等强度下混凝土组分对内部相对湿度和自收缩的影响

Influence of concrete constituents on autogenous shrinkage and interior relative humidity of concrete at same compressive strengths

采用自制的试验装置,研究了聚乙烯醇(PVA)纤维、双掺粉煤灰和矿渣以及减缩剂对7d等强度混凝土早龄期自收缩和内部相对湿度的影响规律和机理以及两者之间的关系。结果表明,减缩剂、双掺矿物掺合料和PVA纤维均明显降低了混凝土的自收缩值,以掺减缩剂效果最佳,自收缩72h(3d)前发展速度很快,可达到672h(28d)的80%以上,但掺减缩剂混凝土自收缩发展速度相对较慢,表现出一定的"滞后效应";各组混凝土试件早龄期内部相对湿度均经历了初期的水汽饱和期和随后的逐渐减少期两个阶段,而掺减缩剂混凝土试件表现出很强的保湿能力;与内部相对湿度相对应,混凝土自收缩也表现出明显的两个阶段,有很好的线性相关性,水汽饱和期所测自收缩主要为化学减缩以及由其引发的少量凝缩,取决于减缩剂、PVA纤维和矿物掺合料对混凝土的保湿能力,减少期自收缩主要为自干燥收缩,由胶凝材料的水化程度和速率所决定。

The influence law and mechanism as well as the relationships of polyvinyl alcohol（PVA） fiber,shrinkage reducing admixture（SRA） and the combined addition of fly ash and slag on autogenous shrinkage and interior relative humidity of concrete with 7d same compressive strengths at early ages were studied by the self-made test device.The results indicate that PVA fiber,SRA and the combined addition of fly ash and slag significantly reduce autogenous shrinkage of concrete,the best effect with SRA;the development speed of autogenous shrinkage is very fast before 72h（3d）,more than 80% of the 672h（28d） value,but the development speed of autogenous shrinkage of concrete with SRA is relatively slow,showing some lag effect;interior relative humidity of concrete at early ages has undergone the initial vapor saturated stage and the subsequent reduction stage,the concrete with SRA showing a strong moisturizing capacity;autogenous shrinkage of concrete also shows 2 distinct stages,corresponding with interior relative humidity,both showing significant linear correlation;the measured autogenous shrinkage of the vapor saturated stage mainly is chemical shrinkage and small amount of settlement shrinkage,depending on the moisturizing capacity of PVA fiber,SRA and mineral admixtures on concrete and autogenous shrinkage of the reduction stage mainly is self-desiccation shrinkage,depending on the hydration degree and rate of cementitious materials.