Size Effect Of Early Age Disturbance On Concrete Performance

In traffic repair operations,pavement cutting operations,slipform construction operations and blasting operations,the newly poured concrete may be disturbed by the vibration of the surrounding environment,the disturbance will affect the hydration reaction,and the internal microcracks will increase,causing mechanical properties.With durability can decline.At the same time,concrete materials are quasi-brittle materials,and there are size effects.At present,the related research on concrete disturbance is based on the same specimen size,and the influence of size is not considered.Based on this,in order to study the relationship between the degree of influence of disturbance on the performance of concrete and the size of the specimen,this paper combines experimental research and theoretical analysis to select three types of specimens(A: 70.7 mm × 70.7 mm × 70.7 Mm,B: 100 mm × 100 mm × 100 mm,C: 150 mm × 150 mm × 150 mm),applying a 30-minute vibration disturbance to the concrete during the hardening period with a penetration resistance of 10.7 MPa to 14.8 MPa.Crack tensile strength,saturated surface dry water absorption and acoustic emission ringing count were used as evaluation indexes,and the size effect of concrete performance affected by disturbance was studied.The experimental results show that the vibration disturbance on concrete specimens in early age decreases the 28-day compressive strength and splitting tensile strength.The compressive strength of A,B and C specimens decrease by 5.95%,7.42% and 10.49%,respectively.The splitting tensile strength decreases by 15.19%,16.68% and 19.02%,respectively.The larger the size of the specimens are,the more the compressive strength and splitting tensile strength of the disturbed concrete decrease.The size effect coefficient of splitting tensile strength is 0.81,0.88 and 1.00,respectively.There is obvious size effect on the strength of the disturbed concrete.The early age disturbance increases the internal cracks of concrete and the dry water absorption of saturated surface.The dry water absorption of saturated surface of A,B and C specimens increase by 7.59%,11.30% and 15.13% respectively in 28 days.The larger the specimen size is,the larger the change of water absorption is.The size effect coefficients of dry water absorption of saturated surface are 0.49,0.75 and 1.00,respectively.The size effectof disturbance on dry water absorption of saturated surface is significant.The results of ultrasonic testing show that the difference of ultrasonic wave velocity between uninterrupted and disturbed specimens A,B and C decrease with the increase of age,And the relative dynamic modulus of elasticity increase from 0.9478,0.9620 and 0.9256 to0.9813,0.9940 and 0.9868.It show that with the increasing of age,the internal damage of the early-age disturbed specimens will has a certain degree of self-healing phenomenon.In uniaxial compression tests,the acoustic emission characteristics of concrete specimens with different sizes are different.In the compaction stage,the difference of cumulative ringing counts of A,B and C specimens is 340,474 and 628,and the difference of average change rates is 13.82,15.92 and 19.61,respectively.There is obvious size effect.The test can provide some theoretical support for the performance evaluation of the disturbed concrete.And the variation rate and size effect coefficient of each physical quantity obtained can provide reference for engineering practice.