纤维混凝土的低温性能和冻融损伤机理研究

研究了低温环境下(气温变化为-15～5 ℃), 聚丙烯腈(PAN)纤维对混凝土力学性能增长趋势的影响, 探讨了快速冻融试验条件下(-17.5～7.5 ℃) PAN纤维混凝土的抗冻融耐久性, 通过扫描电子显微镜(SEM)观察了PAN纤维在混凝土中的分散性以及纤维和混凝土界面结合状况. 结果表明: 掺入PAN纤维增加了混凝土的含气量、改善了混凝土的微观结构, 提高了混凝土抗裂阻力, 因而有利于混凝土低温环境下的强度增长和提高了混凝土的抗冻融耐久性. 混凝土经受冻融循环破坏实质上是疲劳损伤累积的过程. 通过实验研究和理论分析, 探讨了聚丙烯腈纤维混凝土冻融疲劳损伤的机理, 研究了纤维对混凝土抵抗冻融破坏的影响, 建立了聚丙烯腈纤维混凝土冻融损伤的演变方程.

Property of Fiber Reinforced Concrete at Low Temperature and Its Damage Mechanism under Freezing-thawing Cycles

Effect of polyacrylonitrile (PAN) fiber on mechanical properties of concrete at low temperature (air temperature ranging from -15 to 5 ) was studied, and the durability of freezing-thawing resistance of PAN fiber reinforced concrete was also researched under frequent freezing-thawing-cycle condition (temperature ranging from -17.5 to 7.5 ) with two series of concrete specimens. In the first series, cubic concretes with dimension of 100100100 mm~3 were cast for the measurement of compressive and tensile strengths according to the requirements of GBJ 81-85, while the concrete beams with dimension of 100100500 mm~3 were cast for the measurement of flexural strength and toughness index according to the requirements of ASTM C1018. In the second series, concrete prisms with dimension of 100 100400 mm~3 were cast for the measurement of durability of freezing-thawing resistance according to the requirements of GBJ 82-85. By scan electronic microscope (SEM) photography, the PAN fibers were found to be of well-distributed with short spaces, and be of firm interface combined with concrete. Results of the experiments indicate that adding PAN fibers into concrete leads to high air content, improves microstructure, and increases crack-resistance, which are beneficial to strength and durability of concrete at low temperature. Failure of concrete under freezing-thawing cycles is actually accumulative fatigue damage process. Based upon the experimental study and theoretical analysis, the fatigue damage mechanism of PAN fiber reinforced concrete under freezing-thawing cycles is discussed, the effect of PAN fibers on freezing-thawing resistance of concrete is analyzed, and the damage equation for PAN fiber reinforced concrete under freezing-thawing cycles is set up.