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Buenos Aires, Argentina

Cabrera O.A.,National University of Central Buenos Aires | Traversa L.P.,LEMIT | Ortega N.F.,National University of the South
Materiales de Construccion

This article describes an experimental study conducted on fresh mortars and concretes made with crushed sand. The aim of this research was to assess the effect of aggregate particle shape and surface texture as well as dust content on mortar and concrete rheology. The experimental programme also addressed the impact of angular grains on chemical admixture performance and concrete bleeding. The findings showed that the use of crushed sand induces rheological behaviour that differs from the behaviour observed in natural sand and that superplasticisers can improve this behaviour considerably. Source

Villagran-Zaccardi Y.A.,National University of La Plata | Taus V.L.,National University of La Plata | Di Maio A.A.,LEMIT | Di Maio A.A.,National University of Costa Rica
ACI Materials Journal

Blended cement concrete is currently a necessity to reduce the environmental impact of the construction industry. The lower clinker content may affect some durable characteristics of concrete, such as the resistance to chloride ingress. On the other hand, mineral admixtures may present pozzolanic activity that improves concrete performance over time. This paper presents the results of chloride ingress in concrete specimens made with slag and limestone filler blended portland cement (BPC) when located in the marine environment. Parameters including two watercement ratios (W/c), three curing treatments, and two maximum aggregate sizes were analyzed. Water-soluble and total chloride ingress profiles were determined during an exposure period of 3 years. The results allowed the time evolution of both the surface chloride content and diffusivity of BPC concrete to be assessed by natural mechanisms. Copyright © 2010, American Concrete Institute. All rights reserved. Source

Cabrera O.A.,National University of Central Buenos Aires | Traversa L.P.,LEMIT | Ortega N.F.,National University of the South
Materiales de Construccion

The present experimental study explored the relationship between mortar flow ability and the voids content in crushed sand to determine the effect of grain shape and surface texture as well as dust content on the behaviour of fresh mortar. The findings revealed a close correlation between voids content and the volume of paste needed for mortar to begin to flow as a continuous material, mortar flow ability and the water content needed to attain a given flow ability. The comparison of the empirical findings to the results obtained with the Larrard (1, 2) model provided further information on the effect of sand grain morphology on fresh mortars. Source

The ruins of San Ignacio Miní, in NE Argentina, Misiones Province, included by the UNESCO in the list of World Heritage in 1984, were built in the 18th century by the Guarani people under the supervision of the Jesuite Congregation. The ruins are located in a tropical weather zone, exposed to extreme conditions of heat and humidity affecting the rocks used in its construction. These rocks are identified as siliceous sandstones, mainly formed by rounded to subrounded clasts, with scarce angulose particles, containing 96% quartz. Weather characteristics encourage the growth of vascular plants as well as algae and mosses and other organisms that damage materials. Among these, there are 18 lichen species (belonging to 18 genera), 8 foliose, 3 fruticose and 7 crustose. The damaging action of these lichens has been observed through SEM observations and EDAX microanalysis of rock samples colonized by Caloplaca sp. and Buellia sp. Source

A list was made including morphological characteristics of the new records of lichens foundamong the samples obtained by the authors in the forests that border rivers of the Natural Reserve of Punta Lara. Morphological characters as well as histological and spot test were used together with specific keys for identification. A total of 13 species were added; most of them are common to the province except for P. corallina which is a new record for the province of Buenos Aires. Source

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