Our Research
- Ongoing
- Finished
Core projects
Nanocem's on going and finished projects within their core, long term research projects.
The Core Projects under the Programme of Activities are fundamental long term projects research projects carried out by two or more Contractors and funded by the resources of the Nanocem Consortium. Typically 2-3 academic partners work together sharing a PhD or Postdoc student who moves between the partners.
The Core Projects are listed below.
Finished
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Mineralogy of Hydrated Cements
University of Aberdeen, UK
Eidgenössische Materialprüfungs und Forschunganstalt, CH
Date
This project started on 01 August 2004 and ended on 01 January 2007
Status
This project is Finished
Objectives
The central mechanism by which cement works is the hydration reaction, in which the starting phases react and combine with water to give an increase in solid volume, which fills the space originally occupied by water and bind the cement grains together. The resulting cement paste consists of a fine-grained mass of solids many of which are of low crystallinity.
Therefore characterisation of the number and constitution of hydrated substances present has presented many seemingly intractable problems. Many techniques have been applied which reveal partial structural information but it is often difficult to combine and integrate this knowledge into a consistent picture.
However progress in other fields of inorganic structural materials has rested on developing correlations between, on the one hand, physical properties - normally bulk properties such as strength - and on the other, with phase constitution, amounts of substance and microstructure. But progress in developing such correlations for hydrated cements has been slow, owing in part to the above-mentioned difficulties in quantification of the number, composition, amount and microstructural relationships of the constituent solids and, of course, the coexisting aqueous phase.
About 80 years ago, Bogue wrote a series of equations describing the relationship between clinker raw meal chemical composition and the mineralogy of the finished clinker. These enabled the amounts of minerals to be calculated from a bulk chemical composition. Fundamental to the equations was a precise description of the high temperature equilibrium achieved during clinkering.
Hydrated cements are more complex than cement clinkers. Even more complex is the assemblage of hydrate phases which will result from the hydration of a cementitious system, when supplementary cementing materials (SCMs) and fillers such as slags, fly ashes, natural pozzolans, limestones are included. Nevertheless it is not unrealistic to determine the information needed to predict the phase assemblage from the degree of reaction of the composants.
This project aims to define the compositions and stabilities of the hydrated phase assemblages that are likely to occur over the temperature range 0-50°C and represents a fresh attempt to determine these relationships. If successful, it will initiate a new start to the understanding and eventual control of cement properties.
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Pore Structure Characterisation by Magnetic Resonance Techniques
Ecole Polytechnique, FR
University of Surrey, UKDate
This project started on 01 September 2004 and ended on 01 December 2006
Status
This project is Finished
Objectives
Proton NMR is a powerful technique to study the state of water in porous structures and in modelling porous microstructures over many ranges of length scales. Basically we aim at studying the early-age hydration phases of various new cement-based materials using different techniques of proton nuclear relaxation of water.
The main interest of using such non invasive and non destructive techniques is to obtain in situ information on the microdynamics of water precisely at the solid-liquid interfaces. One thus probes continuously the surface area and the pore size distribution in the size range 2-50 nm. We believe that the information obtained on the nanoscale porosity will be of primary importance to improve the long-term performance of the cementitious materials.
The objective of this project was specifically to refine a comprehensive set of state-of-the-art non-destructive, non-invasive instrumental techniques capable of fully-analysing the pore structure of hydrated cements, the degree of filling of the pores with water, and the mobility of water in the (partially saturated) material.
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Organo-aluminates Interactions
Ecole Supérieure de Physique et Chimie de Paris, FRDate
This project started on 01 January 2005 and ended on 01 December 2008
Status
This project is Finished
Objectives
Organic admixtures form an essential part of all modern cementitious formulations. This is particularly true for superplasticizers. As far as the main lines of their rheological action are concerned, we may consider that our current knowledge is satisfactory.
The main mechanisms have been identified, though neither entirely nor quantitatively related to molecular structures yet. The picture is much less satisfactory when it comes to the specific character of their interaction with the different mineral phases or mineral components of cements.
The lack of knowledge on these specific interactions is a source of problems, fortunately not frequent but often unexpected and ill-mastered, which impede the robustness of formulations. It is generally admitted that the main source of problems comes from the interaction of the admixtures with the aluminate phases, mainly 3CaO.Al2O3, which is highly reactive and plays a key role in the fresh paste immediately after mixing. Adsorption, co-precipitation or even intercalation on or in the early hydrates have all to be considered as possible sources of undesired interactions, leading possibly to a loss of availability and a loss of fluidity.
The NANOCEM Core Project 3 "Organo-Aluminate Interactions" is focused on the interaction of superplasticizers with the so-called AFm phases (C4AHx). Parallel work has demonstrated that, as expected from its crystal structure and its low specific surface area, C3A itself cannot be an important source of SP sequestration.
On the contrary, AFm phases, which are formed in the very early times after mixing, are a major potential source of SP sequestration, thanks to their swelling layered structure and their positive layer charge. AFm phases belong to the general family of Layered Double Hydroxides (LDHs), also called anionic clays.
The recent materials chemistry literature contains a wealth of examples showing that these layered minerals are able to form organo-mineral compounds with a wide variety of anionic organics, from simple molecules to large molecular weight polymers, including biopolymers. The formation mechanism may be true intercalation or co-precipitation or, more probably, templated crystal growth. Previous work has shown that super-plasticizers co-precipitated with AFm phases form quasi-amorphous organo-mineral compounds.
The aim of Core project 3 is to establish the structure of these organo-mineral compounds and to understand the conditions for their formation in molecular and cement chemistry terms. So far, the efforts have been focused on the detection of possible intimate interactions between the mineral and the organic molecules. NMR was used as the main tool, for its ability to detect short- and meso-range interactions, even in a disordered environment. This approach makes it possible to study the molecular and cristallochemical parameters of these interactions.
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Reactivity of Mineral Additions
Ecole Polytechnique Fédérale de Lausanne, CH
University of Aarhus, DK
University of Leeds, UK
Technological University of Denmark, DKDate
This project started on 01 November 2005 and ended on 01 December 2009
Status
This project is Finished
Objectives
Traditional Portland cements based purely on interground clinker and calcium sulfate (e.g. gypsum) are being increasingly replaced by blended cements, where part of the clinker is replaced by secondary cementitious materials (SCMs) such as blast furnace slag, fine ground limestone of fly ash from coal fired power stations.
This trend is extremely important for increasing the sustainability of cement manufacture in reducing the consumption of raw materials and of CO2 emissions. Increasing the level of substitution is limited by the ability to well predict the performance of these blends in terms of strength development and durability, particularly when the reactivity of the SCM is variable.
This project will develop a methodology to follow the reaction of the clnker and the SCM component separately in blended cements and so provide the means for understanding the factors determining the reactivity of SCMs and their contribution to the performance of cementitious materials.
The presence of different phases requires the used of complementary techniques. X-ray diffraction (XRD) allows us to investigate the highly crystallized phases whereas Nuclear Magnetic Resonance (NMR) is well adapted to the study of amorphous as well as crystalline materials. Chemical shrinkage, provides a complimentary method to follow the overall reaction. Other methods such as Electronic Microscopy and Thermal Analysis will be used to support understanding of the hydration mechanisms. In parallel the evolution of basic properties such as strength/elastic modulus and absorption will be studied.
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Alkali Activation of Aluminosilicates – An Assessment of Fundamental Mechanisms
Consejo Superior de Investigaciones Cientificas, SP
University of Aberdeen, UKDate
This project started on 01 October 2007 and ended on 01 September 2010
Status
This project is Finished
Objectives
As in all cementiteous systems, the chemical relationship between individual constituents (unhydrated and hydrated phases) during hydration defines the stability of phase assemblages and ultimately, the physical and mechanical properties of the product. Significant progress has been made in Core Project 1 and elsewhere in developing an understanding of phase relations in Portland cement systems and their impacts on properties. Now, Core Project 5 addresses the special case of aluminosilicate activation by highly alkaline solutions.
Aluminosilicates are widely available, naturally occurring materials. They are not cementitious in their own right but some can be activated to provide cementiteous products. These materials have attracted considerable interest in the search for sustainable cement binders because products can be demonstrated to have properties comparable to conventional cement systems; conventional cement manufacture involves the energy intensive and CO2-producing calcination of limestone.
However, if consistent performance of alkali-activated systems is to be addressed and exploited in constructional concretes, more emphasis must be placed on understanding the fundamental mechanisms which underlie the alkali activation process and how these can be optimised in real systems.
Core Project 5 seeks to investigate these basic mechanisms. Alkali-activated aluminosilicates are differentiated from Portland cement systems by their higher initial alkalinity and the absence of lime. This is already sufficient to define quite different hydration products relative to those found in Portland cements such that predictions made based on Portland cement chemistry are inappropriate.
However, the modelling approaches taken successfully in Core Project 1 are capable of translation to the activated aluminosilicate systems, and significantly, to hybrid Portland cement-alkali-activated systems, using thermodynamic data to be aquired in Core Project 5. This core project will investigate:
- relative stability and compatibility of the different N-A-S-H gels and C-(A)-S-H via solubility studies
- compatibility of gel phases with other cement hydration products, e.g. Ca(OH)2 (pozzolanic potential of zeolite precursors)
- mechanisms underlying the acid-base chemistry of activation, using solubility/leaching studies under controlled conditions (varying alkali strength (pH), integrating kinetic factors)
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Atomistic Modelling on Cementitious Systems
Ecole Polytechnique Fédérale de Lausanne, CHDate
This project started on 01 January 2009 and ended on 01 May 2013
Status
This project is Finished
Objectives
Cementitious materials are complex systems with many interfacial interactions over many length scales (dissolution, nucleation, crystallization, polymer adsorption, aggregation). The significant role of the different types of interfaces, which ultimately control the properties of cements and concretes from the early stages to the final microstructures and macroscopic properties, demands a deep knowledge of the roles of the interfaces at an atomistic level.
The composition of cementitious materials is complex with several different mineral phases and the nature of the solid-liquid interfaces where dissolution of the anhydrous phase, adsorption of cement admixtures and growth of new crystalline phases take place are very difficult to access experimentally. The use of atomistic modelling has made great progress over recent years in many different fields such as properties of interfaces, crystal growth and self-assembly[1-3].
The primary objective of this project is the study of different phases of cement, namely portlandite and tobermorite as a C-S-H model structure, and their interfaces with the pore solution and possible defects. The length scale of these structures are at the limit of ab initio methods, therefore the method of choice will be mainly classical molecular dynamics which have been shown to be able to model diffusive processes in certain cases[4].
The second part of the project is to study possible growth mechanisms of the above phases and their exchange with their chemical environment. As the length scale of these processes exceeds the time limits of simple classical molecular dynamics (ns) the use of enhanced sampling algorithms, such as metadynamics, and mesoscale methods, such as kinetic Monte Carlo is envisioned for the future.
To start approaching the macroscopic behaviour of cementitious materials, the basic fundamental data from the atomistic approaches can then be supplied to other modelling groups using continuum approaches such as the finite element method (FEM) to give macroscopic property evaluation and prediction.
1 Allen J.P., Gren W., Molinari M., Arrouvel C., Maglia F., Parker S.C.
Atomistic modelling of adsorption and segregation at inorganic solid interfaces Molecular Simulation 35 584-608, (2009)
2 Spagnoli D., Banfield J.F. and Parker S.C.
Free energy change of aggregation of nanoparticles
Journal of Physical Chemistry C 78, 14731-14736, (2008)
3 Sayle, D.C., Doig, J.A., Maicaneanu S.A., Watson G.W.
Atomistic structure of oxide nanoparticles supported on an oxide substrate
Phys. Rev. B 65, 245414, (2002)
4 Aschauer U., Bowen P., Parker S.C.
Oxygen vacancy diffusion in alumina: New atomistic simulation methods applied to an old problem
Acta Materialia, 57(16), (2009), 4765-72Read more about it
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Fundamental Mechanisms of Cement Prehydration
Technische Universität München, DE
University of Leeds, UK
Slovenian National Building and Civil Engineering Institute, SI
Lund University, SEDate
This project started on 01 January 2009 and ended on 01 February 2013
Status
This project is Finished
Objectives
It is commonly known that the age of cement or inadequate storage can result in different engineering properties of concrete or mortar. In a pre-study, the general phenomenon of prehydration of cement was scientifically investigated in a Nanocem MSc project started in 2007. With "cement prehydration" we mean the interaction between cement and water vapour. In our studies it was possible to reproduce the field problems in the lab and to research the causes by using modern analytical tools.
Currently, the knowledge of very early cement hydration and related analytical methods is still limited. Prehydration of cement is a surface process, whereby only a few methods like XPS and FTIR-ATR spectroscopy can be utilised.
The aim of NANOCEM Core Project 7 is to fill this gap by the enhancement of the current methods and to develop new analytical strategies for surface analysis. Also, we will probe deeper into the prehydration processes on the cement grain surface; and subsequently the related consequences for the bulk cement.
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Non-saturated Transport Properties of Cementitious Materials
Consejo Superior Investigaciones Científicas, ES
Eidgenössische Materialprüfungs- und Forschungsanstalt, CH
Technical University of Denmark, DK
Lund University, SE
Imperial College of Science Technology and Medicine, UK
IFSTTAR, FRDate
This project started on 01 October 2009 and ended on 01 October 2009
Status
This project is Finished
Objectives
The objectives here are the study of moisture transport properties, and their relation to the pore structure of cementitious materials, and of the moisture effects on other transport processes (and in particular on transport properties).
No generally accepted method is available for measuring ion transport properties in non-saturated conditions. Methods of assessment (utilizing the full resources of NanoCem) at different moisture levels will be developed and applied on specimens whose micro- and nano-structure is well documented.
Scientific need / Link to Nanocem goals:
- The moisture conditions of a concrete have a decisive effect on several properties and many parts of deterioration processes.
- The moisture distribution in a concrete structure is determined by the concrete composition, curing and the microclimate in the different parts of the structure.
- A prediction requires access to data on the time-dependency of the binder reactions, moisture fixation and moisture flow, ambient temperature and humidity and computer software for more complicated cases.
- Applications in non-saturated concrete for ion transport, coupled ion/moisture transport and for gas transport, including carbonation, require knowledge on the effect of moisture on various other transport processes.
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Impact of Additions on Hydration Kinetics
Ecole Polytechnique Fédérale de Lausanne, CH
University of Aarhus, DK
Eidgenössische Materialprüfungs- und Forschungsanstalt, CH
University of Aberdeen, Scotland, UKDate
This project started on 01 January 2011 and ended on 01 July 2015
Status
This project is Finished
Objectives
The objectives here are to identify impact of additions on hydration kinetics and integrate into a microstructural model
Scientific need / Link to Nanocem goals:
- Need to have mechanistic understanding of role of additions and a kinetic model to add to the thermodynamic database.
- Need to be able to adapt cementitious systems to locally available materials.
- Need to understand possible problems, due to poor aluminate sulfate balance sometimes occurring in the field.
The background relates to 3 activities:
- "Reactivity of mineral additions" developped new methods to measure the degree of reaction of SCMs in cementitious systems
- "Alkali activation of aluminosilicates – An assessment of fundamental mechanisms" tried, but did not succeed to look at the reaction of syntethic glasses as a function of pH, etc.
- Recent work in the EPFL partner project has led to success in modelling the hydration of mixed silicate / aluminate systems based on 2 principal mechanisms. The first period of slow down and induction period is governed by the dissolution reactions and second, the main heat evolution peak, is controlled by nucleation and growth of hydrates (C-S-H, AFm phase or etringite).
Furthermore it was found that parameters derived from simple systems could be applied in more complex systems – even white cement without modification.
The idea is to extend this background to work towards a model in which we can systematically simulate the effects of additions on hydration kinetics and microstructure.
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Micromechanical Analysis of Blended Cement-based Composites
CTU Prague, CZ
TU Wien, ATDate
This project started on 01 September 2012 and ended on 01 September 2016
Status
This project is Finished
Objectives
Blending Portland cements with supplementary cementitious materials presents attractive approach for cement manufacturers to cut down production cost and CO2 emissions. No matter how well the binders perform in the long-term, they need to meet prescriptive code requirements in terms of early strength gain. The reaction kinetics have been already studied in the Core project 4 and Core project 9 and a chemo-mechanical microstructural link will be established now.
The objectives read:
- Generate a comprehensive database for cement pastes, produced with pure and blended Portland Cements, and test them from one day after the production up to mature stages. Determine compressive and tensile strengths as well as the elasticity modulus during maturing. Obtain complementary microstructural characterization on the hydration degrees of individual microstructural phases and on the porosity.
- Identify the microstructural constituents governing the evolution of macroscopic mechanical properties with increasing degree of hydration.
- Develop predictive micromechanical models for compressive strength evolution from one day after the production to mature stages, i.e. link initial blend composition and hydration degrees to macroscopic compressive strength.
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Carbonation Behaviour of Low-Clinker Cements
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University of Leeds, UK
IFSTTAR, FR
Lund University, SE
ZAG, SI
CSIC, SP
Date
This project started on 01 September 2012 and ended on 01 September 2012
Status
This project is Finished
Authors
University of Leeds, UK
IFSTTAR, FR
Lund University, SE
ZAG, SI
CSIC, SP
Objectives
The ongoing trend towards lower clinker contents in cements is welcome from an environmental perspective, but it presents problems with regards to our understanding of material performance. In many instances the potential technological benefits of using composite cements is compromised by the refusal of contractors to recognise the need for adequate curing. Removal of formwork after a period of hours may be acceptable for CEM I systems, but with more slowly hydrating composite cement systems this may cause problems.
In such instances hydration will be far from complete and the microstructure will not be dense and impervious, but rather open, with a resultant loss of performance and allowing the ingress of aggressive species - affecting durability. Thus, there will be a complex interplay of continuing hydration, drying of the sample surface and phase carbonation (as represented schematically in figure 1).
Each of these processes will affect the pore structure and transport properties, plus the phase assemblage. Therefore, the use of models based on the properties of almost fully hydrated and non-carbonated materials for service life prediction is irrelevant. An understanding of the impact of incomplete curing upon carbonation is imperative.
Figure 1: Schematic representation of the interplay between sample hydration, drying and carbonation.
Furthermore, calcium-bearing hydrate phases (in particular CH) are the main suppliers of alkaline buffering capacity. Therefore, reducing the calcium hydrate content (as is the case with low-clinker binders) is likely to result in an increased rate and extent of carbonation. This, in turn, implies that high volume SCM mixtures are more sensitive to carbonation-induced corrosion. Usually, carbonation in OPC matrices causes microstructural changes which slow down CO2 penetration (i.e. a reduction in porosity and refinement of the microstructure).
However, in high volume SCM mixtures, an increase in porosity and a coarser microstructure can be observed, which can yield a significant increase in permeability and thereby adversely affect durability.
This programme will investigate the phase assemblages, carbonation kinetics, micro- and macrostructure and transport properties of cement systems containing less than 50% clinker.
This is too grand an aim for a single PhD student, both in terms of workload and expertise. However, by having two overlapping (but not entirely concurrent) PhD projects, individual and institutional strengths can be maximised. The overall programme may be separated into three primary aims:
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- An understanding of the phase assemblages and microstructure of low-clinker binders at early ages, i.e. the situation when formwork is likely removed during construction, followed by the coupling between simultaneous early-age hydration, carbonation and desiccation of low-clinker materials in terms of phase assemblage and microstructure.
- Identification and generation of relevant input data for durability models, to account for the coupling between carbonation, moisture transport and hydration. This will entail an understanding of changes in pore structure and transport properties upon simultaneous carbonation, hydration and desiccation.
- Testing of existing carbonation models and refinement where possible or appropriate.
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Influence of the Functionalities of Organic Molecules on the Reactivity and Hydration Kinetics of Cement Phases
Univ. Bourgogne-Dijon, FR
Univ. Surrey, UKDate
This project started on 01 November 2012 and ended on 30 October 2015
Status
This project is Finished
Objectives
The high degree of technology and the specifications of modern concrete construction implies the generalized used of organic chemical admixtures to confer the material specific properties either related to its fresh state (rheology modifiers, accelerators, retarders...) or longer term properties (e.g. strength enhancers, durability improvers....).
Although used since decades those admixtures are often considered from a performance point of view but the underlying mechanisms and their interaction with mineral surfaces are hardly resolved and understood. For instance, the mechanism by which set accelerators or retarders work is more of a guess and strongly relies on empirical knowledge rather than on a sound understanding.
With the extensive diversity of today's cements and the increasing levels of substitution of SCMs in modern concrete, the current lack of knowledge on the interaction between organic molecules and mineral surfaces and their influence on the hydration mechanisms of those phases represent a real limitation in the rational development of new products with increased efficiency and performance.
This research is in line with the objectives of nanocem in the sense that it aims at generating fundamental knowledge on the very first interaction taking place upon hydration of cement between the most important components of concrete : the cement (or binder) itself and the organic chemical admixture. Those later have received very little attention in nanocem and in the Marie Curie projects so far with exception of CP3. All the knowledge generated in nanocem on hydration, reactivity, reaction between cement phases is valuable but remains disconnected from concrete technology since all the mechanisms investigated are strongly influence and modified by the presence of organic molecules which were hardly considered, for simplification of the studied mechanisms.
This project intends to start bringing this lacking complementary knowledge.
Although not of high interest from technological and commercial points of views, the molecules to be used will be chosen as to enable the understanding of simple basic interactions between well defined chemical functionalities and well characterized mineral surfaces.The proposed core project is an experimental approach of the interaction of chemicals with cement hydration. The main goal is to identify not only how they affect cement hydration but also why and to correlate the observed effect and its intensity to their structural and chemical parameters. It is expected that the results could serve as a basis for more predictive modelling approaches.
For this reason the molecules that will be studied are simple ones and do not have necessary an application in cement industry.. Selected small molecules will differ only in the functional group or their stereochemistry like sugars. No special synthesis work is planned, only commercial product. No large molecules such as PCEs or other SPs will be considered because of pre-competitiveness issues but also because of the extensive higher number of parameters involves (chemistry of backbone, side chains, length, charge density, molecular weight distribution...).
The project aims at generating fundamental knowledge on the ionic specificity of small well defined and controlled chemical functionalities of organic molecules and their effects on the main mechanisms of cement hydration.
The project intends to work with model cement phases and Portland cement together with a broad set of small sugar and amine like molecules differing from each other on the basis of their conformation or ending functionalities such as carboxylates, sulfonates, phosphonates...
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Shrinkage and Cracking in Cementitious Materials
Eidgenössische Materialprüfungs- und Forschungsanstalt, CH
Technical University of Denmark, DKDate
This project started on 01 March 2013 and ended on 01 May 2016
Status
This project is Finished
Objectives
The objective of this project is to develop a fundamental understanding of the mechanisms leading to shrinkage cracking in cementitious materials through experimentation and development of reliable models.
The focus is on the impact of different binder compositions on free and restrained drying shrinkage.
When mortars are subjected to drying at early ages, moisture gradients develop between the drying surface and the inside of the specimen (gradients both of the local relative humidity and of the moisture content/degree of saturation).As a consequence, the mortar will tend to shrink differently in the cross section and internal stresses will develop (partially consumed by stress relaxation), which might lead to cracks at the drying surface. In addition, the overall shrinkage of the mortar can lead to macrocracking in case of external restraint. The macroscopic cracking observed in the praxis and in laboratory tests (slabs, ring tests, linear restrained tests) is therefore the result of this complex interplay between external and internal restraint to volume changes, stress relaxation, surface cracking (crazing) and microcracking.
This project aims at linking micro-structural development to fundamental quantities believed to be key factors determining the risk of cracking: free shrinkage, strength, stiffness, fracture toughness and creep/relaxation. The analysis will directly take into account the variability of both shrinkage measurements and mechanical properties involved. The approach will allow assessing the effect of different types of blended cement on the risk of cracking.
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Frost Durability of Low-Clinker Binders
Lund University, SE
NTNU, NODate
This project started on 01 October 2016 and ended on December 2021
Status
This project is Finished
Objectives
Frost deterioration of concrete is an important durability issue for concrete structures exposed to high humidity, frost and deicers. Today when the variety of binder compositions is rapidly increasing, it is more important than ever to understand the mechanism behind the deterioration to be able to obtain frost durable structures.
The combination of high degree of saturation and low temperatures can result in both surface scaling and internal cracking. Frost damage can lead to loss of concrete cover and thus reduced protection of the reinforcement and possible loss of bearing capacity. Frost damage in form of cracking facilitates ingress of aggressive substances and thus other deterioration mechanisms as well. The degree of deterioration depends on the surrounding environment such as temperature, relative humidity, precipitation, deicers, and on the materials properties such as permeability, air void structure and mechanical properties.
Long-term experience shows that concrete structures with high amounts of Portland clinker and various air entraining admixtures can be durable. Field exposure investigations confirm that the existing test methods can usually predict the performance of Portland cement concrete. However, with the increasing substitution of Portland clinker, concrete becomes more sensitive to variations in execution (e.g. air entrainment, curing) and to ageing (e.g. carbonation), which can lead to reduced resistance to salt frost scaling of the hardened concrete. To solve these challenges improved understanding of basic mechanisms is needed.
The research will combine modelling of salt frost deterioration with experimental characterisation of concrete properties that are significant in salt frost degradation such as ice formation, permeability, air void structure and surface strength.
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Activities and Nucleation Processes in the SiO2-CaO-H2O - Organics System
University of Bourgogne-Dijon, FR
Empa, CH
University of Grenoble-Alpes, ISTerre, FRDate
This project started on 01 October 2016 and ended on February 2022
Status
This project is Ongoing
Objectives
This project aims at determining the tendency of complex formation of small organic molecules with Ca and other ions as a first step towards the understanding of the effect of small organic molecules on the nucleation and pre-nucleation processes of C-S-H. The work will involve the determination of the stability and characterization of organic and ions complexes as well as the study of the kinetics and the determination of the reaction path of C-S-H nucleation with and without organics.
Organic additives are commonly used in the concrete industry to improve workability. The presence of organics generally also retards cement hydration, both the dissolution of cement clinker and the nucleation and growth of cement hydrates. The physical and chemical mechanisms responsible for the change in reactivity in presence of such organic additives are presently poorly understood.
The determination of stability and characterization of ion complexes in presence of organic molecules is expected to be a decisive step to understand the role of the latter on the nucleation process of C-S-H. They will be determined and characterized based on a combination of experiments and simulations. The C-S-H pre-nucleation and nucleation stages will be studied both in the homogeneous and heterogeneous case. This will involve measurements of the nucleation rates and induction times under controlled conditions and at various supersaturation degrees.
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Stability and properties of hydrate phase assemblages with high Al content in real microstructure
Ecole Polytechnique Fédérale de Lausanne, CH
Eidgenössische Materialprüfungs- und Forschungsanstalt, CH
Aarhus University, DKDate
This project started on 20 October 2016 and ended on 30 June 2020
Status
This project is Finished
Objectives
Replacing cement clinker with supplementary cementitious materials (SCMs) such as fly ashes or calcined clays leads to changes in microstructure, hydrate assemblage and mechanical properties. Such blends have high Al2O3 and SiO2 contents but are low in CaO compared to Portland cements leading to a hydrate assemblage with less or no portlandite, to C-S-H with low Ca/Si and rich in aluminium and in some cases to the formation of strätlingite. The co-existence of portlandite and strätlingite has been observed experimentally although thermodynamically they are not expected to coexist as shown in Figure 1 below. As the reaction of cement clinker and SCMs proceeds at different speeds, hydrates such as portlandite become destabilised with time while others, e.g. strätlingite, become stable within a microstructure with limited availability of water and space.
Figure 1: Ternary phase diagram showing the effect of fly ash on the hydrate assemblage. The stability area of portlandite is indicated in yellow, the stability area of strätlingite in green.
In addition to portlandite, C-S-H and strätlingite, siliceous hydrogarnet can precipitate. Siliceous hydrogarnet is not well crystalline and difficult to detect by X-ray Diffraction or thermogravimetric analysis in hydrated PC and calcium sulfoaluminate (CSA) cements. The presence of iron seems to promote its formation. Minor amounts of siliceous hydrogarnet have been observed in hydrated PC, but it completely replaces AFm phases at higher temperature and in PC hydrated for several decades.
This project aims to investigate the hydrates, the pore solution and their changes with hydration in low CaO and high Al2O3 and/or SiO2 systems. The study will focus on
- PC with metakaolin, where strätlingite formation will occur only after days – weeks
- CSA cement containing belite, where initially ettringite and strätlingite are formed, while C-S-H precipitates later
The methodology of this study will be based on a multi-technique study of two contrasting systems:
- On the one hand the effect of high alumina content obtained by addition of metakaolin (calcined clay) eventually with limestone. In such systems the hydration of the clinker silicate phases occurs first so the matrix of the paste is still dominated by C-S-H phase as in Portland cements. At longer hydration time strätlingite will occur
- On the other hand systems where ye’elemite is the first phase to react as in BYF or CSA cements. In these system ettringite and hydrates alumina are the first phases to form with strätlingite and possibly C-S-H occurring later.
The contrast between these two systems will make it possible to look at the effects of kinetics and microstructure in addition to thermodynamics. To the extent possible systems with similar overall chemistry will be compared.
The other variables to be included in the study are temperature, iron content, alkalis and water to cement ratio. An array of well-established experimental techniques for microstructural characterisation will be used, these have been chosen to give a complete description of the phase assemblages and microstructure with data which can be compared with that available from thermodynamic modelling. It will also be possible to gain information on the link with mechanical properties and durability.
The main objective will be to identify the kinetics of the different reactions and how these are affected by temperature. The information generated will help understand
- the effect of reaction kinetics of “new cement types” on phase assemblage and microstructure in presence and absence of portlandite;
- the role of kinetics on the hydrate assemblage on the hydrate assemblage;
- the influence of the pore solution on kinetics and hydrates;
and create a basis for modelling the evolution of the microstructure of high Al, Si cements: hydrates, porosity, water content,…
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