Estructura porosa y proceso de carbonatación en pastas mixtas de cal con diferente porcentaje de cemento

The present study aims to gain a fuller understandingof the curing process in lime pastes (100, 90, 80, 70,60, 50 and 40% lime) blended with cement by analyzingcarbonation in these materials. A hydrated, airslaked lime powder and CEM II A/L 32.5 Portlandcement were used for the blends. These materialswere singled out for research primarily because theymay be used in the restoration of heritage monuments.Variation in weight was used as an indicator for carbonation.A new parameter, A, was found to vary inverselywith the percentage of the cement because of theprevalence of Knudsen diffusion in the paste, in turndue to the characteristics of the pore structure, whichwas studied by mercury intrusion porosimetry (MIP).The hygroscopic study conducted on the different pastesprovided information on water content at a givenhumidity and its location, i.e., adsorbed on the surfaceof the pores or condensed inside them, obstructing thediffusion of CO2. The conclusion drawn from this studyof the curing process was that neither drying nor C3Shydration retarded lime carbonation.En este trabajo se estudia el proceso de carbonatacionen pastas mixtas de cal y cemento (100, 90, 80, 70, 60,50 y 40% de cal) con el objeto de obtener un mejorconocimiento del proceso de curado en estos materiales.Para ello se ha empleado una cal aerea hidratada en polvoy un cemento Portland del tipo CEM II A/L 32,5. Enparticular, este estudio investiga estos materiales ya quepueden ser utilizados en la restauracion del PatrimonioCultural. Se ha utilizado la variacion de peso como indicadordel proceso de carbonatacion. Se ha establecidoun nuevo parametro, A, que varia inversamente con elporcentaje de cemento en la pasta, debido al predominiode la difusion de Knudsen como consecuencia de laestructura porosa, que ha sido estudiada por medio deporosimetria de intrusion de mercurio (PIM). El estudiohigroscopico realizado sobre las diversas pastas permiteconocer el contenido en agua a una determinada humedady si esta se adsorbe sobre la superficie de los poroso condensa en ellos bloqueando la difusion del CO2. Delestudio del proceso de curado, se puede concluir que niel proceso de secado ni la hidratacion de C3S retrasan elproceso de carbonatacion de la cal de la mezcla

Proceso de carbonatación en pastas de cal con distinta relación agua/conglomerante

Most research on binder carbonation is based on the analysis of depth changes in the carbonation front. Moreover, previous studies have dealt with mortars, where aggregates play a role in the variations in carbonation patterns. In the approach adopted in the present study, carbonation was determined in terms of the variation in weight resulting from CO2 absorption, and a new parameter (independent of the drying process), denominated A, was established. This parameter was assessed in several lime pastes with different W/B (water/binder) ratios and its variations were correlated to paste microstructure. Due to the type of porosity prevailing in lime pastes, diffusion took place according to Fick's law; water was retained not by capillarity but by surface adsorption. Drying did not retard carbonation in lime pastesLa mayoría de las investigaciones sobre el proceso de carbonatación en materiales conglomerantes estudia el movimiento del frente de carbonatación. Además, los trabajos previos han sido llevados a cabo en morteros, lo que implica variaciones en el comportamiento de la carbonatación debido a la presencia del agregado. En este trabajo, la carbonatación es discutida teniendo en cuenta la variación del peso como consecuencia de la absorción de CO2, al establecer un nuevo parámetro A (independiente del proceso de secado). Este parámetro ha sido evaluado en varias pastas de cal con distinta relación A/C (agua/conglomerante), y su variación se ha correlacionado con la microestructura de las pastas. Durante el proceso de la carbonatación, y debido al tipo de porosidad de las pastas de cal, tiene lugar la difusión de Fick: el agua no es retenida por capilaridad sino por adsorción sobre la superficie. El proceso de secado no retrasa la carbonatación en las pastas de cal

Pore structure and mechanical properties of cement–lime mortars

Studies focusing on materials used in Cultural Heritage conservation projects are becoming increasingly important. In this paper, the pore structure and mechanical properties of lime–cement mortars are evaluated in order to analyze their potential use, because this kind of mortar could reduce the disadvantages presented by both lime-based mortars and cement-based mortars. The microstructure of these blended mortars is studied taking into account porosity, pore size distribution and surface fractal dimension. Compressive and flexural strengths are discussed as a function of several parameters: curing time, binder composition and B/Ag (Binder/aggregate) ratio. The mechanical strength versus the deformation of the material is also evaluated, by analysis of Young's modulus, as well as the elastic and plastic zones. Unlike cement-based mortars, blended mortars with a high percentage of lime present a large plastic zone, which could be useful in the service-life of these mortars as a result of their ability to absorb strains caused by wall movements

The Influence of the Type of Lime on the Hygric Behaviour and Bio-Receptivity of Hemp Lime Composites Used for Rendering Applications in Sustainable New Construction and Repair Works

The benefits of using sustainable building materials are linked not only to the adoption of manufacturing processes that entail reduced pollution, CO2 emissions and energy consumption, but also to the onset of improved performance in the building. In particular, hemp-lime composite shows low shrinkage and high thermal and acoustic insulating properties. However, this material also shows a great ability to absorb water, an aspect that can turn out to be negative for the long-term durability of the building. For this reason, the hygric properties of hemp-based composites need to be studied to ensure the correct use of this material in construction and repair works. The water absorption, drying and transpirability of hemp composites made with aerial (in the form of dry powder and putty) and hydraulic limes were investigated here and related to the microbial growth induced by the water movements within the material. Results show that hemp-natural hydraulic lime mixes exhibit the highest transpirability and drying rate, the lowest water absorption by immersion and capillary uptake and the least intense microbial attack and chromatic change. A microscopical study of the hemp shives also related their great ability to absorb water to the near-irreversible swelling of their structure under dry-wet conditions.The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 326983 (NaturALiMe), and the Spanish project MAT-2012-34473 of the Ministerio de Ciencia y Competitividad. Author MB, owner of the CANNABRIC company, had some role in the design and preparation of mortar samples and in the preparation of this manuscript, but did not have any additional role in data collection and analysis

Pore structure and mechanical properties of cement–lime mortars

Studies focusing on materials used in Cultural Heritage conservation projects are becoming increasingly important. In this paper, the pore structure and mechanical properties of lime–cement mortars are evaluated in order to analyze their potential use, because this kind of mortar could reduce the disadvantages presented by both lime-based mortars and cement-based mortars. The microstructure of these blended mortars is studied taking into account porosity, pore size distribution and surface fractal dimension. Compressive and flexural strengths are discussed as a function of several parameters: curing time, binder composition and B/Ag (Binder/aggregate) ratio. The mechanical strength versus the deformation of the material is also evaluated, by analysis of Young's modulus, as well as the elastic and plastic zones. Unlike cement-based mortars, blended mortars with a high percentage of lime present a large plastic zone, which could be useful in the service-life of these mortars as a result of their ability to absorb strains caused by wall movements

Carbonation process in lime pastes with different water/binder ratio

Most research on binder carbonation is based on the analysis of depth changes in the carbonation front. Moreover, previous studies have dealt with mortars, where aggregatesplaya role in the variations in carbonation patterns. In the approach adopted in the present study, carbonation was determined in terms of the variation in weight resulting from CO2 absorption, anda new parameter(independent ofthe drying process), denominatedA, was established. This parameter was assessed in several lime pastes with different W/B (waterjbinder) ratios andits variations were correlated to paste microstructure. Due to the type of porosityprevaJ'ling in lime pastes, diffusion tookplace according to Fick~ law; water was retained notby capillarity butbysurface adsorption. Drying did not retard carbonation in lime paste

Pore structure and carbonation in blended lime-cement pastes

The present study aims to gain a fuller understanding of the curing process in lime pastes (100, 90, 80, 70, 60, 50 and 40% lime) blended with cement by analyzing carbonation in these materials. A hydrated, air slaked lime powder and CEM II A/L 32.5 Portland cement were used for the blends. These materials were singled out for research primarily because they may be used in the restoration of heritage monuments. Variation in weight was used as an indicator for carbonation. A new parameter, A, was found to vary inversely with the percentage of the cement because of the prevalence of Knudsen diffusion in the paste, in turn due to the characteristics of the pore structure, which was studied by mercury intrusion porosimetry (MIP). The hygroscopic study conducted on the different pastes provided information on water content at a given humidity and its location, i.e., adsorbed on the surface of the pores or condensed inside them, obstructing the diffusion of CO2 . The conclusion drawn from this study of the curing process was that neither drying nor C3 S hydration retarded lime carbonation

Blended pastes of cement and lime: pore structure and capillary porosity

Microstructure of blended pastes of lime and cement were studied in this paper. An increment of complexity of the microstructure was found when pastes increase their percentage in cement. Microstructural characteristics as porosity, morphology of the pores, pore size distribution and surface fractal dimension were evaluated in the different pastes studying the modification with the variation of composition. The capillary water absorption is also evaluated obtaining higher capillary coefficients values for the pastes with higher amounts of lime. The increase of complexity of the microstructure, due to the cement in the pastes, leads to slight deviations of the parallel tube model