19The improvement of geotechnical properties is often achieved by the addition of traditional 20 binders, such as cement or lime. However, the use of such binders implies a considerable 21 financial and environmental cost that needs to be mitigated. An unconventional solution, similar 22 to cement in terms of performance but more environmentally friendly, consists in the use of 23 binders made from alkaline activated industrial residues. The technique consists on the 24 activation of raw materials (such as fly ash or blast furnace slag) rich in Si, Al, or even Ca, with 25 high pH alkaline solutions. The present work was developed aiming the possible stabilization, 26 using different fly ash contents, of a clayey soil with sand. The activator solution was composed 27 of sodium hydroxide and sodium silicate. The extended experimental campaign included 28 unconfined compressive strength (UCS), California Bearing Ratio (CBR), pulse velocity tests 29 and triaxial tests to assess the geomechanical improvement induced by the new binder. As a 30 mean of comparison, the experimental campaign included also the stabilization of the same soil 31 with either cement or lime. The obtained data indicates that the use of alkaline activation as a 32 soil stabilization technique provides competitive geomechanical results, when compared with 33 those obtained with traditional binders.34 35
Mine tailings (MT) could represent a step forward in terms of the quality of the aggregates usually used in civil engineering applications, mostly due to its high density. The Portuguese Neves Corvo copper mine, owned by the Lundin Mining Corporation, produces approximately 3 million tonnes per year. Nevertheless, it cannot be used in its original state, due to its high levels of sulphur and other metals (As, Cr, Cu, Pb, Zn). This paper focuses on the stabilisation/solidification of high-sulphur MT, without any previous thermal treatment, using alkali-activated fly ash (FA). The variables considered were the MT/FA ratio and the activator type and concentration. A fine aggregate was then added to the pastes to assess the quality of the resulting mortar. Maximum compressive strengths of 14 MPa and 24 MPa were obtained for the pastes and mortars, respectively, after curing for 24 h at 85 • C. Thermogravimetric analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, and infrared spectroscopy were used to characterize the reaction products, and two types of leaching tests were performed to assess the environmental performance. The results showed that the strength increase is related with the formation of a N-A-S-H gel, although sodium sulphate carbonate was also developed, suggesting that the total sodium intake could be optimized without strength loss. The solubility of the analysed metals in the paste with 78% MT and 22% FA was below the threshold for non-hazardous waste. potential use of MT as a replacement for natural aggregates, which are usually obtained through an extraction process that severely affects the environment, would not only reduce the consumption of natural resources but also decrease the volume of landfilled MT. However, this waste generates acid mine drainage when exposed to oxygen and water [5], which makes it impractical as an aggregate in common applications, like embankments or roads, if not previously stabilised.Another possible use is inclusion in alkali-activated mortar and concrete, a recent research topic, with promising results in terms of mechanical and environmental performance [5,6]. Some studies focused on the use of MT as a precursor, albeit requiring a previous thermal treatment [7][8][9][10][11], while others used a different approach by considering the MT as a filler and/or coarse aggregate in composite materials, cemented by aluminosilicate gel formed from the alkali activation of fly ash, metakaolin, waste glass, or slags [11][12][13][14][15][16][17][18][19]. Although many of the above-mentioned studies were dealing with tailings resulting from tungsten and gold mines, several studies have also been produced targeting copper mine tailings [16,[19][20][21][22][23]. From an environmental perspective, it is important to highlight that alkaline activation has already proved to be very effective for containing and neutralising different types of wastes [24][25][26][27][28][29][30][31][32][33][34][35] and, specifically, wastes resulting from m...
Alkali activated composites -An innovative concept using iron and steel slag as both precursor and aggregate, Cement and Concrete Composites (2019), doi:
The study reported in this paper focused on the physical-mechanical properties of compacted earth blocks (CEB) stabilised with a sustainable alkali activated cement, completely produced from wastes and residues, including coal fly ash and glass waste (from the production of ophthalmic lenses) activated with an alkaline solution resulting from the aluminium industry. A common Portuguese silty clay was used as the mineral skeleton of the blocks, which were then evaluated based on the protocols of the UNE 41410 and DIN 18945-47 standards. The results evidenced the effectiveness of the alkaline cementing agent in forming a binding matrix for the soil particles, and the resulting material was used to manufacture the earth-based masonry elements. After a careful optimisation of the sustainable binder, an average compressive strength of 17.23 MPa, in unsaturated conditions, was obtained for the blocks. The newly formed soil-binder structure was very capable to withstand wetting and drying cycles, ice-thaw cycles and erosion. The microstructure of the material was further analysed, using scanning electron microscopy and energy dispersive spectroscopy. The results demonstrated the real possibility of using this type of cement as a viable alternative to traditional soil stabilisation binders used in earth construction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.