The large amount of ettringite detected in concrete affected by different failure mechanisms (alkali -silica reaction [ASR], freezing and thawing [FT], and wetting and drying [WD]) in sulfate -free environments has been a matter of concern for many researchers over the past years. Two major lines to approach this issue have been defined. One of them considers ettringite as the main cause of damage and the other assumes that it appears after concrete distress. In order to contribute to the clarification of this phenomenon, research was conducted to cover the above issues. This paper reports on the conclusions arrived at up to date, from studies conducted on concrete affected by different damaging mechanisms: FT, WD, and precracking induced by loading and ASR. Changes in length and mechanical strength of test concrete are reported, as well as the evaluations made by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X -ray analysis (EDAX). Secondary ettringite formation (SEF) is closely linked to pore fluid transport in the mass of concrete. Although it was not possible to define clearly its participation in the damaging processes related to ASR or to FT, secondary ettringite crystallization in concretes subjected to WD cycles seems to be one of the most likely mechanisms to account for the volumetric instability observed in these concretes. D

h i g h l i g h t sIt is feasible to incorporate crushed concrete powder in order to achieve maximum use of the recycled concrete. The influence of admixtures must be studied not only in fresh mixtures but also in hardened concrete. Petrographic studies revealed that the incorporation of crushed concrete powder makes the mortar matrix denser. a b s t r a c tRecycled aggregates are made from crushed waste concretes and can be used as a replacement of natural aggregates in concrete production. Despite having lower density and higher absorption than natural aggregates, they can be used to manufacture conventional concretes with good performance if they are added in the proper amounts. To make self-consolidating concretes, the same aggregates used to manufacture conventional concretes can be used, but in order to increase segregation resistance and keep mix cohesion, a large amount of fine aggregates and a suitable admixture are required. The main goal of this work is to study the influence of recycled aggregates on self-consolidating concrete. Concretes were mixed with 50% of the coarse aggregate replaced by recycled aggregates (Patagonia gravel) and with 20% of the fine aggregate (natural sand) replaced by crushed concrete powders. Fresh concrete properties were tested, and physical and mechanical properties were determined in the hardened state. The petrographic composition of the concrete was examined to assess the interfacial transition zone and the contribution of the powders to the mortar microtexture. The results vary depending on the type of admixture and aggregate. However, it is shown that the inclusion of these crushed aggregates to make good selfconsolidating concrete is feasible.

It has been known for a long time that strained, microcrystalline or cryptocrystalline quartz-bearing aggregates may cause alkali-silica reactions in concrete. Studying the relationship between deformation processes and microstructural characteristics of rocks, the reason for this behaviour can be better understood. Orthogneisses from the metamorphic basement of the Sierra Chica, Córdoba (Argentina), which were locally and differentially deformed in ductile shear zones, were used to analyse such behaviour. Petrographic analyses, accelerated mortar bar tests (ASTM C 1260, 2005) and chemical test (ASTM C 289, 1994) were conducted. Furthermore, corrosion tests were performed on polished rock surfaces using 1 N NaOH solution. It was seen that the reactivity of the quartz-bearing mylonites increased by~30% with respect to the non-mylonitised sample due to the increment in the strained quartz content and specially with the extended subgrain development. The mylonitised rock affected by superimposed cataclasis and the development of pseudotachylytic veins incremented its reactivity by~97% with respect to the nonmylonitised sample due to the combined effects of subgrain formation, grain size reduction and the formation of glassy material. It was also the only sample that showed significant differences in surface corrosion confirming the high reactivity of the rock. These results agree with expansion values measured on the accelerated mortar bar test and with silica leached in the chemical test. We believe that the simultaneous use of different tools to evaluate the potential alkali reactivity of the rocks in concrete is a good strategy rather than the use of isolated tools, which could lead to confusing interpretations of the process and therefore result in erroneous decisions.

AB ST R ACT : In Argentina, the only halloysite deposits found so far are located in the southwest of the province of Rio Negro. The areas are named Mamil Choique and Buitrera, separated by 50 km in a W-E direction. The deposits are located in pyroclastic rocks, rhyolitic tuffs and ignimbrites.The aim of this paper is to determine the origin of the alteration, any relationship between the processes in Mamil Choique and Buitrera, and the factors which controlled the halloysite formation. The work was based on field work, mineralogical and geochemical studies, form and distribution of the alteration. Fresh as well as altered rocks were collected. The first were studied by petrographic and chemical methods. In altered samples, the clay mineralogy was determined by XRD and textures by SEM and TEM. Chemical analyses on fresh and altered samples were used to characterize the alteration process and the rock composition.It was concluded that halloysite has been formed by weathering in a time range from Middle Eocene to Middle Oligocene and extended along 50 km in a W-E direction, independent of the source rock. Particle morphology depends on the original texture of the rock. Spheroidal halloysite is related to rocks with low porosity and tubular particles are related to rocks with open spaces.

The numerous kaolin deposits located in Patagonia, Argentina, have been formed by hypogene or supergene processes. The primary origin has been established from O18 and D isotopic composition of the main minerals, kaolinite and/or dickite, and from the behaviour of certain elements during the alteration. The aim of this paper was to find if there is a tool, other than oxygen-deuterium data, to establish the origin of the Patagonian kaolin deposits. To handle the large number of variables per sample, a statistical multivariate study was used. The Principal Component method defines, on one hand the variables that better characterize each deposit and, on the other hand, the correlation between them. Fifty seven elements were considered and those that were not explained using these two components (which represent 75% of the total variance of the model) were discarded. As a result, the contents of Fe2O3, P2O5, LOI, Sr, Y, Zr, V, Pb, Hf, Rb, S and REE were used and the results show that the two components separate the deposits into two fields that are consistent with the process of formation. The first component indicates that Fe2O3, Y, Rb, U and HREE are more abundant in the supergene deposits, whereas, Sr, Pb, S and V are more abundant in the hypogene deposits. The second component shows that S, P2O5 and the LREE are enriched in the hydrothermal deposits, whereas Zr is more abundant in those formed under weathering conditions.