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Wells used for steam-assisted gravity drainage (SAGD), for cyclic steam stimulation (CSS), for hydrocarbon production in areas with anomalous high geothermal gradient, or for geothermal energy extraction all are operated in high temperature environments where maintaining long term wellbore integrity is one of the key challenges. Changes in cement mineralogy and associated mechanical properties may critically affect the integrity of high temperature wells. In this study, the relation between changes in mineralogy and mechanical properties of API class G cement with 40% silica flour was investigated by exposing samples for 1-4 weeks to temperatures of 60-420°C. The effect of mineralogical changes on mechanical properties was investigated using a combination of chemical and microstructural analysis and triaxial strength tests at confining pressures of 2-15 MPa. The combined effect of changing porosity, microstructure and strength of mineral phases determines changes in mechanical behavior, in particular the formation of stronger mineral phases with higher density affect Young’s modulus, failure strength and residual strength. Deformation of the cement is more brittle at low confining pressures and more ductile at high confining pressures with a considerable residual strength after failure and highest reduction in cement stiffness and increase in strength at temperatures of 250°C.

International audience; Within the H2020 GeoWell project, that aims to develop reliable technologies for high-temperature geothermal wells (>400°C), it is necessary to assess the durability of cements under such thermal stress, especially regarding mineralogical evolution.For modelling above 300°C, the geochemical database and modelling codes need to be extended. This starts by using the HKF model (1, 2), which computes standard molal thermodynamic properties (heat capacity, volume, Gibbs free energy) for aqueous species at temperature and pressure in the supercritical domain. In some cases, the parameters used in the model were determined by Sverjensky et al (3) correlation.A tool was built allowing the calculation of a PHREEQC-V2 (4) database between 0 to 600°C along specific P-T profiles. After comparing the resulting calculations with literature data and other geochemical codes, we focussed on the selection of thermodynamic properties for the relevant cement mineral phases. This was done consistently with the IDDP1 (Iceland Deep Drilling Project) well cement samples analyses and the results of lab experiments. The PHREEQC-V2 calculations with the upgraded database allows predicting potential cement evolutions during temperature and pressure changes in term of mineral phase transitions and their effect on volume and water content.

As modern society is striving to become more sustainable and environmentally friendly, the need for more durable constructions with longer life cycles is increasing. On the other hand, the functional properties of constructions -such as pavements- need to remain at least at the same level or even outperform the current ones as higher quality standards are introduced. Currently used material solutions often fail to provide a combination of adequate durability and functional properties. This means that the limits of these materials have been reached and therefore a new approach to more durable and functional pavements should be taken. In this study a new composite concrete based material –“Flexible concrete”- was designed for longer life cycle as well as excellent functional performance. Concrete performance was measured using tests for both concrete material - compressive and bending strength development- and asphalt material – tensile strength, stiffness and fatigue (four point bending test) and shear strength (Leutner test). The results proved that the material behaves adequately in all tests. The properties developed makes “Flexible concrete” an excellent material for more durable (concrete) pavements.

Overheidsbeleid richting een circulaire economie en de Green

Secondary resources containing (catcium) atuminium-silicate phases, e.g., fly ash, slag or bottom ash are used as precursor for binders such as geopolymers. Because secondary resources can be highly variable in terms of their potential to dissolve and form reaction products, analytical methods are needed to evaluate their potential as a precursor and to optimize the geopolymer mix design. The most commonly used methods (e.g., XRF, XRD) for measuring the characteristics of source materials which influence binder performance, do not capture heterogeneity of the particles and do not necessarily reveal the key parameter that is most dominant for the binder performance. This presentation therefore discusses the applicability of several techniques we have investigated to capture inter- and intra-particle variations of aluminium-silicates and to evaluate the potential influence of these variations on geopolymer performance. The evaluated techniques are: automated phase mapping based on EDS spectral imaging and processing using principal component analysis; feature sizing and chemical typing (fS&CT); semi-quantitative fTIR 29 and solid state Si NMR.

Geopolymers are systems of inorganic binders that can be used for sustainable, cementless concrete and are formed by alkali activation of an aluminium–silicate precursor (often secondary resources like fly ash or slag). The type of aluminium– silicate precursor and its potential variations within one batch may influence geopolymer performance. Therefore, if geopolymers are to be applied for sustainable concrete with reproducible quality, a characterization tool for quality control of precursors and optimizing mix design is needed, which links the (variable) secondary resource characteristics to the performance of geopolymers. This paper shows the potential of using FT-IR and solid state 29Si-NMR for a (semi-)quantitative evaluation of secondary resources suitable for geopolymers. More specifically, the aim is to investigate whether the presence of particular aluminium–silicate phases may have a dominant influence on the strength of a simple geopolymer system. Based on deconvolution of FT-IR and NMR spectra of 9 source materials (fly ash and slag) and their geopolymers, relative amounts of different (aluminium– silicate) phases were estimated and trends with strength were evaluated. A clear trend is observed for bothNMRand FT-IR results: the precursors containing a higher amount of ‘active bonds’, predominantly from silicates with a medium amount of aluminium and alkalis incorporated in their framework, result in higher paste strengths. As such, due to its relatively quick and easy measurements, FT-IR for estimating relative amounts of these aluminium–silicate phases, can be a useful tool for evaluating geopolymer precursors

Producing concrete with secondary raw materials is an excellent way to contribute to a more

Worldwide, the building sector requires the production of 4 billion tonnes of cement annually, consuming more than 40% of global energy. Alkali activated “cementless” binders have recently emerged as a novel eco-friendly construction material with a promising potential to replace ordinary Portland cement. These binders consist of a class of inorganic polymer formed mainly by the reaction between an alkaline solution and an aluminosilicate source. Precursor materials for this reaction can be found in secondary material streams from different industrial sectors, from energy to agro-alimentary. However, the suitability of these materials in developing the polymerisation reaction must be assessed through a detailed chemical and physical characterisation, ensuring the availability of required chemical species in the appropriate quantity and physical state. Furthermore, the binder composition needs to be defined in terms of proper alkali activation dosages, water content in the mix, and curing conditions. The mix design must satisfy mechanical requirements and compliance to desired engineering properties (workability, setting time) for ensuring the suitability of the binder in replacing Portland cement in concrete applications. This paper offers a structured approach for the development of secondary material-based binders, from their identification to mix design and production procedure development. Essential features of precursor material can be determined through chemical and physical characterisation methods and advanced microscope techniques. Important mixing parameters and binder properties requirements are examined and some examples of developed binders are reported.