喷射混凝土抗冻性及冻融损伤力学行为实验研究∗

摘要

In order to systematic research the frost resistance of shotcrete,the rapid freezing and thawing experi-ment of shotcrete with and without steel fiber was done by using quick frost method.Meanwhile,compared with forming concrete by the same mixture,the different of frost resistance of shotcrete was studied.And then, the microstructure of specimen after freeze-thaw cycle was observed and the deterioration mechanism of me-chanical properties was also analyzed.The result showed that with increasing number of freeze-thaw cycle,the relative dynamic of elasticity,mass loss rate,cubic compressive strength and splitting tensile strength was downtrend and the attenuation degree of frost resistance of forming concrete was reduced quickly than shotcrete. The micro-pore internal specimen was connected and extended into micro-creck.At the same time,the structure of CSH gel was loose and lost under the frost-heaving force and osmotic pressure which from supercooled water migration.The micro-pore structure of specimen was significantly improved and the frost resistance was in-creased by steel fiber addition.Simultaneously,the concentric axial compression experiment of specimens after the number of freeze-thaw cycles was 50,100,150 and 200,respectively and the effect of stress-strain curve by freezing and thawing damage was analyzed.With freezing and thawing damage intensificated,the elastic modu-lus (ED)and peak stress (σc)was decreased and the peak strain (εc)and ultimate strain (εc,u)was increased. Under the same number of freeze-thaw cycle,steel fiber reinforced shotcrete had larger ductility and toughness than ordinary shotcrete.%为系统研究喷射混凝土抗冻性能,采用快冻法,对普通喷射混凝土及钢纤维喷射混凝土进行快速冻融实验,并与同配合比模筑混凝土进行对比,研究模筑混凝土与喷射混凝土抗冻性能差异；而后对冻融循环后试件进行微观结构观察,分析其性能劣化机理。结果表明,随着冻融循环次数增加,试件相对动弹性模量、质量损失率、立方体抗压强度及劈裂抗拉强度呈下降趋势,且模筑混凝土性能衰减程度远大于喷射混凝土。而此时试件内部微气孔相互连通继而发展成为微裂缝,凝胶体在冻胀压力及过冷水渗透压作用下结构酥松且部分流失,进一步加剧试件性能劣化速度；钢纤维的加入可显著改善喷射混凝土内部微观孔结构,提高其抗冻性能。同时,对冻融循环50,100,150及200次后试件进行轴心抗压强度实验,分析冻融损伤对试件应力-应变曲线的影响。随着冻融损伤的加剧,试件弹性模量及峰值应力减小,峰值应变和极限应变增大,应力-应变曲线趋于扁平。经相同冻融循环次数作用时,钢纤维喷射混凝土峰值应变和极限应变增大,说明钢纤维的掺入可显著提高喷射混凝土延性及韧性。