Alkaline Cements of Waste Glass and Metakaolin, Strength as a Function of the Chemical Composition
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Alkaline Cements of Waste Glass and Metakaolin, Strength as a Function of the Chemical Composition D. E. Ortega-Zavala1, Alexander Gorokhovsky2 and J. I. Escalante-García1 1 Centro de Investigación y de Estudios Avanzados del IPN (Unidad Saltillo), Av. Industria Metalúrgica No. 1062 Parque Industrial, Ramos Arizpe, Coahuila, C.P. 25900, México, Tel.+52 (844)438-9600 fax 4389610, Email: [email protected] [email protected] 2 Department of Chemistry, Saratov State Technical University, 77 Politekhnicheskaya str., Saratov, 410054, Russia.
ABSTRACT Pastes of waste glass (WG) and metakaolin (MK) were prepared by chemical activation with sodium silicate solutions of modulus Ms = 0.5, 0.75, 1 and 1.25 adjusted with sodium hydroxide. An experimental design was carried out using the Taguchi method. The compressive strength (CS) was followed for up to 120 days and then 4 selected formulations of the higher CS were further characterized by X-ray diffraction and scanning electron microscopy. The results showed that the CS depends on the experimental conditions of %WG, %Na2O and Ms and showed a maximum of 70 MPa after 120 days for the paste with 100%WG (%wt.), 8% Na2O and Ms=1.25; while a Portland cement specimen cured at 20°C reached 43MPa. The WG is more reactive than the MK under less alkaline conditions. The features of the microstructures varied notably with the %WG; however all showed relative dense matrices of reaction products, in agreement with the CS attained.
INTRODUCTION The use of synthetic pozzolanics and waste materials as a partial or total replacement of PC, contributes positively in the reduction of global pollution and growth sustainable development, to reduce the consumption of PC and the utilization of waste materials [1]. The study of the formation of a binder activating alkali developed in 1940 by Purdon [2] finds the generation of two phases, the first in which case the formation of hydroxides of aluminum, silicon and calcium; and the second, with the formation of reaction products of silicon and aluminum, these materials geopolymers [3,4] or alkaline cement (AC) are obtained by a polymerization reaction solutions based on alkali-activating working to dissolve large quantities of silica and alumina [5]. Uses WG on alternative binders are based on three main aspects [6]: as aggregate for concrete, raw materials (SiO2 source) and as a replacement for PC. Currently the PC replacement with 50% WG (wt. %) [7], modifies the behavior of the hydration of CP, leaving a large interest in AC alternative sources of SiO2 as WG and MK replacement levels above 50 % alkali activated to generate new cementitious materials[8]. This paper shows a preliminary study of AC with metakaolin (MK) and waste glass (WG) as a source of SiO2, to generate AC without CP.
EXPERIMENTAL The kaolin mineral was calcined at 720° C for 6h to transform it into MK; the oxide composition obtained by X-ray fluorescence (XRF) was (wt. %) 52.04SiO2, 44.9Al2O3, 0.42Fe2O3 and 1.72TiO2. The MK was mainly amorphous to X-
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