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Resumen Se produjeron ladrillos de arcilla obtenidos con mezcla de arcilla con residuos de un horno eléctrico en desuso y reforzados con fibras cerámicas para la obtención de un material cerámico con características refractarias. Las mezclas de arcilla/partículas recicladas fueron 50:50 en peso, y la incorporación de fibra fue en un 10 y un 20 % en volumen, para obtener un cerámico por sinterización a 1.000 °C durante 2 h. Los materiales diseñados fueron caracterizados por difracción de rayos X, se determinó la resistencia a compresión, flexión, densidad, porosidad y absorción. También se comprobó su desempeño térmico por exposición directa a llama 1.000 °C. Los resultados mostraron que en la medida en que se incorpora fibra cerámica la resistencia a compresión disminuyó un 17,3 % para AF10 y un 17,0 % para AF20. Los valores de resistencia a flexión estuvieron en 3,4 MPa. El coeficiente de conductividad térmica fue de 0,5322 W/mK, y durante la exposición directa a la llama, las muestras lograron un gradiente térmico de -700 °C para muestras de 2 cm de espesor. Las fases mineralógicas obtenidas para los ladrillos fueron mullita, corindón y cordierita, las cuales se consideran refractarias. Abstract The aim of this research was the production of clay-brick, from red clay, waste from a disused electric furnace, reinforced with ceramic fibers, to obtain a ceramic material with refractory characteristics. The clay/waste particle proportion was 50:50 by weight, and the incorporation of fiber was 10% and 20% by volume, to obtain a ceramic by sintering at 1000°C, for 2 hours. The designed materials were characterized by X-ray diffraction, the flexural and compressive strength, density, porosity, and absorption were determined. The thermal performance was also verified by direct exposure to 1000°C flame. The results showed that as ceramic fiber was incorporated, the compressive strength decreased by 17.3% for AF10 and 17.0% for AF20. The flexural strength values were at 3.4 MPa. The coefficient of thermal conductivity was 0.5322 W/m.K, and, during direct flame exposure, the samples achieved a thermal gradient of ~ 700 °C for samples 2 cm thick. The mineralogical phases obtained for the bricks were mullite, corundum, and cordierite, which are considered refractory.

The aim of this research was to evaluate the production of glass ceramics from novel combinations of fly ash, glass cullet, blast furnace slag and copper slag solid wastes. The CaO/SiO2 molar ratios of the mixtures were 0.17–0.39. Glass ceramics were produced by thermal treatment of frits obtained by quenching in water. The results show that samples with a high Fe2O3 content (>4 wt%) are not adequate for glass-ceramic formation, as a result of the effect of ferric iron, Fe3+, which increases the network connectivity, on the stability of the glass. The mechanical properties of the ceramic materials were as follows: elastic modulus of 97.8–106 GPa, Vickers microhardness of 612–701 MPa, fracture toughness of 0.45–0.84 MPa m1/2, and friction coefficient of 0.57–1.0. For the glass ceramics, the mass loss did not exceed 1% in NaOH and 15% in HNO3 as a result of the crystalline phases formed. The ceramic materials developed in this research could be considered for potential applications in the production of glazes for residential or industrial tiles and coatings, among others.

Ceramics tile wastes (CWs) were mechanically conditioned for the preparation of alkali-activated hybrid-cements from CW (90 wt.%) and Portland cement (10 wt.%) mixtures using sodium silicate (SS) + NaOH as alkaline activators. Molar ratios of SiO2/Al2O3 (6.3 to 7.7) and Na2O/SiO2 (0.07 to 0.16) were used. The cements were prepared at room temperature (25 °C) and characterized by mechanical and physical properties and microstructure. The optimized cement was used for the preparation of novel photoactivated composite materials by incorporating 5 and 10 wt.% TiO2 (Ti) and ZnO (Z) nanoparticles, and its self-cleaning and bactericidal properties were evaluated by means of the degradation of rhodamine-B (Rh-B) and the growth inhibition of Klebsiella pneumoniae and Pseudomonas aeruginosa bacteria. The results of this study showed that the 100SS-5Z and 50SS:50G-10Ti cements have an effective photocatalytic activity for Rh-B degradation of 98.4% and 76.4%, respectively, after 24 h. Additionally, the 100SS-5Z and 50SS:50G-10Ti cement pastes and their respective mortars were effective in inhibiting the growth of Pseudomonas Aeruginosa and Klebsiella pneumoniae bacterial strains, evidenced by the formation of bacterial inhibition halos around the sample discs. Finally, these results are novel, and open the possibility of using constructions and demolition tile waste in high proportions for the elaboration of new rendering mortar with innovative properties.

The objective of this study was to evaluate the effect of ZnO content on the physical, mechanical and chemical properties of CaO–Al2O3–SiO2 (CAS) glass-ceramics produced from Colombian wastes, such as fly ash, granulated blast furnace slag and glass cullet. The CaO/SiO2 molar ratio of the mixtures was held constant (0.36). ZnO was added to the mixtures in proportions of 4, 7 and 10 wt%. The glass-ceramics were produced by the controlled crystallization of a parent glass. The values of crystallization temperature (Tp) show a fall up to 7 wt% and then shoots up with 10 wt% concentration of ZnO, but in general, ZnO addition lowers the temperature required for the formation of crystalline phases. In general, anorthite (CaAl2Si2O8) is the main phase observed in all heat treated samples, in addition to albite (Na(AlSi3O8)) and labradorite (Na0.45 Ca0.55 Al1.55 Si2.45 O8). The crystalline phases hardystonite (Ca2ZnSi2O7) and willemite (Zn2SiO4) were also identified in the samples with 7 and 10 wt% ZnO. The densities of the glass-ceramics were between 2658 and 2848 kg/m3, and it was found that ZnO helps to increase the density of glass-ceramics. The elastic modulus was in the 100–105 GPa range, the fracture toughness was between 0.45 and 0.64 MPa m1/2, and the Vickers microhardness was between 632 and 653 MPa. With regards to the durability, the weight loss of the glass-ceramics immersed in alkaline solution (NaOH) did not exceed 1.5 wt% after immersion for 6 h at 80 °C. The results of this study confirm that the vitrification process is a favorable option to utilize these industrial wastes.

This research evaluates the physical and mechanical properties of particulate composites, produced from geopolymer paste with the incorporation of different organic type wastes as expanded polystyrene (EP), corkwood (CK), tire rubber (RB); in percentages by volume of 2, 4, and 6%. Metakaolin was used as a precursor of the geopolymer produced by alkali activation from NaOH and sodium silicate. The geopolymer composites were cured at room temperature. Properties as density, porosity, absorption, compressive strength, thermal conductivity, and acoustic behavior were evaluated. As complementary techniques, light and scanning electron microscopy were used. It was observed that the high alkalinity of the geopolymer mixture causes deterioration of the CK particles. Composites with the incorporation of 4% of the EP and RB particles reported compressive strength of 32 and 45 MPa at 28 days, and apparent density of 1853 and 1922 kg/m3, respectively, which represents a reduction of 6.08% and 2.58% in comparison to the GP reference. The thermal conductivity for composites with 4% of EP and RB was 0.316 and 0.344 W/m.K and the sound absorption coefficient was evaluated at frequencies of 500 Hz, 0.70, and 0.50 respectively. The evaluated performance properties show the feasibility of using 4% of EP and RB for the manufacture of geopolymer composites for applications in thermal and sound insulating panels.

Geopolymer materials based on metakaolin were produced using KOH and ecofriendly silica sources, such as rice husk ash and silica fume. The geopolymer produced by ecofriendly alkaline activators had mechanical properties that are similar to the geopolymer synthesized with commercial potassium silicate. Upon exposure of the geopolymer to high temperatures, it maintained thermal stability. Its residual compression strength after exposure to 600 °C reached 50 MPa, and at 1200 °C, it was 110–150 MPa. Exposure to high temperature resulted in sintering processes, structural rearrangement and formation of crystalline phases such as leucite, kalsilite and mullite. Additionally, upon production of 1 m3 of ecofriendly geopolymer paste, the global warming potential emissions were reduced by 47.45% (RHA100) and 39.4% (SF100) compared with commercial potassium silicate.

In this research, recycling of 100% glass waste was evaluated for the manufacture of self-compacting mortars for applications in translucent building systems. The glass waste (WG) was ground and used as a fine aggregate in mortar mixtures with cement:WG proportion of 1:1.5, 1:1,75 and 1:2.0 with different water/cement (W/C) ratios. Properties such as fluidity, compressive strength, density, porosity, absorption, thermal properties, and characterization of the microstructure by SEM were analyzed. The results showed that as the WG content increases from 1:1.5 to 1:2.0 the compressive strength of the mortar decreases a maximum of 2.8% in samples with W/C:0.47, and this is due to the formation of microcracks and porosities, which cause the formation of a weakened and sparse interfacial zone which could be identified in the SEM tests. Nevertheless, the compressive strengths were between 20.6 MPa − 32.07 MPa, water absorption for mortars was between 12,92–14,74% and porosities from 23.02% to 25.93%. The thermal conductivity of the mortars was between 0.64 and 0.71 W/m.K. Additionally, the results of the spectrophotometry test for light transmission and the simulation in MATLAB allowed to obtain the brightness in the samples, it was possible to observe that the brightness varies according to the shape of the openings of the blocks, being the A design which allowed a greater passage of light (16%), and the materials developed could be classified as green building materials.

Metakaolin-based geopolymer cements were produced by alkaline activation with a potassium hydroxide and potassium silicate solution. To produce the geopolymer composites, 10 wt.% titanium oxide (TiO2) and 5 wt.% copper oxide (CuO) nanoparticles were used. The geopolymer mortar was prepared using glass waste as fine aggregate. The raw materials and materials produced were characterized by X-ray diffraction, electron microscopy, and Fourier-transform infrared spectroscopy techniques. Likewise, the geopolymer samples were characterized to determine their physical properties, including their density, porosity, and absorption. The photocatalytic activity of the materials was evaluated by activating the nanoparticles in a chamber with UV&ndash, Vis light during 24 h, then, different tests were performed to determine the growth inhibition of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa bacteria in nutrient agar for times of up to 24 h. The study results showed that a geopolymer mortar containing glass waste as fine aggregate (GP-G) exhibited a water absorption 56.73% lower than that of the reference geopolymer paste without glass (GP). Likewise, glass particles allowed the material to have a smoother and more homogeneous surface. The pore volume and density of the GP-G were 37.97% lower and 40.36% higher, respectively, than those of the GP. The study with bacteria showed that, after 24 h in the culture media, the GP-G mortars exhibited a high inhibition capacity for the growth of P. aeruginosa from solutions of 10&minus, 4 mL and in solutions of 10&minus, 6 mL for E. coli and S. aureus. These results indicate the possibility of generating antibacterial surfaces by applying geopolymer composite.

Currently, construction and demolition waste (CDW) is the most generated waste worldwide. In Colombia, ~ 22 million tons of CDW are generated per year, of which 1.0 million tons are generated in Santiago de Cali; therefore, the mitigation and reuse of CDW are important for reducing the environmental impact of the construction sector. This article presents a study on the application of CDW alkaline activation technology for the manufacture of pastes and mortars using alkaline activators with lower environmental impact, such as sodium sulfate and sodium hydroxide. Geopolymeric pastes were produced using a mixture of 80%CDW-20%OPC and activator solutions with concentrations of Na2O between 0.44% and 1.31%. The pastes were manufactured with fine aggregate obtained from the same CDW. The materials developed were characterized microstructurally, physically and mechanically. The scanning electron microscopy (SEM-EDX) and XRD results, the reaction products were C-(A)-S-H, C-S-H gels and minority (N),C-(A)-S-H gel. Additionally, in the sodium-sulfate-activated pastes, ettringite was identified as an additional hydration product through SEM and X-ray diffraction (XRD). Binders activated with sodium sulfate 0.8% Na2O (solid-state activator) yielded compressive strengths up to 18 MPa for pastes. These results provide an opportunity for the potential reuse of CDW in new eco-friendly binders.

At present, no production of zeolites is ongoing in Colombia; thus, because of the high demand in the industrial sector, ~2500 tons is imported annually from other countries such as Cuba, Ecuador, Mexico, and the United States. In order minimize the need for these costly imports, the present study sought to evaluate the viability of producing low-silica zeolites through the hydrothermal synthesis of a Colombian kaolin, which contains quartz (40%) and iron-oxide impurities. The kaolin was subjected to a milling process to reduce the particle size to the order of 11 μm, and was heat treated to transform it to metakaolin. Optimization of the synthesis variables (Na2O/SiO2 and H2O/Al2O3 ratios, time, and temperature) was accomplished by applying an experimental design based on the ‘Response Surface Methodology’ technique. The degree of crystallinity and the cation exchange capacity (CEC) were used as response variables. The CEC was determined from the NTC 5167 standard. In addition, the mineralogical composition and the zeolite microstructure were evaluated using techniques such as scanning electron microscopy, X-ray diffraction, and solid state nuclear magnetic resonance spectroscopy. The results indicated that synthetic type A zeolites with a CEC value of 442 cmol(+)/kg can be obtained from the Colombian kaolin, with the following optimal processing conditions: Na2O/SiO2 molar ratio of 2.7, H2O/Al2O3 molar ratio of 150, temperature = 66°C, and processing time = 8 h. Note that this value (442 cmol(+)/kg) is greater than that reported for an imported commercial zeolite (408 cmol(+)/kg) of the same type, which is currently being used in industry in Colombia. The nationwide availability of the raw material and the quality of the final product present opportunities to make this material available to the Colombian market.

ResumenEn este artículo se presenta un estudio de la producción de zeolita sintética A de baja sílice por medio de la síntesis hidrotermal a partir de un caolín colombiano. La técnica Metodología de Superficie de Respuesta se emplea con el fin de encontrar las condiciones óptimas de proceso (como las relaciones molares Na2O/SiO2 y H2O/Al2O3, tiempo y temperatura) que garanticen la calidad de las zeolitas obtenidas. El grado de cristalinidad y la capacidad de intercambio catiónico, se usaron como variables de respuesta. La capacidad de intercambio catiónico se determinó a partir de la Norma NTC 5167. La composición mineralógica y la microestructura de las zeolitas producidas se caracterizaron a través de técnicas como microscopía electrónica de barrido, difracción de rayos X y resonancia magnética nuclear. Los resultados indican que sí es posible la obtención de zeolitas sintéticas a partir del caolín colombiano evaluado. Zeolita tipo A con capacidad de intercambio catiónico 442cmol/Kg (valor mayor al obtenido con una zeolita comercial importada empleada en la industria colombiana, 408cmol/Kg) se obtuvo bajo las siguientes condiciones óptimas de procesamiento: relaciones molares Na2O/SiO2 de 2.7, H2O/Al2O3 de 150, temperatura de 66°C y tiempo de procesamiento de 8 horas.AbstractThis paper presents a study of the production of a synthetic zeolite of low-silica content by hydrothermal synthesis from Colombian kaolin. The statistical technique Response-Surface Methodology was used to find the optimum process conditions (i.e., molar ratios Na2O/SiO2 and H2O/Al2O3, time and temperature) and to ensure the quality of the zeolites obtained. The cation exchange capacity and the degree of crystallinity were used as response variables. The cation exchange capacity was determined following Standard NTC 5167. The mineralogical composition and microstructure of the zeolites produced were characterized through the application of scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance. The results indicate that it is possible to obtain a good quality synthetic zeolite from the Colombian kaolin evaluated. A zeolite type A with a cation exchange capacity of 442cmol/Kg, a value higher than that exhibited by the same type of zeolite imported for applications in the Colombian industry (i.e., 408cmol/Kg), was obtained with the following processing conditions: molar ratios Na2O/SiO2 of 2.7, H2O/Al2O3 of 150, at temperature 66°C and processing time of 8hours; yielded.

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.

In the present study, properties such as density, absorption, porosity, compressive strength, thermal conductivity and photocatalytic activity of alkali-activated mortars based on metakaolin added with TiO2 particles were evaluated. TiO2 particles were incorporated in proportion of 10 wt%. Ground glass (GB) obtained from glass bottle waste was used as an alternative fine aggregate in proportion up to 100% as replacement of natural sand (S). The alkaline activator was a mix of potassium silicate and hydroxide. The photocatalytic activity was measured by the removal of Rhodamine B and the microstructure of the developed material was studied by scanning electron microscopy. The results obtained in this study reveal a reduction in the percentage of absorption of 16.3%, and porosity of 7% for mortars when S is replaced by GB. The mortar prepared with 100% GB reached a compressive strength of 31.5 MPa compared to 28.0 MPa for reference mortar (100% S). The thermal conductivity was reduced by approximately 25%. Finally, the self-cleaning photocatalytic capacity using GB as fine aggregate increased 72.4%. This type of cementitious materials contributes to mitigate environmental pollution and reduces the maintenance costs of structures.

The production of geopolymeric binders based on metakaolin (MK), coal boiler slag (BS) and alternative silica sources (rice husk ash (RHA) and silica fume (SF)) to produce potassium waterglass was successfully carried out. The binders were characterized microstructurally and mechanically at different ages. Monitoring of the reactions of the cements was carried out by techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA/DTG). The results show that byproducts such as BS and RHA can be used with MK as starting materials for the preparation of geopolymer binders. The using of by-product rich on silica produces materials with microstructures similar to those traditionally obtained with commercial potassium silicate (PS). Regarding SF-based binders, the strength declines over time, with late-age instability. The most stable or homogeneous binders over time are those based on RHA. The MK/BS30 binder exhibits good mechanical performance 42.1, 51.04 and 48.3 MPa at 7, 180 and 360 days respectively. The MK/BS30 binder shows a high degree of geopolymerization, a more homogeneous and enhanced connectivity between the grains and geopolymer gel and likewise, a lower content of MK unreacted. In general, the results indicate that geopolymers manufactured with RHA could replace materials produced with commercial silicates.

Mezclas ternarias de geopolímeros fueron obtenidas a partir de la activación alcalina de metacaolín (MK), ceniza de parrilla (BS) usando como activador alcalino una mezcla de hidróxido de potasio con ceniza de cascarilla de arroz (RHA). Los materiales producidos fueron caracterizados mecánica, térmica y microestructuralmente. Las propiedades de los geopolímeros y microestructura final indica que la adición de la escoria de parrilla (con grandes cantidades de material sin quemar, 16.36%), permite un mayor grado densificación y una mayor homogeneidad del geopolímero, resultando en una mayor estabilidad de la resistencia para largas edades. La sustitución del 30% del MK por BS genera un incremento de la resistencia a compresión hasta del 21% y 122% después de 28 y 180 días de curado respectivamente. Los resultados aquí obtenidos demuestran la posibilidad de usar geopolímeros basados en MK son adición de BS y RHA en el sector de la construcción para obtener materiales cementicios con bajo impacto ambiental.