Experimental Study On Fracture Properties Of Concrete Under Simulated Acid Rain Environment

With the acceleration of the country’s industrialization process,the content of acid-causing gases such as sulfur dioxide SO₂,nitrogen oxides NO_x,and ammonia NH₃ in the atmosphere has gradually increased,resulting in a continuous decrease in the p H value of atmospheric precipitation,thereby forming acid rain.Due to the existence of micro-cracks in concrete,it is more likely to occur brittle fracture phenomenon under the deterioration of acid rain corrosion.At present,many scholars study the mechanical properties of concrete after acid rain erosion,but there are few experimental study on fracture properties of concrete under simulated acid rain environment.Therefore,this paper studies the influence of acid rain corrosion on the mechanical properties and fracture properties of concrete through three aspects:basic mechanical performance test,three-point bending beam fracture test and theoretical calculation of K_R resistance curve.The main research works and conclusions are as follows:（1）Experimental study on basic mechanical properties of concrete under simulated acid rain environmentThe mechanical properties of reference specimens,long-term immersion specimens,and dry-wetting cycle specimens were measured respectively at curing of 28 days,after corrosion time of 21,42,63 and 84 days.The variation of cubic compressive strength,split tensile strength,elastic modulus,and axial compressive strength with corrosion time and corrosion depth are studied,and mechanical parameters are provided for subsequent fracture properties calculations.The test results show that the mechanical properties of the dry-wetting cycle specimens first increase and then decrease with the increase of corrosion time and corrosion depth,and there is an obvious enhancement stage.The long-term immersion specimens basically show a downward trend with the increase of corrosion time and corrosion depth.Long-term immersion specimens deteriorate more than dry-wetting cycle specimens.（2）Experimental study on fracture properties of concrete under simulated acid rain environmentThe three-point bending beam tests is used to study the effect of corrosion time and corrosion depth on the fracture properties of reference specimens,dry-wetting cycle specimens,and long-term immersion specimens,and fracture parameters such as load-crack mouth opening displacement（P-CMOD）curve,load-vertical displacement（P-δ）curve,crack tip opening displacement（CTOD）,the initial cracking load were measured respectively at curing of 28 days,after corrosion time of 21,42,63 and 84 days.The test results show that the ratio of the initial cracking load P_ini to the peak load P_max of the corrosion specimens gradually increased with the increase of the corrosion time,and the brittleness of concrete increased.The unstable fracture toughness and fracture energy of the corrosion specimens decreased significantly compared with the reference specimens when the corosion time was84 days.When the corrosion depth was shallow,the degradation degree of long-term immersion specimens was greater than that of dry-wetting cycle specimens.With the increase of corrosion depth,dry-wetting cycle specimens deteriorated greatly.（3）Study on K_R resistance curve of concrete three-point bending beam under simulated acid rain environmentThe unsteady expansion K_R resistance curve of the three-point bending beam based on the cohesive force was calculated by Matlab,and the influence of the simulated acid rain corrosion time on the K_R resistance of concrete and the length of the fracture process zone was studied.The results show that the K_R resistance of the dry-wetting cycle specimens increases first and then decreases with the increase of the corrosion time.The K_R resistance of the long-term immersion specimens first maintains stable and then gradually decreases with the increase of the corrosion time.The length of the complete fracture process zone changes little under acid rain corrosion.