Edgardo F. Irassar

Calorimetric characterization of Portland limestone cement produced by intergrinding

The calorimetric technique provides continuous, direct, and general measurements of the course of coexisting reactions and their interactions during hydration of blended cement at early age. In this article, this technique is used to analyze the influence of compositional and process variables on the early age hydration of Portland limestone cements (PLC) made by intergrinding in a full size-cement plant. Eight cements, the vertices of 23 factorial design, were made with a limestone filler content (LF) of 0 and 24%, a gypsum content (GC) of 2.5, and 5.0%; and a fineness, measured as that fraction retained on a 45xa0μm sieve (R45), of 5 and 18%, to study their effects on the heat released. In addition, a PLC with a composition nearly to the center point of 23 designs was analyzed. Measurements were performed on cement pastes (w/cmxa0=xa00.4) using a semiadiabatic differential calorimeter operating at 20xa0°C during 48xa0h. At different time, the heat released was determined and it was modeled using a linear mathematical model including the three variables (LF, R45, CG) and their interactions. The significance of the model, the variables and the interactions was judged using the analysis of variance. Results of model show that heat released is reduced by LF due to physically dilution phenomenon, which is directly proportional to LF content. The R45 exerts its major influence during the development of second peak (12–21xa0h) but later its effect declines to null contribution. GC retards and attenuates the hydration reactions moderately until 30xa0h, and then its increase contributes to Qt due to the formation of ettringite and its transformation. The only significant interaction was LF with R45 during the second peak development. Results present good correlation with the isolate measurement of compressive strength at 12, 24, and 48xa0h.

Calcined Illitic Clays as Portland Cement Replacements

Different illitic clays (Buenos Aires Province, Argentine) were selected to study their potential pozzolanic activity. Clays were characterized by X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR) and thermal analysis (TG). Clays are calcined at 300, 600 and 950 °C and ground until 85 % mass passed through a 45 µm sieve. The pozzolanic activity was evaluated by the Frattini test and the strength activity index (SAI) at 2, 7 and 28 days on blended cements containing 25 % by weight of calcined clay. Results indicates that calcined illitic clays are suitable as raw material to prepare calcined clay pozzolan when they are fired at 950 °C as revels the Frattini test and they have a SAI from 0.75 to 0.94 at 28 days depending the amount of clayed minerals in the raw shale-stone. Secondary clay minerals don’t change significantly the pozzolanic behavior of illitic calcined clays.

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.

Effect of cement composition on the early hydration of blended cements with natural zeolite

This paper studies the addition (0–40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium C3A content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low C3A cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium C3A cement, the curve shows the C3S peak in advance and a high intensity of third peak attributed to C3A hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini’s test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28xa0days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28xa0days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements.

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.

Sulfate and Alkali-Silica Performance of Blended Cements Containing Illitic Calcined Clays

Studies of illitic calcined clays are less developed than that corresponding to kaolinitic clays, but illite is one of the more abundant clayed minerals of the earth’s crust, as occurs in the Center of the Buenos Aires Province (Argentina) where the largest cement factories are located. Illite clays develop pozzolanic properties when they are thermally treated at 950 °C, causing dehydroxilation and collapse of structure to form a metastable or amorphous aluminosilicate. Illitic calcined clays don’t present a significant water demand and the compressive strength of blended cements attains to the corresponding to portland cement at 90 days. It is characterized as slow pozzolana. Illite incorporates certain proportion of reactive alumina and high proportion of alkalis, modifying the pore structure. From durability point of view, the incorporation of illite can affect the sulfate resistance of portland cements or the alkali-silica reaction (ASR).

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.