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Ruby Mejia

Universidad del Valle - Colombia, Ingenieria de Materiales, Faculty Member

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93 Papers
1 Papers Vol. 10 núm. 19 enero-junio 2014
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- 1 Issue 190
- 1 Issue 194

Papers by Ruby Mejia

PUZOSIL Sílice amorfa de cascarilla de arroz obtenida por un metodo termoquímico como material cementicio suplementario

IP 1106-08-12282Aspectos generales del proyecto--Estado del arte--Procesos de obtención de PUZOSI... more IP 1106-08-12282Aspectos generales del proyecto--Estado del arte--Procesos de obtención de PUZOSIL--Evaluación del producto en morteros--Efecto de la incorporación de CCA (Cascarilla de Arroz) en concretos--Diseño y construcción de planta experimental--Estudio de factibilidad preliminar para el establecimiento de un planta de producción de ceniza de cascarilla de arro

Study of a repair technique in carbonated blended mortars: Electrochemical re-alkalization

DYNA, 2016

The present article studies the influence of two pozzolanic additions, metakaolin (MK) and silica... more The present article studies the influence of two pozzolanic additions, metakaolin (MK) and silica fume (SF), and the water/binder ratio (w/b) on the electrochemical re-alkalization (ER) of reinforced mortars as a technique to prevent reinforcement corrosion in carbonated concrete. Mixtures with a 10% (by weight) addition as a replacement for cement at w/b ratios of 0.45 and 0.65 were prepared. Test specimens were exposed to carbonation in a chamber under controlled conditions (1% CO2, 65%RH, and 25°C), until reaching two levels of carbonation (50% and 100%). ER was applied for a period of 15 days using sodium carbonate as the electrolyte and a current density of 1 A/m2. From the evaluated additions, MK is highlighted, which generated a resistance increase of 53.51% relative to that of the reference mixture and contributes to improvements of durability properties. Regarding the ER technique, the specimens with greater w/b ratios and partial carbonation were more effective.

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Mechanical and thermal performance of a geopolymeric and hybrid material based on fly ash

DYNA, 2016

This article presents an evaluation of the thermal behavior of a hybrid (FA/OPC) and geopolymer (... more This article presents an evaluation of the thermal behavior of a hybrid (FA/OPC) and geopolymer (FA100) material. The FA100 system is based on fly ash (FA), which has an elevated content of unburned material (14.8%). The FA/OPC system is comprised of a mixture of fly ash and ordinary Portland cement (OPC) at a proportion of 80/20. The thermal performance was evaluated by several tests, such as exposure to high temperatures (up to1000°C) and direct flame resistance. In addition, the effect of cyclic exposure was studied at 700°C for 10 cycles. FA/OPC hybrid material retains 92% of its initial strength and FA100 retains 113.3% of its initial strength at 700°C. Both materials can withstand 10 exposure cycles with a strength loss of less than 45%. In direct flame exposure, a temperature gradient of about 500°C was observed. These results indicate that these types of materials could possibly be used as fire-resistant materials in civil structures.

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Materiales vitrocerámicos obtenidos a partir de residuos sólidos tales como cenizas, escorias y vidrio: revisión

Informador Técnico, 2020

Glass-ceramic obtained from solid waste such as ash, slag, and glass waste: review Resumen El uso... more Glass-ceramic obtained from solid waste such as ash, slag, and glass waste: review Resumen El uso de residuos y subproductos industriales como reemplazo parcial o total de materias primas vírgenes para la producción de nuevos materiales, se ha convertido en una parte vital de la gestión de desechos, lo cual ha dado lugar a tecnologías innovadoras que permiten extender su aplicación al desarrollo de nuevos productos, contribuyendo así a la menor contaminación ambiental y a los conceptos de la economía circular. En los últimos años, la tecnología de vitrificación de residuos se ha considerado un procedimiento atractivo para el tratamiento de diferentes tipos y mezclas de residuos para la obtención de vidrios y vitrocerámicas. El presente artículo realizó una revisión de investigaciones relacionadas con la producción de vitrocerámicas densas realizadas entre 1994 y 2019, específicamente las que han utilizado cenizas, escorias y residuos de vidrio. La revisión revela que se han acumulado considerables conocimientos y experiencia en el proceso de transformación de los desechos base silicatos, en productos útiles de vidrio y vitrocerámicas con propiedades similares o incluso superiores a los obtenidos a partir de materias primas no renovables, abriendo nuevos campos de aplicación en cerámicas avanzadas.

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Alkali-activated materials: cementing a sustainable future

This paper presents an overview examining the microstructural and macrostructural properties of a... more This paper presents an overview examining the microstructural and macrostructural properties of alkali-activated binders based on granulated blast furnace slags, metakaolin and their blends, developed by the Composite Materials Group of Universidad del Valle over the past decade. Durability results of activated binders when exposed to aggressive agents such as chlorides, and carbon dioxide are reported. The results of this research have elucidated the great feasibility of adopting alkali-activation technology in Colombia for producing high strength concretes based on industrial by-products, with a wide range of properties that can be suitable for different civil infrastructure applications, and contribute to the valorization of low-cost industrial by products through production of more environmentally friendly building materials. Our research highlights the fact that a deep understanding of the chemistry of these systems allows the manipulation of the microstructure and therefore th...

$Figure 2. Isothermal calorimetry (25 °C) curves showing heat release from alkali-activated slag (GBFS)/metakaolin (MK) blends with GBFS(GBFS+MkK) ratios of (A) 1.0, (B) 0.9 and (C) 0.8. The highlighted areas in the inset panels correspond to the setting period (from initial set to final set) determined for each mix by the Vicat test. Data from (Bernal et al. 2011la). (— Ms 2.4, (—) Ms 2.0, and (—) Ms 1.6. The setting times identified for these binders are very low compared with what is specified for Portland cement, which is generally required to have a minimum initial setting time of 45 min (Hewlett 1998). However, calorimetric measurement of the heat evolution from the reaction taking place during setting of silicate- activated slags (Bernal et al. 2011a) revealed that there is not a direct correlation between the measurements of setting times via the Vicat test (Hewlett 1998) and the formation and precipitation of reaction products in activated slag binders, as Detailed structural evolution of silicate-activated slag binders was also studied via X-ray diffraction (Bernal et al. 2010, Bernal et al. 2011a). X-ray diffractometry was carried out using a high- resolution high-throughput synchrotron powder X-ray diffractometer with a system of twelve simultaneous analyzer/detectors at beamline 1-BM at the Advanced Photon Source (APS), Argonne National Laboratory, USA. The formation of calcium silicate hydrate (C-S-H) is identified (Figure 3(a)), as the main reaction product in silicate-activated slags, in good agreement with the reported in other studies Wang & Scrivener 1995, Fernandez-Jiménez & Puertas 2003). Formation of the aluminosilicate zeolite gismondine is also observed. No crystalline hydrotalcite-type phases were observed in any of the samples studied, due to the very low Mg content of the slag used. This is one of the key differences between the Colombian activated slag binders and those produced and assessed in Europe and Australia, where the slags contain higher levels of Mg and such phases are usually identified.$

$Figure 3. (a) High resolution synchrotron X-ray diffraction patterns of pastes ( = 0.401738 A) based on alkali-activated GBF with Ms = 2.4, at different times of curing; (b) Fourier transform infrared spectra of pastes of silicate activated slag with Ms = 2.4 as a function of the curing time. Data from (Bernal et al. 201 1a).$

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Permeation properties of Concrete Added with a Petrochemical Industry Waste

Ingeniería e Investigación, 2017

The aim of this study is to evaluate the permeation properties of concrete added with a residue o... more The aim of this study is to evaluate the permeation properties of concrete added with a residue of a petrochemical industry located in Colombia, called catalytic cracking catalyst residue (FCC). Concrete samples with 10, 20 and 30 % of FCC incorporated as cement replacement were evaluated. As reference materials, concrete without addition and concrete added with 20 % of metakaolin (MK) were used. MK is a high performance pozzolan of chemical composition similar to the FCC. The properties studied, in addition to the compressive strength, were: water absorption by total immersion, porosity, surface absorption and capillary sorption. The results showed that the concrete added with FCC and MK had similar behavior, and were slightly higher than the control sample. The total absorption and porosity were below 5 % and 10 % respectively for all samples; this means that the incorporation of the addition reduces the permeability of concrete. In this sense, FCC is considered as a good alternat...

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Developing high-performance concrete incorporating highly-reactive rice husk ash

Revista Ingenieria E Investigacion, May 1, 2013

The aim of this study is to present results of an investigation about the developing of a highper... more The aim of this study is to present results of an investigation about the developing of a highperformance concrete (HPC) usin g a highly reactive pozzolan made from chemically treated rice husk ash (ChRHA) prepared by a chemical-thermal attack to the rice husk. This particular rice husk ash (RHA) consists of 99% of silica, highly amorphous, w hite in color and of greater pozzolan ic activity than the silica fume and another rice husk ash prepared with only by a thermal treatment. The results of the physical, chemical and mineralogical characteristics of ChRHA are analyzed. In this study, the compressive strength, flex ural strength, w ater absorp tion, resistance to carbonation, total charge-passed derived from rapid chloride permeability test (RCPT) and modulus of elasticity of hardened concrete were determined in the laboratory. Test results indicate that it is possible to produce HPC with the incorp oration the chemically treated RHA. The incorporation of the chemically treated rice husk ash into the concrete enhances the compressive strengthand the durability properties being comparable to the properties of high performance concretes with silica fume (SF) made w ith the same replacement levels.

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Estabilización química de suelos - Materiales convencionales y activados alcalinamente (revisión)

Informador Técnico, 2020

El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradic... more El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradicionales en aplicaciones geotécnicas, tales como cemento y cal, se debe en gran medida a los retos ambientales y costos asociados en este tipo de aplicaciones. Los cementantes activados alcalinamente surgen como una de las alternativas de mayor sostenibilidad, particularmente por su bajo consumo energético y en teoría la baja huella de carbono en su fabricación; además, tienen la posibilidad de utilizar residuos y subproductos industriales como materiales precursores en su fabricación. Este artículo presenta un estado del arte de los diversos materiales empleados convencionalmente en la estabilización química de suelos y realiza una revisión de los artículos publicados en relación con la implementación de cementantes activados alcalinamente, su viabilidad técnica, los impactos ambientales asociados y los retos que se deben superar para lograr posicionarlos como una alternativa sostenible para procesos geotécnicos.

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Resistencia química de concretos de activación alcalina ceniza volante/ escoria: Sulfatos y ácidos

Informador Técnico, 2018

Una de las características más importantes del concreto en adición a sus propiedades mecánicas es... more Una de las características más importantes del concreto en adición a sus propiedades mecánicas es su durabilidad, que se asocia con la vida en servicio de las estructuras expuestas a ciertas condiciones o ambientes; esta propiedad es requerida para definir los potenciales campos de aplicación y facilitar la comercialización de nuevos materiales cementantes. En este estudio, se evaluó la resistencia química de un concreto de activación alcalina basado en cenizas volantes (CV) y escoria de alto horno (ESC) en relación 80/20; como material de referencia se utilizó un concreto a base de cemento convencional (OPC). La resistencia a la compresión del concreto Geo CV /ESC a 28 días de curado normal fue de 42,9 MPa, 26% superior a la reportada por el concreto OPC. Geo CV/ESC expuesto a sulfatos hasta la edad de 180 días no muestra expansión y la pérdida de resistencia a la compresión no es significativa (2%) en comparación con OPC (39%). En el caso de la exposición a los ácidos, Geo CV/ESC ...

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Evaluación térmica de sistemas geopoliméricos basados en metacaolín con incorporación de humo de sílice y ceniza de cascarilla de arroz

Informador Técnico, 2014

Se presentan los resultados obtenidos al someter un material geopolimérico basado en metacaolín ... more Se presentan los resultados obtenidos al someter un material geopolimérico basado en metacaolín a una temperatura de 1.200 °C utilizando como activador alcalino una mezcla de hidróxido de potasio con diferentes fuentes de sílice: un silicato comercial de tipo potásico (SP), ceniza de cascarilla de arroz (CCA) o humo de sílice. Se ajustaron las proporciones de metacaolín y activador en la mezcla para obtener relaciones molares de SiO2/Al2O3 de 2,5 y K2O/SiO2 de 0,28. También se estudió la sustitución del 50% del silicato comercial por CCA y humo de sílice, y se evaluó la resistencia a la compresión después de exponer la mezcla a diferentes temperaturas que variaron entre 300 y 1.200 °C. Se realizaron los respectivos análisis físicos, por ejemplo determinación de cambios volumétricos, y el estudio se complementó con un análisis microestructural realizado mediante difracción de rayos X y microscopia electrónica. A temperatura ambiente, los geopolímeros producidos reportan resistencias...

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Técnicas aceleradas para evaluar la susceptibilidad a corrosión de aceros embebidos en morteros con adiciones minerales expuestos a cloruros

Informador Técnico, 2015

Este artículo estudia el comportamiento a la corrosión de morteros reforzados de cemento portland... more Este artículo estudia el comportamiento a la corrosión de morteros reforzados de cemento portland, sin adiciones y con adiciones de metacaolín (MK) y humo de sílice (SF), en presencia de cloruros. La proporción de la adición utilizada en las mezclas fue del 10% en peso como reemplazo del cemento. Se prepararon prototipos sin y con acero de refuerzo. En los primeros se determinó la resistencia a la compresión, absorción, porosidad, y permeabilidad a los cloruros. Las probetas de mortero reforzado se expusieron a cloruros (NaCl 3,5%) y se aplicaron dos técnicas aceleradas de corrosión: ciclos de humectación-secado y voltaje impreso; en ambos casos se utilizó como ambiente de referencia agua potable. El avance del proceso de corrosión en el acero se evaluó mediante la técnica electroquímica de resistencia a la polarización lineal (LPR). Los resultados mostraron que tanto a 28 como a 90 días de curado, las adiciones aumentan la resistencia a la compresión del mortero y contribuyen posit...

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Engineering properties of blended concrete with Colombian rice husk ash and metakaolin

The effects of partial replacements of Portland cement by Metakaolin (MK) and Rice Husk Ash (RHA)... more The effects of partial replacements of Portland cement by Metakaolin (MK) and Rice Husk Ash (RHA) on the mechanical and durability properties of concrete mixtures were investigated. Two types of RHA-thermal (TRHA) and chemical treated (ChRHA)-and a sample of MK, at different percentages of replacement by weight, were studied. MK was produced by heat treatment (700 °C for 2 hours) of a Colombian kaolin. The properties of the investigated concrete include compressive strength and durability. The durability aspects tested were: water absorption, chloride ion penetration, carbonation and sulfate resistance. The results were compared with those of cementitious materials without the pozzolanic admixtures and with addition of Silica Fume (SF). It was noted,in general an enhanced performance on the mechanical and durability properties of the concretes, proving the feasibility of its rational utilization in engineering as supplementary cementing materials for environmental sustainability.

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Synthesis of ternary geopolymers based on metakaolin, boiler slag and rice husk ash

DYNA, 2015

Ternary mixtures of geopolymers obtained from the alkaline activation of metakaolin (MK), boiler ... more Ternary mixtures of geopolymers obtained from the alkaline activation of metakaolin (MK), boiler slag (BS), and rice husk ash (RHA) using a solution of potassium hydroxide were mechanically, thermally, and microstructurally characterized. The geopolymer properties and final microstructures indicate that the addition of BS, despite containing large amounts of unburned material (16.36%), allows for greater densification and greater homogeneity of the geopolymeric gel, which results in greater stability in strength at long curing ages. Substitution of 30% of MK by BS results in an increase in compressive strength of up to 21% and 122% after 28 and 180 days of curing, respectively. These results demonstrate the possibility of the construction sector using geopolymers based on MK and adding BS and RHA to obtain cementitious materials with a lower environmental impact.

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Evaluation of the toxicity characteristics of two industrial wastes valorized by geopolymerization process

DYNA, 2015

This paper evaluates the toxicity associated with two industrial wastes used as raw material of g... more This paper evaluates the toxicity associated with two industrial wastes used as raw material of geopolymers. These wastes are fly ash (FA) and spent catalyst catalytic cracking (FCC). The residues were characterized using techniques such as XRF, XRD, SEM and laser granulometry. Two geopolymers systems based on FA-100% and FCC-100% were produced using…

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Optimización de la resistencia mecánica de cementos binarios MK/GBFS activados alcalinamente por Metodología de Superficie de Respuesta

Ingeniería y Ciencia, 2014

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Estabilización química de suelos - Materiales convencionales y activados alcalinamente (revisión)

by Informador Técnico and Ruby Mejia

Informador Técnico , 2020

El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradic... more El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradicionales en aplicaciones geotécnicas, tales como cemento y cal, se debe en gran medida a los retos ambientales y costos asociados en este tipo de aplicaciones. Los cementantes activados alcalinamente surgen como una de las alternativas de mayor sostenibilidad, particularmente por su bajo consumo energético y en teoría la baja huella de carbono en su fabricación; además, tienen la posibilidad de utilizar residuos y subproductos industriales como materiales precursores en su fabricación. Este artículo presenta un estado del arte de los diversos materiales empleados convencionalmente en la estabilización química de suelos y realiza una revisión de los artículos publicados en relación con la implementación de cementantes activados alcalinamente, su viabilidad técnica, los impactos ambientales asociados y los retos que se deben superar para lograr posicionarlos como una alternativa sostenible para procesos geotécnicos.

Resistencia química de concretos de activación alcalina ceniza volante/ escoria: Sulfatos y ácidos

by Informador Técnico, Daniela Eugenia Angulo-Ramírez, and Ruby Mejia

Informador Técnico, 2018

Una de las características más importantes del concreto en adición a sus propiedades mecánicas es... more Una de las características más importantes del concreto en adición a sus propiedades mecánicas es su durabilidad, que se asocia con la vida en servicio de las estructuras expuestas a ciertas condiciones o ambientes; esta propiedad es requerida para definir los potenciales campos de aplicación y facilitar la comercialización de nuevos materiales cementantes. En este estudio, se evaluó la resistencia química de un concreto de activación alcalina basado en cenizas volantes (CV) y escoria de alto horno (ESC) en relación 80/20; como material de referencia se utilizó un concreto a base de cemento convencional (OPC). La resistencia a la compresión del concreto Geo CV /ESC a 28 días de curado normal fue de 42,9 MPa, 26% superior a la reportada por el concreto OPC. Geo CV/ESC expuesto a sulfatos hasta la edad de 180 días no muestra expansión y la pérdida de resistencia a la compresión no es significativa (2%) en comparación con OPC (39%). En el caso de la exposición a los ácidos, Geo CV/ESC presenta una pérdida de resistencia del 39% y OPC de hasta el 80%. Estas características demuestran una mayor resistencia química del concreto de activación alcalina y por tanto su potencial uso en ambientes agresivos.

Effect of kaolin treatment temperature on mortar chloride permeability

ABSTRACT

Alkaline cement mortars. Chemical resistance to sulfate and seawater attack

Materiales de Construcción

Alkaline cement mortars. Chemical resistance to sulfate and seawater attack

format_quoteActivated cement mortars showed high durability against sulfate and seawater, but NaOH activated mortars were most sensitive to environmental attacks, forming gypsum and ettringite.format_quote

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Thermal properties of novel binary geopolymers based on metakaolin and alternative silica sources

Applied Clay Science, 2015

The objective of this study was to evaluate the thermal properties of geopolymers based on metaka... more The objective of this study was to evaluate the thermal properties of geopolymers based on metakaolin (MK) and alternative silica-based activators. These activators were produced by mixing rice husk ash (RHA) and silica fume (SF) with potassium hydroxide (KOH). In addition, boiler slag (BS) was used as partial substitute for the MK aluminosilicates precursor. The thermo-physical properties of the geopolymers prepared with alternative activators were compared to geopolymers activated with commercial potassium silicate (KS). In general, thermal conductivity, diffusivity and specific heat are related to porosity of the geopolymer. The values of thermal conductivity were between 0.170-0.353 W/m·K. The coefficient of thermal expansion varies between 1.06 and 1.13 × 10 −4 K −1 and the thermal diffusivity was 0.16-0.27 mm 2 /s. The geopolymer with RHA (G-RHA) showed low bulk density (1338 kg/m 3 ) and high porosity (35%). Additionally this material has the lowest thermal conductivity (0.17 W/m·K) and thermal diffusivity (0.16 mm 2 /s). The results obtained show that geopolymers here developed can be considered potentially useful for applications such as thermal insulation. In addition, they constitute a better ecological choice because of the type of source of alkaline activator making their production environmentally friendly.

$Fig. 2. SEM images of the fracture surfaces of geopolymers (a) G-KS, (b) G-RHA, (c) G-SF, (d) G-MK/BS. In the temperature range 200 °C-920 °C, the thermal expansion co- efficients (TEC) are 1.10 x 10°-*K~ !, 1.06 x 10°-4K~!, 1.07 x 10°4K7}, and 1.13 x 10-4 K~', in geopolymers G-KS, G-RHA, G-SF and G-MK/BS respectively. These values are similar to values from common materials such vitreous silica (1.36 x 10-4 K~'). The physical evolution of geopolymer materials during heating is a critical factor in determining their suitability for applications including construction and refractory materials (Duxson et al., 2006d). The total linear shrinkage of the geopolymers in the present study was 7.15%, 7.64%, 9.16% and 9.40% to 920 °C for G-KS, G-RHA, G-SF and G-MK/BS respectively. Other stud- ies have reported overall shrinkage values of approximately 8% All specimens exhibited similar DSC thermograms, as shown Fig. 3b. Two characteristic features were observed in all thermograms; a large endothermic peak in the lower temperature region and a small exother- mic peak in the higher temperature region. The large endothermic peaks in the DSC curves extended from 40 °C to 300 °C and were attrib- uted to the evaporation of free water in the geopolymer, as indicated by thermogravimetric analysis. In the high temperature region the exo- thermic peak (around 1150 °C) was caused by leucite crystallization (KAISiz0g¢), which had been demonstrated in our recent study (Villaquiran-Caicedo et al., 2015). Bell et al. (2009) and Zhang et al. (2007) respectively also observed an exothermic peak due to leucite crystallization from the potassium based geopolymer and hydrothermal silica precursor. According to the DSC analysis, the activation energy of leucite crystallization and the thermal parameters are shown in Table 4. Compared to the KS silica source, the activation energy for G- SF and G-RHA increased by 60.8% and 160% respectively. There is no previous study on the activation energy of crystallization of leucite from the geopolymer precursor. The activation energy for direct crystal- lization of leucite is unknown.$

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