Effect of sulfate solution concentration on the deterioration mechanism and physical properties of concrete

Effects of sodium sulfate solution concentration and erosion age on axial compressive strength, sulfate ion distribution, dynamic elastic modulus, electrochemical performance and load-displacement curves of concrete were investigated. Based on the chemical thermodynamics theory, the internal relationship between sodium sulfate solution concentration and sulfate products was deduced. The porosity and pore distribution, phase composition, Nyquist spectrum, micro structure and morphology of concrete before and after sulfate attack were also analyzed by different testing instruments. The results indicate that the axial compressive strength and load-displacement curves of concrete first increase and then decrease with increasing sodium sulfate solution concentration. With increase of erosion age, the lower the strength grade of concrete is, the larger the reduction of axial compressive strength of concrete attacked by sulfate. The main products of sulfate attack are claviform ettringite and lamellar gypsum, which play double effects on performance of the concrete. The sulfate ion content in concrete surface increases with the increasing of sulfate solution concentration, and it also increases first and then decreases until to a certain value with depth. The transverse and longitudinal dynamic elastic moduli of concrete attacked by sulfate solution change with increasing of the sulfate solution concentration. The envelope curves of the waveform change of transverse and longitudinal dynamic elastic moduli of concrete can be represented as exponential function. The change of electric resistance of pore solution and charge-transfer resistance increases with sulfate solution concentration, which indicates the micro structure of concrete specimens are degraded by sulfate attacked. (C) 2019 Elsevier Ltd. All rights reserved.