S. Tsivilis

Thermal treatment of kaolin: the effect of mineralogy on the pozzolanic activity

This paper reports an investigation on the effect of mineralogy on the pozzolanic activity of fired kaolin. Representative samples of Greek kaolin (Milos Island) and a commercial kaolin of high purity are studied. The samples are tested by X-ray diffraction (XRD), Differential Thermal Analysis (DTA) and Infrared (IR) Spectroscopy in order to determine their mineralogical composition and structural differences. Calcination of samples is carried out at 650°C for 3 h. The decomposition of kaolinite and alunite is recorded using methods of thermal analysis. The resultant products are identified by XRD. The reactivity of the thermally treated samples is evaluated based on Chapelle test. It is concluded that the pozzolanic activity of metakaolinite is strongly related to the crystallinity of the original kaolinite. Well-ordered kaolinite is transformed into less reactive metakaolinite.

A STUDY ON THE PARAMETERS AFFECTING THE PROPERTIES OF PORTLAND LIMESTONE CEMENTS

Abstract In this paper the parameters affecting the properties of Portland limestone cements are investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two kinds of clinker of different chemical composition, mineralogical composition and strength development and three limestones, with different contents of calcite, dolomite, quartz and clay, have been used. It is concluded that the appropriate choice of the clinker quality, limestone quality, % limestone content and cement fineness can lead to the production of a limestone cement with the desired properties. Limestone cements, having up to 10% limestone content and fineness up to a limit value, develop almost the same compressive strength, as the corresponding pure cements. The limestone cements, generally have lower paste water demand than the relative pure cements and the water demand decrease is mainly affected by the clinker type and limestone quality. In any case the properties of the limestone cements are affected by the interaction of the two components rather than their individual properties.

THE PERMEABILITY OF PORTLAND LIMESTONE CEMENT CONCRETE

Abstract The effect of limestone addition on the air permeability, water permeability, sorptivity, and porosity of limestone cement concrete has been investigated. Six Portland limestone cements (PLCs) with different limestone content (10–35% w/w) were produced by intergrinding clinker, gypsum, and limestone. A water-to-cement ratio (w/c) of 0.70–0.62—depending on the cement strength class—was used to prepare concrete of the compressive strength class C20/25 of EN 206-1. A modified commercial triaxial cell for 100-mm-diameter samples was used for the determination of the gas (N2) and the water permeability of concretes. In addition, the sorptivity and porosity of the samples were measured, while thin sections of the concrete specimens were examined by means of optical microscopy. It is concluded that the PLC concrete indicates competitive properties with the ordinary Portland cement (OPC) concrete. Furthermore, the limestone addition has a positive effect on the water permeability and the sorptivity of concrete.

An analysis of the properties of Portland limestone cements and concrete

In this paper the main factors affecting the properties of Portland limestone cements are discussed while the hydration behavior of limestone cements is examined. In addition, the intergrinding process, concerning the production of the limestone cements, is studied. Finally the properties and the behavior of limestone cement concrete as well as the corrosion behavior of limestone cement mortar are investigated. It is concluded that the fineness of clinker and limestone is strongly connected with the limestone content and the fineness of the cement. The limestone cements indicate satisfactory strength and generally demand less water than the relative pure cements. The limestone addition improves the clinker reactivity and the exploitation of its hydraulic potential. The Portland limestone cements indicate competitive concrete properties and improve the corrosion performance of the concrete.

A study on the hydration of portland limestone cement by means of TG

Subject of this paper is to investigate the hydration process of Portland limestone cement containing 10-35% limestone. Cements, produced by co-grinding of clinker, limestone and gypsum, were hydrated for periods 6 h to 28 d and were studied by means of TG and XRD. The Ca(OH)2 content of the cements containing limestone is higher than in pure cements, specifically for 10% limestone content and ages more than 1 day. These results are in accordance with the strength development of the studied cements. In earlier ages the Ca(OH)2 content is slightly lower in the limestone cements and independent of the limestone content. After 1 day curing, the increase of limestone addition causes a relative increase of the non evaporable water. The XRD patterns indicated the presence of carboaluminates in the hydrated limestone cements.

Use of mineral admixtures to prevent thaumasite formation in limestone cement mortar

Abstract Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. In this work the effect of natural pozzolana, fly ash, ground granulated blastfurnace slag (ggbs) and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement containing 15% w/w limestone was used. Mortar specimens were prepared by replacing a varying part of the limestone cement with the above minerals. Siliceous and calcareous sand was used in order to study the effect of the sand type on the thaumasite formation. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 °C. The formation of thaumasite was checked and confirmed by visual inspection, strength tests, ultrasonic pulse velocity measurements, XRD and TGA. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits the thaumasite formation in limestone cement mortar.

The effect of clinker and limestone quality on the gas permeability, water absorption and pore structure of limestone cement concrete

In this paper the effect of clinker and limestone quality on the air permeability, water absorption and pore structure of limestone cement concrete is investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two clinkers with different chemical composition, mineralogical composition and strength development as well as three limestones, differing by their calcite, dolomite, quartz and clay contents, have been used. It is shown that the clinker quality significantly affects the gas permeability and sorptivity of the limestone cement concrete. Limestone cements with high C3A and alkalis content seem to be more appropriate for improving the permeability properties of concrete. In addition, the effect of the limestone quality on the concrete permeability is not well established. The pore size distribution and more specifically the mean pore size affects the gas permeability and the sorptivity of the concrete. Finally it is concluded that, depending on the clinker quality and the cement fineness, limestone cement concrete, with an optimum limestone content, can give lower gas permeability and water absorption rate as compared with pure cement concrete.

Effect of the Kaolin Particle Size on the Pozzolanic Behaviour of the Metakaolinite Produced

This paper reports an investigation of the effect of the particle size of kaolin on its transformation to metakaolinite. Kaolin from the island of Milos was either crushed or ground in order to produce four samples with different degrees of fineness (residue at 500 µm: 0–71.8%). The samples were treated thermally under different conditions in order to determine the optimum treatment conditions. The conversion of kaolinite to metakaolinite and the structural changes in the material during treatment were investigated by means of TG and XRD, respectively. Each sample was incorporated into a type I cement, at 20% by mass of cement, and the compressive strengths of the resulting blended cements were measured. It is concluded that the particle size of the raw kaolin does not affect the thermal conversion or the pozzolanic activity of the material. The use of crushed kaolin has many benefits since the furnace load can be increased, while the grinding process is needed only to reduce the size of the metakaolinite particles.

Parameters affecting thaumasite formation in limestone cement mortar

Abstract Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the factors affecting thaumasite formation in cement mortars and particularly the limestone content, the curing conditions and the type of sand used. Three types of cement were examined: (i) OPC, (ii) Portland limestone cement containing 15% w/w limestone and (iii) Portland limestone cement containing 30% w/w limestone. Mortar specimens were prepared using calcareous and siliceous sand. The specimens were immersed in a 1.8% MgSO 4 solution and cured at: (i) 5 °C and (ii) 25 °C. The formation of thaumasite was checked and confirmed by XRD and TGA. In addition visual inspection, strength tests and ultrasonic pulse velocity measurements were carried out for several months. It is concluded that mortars containing limestone, either as sand or as a main constituent of the cement, suffer from the thaumasite form of sulfate attack at low temperature. At room temperature, no sulfate attack was observed after a year of exposure.

Differential Scanning Calorimetry A Useful Tool for Prediction of the Reactivity of Cement Raw Meal

DSC was used in order to evaluate the reactivity of cement raw meal. Two groups of samples were studied: five industrial raw meals for ordinary Portland cement production, with similar compositions, but differences in granulometry; and five industrial raw meals for white Portland cement production, with similar granulometric features, but different compositions. The burnability indices of the samples were correlated with certain data obtained from the DSC curves. It is concluded that the DSC curve data, and especially the temperature and enthalpy effect of belite formation, are strongly correlated with the burnability of the cement raw meal. The temperature of belite formation is affected by chemical and mineralogical factors, while the enthalpy effect is additionally affected by the fineness of the raw meal.