The Effect of the Activator/Precursor Ratio on the Rheological Properties of the Alkali-activated Mining Waste Mud Paste
To determine the properties of paste, mortar or concrete, it is necessary to understand its rheological behaviour first. This study discusses the effect of the activator/precursor ratio on the rheological properties of the alkali-activated paste. The pastes consisted of a mix of 70 % of tungsten mining waste mud, 15% waste glass and 15% of metakaolin. This mix was activated by combining sodium hydroxide and sodium silicate. Five activator/precursor (a/p) ratios were studied: 0.37, 0.38, 0.39, 0.40 and 0.41. The result obtained shows that the rheology of the pastes is affected by the activator/precursor ratio. The rheological behaviour of the paste fits the Bingham model. The yield stress (τ0) and plastic viscosity (μ) increase inversely with the activator/precursor ratio (e.g. a/p=0.37 gives τ0=84.19 and μ=0.4185; a/p=0.41 gives τ0=30.389 and μ=0.2937). The workability increases proportionally with the activator/precursor ratio (e.g. a/p=0.37 gives a slump=133 mm; a/p=0.41 gives a slump=158 mm). The compressive strength decreases when the activator/precursor ratio increases (e.g. at 28 days for a/p=0.37, the compressive strength was 19.6 MPa; for a/p=0.41, the compressive strength was 13 MPa). Finally, the ideal ratios were 0.38 and 0.39.
 European Parliament, Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom a. Off J Eur Commun L13, (2014) 1–73. https://doi.org/doi:10.3000/19770677.L_2013.124.eng.
 M. C. Bignozzi, S. Manzi, M. E. Natali, W. D. A. Rickard, & A. Van Riessen, Room temperature alkali activation of fly ash: The effect of Na 2O/SiO2 ratio. Construction and Building Materials, 69 (2014) 262–270. https://doi.org/10.1016/j.conbuildmat.2014.07.062.
 R. B. V. Hardjito D., Wallah S. E. Sumajouw D.M.J., On the Development of Fly AshBased Geopolymer Concrete. ACI Materials Journal/November-December, (2004) 467–472.
 J. P. Castro-Gomes, A. P. Silva, R. P. Cano, J. Durán Suarez, & A. Albuquerque, Potential for reuse of tungsten mining waste-rock in technical-artistic value added products. Journal of Cleaner Production, 25 (2012) 34–41. https://doi.org/10.1016/j.jclepro.2011.11.064.
 G. H. Tattersall & P. F. G. Banfill, The rheology of fresh concrete (Pitman Advanced Publishing Program, 1983).
 R. Bhattacharjee & A. I. Laskar, Rheological behavior of fly ash based geopolymer concrete. 35th Conference on OUR WORLD IN CONCRETE & STRUCTURES, (2010).
 A. Poulesquen, F. Frizon, & D. Lambertin, Rheological behavior of alkali-activated metakaolin during geopolymerization. Cement-Based Materials for Nuclear Waste Storage, 357 (2011) 225–238. https: //doi.org/10.1007/978-1-4614-3445-0_20.
 M. Romagnoli, C. Leonelli, E. Kamse, & M. Lassinantti Gualtieri, Rheology of geopolymer by DOE approach. Construction and Building Materials, 36 (2012) 251–258. https://doi.org/10.1016/j. conbuildmat.2012.04.122.
 N. Cristelo, E. Soares, I. Rosa, T. Miranda, D. V. Oliveira, R. A. Silva, & A. Chaves, Rheological properties of alkaline activated fly ash used in jet grouting applications. Construction and Building Materials, 48 (2013) 925–933. https://doi.org/10.1016/j.conbuildmat.2013.07.063.
 A. Kashani, J. L. Provis, G. G. Qiao, & J. S. J. Van Deventer, The interrelationship between surface chemistry and rheology in alkali activated slag paste. Construction and Building Materials, 65 (2014) 583–591. https://doi.org/10.1016/j.conbuildmat.2014.04.127.
 A. Aboulayt, M. Riahi, S. Anis, M. O. Touhami, & R. Moussa, Rheological behavior of a fresh geopolymer based on metakaolin: effect of the introduction of calcium carbonate. International Journal of Innovation and Applied Studies, 7 (2014) 1170–1177.
 F. Puertas, C. Varga, & M. M. Alonso, Rheology of alkali-activated slag pastes. Effect of the nature and concentration of the activating solution. Cement and Concrete Composites, 53 (2014) 279–288. https://doi.org/10.1016/j.cemconcomp.2014.07.012.
 K. Vance, A. Dakhane, G. Sant, & N. Neithalath, Observations on the rheological response of alkali activated fly ash suspensions: the role of activator type and concentration. Rheologica Acta, 53 (2014) 843–855. https://doi.org/10.1007/s00397-014-0793-z.
 M. Torres-Carrasco, C. Rodríguez-Puertas, M. Del Mar Alonso, & F. Puertas, Alkali activated slag cements using waste glass as alternative activators. Rheological behaviour. Boletin de la Sociedad Espanola de Ceramica y Vidrio, 54 (2015) 45–57. https://doi.org/10.1016/j.bsecv.2015.03.004.
 P. A. Wedding & D. L. Kantro, Influence of Water-Reducing Admixtures on Properties of Cement Paste-A Miniature Slump Test. Cement Concrete and Aggregates, 2 (1980). https://doi.org/10.1520/CCA10190J.
 I. M. Krieger & T. J. Dougherty, A Mechanism for Non-Newtonian Flow in Suspensions of Rigid Spheres. Transactions of the Society of Rheology, 3 (1959) 137–152. https://doi.org/10.1122/1.548848.