Durability evaluation of cement exposed to combined action of chloride and sulphate ions at elevated temperature: The role of limestone filler

• Limestone filler role on cement durability exposed to SO4/Cl− ions, at elevated temperature.
• Limestone presence led to less expansion and higher compressive strengths.
• Non-expansive Friedel’s salt was formed in chloride baths reducing DEF.
• Limestone filler reduced DEF and led to refinement of paste pore structure.

In the present investigation, the influence of sulphate and chloride ions combined action on cement durability and the role of limestone filler were investigated. Samples of a reference white CEM I42.5 (CRef) and the corresponding of a white CEM II42.5 (CL15) with a 15 wt% limestone replacement were exposed for a period of 90 days into three different curing baths (saturated Ca(OH)2 solution, 5 wt% Na2SO4 solution and a composite solution of 5 wt% Na2SO4 and 5 wt% NaCl), at 50 °C. Their compressive strengths were determined after 28, 56 and 90 days of curing, whereas their expansion was estimated on a weekly basis by the length change measurement. The deterioration products characterization was carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectrometry (FT-IR), Thermal Analysis (TG-DSC) and Mercury Intrusion Porosimetry (MIP). According to the results the addition of limestone filler led to the durability increment, as the corresponding mixtures presented lower expansion and higher compressive strengths, while in all cases the Cl ions presence mitigated the external sulphate attack, a fact that was mainly attributed to the Friedel’s salt formation.