M.P. Luxán

Rapid evaluation of pozzolanic activity of natural products by conductivity measurement

Abstract In view of the increasing use of pozzolanic materials in hydraulic binders, there is great interest in designing a rapid and efficient method to evaluate their reactivity. The present paper describes a method for the evaluation of pozzolanic activity based on the measurement of compensated conductivity of a calcium hydroxide saturated solution, to which the material is added, over time which is applicable to natural products. Results can be obtained as from a minimum time of two minutes.

Characteristics of the slags produced in the fusion of scrap steel by electric arc furnace

The use of industrial by-products requires knowledge of the characteristics of the materials. This work presents characterization data on slags produced in the fusion of scrap steel by electric arc furnace. It includes the chemical, mineralogical, and microstructural analysis and physical characteristics. Mineralogically, scrap steel from electric arc furnace are a mix of anhydrous calcium silicates and iron composites and manganese oxides. No dimensional instability was detected.

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.

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.

Activation of the fly ash pozzolanic reaction by hydrothermal conditions

The effect of hydrothermal treatment on the pozzolanic reaction of two kinds of Spanish fly ashes from coal combustion (ASTM class F) is discussed. Characterization of the compounds formed as a result of hydrothermal treatment and the changes provoked in the starting fly ashes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared (IR) spectroscopy. α-C2SH, CSH gel, different solid solutions of katoites (the cubic crystallographic variety of hydrogarnets series (C3ASH4)) and a mixed oxide (CaFe2O4) were formed depending on the kind of fly ash. The hydrated compounds are precursors of a new kind of low-energy cement called fly ash belite cement (FABC); besides, they have potential properties to intercalate toxic ions and therefore can be used as immobilization systems of these ions.

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.

Mechanical properties, pore size distribution, and pore solution of fly ash-belite cement mortars

The mechanical properties, pore size distribution, and extracted pore solution of fly ash-belite cement (FABC) mortars were studied for a period of 200 days. The influence of the calcination temperature, which ranged from 700 to 900°C, of the fly ash-belite cement was discussed. The evolution with hydration time of the pore size distribution was followed by mercury intrusion porosimetry, and the results correlated with those of flexural and compressive strength. The pore solution was expressed and analyzed at different times of hydration.

Effect of the starting fly ash on the microstructure and mechanical properties of fly ash–belite cement mortars

Abstract The effect of two kinds of Spanish fly ashes ASTM (class F) on the mechanical and microstructure parameters of fly ash–belite cement (FABC) mortars was studied for up to 200 days from mixing. Pore-size distribution analyses were carried out by mercury intrusion porosimetry, and microstructure was investigated by scanning electron microscopy (SEM). The pore solution was expressed and analyzed at different periods of hydration. The results showed that the alkali and iron content of the starting fly ash strongly influenced the kinetics of hydration of the FABC cements. If the time factor is deleted, general correlation is obtained between the mechanical and microstructure parameters studied, irrespective of both the starting fly ash characteristics and the calcination temperature.

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.

Potential expansion of cement mortars in the presence of K2SO4 and pozzolan

The hydration of cements is a very complex process and the alkalis have important influence on its properties. A study is presented on the influence which the incorporation of Na[sub 2]CO[sub 3] and K[sub 2]SO[sub 4] has on different types of portland cement, with high and low expansion effect being observed due to the presence of the alkalis. The addition of natural pozzolan in proportion of 5 and 15% modifies the results obtained, due to its reactivity.