Optimizing lightweight geopolymer concrete mixes

Abstract

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 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 stabilizer slightly reduced density (by up to 7%) and caused compressive-strength reductions ranging from a 4% to 42% within the tested mixes, increasing with 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. Within the tested range, intermediate foaming-agent dosages (around 60–80 kg/m³) yielded the highest specific compressive strength, depending on stabilizer content. Additionally, a new set of equations was proposed to predict the compressive strength and dry density of lightweight foamed geopolymer concrete, with strong correlation to experimental results (R² = 0.93 for compressive strength and R² = 0.96 for dry density).