Use of Magnetite Derived from Acid Mine Drainage in the Stabilization of Foam for Foamed Mortar

Foam stabilization plays a critical role in the production of foamed mortar, a material widely applied in civil construction due to its thermal insulation and lightweight structural benefits. This study investigates the use of magnetite derived from acid mine drainage (AMD) as a sustainable foam-stabilizing agent. Magnetite’s magnetic properties enhance foam stability by improving air bubble distribution within the mortar. A total of 30 different mixtures were produced, varying the sand-to-cement ratio, type of cement and magnetite content. The compressive strength and tensile flexural strength of the foamed mortars ranged from 0.62 ± 0.04 MPa to 7.33 ± 0.30 MPa and from 0.44 ± 0.12 MPa to 2.82 ± 0.16 MPa, respectively; porosity ranged from 31.8% ± 1.86 to 75.6% ± 2.2; dry and wet bulk density ranged from 423 ± 23 kg.m−3 to 1576 ± 96 kg.m−3 and from 615 ± 9 kg.m−3 to 1828 ± 122 kg.m−3, respectively; water absorption ranged from 8.9% ± 0.9 to 45.8% ± 10.6; and thermal conductivity ranged from 0.54 ± 0.03 W·m−1·K−1 to 0.17 ± 0.03 W·m−1·K−1. Results demonstrated that increasing magnetite content led to greater foam stability and porosity but decreased mechanical strength and density. The sand-to-cement ratio significantly affected all measured properties, while the type of cement had minimal influence. These findings suggest that AMD-derived magnetite is a promising additive for optimizing the performance of lightweight, sustainable foamed mortars.