IMAN-79
Transport des remblais miniers en pâte cimentés
Introduction
Cemented paste backfill (CPB) is used worldwide for underground backfilling of mined-out stopes. It is a highly efficient technique for providing secondary ground support and maintaining a safe working environment when contiguous pillars either collapse or are removed, allowing maximum ore recovery (Brackebusch 1994, Landriault, Verburg et al. 1997, Belem and Benzaazoua 2008, Sheshpari 2015). Backfilling is also recognized as an environmentally friendly and safe tailings management method that reduces the amount of harmful tailings (up to 50%) that would otherwise be deposited on the surface. CPB is an engineered material made by mixing filtered tailings cake (78-85% solid content, Cw ), a binding agent (3-7% by dry mass of tailings), and mixing water. The binder hydration process evolving into CPB and self-consolidation of backfill lead to development of high enough mechanical strength (Fall, Célestin et al. 2010, Yilmaz, Belem et al. 2011, Yilmaz, Be lem et al. 20 15). V arious hydraulic binder types are currently used in CPB, including portland cements and their combination with different mineral admixtures for reducing backfilling operation cost (Peyronnard and Benzaazoua 2012, Tariq and Y anful 2013, Sheshpari 2015).
CPB is usually transported from the backfill plant to the pouring stopes through pipelines and boreholes (Thomas 1979, Pullum, Graham et al. 2006, Wu, Fall et al. 2013). The design of pipeline reticulation systems for CPB transport requires a good knowledge of the mixture’s rheological parameters, defined in terms of yield stress and viscosity. The yield stress is defined as the minimum pressure needed to start the flow while viscosity expresses the frictional resistance between two layers of fluid (Bames, Hutton et al. 1989). CPB mixtures (solid content ranging from 70-85%) should be proportioned to obtain a target slump in order to facilitate transport (Belem and Benzaazoua 2008) and provide adequate rheological parameters. Depending on the mineralogy and physical characteristics of the tailings, slumps (AS TM-standard C143 (2012)) ranging from 6 to 10 inches (152-254 mm) are generally reported to meet the criteria for successful transport and backfilling (Landriault, V erburg et al. 1997, Belem and Benzaazoua 2008). In addition, the rheological parameters must be known to estimate the pressure gradient and flow velocity for pipeline flow (Nguyen and Boger 1998, Wennberg and Sellgren 2007, Hallbom 2008, Graham, Pullum et al. 2009, Boger 2012). Knowledge of the pressure gradient can help optimize the pumping energy consumption (Nguyen and Boger 1998, Paterson, Williamson et al. 2004, Paterson 2012). Furthermore, CPB with relatively high solid content and high rheological parameters may plug the pipeline. To prevent this problem, costly positive displacement pumps (PDP) involving high pumping energy consumption are generally required. CPB with improved rheological properties can allow using more economical gravity transport systems and/or centrifugai pumps (CP) instead. In the case of centrifugai pumps for pipeline transport, Addie, Whitlock et al. (2005) reported that CPB with yield stress less than 200 Pa are required. Unfortunately, no clear criterion was prescribed for CPB viscosity, although this parameter may affect the pressure head loss. Due to the importance of these parameters for effective pipeline flow design, various studies have been conducted to assess the effect of CPB mixture designs on rheological behavior (Pashias, Boger et al. 1996, Sofri and Boger 2002, Kwak, James et al. 2005, Klein and Simon 2006, Ouattara, Mbonimpa et al. 2010, Ouattara 2011, Ouattara, Yahia et al. 2013, Simon and Grabinsky 2013). Yield stress has be en found to increase with increasing solid content (Cw) (Clark, Vickery et al. 1995, Nguyen and Boger 1998, Gawu and Fourie 2004, Alejo and Barrientos 2009, Ouattara 2011, Wu, Wang et al. 2015). However, for a given binder type and content, increased solid content significantly improves mechanical performance (Cayouette 2003, Belem, El Aatar et al. 2006, Yin, Wu et al. 2012). Therefore, the most economical option for obtaining high strength CPB mixtures consists to increase the solid content rather than the binding agent content, as the binding agent accounts for from 75 to 80% of the total cost of backfilling operations (Grice 1998). Another advantage of increasing the solid content of CPB is that it further reduces the amount of tailings that are deposited in surface tailings storage facilities, hence reducing the environmental footprint. However, highly concentrated CPB mixtures ( ~80%) undergo high flow resistance that affects the pipeline flow during casting operations.
The workability of cementitious materials with high solid content can be improved by incorporating high-range water reducer (HRWR) admixtures. HRWR admixtures are synthetic organics that act to disperse charged particles, hence improving the rheological properties. Three successive generations of HRWR have been developed over the years (Ramachandran 1995, Jolicoeur, Mikanovic et al. 2002, Liu, Wang et al. 2014). The main active chemical components of the first generation were sulphonated naphthalene formaldehydes (SNF) or polynaptalene sulphonates (PNS). Sulphonated melamine formaldehydes (SMF) or polymelamine sulphonates (PMS) were used for the second generation (Ramachandran 1995, Rixom and Mailvaganam 2002). The dispersing mechanisms ofthese two generations are electrostatic repulsive forces that are induced when the HRWR polymers are adsorbed on the surface of cement particles (Ramachandran 1995, Rixom and Mailvaganam 2002). The third generation of HRWR are polyacrylate superplasticizers. They are produced by polymerization of carboxylic acid groups (polycarboxylates) as the main backbone molecules. Side-chain copolymers such as ethylene glycol are grafted onto the main backbone to provide the admixture with a comb structure with high molecular weight (Y oshioka, Sakai et al. 1997). This structure promotes the dispersing mechanisms by means of steric hindrance (i.e., repulsion between groups positioned on the same side of a double bond) to prevent particle agglomeration. Currently, polycarboxylate HR WRs are widely used in the concrete industry, and are preferred over PNS and PMS admixtures due to their effectiveness even at lower dosages (Sakai, Kawakami et al. 2003, Sakai, Kasuga et al. 2006). Steric hindrance is a more effective mechanism than electrostatic repulsion (Uchikawa, Hanehara et al. 1997, Yoshioka, Sakai et al. 1997). Moreover, dispersing mechanisms based on steric repulsion are less dependent on cement composition than are PNS and PMS admixtures, and accidentai overdosage does not significantly affect material stability (Greisser 2002).The use of superplasticizers in CPB remains limited despite the expected benefits for improving the rheological properties and flow performance (Huynh, Beattie et al. 2006, Ercikdi, Cihangir et al. 2010, Ouattara, Yahia et al. 2013) as well as mechanical properties of CPB (Weatherwax, Bosko et al. 2010, Simon, Grabinsky et al. 2011). The limited use of HRWR in CPB mixtures is probably due to the additional costs (Farzam, Rispin et al. 1998) as well as the lack of knowledge about the mechanisms within the mixtures and their beneficiai effects. However, Ercikdi, Cihangir et al. (2010) reported that the use of PNS- and PC-based polymers improved the rheological and mechanical properties of CPB mixtures. Water content was reduced by 6.6% for CPB containing HRWR superplasticizers compared to a control CPB mixture (without HRWR), for a constant slump (Ercikdi, Cihangir et al. (2010)). The se authors also found that HR WR admixtures reduced micro cracking induced by internai sulphate attack in hardened CPB. However, Agarwal, Masood et al. (2000) highlighted the need to optimize the HR WR dosage bef ore use in cementitious materials. The effectiveness of HR WR in cementitious systems depends on the mix proportioning, solid concentrations, water hydrochemistry, HRWR type and dosage, and HRWR-binder compatibility (Golaszewski and Szwabowski 2004). The effectiveness of superplasticizers is also sensitive to their addition mode (Uchikawa, Sawaki et al. 1995, Jolicoeur and Simard 1998, Flatt and Houst 2001, Aiad 2003, Golaszewski and Szwabowski 2004) as well as the mixing energy (Chopin, Cazacliu et al. 2007). Therefore, for complex CPB materials, it is important to investigate the main influential factors on the rheological parameters, including superplasticizer type and addition mode, binder type and content, solid content and rheological age.
The objective of this study was to assess the effects of two polycarboxylate-based polymers (PC1 and PC2) on the rheological behaviour of CPB mixtures. The overall aim was to improve the understanding of the behaviour of HR WR admixtures in highly concentrated CPB systems to ensure their effective use to improve rheological and mechanical properties.
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Table des matières
AVANT-PROPOS
LISTE DES FIGURES
LISTE DES TABLEAUX
LISTE DES SIGLES ET ABRÉVIATIONS
LISTE DES LETTRES ET SYMBOLES GRECS
RÉSUMÉ
CHAPITRE I
INTRODUCTION
1.1 Généralités
1.2 Technologie de remblayage minier
1.3 Problématique de transport des RPC
1.5 Objectifs et hypothèses de l’étude
1.6 Structure de la thèse
1. 7 Avancements et limites de l’ étude
CHAPITRE II
REVUE DE LITTÉRATURE SUR LE TRANSPORT DES REMBLAIS MINIERS EN PÂTE CIMENTÉS ET LES SUPERPLASTIFIANTS
2.1 Transport des remblais miniers en pâte cimentés
2.1.1 Paramètres de transport des suspensions minérales
2.1.2 Notions de rhéologie et principaux comportements rhéologiques des fluides
2.1.3 Rhéométrie expérimentale
2.1.4 Autres méthodes indirectes d’évaluation des paramètres rhéologiques du RPC
2.1.5 Méthode d’évaluation des paramètres de transport des remblais à partir des paramètres rhéologiques
2.2 Superplastifiants
2.2.1 Classification des SPs
2.2.2 Définitions sur le dosage de SP
2.2.3 Compatibilité liant et superplastifiants
2.3 État des lieux sur l ‘utilisation des SPs dans les remblais en pâte cimentés
2.4 Discussions sur l ‘utilisation des SPs dans les RPCs en pâte cimentés et besoin en recherche
CHAPITRE III
EFFECTS OF SUPERPLASTICIZER ON RHEOLOGICAL PROPERTIES OF CEMENTED PASTE
BACKFILLS
Abstract
Résumé
3.1 Introduction
3.2 Experimental program and test methods
3 . 2 .1 Material characteristi cs
3 .2.2 Test methods
3.2.3 CPB mixture proportioning and mixing methods
3.2.4 Mixture proportions
3.3 Test results and analysis
3.3.1 Effect of the PC addition sequence
3.3.2 Superplasticizer saturation dosage
3.3.3 Rheological properties of CPB
3.3.4 Effect of solid content on rheological parameters of CPB
3.4 Discussions
3.4.1 PC dosages for CPB pipeline transport
3.4.2 Correlation between mini-cone slump and yield stress of CPB mixtures
3.4.3 Preliminary PC cost estimation
3.5 Concluding remarks
3.6 Acknowledgements
3. 7 References
CHAPITRE IV
INVESTIGATIONS OF THE PERFORMANCE OF SUPERPLASTICIZERS ON RHEOLOGICAL
PROPERTIES OF HIGHLY VISCOUS CEMENTED PASTE BACKFILL MIXTURES
Préambule
Abstract
Résumé
4.1 Introduction
4.2 Experimental program
4.2.1 Materials
4.2.2 CPB mixtures proportioning
4.2.3 Testing method
4.3 Test results
4.3.1 Impact of solid content on rheological behavior of CPB without SP
4.3.2 Effect ofHRWR dosages on CPB rheology and determination of minimum dosage
4.3.3 Effect of PC addition mode on rheological parameters
4.3.4 Influence of HRWR types on the rheological parameters of CPB
4.3.5 Influence of binder type and content
4.3.6 Effect ofthe characteristics of tailings on the PC performance
4.3.7 Correlation between the consistency and flow indexes
4.3.8 Effect of PC dosage on the viscosity of CPB
4.4 Concluding remarks
4.5 Acknowledgment
4.6 References
CHAPITRE V
EFFECT OF SUPERPLASTICIZERS ON THE CONSISTENCY AND UNCONFINED COMPRESSIVE STRENGTH OF CEMENTED PASTE BACKFILLS
Préambule
Abstract
Résumé
5.1 Introduction
5.2 Materials and test methods
5.2.1 Materials
5 .2.2 CPB mixture proportioning and preparation
5.2.3 Testing methods
5.3 Tests results
5. 3.1 Impact of solids content on slump value and UCS of CPB without HR WR
5.3.2 Effect of HRWR addition mode on slump and UCS of CPB
5.3.3 Effect of HRWR dosage on consistency and compressive strength
5.3.4 Effect of HRWR on consistency and compressive strength of CPB with different binder contents Bw
5.3.5 Effect ofHRWR on compressive strength ofCPB with GU binder
5.3.6 Effect ofHRWR type on CPB consistency and compressive strength
5.3.7 Effect of PC HRWR on the compressive strength ofCPB made with tailings T2 an analysis of the influence of tailings characteristics on HRWR performance
5.4 Discussion
5.4.1 HRWR and water-to-binder ratio for CPB curing
5.4.2 HRWR and CPB microstructure
5.4.3 Contribution of solids content and HRWR to the UCS of CPB
5.4.4 HRWR and the potential reduction ofthe binder content
5.5 Conclusion
5.6 Acknowledgements
5. 7 References
CHAPITRE VI
DISCUSSIONS GÉNÉRALES ET ANALYSE ÉCONOMIQUE DE L’UTILISATION DES
SUPERPLASTIFIANTS DANS LES RPCS
6.1 Discussions des résultats rhéologiques
6.1.1 Comparaison de quelques résultats des rhéomètres Con tee et AR 2000
6.1.2 Effet de cisaillement cyclique sur la rhéologie des remblais
6.2 Analyse du potentiel zêta et du pH des suspensions de remblais
6.3 Implications économiques de l’utilisation des superplastifiants dans les recettes de remblais
6.3.1 Méthodologie générale de l’analyse économique de l’utilisation des superplastifiants
dans les recettes de remblais
6.3.2 Analyse économique appliquée aux RPCs étudiés
CHAPITRE VII
CONCLUSIONS ET RECOMMANDATIONS
7.1 Sommaire
7.2 Chapitre 3
7.3 Chapitre 4
7.4 Chapitre 5
7.5 Chapitre 6
7.6 Dernières remarques, recommandations et perspectives
BIBLIOGRAPHIE GÉNÉRALE
ANNEXE A
FICHES TECHNIQUES DES PRINCIPAUX SUPERPLASTIFIANTS UTILISÉS DANS LE CADRE DE CETTE ÉTUDE
ANNEXE B
AJUSTEMENT DES COURBES D’ÉCOULEMENT DES REMBLAIS ÉTUDIÉS AUX CHAPITRES 3 ET 4
ANNEXE C
MÉTHODE D’ANALYSE DU POTENTIEL ZÊTA DES SUSPENSIONS DE REMBLAIS
ANNEXE D
CALCUL DES PERTES DE CHARGE POUR LES REMBLAIS DE RÉFÉRENCE ET ÉQUIVALENTS
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