Papers by J Ivan Escalante
Pastes of pulverised fly ash (PFA) and blast furnace slag (BFS) in proportions of 100–0, 75–25, 5... more Pastes of pulverised fly ash (PFA) and blast furnace slag (BFS) in proportions of 100–0, 75–25, 50–50, 25–75 and 0–100 (wt-%) were chemically activated using sodium silicate with modulus (SiO 2 /Na 2 O) of 0, 0. 75, 1, 1. 5 and 2; the %Na 2 O was added at 4, 6 and 8% relative to the binder weight. The pastes were cured for 24 h at 75uC and then 28 days at 20uC. For 100%PFA pastes, the higher %Na 2 O, the better the strength; 4%Na 2 O was ineffective, whereas the highest strength of 25 MPa was reached using modulus 1. For 100%BFS pastes, the highest strengths were for 4%Na 2 O (80–85 MPa); the optimum modulus was 1. 5. The addition of BFS to PFA rich pastes was favourable; for 50% blends, the strengths were between the above mentioned figures and the best modulus was 1–1. 5 (45–48 MPa). The lower glass content of PFA (70%) compared with the BFS (.90%), together with the porous nature of the PFA, were considered to have reduced the strength in PFA blends.
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Cement and Concrete Research, 2003
Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 da... more Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 days. The binder was activated by 6 wt.% Na2O equivalent of NaOH and water glass. The presence of the silica enhanced the formation of hydration products as shown by nonevaporable water (NEW) results. Backscattered electron images indicated that the microstructures of blended slag had less porosity than those of neat slag mortars and the interfacial zone between aggregate and hydration products was dense and of homogeneous composition similar to the matrix of hydration products. The main hydration products were C-S-H and for NaOH a hydrotalcite type phase was found as finely intermixed with the C-S-H.
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Cement and concrete …, 1999
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… Materials Transactions A, 2002
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… Materials Transactions A, 2001
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Cement and concrete …, 2001
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Journal of Non-crystalline Solids, 2009
The vitrification and crystallization behavior of melts produced at 1400 °C in the ternary system... more The vitrification and crystallization behavior of melts produced at 1400 °C in the ternary system of K2O–B2O3–TiO2 is investigated. It is shown that there are two fields of compositions (indicated in mol%) which allow obtaining the glass-ceramic materials with continuous glassy matrix after the cooling of molten compositions. In the first field [TiO2] = 25–57, [K2O] = 30–50 and [B2O3] = 0–25, the glass-ceramics consisted of the potassium–titanium–borate glassy phase and different crystalline potassium titanates (K4Ti3O8, K2Ti2O5, K2Ti4O9, K2Ti6O13). The ratio of TiO2:K2O in the obtained titanates increases with [TiO2] and [B2O3]. In the second field, [TiO2] = 7–37, [K2O] = 0–25 and [B2O3] = 52–93, the obtained glass-ceramics consisted of a similar vitreous phase, as mentioned above, and TiO2 crystals. During the cooling of the melts, short whiskers-like crystals of anatase formed in the compositions with relatively low [TiO2] and relatively high [K2O], whereas long fiber-shaped crystals of rutile appeared with the compositions characterized with relatively high [TiO2] and relatively low [K2O]. The possible application of the obtained glass-ceramic materials as a source of fibrous TiO2, for composite reinforcement, and as solid lubricants is discussed.
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Journal of The American Ceramic Society, 2010
This investigation statistically examines the strength development on alkaline activation of meta... more This investigation statistically examines the strength development on alkaline activation of metakaolin (Mk)/blast furnace slag (BFS) pastes. The main parameters studied are: BFS/Mk weight ratio (100/0, 80/20, 50/50, 20/80, and 0/100), modulus of the alkaline solutions of sodium silicate (M=SiO2/NaO2 at 0, 1, 1.5, 2), %Na2O (5%, 10%, and 15%), and curing time. Cubes were cured at 20°C for up to 360 days; the compressive strength and other characteristics were investigated. A fully factorial experimental design was used to determine the influence of each variable. The curing time and the interaction of the factors BFS/Mk ratio-%Na2O were the most important, followed by the modulus and then the %Na2O; others such as the interaction BFS/Mk ratio modulus were less important. The results indicated that the addition of Mk to BFS reduced the strength, more notably at contents above 50%. For strength development, the most effective modulus was Ms=1 and higher %Na2O were required with higher Mk loads.
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Journal of Non-crystalline Solids, 2007
The structural behavior of nickel oxide in glassy and glass-ceramic materials, obtained in the sy... more The structural behavior of nickel oxide in glassy and glass-ceramic materials, obtained in the system of Na2O–CaO–MgO–Fe2O3–Al2O3–SiO2, was investigated. The influence of the NiO content on the vitrification, crystallization, structure and exploitation properties of two model compositions, with different ratios [CaO]/[MgO] was analyzed. On the basis of DSC and XRD data, it is shown that NiO promoted the formation of bunsenite crystals, as nuclei for crystallization. On the other hand, NiO promoted formation of pyroxenes even for compositions with low MgO contents, which formed gehlenite without NiO admixtures. It is shown that in the composition with relatively high MgO contents, NiO could participate in the formation of two types of pyroxenes with the structure and chemical composition similar to (MgO0.4NiO0.6)(CaO0.9NiO0.1)Si2O6 and diopside–hedenbergite solid solutions. The optimal contents of NiO in both model compositions was about of 7 wt%, since higher contents reduced the exploitation properties. The glass-ceramics with optimal contents of NiO were also produced using Ni bearing galvanic slurry and coal ash; the resulting materials showed similar exploitation properties to those mentioned above.
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Glass Physics and Chemistry, 2002
The influence of PbO, B2O3, and Al2O3 additives on the glass formation and crystallization of gla... more The influence of PbO, B2O3, and Al2O3 additives on the glass formation and crystallization of glasses with a high total content of BaO and TiO2 (65–75 wt % or 76–86 mol %) is investigated. It is shown that glasses of the compositions (wt %) 31–35 BaO, 12–17 PbO, 34–42 TiO2, 10–13 Al2O3, and 2–3 B2O3 are promising materials for use in preparing glass-ceramic ferroelectrics based on the melting–molding–crystallization technology. These compounds are characterized by a relatively low melting temperature (1450°C), the absence of spontaneous crystallization during molding, and the possibility of controlling the phase composition of the material through the appropriate choice of the crystallization temperature.
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Technical Physics Letters, 2010
The influence of compacting pressure on the structure and mechanical properties of sintered ceram... more The influence of compacting pressure on the structure and mechanical properties of sintered ceramics based on weakly crystalline potassium polytitanate with a composition close to K2O · 6TiO2 has been studied. It is established that an increase in the pressure during the uniaxial cold pressing of compacts leads to the formation of a ceramic structure that consists of layers formed by compacted nanofibers of crystalline potassium hexatitanate. Relationship between the structure and mechanical properties of obtained ceramics is analyzed.
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Construction and Building Materials, 2010
This work investigated geopolymeric lightweight concretes based on binders composed of metakaolin... more This work investigated geopolymeric lightweight concretes based on binders composed of metakaolin with 0% and 25% fly ash, activated with 15.2% of Na2O using sodium silicate of modulus SiO2/Na2O = 1.2. Concretes of densities of 1200, 900 and 600 kg/m3 were obtained by aeration by adding aluminium powder, in some formulations lightweight aggregate of blast furnace slag was added at a ratio binder:aggregate 1:1; curing was carried out at 20 and 75 °C. The compressive and flexural strength development was monitored for up to 180 days. The strength diminished with the reduction of the density and high temperature curing accelerated strength development. The use of the slag had a positive effect on strength for 1200 kg/m3 concretes; reducing the amount of binder used. The thermal conductivity diminished from 1.65 to 0.47 W/mK for densities from 1800 to 600 kg/m3. The microstructures revealed dense cementitious matrices conformed of reaction products and unreacted metakaolin and fly ash. Energy dispersive spectroscopy and X-ray diffraction showed the formation of amorphous silicoaluminate reaction products.
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Journal of The American Ceramic Society, 2004
This work presents the results of an investigation on producing diopside glass-ceramic materials ... more This work presents the results of an investigation on producing diopside glass-ceramic materials based on various combinations of quartz-feldspar waste from ore refining and limestone dust. Other industrial wastes were added to contribute as nucleation agents; when the concentration of the latter was insufficient, they were added in the pure state. Additionally, relatively high concentrations of alkalis were used to accelerate glass melting. Low-cost materials with promising exploitation properties were produced. A two-stage regime of crystallization of the basic glass composition was determined, including nucleation at 720°C and crystal growth at 950°C. Local environmental regulations must be considered for the selection of the type of admixtures and the combination of wastes.
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Journal of the European …, 2004
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Construction and Building Materials, 2009
The performance and water resistance of binders 30–50% blast furnace slag and hemihydrate from wa... more The performance and water resistance of binders 30–50% blast furnace slag and hemihydrate from waste gypsum were investigated. Mortars of various aggregate:binder ratios were prepared with granulated BFS and silica sand. The cements with 50% slag were the best in terms of strength; higher aggregate loads reduced the strength. The solidification of mortars by the formation of an initial gypsum framework was indicated by the very fast setting, low 1 day strength and high non-evaporable water. Further strength development was due to the slag reactions. The microstructures of polished samples were dense and conformed by gypsum crystals surrounded by C–S–H. The use of BFS sand was more efficient, in terms of strength, than silica sand; this was due to the participation of the slag aggregate in the hydration reactions, improving the bonding in the interfacial zone. The lower density of the former makes them potentially more insulating efficient.
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Journal of Materials Science, 2004
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Advances in Cement Research, 2000
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Cement & Concrete Composites, 2010
This paper reports the results of the utilization of a silica waste from a geothermal power gener... more This paper reports the results of the utilization of a silica waste from a geothermal power generation plant as partial replacement of portland cement. To evaluate the reactivity of the silica waste, the effect of the curing temperature was analyzed by means of the estimation of nonevaporable water (NEW) and calcium hydroxide (CH) contents. Pastes of portland cement substituted with 0%, 5%, 10% and 15% of geothermal silica waste (GSW) and water/solid ratio of 0.50 were cured at 10, 20, 40 and 60 °C for up to 540 days. The pastes were characterized by thermogravimetric analysis. According with the CH estimations, the geothermal silica showed a strong pozzolanic behavior. Nevertheless, the NEW contents were lower compared to those of neat cement, in agreement with other reports. The results of NEW contents of neat and blended cements were processed to obtain a modified NEW (mNEW) that excluded the water corresponding to the CH. The mNEW data indicated that the blended cements reached higher contents of nonevaporable water.
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Papers by J Ivan Escalante