Mónica A. Trezza

Hydration study of ordinary portland cement in the presence of zinc ions

Hydration products of Portland cement pastes, hydrated in water and in the presence of zinc ions were studied comparatively at different ages. Hydration products were studied by X ray diffractions (XRD) and infrared spectroscopy (IR). Although IR is not frequently used in cement chemistry, it evidenced a new phase Ca(Zn(OH)3)2. 2H2O formed during cement hydration in the presence of zinc. The significant retardation of early cement hydration in the presence of zinc is assessed in detail by differential calorimetry as a complement to the study carried out by IR and XRD, providing evidence that permits to evaluate the kinetic of the early hydration.

Scrap tire ashes in portland cement production

Scrap tires are not considered harmful waste, but their stocking and disposal are a potential health and environmental risk. Properly controlled calcinations at high temperatures make tire combustion an interesting alternative due to its high calorific power, comparable to that of fuel-oil. Consequently, using them as an alternative combustible material in cement kilns makes it possible to give it a valuable use. However, it remains to be assured whether the impurities added to the clinker through these fuels do not affect its structure or properties.This paper shows the studies carried out on different clinkers under laboratory conditions with different levels of addition of scrap tire ashes, added by partially replacing traditional fuel in cement kilns.

Activación térmica de bentonitas para su utilización como puzolanas

Se analiza la reactividad de dos bentonitas calcinadas, procedentes de diferentes regiones de Argentina para su utilizacion como adiciones puzolanicas al cemento Portland. A traves de tecnicas de: DRX, espectroscopia IR, ensayos de reactividad con Ca(OH)2. porosimetria por intrusion de mercurio y resistencia a la compresion; se relacionan los cambios estructurales producidos durante el tratamiento termico con el comportamiento puzolanico. Palabras clave: Puzolanas, bentonitas, cemento.

Red Ceramic Wastes: A Calcined Clay Pozzolan

The properties and hydration of blended cements containing from 8 to 40 % by mass of ceramic waste (CW) from different countries (Argentine and Czech Republic) are investigated. The mini slump, the heat released rate up to 48 h, the pozzolanic activity and the compressive strength at 2, 7 and 28 are determined. Hydration process is characterized by XRD analysis and the pore size refinement is accessed by MIP. Results show that both CWs increase the water demand with increasing the cement replacement level, and they possess pozzolanic activity after 7 days. At early age, the heat released and the compressive strength are lower than that of the Portland cement (PC) for all replacement levels. At 28 days, the pozzolanic reaction significantly improves the compressive strength. From XRD analysis, it is evident that CW reacts to form AFm phases (hemicarboaluminate at 7-28 and later transformed to monocarboaluminate) depending on the replacement level and CW used. CH peak reduction due to the pozzolanic reaction appears at 28 days. The reduction of porosity up to 16-24 % of CW replacement is in accordance with the compressive strength results.

Estudio comparativo de clinkers producidos con diferentes reemplazos de combustibles residuales

In the last decades the cement industry has used, as a partial substitute for traditional fuel, different industrial wastes in order to profit their residuals energy. In the present work the physicochemical characteristics of clinker, obtained using trade marked alternative fuel for clinker kiln, were evaluated. X-ray diffraction (XRD), Blaine specific surface, pyrometric cone equivalent (PCE), differential thermal analysis-thermal gravimetry simultaneous (DTA-TG), differential calorimetry, porosimetry and mechanical strength were used as the main evaluation techniques of the characteristic of clinker and their behaviors in the early hydration. The additions of the wastes, within the percentages and under the conditions of this test, does no significantly alter the clinker properties but generates a greater crystallinity of the principal clinker phases.

Thermal Activation of Two Complex Clays (Kaolinite-Pyrophillite-Illite) from Tandilia System, Buenos Aires, Argentina

The aim of this work is focused to identify natural resources with industrial potential to be used as supplementary cementitious materials (SCMs) in Portland blended cements. Two clays obtained from the quarries near to Barker in Tandilia System (Buenos Aires- Argentina) were studied. The geneses of these rocks are by a hydrothermal alteration and include the presence of pyrophillite. Whole-rock were characterized by XRD and FTIR spectroscopy indicating that main clayed minerals are kaolinite (Si2Al2O5(OH)4), illite (K0.66Si3.33Al2.66O10(OH)2) and pyrophillite (Si4Al2O10(OH)2) associated with feldspar. The thermal transformation was studied by differential thermal analysis and the phase changes were confirmed by XRD and FTIR. Samples of clays were calcined at different temperature (550 to 1050 °C), the electrical conductivity was measured and the dissolved silica in simulated pore water solution was quantified. The pozzolanic activity was measured by the compressive strength activity index, on blended cement mortars containing 25% by weight of calcined clays.

Blended Cements with Calcined Illitic Clay: Workability and Hydration

In this paper, the paste workability and hydration progress of blended cements containing different calcined illitic clays were studied. For blended cements with different replacement percentages, the particle packing, the water film thickness (WFT) and the flow spread was modelled and measured. Results indicate that blended cement with ground illitic calcined clays maintain or reduce the packing, so the flow spread of blended cement pastes decrease when the replacement percentage increases. For blended cements with 25% of calcined illitic clay, the early hydration was described by the calorimetric curve, and later the hydration products were analysed by XRD and TG analysis and the pore size distribution (MIP) at 2, 7, 28 and 91 days. Finally, the performance of blended cements was evaluated by the compressive strength. For blended cements, the hydration products are similar to that corresponding to ordinary Portland Cement (OPC) and it also produce a pore size refinement that improve the compressive strength at later age.

Thermal Transformation of Illitic-Chlorite Clay and Its Pozzolanic Activity

Illite-chlorite clay from quarry located at Buenos Aires Province (Argentine) was characterized by XRD, FTIR and TG-DTA. Mineralogical transformations during clay firing under oxidizing conditions were studied from 100 to 1100 °C by XRD and FTIR. From select temperatures, calcined clay was ground (85% passing to 45 µm sieve) and the pozzolanic activity of blended cements (25% w/w) was evaluated by the Frattini test and the strength activity index (SAI). Finally, the hydration phase assemblage of blended cements was studied using XRD analysis.

Blended Cements with Kaolinitic Calcined Clays: Study of the Immobilization of Cr(VI)

Numerous investigations on the immobilization of chromium in cement-based systems were carried out in the recent years. The aim of this study is to analyze the influence of the crystallinity of kaolinite used to make calcined kaolinitic clay when are used in pastes for immobilization of Cr(VI). In previous study, it was found that the reactivity of kaolinitic calcined clays used as partial replacement of Portland cement largely depends on the crystallinity of kaolinite in the raw clay. Calcined clays obtained from raw materials containing kaolinite with disordered structure presents a very high pozzolanic activity allowing high-percentage replacement (30 %) in blended cements. In this study, pastes of blended cement with 15 % and 30 % by mass of two kaolinitic calcined clays (order and disorder structure of kaolinite) were elaborated using a solution of 5000 ppm of K2Cr2O7 and a solution-to-cementing material ratio of 0.50. The immobilization efficiency was measurement by lixiviation test and the modifications in the hydrated phases was studied by X-ray diffraction and SEM/EDS analysis. The results shown that kaolinitic calcined clay from ordered kaolinite was more efficient than disordered kaolinite to retention of Cr(VI), reaching values higher than that of PC-paste.