دانلود رایگان مقاله لاتین سینتیک خوردگی سیمان پرتلند از سایت الزویر
عنوان فارسی مقاله:
مطالعه محلی از سینتیک خوردگی سیمان پرتلند سخت شده تحت حمله اسید
عنوان انگلیسی مقاله:
Local study of the corrosion kinetics of hardened Portland cement under acid attack
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
The extension of the durability of concrete buildings necessitates the understanding of its limiting factors, like creep, crack propagation by water freezing, degradation due to aggressive environments, etc. Among chemical attacks reducing the service life of construction materials, acid attack is particularly detrimental to materials as alkaline as cementitious materials. Indeed the hydration products of cement are neutralized by protons, inducing dissolution and precipitation of new salts, destroying the microstructure of this hydraulic binder. The mechanisms of action of acid reagents on concrete, mainly originating outdoor in air pollution (dry deposition) and acid rains (wet deposition), have been investigated for a few decades, and the basic features are now identified [1–3]. These modes of action have also been studied indoor in the case of industrial constructions involving acidic environments [4,5]. These mechanisms, including heterogeneous reactions, ion substitution, mass loss, diffusion of solution in pores, strain, porosity evolution, leaching, etc. are complex, interact with each other, and lead to a loss of strength and stiffness of the material. The investigation of acid attack on cement-based materials has been performed either with field measurements in urban areas [6,7],or with laboratory measurements. The latter have used either simulated acid rain solutions [7–9], or concentrated acid aqueous solutions [10], in order to accelerate the reactions. Sometimes, different reagents are tested simultaneously or alternatively [4,10]. In the course of these studies, three parameters are generally evaluated: the chemical composition of the runoff solution, the change of mass or size of the samples, and their strength decrease. Due to the complexity of the phenomenon, a quantity is generally not measured, although being the fundamental parameter of chemical kinetics: the reaction rate. Up to now, models of degradation of concrete under acid attack use empirical dissolution laws [11]. We think that the knowledge of well-defined reaction parameters may help in the elaboration of the predicting tools of acid corrosion. As the reaction of dissolution is always combined with other phenomena like precipitation, flow of the solution, diffusion of dissolved species, etc. in standard acid attack setups, these experiments are not usable for pure corrosion rate measurement. Therefore we propose in this article an original methodology, using holographic interferometry, to access to the reaction rate of cementitious materials in acid solutions. We provide values of the pure dissolution rate of hardened Portland cement in three strong acids — nitric, sulfuric and hydrochloric acids — at various pH as first examples of measurements. Our investigation of hydrated cement acid attack follows a nonconventional procedure, focusing on one single step of the phenomenon, namely on the first one, dissolution. Accordingly a comparison of our results with standard studies on the resistance of
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کلمات کلیدی:
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