Use of Artificial Neural Networks as a Predictive Tool of Dissolved Oxygen Present in Surface Water Discharged in the Coastal Lagoon of the Mar Menor (Murcia, Spain).

The Mar Menor is a Mediterranean coastal saltwater lagoon (Murcia, Spain) that represents a unique ecosystem of vital importance for the area, from both an economic and ecological point of view. During the last decades, the intense agricultural activity has caused episodes of eutrophication due to the contribution of inorganic nutrients, especially nitrates. For this reason, it is important to control the quality of the water discharged into the Mar Menor lagoon, which can be performed through the measurement of dissolved oxygen (DO). Therefore, this article aimed to predict the DO in the water discharged into this lagoon through the El Albujón watercourse, for which two theoretical models consisting of a multiple linear regression (MLR) and a back-propagation neural network (RPROP) were developed. Data of temperature, pH, nitrates, chlorides, sulphates, electrical conductivity, phosphates and DO at the mouth of this watercourse, between January 2014 and January 2021, were used. A preliminary statistical study was performed to discard the variables with the lowest influence on DO. Finally, both theoretical models were compared by means of the coefficient of determination (R2), the root mean square errors (RMSE) and the mean absolute error (MAE), concluding that the neural network made a more accurate prediction of DO.

Application of Concretes Made with Glass Powder Binder at High Replacement Rates.

Glass is a material that can be reused, except for a small part that, due to its residual characteristics, cannot be reused and becomes a nonbiodegradable waste to accumulate in landfills. The chemical composition and pozzolanic properties of waste glass are encouraging for the use of these wastes in the cement and concrete industries and for providing technically and environmentally viable solutions. In this study, we propose the production of deactivated concretes with a high content of glass powder in the binder. The substitution percentage of glass powder for cement used in this work was between 70% and 80%. Consistency, air content, bulk density, workability, compression strength, and permeability tests were performed. Regarding compressive strength, the results obtained at 90 days for percentages of cement substitution by glass powder of 70 and 80%, respectively, were 14.2 and 8.6. The chemical analysis of leachates showed concentrations of Fe, Cu, V, Ni, and Mo, in mg L-1, of 1.57, 1.38, 0.85, 0.95, and 0.44, respectively. The results obtained, compared with the relevant legislation, have proved that the inclusion of glass powder in a high percentage of substitution and with a granulometry of 20 µm in the manufacture of deactivated concretes is feasible for exterior pavements.

Eco-Friendly Pavements Manufactured with Glass Waste: Physical and Mechanical Characterization and Its Applicability in Soil Stabilization.

The use of glass waste, which by its nature cannot be recycled, might be a viable alternative in the manufacture of cements and concrete that is also economical and environmentally friendly. This alternative can reduce landfill areas with this inert residue but also limit the use of raw materials employed in the manufacture of cement and concrete and, consequently, contribute to minimize the environmental impact generated by this activity. In this research, the feasibility of using a limestone-type material treated with a binder manufactured with micronized glass powder and basic reagents, in the preparation of a gravel-cement- or soil-cement-type material, was analyzed. For this purpose, the strength, compactability, structural capacity, resistance to the action of water, stiffness and durability of the material obtained were characterized. From the tests that were carried out and the results obtained, it can be concluded that the use of glass powder, with a particle size of 16 µm, is ideal for the production of a gravel-cement- or soil-cement-type material. This material could be used as an environmentally-friendly pavement, especially suitable for peri-urban roads and park roads, where it can be used without coating, or as a base layer or sub-base for road surfaces, with little cracking due to shrinkage.