Failures of tailings dams, primarily due to liquefaction, have occurred in Brazil in recent years. These events have prompted the Brazilian government to place restrictions on the construction of new dams, as iron ore tailings deposited behind upstream dams by spigotting have been shown to have low in situ densities and strengths and are prone to failure. This work proposes a new trend for tailings disposal: stacking compacted filtered ore tailings–Portland cement blends. As part of the proposal, it analyses the behaviour of compacted iron ore tailings–Portland cement blends, considering the use of small amounts of Portland cement under distinct compaction degrees. With the intention of evaluating the stress–strain–strength–durability behaviour of the blends, the following tests were carried out: unconfined compression tests; pulse velocity tests; wetting–drying tests; and standard drained triaxial compression tests with internal measurement of strains. This is the first study performed to determine the strength and initial shear stiffness evolution of iron ore tailings–Portland cement blends during their curing time, as well friction angle and cohesion intercept. This manuscript postulates an analysis of original experimental results centred on the porosity/cement index (η/Civ). This index can help select the cement quantity and density for important design parameters of compacted iron ore tailings–cement blends required in geotechnical engineering projects such as the proposed compacted filtered iron ore tailings–cement blends stacking.

Dry stacking of iron ore tailings (IOTs) with cementitious materials is a viable disposal option, but its large scale implementation faces challenges. Therefore, this study investigates the key factors influencing compaction in real field conditions, including moisture content (optimum moisture content and less than optimum moisture content), vibration frequency (0 Hz and 35 Hz), and number of roller passes (4P and 6P). To achieve this objective, an experimental IOT stack was constructed in five different layers using a specific amount of Portland cement as a cementing agent (2.5% by dry solid weight). Then, laboratory tests, such as unconfined compression, splitting tensile, and ultrasonic pulse velocity (UPV), were conducted on undisturbed samples to evaluate the unconfined compressive strength (qu), splitting tensile strength (qt), and initial shear modulus (G0). Based on the laboratorytests conducted on the field-collected specimens, it was concluded that samples with moisture contents closer to the optimum moisture content (OMC), exposed to vibration, and subjected to six-roller passes exhibited superior mechanical performance. This study provides insights into optimizing the compaction process for large-scale IOT stack structures.

Alternative materials to ordinary Portland cement (OPC), with lower environmental impacts and similar mechanical performance, are growing in interest of geotechnical techniques, such as soil stabilization. The present study evaluates the alkali activation of a system composed of ceramic wastes, carbide lime and sodium hydroxide solution as a green stabilization for granular soil. To analyze the performance of the alkali-activated cement (AAC), mechanical tests were carried out based on unconfined compression strength and split tensile strength due design mix focusing on different water content, precursor combinations and time of curing. The results have shown an enhanced in mechanical response, but in specific samples the additional water to achieve the molding moisture weakens the solution, reducing strength. The correlation of the mechanical parameters with the porosity by volumetric content of binder index (η/Biv) was an appropriate parameter for evaluating stabilization for granular soil.