The production of Portland cement clinker has a share of about 6% to 8% on the global CO2-emissions . Approximately 60% of those emissions are attributable to the decarbonation of limestone. A widespread approach for the reduction of the CO2-emissions is to
replace the clinker in the cement by pozzolanic waste materials, e.g. fly ash. The reaction of fly ash is generally slow. Due to this slow reaction cement pastes mixed of Portland cement and fly ash have a slower strength development than pure Portland cement, at least at early ages up to 7 days. The goal of this study was to increase early strength properties of Portland cement/fly ash blends by increasing the early ettringite formation in order to decrease the porosity. Therefore various amounts of anhydrite and laboratory synthesised C3A were added to Portland cement/fly ash systems that contained 30% fly ash. The behavior of these systems in terms of kinetics, phase development and microstructure was studied by means of strength tests, isothermal calorimetry, thermogravimetric analysis, chemical shrinkage, X-ray diffraction, backscattered electron image analysis, mercury intrusion porosimetry and thermodynamic modeling. In addition the activation by Na2SO4 was investigated on certain systems.
It was found that the amount of ettringite formed increases gradually with increasing amounts of anhydrite and C3A. The formation of ettringite was completed at approximately 1 day. Further the activation with Na2SO4 increased the amount of ettringite
and shifted the completion of its formation to approximately 2 days. Due to the addition of anhydrite and C3A the porosity decreased corresponding to the amount of ettringite formed. The effects on the development of early strength were most distinct for very high
additions and for systems activated by Na2SO4. All systems showed equal strengths at 7 d and 28 d. For later ages up to 90 days, the benefits at early ages were found to be inversed, leading to lower strength values compared to systems without or with low additions
of anhydrite, C3A or Na2SO4. Eventually the increase in early strength was either too low to be significant or only relevant at very high additions of anhydrite and C3A with simultaneous system activation by Na2SO4. In terms of kinetics a remarkable impact of
the added C3A was observed as this seemed to significantly accelerate the silicate reaction of the Portland cement.
Table of Contents
- Chapter 1 Introduction
- 1.1 Outline of the Development of Ordinary Portland Cement
- 1.2 Research Objectives
- Chapter 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
- 2.1 Ordinary Portland Cement
- Chapter 3 Materials
- 3.1 Portland Cement
- 3.2 Fly Ash
- 3.3 Anhydrite
- 3.4 Laboratory synthesised C3A
- Chapter 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
- Chapter 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
- 5.1 Effect of Fly Ash, Anhydrite and C3A on the development of compressive strength
Objectives and Key Themes
The main objective of this study was to improve the early strength properties of Portland cement/fly ash blends by reducing porosity through increased ettringite formation. This was achieved by adding various amounts of anhydrite and laboratory-synthesized C3A to the cement/fly ash systems.
- Influence of supplementary cementitious materials (SCMs) on Portland cement hydration
- Early strength development in Portland cement/fly ash blends
- Effect of anhydrite and C3A additions on ettringite formation and porosity
- Impact of Na2SO4 activation on fly ash reactivity
- Relationship between microstructure, phase development, and mechanical properties
Chapter Summaries
Chapter 1 Introduction: This chapter provides a historical overview of cement development, from early hydraulic binders to modern Ordinary Portland Cement (OPC). It highlights the environmental concerns associated with OPC production, particularly CO2 emissions, and introduces the use of supplementary cementitious materials (SCMs) like fly ash to mitigate these issues. The chapter concludes by outlining the research objectives of the thesis, focusing on enhancing early-age strength in OPC/fly ash blends by manipulating ettringite formation and fly ash reactivity.
Chapter 2 Fundamentals: This chapter details the fundamental principles relevant to the thesis. It covers the chemistry and hydration of OPC, including the mechanisms of hydration for the main clinker phases (C3S, C2S, C3A, C4AF) and the development of microstructure. The chapter also delves into the characteristics of fly ash, the pozzolanic reaction, interactions between OPC and fly ash, and methods for activating fly ash reactivity.
Chapter 3 Materials: This chapter describes the materials used in the study, providing detailed chemical and phase composition analyses for the Portland cement (CEM I 42.5 R), fly ash (type V), anhydrite, and the laboratory-synthesized tricalcium aluminate (C3A). The synthesis method for C3A is also detailed, including quality control measures.
Chapter 4 Sample Preparation and Methods: This chapter outlines the experimental methodology. It describes the mix designs for the various cement blends, the procedures for preparing paste and mortar samples, and the techniques employed for analyzing compressive and flexural strength, isothermal calorimetry, thermogravimetric analysis, chemical shrinkage, X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry. Thermodynamic modeling using the GEMS-PSI geochemical code is also explained.
Chapter 5 Experimental Results and Discussion: This chapter presents and discusses the experimental results obtained using the methods described in Chapter 4. The chapter is divided into sections covering the effects of different variables on the properties of the cement blends. Each section includes an extensive analysis of the data from various characterization techniques.
Keywords
Portland cement, fly ash, supplementary cementitious materials, anhydrite, tricalcium aluminate (C3A), ettringite, hydration, early strength development, porosity, Na2SO4 activation, microstructure, thermodynamic modeling, GEMS-PSI.
Frequently Asked Questions about "A Comprehensive Language Preview"
What is the overall topic of this document?
This document provides a comprehensive preview of a research study focusing on improving the early strength properties of Portland cement/fly ash blends by manipulating ettringite formation and fly ash reactivity. It includes a table of contents, research objectives, chapter summaries, and keywords.
What are the main research objectives?
The primary objective is to enhance the early strength properties of Portland cement and fly ash mixtures by reducing porosity through increased ettringite formation. This is achieved by varying the amounts of anhydrite and C3A added to the cement/fly ash systems.
What materials are used in the study?
The study uses Portland cement (CEM I 42.5 R), fly ash (type V), anhydrite, and laboratory-synthesized tricalcium aluminate (C3A). The synthesis method for C3A is detailed in the document.
What are the key themes explored in the research?
Key themes include the influence of supplementary cementitious materials (SCMs) on Portland cement hydration, early strength development in Portland cement/fly ash blends, the effect of anhydrite and C3A additions on ettringite formation and porosity, the impact of Na2SO4 activation on fly ash reactivity, and the relationship between microstructure, phase development, and mechanical properties.
What methods are used to investigate the materials?
The research employs a range of techniques including mix design for paste and mortar samples, compressive and flexural strength testing, isothermal calorimetry, thermogravimetric analysis, chemical shrinkage measurement, X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, and thermodynamic modeling using the GEMS-PSI geochemical code.
How are the experimental results organized and presented?
Chapter 5 presents and discusses the experimental results. It is structured to show the effects of fly ash, anhydrite, and C3A on compressive strength, and further explores the influence of elevated anhydrite and C3A contents in the presence of fly ash. The impact of Na2SO4 activation is also investigated. Each section includes detailed analysis from various characterization techniques, including data from isothermal calorimetry, thermogravimetric analysis, chemical shrinkage measurements, X-ray diffraction, SEM image analysis, and mercury intrusion porosimetry. Thermodynamic modeling results are also included.
What are the key findings (in general terms)?
The study aims to determine how different additions (anhydrite, C3A, Na2SO4) affect the early-age strength, porosity, and microstructure of Portland cement/fly ash blends. The detailed findings are presented in Chapter 5, but the overall goal is to improve the early strength properties by controlling ettringite formation and fly ash reactivity.
What are the keywords associated with this research?
Keywords include: Portland cement, fly ash, supplementary cementitious materials, anhydrite, tricalcium aluminate (C3A), ettringite, hydration, early strength development, porosity, Na2SO4 activation, microstructure, thermodynamic modeling, GEMS-PSI.
What is the purpose of the thermodynamic modeling?
Thermodynamic modeling, using the GEMS-PSI geochemical code, helps to understand the phase development and volume changes in the cement blends over time, providing further insight into the observed experimental results.
- Citar trabajo
- Axel Schöler (Autor), 2012, Study of hydration processes of Portland cements blended with supplementary cementitious materials, Múnich, GRIN Verlag, https://www.grin.com/document/199418
