Lanas, J. (Javier)
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- Study of the mechanical behavior of masonry repair lime-based mortars cured and exposed under different conditions(Elsevier, 2006-05) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio)Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments in order to study their mechanical behavior and durability. Outside exposure, weathering cycles in a climatic chamber, SO2-rich environment, freezing–thawing cycles and indoor exposure were selected to expose (as control group) the mortars. Flexural and compression strength tests were performed at 7, 14, 21 and 28 days. Porosity values and SEM/EDAX analysis were used to evaluate the microstructural changes. Flexural strength has been strongly influenced by the RH of the environments. Outside exposure improves, in general, the compressive strength, whereas SO2 chamber only provides the strength in hydraulic specimens. Porosity reduction has been related with a strength increment. In climatic chamber, the porosity increment matches a gradual higher degree of alteration. A strength reduction has been determined through a fracture mechanism using the cracks of climatic alteration. In SO2 chamber, sulfation appears as a surface phenomenon, giving gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens, as SEM/EDAX confirms. Freezing–thawing cycles showed a high destruction capacity. Hydraulic specimens endured better durability tests than aerial specimens: a discussion on the mortar durability was also introduced.
- Influence of nanosilica and a polycarboxylate ether superplasticizer on the performance of lime mortars(Elsevier, 2013-01-01) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)The effect of individual and combined addition of both nanosilica (NS) and polycarboxylate-ether plasticizer (PCE) admixtures on aerial lime mortars was studied. The sole incorporation of NS increased the water demand, as proved by the mini-spread flow test. An interaction between NS and hydrated lime particles was observed in fresh mixtures by means of particle size distribution studies, zeta potential measurements and optical microscopy, giving rise to agglomerates. On the other hand, the addition of PCE to a lime mortar increased the flowability and accelerated the setting process. PCE was shown to act in lime media as a deflocculating agent, reducing the particle size of the agglomerates through a steric hindrance mechanism. Mechanical strengths were improved in the presence of either NS or PCE, the optimum being attained in the combined presence of both admixtures that involved relevant microstructural modifications, as proved by pore size distributions and SEM observations.
- Characterization of aerial lime-based mortars modified by the addition of two different water-retaining agents(Elsevier, 2011-02) Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio); Izaguirre, A. (Ana)Two different commercial additives that have been reported to act as viscosity enhancing, water retaining admixtures, namely hydroxypropyl methylcellulose and a guar gum derivative, were added to lime-based mortars in order to test their performance. Different properties of lime-based mortars were evaluated: fresh mixture behaviour through water retention, air content and setting time; hardened mixtures properties such as density, shrinkage, water absorption through capillarity, water vapour permeability, long-term compressive strengths, pore structure through mercury intrusion porosimetry and durability assessed by means of freezing–thawing cycles. Hydroxypropyl methylcellulose, unlike its well-known effect in cement-based materials, showed a very limited viscosity enhancing behaviour in aerial lime mortars. An adsorption mechanism of this additive on the Ca(OH)2 crystals was reported to reduce its entanglement between chains and hence the viscosity of the pastes as well as its water retention ability. The guar gum derivative, which has a larger quantity of ionized groups at alkaline pH, reduced its adsorption onto slaked lime particles and gave rise to a clear increase in viscosity. However, this involved a larger water-retention capacity, which in fact resulted in a delay in setting time. The guar gum derivative proved to raise the air content, and changed the pore size distribution of the hardened mortars, thus improving the water absorption through capillarity and durability in the face of freezing–thawing cycles.
- Ageing of lime mortars with admixtures: durability and strength assessment(Elsevier, 2010-07) Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio); Izaguirre, A. (Ana)Lime-based mortars modified with admixtures were prepared and subjected to different environments such as outdoor and indoor exposures, climatic chamber, SO2-chamber, and freezing-thawing cycles. The influence that the different admixtures (water repellents, water retainers, polypropylene fibre and a viscosity modifier) had on the pore size distribution of the hardened specimens was assessed and related to the water absorption capacity, and hence to the durability. Ageing resistance and mechanical strengths improved when additives reduced the water intake and increased the air-content. High dosages of water repellents were necessary to enhance the durability, sodium oleate being the most effective additive to endure freezing processes. Also the low tested dosage of fibre, a water retainer (guar gum derivative), and a starch proved to be useful. SO2 deposition caused the formation of calcium sulphite hemihydrate as the main degradation product. A very small amount of calcium sulphate dihydrate was observed. A crystal habit composed of acicular agglomerates of calcium sulphite hemihydrate was detected in SO2 deposition on calcareous materials.
- Compositional changes in lime-based mortars exposed to different environments(Elsevier, 2005-05-15) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio)Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments to study their compositional changes during setting, hardening and exposure to environment. Outside exposure, weathering cycles in a climatic chamber, SO2-rich environment and indoor exposure (as control group) were selected to expose the mortars. XRD, FT-IR and TG-DTA analyses were performed at 7, 14, 21 and 28 days to determine the chemical and mineralogical composition, as well as the formation of the degradation products. Outside and SO2-chamber exposures and increasing the relative humidity allowed faster carbonation (enhancing CO2(g) dissolution) and hydration of hydraulic compounds. In SO2-chamber, sulfate attack appears as a surface phenomenon, giving: gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens.
- Obtaining of repair lime mortars by mixing aerial lime and nanosilica(University of the West of Scotland, 2013-12-31) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)This work deals with the effect of the nanosilica addition on the performance of aerial lime mortars. Several lime mortars were prepared and modified upon the addition of 3, 6, 10 and 20 wt.% of nanosilica. The presence of nanosilica increased the water demand of the fresh mixtures and reduced the appearance of superficial cracks after the spreading of the mortars onto a porous stone. Setting time underwent a delay when the amount of nanosilica ranged from 3 to 10 wt.%. However, samples with 20 wt.% of nanosilica showed a shortened setting time compared to plain lime mortars. Nanosilica reacted with Ca(OH)2 particles, yielding C-S-H compounds and, acting as a nanofiller, nanosilica also caused a pore blockage in the mesoporous range. These facts resulted in an increase in both compressive strength and durability after undergoing freezing-thawing processes. Overall, the addition of nanosilica clearly improves several characteristics of the aerial lime mortars in order to prepare enhanced mixtures to be used for restoration works.
- Mechanical properties of natural hydraulic lime-based mortars(Elsevier, 2004-12) López, M.A. (Miguel A.); Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio); Perez, J.L. (José Luis)180 different mortars made with a natural hydraulic lime and different kinds of aggregates were prepared in order to be used in restoration works. The factors affecting the mechanical behavior have been studied at long-term test. Compressive and flexural strengths of the specimens were discussed according to curing time, binder:aggregate ratios, attributes of the aggregates and porosity. Three phases of hardening have been established as a function of the chemical composition: C3S contributes to the strength at early ages. C2S and the carbonation process give their strengths at long term. Specimens with larger binder amounts have shown higher porosity and strength. The characteristics of the aggregates have been correlated with the strength and porosity. Limestone aggregates contribute to the strength. Rounded shaped aggregates, increasing large pores, cause a strength reduction, so their use is not advisable. Aggregates with small grain size show a good cohesion at the interface improving the strength.
- Dolomitic lime: thermal decomposition of nesquehonite(Elsevier, 2004-11-01) Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio)Nesquehonite (MgCO3·3H2O) (N) can be obtained from a dolomitic quicklime paste in a CO2-rich atmosphere. Thermal decomposition of this synthetic nesquehonite has been studied by TG-DTA analysis. It is very similar to the hydromagnesite (HY) thermal decomposition, as it show similarities in the decarbonations at 440 and 550 °C, and an exothermic phenomenon at 510 °C. It has been reported in the literature that some intermediate in N→HY transformation occur, but this process cannot be directly detected during the heating. Samples were heated at 115, 230, 280, 370, 460, 520, 600, 800 and 1000 °C and XRD and FT-IR were used in order to determine the structural changes in nesquehonite and the intermediate phases formed. Results show that nesquehonite transforms at lower temperatures (115 °C) into a stable amorphous magnesium carbonate with chemical composition very close to that of HY. Thermal decomposition of nesquehonite, during a gradual temperature increase, proceeds via the formation of this compound. At higher temperatures (460 °C/short heating times), nesquehonite transforms into HY. The occurrence of an exothermic peak at 510 °C has been also discussed.
- Biocomposites for building purposes: effect of a guar gum derivative and a potato starch as viscosity modifiers for aerial lime-based mortars(Mahatma Gandhi University, 2010-09-24) Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María); Izaguirre, A. (Ana)Invited lecture presented by Dr. Álvarez on 24th September 2010 at the Windsor Castle on ocassion of the Second International Conference on Natural Polymers held in Kottayam, India.
- Effect of a biodegradable natural polymer on the properties of hardened lime-based mortars(CSIC, 2011-04) Lanas, J. (Javier); Alvarez-Galindo, J.I. (José Ignacio); Izaguirre, A. (Ana)As an environmentally friendly and energy-saving alternative to cement-based materials and to some chemically obtained water-reducers, a commercialized starch was incorporated into aerial lime-based matrix. Five different dosages were tested in order to study the influence that the amount of additive exerted on the properties of the material. Density, shrinkage, water absorption through capillarity, water vapour permeability, mechanical strengths, porosity, pore size distribution, and durability in the face of freezing-thawing cycles were studied in the polymer modified mortars. The tested starch acted as a thickener for dosages up to 0.30%, and changed its behaviour for the largest dosage (0.50%): in that case it behaved as a plasticizer, dispersing the lime through the fresh mass and generating a more workable material. As a result, the matrix of the hardened mortar presented great coherence, owing to its large density and low porosity, characteristics which led to lower capillarity and permeability absorptions, better mechanical properties and improved durability.