An Experimental Study On Carbonation Of Shotcrete Under Benging Loads

Shotcrete has been widely used. in underground engineering, geotechnicalengineering, thin-walled structural engineering, repair reinforcement works, fireprotection engineering works in recent years. Under normal atmospheric conditions,sprayed concrete not only suffer from CO2erosion, and often bear the load of the role,coupled with the environment of this load will further accelerate the degradation of thematerial damage. This article has been carrying shotcrete rapid carbonation test. Themain contents are as follows:(1) A loading device which is suitable for the test in this paper is designed based onthe devices adopt at home and abroad and is used to finish the experiment.(2) The carbide development rule of concrete is analysed from three statesconcluding unstress state，tensile stress state and compressive stress state and drawsconclusions including：carbonation depth is proportional to the square root of thecarbonization time; the carbonation depth under the tensile stress and compressive stressstate is bigger, and the higher the stress level, the greater the carbonation depth；Underthe same stress level, the carbonation depth under tensile stress is bigger than that underthe compressive stress；The growth rate of carbonation depth under tensile stress isbigger than that under the compressive stress and the gap is bigger as stress level rises.At last， the relationship between stress influence coefficient and stress level isestablished. The change of the concrete carbonization performance because of theconstruction technology and steel fiber is discussed and draws conclusions including：Carbonation resistance of sprayed concrete is better than that of ordinary concrete no matter whether there is a stress；Carbonation resistance of steel fiber reinforced concreteis better than the concrete without steel fiber under same conditions.(3) The rupture strength of concrete before and after carbonization is analyzed andthe influence of construction technology and steel fiber is discussed，it is concluded thatthe rupture strength of concrete presents the overall downward trend with theprolongation of the carbide. The declining rate is relatively bigger at the beginning ofthe test and gradually slow down or even changes nothing in the latter period. As to therupture strength of concrete before and after carbonization，the sprayed concrete islower than that of ordinary concrete and steel fiber reinforced concrete is higher than theconcrete without steel fiber.(4) The carbonation depth prediction model of sprayed concrete under load isestablished combined with the experimental results, which provides an importantreference for the existing buildings (structures) durability assessment, repair,reinforcement and durability design.