Impact of NaCl on deterioration of hardened cement paste due to sulfuric acid attack

In sewage pipelines, H₂SO₄ is formed by the action of H₂S gas generated from sewage and bacteria inhabited on the walls, resulting in H₂SO₄ attack on the concrete above the sewage level. In Osaka city, Japan, it was found that the deterioration degree of sewage pipelines became greater in coastal areas. In the coastal areas, the groundwater derived from seawater flowed through the joints of the sewage pipes. We assumed that seawater with high Cl content may accelerate the deterioration of concrete by adding the effect of NaCl to H₂SO₄ attack. In this study, hardened cement paste specimens were immersed in a solution of 0.1 mol/L H₂SO₄ mixed with NaCl to clarify the effect of NaCl, the main component of seawater, on H₂SO₄ attack of concrete. The specimens were analyzed using EPMA, XRD, and FT‐IR after the immersion test, and the immersion solution was analyzed using ion chromatography. The deterioration degree of the specimens increased as the amount of NaCl added to H₂SO₄ increased. Relatively more gypsum was formed and delaminated under the condition of 2 % Cl addition. It has been reported that HCl causes the formation of highly soluble salt (CaCl₂) and the dissolution of Ca. The addition of NaCl to H₂SO₄ is assumed to accelerate the deterioration degree of hardened cement paste by adding the effect of HCl acid.