The Laboratory Test Research Of Tunnel Shotcrete's Frost Resistance

Shotcrete has a wide range of applications in a variety of civil engineering field,and it is main bearing units of tunnel structure in tunnel project.Currently, frost resistance in concrete terms, has done a lot of research and has achieved fruitful results at home and abroad, but frost resistance of sprayed concrete are relatively few. Therefore, this article uses the theoretical analysis and laboratory test methods, conducted a study on frost resistance of C20 and C25 shotcrete, mainly the following results:1. After 60 freeze-thaw cycles, the specimen surface of C20 sprayed concrete flaks proliferately, dynamic elastic modulus decreases more obvious, most of the specimen is close to the damage. After 100 freeze-thaw cycles, the specimen surface flaking of C25 sprayed concrete began to proliferate, dynamic elastic modulus of decline is more obvious, most of the specimen is close to destruction. Thus, C25 sprayed concrete can withstand more freezing times than C20 sprayed concrete, but the frost resistance are more general.2. Initial dynamic elastic modulus of C20 sprayed concrete specimen averaged 34.52GPa, dynamic elastic modulus and freeze-thaw number of linear regression relationship as E =-0.215N+34.94 (E is dynamic elastic modulus, N is times of freeze-thaw), and C25 sprayed concrete respectively 39.69GPa and E=-0.135N+39.55. Suffice it to say, with the increasing number of freeze-thaw, dynamic elastic modulus of C25 sprayed concrete decreases more slowly than C20 sprayed concrete, and the initial dynamic elastic modulus is bigger, signifying frost resistance of C25 sprayed concrete is better than C20 sprayed concrete.3. Quality loss of C20 sprayed concrete samples and freeze-thaw number of linear regression relationship isω=0.1975N-0.346 (ωis the quality loss, N is times of freeze-thaw), and C25 sprayed concrete asω=0.1925N-0.523. Suffice it to say, with the increasing number of freeze-thaw, C20 sprayed concrete quality loss rate of increase in speed is almost the same with C25 sprayed concrete, and in most early freeze-thaw test specimen are present the phenomenon of increasing as the freeze-thaw cycle of their quality, thereby increasing the quality of this indicator cannot be precisely reflect C20 and C25 sprayed concrete frost resistance of the differences.Research findings show: cold regions tunnel project, C20 sprayed concrete frost resistance of poor durability to the tunnel structure, as well as security has stronger impact, and frost-resistance of C25 sprayed concrete is good, it has significance and utility value to the tunnel design.