早期受冻混凝土服役性能损伤探究

Damage Study on Service Performance of Early Frozen Concrete

通过不同起冻时刻早期受冻混凝土服役性能的测试,分析了起冻时刻对混凝土损伤形态、强度损失、相对动弹性模量、渗透性及孔隙结构的影响规律及影响机理.结果表明:起冻时刻对混凝土服役性能的影响程度表现为2.0h受冻最显著,0.5h受冻与8.0h受冻损伤程度相当、次之,1,3d受冻时损伤程度最小且随着起冻时刻的推迟损伤程度减轻;受冻混凝土劈拉强度损失最显著,相对动弹性模量损失次之,抗压强度损失最小;3d受冻试件的抗渗性略差于未冻混凝土,1d受冻试件更差,而0.5,2.0,8.0h受冻试件最差,甚至超出AutoClam设备的测试范围.随着起冻时刻的推迟,终凝后受冻混凝土的孔隙结构趋近于未冻混凝土;初凝前受冻混凝土部分损伤可修复,浆体自身、浆体与粗骨料间有肉眼可见裂缝,孔径0~0.06mm的弦长频率明显降低,各孔径梯度的含气量(体积分数)均不同程度增大;初凝后终凝前受冻混凝土浆体自身、浆体与粗骨料间均有明显裂缝,细骨料颗粒显露明显,孔径1.70~4.00mm的弦长频率、孔径2.00~4.00mm的含气量明显增大.

The influence and damage mechanism of frozen up time on the damage mode,compressive strength,splitting tensile strength,relative dynamic elastic modulus,permeability and pore structure of early frozen concrete were studied by the service performance test for the early frozen concrete with different frozen up times.The results show that the influence is the most significant for the concrete with frozen up time of 2.0 hours,and the influence is next to that for the concrete with frozen up time of 0.5 and 8.0 hours.Moreover,the damage degree of frozen concrete after final set（1,3 d）is the slightest and reduces gradually with the increasing frozen up time.In addition,the degradation of splitting tensile strength is the greatest,the reduction of dynamic elastic modulus takes the second place and the degradation of compressive strength is slightest.Furthermore,the anti-permeability of concrete with frozen up time of 3 days is slightly worse than that of non-freezing concrete,and the anti-permeability of concrete with frozen up time of 1 day is worse than that of 3 days,the anti-permeability of concrete frozen at 0.5,2.0 and 8.0 hours are the worst and even beyond the test range of AutoClam equipment.The pore structure of concrete frozen after final set is close to that of non-freezing concrete with increasing frozen up time.With regard to the concrete frozen before initial setting time,the frost damage can be partially repaired,some visible cracks appear in the paste or paste-aggregate interface,the chord length frequency of 0-0.06 mm reduces significantly and the air contents（by mass）under different chord lengths increase in varying degrees.For the concrete frozen between initial set and final set,notable cracks at the paste or paste-aggregate interface and fine aggregate particles are observed,moreover,the chord length frequency of 1.70-4.00 mm and the air content of 2.00-4.00 mm increases significantly.