硝酸侵蚀/碳化交替作用下衬砌喷射混凝土的中性化研究及预测模型

Neutralization Performance and Prediction Model of Lining Shotcrete on Alternation Effects of Nitric Acid and Carbonation

以一般大气环境喷射混凝土衬砌长大公路隧道为工程背景,开展汽车尾气氮氧化物和碳氧化物作用下衬砌喷射混凝土中性化研究。采用硝酸浸泡(pH值为2)法和快速碳化法,开展喷射混凝土硝酸浸泡和快速碳化交替试验,研究硝酸侵蚀、混凝土成型方式及配合比参数对喷射混凝土中性化深度的影响。对喷射混凝土中性化层pH值及NO 3-含量、矿物组成及微观形貌进行表征,研究交替作用喷射混凝土中性化过程和机理。硝酸侵蚀加快喷射混凝土中性化速度。同侵蚀龄期,喷射混凝土中性化深度大于碳化深度,且二者之间的差值随龄期延长逐渐增大。交替作用喷射混凝土相对抗压强度早期增长较慢,后期增长快。喷射混凝土中性化系数与水胶比呈线性增大,与粉煤灰掺量呈二次关系,与钢纤维掺量呈指数关系。本研究建立了考虑硝酸侵蚀、混凝土成型方式及喷射混凝土配合比参数的中性化深度预测模型。

Neutralization process of long highway tunnel lining shotcrete in general atmospheric environment which was corroded nitrogen and carbon dioxide in automobile exhaust was researched.The nitric acid attack and accelerated carbonation alternation experiment were carried out using nitric acid(pH=2)immersion method and accelerated carbonation.The influence of nitric acid attack,formed mothed of concrete and the mixtures on shotcrete neutralization depth were studied.For testing the pH value and nitrate ion content and characterizing the mineral composition and microscopy of neutralization layer,the neutralization mechanism was studied.Nitric acid attack accelerated shotcrete neutralization.With the same equivalent carbonization age,neutralization depth was much more than carbonation depth.And the difference between neutralization depth and carbonation depth increased with increasing of the equivalent carbonation age.Compressive strength growth rate of shotcrete was first low and then very high.The relationship between neutralization coefficient and mixture index which was in terms of water to binder ratio,dosage of fly ash and steel fiber content were subject to liner,parabola,and exponential distribution,respectively,and the neuralization depth prediction model was established.