不同水胶比高性能混凝土内部自干燥与干湿循环影响试验

Experiment on Self-Drying and Dry-Wet Cycle of High Performance Concrete under Different Water-Binder Ratio

混凝土内部相对湿度是影响混凝土性能状态的重要因素。为研究不同水胶比、不同粉煤灰(FA)掺量对高性能混凝土自干燥效应的影响以及干湿循环过程中混凝土内部相对湿度(IRH)变化规律,首先对4种不同配合比的混凝土试件采用双层锡箔纸密封包裹处理,并对其自干燥现象持续70 d监测,然后对不掺粉煤灰0. 3水胶比的混凝土试件进行不同时段的浸水和自然干燥多次循环试验,模拟混凝土在干湿循环历程中其IRH变化规律。试验表明:在密封状态下,高性能混凝土内部相对湿度变化存在两个时期,即湿度饱和期(相对湿度100%)和湿度下降期;相同水胶比下,随着粉煤灰掺量的增加,混凝土的湿度饱和期增长,自干燥作用较缓慢,掺量35%FA的混凝土尤为明显; 0. 4水胶比掺35%FA的混凝土试件内部相对湿度基本无变化,几乎不存在自干燥现象。在干湿循环过程中,湿度上升(浸水)的速率明显大于湿度下降(干燥)的速率,随干燥时间增长,其内部相对湿度下降的速率逐渐变慢;随着干湿循环次数的增加,混凝土内部相对湿度变化速率逐渐减小。

The internal relative humidity of concrete plays an important role in the performance of concrete.Self-drying of high performance concrete is related to water-binder ratios and fly ash(FA)dosage.Whereas the change rule of internal related humidity(IRH)of concrete under wet-dry cycle is important.The self-drying of concrete specimens with four water-binder ratios,which were wrapped with tin foil,was monitored for 70 d.Then wet-dry cycle test of concrete specimen with the water-binder ratio of 0.3 was conducted to investigate the change rule of IRH of concrete under soaking and naturally drying.The experiment results show that internal relative humidity of high-performance concrete in the sealed state has two periods,namely the humidity saturation period(relative humidity 100%)and the humidity drop period.With the same ratio of water to cement,the increase of fly ash content,the humidity saturation period of concrete increases,the self-drying effect slowly,and the concrete with 35%of concrete content is particularly noticeable.The concrete specimens which 0.4 with water-binder ratio mixed with 35%fly ash is basically unchanged,there is almost no self-drying effect.Under dry-wet cycle environment,the rate of increase in humidity(water immersion)is significantly greater than the rate of decrease in humidity(dryness),as the drying time increases,the rate of decrease of its internal relative humidity gradually slows down.With the increase in the number of wet-dry cycles,the rate of change of the relative humidity inside the concrete gradually decreases.