Study on the development of CO2-absorbing non-fired bricks using fly ash from the waste-to-energy plant, coconut fiber and superplasticizer activators

Abstract

The Greenstar waste-to-energy plant (Bac Ninh) generates more than 4.000 tons of fly ash annually, most of which is landfilled, causing resource wastage and environmental pollution. This study proposes the development of CO₂-absorbing non-fired bricks using a mixture of fly ash, ground granulated blast furnace slag, coconut fiber and a alkaline solution (NaOH, Na₂SiO₃) solution serving as a geopolymer activator. Mix proportions were designed according to Vietnamese standards (TCVN), followed by sample preparation and testing of physical–mechanical properties (compressive strength, flexural strength, bulk density, water absorption, porosity) as well as CO₂ uptake capacity. The results show that all brick samples met grade M100 with compressive strengths ranging from 12,7 to 14,5 MPa, smooth surfaces, low water absorption and reduced porosity (6,5–10,9%). Notably, hollow bricks produced with Mix-ID-04 absorbed an average of 12,5–14,2 g CO₂ per brick within 20–30 minutes of testing, attributed to the carbonation of Ca(OH)₂, fly ash and slag. This research demonstrates the feasibility of combining industrial waste and agricultural by-products to manufacture CO₂-absorbing non-fired bricks, contributing to greenhouse gas reduction, resource conservation and the pursuit of the Net Zero 2050 target.