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Effect of Ground Granulated Blast Furnace Slag on Cement Concrete

    

Effect of Ground Granulated Blast Furnace Slag on Cement Concrete
Abstract
Ground Granulated Blast Furnace Slag (GGBFS) has emerged as one of the most widely adopted supplementary cementitious materials in concrete production, offering substantial sustainability benefits alongside notable improvements in durability and long-term strength . This study investigates the effect of GGBFS as a partial replacement for Ordinary Portland Cement on the fresh and hardened properties of concrete. Through comprehensive analysis of existing literature, the research examines the hydration mechanism, optimal replacement levels, strength development characteristics, and durability performance of GGBFS concrete. Findings demonstrate that GGBFS exhibits both latent hydraulic and pozzolanic reactivity, consuming calcium hydroxide to form additional calcium silicate hydrate gel. Optimal replacement levels range from 20% for strength-driven applications to 60–70% for superior durability in aggressive environments, with 40% delivering the highest composite performance under balanced criteria . GGBFS concrete typically exhibits reduced early-age strength but surpasses control mixes by 56 days and beyond, with significant improvements in chloride penetration resistance, sulfate resistance, and microstructure densification . The study concludes that GGBFS is a highly effective cement replacement material when used at appropriate levels, contributing to sustainable construction while maintaining or enhancing concrete performance.
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CHAPTER ONE: INTRODUCTION
1.1 Background of the Study
Concrete is the most extensively used construction material globally, and its production is 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 . The construction industry has increasingly adopted industrial by-products to reduce cement consumption and mitigate CO₂ emissions, with particular emphasis on the growing use of ground granulated blast furnace slag (GGBFS) .
GGBFS is a by-product of the iron and steel industry, produced by quenching molten blast furnace slag in water or air to form a glassy, granular material that is subsequently ground to a fine powder. The chemical composition of GGBFS consists primarily of calcium oxide (30–45%), silicon dioxide (30–40%), aluminum oxide (8–18%), and magnesium oxide (5–10%), with minor amounts of sulfur trioxide, iron oxide, and alkalis . This composition gives GGBFS both latent hydraulic and pozzolanic properties, enabling it to react with water and with calcium hydroxide liberated during cement hydration to form additional binding phases .
The use of GGBFS in concrete offers multiple benefits: it reduces the environmental impact of cement production, provides a beneficial use for an abundant industrial by-product, improves concrete durability, and enhances long-term strength development . While GGBFS is effective in reducing heat of hydration and is particularly suited for mass concrete applications, higher replacement levels often delay early strength development and may require adjustments in mix design and curing practices .
1.2 Statement of the Problem
Despite the widespread acceptance of GGBFS as a supplementary cementitious material, significant challenges remain in optimizing its use. The optimal replacement level of GGBFS varies considerably depending on the performance criteria prioritized: strength, durability, or sustainability . Identifying the optimal replacement level that balances mechanical performance, durability, and sustainability remains challenging .
The relationship between GGBFS content and early-age strength development is a practical concern. GGBFS concrete typically exhibits delayed early-age strength gain due to the slower reaction kinetics of slag compared to cement clinker . This delay may limit the application of high-volume GGBFS concrete in projects requiring rapid formwork removal or early loading.
Furthermore, the influence of GGBFS on workability and rheological properties requires consideration. Research indicates that GGBFS enhances the rheological behavior of fresh concrete by lowering both plastic viscosity and yield stress, improving flowability and pumpability . However, the specific effects depend on replacement level, slag fineness, and mix design parameters.
1.3 Aim and Objectives of the Study
1.3.1 Aim
The aim of this study is to investigate the effect of ground granulated blast furnace slag as a partial replacement for cement on the properties of concrete, with particular emphasis on strength development and durability performance.
1.3.2 Objectives
The specific objectives of this research are:
1. To examine the chemical composition and hydration mechanism of GGBFS in concrete.
2. To determine the optimal GGBFS replacement level for various performance criteria.
3. To assess the influence of GGBFS 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 GGBFS utilization in sustainable concrete production.
1.4 Research Questions
This study seeks to answer the following research questions:
1. What is the mechanism by which GGBFS contributes to concrete strength and durability?
2. What is the optimal replacement level of GGBFS for different performance criteria?
3. How does GGBFS replacement influence the workability and rheological properties of concrete?
4. How does GGBFS replacement affect strength development over time?
5. What are the practical implications of GGBFS 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 GGBFS 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 steel industry, the study supports beneficial utilization of an abundant by-product. The research also aligns with Sustainable Development Goal 11 (Sustainable Cities and Communities) by promoting sustainable infrastructure development .
1.6 Scope and Limitations of the Study
1.6.1 Scope
This study focuses on the investigation of GGBFS as a partial replacement for Ordinary Portland Cement in concrete. The investigation covers:
• Chemical composition and hydration mechanism of GGBFS.
• Optimal replacement levels for various performance criteria.
• Influence of GGBFS on workability and rheological properties.
• Compressive strength development at various curing ages.
• Durability characteristics including chloride penetration, sulfate resistance, and carbonation.
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 mechanical indicator, though other mechanical properties are discussed where relevant. The investigation is limited to normal and high-strength concrete and does not comprehensively address ultra-high-performance or specialty concrete applications.
1.7 Definition of Terms
Ground Granulated Blast Furnace Slag (GGBFS): A by-product of the iron and steel industry, produced by quenching molten blast furnace slag and grinding the resulting glassy granules to a fine powder.
Latent Hydraulic Activity: The property of GGBFS to react with water over time to form cementitious hydration products without the need for an external activator .
Pozzolanic Reaction: The chemical reaction between reactive silica/alumina in GGBFS and calcium hydroxide from cement hydration to form additional calcium silicate hydrate 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.
C-A-S-H Gel: Calcium aluminosilicate hydrate, the primary binding phase in GGBFS-blended cement systems, incorporating aluminum into the C-S-H structure .
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CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews existing literature on the use of ground granulated blast furnace slag as a partial replacement for cement and its effect on concrete properties. The review examines the chemical composition and hydration mechanism of GGBFS, the influence of GGBFS on fresh and hardened concrete properties, and optimal replacement levels reported in the literature.
2.2 GGBFS: Production, Composition, and Characteristics
2.2.1 Production Process
GGBFS is produced through a three-stage process: (1) molten blast furnace slag from iron production is rapidly quenched with water to form a glassy, granular material; (2) the granules are dried and ground to a fine powder; and (3) the ground slag is blended with Portland cement or added as a separate component in concrete mixing. The rapid quenching is critical to prevent crystallization and preserve the amorphous structure that gives GGBFS its hydraulic reactivity.