Abstract

This study evaluated the potential of sugarcane bagasse fly ash, collected from boiler exhaust stacks via a bypass pipe, as a renewable supplementary cementitious material. The bagasse fly ash was ground into three different particle sizes (D50 of 10, 20, and 30 μm) and characterized in terms of morphology, porosity, specific surface area, and pozzolanic activity. The influence of the ashes on paste hydration was investigated using isothermal calorimetry. Mortars were then tested with 20% cement replacement by fly ash, analyzing packing density, compressive strength evolution, and durability against sulfuric acid. Results indicated the suitability of the fly ash as a supplementary cementitious material, with low contamination and greater pozzolanic activity at smaller particle sizes. This enhanced initial hydration and long-term strength, with finer ashes showing superior mechanical properties when compared to the reference mortar (an 8% increase). Mortars with fly ash exhibited higher packing density and reduced mass loss under sulfuric acid attack, but increased water absorption and capillarity, alongside decreased compressive strength compared to the reference. Briefly, the findings highlighted that the potential of bagasse fly ash as a promising low cost and eco-beneficial material for sustainable construction practices.

Introduction

It is imperative to act now to reduce global environmental impacts by combating CO2 emissions and preserving our planet for future generations. The cement industry plays a pivotal role in the necessary reduction of global emissions, requiring innovation and more sustainable practices to build a greener and healthier future for our planet. On the other hand, industrial waste discharged into the soil poses a significant environmental threat and can lead to soil contamination, compromising agricultural land quality, groundwater, and overall ecosystem health ( Mohan et al., 2023 ). Sales and Lima (2010) emphasized the negative impact of improper disposal and the use of these residues as fertilizers, especially in powder form, due to their low soil enrichment potential.

In this scenario, sugarcane bagasse ash (SCBA), an abundant residue generated globally every year, is of paramount importance, particularly in the cement industry, with its silica-rich composition making it an attractive and valuable resource. Thus, SCBA is a promising pozzolanic material, recognized in several studies conducted in recent decades ( Ahmad et al., 2021 ; Minnu et al., 2021 ). It is mainly generated via the conventional methods used in the sugar and ethanol agroindustry, which involve storing sugarcane bagasse outdoors for subsequent calcination in boilers.

Conclusions

The following conclusions were drawn from the study on producing finely ground bagasse fly ash and its application in pastes and mortars. The chemical composition of the bagasse fly ash was suitable for use as a supplementary cementitious material, largely because of the presence of 24% amorphous silica and low loss on ignition (2.8%). Moreover, the ashes showed increased pozzolanic activity with a decline in particle size, resulting in accelerated hydration in the initial hours and greater long-term compressive strength of the mortars. A good correlation was observed between packing density and ash particle size, with finer ash resulting in higher mortar packing density. Thus, finer ash exhibited the best mechanical performance, although adequate ash can be produced with D50 of 20 μm. In terms of durability, the acid-attacked M-REF specimens experienced greater mass loss during sulfuric acid attack. However, given the different degradation mechanism of the attacked mortars containing SBFA samples, water absorption increased and compressive strength declined when compared with their nonattacked counterparts and the attacked reference specimens.

In summary, while the use of ultrafine bagasse fly ash in cementitious materials offers several advantages, such as enhanced mechanical performance, accelerated hydration, and environmental benefits, there are also limitations related to durability and mechanical performance with coarser particles. Overall, proper consideration of these factors is necessary for effective large-scale use of sugarcane bagasse fly ash in cementitious applications. Further research should focus on (i) understanding the long-term performance of cementitious materials containing bagasse fly ash; (ii) performing life-cycle assessments to evaluate the environmental impact of using bagasse fly ash as a supplementary cementitious material compared to conventional materials; (iii) investigating the economic feasibility of incorporating bagasse fly ash into cementitious materials, including cost-benefit analyses and assessing the potential for commercial-scale production. By addressing these research directions, further advances can be made in harnessing the potential of bagasse fly ash as a sustainable and effective supplementary cementitious material, contributing to the development of eco-friendly construction practices.