Ecole Centrale de Nantes

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SCIENCESPOURL’INGENIEUR,GEOSCIENCES,ARCHITECTURE Année 2010

Thèse de D

et par L’Université Libre de Bruxelles, d’autre part

Spécialité : Génie Civil

Présentée et soutenue publiquement par : MUHAMMAD IRFAN AHMAD KHOKHAR

le 14 septembre 2010 à l’Ecole Centrale de Nantes

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EFFECT ON MICROSTRUCTURE

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Président : M. Abdelkarim AÏT-MOKHTAR Professeur à l’Univeristé de la Rochelle Rapporteurs : Mme Nele DE BELIE Professeure à l’Université de Gand

M. Gilles ESCADEILLAS Professeur à l’Université de Toulouse

Examinateurs : Mme Marie-Paule DELPLANCKE Professeure à l’Université Libre de Bruxelles M. Bernard ESPION Professeur à l’Université Libre de Bruxelles M. Frédéric GRONDIN Maître de Conférences à l’Ecole Centrale de Nantes M. Ahmed LOUKILI Professeur à l’Ecole Centrale de Nantes

Mme Stéphanie STAQUET Professeure Assistant à l’Université Libre de Bruxelles

Directeur de thèse : Ahmed LOUKILI, Professeur

Laboratoire : Institut de Recherche en Génie Civil et Mécanique, GeM, UMR CNRS 6183 Co-directeur de thèse : Stéphanie STAQUET, Professeure Assistant

Laboratoire : Service BATir, Université Libre de Bruxelles Co-encadrant : Frédéric GRONDIN, Maître de conférences

Laboratoire : Institut de Recherche en Génie Civil et Mécanique, GeM, UMR CNRS 6183

N° ED 498-119

To my parents-they illuminated my path and inspired me throughout my life,

I gratefully dedicate this work.

Acknowledgement

The research project, which has resulted in this thesis, was performed while the author was a doctoral student at the Research Institute of Civil and Mechanical Engineering, Ecole Centrale de Nantes, France and Civil Engineering Department, Université Libre de Bruxelles, Belgium. The financial support of the Higher Education Commission of Pakistan, the Research Institute of Civil and Mechanical Engineering, the Belgian National Foundation for Scientific Research (FNRS) and the French National Research Agency (ANR) is gratefully acknowledged.

I would like to express my deep and sincere gratitude to my supervisors, Professor Ahmed Loukili, Ph.D., Research Institute of Civil and Mechanical Engineering, Ecole Centrale de Nantes, France and Assistant Professor Stéphanie Staquet, Ph.D., Civil Engineering Department, Université Libre de Bruxelles, Belgium. Their wide knowledge and their logical way of thinking have been of great value for me. Their understanding, encouraging and personal guidance have provided a good basis for the present thesis.

I am deeply grateful to my co-supervisor, Frédéric Grondin, Ph.D., Associate Professor, Research Institute of Civil and Mechanical Engineering, Ecole Centrale de Nantes, France, for his detailed and constructive comments, and for his important support throughout this work.

I also wish to express thanks to the official referees, Professor Nele De Belie, Department of Structural Engineering, University of Gent, Belgium and Professor Gilles Escadeillas, Laboratory of Materials and Construction Durability, Université Paul Sabatier-Toulouse, France for their detailed review, constructive criticism and excellent advice during the preparation of this thesis.

My warm thanks are due to Professor Abdelkarim Aït-Mokhtar, LEPTiAB, Université de La Rochelle, France, Professor Bernard Espion and Professor Marie-Paule Delplancke- Ogletree, Université Libre de Bruxelles, Belgium for their participation in defense jury.

I warmly thank Philippe Turcry, Associate Professor, Pierre Mounanga, Professor, and.

Emmanuel Roziere, Associate Professor, for their valuable advice and friendly help. Their extensive discussions around my work and interesting explorations during the experimental work have been very helpful for this study.

I wish to express my warm and sincere thanks to Dr Aveline Darquenne for her technical support during this study.

I am grateful to Professor Bernard Espion of Civil Engineering Department and Professor Marie-Paule Delplancke-Ogletree of Department of Chemicals and Material of Université Libre de Bruxelles for allowing me to use the equipment and facilities at their respective departments.

It was not possible to carry out the extensive experimental work during this study without the active support and participation of the laboratory technicians. I wish to thank Mr. Jean- Yves Letouzo, Mr. Patrick Denain and Mr. Marc Schaba from Ecole Centrale de Nantes, Mr.

Gilles Vanhooren and Olivier Leclercq from Service BATir of ULB, Ms Titiana Segato and Mr Patrizio Madau from Department of Chemicals and Materials.

I owe my most sincere gratitude to colleagues at the Ecole Centrale de Nantes and Université Libre de Bruxelles and students who have been involved in research project are acknowledged for their stimulating collaboration. I would like to mention in particular among the students: Rana El-Hachem, Nicolas Poncelet, Yannick Thomas and Thomas Gehlen.

My sincere thanks go to my Pakistani friends in France and particularly in Nantes as well. I enjoyed very much the time in the evening or during the weekends when we were cooking together, playing games, traveling around, or simply chatting. Many of them deserve my special thanks because beside the wonderful hours we stayed together, they helped me with my research as well. An incomplete list includes: Afaque, Amir Baqai, Amir Shehzad, Atif, Bilal, Hassan, Jamil, Kamran, Kashif, Quaid, Raza, Sami, Shoaib and Yasir.

Finally, I express my deepest gratitude to my family for all their love, support, and encouragement throughout my life to this point. Without their guidance and encouragement this work would not have been possible. I especially want to thank my parents for their many sacrifices that have provided me with the opportunities that enable me to pursue this type of study. I will always be grateful for everything they have done and owe them a debt that can never be repaid – Thank you for everything.

My special gratitude is due to my brothers and my sister for their loving support. I owe my loving thanks to my wife Shumaila Irfan and my son Muizz Ahmad Khokhar. I can’t forget the positive support of my in-laws specially my parents-in-law, during the difficult times while my stay abroad. Without their encouragement and understanding it would have been impossible for me to finish this work.

M. Irfan Ahmad Khokhar

Table of Contents

Acknowledgement___________________________________________________________ 4 Résumé __________________________________________________________________ 10 Abstract __________________________________________________________________ 11 Introduction ______________________________________________________________ 13 1 Standard Recommandations and Bibliography ______________________________ 17

1.1 Standard Recommendations for the use of mineral additions and concept of

equivalent binder content_______________________________________________________ 17 1.1.1 The traditional approach or standard requirement____________________________________ 18 1.1.2 The French Standard specificities ________________________________________________ 20 1.1.3 The equivalence of performance and limitations of the prescriptive approach ______________ 21 1.2 The cement properties in concrete _________________________________________ 22 1.2.1 Hydration of cement __________________________________________________________ 22 1.2.2 Evolution of setting of cement concrete ___________________________________________ 25 1.2.3 Early-age behaviour of cement concrete ___________________________________________ 26 1.2.4 Durability __________________________________________________________________ 27 1.3 Mineral Additions properties _____________________________________________ 27 1.3.1 Ground granulated blast furnace slag (GGBFS) _____________________________________ 28 1.3.2 Fly ash _____________________________________________________________________ 33 1.3.3 Limestone Filler _____________________________________________________________ 35 1.3.4 Blended Cements ____________________________________________________________ 37 1.4 Environemental impact of cement replacement by mineral additions in concrete __ 38 1.4.1 Calculation of the CO₂ emissions ________________________________________________ 38 1.4.2 Influence of mineral additions in reducing the CO₂ emissions __________________________ 40 1.5 The Project “Ecobéton” (Green Concrete) __________________________________ 41 1.5.1 State of art of green concrete projects _____________________________________________ 41 1.5.2 Presentation of the Project Ecobéton______________________________________________ 42 1.5.3 Interest of the project Ecobéton__________________________________________________ 43

2 Mix design and Optimisation _____________________________________________ 45 2.1 Feasibility study and substitution principle__________________________________ 45

2.1.1 Mix design of mortars with binary binders (mono-additions)___________________________ 45 2.1.2 Mix design of mortars with ternary binders (bi-additions) _____________________________ 45 2.2 Materials used in the study _______________________________________________ 49 2.2.1 Cementitious Materials ________________________________________________________ 49 2.2.2 Physico-chemical characterisation _______________________________________________ 53 2.2.3 Aggregates _________________________________________________________________ 54 2.2.4 Water reducing admixtures (Superplasticizers)______________________________________ 56 2.3 Main properties measured in the case of a simple substitution __________________ 56 2.3.1 Setting time _________________________________________________________________ 56 2.3.2 Compressive strength _________________________________________________________ 60 2.3.3 Carbonation (Aspect durability) _________________________________________________ 62 2.4 Optimisation of the concrete mixtures ______________________________________ 65 2.4.1 Mixture Proportioning Method __________________________________________________ 65 2.4.2 Mixture proportions and experimental procedures ___________________________________ 67 2.4.3 Experimental results for optimised concrete mixtures ________________________________ 70 2.4.4 Synthesis of the optimisation approach____________________________________________ 79 2.5 Suggestion on activation _________________________________________________ 80 2.5.1 Direct Activation _____________________________________________________________ 81 2.5.2 Indirect Activation ___________________________________________________________ 84 2.5.3 Discussion on the influence of activators __________________________________________ 86

3 Hydration and Activation Energy _________________________________________ 87 3.1 Study of setting of concretes by Ultrasonic method ___________________________ 87

3.1.1 Setting determination by ultrasonic waves _________________________________________ 88 3.1.2 The FreshCon device__________________________________________________________ 89 3.1.3 Experimental results __________________________________________________________ 92 3.1.4 Synthesis __________________________________________________________________ 102 3.2 Heat of hydration ______________________________________________________ 103 3.2.1 Monitoring the evolution of heat release in mortars by Isothermal calorimeter ____________ 103 3.2.2 Monitoring the evolution of heat release in concretes by adiabatic calorimeter ____________ 107 3.3 Determination of activation energy _______________________________________ 119 3.3.1 Maturometry and equivalent age concepts ________________________________________ 119 3.3.2 Apparent Activation Energy (AE)_______________________________________________ 120 3.3.3 Determination of Ea by calorimetric method ______________________________________ 121 3.3.4 Experimental results of Ea ____________________________________________________ 124 3.4 Advancement of degree of hydration ______________________________________ 131 3.4.1 Method based upon determination of heat flow ____________________________________ 132 3.4.2 Experimental results _________________________________________________________ 134 3.4.3 Synthesis __________________________________________________________________ 137

4 Microstructure _______________________________________________________ 139 4.1 Evolution of porosity ___________________________________________________ 139

4.1.1 Method of determining the porosity _____________________________________________ 140 4.1.2 Influence of mineral additions on the porosity distribution____________________________ 141 4.2 Investigation on microstructure constituents _______________________________ 148 4.2.1 Microscopic Observations_____________________________________________________ 148 4.2.2 Determination of the components content_________________________________________ 156 4.2.3 Synthesis __________________________________________________________________ 161

5 Effect of mineral additions on shrinkage __________________________________ 163 5.1 A brief state of the art of the shrinkage phenomenon ________________________ 163

5.1.1 Shrinkage of the concrete in fresh state (Plastic shrinkage) ___________________________ 163 5.1.2 Autogenous shrinkage ________________________________________________________ 163 5.1.3 Drying shrinkage ____________________________________________________________ 165 5.2 Plastic shrinkage ______________________________________________________ 166 5.2.1 Experimental procedures______________________________________________________ 167 5.2.2 Experimental Results_________________________________________________________ 168 5.2.3 Cross-analysis at early age ____________________________________________________ 170 5.2.4 Discussion _________________________________________________________________ 174 5.2.5 Synthesis of study over plastic shrinkage _________________________________________ 181 5.3 Shrinkage of hardened concrete __________________________________________ 182 5.3.1 Free Shrinkage Measurement __________________________________________________ 182 5.3.2 Restrained shrinkage Measurement by Ring test ___________________________________ 186 5.3.3 Shrinkage behaviour of optimised mixtures _______________________________________ 188 5.3.4 Synthesis __________________________________________________________________ 192

Conclusion and future work ________________________________________________ 193 References_______________________________________________________________ 197 6 Annexes_____________________________________________________________ 209 6.1 Annex 1: Annexe NA.F of the French Standard NF EN 206-1 _________________ 209 6.2 Annex 2: Materials_____________________________________________________ 212 6.2.1 Materials characteristics ______________________________________________________ 212 6.2.2 Particle size distribution data __________________________________________________ 213 6.2.3 Technical details of the materials used ___________________________________________ 215

6.3 Annex 3: Experimental Techniques _______________________________________ 225 6.3.1 Isothermal Calorimeter _______________________________________________________ 225 6.3.2 Adiabatic calorimetry ________________________________________________________ 226 6.3.3 Mercury Porosimeter_________________________________________________________ 227 6.4 Annex 4: Characteristics values of hydration _______________________________ 228

Résumé

Le ciment utilisé dans la construction est issu de la décarbonatation du calcaire à très haute température, impliquant une émission considérable de CO2. Cette thèse s’inscrit dans le cadre du projet ANR EcoBéton piloté par le GeM, Ecole Centrale de Nantes et dont le but est de montrer la faisabilité d’une substitution massive du ciment par des additions minérales telles que les laitiers de hauts-fourneaux, des cendres volantes et des fillers calcaires. Cette substitution implique généralement une diminution de la résistance en compression au jeune âge. Pour résoudre ce problème, une méthode d’optimisation de la formulation des bétons utilisant la relation de Bolomey a été proposée. Au vu des bons résultats obtenus sur mortiers, une série d’essais sur bétons contenant différents taux de substitution a alors été réalisée dans le but de valider la méthode d’optimisation. Pour répondre aux exigences des constructeurs sur les performances des bétons au jeune âge qui conditionnent leur durabilité, une étude expérimentale complète a été réalisée. Des tests standards de mesure des propriétés mécaniques (compression, traction, prise) ont d’abord permis de valider le choix des formulations avec des additions minérales sur la base d’une équivalence de performances.

Ensuite, les travaux se sont focalisés sur le processus d’hydratation des écobétons dans le but d’expliquer les évolutions des propriétés mécaniques. Une méthode de mesure par ultrasons de la prise à différentes températures (10°C, 20°C et 30°C) a montré que le laitier et les cendres volantes retardent la prise du béton, alors que les fillers calcaires peuvent avoir un effet accélérateur. Les études calorimétriques sur mortiers et bétons ont permis de calculer les énergies d’activation des différents mélanges et d’observer une baisse de la chaleur d’hydratation des bétons avec additions ce qui est bénéfique pour les ouvrages massifs. Les observations au microscope électronique à balayage et les analyses thermiques ont de plus apporté quelques informations riches sur le processus d’hydratation. Il a été observé que les produits hydratés, quelque soit les formulations, sont les mêmes à long terme, mais leur temps de formation et leur volume sont différents.

La dernière partie de la thèse a été consacrée à l’étude des principaux types de retrait. Dans un premier temps, les déformations mesurées sur béton frais ont été corrélées à l’hydratation, à la dépression capillaire et à l’évolution de la porosité. Les résultats ont permis de mettre en évidence que l’utilisation des additions minérales a un effet sur le retrait plastique, mais son impact n’est pas proportionnel à la quantité d’additions. La substitution du ciment par les additions semble avoir un effet prononcé sur la cinétique sans influencer l’amplitude à long terme. L’étude du retrait empêché à l’anneau en conditions de séchage a montré que les bétons contenant des laitiers semblent être plus sujets à la fissuration à long terme que les bétons formulés avec du ciment Portland.

Mots-clés: additions minérales, laitiers, cendres volantes, filler calcaire, optimisation, jeune âge, résistance, microstructure, retrait, durabilité

Abstract

The cement being used in the construction industry is the result of a chemical process linked to the decarbonation of limestone conducted at high temperature and results in a significant release of CO₂. This thesis is part of the project EcoBéton (Green concrete) funded by the French National Research Agency (ANR), with a purpose to show the feasibility of high substitution of cement by mineral additions such as blast furnaces slag, fly ash and limestone fillers. Generally for high percentages of replacements, the early age strength is lower than Portland cement concrete. To cope with this problem, an optimisation method for mix design of concrete using Bolomey’s law has been proposed. Following the encouraging results obtained from mortar, a series of tests on concretes with different substitution percentages were carried out to validate the optimisation method. To meet the requirements of the construction industry related to performance of concrete at early age, which determine their durability, a complete experimental study was carried out. Standard tests for the characterization of the mechanical properties (compressive strength, tensile strength, and setting) allowed to validate the choice of mix design on the basis of equivalent performance.

We focused on the hydration process to understand the evolution of the mechanical properties. Setting time measurement by ultrasound device at different temperatures (10°C, 20°C and 30°C) showed that ground granulated blast furnace slag (GGBFS) and fly ash delayed the setting process, while use of limestone filler may accelerate this process.

Calorimetric studies over mortars and concretes made possible to calculate the activation energy of the different mixtures and a decrease in heat of hydration of concretes with mineral additions was observed which is beneficial for use in mega projects of concrete. Scanning Electron Microscopy observations and thermal analysis have given enough information about the hydration process. It was observed that the hydration products are similar for different concrete mixtures, but the time of their appearance and quantity in the cement matrix varies for each concrete mix.

Last part of the thesis was dedicated to the study of main types of shrinkage. First of all, deformations measured were correlated to hydration, capillary depression and porosity evolution. Results allowed concluding that the use of mineral additions has an actual effect on the plastic shrinkage behaviour, but its impact is not proportional to the percentage of additions. Substitution of cement by the additions seems to have a marked influence on the kinetics of the shrinkage without any effect on its long term amplitude. The study of restrained shrinkage under drying conditions by means of ring tests showed that concretes with high percentage of slag addition seem more prone to cracking than the Portland cement concretes.

Keywords: Mineral additions, slag, fly ash, limestone filler, optimisation, early age, strength, microstructure, hydration, delayed strains, durability.

Introduction

Within the context of sustainable development, the construction sector is often held responsible for excessive carbon dioxide (CO2) emissions. This is despite the efforts by stakeholders in the construction industry to innovate in the construction, demolition and waste treatment. CO₂ emissions are of diverse origins: manufacture of cement, poor insulation of building, transport of materials, and others. Some solutions have been suggested to limit these CO2 emissions (Damtoft et al. 2008). As a major part of the world economy, the concrete industry must play an active role in sustainable development. It has been found that the use of concrete can absorb CO2 (Lagerblad 2005), but reducing the CO2 emissions from manufacturing of Portland cement is not sufficient. The cement industry ever uses alternative fuel and raw materials for the combustion of calcareous in the manufacturing of cement, because producing one ton of cement thereby produces almost 0.8 ton CO2. But the better solution to reduce CO2 emissions from the manufacturing of Portland cement seems to be the minimization of the use of cement clinker. Reduction in clinker production can be balanced by the use of supplementary cementitious materials and high-range water-reducing admixtures (superplasticizers) (Cassagnabère et al. 2010). Replacing cement with mineral additions directly into the concrete mixer is a feasible and very effective solution. Mineral additions that can be used to replace Portland cement in concrete are available in large quantities. These include fly ash, ground granulated blast-furnace slag (GGBFS), natural pozzolans, silica fume and limestone filler (Malhotra 2006). Since many mineral additions are by-products of other industries, these waste by-products can be used to reduce the amount of cement required, thus, in some cases reducing the cost of the concrete (Toutanji et al. 2004).

Recently, the use of mineral additions has substantially increased due to increase in environmental awareness. Use of limited percentage of mineral additions in concrete is already in practice, but use of mineral additions in large proportions in concrete needs detailed investigation of the behaviour of concrete, especially at early age which includes the setting phenomenon.

Research concerning the use of mineral additions to improve the properties of concrete has been going on for many years (Malhotra 1993; Mehta et al. 2008; Toutanji et al. 2004).

Mineral additions such as silica fume, fly ash, and GGBFS improve the mechanical properties and performance of concrete when they are used as mineral additions or as partial cement replacements (Malhotra 1996; Hassan et al. 2000). Research works suggest that these mineral additions due to their pozzolanic properties improve several performance characteristics of the concrete such as strength, workability, permeability, durability and corrosion resistance (Babu 2000). Higher early strength can be found in some modern cements due to more Ca(OH)₂ formation, but this may adversely effect the durability and cost of concrete (Chan et al. 2000).

According to Malhotra (2006), the combined use of mineral additions and superplasticizers can lead to an economical and high-performance concrete with enhanced durability. In terms of concrete durability, benefits of using additional binder materials are well established

(Malhotra 1993; Bijen 1996; Lachemi et al. 1998; Ballimand Graham 2009) and use of materials such as silica fume and GGBFS are now considered very common (Alexander et Magee 1999). Researchers have proposed the use of mineral additions to alleviate the concerns of engineers for the durability of structural members (Toutanji et al. 2004).

Low calcium fly ash and GGBFS have been in the market for a long time. The main reasons for the slow acceptance of fly-ash, GGBFS and silica fume in the ready-mixed concrete industry were corporate policy, lack of economic incentives, inadequate specifications and quality of these materials (Malhotra 1993). Economic (lower cement content) and environmental considerations have also played a great role in the rapid increase of using mineral additions. Compared to Portland cement, cement with addition of pozzolans helps to have concrete with less permeability and a denser calcium silicate hydrate (C-S-H) is obtained. Compared to fly ash, the availability of GGBFS and silica fume is rather limited.

One of the major institutional barriers against the use of fly ash and other mineral additions is the prescriptive approach of specifications and standards (Oner et al. 2005). These mineral additions should be studied in order to understand their ability to enhance the properties of concrete. Each of these mineral additions possesses different properties and reacts differently in the presence of water.

Beside the significant technical interest, this study allows the valorisation of industrial co- product, such as GGBFS and fly ash. Thus, the environmental benefit of this research is twofold: we want to provide safe methods of reduction of use of pure cement and we evaluate the industrial wastes for the concrete manufacture. For this, an effort of scientific and technological research is needed to effectively promote the replacement of cement with additions. The objective of this thesis work is to make a fairly complete study from early age to the working condition of concrete with low cement content and with a massive addition of mineral additions; we call it “Ecobétons” (green concrete). The scientific approach is to accurately characterize the mechanisms of hydration of cementitious materials, the interactions existing between the clinker, additions and superplastcizers and the mechanical properties of these concretes.

As the French standards have restricted the use of large quantity of mineral additions in concrete, it seems necessary to present a state of the art of standard prescription for the manufacturing of concrete. Because it is relevant to note that the standard allows the use of blended cements (GGBFS, fly ash) with a high mineral addition content while it is strictly forbidden to produce in-situ concrete with equivalent content of additions. Interest of this thesis work is to show that during concrete manufacturing the additions can be used above the value of standard limits and that the use of blended cements is not the only existing solution.

About CO2 emissions, we have no data on cement plants manufacturing blended cements by combined grinding method. It is essential point of this work over which this study started:

estimating the CO₂ emissions from the concrete mixes of the proposed study.

The design of environment friendly concrete can not be done without mastering completely the early age and long-term properties of materials. In fact, sustainable development is based on several key principles: environmental sustainability, economics and social set up. The latter two points are difficult to assess here because we must take into account demographic

characteristics, financial status of the country and existing resources etc. Work proposed here first showed the feasibility of a new formulation of concrete. We then focus on the study on the solidification of the concrete (hydration, setting, shrinkage) in order to predict its behaviour in working conditions. Indirectly, the working conditions are also related to economics, at least in a first form that we will not review here, this concerns the need for constructors to have a structure with removal of its formwork at 24 hours. For this, the concrete must have attained sufficient strength estimated by the compressive strength in the range of 10 MPa at 48 hours. It is then essential that the concretes with high content of mineral additions fulfill this condition. A second important criterion for constructors is the limitation of early age cracking and long-term shrinkage of concrete. The shrinkage is caused by several phenomena: Le Chatelier contraction resulting from a reduction in the volume of hydrated materials, followed by a coupling between self-desiccation and drying shrinkage. Self-desiccation occurs during the hydration of the binder (cement clinker, addition) and consequently a decrease in the volume of water in the pores which causes a negative pressure (depression) in the capillary pores. Effects of traction are exerted on paste in the microstructure which results in a macroscopic shrinkage. Drying shrinkage observed the same effect, but the causes are due to a movement of water to the exterior of the material through the capillary network due to a lower humidity of the surrounding environment.

Monitoring of these phenomena requires a good understanding of the microstructure evolution of the materials. For this, we have proposed the measurement of the porosity evolution of the Ecobétons over a period of time and evolution of the phases formed or consumed during the hydration process. Shrinkage is also measured at very early age and in the hardened state, taking drying into account or without it. After being put in service, the concrete structure is subjected to various stresses, particularly related to environment. The study of concrete in aggressive environment is long and complex. We propose a first phase of this study on the problems of concrete carbonation reactions of the hydraulic binder with CO₂ from the ambient atmosphere.

This PhD thesis begins with a brief explanation of the problem associated to the standard recommendations for the use of mineral additions in the concrete. A short description of the project Ecobéton is also included in this first chapter. A brief introduction of the cementitious materials including cement and the mineral additions i.e. GGBFS, fly ash and limestone filler is summarised.

The main portion of the thesis consists of three parts. In the first part, we present a feasibility study on mortars to assess the possibility of using mineral additions like GGBFS, fly ash and limestone filler in higher percentages as replacement of cement. It includes early age properties like setting time, compressive strength as well as a short study on durability of these mortar mixtures against carbonation. Depending on this feasibility study, we will develop an approach to optimise the mix design using the Bolomey’s relation (Bolomey 1927) to improve early age strength of the mortars and the concrete mixtures.

Next part comprises the characterisation of the mortars and concrete mixtures prepared using mineral additions studying their hydration kinetics. To better understand the early age behaviour of these concretes, the evolution of the setting process of the concrete mixtures

using the ultrasonic wave velocity method will be described as well as effect of the temperature on the setting evolution. The effect of the initial temperature on the heat evolution of these mixtures will be presented too. This follows the study of the evolution of the microstructure (porosity, nature and formation of hydrates) of these mixtures with high percentage of mineral additions. Distribution of the pores and evolution in their size as a function of time will be investigated for these different mixes. Scanning electron microscopy will be an essential part of the microstructural study to show the nature of the hydrates formed.

In the last part of the thesis, we are going to explore the evolution of deformation in the concrete at very early age and long term, which includes evolution of plastic shrinkage, free shrinkage and restrained shrinkage supported by a study of mass loss, capillary depression development. These tests determine the influence of the slag and fly ash additions in the concrete on the evolution of deformation and risk cracking and results will be compared with the micro structural development and setting behaviour of this concrete.

1 Standard Recommandations and Bibliography

The most important use of cement is the production of mortar and concrete. Concrete, by definition, is a composite material which includes particles or fragments of relatively inert filler. This inert filler can be found largely, natural or artificial, fine or rough aggregates. The binding medium is called the cement paste. Concrete is now the most common construction material in the world, twice the total of all other construction materials, including wood, steel, plastic and aluminium (CCI 2010). The annual global production of concrete is approximately 5 billion cubic meters. At least three advantages can be presented for its wider application:

- its high durability against the effects of normal environment,

- its relatively low cost (most of the constituents are available locally), - it can easily be moulded.

The large scope of concrete application leads to a strong demand for cement being primary binder in concrete (Figure 1-1). The worldwide cement production in 2005 was estimated to 2200 million tons (MT).

Figure 1-1 : Cement consumption in European countries during 2004 (Lacroux 2004).

1.1 Standard Recommendations for the use of mineral additions and concept of equivalent binder content

The European Standard NF EN 206-1, “Concrete, Part 1: Specification, performance, production and conformity” is the base line to start this study. This standard allows to use mineral additions in concrete in restricted dosages; it takes mineral additions into account in the determination of water-to-cement (w/c) ratio and cement content, but at the same time limits the use of additions in concrete.

The introduction of mineral additions has been presented in the standard as a secondary aspect. The environments are redefined and for each of these environments or "exposures"

prescriptive requirements or the requirements are derived from performance-related design method (NF EN 206-1, § 5.3.1). In other words, the performance requirements for concrete do not overlap with those relating to its composition, but may substitute for a target property.

1.1.1 The traditional approach or standard requirement

The prescriptive approach, or standard requirement, is the traditional approach of additions in concrete, since the definition of constituents and their respective proportions has long been much easier than the performance of the resulting material. In particular, in this approach, the degree of trust on the properties of cement outweighs that of other components of concrete and is the basis for this set of specifications. The requirements for this approach are detailed in Section 5.3.2 of the standard EN 206-1, "Limiting values for concrete composition”. They focus on:

- constituent properties, - maximum of w/c ratio, - minimum cement content.

The limiting values are given in Annex - normative - NA.F of standard NF EN 206-1, in the form of two tables (see Annex 6.1):

- NA.F.1, Limiting values applicable in France for composition and properties of concrete according to the exposure,

- NA.F.2, Limiting values applicable in France for composition and properties of concrete, concrete products precast in plant according to exposure class.

The table NA.F.1 is the reference table while the table NA.F.2 is applicable to certain families of elements by prefabricated concrete. The given limit values take into account the requirements on the basis of a presumed life of the structure of at least 50 years, provided that the coating of reinforcements, the placement and curing should conform and adapted.

The limiting values of maximum w/c ratio and minimum cement dosage is adapted from Annex F - Informative - the European standard, and agree to use the CEM I, kind of cement composed of at least 95 % of Portland cement clinker (according to standard NF EN 197-1).

In practice, the concrete composition may include the use of additions. French Table NA.F.1, therefore, gives the limiting values of maximum effective water-to-equivalent binder (Weff/Eq. Binder) ratio and minimum equivalent binder content (Eq. Binder). The equivalent binder is defined in the paragraph 5.2.5.2 “Concept of the coefficient k” of the standard NF EN 206-1:

kA C Binder

Eq. = + Eq 1-1

where C is the quantity of cement per cubic meter of concrete (kg/m³) of type CEM I 42.5 N or CEM I 42.5 R or CEM I 52.5 N or CEM I 52.5 R. A is the quantity of mineral addition per cubic meter of concrete (kg/m³), and shall not exceed, neither for the calculation of equivalent binder, nor for calculating the Weff /Eq. binder ratio, the maximum value defined by the A/(A+C) for each type of addition and each exposure class in Table NA.F.1. k is the coefficient taking account of the addition in consideration. Additions can be taken into

account in calculating the equivalent binders, whose general suitability for employment is determined according to standards.

Three additions are known as Type II due to pozzolanic nature or property of latent hydraulic and the next two of Type I that is virtually inert (NF EN 206-1, § 3.1.2.3). The coefficient k depends on the type of addition and varies between 0 and 2 (Figure 1-2).

Figure 1-2: National Annex NA.5.2.5.2.2 of the standard NF EN 206-1.

1.1.2 The French Standard specificities

Standard NF EN 206-1 also poses the coherence problem of the national standards resulting from the European standard, which has been added as national annexes (NA). Thus the French table NA.F.1 differs from Table F.1, with both values (w/c ratio and minimum cement content) and specifications. For example, European table F.1 put no limitations on the maximum proportion of additions taken into account in the calculation of the equivalent binder. In fact, even if a quantity of additions higher than that taken into account in the calculation of the equivalent binder can effectively be incorporated in the concrete, this approach strongly limits the use of the additions (even of type II), due to its cost but also water content, as the following example on the slag (coefficient K = 0.9) shows (Note: All the replacements of the cement by slag are by mass):

Eq. binder = 350 kg/m³ Weff/Eq. binder = 0.6 A/(A+C) = 0.5 > 0.3

Eq. binder = 242 kg/m³ Weff/Eq. binder = 0.87 > 0.6 A/(A+C) = 0.3

Eq. binder = 242 kg/m³ Weff/Eq. binder = 0.6 A/(A+C) = 0.3

The composition n°1 was designed for an environment of the type XC3 (risk of carbonation, moderate humidity). According to the table NA.F.1, it should thus satisfy the three following criteria:

- Eq. binder ≥ 280 kg /m³ - Weff/Eq. binder ≤ 0.60 - A/A + C ≤ 0.30

This composition is similar to concrete compositions commonly used in other European countries. However, it does not verify the third criterion, which makes it possible to substitute only 30% of cement by standardized slag. It is then possible to take into account only the corresponding quantity of slag in the calculation of the equivalent binder (composition n°2), but the two first criteria are not verified any more. The composition n°3 verifies the second criterion but the reduction in volume of water and binder affects the consistency and the composition cannot be implemented.

Aggregates

Cement (C):

175kg Weff = 210L Addition (A):

Slag : 100kg Slag : 75kg

Aggregates

Cement (C):

175kg Weff = 145L Addition (A):

Slag : 100kg Slag : 75kg Aggregates

Cement (C):

175kg Weff = 210L Addition (A):

Slag : 175kg

1 2 3

1.1.3 The equivalence of performance and limitations of the prescriptive approach

The standard NF EN 206-1 (§ 5.3.3) introduced performance-related design method as an alternative to limiting values for the composition of concrete. This prescriptive requirement results in particular in a minimal cement content and on the concept of the coefficient k presented below. The performance-based approach suggested by the standard is founded on the concept of equivalent concrete performance (§ 5.2.5.3). This concept makes possible to qualify a concrete - whatever its composition is- provided that it behaves good as well from the point of view of its durability as a concrete in conformity with the obligation of means:

“It shall be proven that the concrete has an equivalent performance especially with respect to its reaction to environmental actions and to its durability when compared with a reference concrete in accordance with the requirements for the relevant exposure class (Standard NF EN 206-1, § 5.2.5.3)”.

The standard requires a continuous evaluation of the concept of equivalent performance, when the concrete is made according to these procedures, taking account of the variations of cement and the addition. This state of regulatory limit allows establishing methodology for applying the concept of equivalent performance, for each exposure class and each derogation of standard requirement. Similar approaches were already proposed in other European countries (Belgium, Netherlands and Portugal). The justifications are based on performance- based tests and durability indicators specific to the degradation mode considered. The aim is to provide an additional degree of freedom in the materials proportions (cement, additions and aggregate) according to corresponding standardized tests, for the same objective of durability.

Thus, the use of the demonstration of equivalence of performances can be considered whenever the composition derogates from the regulations prescribed in the tables NA.F.1 or NA.F.2 or where these regulations do not take into account the characteristics of a composition, to ensure that it provides an equal or lower level of risk. Methodologies suggested are based on results of the studies detailed in the documents referred to or undertaken within the framework of the PhD thesis entitled “study of the durability of concrete using a performance-based approach” (Rozière 2007).

The inclusion of the traditional prescriptive approach in the performance-based approach, responsible for defining exposure classes creates ambiguities or inconsistencies (cf. table NA.F.1, Annex 6.1). The approach focuses on the definition of binder, but gives no specification on the quality of granular stacking and aggregate. The volume of binder can also be an important parameter in terms of durability. The French requirements are also source of incoherence. The maximum proportion of slag taken into account in the equivalent binder is 0.15 for the classes XA1 and XA2 and 0 for the class XA3, when the class of aggressiveness results from the presence of sulphates (notes k and n in table NA.F.1). The same note specifies that in the case of chemical attack, cement must comply with the requirements of the standard XP P 15-319, on the cement for work in waters with high content of sulphate ions.

However cements made up with the slag of the type CEM III in conformity with this standard must comprise of at least 60% of slag. That highlights a contradiction of the prescriptive documents, although it is argued that the reconstituted mixture during the manufacture of concrete does not have the same properties as the mixture worked out in cement factory. The

prescriptive approach of the French standard on the concrete does not take into account certain relevant parameters from the point of view of durability. It concentrates on the composition of binder and in a rather constraining way to reduce the use of all types of additions, while recognizing the interest of certain blended cements. Such an approach thus does not make it possible to qualify certain compositions of concrete however technically interesting - at equal cost - from where the performance-based approach steps up.

1.2 The cement properties in concrete

Portland cement consists of a hydraulic material called clinker which is obtained after calcination of a mix of limestone, aluminium and silicates present in the clay and clayey schist at a temperature of 1450°C. These materials are first mixed and then cooled very rapidly which results in a product called as clinker. To obtain a Portland cement, this material is grinded and a setting agent like gypsum is added.

Principally, the clinker is composed of four mineral phases: tri-calcium silicate, bi-calcium silicate, tri-calcium aluminates and tetra-calcium ferro-aluminates. Their mass fractions in a clinker used for a Portland cement are given in Table 1-1. In addition to these four phases, other minerals may be present in the clinker like alkaline sulphates, free lime etc.

Table 1-1 : Chemical composition and mineral phases of a Portland cement

Compound Formula Mass fraction (%)

Alite C3S 50-70

Belite C2S 15-30

Aluminate C3A 5-10

Ferrite C4AF 5-15

1.2.1 Hydration of cement

Being a hydraulic binder, after contact with water, cement forms a paste which hardens in response to chemical reactions of hydration. The reaction product is insoluble mineral, which remains stable and resistant even under water. There are various cement constituents who affect differently the hydration process and ultimately the final properties of concrete. Hydration reactions of different phases of clinker and their interaction, which continue for several years, are extremely complex and not yet fully known. The hydration of cement gives four main types of solid products.

a) Calcium silicate hydrates, written as C-S-H, represent 50-60% of volume of hydration products of Portland cement. The exact internal structure of C-S-H is still poorly understood, its composition is variable and not well defined. The C/S ratio varies between 1.7 and 1.8 (Odler 1998). The morphology may also vary from crystalline fibres to reticular network.

b) Calcium hydroxide (CH), also called as portlandite, constitutes 20-25% of the volume of hydration products. Its composition is well defined as Ca(OH)₂. The contribution of portlandite crystals in the strength of the cement paste is limited.

c) Hydrated Calcium Sulphoaluminates are present in small amounts (15-20% by volume), they play a minor role in the properties of cement paste. The hydrated calcium trisulfoaluminates, called "ettringite,C AS H_{6 3 32}, also termed as AFt are formed early in the hydration reaction. They eventually become hydrated calcium monosulfoaluminates,

4 12

C ASH also termed as AFm. Presence of unhydrated clinker grains depends on the w/c ratio and the initial degree of hydration. The chemical reactions of pure phases of cement are defined as follow (Powers 1948):

CH a SH

C O H a g S

C₃ +(3+ − ) ₂ → _{a g} +(3− ) Eq1-2

CH a SH

C O H a g S

C₂ +(2+ − ) ₂ → _{a g} +(2− )

Eq1-3 Hg

AS C H g H S C A

C₃ +3 ₂ +( −6) → _{6 3 Eq1-4}

Hg

S A C H g

H S C A

C_{3 6 3 32} (3 32) 3 ₄

2 + + − → _Eq1-5

CH FH

H S A C H g H S C AF

C4 +3 2 +( −2) → 6 3 _g + 3 +

Eq1-6 CH

FH H

S A C H g

H S A C AF

C (3 24) 3 _g 2 2

2 ₄ + _{6 3 32} + − → ₄ + ₃ + _{Eq 1-7}

Where ‘a’ is C/S ratio and ‘g’ is H/S ratio of C-S-H.

In the absence of sulphates, C3A hydration reaction is very rapid and accompanied by a large heat release. Hydration of Aluminates (Eq 1-4) and ferrites (Eq 1-6) starts directly when cement comes into contact with water (Odler 1998). Afterwards it is characterised by a dormant period which is followed by a second hydration (Figure 1-3).

Figure 1-3 : Typical hydration kinetics of pure clinker minerals paste hydration at ambient temperature (Odler 1998).

d) Crystalline products of the form C₃AH₆, or C₄AH₁₉ and C₂AH₁₈ are formed very rapidly for most construction applications. The presence of gypsum (CSH ) in the cement can slow ₂ the hydration reaction and thus prevent flash setting thanks to the presence of sulphates (Waller 2000) and ettringites are formed. When there is not enough calcium sulphate to form

ettringites, this hydration product starts to decompose and reacts with alumino-ferrite to form monosulphoaluminates (Eq 1-5 and Eq 1-7).

On the other hand, hydration of silicates is relatively inert during first hours. The hydration of C2S is slower (10-30 times) than that of C3S Waller (2000). Their hydration products are C-S-H and portlandite (Eq 1-2 and Eq 1-3). Hydration products are formed with different kinetics with the advancement of hydration reaction (Figure 1-4). However hydration product C-S-H varies for different cements. C-S-H content increases at a high rate after the dormant period. Evolution of portlandite follows the hydration of alite and belite, though it is formed in a very low quantity during the hydration of belite. Rate of formation of ettringites and monosulphates depends upon the aluminates and ferrite contents along with the content of setting regulating agent in the cement paste.

Hydration kinetics of the clinker minerals has been illustrated in Figure 1-4. In the laboratories, generally the hydration kinetics is measured by calorimetric analysis, assuming the hydration of cementitious materials characterised by only a single reaction with five different phases (Figure 1-5) (Mindess et al. 2003). Directly after the water cement contact, hydrolyse is produced and the alkaline present in the cement is dissolved in the solution very rapidly. Afterwards controlled by nucleation phenomenon, dormant period starts and Ca²⁺ and OH^- are released, which raises the pH level of solution to approximatively 12.5 (Pertué 2008).

This phase is characterised by a minimum heat release and initialisation of setting process.

This dormant period is important in concrete technology because during this period the concrete can be transported and shaped on the construction site.

Figure 1-4 : Formation of hydration products in Portland cement paste as a function of hydration time at ambient temperature (From Locher et al. 1976).

An acceleration period follows the dormant period, during which the hydration progresses rapidly (Stage III). This phase starts when concentration of Ca²⁺ and OH^- ions in the solution becomes critical. Because this saturation of ions causes the precipitation of portlandite, but other hydration products are also formed (C-S-H and ettringite). This period corresponds to the main exothermic peak in the curve in Figure 1-5. This period determines the final set of concrete and the strength development at early ages.

After the acceleration period follows the deceleration and steady state period (stages IV and V) during which the hydration rate is relatively slow. The strength of the concrete keeps increasing and the heat release is much reduced compared to that of the acceleration period.

The layers of the hydrates are deposited around anhydrous particles of cement progressively and ion exchange becomes difficult.

Figure 1-5 : Heat release during hydration of Portland cement (Mindess et al. 2003).

Figure 1-6 : Setting process from a chemical point of view.

1.2.2 Evolution of setting of cement concrete a) Phenomenological point of view

When water and cement are mixed, a plastic workable paste is produced. The paste properties remain unchanged for a time period (dormant period). Once this phase is over, the paste stiffens and loses its workability. This phenomenon is also known as initial setting. In other words, initial set corresponds to the time during which the mixture stays plastic and workable. The paste will then continue to consolidate until it becomes a rigid material. The obtaining of a solid cement paste corresponds to the final setting. The final setting is less easily identifiable. Van der Wilden (1990) added three more tests to quantify the mix workability:

the formed mixture does not get back to its original shape when compressed by a vertical force,

the vibration needle leaves a hole in the concrete,

bonding between two successive castings is very poor.

Then the mixture obtains a compressive strength (hardening) with time (Robeyst 2009).

b) Chemical point of view

Even if setting is a visible phenomenon, its origins result from the chemical reaction of hydration. As described before (§ 1.2.1), the latter is divided in five main phases well illustrated in Figure 1-5 & Figure 1-6.

c) Structural point of view

Figure 1-7 shows that as the hydration reaction proceeds, cement grains are covered by a dense layer of hydrated products that thickens. This implies that spacing amongst cement grains decreases. Initial set corresponds to the moment when friction between hydrated grains is such that the paste becomes unworkable. By further expansion, the grains create a solid continuity in the structure.

Percolation theory explains the existence of this solid continuity. It stipulates that hydrates (formed around cement grains) create random links between one another and give birth to clusters. The proliferation of these links generates eventually a continuous path between grains. The path is called percolation threshold (Boivin 2001). From then, percolation continues until all cement grains are bonded to each other. This corresponds to final setting.

Hardening is only the growth and consolidation of all the hydrated products links (Robeyst 2009).

Figure 1-7 : Schematic diagram of solid percolation (From Robeyst 2009).

d) Parameters influencing setting

The parameters influencing setting are obviously related to the ones influencing the hydration of cement. For example, fine cement grains offer a higher exposed surface and therefore the hydration and the setting will be swift. In addition, a lower w/c ratio implies that portlandite will precipitate earlier; this means that setting will be accelerated. Finally, a higher temperature will also decrease the time of initial setting.

Setting of concrete is defined as the onset of solidification a fresh concrete mixture, while the time taken to solidify completely marks the final set. The principal factors controlling the setting time of concrete are cement composition, w/c ratio, temperature and mix design. In general, the higher the w/c ratio, the longer the time of set. On the other hand the lower the temperature, the longer the time of set.

1.2.3 Early-age behaviour of cement concrete

For the early age behaviour of the OPC concrete, the most important factors are the cement content, water-cement ratio and the temperature. For the fresh concrete, the slump value

which is a measurement of its workability is decreased with the decrease in temperature and water-cement ratio. Compressive strength is considered as one of the most important concrete properties because it represents a global image of the concrete itself. Compressive strength of an OPC concrete depends upon the mass ratio between cement and water added, mass ratio between cement and aggregates, granulometry, texture, shape and strength of aggregates.

Concretes with very low cement content and high water-cement ratio are prone to show a very low compressive strength while using the large dimension aggregates.

1.2.4 Durability a) Carbonation

Carbonation is a risk for reinforced concrete because it can lower the alkalinity of concrete to such an extent that, when the pH is reduced below 9, iron may rust and spalling of the cover occurs. To minimise the risk of corrosion of the reinforcement, the concrete must be dense and the cover sufficiently thick. Prolonged curing before exposure to carbon dioxide reduces the depth of carbonation of mortar and concrete. Carbonation is deeper in a concrete exposed to a marine environment, and this irrespective of the type of cement.

b) Leaching

Deterioration of concrete caused by pure or acidic water poses a serious risk for hydraulic structures such as dams, channels and pipes, but it can involve those parts of the structure which are in contact with soft or acidic ground waters. Acid waters containing aggressive CO₂ increase the rate of lime leaching.

c) Chloride attack

Chloride attack can harmfully affect the durability of both concrete and reinforcement.

Chloride dissolved in waters increases the rate of leaching of portlandite thus increasing the porosity of mortars and concrete. As a consequence of the chloride attack, concrete swells, loses stiffness and strength and becomes more sensitive to the other environmental attacks (sulphate, frost, etc).

d) Sulphate attack

Sulphates are harmful to concrete as they can cause expansion, loss of strength and eventually transform the material into a musky mass. CaSO4 reacts on calcium aluminate hydrates, thus forming expansive ettringite. Na₂SO₄ reacts on calcium hydroxide and forms expansive gypsum, which in the presence of aluminates may in turn give the ettringites.

Cements with low C₃A and low lime contents minimise the risk of sulphate expansion. The depth and rate of the sulphate attack strongly depends also on the characteristics of mortar and concrete, namely their strength, porosity and permeability. Expansion of Portland cement mortars increases by increasing the w/c ratio and decreasing the cement content i.e. by increasing porosity and permeability.

1.3 Mineral Additions properties

The production of Portland cement demands the consumption of a lot of energy, requires approximately 4 GJ of energy per tonne of finished product. That is why; one of the solutions

to minimize the environmental impact of cement production is the use of mineral additions in concrete. The properties of these materials are:

they are normally by-products from other industries or natural materials, which may or may not be further processed for direct use in concrete. These are easily available materials and are cheaper than cement,

they are sometimes referred to as mineral admixtures,

some of them do not posses any binding capacities at all, and can only be used together with some other materials.

The later family of materials is sometimes called pozzolanic material like fly ash. Other mineral additions might show cementitious properties themselves, like slag, in an appropriate environment (Chen 2007).

The mineral additions that are less energy intensive readily available in the world are silica fume (a by-product of the fusion process uses in the production of siliceous metals and ferrosiliceous alloys), fly ash (a by-product of burning pulverized coal used in thermal power stations), blast furnace slag (a product resulting from the manufacture of the cast iron in blast furnace) and limestone filler available in large quantities in nature.

1.3.1 Ground granulated blast furnace slag (GGBFS) 1.3.1.1 Presentation of the Blast Furnace Slag (BFS)

Granulated blast-furnace slag is defined as the glassy granular material formed when molten blast-furnace slag is rapidly chilled as by immersion in water (ACI 1994). Fast cooling results with minimum crystallization and converts the molten slag into fine aggregate sized particles (smaller than 4 mm), composed of predominantly non-crystalline material and then ground to fine powder.

Blast furnace slag is produced when iron ore is reduced by coke at about 1350-1550°C in a blast furnace. The molten iron, main product of a blast furnace, is formed from the ore, while the other components form a liquid slag. When flowing to the bottom of the furnace, the liquid slag forms a layer above the molten iron due to the smaller density of slag. After being separated from the molten iron, the liquid slag is cooled down in the air or with water and is prepared for further use. Typically, about 220 to 370 kg of blast furnace slag are produced per metric ton of pig iron. Lower grade ore results in more slag-sometimes as much as 1.0 to 1.2 tons of slag per ton of pig iron (Kalyoncu 1998). The liquid slag crystallizes if cooled slowly, and forms a glass if cooled rapidly. There are three main types of blast furnace slag, categorized by the way of cooling it:

1. The granulated slag is produced by quenching the liquid slag with large amount of water to produce sand-like granulates. Granulates normally contain more than 95% of glass.

Normally, they are ground to fine powder, called ground granulated blast furnace slag (GGBFS).

2. The pelletized slag is produced by partially cooling the slag with water, and then flinging it into air. The pellets contain much less glass content if compared to the granular slag, as low as 50%. Part of the pelletized slag is used as concrete aggregate and much is used in cement production as raw material as well.