冻融循环对混凝土碱硅酸反应二次损伤的影响

Influence of freeze-thaw cycles on secondary deterioration of concrete caused by alkali silica reaction

研究了早期受到不同程度冻融循环作用的混凝土在进一步受到碱硅酸反应作用时的损伤破坏特点和规律.混凝土试件先进行冻融循环30次和60次,然后在60℃的1molNaOH溶液中浸泡进行加速碱硅酸反应试验,每周一次监测混凝土的超声速度,并用其转换的相对动态弹性模量作为混凝土内部损伤的指标.试验结果表明早期冻融循环会成为混凝土进一步碱硅酸反应损伤的诱因,从而加速混凝土的损伤失效过程;早期冻融损伤越严重,后期碱硅酸反应损伤也越严重.与未预先受到冻融作用的混凝土试件相比,除了早期损伤速率加快之外,损伤的规律性基本没有变化.早期冻融循环的作用相当于混凝土在后期受到更严重的碱硅酸反应作用.早期损伤形成混凝土内部缺陷以及改变混凝土的内部结构,是产生这些影响的原因.

Experiments were conducted for concrete suffered from various freeze-thaw cycles to investigate their damage characteristic under subsequent effect of alkali silica reaction （ASR）. Both fast freeze-thaw cycles and accelerated ASR were carried out. Concrete specimens were undergone 30 and 60 freeze-thaw cycles first, then were immerged into 1 mol NaOH solution at 60℃ to suffer from ASR. Once a week, the ultrasonic velocity of specimens were measured and transferred into relative dynamic modulus to represent the deterioration of concrete. Experimental results show that initial freeze-thaw cycles induce the subsequent ASR damage and accelerate the deterioration of concrete. The severer the initial frost damage, the severer the later ASR damage. Compared with specimens without initial frost effect, the damage regularities show little change, except the acceleration of the damage rates. The effect of initial freeze-thaw cycles is equivalent to a severer ASR effect later on. The formation of internal defects and change of internal structure caused by the initial effect accounts for the results.