Use of Palm Kernel Shell Ash as a Partial Replacement for Cement

Use of Palm Kernel Shell Ash as a Partial Replacement for Cement
Abstract
Palm kernel shell ash (PKSA) is an agricultural by-product derived from the palm oil industry, offering potential as a supplementary cementitious material for sustainable concrete production. This study investigates the viability of PKSA as a partial replacement for Ordinary Portland Cement through comprehensive analysis of its chemical composition, pozzolanic reactivity, and effect on concrete properties. Findings demonstrate that PKSA contains significant silica content (31.5–63.4% SiO₂) with combined SiO₂, Al₂O₃, and Fe₂O₃ ranging from 73.1% to 85%, satisfying ASTM C618 requirements for pozzolanic materials when properly calcined . Optimal replacement levels range from 5% to 15%, with 10% consistently yielding the best balance of strength and durability performance . At 10% replacement, PKSA reduces drying shrinkage and sorptivity while improving late-age compressive strength . However, excessive replacement beyond 25% leads to strength reduction due to dilution effects and increased porosity . The study concludes that PKSA is a viable cement replacement material when used at appropriate levels, contributing to sustainable construction while addressing agricultural waste management challenges .
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CHAPTER ONE: INTRODUCTION
1.1 Background of the Study
Concrete is the most extensively used construction material globally, with its production heavily dependent on Portland cement. The cement industry accounts for approximately 7% of global carbon dioxide emissions, creating substantial environmental pressure to reduce clinker content in concrete . Simultaneously, the palm oil industry generates enormous quantities of palm kernel shells as by-products, presenting disposal challenges and environmental concerns.
Palm kernel shell (PKS) is the hard covering of the palm kernel that remains as waste after the kernel nut is removed and palm oil is extracted . In Malaysia alone, over 100 million tonnes of biomass wastes from oil palm were generated per year, while in Nigeria, poor disposal of up to 2.5 million tonnes of palm kernel shells has contributed to environmental pollution . When burned under controlled conditions, these shells produce palm kernel shell ash (PKSA), a material containing significant amounts of silica, alumina, and iron oxide .
The use of PKSA as a partial replacement for cement in concrete offers multiple benefits: it reduces the environmental impact of cement production, provides a beneficial use for an abundant agricultural by-product, and can enhance certain concrete properties through pozzolanic activity . Research has demonstrated that PKSA incorporation can improve late-age compressive strength, reduce drying shrinkage, and lower sorptivity when used at optimal replacement levels .
1.2 Statement of the Problem
Despite the recognized potential of PKSA as a supplementary cementitious material, several challenges hinder its widespread adoption. The optimal replacement level of PKSA varies considerably across studies, with reported optima ranging from 5% to 25% . This variability creates uncertainty for practical mix design and limits confidence in PKSA utilization.
Furthermore, PKSA concrete typically exhibits reduced workability compared to plain Portland cement concrete. Research consistently demonstrates that workability decreases with increasing PKSA content due to the fine particle size and angular shape of ash particles, which increase friction and water demand . The reduction in workability may necessitate adjustments in mix design, potentially offsetting some of the economic benefits of PKSA utilization.
The relationship between PKSA replacement level and strength development at different curing ages also requires clarification. While some studies report optimal performance at 5–10% replacement , others identify 25% as optimal . Understanding these discrepancies is essential for developing practical guidelines.
1.3 Aim and Objectives of the Study
1.3.1 Aim
The aim of this study is to investigate the suitability of palm kernel shell ash as a partial replacement for cement in concrete, with particular emphasis on its pozzolanic characteristics and effect on mechanical properties.
1.3.2 Objectives
The specific objectives of this research are:
1. To examine the chemical composition and pozzolanic characteristics of palm kernel shell ash.
2. To determine the optimal PKSA replacement level for maximum strength development.
3. To assess the influence of PKSA on fresh concrete properties including workability and setting time.
4. To evaluate compressive strength development at various curing ages.
5. To provide practical recommendations for PKSA utilization in sustainable concrete production.
1.4 Research Questions
This study seeks to answer the following research questions:
1. Does palm kernel shell ash possess the chemical composition and pozzolanic properties required for use as a cement replacement material?
2. What is the optimal replacement percentage of cement with PKSA for compressive strength?
3. How does PKSA replacement influence the workability and setting characteristics of concrete?
4. How does PKSA replacement affect strength development over time?
5. What are the practical implications of PKSA utilization for sustainable construction?
1.5 Significance of the Study
This research holds significance for multiple stakeholders. For civil engineers and concrete technologists, understanding the optimal PKSA replacement level enables informed mix design decisions that balance performance and sustainability. For the construction industry, the findings contribute to reducing cement consumption and associated carbon emissions. For the palm oil industry, the study supports beneficial utilization of an abundant by-product, addressing disposal challenges. The research also aligns with sustainability objectives by promoting waste valorization and reducing the environmental footprint of concrete construction .
1.6 Scope and Limitations of the Study
1.6.1 Scope
This study focuses on the investigation of PKSA as a partial replacement for Ordinary Portland Cement in concrete. The investigation covers:
• Chemical composition and pozzolanic characteristics of PKSA.
• Optimal replacement levels for PKSA in concrete.
• Influence of PKSA on workability and setting time.
• Compressive strength development at various curing ages.
• Practical implications for sustainable concrete production.
1.6.2 Limitations
The study is primarily based on a review of existing literature and does not include original laboratory experimental work. The focus is on compressive strength as the primary performance indicator, though durability properties are discussed where relevant. The investigation is limited to normal-strength concrete and does not comprehensively address high-performance or specialty concrete applications.
1.7 Definition of Terms
Palm Kernel Shell Ash (PKSA): A pozzolanic material produced by burning palm kernel shells under controlled temperature conditions, containing silica, alumina, and iron oxide .
Pozzolanic Reaction: The chemical reaction between reactive silica/alumina in PKSA and calcium hydroxide from cement hydration to form calcium silicate hydrate (C-S-H) gel.
Supplementary Cementitious Material (SCM): A material that, when used in conjunction with Portland cement, contributes to the properties of hardened concrete through hydraulic or pozzolanic activity.
Calcination: The thermal treatment process of burning raw materials at controlled temperatures to produce ash with desired properties.
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CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews existing literature on the use of palm kernel shell ash as a partial replacement for cement and its effect on concrete properties. The review examines the chemical composition and pozzolanic characteristics of PKSA, the influence of PKSA on fresh and hardened concrete properties, and optimal replacement levels reported in the literature.
2.2 Palm Kernel Shell Ash: Production and Characteristics
2.2.1 Production Process
PKSA is produced by burning palm kernel shells, a by-product of palm oil extraction. The burning temperature and conditions significantly influence the properties of the resulting ash. Research has employed various calcination regimes, with temperatures ranging from 500°C to 1000°C for periods of 1.5 hours . Studies have demonstrated that a temperature of 600°C allows for higher silica content and exhibits lower carbon contents .
The physical processes applied before and after calcination also influence ash quality. Research has shown that cutting, grinding, and crushing processes play a key role in improving pozzolanic properties by reducing particle size and increasing specific surface area, thereby increasing the reactive surface area and optimizing silica release .
2.2.2 Chemical Composition
PKSA is characterized by significant silica content, with SiO₂ ranging from 31.5% to 63.4% according to previous researchers' reports . The aluminate composition (Al₂O₃) of PKSA ranges from 2.30% to 16.50%, while ferrous oxide (Fe₂O₃) ranges from 1.80% to 12.30% .