# Sustainable Optimization of Lightweight Aggregate Production from Bauxite Residue via Nonlinear Programming

## TL;DR

This paper shows how bauxite residue can be used with clay to create lightweight construction materials through optimized mixing.

## Contribution

A nonlinear programming model was developed to optimize lightweight aggregate composition from bauxite residue and clay.

## Key findings

- A mixture of 30.50% bauxite residue and 69.50% clay produced a lightweight aggregate with 0.78 g/cm³ density.
- The model maximized porosity and reduced density without compromising structural integrity.
- Bauxite residue use is presented as a sustainable alternative for civil construction materials.

## Abstract

In this work, lightweight
aggregates were developed from mixtures
of bauxite residue and clay, using a nonlinear programming model to
determine the optimum composition. The aggregates were characterized
using TGA/DTG/DSC analysis, X-ray diffraction, scanning electron microscopy
and physical tests of apparent density, porosity and water absorption,
carried out on three samples (BR50, BR30.50 and BR0). The results
showed that the bauxite residue favored the formation of amorphous
and porous phases, reducing the density of the aggregates. A nonlinear
programming model was developed to determine the optimal composition
of a lightweight aggregate, resulting in a mixture containing 30.50%
bauxite residue and 69.50% clay. This composition yielded a material
with a density of 0.78 ± 0.03 g/cm3, porosity of 14.54
± 1.13%, and water absorption of 14.05 ± 1.72%, confirming
its classification as a lightweight aggregate. The reference sample,
with 100% clay (BR0), had a density of 2.20 ± 0.02 g/cm3 and a more compact structure. The proposed model proved effective
in maximizing density and porosity without compromising the integrity
of the aggregate, indicating that the use of bauxite residue is a
promising and sustainable alternative to produce materials for use
in civil construction.