Effect Of Early Disturbance On Properties Of Concrete

At present, a large number of infrastructure have being constructed. In order to ensure the continuity and progress of the whole project, blasting excavation, piling and other construction vibration were often carried out in parallel with pouring concrete, leading construction vibration inevitably exists with the concrete structure. Impact, vibration and other disturbances will damage the concrete which have just completed and not stabled, resulting in some unbridgeable microcracks, adversing effects on the strength and durability of concrete, because of the low early age concrete strength. Therefore, to study the impact of early disturbance on concrete performance is necessary.This paper focuses on the issue of disturbance between initial setting to final setting of C40 concrete. The concrete were applied 10,20,30,40 min sinusoidal vibration at different ages with using horizontal vibration table, vibration frequency is 15 Hz and maximum speed is 37.7cm/s. To characterize penetration disturbed age by resistance, the effect of disturbed age and disturbing time on concrete strength were compared and analyszed. Combined with ultrasonic detection technology, the damage of concrete after being early disturbanced was explored. Rebound values of disturbed concrete were studied, the relevance between compressive strength and rebound value were analyzed.The results show that the disturbance had the biggest influence on the concrete when the concrete penetration resistance value is 10.7 to 14.8MPa, the compressive strength and flexural strength loss rate were over 20%, and late damage increased with 6% damage evolution value. The disturbance on the initial setting and final setting had smaller effect on concrete, the strength loss was about 10% and late damage did not exacerbate. The strength loss of concrete increased with the extension of vibration duration and there was a threshold of the disturbance energy. Strength reduced more gently, the strength loss was about 10% and without early damage when the vibration time is less than 30 min. The compressive strength loss was 20%, and the flexural strength loss reached 30% when the vibration time is 40 min. As the same time, the early damage was maxium with 5% damage value, but the damage exacerbate was minimum. The rebound value of disturbed concrete was not less 90% than the reference group, the rebound value were increased by 15% when the concrete penetration resistance value is 14.8 to 19.6MPa, show that disturbance increased rebound value. Because the transition zone between cement paste and aggregate in concrete was affected by early disturbance, making the correlation of between disturbed and compressive strength of concrete was not significant. The rebound value did not reflect the degree and laws of disturbance effect on the concrete strength, rebound method is not suitable for detecting disturbed concrete strength.