Search

Although primarily deemed to be an ornamental stone, granite may also be ground into fines for use in cement mortars, where it exhibits high strength and durability. Both the 40K present in the stone and the natural decay series of its uranium, thorium and actinium components exhibit high activity concentrations. An understanding is therefore needed of the correlation among the different particle sizes in granite aggregate to assess their contribution to a mortar's activity concentration index (ACI). This study analyses the variation in ACI with particle size in three types of granite based on the chemical, mineralogical and radiological characterisation of five size fractions. The activity concentrations of the thorium and uranium natural decay series were highest in the finest fractions. A correlation was observed between thorium and the MgO and Fe2O3 normally present in mica group phyllosilicates. In two of the three granites, the mortars prepared with the smallest size particles had ACI values >1.

The manufacture of Portland cement entails high energy and environmental costs, and various solutions have been implemented in recent years to mitigate this negative impact. These solutions include improvements in the manufacture of cement clinker or the use of supplementary cementitious materials (SCMs), such as fly ash (FA) or slag as a replacement for a portion of the clinker in cement. The incorporation of these SCMs in cement may increase its radiological content as they are naturally occurring radioactive materials (NORMs). The Activity Concentration Index (ACI) is a screening tool established in the European EURATOM Directive 2013/59 to determine the radiation protection suitability of a final construction material. The ACI is determined by the activity concentrations of 226Ra, 232Th and 40K, usually determined by gamma spectrometry. The methodology of gamma spectrometry is accurate and appropriate, but this technique is not available in all laboratories. For this reason, and taking into account that there is a relationship between the chemical and radiological composition of these building materials, a new approach is proposed to determine the radiological content of these materials from a chemical analysis such as X-ray fluorescence (XRF). In this paper, principal component analysis (PCA) is used to establish the relationships between the chemical composition and radiological content of cements, FAs, and slags of different natures. Through PCA it was possible to group the cements based on two variables: CaO content and Fe2O3–Al2O3–TiO2 content. A lower correlation was observed for the FAs and slags, as the sample scores were centered around the origin of the coordinates and showed greater dispersion than the cements. The clusters obtained in the HJ–Biplots allowed the determination, using multiple regression, of models relating the activity concentration of 226Ra, 232Th (212Pb), and 40K to the oxide percentages obtained for the three matrices studied. The models were validated using five cements, one FA and one slag with relative percentage deviations (RSD(%)) equal to or less than 30% for 89% of the activity concentrations and 100% of the ACI determined.

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic specimens in alkaline pastes was found to be valid. The variables involved in hybrid cement activation were shown to have no impact on specimen radioactive content. The powder samples, however, emanated 222Rn (a descendent of 226Ra), possibly due to the deformation taking place in fly ash structure during alkaline activation. Further research would be required to explain that finding.

This research aims at gaining a further understanding of the impact of accelerating admixtures on the reactivity of supplementary cementitious materials (SCMs), which are widely used as a clinker replacement in blended cements. This was done on synthetic glasses with controlled composition and structure that mimic two types of real SCMs (slag and calcium-rich fly ash). The effects of DEIPA, TIPA, NaSCN and Na2S2O3 on the glass dissolution, hydration kinetics and reaction products were investigated. The obtained results concluded that the pH of the NaOH solution and the composition of the synthetic glass play a key role on the effect of the admixtures. In 0.1 M NaOH (pH = 13.0), all the studied admixtures inhibited the dissolution of slag-like glasses while they enhanced the dissolution of Ca-rich fly ash-like glasses, being Na2S2O3 the admixture that led to the highest increase of the dissolution rate of the Ca-rich fly ash-type glasses. In 1 M NaOH solutions (pH = 13.8), only the alkali admixtures (NaSCN and Na2S2O3) enhanced the degree of reaction of both glasses. In slag-type glasses pastes mixed with 1 M NaOH, the addition of 2% Na2S2O3 induced the highest increase of their reactivity as inferred by the total heat release and the amount of bound water. This is related to the formation of a high amount of S(II)-AFm, in addition to C-A-S-H, that would increase the aluminium undersaturation of the pore solution and consequently the further dissolution of the glass.

The study reported the effect of granite sand on strength and microstructural developments in mortars prepare from OPC with a high coal fly ash (FA) content or from hybrid alkaline cements. The radiological behaviour of the resulting mortars was compared to materials prepared with siliceous sand (with particles sizes of 0.96, which would ultimately limit their use. A conclusion of interest is that where information is at hand on the starting materials (OPC, FA, sand, admixtures), their proportions in the mortar and the mixing liquid content (water or alkaline activators) their radiological content is accurately predicted. The inference is that a mortar’s radiological content and ACI can be known prior to mixing, providing a criterion for determining its viability. That in turn lowers environmental risks and the health hazards for people in contact with such materials.

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

The effect of two precursors (slag and fly ash), different particle size distribution, and three types of aggregate (siliceous sand, limestone, and recycled concrete) on alkali-activated material (AAM) mortar rheology were studied and compared to their effect on an ordinary Portland Cement (OPC) mortar reference. Stress growth and flow curve tests were conducted to determine plastic viscosity and static and dynamic yield stress of the AAM and OPC mortars. In both OPC and AAM mortars, a reduction of the aggregate size induces a rise of the liquid demand to preserve the plastic consistency of the mortar. In general terms, an increase of the particle size of the siliceous aggregates leads to a decrease of the measured rheological parameters. The AAM mortars require higher liquid/solid ratios than OPC mortars to attain plastic consistency. AAM mortars proved to be more sensitive than OPC mortars to changes in aggregate nature. The partial replacement of the siliceous aggregates with up to 20% of recycled concrete aggregates induced no change in mixing liquid uptake, in either AAM or OPC mortars. All the AAM and OPC mortars studied fitted to the Bingham model.

The purpose of this study is to investigate news activators in the preparation of alkali-activated materials (AAMs) alternative to Portland cements by reusing waste glass. Alkali-activated blast furnace slag (AAS) constitutes an alternative to Portland cement due to high energy and environmental pollution associated with industrial Portland cement. Moreover, alkali activated materials offer a series of higher properties than ordinary Portland cement (OPC), such as better strength and durability behaviour. However, the rheology of these materials has been much less intensely researched. The present study aimed to study the effect of waste glass as activator and as replacement of blast furnace slag on the rheological behaviour of AAS pastes, with a comparison between the rheological parameters and fluidity of these pastes to the same parameters in standard cements (CEM I and CEM III/B). The findings show that AAS paste behaviour of rheology when the activator was a commercial waterglass solution or NaOH/Na2CO3 with waste glass was similar, fit the Herschel-Bulkley model. The formation of primary C-S-H gel in both cases were confirmed. However, the rheological behaviour in standard cements fit the Bingham model. The use of the waste glass may be feasible from a rheological point of view in pastes can be used.

The optimal temperature transformation of kaolin sand to metakaolin sand (MKS) resulting in complete conversion of kaolinite to pozzolanic active metakaolinite (MK) is 650°C in the time of 1 hour. To obtain information on mechanism of pozzolanic reaction in studied binary system, the cement pastes with two MKS at substitution level of Ordinary Portland cement (OPC) with MKS by 10, 20 and 40 wt. % corresponding to 3.6 - 16.0 % MK content in pastes, were tested. Pozzolanic reaction of MK with hydrating OPC was clearly confirmed mainly by XRD and thermal analyses. This process accompanied with gradual reduction of Ca(OH)2 content was the most intense in pastes with the highest MK contents (14.4 and 16.0 %). The decrease of micropore and total pore volume until MK content in paste of 7.2 % is measure of pore structure improvement specified as pore structure refinement. Until MK content of 8.0 % in paste, micropores portion with pore radius less than 10 nm rises and pore radius in the range between 10 and 100 nm declines. Resulted compressive strengths of related cement pastes with various MK content were comparable with strengths of pastes without MK. The obtained results confirmed that MKS can be used as promising additive in OPC to form prospective blended cements.

En esta comunicación se presenta una revisión de las principales revistas científicas en el ámbito de los materiales de construcción, centrando la atención en la evolución histórica, situación actual y perspectivas de la revista "Materiales de Construcción", que edita el CSIC y que se dirige y gestiona en el Instituto de Ciencias de la Construcción Eduardo Torroja. Se muestran los resultados obtenidos sobre la influencia de la incorporación de la revista a los listados del Journal Citation Reports, así como los datos disponibles en torno a difusión (Bases de Datos en las que está recogida), implantación nacional e internacional. También se presentarán resultados sobre la procedencia de los artículos recibidos.

La Comisión Mujeres y Ciencia del Consejo Superior de Investigaciones Científicas (CSIC) fue creada en 2002 como comisión asesora de la Presidencia para temas de género. En sus diez años de funcionamiento, la comisión ha contribuido a mejorar la carrera científica de las mujeres investigadoras del CSIC y a aumentar la visibilidad de los resultados de sus investigaciones. En este trabajo se resumen los orígenes y objetivos de esta comisión, así como las actividades realizadas desde 2002, y se analiza la historia de la plantilla investigadora en ese periodo. Se recogen, también, los cambios producidos desde 2005 en la legislación española y europea en materia de igualdad de género. Al analizar específicamente los datos de la situación de las mujeres en 2003 y en 2012 desagregados por áreas de conocimiento, se muestra un avance en la proporción de mujeres en casi todas las áreas pero se está aún lejos del objetivo de paridad. El déficit en la presencia de mujeres es mayor en ciertas áreas y en el nivel profesional más alto, por lo que siguen siendo necesarias medidas activas para promover la igualdad, lo que a su vez contribuirá a la excelencia en las actividades científicas del CSIC.

This paper presents the study of the nature and conservation state of different stuccos and Roman concretes from the Roman city of Baelo Claudia (Cádiz). The chemical, mineralogical and microstructural compositions of the said materials have been established. Different causes of their decay have been found, among which we should emphasize the loss of the binding material (lime), basically due to the processes of partial solubilization; the lack of bond between the stuccos and the support stone, due to the different characteristics and properties of these two materials; and finally, the biological-type attack with the proliferation and colonization of different organisms in the said materials.

This paper constitutes a compilation as well as an interpretation of the present state of knowledge about the different microstructures developed in the interface areas of concrete, that is, the cement paste-aggregates, the cement paste-reinforcement, the cement paste-fiber, etc. The Chemical reactions taking place in interface areas, the development and morphology of such areas and their strength ^since interfaces are taken as the weakest points of concrete) are the aspects dealt with in some detail in this work.

LGTJU