A New Smart Additive of Reinforced Concrete Based on Modified Hydrotalcites: Preparation, Characterization and Anticorro
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A New Smart Additive of Reinforced Concrete Based on Modified Hydrotalcites: Preparation, Characterization and Anticorrosion Applications Zhengxian Yang1, 2, Hartmut Fischer3 and Rob Polder2, 4 1 Materials innovation institute (M2i), 2600GA Delft, The Netherlands 2 Section of Materials and Environment, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628CN Delft, The Netherlands 3 TNO Materials Performance, 5612AP Eindhoven, The Netherlands 4 TNO Building Materials, 2600AA Delft, The Netherlands ABSTRACT A carbonate form of Mg-Al-hydrotalcite and its p-aminobenzoate (pAB) modified derivative (i.e.,Mg(2)Al-pAB) were synthesized and characterized by means of XRD and FT-IR. The anticorrosion behavior was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and chloride-exchange experiments. The preliminary results shown in this study demonstrated that ion-exchange indeed occurred between chlorides and the intercalated pAB anions in Mg(2)Al-pAB structure, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released inhibitive pAB anions were found to exhibit the envisaged inhibiting effect and caused corrosion initiation of the steel shifting to a higher chloride concentration than without the modified hydrotalcites. INTRODUCTION Corrosion of the reinforcing steel is a major threat to the durability of concrete structure. Normally, steel in concrete is protected from corrosion by a passive film formed in the high alkalinity of the concrete internal environment. However, this protective film can be destroyed by the ingress of chlorides and carbonation of concrete. In normal practice, carbonation is mild and relatively easily avoided compared to chloride-induced corrosion [1]. In the last two decades, more research interest has been attracted in developing new or modified compounds able to prevent or stop corrosion of reinforced concrete. Among them, modified hydrotalcites (MHTs) may represent a promising option for use in concrete as a new type of functional additive [2, 3]. MHTs are anion-exchangeable substances consisting of stacks of positively charged mixed-metal hydroxide layers between which negatively charged anionic species and water molecules are intercalated. The MHTs’ structure can be represented by a general formula [MII1-xMIIIx(OH)2]x+[(An-x/n)]x-·mH2O, where MII and MIII are di- and trivalent metals respectively, and An- is an exchangeable interlayer anion that could be inorganic or organic species with valence n. The key feature of MHTs is their high anionic exchange capacity which makes exchange of the interlayer ion by a wide range of anions versatile and easily achieved [4, 5]. Hydrotalcite or hydrotalcite-like phases have been found in hydrated slag cements, which are known to bind more chloride ions than pure Portland cements [6, 7]. For the envisaged use as an additive to concrete against chloride attack, certain inhibitive inorganic or organic anions could be intercalated
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