Alejandra Tironi

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.

Blended Cements with Limestone Filler and Kaolinitic Calcined Clay: Filler and Pozzolanic Effects

AbstractIn this paper, binary and ternary blended cements (BC) based on calcined clay (CC, 0–30%) obtained from low-grade kaolinitic clay and limestone filler (LF, 0–10%) were developed and the int...

Ternary Blended Cement with Limestone Filler and Kaolinitic Calcined Clay

The use of calcined clays providing from low grade kaolinitic clays combined with the limestone filler in ternary blended cement formulation has received considerable attention in recent years. This paper describes the results of a research project to study the behavior of kaolinitic calcined clays (CC) in combination with limestone filler (F). Blended cements were obtaining replacing CC (0–30 %) and F (0–10 %) by mass by Portland cement (PC). The pozzolanicity of blended cement was assessed by the Frattini tests at 2, 7 and 28 days. The response of the system was evaluated in terms of flow, and the compressive strength at 2, 7 and 28 days. The hydration progress was determined by the type and amount of hydration compounds at 2, 7 and 28 days using the Rietveld method. The change in pore size distribution was determined by mercury intrusion porosimetry (MIP). Hydrated phases obtained correspond to the pozzolanic reaction (contribution CC) and phase stabilization (contribution F) modifying the pore structure and all factors contribute to develop acceptable mechanical properties with a large reduction of energy consumption and CO2 emission.

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.

Hydration of Blended Cement with Halloysite Calcined Clay

The effects of calcined kaolinitic clays as supplementary cementitious materials (SCMs) on the performance of pastes and mortars have been well studied. Less attention has been paid to the thermal transformation of halloysite than that of kaolinite and its possibility to be used as SCMs. Halloysite and kaolinite have identical chemical composition, except that halloysite may have two molecules of H2O, as interlayer water. The content of additional water in the interlayers of halloysite has a decisive influence on the crystal morphology, which is generally curled rather than platy as in kaolinite. Common forms are elongated tubes and spheroids. The aim of this investigation is to study the hydration of blended cements with 25% of different calcined clays to evaluate the influence of the content and the morphology of halloysite in the development of the hydratation compounds, and compressive strength of mortars. Three clays with different halloysite/kaolinite content, and different morphology were analyzed. The hydrated phases present in pastes at 2, 7, and 28 days were identified by X-ray diffraction (XRD), and the content of CH by differential thermal analysis (DTA/TG). The compressive strength of mortars was tested at 2, 7, and 28 days. The pozzolanic reactivity of the calcined clays was influence by the kaolinite content and morphology of halloysite in natural clays. This results in different crystalline and amorphous aluminic phases obtained at different ages, and that the ensemble results differ, this affects the porosity and the compressive strength.

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.

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.