Investigation of the Use of Sawdust Ash as a Cement Replacement Material

Investigation of the Use of Sawdust Ash as a Cement Replacement Material
Abstract
The partial replacement of cement with sawdust ash (SDA) represents a promising approach to sustainable concrete production, offering dual benefits of reducing cement consumption and providing beneficial utilization of an abundant wood-processing by-product. This study investigates the suitability of SDA as a supplementary cementitious material through comprehensive analysis of its chemical composition, pozzolanic reactivity, and effect on concrete properties. Findings demonstrate that SDA possesses pozzolanic characteristics, with combined SiO₂, Al₂O₃, and Fe₂O₃ content exceeding 70% as required by ASTM C618 . Optimal replacement levels range from 5% to 15%, with 10% consistently yielding the best balance of strength and durability performance . At 10% replacement, compressive strength improvements of up to 51.5% compared to control mixes have been reported . However, excessive replacement beyond 15–20% reduces strength due to dilution effects and increased porosity . The study concludes that SDA is a viable cement replacement material when used at appropriate levels, contributing to sustainable construction practices while maintaining adequate concrete performance.
________________________________________
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 wood-processing industry generates large quantities of sawdust as a by-product, presenting disposal challenges and environmental concerns.
Sawdust ash (SDA) is produced by burning sawdust, a fine powdery wood waste generated during sawing, grinding, drilling, and sanding operations . When burned under controlled conditions, sawdust produces ash containing significant amounts of silica (SiO₂), alumina (Al₂O₃), and iron oxide (Fe₂O₃) . Research has confirmed that when the combined content of these three oxides exceeds 70%, the material exhibits pozzolanic properties as defined by ASTM C618 .
The use of SDA 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/industrial by-product, and can enhance certain concrete properties through pozzolanic activity . Research has demonstrated that SDA incorporation can improve compressive strength at optimal replacement levels, reduce permeability, and contribute to sustainable construction practices .
1.2 Statement of the Problem
Despite the recognized potential of SDA as a supplementary cementitious material, several challenges hinder its widespread adoption. The optimal replacement level of SDA varies considerably across studies, with reported optima ranging from 5% to 15% . This variability creates uncertainty for practical mix design and limits confidence in SDA utilization.
Furthermore, SDA concrete typically exhibits reduced workability compared to plain Portland cement concrete. Research consistently demonstrates that slump decreases as SDA content increases, attributed to the fine particle size and angular shape of SDA 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 SDA utilization.
The relationship between SDA replacement level and strength development at different curing ages also requires clarification. While some studies report optimal performance at 5% replacement , others identify 10% as optimal , and still others report beneficial effects up to 15% . 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 sawdust 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 sawdust ash.
2. To determine the optimal SDA replacement level for maximum strength development.
3. To assess the influence of SDA 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 SDA utilization in sustainable concrete production.
1.4 Research Questions
This study seeks to answer the following research questions:
1. Does sawdust 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 SDA for compressive strength?
3. How does SDA replacement influence the workability and setting characteristics of concrete?
4. How does SDA replacement affect strength development over time?
5. What are the practical implications of SDA 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 SDA 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 wood-processing industry, the study supports beneficial utilization of sawdust, 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 SDA as a partial replacement for Ordinary Portland Cement in concrete. The investigation covers:
• Chemical composition and pozzolanic characteristics of SDA.
• Optimal replacement levels for SDA in concrete.
• Influence of SDA 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
Sawdust Ash (SDA): A pozzolanic material produced by burning sawdust under controlled temperature conditions, containing silica, alumina, and iron oxide.
Pozzolanic Reaction: The chemical reaction between reactive silica/alumina in SDA 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.
Optimal Replacement Level: The percentage of cement replacement with SDA that yields maximum performance benefits without compromising concrete properties.
C-S-H Gel: Calcium silicate hydrate, the primary binding phase responsible for strength development in hardened concrete.
________________________________________
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews existing literature on the use of sawdust ash as a partial replacement for cement and its effect on concrete properties. The review examines the chemical composition and pozzolanic characteristics of SDA, the influence of SDA on fresh and hardened concrete properties, and optimal replacement levels reported in the literature.
2.2 Sawdust Ash: Production and Characteristics
2.2.1 Production Process
Sawdust ash is produced by burning sawdust, a by-product of wood processing operations. The burning temperature and conditions significantly influence the properties of the resulting ash. Research has employed various calcination regimes, including burning at 600°C for 1–2 hours , 700°C for 1 hour , and 800°C . Controlled calcination at 600°C for 2 hours has been found to provide the best balance of pozzolanic reactivity .