Cementos químicos formulados con subproductos de óxido de magnesio

Abstract

Es posible obtener cementos de fosfato de magnesio y potasio (KMgPO 4 ·6H 2 O; K-estruvita), mediante la reacción en medio acuoso del óxido de magnesio y el dihidrogenofosfato de potasio, siendo ésta una reacción exotérmica muy rápida que permite el fraguado del material en pocos minutos. Estos cementos, formulados a partir de óxidos de magnesio de elevada pureza y coste elevado, se encuentran descritos en la bibliografía para su utilización en el encapsulamiento de residuos especiales y como morteros de cemento para la reparación de hormigón. Sin embargo cabe la posibilidad de poder formular este mismo tipo de cementos con óxidos de magnesio de bajo contenido, cuyo precio es del orden de 10 a 15 veces más barato que el óxido de magnesio de elevada pureza. En el presente estudio se evalúa la utilización de óxidos de magnesio de bajo contenido (≈70% MgO), obtenidos en el proceso de calcinación de la magnesita natural, para la formulación de cementos de K-estruvita. En este estudio se pretende determinar la formulación óptima de estos cementos a partir de la evaluación tanto de las propiedades mecánicas como de los tiempos de fraguado de las diferentes composiciones. Palabras clave: cementos de fosfato; K-estruvita; cementos químicos; fosfato de magnesio y potasio.Chemically bonded cements formulated with by-products of magnesium oxide.The casting of magnesium and potassium phosphate (KMgPO 4 ·6H 2 O; K-struvite) cements becomes possible after the aqueous reaction between magnesium oxide and potassium dihydrogen phosphate. This reaction is quite exothermic and allows the resulting paste setting in just few minutes. Those cements, when are cast with magnesium oxides of high purity, are used to retain and encapsulate special residues and as repairing concrete mortar, as it is described in the bibliography. However, it is also possible formulate those cements using low grade magnesium oxides, which cost are nearly 10 or 15 times cheaper than those of high grade. The aim of this work is to evaluate the possibility of using low grade magnesium oxides (≈70% MgO), obtained from the calcinations process of natural magnesites, for KMgPO 4 ·6H 2 O cement casting. The research and selection of the best formulation for obtaining that cement will be done also from the point of view of their mechanical properties as for their setting time.Key words: phosphate cement, K-struvite, chemical cement, magnesium and potassium phosphate. INTRODUCCIóNEl cemento Pórtland es el cemento más utilizado, dado que abarca un amplio rango de propiedades y posibilidades de uso, siendo a su vez un material económico. Sin embargo, en los últimos años se han desarrollado otros tipos de cementos más específicos que permiten ampliar el rango de trabajo y la aplicación de los mismos en otros campos de la tecnología. Entre estos tipos de cementos de nuevo desarrollo se incluyen los denominados cementos cerámicos enlazados químicamente.En general, estos cementos se obtienen a partir de la reacción química ácido-base entre un metal catiónico y una fuente ...

Engineering applications of chemically-bonded phosphate ceramics

“…Several authors have tried to link alternative raw materials and additives of low environmental impact in the formation of cements. The review of some researches evidenced the use of substitute raw materials that reduce manufacturing costs and reuse of industrial waste as source of raw materials (Formosa et al, 2008;Gardner et al, 2015;Choi, Um, and Choung, 2014;Kinnunen et al, 2018). This fact has a substantial impact, since it allows to diminish the environmental impact produced by the exploitation and transformation of conventional raw materials.…”

“…Wang, Zhang, Li, Ma, and Liu, 2013). Formosa et al (2008) proposed the evaluation of a magnesium phosphate cement, composed of potassium hydrogen phosphate (KH 2 PO 4 ) and magnesium oxide (MgO), with contribution percentages between 65%-45% (MgO) and 45%-35% (KH 2 PO 4 ) and a water/solids ratio between 0,24-0,28. The authors found that increasing the water content and/or magnesium oxides decreases the compressive strength.…”

Magnesium Phosphate Cements formulated with a low-grade MgO by-product: Physico-mechanical and durability aspects

“…In order to overtake the economical limitation, the authors have studied the possibility of obtaining a MPC formulated with a low-grade magnesium oxide (LG-MgO) [43,44], which is obtained as a by-product from the calcination process of natural magnesite [45]. By this manner, the cost of the products could be substantially diminished, and the mortar obtained would be a competitive alternative, while enhancing sustainability criteria and recyclability.…”

Magnesium phosphate cement formulated with low grade magnesium oxide with controlled porosity and low thermal conductivity as a function of admixture

“…The main purpose of this study is based on the research group previous experience in obtaining sust-MPC [35][36][37][38][39]. Nowadays, the sust-MPCs obtained has been considered as construction repairing materials [38].…”