COMPLETE SCHOOL PROJECT TOPICS & MATERIALS :
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RICE HUSK ASH AND SAWDUST ASH AS CHEAPER CEMENT REPLACEMENTS IN CONCRETE FOR TROPICAL AREAS
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Concrete remains the most widely used construction material globally due to its strength, availability, and versatility in constructing houses, roads, bridges, and other infrastructure. However, the production of ordinary Portland cement (OPC), the primary binder in concrete, is highly energy-intensive and accounts for approximately 8% of global carbon dioxide (CO₂) emissions. In tropical countries such as Nigeria, where rapid population growth and urbanization drive high demand for construction, the elevated cost of cement and its environmental impact pose significant challenges to affordable and sustainable building.
Tropical climates, characterized by high humidity, heavy rainfall, intense heat, and temperature fluctuations, impose additional stress on concrete structures. These conditions can lead to issues such as increased water penetration, cracking, reduced durability, and higher maintenance costs over time. Concurrently, Nigeria generates substantial quantities of agricultural and industrial waste, including rice husks from milling operations and sawdust from timber processing industries, particularly in regions like Edo State with active agricultural and timber sectors.
Rice husk ash (RHA) is produced through the controlled combustion of rice husks, yielding a fine ash rich in amorphous silica (typically 80–95%). This high silica content renders RHA a pozzolanic material, capable of reacting with calcium hydroxide, a byproduct of cement hydration, to form additional cementitious compounds. This process enhances concrete strength, reduces permeability, and improves long-term durability. Sawdust ash (SDA), obtained from the controlled burning of sawdust, contains silica and other oxides and can function as a supplementary cementitious material, albeit with generally lower pozzolanic activity compared to RHA. Both materials reduce the required amount of OPC, lower production costs, divert waste from open burning or landfills (which contribute to air pollution and health hazards), and diminish the overall carbon footprint.
Recent studies indicate that RHA can replace 10–20% of cement while maintaining or even enhancing compressive strength, particularly at later ages due to pozzolanic reactions. Optimal replacement levels often produce strengths suitable for structural and non-structural applications in tropical environments. SDA performs optimally at lower replacement levels (5–10%), contributing to lighter concrete mixes and improved thermal properties. Whether used individually or in combination, these ashes facilitate greener, more economical concrete production by utilizing local resources, reducing dependence on costly imported cement, and promoting waste valorization in tropical developing regions (Haruna et al., 2025; Agboola et al., 2022; Tesfaye et al., 2026).
In Nigeria, where rice production and timber processing generate substantial waste, integrating RHA and SDA into concrete presents a viable pathway to sustainable, low-cost construction, aligning with national objectives for affordable housing and environmental conservation.
1.2 Statement of the Problem
The high cost and environmental impact of cement production constrain the feasibility of affordable and sustainable construction in tropical regions such as Nigeria. Conventional concrete predominantly relies on ordinary Portland cement (OPC), elevating both project expenses and carbon emissions. Concurrently, rice husks and sawdust despite their abundance are frequently subjected to open burning or indiscriminate disposal, exacerbating air pollution, posing health risks, and reflecting inadequate waste management practices.
Although rice husk ash (RHA) and sawdust ash (SDA) exhibit recognized pozzolanic properties, localized research on their optimal utilization whether combined or singular in concrete formulations adapted to tropical climates remains insufficient. Critical knowledge gaps persist concerning appropriate replacement ratios, implications for workability, strength progression, durability under elevated humidity and thermal fluctuations, as well as broader economic and environmental advantages. In the absence of focused inquiry, these indigenous materials remain underleveraged, hindering the large-scale implementation of cost-effective, ecologically sustainable concrete alternatives.
1.3 Aim and Objectives of the Study
This study aims to examine the viability of RHA and SDA as economical partial substitutes for cement in tropical concrete applications.
The specific objectives are to:
- Characterize the physicochemical attributes of RHA and SDA.
- Identify optimal cement replacement proportions using RHA and SDA.
- Formulate and experimentally assess concrete mixes incorporating RHA and SDA.
- Analyze mechanical performance, with particular emphasis on compressive strength.
- Quantify the cost efficiency and environmental merits of employing RHA and SDA in concrete production.
1.4 Research Questions
- What physicochemical properties distinguish RHA and SDA?
- What proportions of cement can feasibly be replaced by RHA and/or SDA?
- What methodologies are appropriate for producing and evaluating RHA- and SDA-modified concrete mixes?
- How does compressive strength behave in concrete specimens containing RHA and SDA?
- What economic and ecological benefits arise from utilizing RHA and SDA as cement replacements?
1.5 Significance of the Study
By valorizing agricultural waste into functional cementitious materials, this research advances sustainable and economically viable construction practices. Positive findings may yield reductions in concrete production expenditures, diminished cement demand and associated CO₂ output, enhanced waste valorization, and the development of climatically resilient concrete. The outcomes hold relevance for civil engineers, construction professionals, regulatory bodies, housing authorities, and researchers pursuing low-cost, environmentally conscious infrastructure solutions in Nigeria and analogous tropical developing contexts.
1.6 Scope of the Study
The investigation encompasses laboratory-based processing of RHA and SDA, partial cement substitution (typically 0–30% by mass), production of standardized concrete mixes, and evaluation of both fresh and hardened properties with compressive strength as the primary metric. A preliminary cost-benefit and environmental impact assessment is included. The resultant concrete is intended for low- to moderate-strength tropical construction applications.
1.7 Limitations of the Study
Results are contingent upon waste material sourcing and processing methods, controlled laboratory conditions, and short-term testing protocols. Long-term performance under actual tropical field exposure lies beyond the study’s purview, as does industrial-scale manufacturing feasibility.
1.8 Definition of Key Terms
- Rice Husk Ash (RHA) — Fine pozzolanic ash produced from controlled burning of rice husks, high in amorphous silica.
- Sawdust Ash (SDA) — Ash from controlled burning of sawdust, used as a partial cement replacement.
- Partial Cement Replacement — Substituting a percentage of ordinary Portland cement with waste ashes.
- Tropical Areas — Hot, humid regions with heavy rainfall and temperature variations, such as most parts of Nigeria.
This chapter establishes the foundation for material characterization, mix design, experimental work, results, and conclusions in the subsequent chapters.
References
Agboola, S. A., Yunusa, U., Tukur, M., & Bappah, H. (2022). Strength performance of concrete produced with rice husk ash as partial replacement of cement. African Journal of Environmental Sciences and Renewable Energy, 5(1), 1–15.
Haruna, A. M. S., Kado, B., & Suleiman, A. (2025). Sustainable utilization of agricultural waste ashes in concrete through experimental evaluation of rice husk ash and sawdust ash as partial cement replacements. ResearchGate. https://www.researchgate.net/publication/397648876
Tesfaye, M., Puspitasari, S. D., Setyandito, O., Elamin, A., & Kamau, W. (2026). Sustainable concrete production through partial cement replacement using fly ash and rice husk ash. Tropical Environment, Biology, and Technology, 4(1), 1–10. https://doi.org/10.53623/tebt.v4i1.870