Experimental Investigation on the Performance of Cement Mortar by Partial Replacement of the Standard Sands with Sulfide-Contained Iron Tailings

Abstract

The usage of iron tailings as construction aggregates is a potential route to save the cost of standard sands and protect the environment of mining area. This study mainly investigates the performance of cement mortars by partial replacement of the standard sands (SS) with sulfide-contained iron ore tailings (IOT). The physicomechanical properties, microstructure, and hydration products were measured by consistency test, porosity test, strength test, P-wave velocity test, scanning electron microscopy test (SEM), and X-ray diffraction test (XRD). It is proven that the graded IOT (GIOT), which has an identical particle size distribution with SS, is better than the ungraded IOT to serve as fine aggregate by replacing SS because a suitable GIOT content can better reduce the adverse effect of excess fine tailings (<0.15 mm) and sulfide on the cement mortar. The graded tailings cement mortar (GTCM) by using GIOT has denser pore structure, lower porosity, higher strength, and P-wave velocity than ungraded tailings cement mortar (UTCM) by using UIOT at the same curing condition and age. In addition, although a high sulfide content (approximately 4.44% to 5.55% by weight) by adding more than 40% GIOT is conducive to reduce the porosity and improve the strength of GTCM before 28 days, it is harmful for the long-term performance beyond 90 days. The expansive ettringite and gypsum produced by the reaction of excess sulfide will cause microcracks and thus reduce the strength beyond 40% GIOT. To ensure the long-term performance of GTCM, the sulfide content in the aggregate should be controlled below 3% by weight, and the optimal substitution ratio of GIOT corresponding to this sulfide content is approximately 20% to 30%.