Analysis on Mechanism of concrete frost damage in

2022-08-07
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Analysis on Mechanism of concrete frost damage in winter I. definition of concrete construction in winter

in accordance with the national standard code for construction and acceptance of concrete structures (GB50204 ­­--- 92) according to Chapter 7, according to the local temperature data for many years, when the outdoor daily average air paper industry competition pattern tends to be stable and the temperature is stable below 5 ° C for 5 consecutive days, the concrete engineering construction, i.e. polyethylene (PE) and polypropylene (PP) account for 2/3 of the world's plastics, should enter the winter construction

China has a continental monsoon climate, which is often affected by the Siberian cold current, and the temperature changes greatly and frequently. However, according to the research on China's climate characteristics by the meteorological department, in the autumn and winter temperature change season, when the temperature continuously drops to the daily average temperature below 5 ° C and has not been higher than 5 ° C for 5 consecutive days, it is less likely that the temperature will rise again in the future. At this time, the first day when the temperature is stable below 5 ° C for 5 consecutive days is taken as the initial day of winter construction. Similarly, when the temperature rises, the last day when the temperature is higher than 5 ° C for 5 consecutive days is taken as the termination date of winter construction

therefore, the winter construction period of concrete can be determined as: according to historical meteorological data, in autumn and winter, when the temperature is stable below 5 ° C for 5 consecutive days to the end of the next spring when the temperature is stable above 5 ° C for 5 consecutive days, the specific date of winter construction of concrete is the date. However, it should also be noted that outside the above-mentioned period, sometimes the temperature may suddenly drop below 0 ° C due to the cold current, but the sun weather occurs after the cold current, and the temperature rises again. Therefore, in this sudden cooling period, attention should also be paid to prevent the concrete from freezing damage. The winter construction of concrete works is different from the normal temperature construction. Since the natural temperature has been reduced to below 0 ° C, corresponding measures such as heat preservation, antifreeze, wind prevention and water loss prevention should be taken from all links of the whole construction process. Try to create a positive temperature curing environment for the concrete, so that the concrete can set, harden and increase its strength, so as to avoid and reduce the frost damage to the concrete

II Classification of concrete frost damage

therefore, you must keep this in mind

during the construction of concrete works in winter, the concrete freezing can be divided into the following three types according to different stages

(I) freezing of concrete

freezing of fresh concrete means that the newly poured concrete is frozen before final setting. The main reason is that the air temperature and concrete temperature are very low, and the construction measures are inappropriate. Generally speaking, this kind of freezing will not deteriorate the concrete. As long as the concrete is vibrated and compacted immediately after thawing and before final setting, and the maintenance is strengthened, the concrete will not be frozen again, and the performance of the concrete will not be damaged. This kind of situation can be encountered in the construction of thin-wall structure, thin plate and road surface

(II) early freezing of concrete (also known as early freezing injury or early freezing of concrete)

early freezing of concrete refers to the freezing of concrete during curing and hardening after pouring, which can damage a series of concrete properties. This problem is often encountered in concrete construction in winter and is worth paying attention to. This kind of frost damage is mainly caused by improper selection of construction methods and low or irresponsible technical level of construction personnel. It can reduce a series of physical and mechanical properties of concrete, so that it can not meet the design strength requirements, affect the engineering application, reduce the durability, and even cause rework

the main indexes to evaluate the early frost damage of concrete are compressive strength, tensile strength and bond strength between concrete and reinforcement. The test method is to use various freezing temperatures to freeze and thaw the hardened concrete at different ages for one or more times, and then carry out the test according to the standard test method for ordinary concrete. It comprehensively reflects the level of concrete raw materials, mix proportion and curing conditions

one of the important indexes to evaluate the early frost damage of concrete is the early allowable critical strength

(III) frost damage of concrete (also known as the frost resistance durability of concrete)

frost damage of concrete refers to that the hardened concrete is affected by the natural temperature during the use of the engineering structure, and is subject to the freezing and thawing effects of the natural temperature for many years, resulting in the gradual reduction of various properties

the main index to evaluate the frost damage of concrete is the loss value of compressive strength or dynamic elastic modulus. Take the concrete specimen hardened for 28d under standard conditions, and measure the loss value of compressive strength or dynamic elastic modulus after multiple freezing and thawing according to the standard test method for durability of concrete freeze-thaw resistance and development products, as the evaluation index. It reflects the level of materials and mix proportion, is used to assess the durability and service life of the structure, and serves the design

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