appearance quality in

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Treatment method for concrete appearance quality in construction engineering regardless of the site management level, the concrete construction cannot be carried out under very ideal conditions. Usually, due to various reasons, or the special structural type, or the bad weather conditions, or the non-standard construction method and construction process, it is easy to produce surface defects during the concrete pouring process or just after the construction. The surface defects of concrete can be summarized into the following four aspects:

1) surface cracks

2) surface damage

3) uneven surface color

4) surface reinforcement leakage

no matter what kind of surface defect, it will have an adverse impact on the appearance quality of concrete. Therefore, find out the internal causes of concrete surface defects, take targeted preventive measures during construction, and repair the existing defects to improve the appearance quality of concrete

1. Cracks on the surface of concrete and soil

cracks on the surface of concrete are mostly caused by shrinkage. There are two main types: one is caused by the evaporation and drying of the water on the surface of the concrete just poured, and the other is caused by the temperature difference between the inside and outside of the concrete caused by the hydration heat when the concrete is hardened

the concrete that has just been poured often becomes dry due to high external temperature and low relative humidity in the air, while its interior is still a plastic body, resulting in cracks due to plastic shrinkage. Such cracks are usually discontinuous and rarely develop to the edge, generally in diagonal diagonal shape, with a length of no more than 30cm. However, in serious cases, the cracks will also be connected with each other. The most effective preventive measure against such cracks is to protect the concrete pouring surface during concrete pouring to avoid wind and sun. After concrete pouring, the surface shall be covered immediately and watered for curing in time. In addition, adding an appropriate amount of air entraining agent to the concrete will also help to reduce shrinkage cracks

for the deeper concrete, during the pouring of the upper concrete, it will continuously settle under the action of the market in a short time or the self weight of the consolidation. When the concrete starts to set initially but before the final setting, if it encounters the connecting bolts of reinforcement or formwork, such settlement will be obstructed and cracks will occur immediately. In particular, when the surface of the formwork is uneven or the release agent is applied unevenly after the activity, the friction of the formwork will prevent this settlement, which will produce cracks on the vertical surface of the concrete. This situation usually occurs at the corners of concrete columns or other narrow and long structures. The second vibration before the initial setting of concrete is the best way to avoid such defects

during the hardening process of concrete, a large amount of hydration heat will be released, making the internal temperature of concrete rise continuously. In mass concrete, hydration heat makes the temperature rise more obvious, forming a very high temperature difference between the concrete surface and the inside. Especially in the construction of large-scale bridge cushion cap, the measured temperature difference between the internal and external concrete sometimes reaches more than 50 ℃. The shrinkage of surface concrete is hindered, and the concrete will be tensioned. Once the strain capacity of concrete is exceeded, cracks will occur. In order to reduce the shrinkage constraint as much as possible so that the concrete can have enough strength to resist the stress caused, it is necessary to effectively control the internal temperature rise rate of the concrete. Adding proper amount of mineral fly ash into concrete can slow down the release rate of hydration heat; The temperature of raw materials shall be controlled, and the hydration heat energy can be released in time by circulating water through the cooling pipe inside the concrete structure

it is worth mentioning that liquid crystalline polymers refer to high molecular materials that can form liquid crystalline state under certain conditions. The mixing of different brands of cement will also cause cracks in concrete. The fineness, strength, initial and final setting time, stability and chemical composition of different brands of cement are different, and there are compatibility problems. During concrete construction, cement of different brands and grades shall not be mixed together

alkali aggregate reaction will also cause concrete cracking. Because the Portland cement contains alkaline metal components (sodium and potassium), the content of hydroxyl ions in the liquid in the pores of the concrete is high. This high alkaline solution can react with the active silicon dioxide in some aggregates to produce alkali silica gel. The expansion force generated by the expansion of alkali silica gel after absorbing water and water causes the concrete to crack

for the repair of shallow cracks through the combination of demand side pull and supply side push, it is usually painted with cement slurry or low viscosity polymer to prevent water intrusion; For deep or wide cracks, pressure grouting technology must be used to repair

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