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Use of Waste Glass Powder as a Partial Replacement for Cement

    

Use of Waste Glass Powder as a Partial Replacement for Cement
Abstract
Waste glass powder (WGP) is a silica-rich industrial by-product with pozzolanic properties, offering significant potential as a supplementary cementitious material for sustainable concrete production. This study investigates the viability of WGP 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 WGP contains high amorphous silica content (approximately 80% SiO₂), satisfying pozzolanic material requirements . Optimal replacement levels range from 10% to 20%, with 10% consistently yielding improved compressive strength, enhanced chloride resistance, and reduced water absorption . At 10% replacement, concrete exhibits greater compressive strength than control mixes and significantly improved resistance to chloride ion penetration . However, excessive replacement beyond 25–30% reduces compressive strength due to decreased flowability and increased porosity . WGP concrete demonstrates enhanced durability through micro-filling and pozzolanic reactions, forming secondary C-S-H gel that densifies the microstructure . Life cycle assessment indicates a 25.7% reduction in CO₂-equivalent emissions with WGP incorporation . The study concludes that WGP is a viable cement replacement material when used at appropriate levels, contributing to sustainable construction while addressing glass 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 5–9% of global anthropogenic carbon dioxide emissions, creating substantial environmental pressure to reduce clinker content in concrete . Simultaneously, vast quantities of waste glass are generated annually, with significant portions ending up in landfills due to impurities, undesirable colors, or cost concerns .
Waste glass is a highly accessible material that can serve as an alternative to cement. Only a portion of waste glass is repurposed through recycling to create fresh glass products; the remainder is discarded due to contamination or mixed colors . Globally, yearly manufacture of waste glass exceeds one million tons, presenting both environmental challenges and opportunities for beneficial utilization .
Crushed waste glass is notable for its composition, comprising substantial quantities of calcium and silicon along with an amorphous structure. These characteristics give waste glass cementitious or pozzolanic attributes, making it a viable partial substitute for cement . The utilization of waste glass powder (WGP) as a pozzolanic additive dates back to the 1970s, arising as a solution to mounting glass waste accumulation . Research has demonstrated that recycling glass waste into concrete can help reduce pollution, save natural resources, and produce more affordable and sustainable concrete .
1.2 Statement of the Problem
Despite the recognized potential of WGP as a supplementary cementitious material, several challenges hinder its widespread adoption. The optimal replacement level of WGP varies across studies, with reported optima ranging from 10% to 20% depending on mix design, glass fineness, and performance criteria . This variability creates uncertainty for practical mix design.
Furthermore, WGP concrete typically exhibits reduced early-age strength compared to plain Portland cement concrete. Research demonstrates that early-age strength is lower due to slower and delayed hydration processes, leading to low early strength and high strength after prolonged curing . The reduction in early strength may limit application in projects requiring rapid strength development.
The relationship between WGP replacement level and durability characteristics also requires clarification. While some studies report improved chloride resistance and reduced water absorption , others report increased water absorption with higher WGP content due to insufficient calcium hydroxide to trigger pozzolanic reaction . 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 waste glass powder as a partial replacement for cement in concrete, with particular emphasis on its pozzolanic characteristics and effect on strength and durability properties.
1.3.2 Objectives
The specific objectives of this research are:
1. To examine the chemical composition and pozzolanic characteristics of waste glass powder.
2. To determine the optimal WGP replacement level for maximum performance.
3. To assess the influence of WGP 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 WGP utilization in sustainable concrete production.
1.4 Research Questions
This study seeks to answer the following research questions:
1. Does waste glass powder 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 WGP for compressive strength?
3. How does WGP replacement influence the workability and setting characteristics of concrete?
4. How does WGP replacement affect strength development over time?
5. What are the practical implications of WGP 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 WGP 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 waste management authorities, the study supports beneficial utilization of glass waste, 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 WGP as a partial replacement for Ordinary Portland Cement in concrete. The investigation covers:
• Chemical composition and pozzolanic characteristics of WGP.
• Optimal replacement levels for WGP in concrete.
• Influence of WGP on workability and setting time.
• Compressive strength development at various curing ages.
• Durability characteristics including chloride resistance and water absorption.
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
Waste Glass Powder (WGP): A fine powder produced by crushing, grinding, and sieving waste glass, containing high amorphous silica content with pozzolanic properties.
Pozzolanic Reaction: The chemical reaction between reactive silica in WGP and calcium hydroxide from cement hydration to form calcium silicate hydrate (C-S-H) gel.
Amorphous Silica: Non-crystalline silicon dioxide with high reactivity, essential for pozzolanic activity.
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.
C-S-H Gel: Calcium silicate hydrate, the primary binding phase responsible for strength development in hardened concrete.
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CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews existing literature on the use of waste glass powder as a partial replacement for cement and its effect on concrete properties. The review examines the production and characteristics of WGP, the pozzolanic reaction mechanism, the influence of WGP on fresh and hardened concrete properties, and optimal replacement levels reported in the literature.