自密实混凝土早期收缩开裂影响因素分析与评价

Analysis and evaluation of shrinkage cracking of self-compacting concrete at early age

研究了矿物掺合料、水胶比和胶凝材料用量对自密实混凝土早期收缩开裂性能的影响,采用椭圆环约束收缩试验方法直接评价自密实混凝土砂浆的早期收缩开裂趋势,并结合自由收缩试验综合评价自密实混凝土的收缩开裂性能。试验表明:粉煤灰的掺入显著降低了自密实混凝土砂浆早期干燥条件下的约束开裂敏感性和混凝土自由收缩速率及收缩值;与单掺20%粉煤灰试样相比,复掺样中5%硅粉的掺入增加了粉煤灰砂浆早期干燥条件下开裂敏感性,但在复掺体系中加强早期养护有利于掺硅粉自密实混凝土抗裂性的提高;在0.3、0.35、0.4三个不同水胶比体系中,水胶比较大自密实混凝土砂浆在早期干燥条件下表现出易开裂的特征,应结合体系中实际水灰比、矿物掺合料组分以及养护条件等因素来综合评价混凝土收缩开裂性能;在本试验三组不同用量多元胶凝材料体系中,随着胶凝材料用量的降低,开裂敏感性和自由收缩量均降低,当胶凝材料总量降到450kg/m3时,砂浆初始开裂时间显著延长。

The influence of mineral admixtures, water-binder ratio and cementitious material content on shrinkage cracking of self-compacting concrete （SCC） at early age were investigated by using a new ellipse-ring shrinkage cracking testing apparatus to evaluate cracking sensitivity of mortar sieving from SCC.Meanwhile, free shrinkage of SCC was also measured to investigate the effect of them on shrinkage cracking on SCC. The results showed that the cracking sensitivity of mortar at cured under drying-stored condition early age at was reduced greatly incorporating with FA, the shrinkage rate and value of SCC were also reduced.Compared to sample containing 20% FA,the cracking sensitivity of multiple-adding of 20% FA and 5% SF was increased.However, fully curing at early-age is important to SCC incorporating with SF.The mortar sample was prone to cracking with the increase of wfo under the experimental condition of this test.Besides, the cracking sensitivity was reduced with the decrease of binder content, especially when it reached 450 kg/m^3, the initial cracking time was delayed markedly.