A 10 % replacement of metakaolin with paper mill sludge ash (PMSA) significantly boosts geocrete performance, demonstrating a sustainable way to repurpose industrial waste while supporting low-carbon construction.
Image Credit: Denis Torkhov/Shutterstock.com
Researchers have explored the impact of Paper Mill Sludge Ash (PMSA) on the mechanical, microstructural, and durability characteristics of metakaolin-based geocrete. Their findings, published in Scientific Reports, show that this industrial by-product not only enhances concrete performance but also supports resource-efficient and environmentally responsible construction.
Rethinking Construction Materials for Sustainability
The construction sector continues to pivot toward greener solutions in an effort to reduce its carbon footprint and manage waste more effectively. Traditional Portland cement (PC), a major contributor to global CO2 emissions, is increasingly being replaced or supplemented with alternative binders.
Geocrete, or geopolymer concrete, has emerged as a strong candidate. It uses aluminosilicate-rich materials like metakaolin, fly ash, and slag, activated by alkaline solutions. This chemical process creates a durable, three-dimensional polymer network with reduced reliance on PC. Integrating by-products such as PMSA enhances sustainability by repurposing industrial waste and reducing the demand for virgin raw materials.
Study Approach: Blending PMSA into Geocrete
To assess the potential of PMSA as a partial substitute for metakaolin, the researchers tested replacement levels of 5 %, 10 %, 15 %, and 20 %. The geocrete was activated with sodium hydroxide and sodium silicate, and mixed according to standard protocols to ensure consistent testing conditions.
Mechanical properties were measured via compressive and flexural strength tests at various curing stages. Durability was assessed through rapid chloride penetration tests (RCPT), water absorption rates, and porosity analysis. Additionally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) provided insights into the material’s internal structure and chemical bonding.
Results: Improved Strength and Durability with Optimal PMSA Use
The experiments revealed that adding PMSA meaningfully altered geocrete performance. At a 10 % replacement level (specifically in G2 and G6 mix designs), compressive strength peaked between 39–44 MPa at 90 days, depending on the activator/binder (A/B) ratio.
While lower PMSA contents improved performance, higher substitution levels (15–20 %) reduced strength due to a lower Si/Al ratio and incomplete geopolymerization. SEM images showed denser microstructures and better particle integration, contributing to fewer pores and stronger bonding. Durability also improved across several metrics, with PMSA mixes absorbing less water and exhibiting greater resistance to chloride ion ingress.
Flexural strength followed a similar trend. It increased with 10 % PMSA but declined at higher levels. This suggests that ductility and crack resistance are enhanced within a narrow optimal replacement range.
Real-World Implications for Green Building
This research offers practical benefits for builders and designers seeking low-carbon alternatives to traditional concrete. Geocrete blended with 10 % PMSA shows promise in a variety of applications, whether that be residential buildings, pavements, infrastructure, or precast elements.
Beyond the environmental gains, there are cost advantages too. Using PMSA reduces the need for high-grade raw materials and lowers waste disposal costs for paper mills. It aligns with circular economy principles by diverting waste from landfills and reintegrating it into valuable construction products.
Next Steps: Scaling Up and Field Testing
This study underscores PMSA’s potential to enhance the performance and sustainability of geocrete. Mixes with higher activator ratios (A/B = 0.45) achieved superior results, highlighting the need for careful mix optimization to maximize strength and durability.
Moving forward, research should explore additional performance factors such as thermal stability and long-term aging under real-world conditions. Field trials will be essential to confirm the material’s behavior outside the lab and evaluate its performance at scale.
Journal Reference
Yuvaraj, K., & et al. (2026). Influence of paper mill sludge ash on mechanical, microstructural and durability properties of metakaolin based geocrete. Sci Rep. DOI: 10.1038/s41598-026-37581-0, https://www.nature.com/articles/s41598-026-37581-0
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.