Optimizing Lightweight Geopolymer Concrete Mixes

The development of geopolymer concrete is advancing rapidly worldwide. However, issues related to workability and setting time in geopolymer mixes, compared to traditional concrete mixtures, remain a challenge. These problems could be particularly concerning if geopolymer is used for masonry applications. The short setting time and rapid hardening may enhance the production rate of masonry units but require careful consideration to ensure practicality and quality control. This study examines the performance of lightweight geopolymer concrete (LWGPC) as an alternative to traditional lightweight concrete in order to be used in masonry unit’s production. The investigation focuses on the effects of free water, foaming agent content, and foam stabilizer on the mechanical and physical properties of LWGPC. Experimental results indicate that reducing the free water content increased the dry density from approximately 810 kg/m³ to 1030 kg/m³ and enhanced the compressive strength from 3.25 MPa to 5.61 MPa after 28 days. Conversely, increasing the foaming agent content decreased the dry density from 1024 kg/m³ to 680 kg/m³, accompanied by a reduction in compressive strength from 5.52 MPa to 2.28 MPa. The inclusion of foam stabilizers further reduced the density (by up to 7%) but caused significant strength losses, with compressive strength decreasing by 51–71%, depending on the foaming agent content. These findings highlight the trade-offs between density, strength, and workability, offering valuable insights for optimizing LWGPC for masonry used in structural applications, and insulation purposes. Additionally, a new set of equations was proposed to predict the compressive strength and dry density of lightweight foam geopolymer concrete.