CTH Navarra

Spain

CTH Navarra

Spain

Time filter

Source Type

Fernandez J.M.,University of Navarra | Duran A.,University of Navarra | Navarro-Blasco I.,University of Navarra | Lanas J.,CTH Navarra | And 2 more authors.
Cement and Concrete Research | Year: 2013

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. © 2012 Elsevier Ltd. All rights reserved.


Izaguirre A.,University of Navarra | Lanas J.,CTH Navarra | Alvarez J.I.,University of Navarra
Carbohydrate Polymers | Year: 2010

Different dosages of a commercialized potato starch were added to aerial lime-based mortars in order to check its efficiency as a rheological modifier. Several fresh state properties of the mortars were studied: consistency, density, air content, water retention capacity, setting time and evolution when applied on support. The effect of the starch on ζ-potential of the lime particle surface as well as the particle size distribution and viscosity changes in lime pastes were also assessed in order to elucidate the action mechanism of the polymer. The behaviour of this starch polymer was found to be strongly dosage-dependent: it acted as a thickener when the incorporated dosage was up to 0.30% of lime weight; conversely, above that dosage, it behaved as a plasticizer. The thickening effect took place because polymer molecules were adsorbed onto lime particles acting as a flocculant, as confirmed by zeta-potential and particle size distribution results. For large amounts of polymer, steric hindrance and electrostatic repulsive forces appeared, leading to a dispersion mechanism which explained the plasticizing effect as well as the fresh mortar behaviour. © 2009 Elsevier Ltd. All rights reserved.


Izaguirre A.,University of Navarra | Lanas J.,CTH Navarra | Alvarez J.I.,University of Navarra
Construction and Building Materials | Year: 2011

A polypropylene fibre was added to lime-based mortars in order to check whether they were improved by this admixture. Different properties of lime-based mortars were evaluated: fresh state behaviour through water retention, air content and setting time; hardened state properties such as density, shrinkage, water absorption through capillarity, water vapour permeability, long-term flexural and compressive strengths, pore structure through mercury intrusion porosimetry, and durability assessed by means of freezing-thawing cycles. An improvement in some properties of aerial lime-based mortars - such as permeability, mechanical strengths, reduction in macroscopic cracks or durability in the face of freezing-thawing cycles - was achieved when fibre was added at a low dosage. When a larger amount of additive was used, only the reduction in cracks and the durability of the material were improved. © 2010 Elsevier Ltd. All rights reserved.


Izaguirre A.,University of Navarra | Lanas J.,CTH Navarra | Alvarez J.I.,University of Navarra
Cement and Concrete Composites | Year: 2011

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. © 2010 Elsevier Ltd. All rights reserved.


Izaguirre A.,University of Navarra | Lanas J.,CTH Navarra | Alvarez J.I.,University of Navarra
Materiales de Construccion | Year: 2011

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. 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 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, better mechanical properties and durability.


Izaguirre A.,University of Navarra | Lanas J.,CTH Navarra | Alvarez J.I.,University of Navarra
Cement and Concrete Research | Year: 2010

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. © 2010 Elsevier Ltd. All rights reserved.

Loading CTH Navarra collaborators
Loading CTH Navarra collaborators