Glass Lightweight Aggregates from Glass Cullet and Mining and Food Industry Carbonate Waste

Abstract

Lightweight aggregates are extensively used in construction and other industrial applications due to their technological characteristics. The extraction of natural aggregates results in serious environmental effects. Thus, within the circular economy concept, the valorization of waste through the optimization of materials and product design is encouraged. In this work, glass lightweight aggregates were prepared from mixtures of white glass cullet and carbonate wastes from mining (wastes originating from the extraction, manufacture and marketing of magnesite and its derivatives) and the food industry (eggshell and mussel shell). The effects of different processing parameters, such as the particle size of the base glass, percentage of the blowing additive, shaping method, heating rate, temperature and processing time, were evaluated. The results indicate that the mineralogical composition of the blowing agent and the particle size of the base glass are the two processing parameters with the greatest impact on expansion efficiency. Thus, glass artificial aggregates were obtained with characteristics similar to those of commercial products (density values ranged between 0.3 and 0.8 g/cm3 and mechanical strength between 0.7 and 1.5 MPa) from thermal shock expansion treatments in the temperature range 800–900 °C and with dwell times no longer than 15 min.

Development of Lightweight Mortars Using Sustainable Low-Density Glass Aggregates from Secondary Raw Materials

“…As the temperature increases, particle rearrangement occurs, while the initial open porosity decreases and becomes closed porosity [ 57 ]. The decarbonation processes of CaCO 3 in MS and FT start at 750 and 800 °C, respectively [ 49 ], which are far above the Tg of the base glass. Gases are discharged into a viscous sintered matrix with reduced open porosity, becoming trapped, leading to matrix blowing and resulting in high porosity aggregates.…”

“…Gases are discharged into a viscous sintered matrix with reduced open porosity, becoming trapped, leading to matrix blowing and resulting in high porosity aggregates. Conversely, the decarbonation of MgCO 3 in CF and PC8 additives starts below 600 °C [ 49 ], which is before the Tg of the base glass is reached. In such cases, the released gases escape through the open porosity before the sintering of the glass particles progresses, resulting in aggregates with reduced porosity.…”

“…The tested compositions were GC-5MS, GC-15FT, GC-10CF, and GC-10PC8, where the number preceding the abbreviation of the foaming additive indicated its percentage in the mixture. The optimization of the composition and the processing conditions were comprehensively described in a previous study [ 49 ]. For the manufacture of glass aggregates, 500 g of each composition was mixed and homogenized in a planetary ball mill (TURBULA) for 15 min.…”

“…Moreover, the GC-10CF and GC-10PC8 aggregates were the densest, with porosity values of 20% and 8%, respectively. The observed differences in the density and porosity values of the different aggregates were the result of the different mineralogical compositions of the additives used as foaming agents and, more specifically, the gaps between the decomposition temperatures of the carbonates present in the additives and the glass transition temperature (Tg) of the base glass (approximately 610 • C) [49]. In these materials, the expansion of the aggregate was caused by the release of CO 2 gas because of the decomposition of the carbonates in the additives.…”

“…Another method for reusing container waste glass is through its transformation into lightweight expanded glass aggregates, which can be used in the manufacture of lightweight mortars. Lightweight glass aggregates have a low density because of their cellular structure and high compressive strength [ 49 ]. In addition, these materials combine other characteristics of glass, such as chemical resistance and durability.…”