M.I. Sánchez de Rojas

The effect that the pozzolanic reaction of metakaolin has on the heat evolution in metakaolin-cement mortars

Abstract The hydration heat of mortars or concretes may be decreased by means of pozzolanic additions. Materials that exhibit pozzolanic activity can decrease the hydration heat by means of cement substitution, which increases the heat generated in hydration due to the pozzolanic reaction. Thus, the evolution of the hydration heat with time represents a reference point when establishing the pozzolanic activity of materials; by monitoring this heat, the behaviour of mortars or concretes during hydration can be established. In this work, the influence of the pozzolanic activity of the metakaolin (MK) on the hydration heat has been studied in comparison to the behaviour of other traditional pozzolanic materials such fly ash and silica fume. The results revealed that MK mortars produce a slight heating increase when compared to a 100% Portland cement mortar, due to the high pozzolanic activity of MK. With respect to the hydration heat, MK-blended mortar showed closer behaviour to silica fume than to fly ash.

The pozzolanic activity of different materials, its influence on the hydration heat in mortars

Abstract This work presents the relationship that exists between pozzolanic activity in certain materials (opaline rocks, fly ash and silica fume) and hydration heat, measured using the Langavant calorimeter method. Pozzolanic activity is evaluated using an accelerated method that establishes the reaction speed of the different materials considered. While replacement of part of the cement in a mortar or concrete typically reduces the overall heat of hydration, it is shown that, compared to a control cement, silica fume and opaline rock mixes with cement give increased heat output during early hydration. This is due to their rapid and strong limepozzolanic reaction. The much less reactive fly ash decreased early heat output, compared to the control cement, a good correlation of between pozzolanic activity and hydration heat found.

The influence of different additions on portland cement hydration heat

Abstract This paper presents the results obtained using the Langavant Calorimeter method on portland cements with different addition materials that are commonly used in the manufacture of commercial cements. The effects of these materials on the hydration heat with respect to a control cement were studied. The first hours show that most of the additions, which present highet activity at early stages, increase the hydration heat of their mixed cements in relation to the control cement. The use of pozzolans reduces the heat given off by the cements during hydration. However, the reactions of the pozzolanic materials with the lime also produce heat and the decrease should not be proportional to the level of clinker substitution in the mixed cements.

Influence of the microsilica state on pozzolanic reaction rate

Silica fume is generally supplied as an ultrafine powder in its original state, densified or in suspension. The difference in states should not influence the pozzolanic behaviour of this by-product in a cementitious matrix. In the present work, experimental results relating to pozzolanic reaction have been obtained by different methods: a chemical method, in which lime fixed by pozzolanic material through time is quantified, and a physicochemical method based on the Langavant calorimeter. By the second method, information regarding silica fume is obtained from the value of heat of hydration released by a mortar containing this by-product. These results show that the silica fume in its densified state considerably decreases its chemical reactivity with calcium hydroxide (pozzolanic activity).

Investigations on the fly ash-calcium hydroxide reactions

Abstract The fly ashes are incorporated to the portland cement and concrete as active additions, due to their capacity for reacting with the lime, principally originated during the hydration of the portland cement, and forming hydraulic compounds. In this paper a study of the evolution of the fly ash - calcium hydroxide reaction by the time, is presented. Ten fly ashes from Spanish power stations are selected. They are different in the original coal, chemical composition, … No previous treatment (sieving, grinding, …) had been made on the fly ashes. The study of the behaviour of every fly ash with the lime are carried out by a chemical test at several ages. With the use of the instrumental technique, X-ray diffraction and infrared absorption spectroscopy, it has been verified the disappearance of existent mineralogical components in the original samples as well as the formation of compounds coming from the fly ash - lime reaction (hydrated calcium aluminates, …). The effect of the CaO content of the fly ash is observed.

Microstructural alterations in fly ash mortars: Study on phenomena affecting particle and pore size

Abstract In the last years, relation among porosity, permeability and durability of mortar has been investigated, and a direct relation among them has been verified. However, these properties (mainly in the case of fly ashes) are influenced by vibration and stirring processes to which cementitious mass is subjected during its elaboration (mixing and moulding). These processes could provoke the breaking of fly ash plenospheres. This fact modifies the behaviour of mortars and concretes with this industrial by-product. In the present work a laboratory study is carried out. Fly ash granulometric variations provoked by vibration and stirring processes and their influence on mortar properties is shown.

Determination of specific surface area by the laser diffraction technique. Comparison with the blaine permeability method

Abstract The present paper highlights the applicability of the laser diffraction technique in the determination of the specific surface area of materials. The results obtained show that this technique may offer an alternative to other conventional methods such as the Blaine permeability. A comparative study is made, comparing the results obtained with both techniques.

Contribution of toxic elements: Hexavalent chromium in materials used in the manufacture of cement

Abstract One of the problems currently affecting certain industries, and more specifically cement companies, is the need to determine and control the content of water soluble hexavalent chromium because, due to its toxic effects, it may soon be regulated. The study covers the determination of hexavalent chromium in materials related to the construction sector, namely raw materials, clinker and additions. Spectrophotometric and inductively coupled plasma emission spectrometry (ICP) techniques are compared. Also included is the setting up of the most favourable test conditions for chromate extraction and a study of possible interferences in the colorimetric quantification.

Determination and quantification of total chromium and water soluble chromium contents in commercial cements

Abstract It is common knowledge that the compounds of chromium VI can cause allergies, nasal lesions, bronchitis and especially dermatitis in professionals who work in the construction sector. This paper deals with the quantification of total chromium and hexavalent chromium contents in different types of national cements (Types I and II) as well as with a comparative study of various imported cements (Type I), in order to know the contents of water soluble chromium in the cements made today. These studies are a continuation of earlier research by the same authors and represent a contribution to the establishing of possible limitations of these compounds in future standards.

Using Ceramic Materials in Ecoefficient Concrete and Precast Concrete Products

The industrial and economic growth witnessed in recent decades has brought with it an increase in the generation of different types of waste (urban, industrial, construction, etc.) despite the waste management policies which have been adopted nationally and internationally. The practice of dumping and/or the inadequate management of waste from the various manufacturing sectors have had a notable impact on the receiving environment, leading to water, soil, air and noise pollution, amongst other complications, and adding to existing environmental problems. At the same time, these practices represent an economic cost. However, if waste is managed correctly it can be converted into a resource which contributes to savings in raw materials, conservation of natural resources and the climate, and promotes sustainable development, all of which complies with strategies for sustainable development within the European Union and Spain. Spain occupies an important position in the ceramics industry world market, second only to China as a producer of wall and floor tiles and, according to data from the Spanish Ministry for Industry, Tourism and Commerce (Subdireccion General de Estudios y Planes de Actuacion, 2009) , the world leader in the ceramic sanitary ware industry. Within the European Union, Spain is the leading manufacturer of ceramics: 26.11 % of all ceramics manufacturing facilities in the European Union are located in Spanish territory (Fraunhofer Institute for Systems and Innovation Research Oko-Institut, November 2009). The Spanish ceramics industry includes the following sectors: ceramic flooring and wall coverings (ceramic floor and wall tiles, respectively), ceramic sanitary ware, bricks and roofing tiles, refractory materials, ceramics for technological applications (insulators, etc.), and ceramic objects for domestic and decorative purposes (tableware and ornaments). This sector has witnessed a fall in production as a direct result of the continuing world economic crisis. Nevertheless, production figures for the main ceramics subsectors in Spain for 2008 were as follows: the brick and roofing tile subsector, 20 million tons (according to data from HISPALYT); the tiles and flooring subsector, 495.2 million m2 (according to ASCER); and the ceramic sanitary ware subsector, 7 million items, providing an indication of the volume of waste involved. The percentage of items rejected for sale and thus discarded depends on the type of industry in question, on product requirements and on