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.

The search for innovative solutions that reduce the need for exploitation of natural resources and make use of residues to produce alternative construction materials is a necessity. Eggshell residues are a solid waste material rich in calcium carbonate (${\mathrm{CaCO}}_3$ ). The present research investigates quicklime and hydrated lime produced from eggshell residues and blended with ground waste glass, analyzing their possible usage as a binder material for soil stabilization. The quicklime and hydrated lime studied herein are produced from the calcination of eggshell residue. Eggshell quicklime (EQL) and eggshell hydrated lime (EHL) were characterized for their physical properties (grain-size distribution, specific surface area, photo microscopy, and X-ray spectroscopy), mineralogy (X-ray diffraction and thermogravimetric analysis), and chemical composition (X-ray fluorescence spectrometry). EQL and EHL consist predominantly of calcium oxide (CaO) and calcium hydroxide [$\mathrm{Ca}(\mathrm{OH}{)}_2$ ], respectively. Increasing the amount of eggshell quicklime/hydrated lime resulted in the increase of the blend’s mechanical properties, such as strength and stiffness. In general, the results show that both EQL and EHL retain outstanding physical, mineralogical, and chemical characteristics suitable for soil stabilization with an alternative pozzolanic material.

Upstream tailings dams are high-risk structures that have experienced several failures worldwide, particularly with iron ore tailings (IOT). In this study, new disposal methods/techniques, such as cement-stabilized dry stacking, are discussed that provide enhanced mechanical behavior while reducing failure risks. Alkali-activated materials are used as cementing agents due to their mechanical and environmental advantages compared to ordinary Portland cement. This study evaluates the mechanical and microstructural behavior of IOT stabilized with an alkali-activated cement (AAC) composed of two by-products from the IOT beneficiation process, metakaolin and sodium silicate, tested under plane strain conditions. Simple shear tests and microstructural analysis were performed. Mixtures of IOT were produced with 0%, 1%, 3%, and 5% AAC to examine the influence of such variables on strength and deformability parameters under undrained conditions. The mixtures with 3% and 5% AAC showed the greatest impact on the strength; however, the addition of 1% AAC was able to reduce positive pore-pressure generation. Cementitious bounds were evidenced by forming a sodium aluminosilicate hydrate gel. The studied AAC was effective in stabilizing IOT, even at small contents.

The present research aims to evaluate the potential of combining two wastes, finely ground waste glass (GWG) and carbide lime (CL), together with a sodium hydroxide solution (SHS) to form a new material which, when compacted, can develop cementitious properties over time. Such blends have potential application in the construction of stabilized rammed walls, as well as in earthworks such as beds of pipelines, spread footings, fill materials, and generally, as a new material for replacement of geomaterials of inadequate specifications in localized geotechnical works. Blends compacted exclusively with water were also produced in order to understand and differentiate, in a comparative manner, the effects of the addition of SHS on the mechanical, mineralogical, and microstructural properties resulting from alkaline reactions. The effects of the CL content, degree of compaction, and inclusion of a SHS on the evolution of strength and stiffness at 7 and 28 days under controlled curing conditions ($23°\mathrm{C}\pm 2°\mathrm{C}$ and 95% relative humidity) were determined. An original parameter, called the porosity/lime index ($\eta /L_{iv}$ ), was used to normalize the behavior of unconfined compressive strength ($q_u$ ) and shear modulus in small strains ($G_0$ ) of the blends. The results have shown that the GWG-CL blends (compacted with water and SHS) developed an evolution of the mechanical properties over time with increasing CL content and degree of compaction. This results from the reaction between the dissolved aluminosilicates present in the GWG and the calcium (${\mathrm{Ca}}^{2+}$ ) in CL, as a product of the pozzolanic and geopolymerization reactions in a high-alkalinity medium by the addition of CL and SHS, respectively. The formation of stable compounds, hydrated calcium silicate (C─ S─ H) type, analogous to those produced in the hydration processes of portland cement after 28 days of curing in alkali-activated blends with SHS, has been verified. Additionally, correlation equations were established between the mechanical response of the blends and the $\eta /L_{iv}$ index, as a function of the curing time and the type of activating solution, which can be considered as dosage curves for the prediction of a required mechanical response.

Ordinary portland cement (OPC) has been extensively used for decades to improve the engineering properties of a variety of soils. However, the environmental issues related to the production of OPC have created an urgent need to develop and use alternative binders such as alkali-activated cements (AAC). Thus, this work assesses the mechanical performance of a sandy soil amended with an AAC composed of ground waste glass (GWG), carbide lime (CL), and sodium hydroxide (NaOH). The effect of key factors, such as the presence of a NaOH solution, the dry unit weight, and the amount of binder were evaluated on the unconfined compressive strength ($q_u$ ), initial shear modulus ($G_0$ ), and accumulated loss of mass (ALM) of compacted sand-binder specimens cured for 7 days. When analyzing the curves that correlated the mechanical behavior of the blends ($q_u$ , $G_0$ , and ALM) with the $\eta /B_{iv}$ index, the results show that the alkaline solution has a significant positive influence on the mechanical response of the tested specimens. The improved mechanical performance of the alkali-activated treatments was associated with the formation of a blend of C─ S─ H and (C,N)─ S─ H cementitious compounds coexisting in the same cementitious matrix (alkaline hybrid cement), of heterogeneous structure and composition, and characterized by developing in greater quantity than those produced from a pozzolanic reaction.