Durability of high-performance concrete to an attack by a mixture of sulfuric acid and acetic acid

Agrifood and industrial effluents, such as acetic acid (CH3COOH) and sulfuric acid (H2S04), are very aggressive media for concrete structures. The mixture of sulfuric and acetic acids (strong acid and weak acid) can be encountered in the environment due to industrial and agrifood effluents; the behavior of cementitious materials in particular high performance concrete under the combined effect of sulfuric (H2S04) and acetic (CH3COOH) acid is not studied until now. In this regard, the present study was devoted to investigating (i) the durability of two high performance concrete (HPC) based on maximum compactness granular mix with and without silica fume to the unique effects of two types of acid, sulfuric acid (H2S04) and acetic acid (CH3COOH) and (ii) the durability of HPC with and without silica fume to the effects of a mixture of 5% H2S04 and 5% CH3COOH at an ambient temperature of 20±2 °C. The chemical resistance to acids was determined by monitoring the relative mass loss, compressive strength loss, and macroscopic changes (altered depth and porosity). A microscopy study including x-ray diffraction and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analysis was also performed. The experimental results showed very good compressive strength of HPC to the acid attack by CH3COOH. The physico-mechanical properties were slightly influenced by the acetic acid attack. In contrast, the durability of HPC to attacks by H2S04 and the mixture of the two acids (CH3COOH) and (H2S04) showed a remarkable modification in the initial properties of the HPC. The deterioration of HPC by the acid mixture was the most serious, with the maximum value of the mass loss reaching 6 times the mass loss due to acetic acid and almost twice the mass loss resulting from the sulfuric acid attack. X-ray diffraction analysis (XRD) showed the presence of calcium sulfate CaS04-2H20 (gypsum) in the samples after the attack by sulfuric acid and after the attack by a mixture of the sulfuric acid and acetic acid.