Synthesis and mechanical characterization of geopolymeric mortars derived from inorganic industrial waste from Peruvian informal mining

Abstract

The geopolymeric mortars obtained by the chemical process of geopolymerization of waste from the Peruvian informal mining industry and subsequent addition of fine sand, were mechanically evaluated under ambient temperature and atmosphere conditions. The mechanical results found in the geopolymer mortars were compared with those found in conventional Portland cement mortars (control). The maximum uniaxial compressive stress values for the geopolymer mortars ranged from 7.5 to 27.1 MPa, with the best results when a binder:fine sand ratio of 1:2, molarity of the hardener solution of 20 M and a hardener solution:binder ratio of 0.6 was considered. The microstructure found for both types of mortars studied (control and geopolymeric) consisted of a continuous interconnected phase of binder (cement or geopolymerized inorganic mining residue) and a dispersed phase of small fine sand particles, located within the binder phase. The average real density and porosity of the geopolymeric materials studied were 2.71 g/cm³ and 27%, respectively.

Introduction

Geopolymeric materials are compounds of inorganic nature obtained by chemical processes of geopolymerization of aluminosilicates, such as: burnt clays, industrial waste, among others, and an alkaline compound in aqueous solution, typically sodium hydroxide [1], [2], [3], [4]. Recently, the international scientific community has shown a growing interest in the study of this type of materials, mainly due to the breadth of applications in which they can be used, this in turn, due to their low density, resistance to fire, and relatively low cost. , simple manufacturing, chemical stability and friendly synthesis with the environment [5]. Therefore, geopolymers are considered revolutionary materials with high potential as substitutes for Portland cement [3], [13]. Several works have been reported in the literature where the methodology for obtaining geopolymeric concretes with up to 70% compressive strength in the first 4 h of hardening is presented [6], unlike its Portland cement counterpart, which as is well known, it takes several weeks. On the other hand, studies related to the drying contraction of geopolymeric concretes revealed that after a year of being manufactured, they presented between 5 and 7 times less contraction, compared to their Portland cement counterparts [7], [8]. Other studies have evaluated the strength of geopolymeric concretes at relatively high temperatures and its comparison with their Portland cement counterparts. For example, Kong et al. [9] evaluated the compressive strength of geopolymer and Portland cement pastes, after being treated at high temperatures, found that at 800° C geopolymers improve their mechanical response, while at 400° C, cement pastes Portland lose all their stamina. It should also be remembered that during the obtaining of Clinker (main component of Portland cement) high CO₂ emissions are generated, thus, it has been determined that for each ton of Portland cement manufactured, up to one ton of CO₂ can be generated [10].

Finally, one of the most urgent environmental problems to solve in Peru is the large amounts of inorganic mining waste that are generated every year and today only accumulate in gigantic tailings fields [11], [12]. Due to all the above, in this work various mixtures of geopolymeric mortars derived from mining tailings and controlled quantities of fine sand were studied for their potential use as an alternative construction material to Portland cement mortar.