This paper introduces a proposal to produce artificial pozzolans by means of activation of low grade clays, as an alternative to metakaolin production. Basically the work considered clay mineral enriched soils, mainly kaolin. Such material was sediment and later calcined at 900 Celsius degrees. The same process was conducted with non-sediment material. Due to calcinations, the specific surface decreased significantly, and therefore, its pozzolanic activity, which was assessed by monitoring the CH consumption in cement pastes of several ages, as well as compressive strength in cement mortars. Calcined material, apparently inert, was ground until achieving high finesse. An experimental series made of sugar cane straw ash was introduced, as a reference to the pozzolans previously studied. Ground calcined clays increased its pozzolanic activity at a huge extent, which is characterized by a higher consumption of CH in cement pastes and by a higher compressive strength in cement mortars. Apparently this change takes place due to grinding effect on the reactivity of calcined clayey soils. The best results were obtained from sediment samples before their calcinations. The compressive strength of cement mortars, replacing a 30% the cement weight by such material, is similar to the control (100% cement) at 7 days, and higher at 28 and 60 days. Although such replacement does not decrease total porosity, it does decrease sorptivity, mainly in samples produced with calcined and ground sedimented material. Probably this phenomenon occurs because of pores capillary refining process induced by the precipitation of products of pozzolanic reaction.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 329-352. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300001

In the intersections, the drivers confront many options related to the way, speed and trajectory, which ones in combination to many options of traffic movements, they make difficult the task of the conductor and considerably increase the potential occurrence of an accident. In this paper, data of traffic conflicts are used, taken in rural T-form intersections from Talagante district in the Metropolitana region, Chile. Using the principal component analysis, an index are proposed that represents the risk level of each traffic conflict in an intersection, determining that the highest values of the index are related to a greater risk of than a traffic conflict it finished in accident, whereas low values indicate a smaller risk. After that, a model of classification of the risk in intersections is developed, applying the theory of decision trees. Finally, Time to Evasion is validated like quantifying variable of the traffic conflicts, taking as it bases studied variables at world-wide level, like Time to Collision and Post – encroachment Time.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 353-370. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300002

The authors have been involved in the creation, preliminary tests and development of the “Torrent Method”, which is intended to test air permeability in concrete. It’s been more than 15 years since such foundational research and, now, this paper presents a review of the evolution and current situation of the Method, included in the Switzerland standards in 2003. Application examples conducted in laboratory and civil works (bridges, tunnels, and so on) are introduced, including data from different countries worldwide. Correlations between the air permeability coefficient kT and other durability indicators, such as chloride migration (ASTM C1202), penetration of water under pressure (EN 12390-8) or capillary action are presented. Finally the future prospective uses are discussed, as quality control tool for new structures, considering relevant implications they would lead to, as well as the diagnosis on existing structures.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 371-382. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300003

Over the past 10 years, Extradosed bridges have become an attractive structural type around the world, due to the good results obtained with the first bridges constructed in Japan. This new typology, generally recognized as an intermediate solution between cable stayed bridges and cantilever constructed prestressed box-girder bridges, because these take advantages of design and constructions methods of the other two typologies, has become an interesting option. Therefore, given the interest that exist about this type of bridge, in this paper the historical context that describes its origin, the influence of the principal structural elements and the design criteria proposed by researchers are presented. In this way it is expected to offer a general insight into the design conception and structural behavior of Extradosed Bridges, so that they may be considered as an alternative structure for bridges in the Americas.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 383-398. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300004

This work describes the formulation, implementation and application of a cohesive crack discrete model, which can simulate the fracture process in mode I of simple concrete beams with defined cracking pattern. In the fracture process, a relationship between the cohesive normal stress and crack opening is established, where the material outside the fracture zone has a lineal elastic behavior in loading and unloading, whereas the material inside the fracture zone has an inelastic behavior with strain softening. In the mesh, pairs of nodes at the same spatial position are put on the cracking pattern and disconnect the adjoining two-dimensional elements. These duplicated nodes are connected to elasto-plastic springs that represent fracture process. Three concrete beams subjected to load at the middle with different dimensions are numerically simulated. Each numerical simulation is a nonlinear finite elements analysis in plane stress state, considering infinitesimal strain and applying an incremental vertical displacement on the top side of the mid-span of the beam. Satisfactory results of the structural response are obtained, as compared with experimental tests and numerical modeling carried out by other authors.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 399-418. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300005

Pozzolanic materials in portland cement concrete mixtures hydrate forming new calcium silicate hydrates which improve durability of concrete structures. The aim of this research was to enhance the understanding of the role of natural pozzolans in concrete performance. This study characterized porosity and pore connectivity of concrete mixtures as function of the con   tent of natural pozzolans. The experimental program measured compressive strength and permeability of concrete mixtures with different levels of cement replacement by natural pozzolans between 28 and 84 days of age, so the effect of pozzolans could be assessed as a function of time. Results clearly show that the gain in impermeability of concrete due to the use of natural pozzolans is much more pronounced that the effect in compressive strength. For instance, concrete with 33% of cement replaced by natural pozzolans had a compressive strength 27% lower that those with no pozzolans replacement; nevertheless, their impermeability was approximately 200% superior to those with no pozzolans replacement. Chloride ion permeability and rate of water absorption showed low variability and good correlation with pozzolanic reactions. It can be concluded that it is important to control compressive strength and permeability independently because they are affected very differently by pozzolanic reactions; also, for taking advantage of natural pozzolans in concrete, it is important to specify and measure permeability at late ages.

Rev. ing. constr. [online]. 2010, vol.25, n.3, pp. 419-431. ISSN 0718-5073.  http://dx.doi.org/10.4067/S0718-50732010000300006