Sustainable foam concrete development: Enhancing durability and performance through pine cone powder and fly ash incorporation in alkali-activated geopolymers

Abstract

Pine cone powder (PCP) as a fine aggregate in geopolymers is an emerging concept that focuses on utilizing agricultural or plant-based waste materials to enhance the sustainability and performance of geopolymer composites. This study aims to produce eco-friendly alkali-activated foam concrete (AAFC) by investigating the combined impact of using fly ash (FA) and PCP as partial replacements for granulated blast-furnace slag (GBFS) and silica sand (SS), respectively. In this study, AAFC mixtures were developed with varying FA contents of 0 %, 25 %, and 50 % as partial replacements for GBFS, and PCP contents of 0 %, 25 %, 50 %, and 100 % as partial replacements for SS. A total of twelve AAFC mixtures were prepared, maintaining a constant alkaline solution-tobinder (A/B) ratio of 0.45. The mixtures were initially cured at 75 degrees C for 24 hours, followed by ambient curing for 7, 28, and 91 days. The impact of varying PCP and FA contents on the oven-dry density, flowability, water absorption, porosity, sorptivity, thermal conductivity, compressive strength, flexural strength, high-temperature resistance, and resistance to sulfate attack (MgSO4 and Na2SO4) of the AAFC mixtures was assessed. The microstructure of the mixtures was further examined using scanning electron microscopy (SEM). The results revealed that the AAFC mixture with 50 % PCP and 100 % GBFS exhibited the highest mechanical performance, attaining a compressive strength of 12.48 MPa. This represents strength improvements of 158.1 %, 265.4 %, and 256.6 % at 7, 28, and 91 days, respectively, compared to the reference mixture (F0P0). The same mixture had the lowest sorptivity, highest dry unit weight, and best high-temperature resistance. Mixtures with 25 % FA showed improved high-temperature resistance with added PCP. The thermal conductivity of the mixes varied from 0.527 to 0.662 W/mK, with the lowest value in the 100 % PCP mixture and the highest in the 50 % PCP mixture, both without FA. The mixture with 50 % FA and 0 % PCP showed the lowest strength loss after 60 days in a 5 % MgSO4 solution.