Study on the Discussion and Improvement Methods of Early Cracking Tests of Concrete

ABSTRACT The standard GB/T 50082-2009, Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete, specifies the requirements for early cracking tests of ordinary concrete in Chapter 9. However, because of the lack of detailed specifications in the standards, the experimental procedures in existing related papers vary; moreover, since wind is divergent, if there is no shielding device to restrict the wind, the test accuracy will significantly decrease, adding unstable factors to the test results. To address the aforementioned issues, this paper first analyzes the cracking tests in existing literature and finds that researchers have varying degrees of difference in the specific settings of test conditions, leading to discrepancies in test results. Therefore, this paper studies the impact of fan size, wind speed, gas duct size, and the distance between the fan and the concrete specimen on wind speed and wind surface. The following conclusions were drawn from the aforementioned experiments: a fan diameter of 750 mm, a total length of 1,600 mm for the gas diffuser (a main body length of 1,300 mm + an air inlet shroud length of 300 mm), a main body width of 900 mm, and a front-side air inlet diameter of 750 mm can make the fan’s airflow converge and stabilize uniformly, and suppress some turbulence generated by the wind blowing toward the concrete specimen; a distance of 300 mm between the concrete specimen and the air inlet side of the gas diffuser (600 mm from the entire device’s fan air inlet) can help mitigate wind speed; a fan wind speed of 8 m/s can ensure that the wind speed is within 5 ± 0.5 m/s at 100 mm over the upper surface of the concrete specimen. The aforementioned experimental conclusions provide strong practical support for standardizing early cracking tests of ordinary concrete.