Influence of Coconut Fiber Waste and Rice Husk Ash on Green Concrete
Authors: Morato Bruna Nitzsche , Guedes Verenna Santos , Barbosa Ricardo Antônio , Branco Luiz Antônio Melgaço Nunes , Ribeiro Sidnea Eliane Campos , Flor Jacqueline Maria , De Oliveira Danielle Meireles , Almeida Marys Lene Braga 
Published: December 2023

Purpose: To develop cementitious materials, concrete, incorporating coconut fiber waste (CFW) and rice husk ash (RHA), with the aim of producing innovative, cost-effective, and readily available products for use in economically and environmentally friendly construction applications. Environmental impacts can be minimized by making these practices efficient and sustainable through the utilization of these waste materials.

Theoretical framework: The use of agro-industrial waste in concrete matrices has been extensively studied due to their effectiveness in influencing material properties. The incorporation of coconut fiber waste and rice husk ash into concrete can lead to improvements in compressive strength, increased durability, and a reduction in the amount of CO2 generated during production. The concrete developed with the incorporation of waste products has the potential to minimize environmental impacts, reduce costs, and extend its lifespan. The pursuit of sustainability drives the exploration of innovative materials to preserve natural resources and mitigate ecological impact in the construction industry.

Method: The coconut fiber waste was subjected to 24-hour drying process in an oven at 100°C to remove moisture and was subsequently crushed in a ball mill until its particle size exhibited characteristics similar to the binder. The CFW and RHA were characterized through Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Specific Surface Area analysis. Different percentages of CFW (0.25% - 0.75%) and RHA (2% - 10%) were separately incorporated into the concrete mix. The mixing ratio used was 1:1.9:3.1 (cement, sand, aggregate), with a water-to-cement (w/c) ratio of 0.60. Workability tests, electrical resistivity tests, capillary water absorption by capillary rise, and axial compressive strength tests were conducted. Additionally, a sulfate ion penetration test was performed by immersing specimens in a 2.5% sulfuric acid (H2SO4) solution for 7 days.

Results: SEM images of CFW reveal an angular and fibrous microstructure, maintaining the original properties of the waste even after its transformation into ash. RHA particles exhibit irregular shapes and sizes with microporous cellular structures on the surface, consistent with literature. X-Ray Diffraction patterns of CFW indicate a material without a distinct crystalline structure. However, Electron Dispersive Spectroscopy analysis suggests the predominance of carbon (C), potassium oxide (K2O), and silica (SiO2). RHA shows broad amorphous diffraction at 22° and some sharp diffraction peaks, suggesting the formation of crystallites, consistent with cristobalite. There was a slight improvement in the workability of fresh concrete compared to the reference mix as the percentage of waste incorporation increased. The electrical resistivity of the produced specimens showed a significant increase in all cases, except for the 0.25% RHA sample. The 5.0% CFW content exhibited the best performance, with a 29.47% increase, indicating a microstructure with few voids and suggesting greater material durability. Samples with higher fiber percentages showed higher water absorption values. Concrete incorporated with RHA exhibited higher porosity and suboptimal performance. However, the incorporation of 0.25% CFW showed a slight improvement compared to the reference concrete. The best performances observed in the compressive strength test were with 5.0% RHA and 0.5% CFW, with the latter showing the best result compared to the reference specimens. In the sulfate attack test, only the concrete with 5.0% RHA showed better performance in an aggressive environment. Increasing the percentage of CFW also reduced mass loss, suggesting potential improvement of the compound at higher proportions. The study demonstrated that agro-industrial residues can be satisfactorily utilized in construction, and the implementation of this new process can reduce global warming and mineral resource depletion.

Research implications: This work contributes to a sustainable circular economy with a novel process for utilizing agro-industrial waste in concrete.

Originality/Value: The findings will be promising for the utilization of coconut fiber waste and rice husk ash in the production of environmentally sustainable concrete.