Study of hydration processes of Portland cements blended with supplementary cementitious materials

Table of Contents

1 Introduction

1.1 Outline of the Development of Ordinary Portland Cement

1.2 Research Objectives

2 Fundamentals

2.1 Ordinary Portland Cement

2.1.1 Mechanisms of Portland Cement Hydration

2.1.2 Development of Microstructure

2.1.3 The System C3A-CaSO4-H2O

2.2 Fly Ash

2.2.1 The Pozzolanic Reaction and the Hydration of Fly Ash

2.2.2 Interactions between Ordinary Portland Cement and Fly Ash

2.2.3 Activation of Fly Ash

3 Materials

3.1 Portland Cement

3.2 Fly Ash

3.3 Anhydrite

3.4 Laboratory synthesised C3A

4 Sample Preparation and Methods

4.1 Mix Design

4.2 Procedures of Sample Preparation

4.2.1 Paste Samples

4.2.2 Mortar Samples

4.3 Investigation of Flexural and Compressive Strength

4.4 Isothermal Calorimetry

4.5 Thermogravimetric Analysis

4.6 Chemical Shrinkage

4.7 X-Ray Diffraction

4.8 Scanning Electron Microscopy

4.9 Mercury Intrusion Porosimetry

4.10 Thermodynamic Modelling

5 Experimental Results and Discussion

5.1 Effect of Fly Ash, Anhydrite and C3A on the development of compressive strength

5.1.1 Compressive strength

5.1.2 Isothermal Calorimetry

5.1.3 Thermogravimetric Analysis

5.1.4 Chemical Shrinkage

5.1.5 X-ray Diffraction

5.1.6 SEM Image Analysis

5.1.7 Mercury intrusion Porosimetry

5.2 Effect of elevated Anhydrite and C3A contents upon presence of Fly Ash

5.2.1 Compressive strength

5.2.2 Isothermal Calorimetry

5.2.3 Thermogravimetric Analysis

5.2.4 Chemical Shrinkage

5.2.5 X-ray Diffraction

5.2.6 SEM Image Analysis

5.2.7 Mercury Intrusion Porosimetry

5.3 Effect of System Activation via Na2SO4

5.3.1 Mechanical Properties

5.3.2 Isothermal Calorimetry

5.3.3 Thermogravimetric Analysis

5.3.4 Chemical Shrinkage

5.3.5 X-ray Diffraction

5.3.6 SEM Image Analysis

5.3.7 Mercury intrusion Porosimetry

5.4 Thermodynamic Modelling

5.4.1 Calculated volume of the phases as a function of time

5.4.2 Calculated volume of the phases at complete reaction

6 Conclusions

Research Objectives and Key Themes

This thesis investigates methods to improve the early strength development of Portland cement/fly ash blends, which typically show slower strength gain than pure Portland cement due to the slow pozzolanic reaction of fly ash. The research aims to decrease early-age porosity by increasing early ettringite formation through the addition of anhydrite and synthetically produced tricalcium aluminate (C3A), as well as by investigating chemical activation using sodium sulfate (Na2SO4).

• Optimization of early-age compressive strength in blended cement systems.
• Impact of anhydrite and C3A additions on hydration kinetics and ettringite formation.
• Chemical activation of fly ash systems using Na2SO4.
• Microstructural and phase development characterization using advanced analytical techniques.
• Thermodynamic modeling to predict hydrate phase evolution.

Excerpt from the Book

Summary of Chapters

1 Introduction: Provides an overview of the development of Portland cement, its industrial significance, and the research objectives regarding the acceleration of fly ash-blended cements.

2 Fundamentals: Covers the basic chemistry of Portland cement hydration, the role of supplementary cementitious materials like fly ash, and the relevant theories behind the hydration and pozzolanic reactions.

3 Materials: Details the chemical and physical properties of the materials used in the study, including Portland cement, fly ash, anhydrite, and the synthesised tricalcium aluminate.

4 Sample Preparation and Methods: Describes the experimental design, the mixing procedures, and the analytical methods employed, such as calorimetry, TGA, XRD, SEM, MIP, and thermodynamic modeling.

5 Experimental Results and Discussion: Presents and discusses the findings from the experimental matrix, analyzing the influence of fly ash, anhydrite, C3A, and Na2SO4 on hydration kinetics, phase development, and mechanical properties.

6 Conclusions: Summarizes the key findings of the research, noting that while the additions and activation affected hydration products like ettringite and porosity, they did not lead to significant long-term strength improvements.

Keywords

Portland cement, fly ash, hydration, ettringite, anhydrite, tricalcium aluminate, pozzolanic reaction, compressive strength, porosity, thermogravimetric analysis, mercury intrusion porosimetry, thermodynamic modeling, sodium sulfate, cement chemistry, microstructure.

Frequently Asked Questions

What is the primary goal of this research?

The primary goal is to improve the early-age compressive strength of Portland cement blended with fly ash, as these blends typically exhibit slower strength development compared to pure Portland cement.

What are the central themes of the work?

The central themes include cement hydration mechanisms, the influence of supplementary cementitious materials (fly ash), the role of ettringite in strength development, and the effectiveness of chemical activation in modifying the cement paste structure.

Which scientific methods are used in this study?

The study employs a variety of analytical techniques, including strength testing, isothermal calorimetry, thermogravimetric analysis (TGA), chemical shrinkage measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and thermodynamic modeling via GEMS.

What is the role of ettringite in these cement systems?

Ettringite formation is essential for set regulation and contributes to strength development by reducing the porosity of the hydrating system through the growth of solid phases in air voids.

What does the main part of the thesis cover?

The main part focuses on the experimental results divided into three groups: the effect of basic additions (fly ash, anhydrite, C3A), the effect of elevated levels of anhydrite and C3A, and the impact of chemical activation using sodium sulfate (Na2SO4).

What are the key technical terms characterizing this research?

Key terms include Ordinary Portland cement (OPC), pozzolanic reaction, hydration kinetics, microstructure, ettringite, C-S-H (calcium silicate hydrate), and phase development.

Does the addition of anhydrite and C3A consistently improve strength?

The study indicates that while these additions influence phase development and porosity, they do not lead to significant, consistent increases in compressive strength compared to the base blends across all time intervals.

What specific effect does sodium sulfate (Na2SO4) have on the activation of fly ash?

Na2SO4 acts as a chemical activator that generally accelerates the hydration processes in the short term, though this beneficial effect on early strength is often lost or inverted at later stages of hydration (e.g., from 7 days onwards).