Study On The Evaluation Methods And Influencing Factors Of Cracking Resistance Capability Of Concrete

Cracking is a key factor influencing the durability of concrete structure. Theinvasion of harmful ions through the cracking of concrete leads to a damage ofmaterial microstructure and corrosion of rebar, which has a harmful effect on thedurability of concrete structure. The tensile stress caused by an autogenousdeformation of concrete is a main factor leading to the cracking of concrete. In thispaper, the crack resistance factor K was proposed to evaluate the crack resistanceperformance of concrete under restrained condition. The influence of fly ash andexpansive agent on the crack resistance performance of concrete under the conditionof different temperature and humidity was studied using improved ring test. The maincontents and conclusions are listed as follows:1. The mechanical and deformation properties of concrete of different strengthgrades were studied. The crack resistance factor K was proposed based on mechanicaland deformation parameters. The crack resistance factor K was used to evaluate thecrack resistance performance of concrete of different strength grades. The early crackresistance ability of concrete becomes poor with the increase of its strength grade.2. The cracking properties of concrete of different strength grades were studiedusing improved ring test. The cracking time of concrete can be measured accuratelythrough the improved ring test. The results show that visible cracks appear early withthe increase of strength grade of concrete, which implies that the crack resistanceability of concrete becomes poor with the increase of strength grade. This conclusionis consistent with that drawn by crack resistance factor K method.3. The influence of fly ash and expansive agent on the crack resistanceperformance of C30concrete was studied using crack resistance factor K as the indexof crack resistance ability. The results show that addition of fly ash decreases theearly strength, drying shrinkage, and elastic modulus of concrete. Overall, addition offly ash is benefit to the crack resistance ability of concrete. The appropriatepropertion of expansive agent decreases the shrinkage of concrete and improves its strength, which is benefit to the crack resistance ability of concrete. The effect ofcomposite addition of fly ash and expansive agent is poor. As to the concretecontaining high content of fly ash, the addition of expansive agent decreases the crackresistance ability of concrete sharply.4. The influence of fly ash and expansive agent on the cracking resistanceperformance of concrete under the condition of different temperature and humiditywas studied using ring test. The results show that the influence of fly ash andexpansive agent on the cracking resistance performance of concrete changes with thetemperature and humidity condition. The addition of fly ash improves the crackresistance ability of concrete in the moderate environment, but decreases the crackresistance ability of concrete by accelerating its cracking in the hot and dryingenvironment. The appropriate addition of expansive agent can delay or prevent thecracking of concrete. However, the composite addition of expansive agent and highvolume fly ash decreases the crack resistance ability of concrete.