Percorrer por autor "Brito, J. de"
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- Behaviour of Glass in Cement-Based Materials: Its Role on ASRPublication . Serpa, D.; Silva, António Santos; Soares, D.; Santos, M. Barreto; Brito, J. deOne of the most worrying degradation mechanisms in hardened concrete is the occurrence of chemical expansive reactions, namely due to alkali-silica reactions (ASR). This pathology involves the formation of expansive products inside the material. This situation is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by ASR. Hence, there is an urgent need to find preventive methods that may inhibit these reactions in new concrete structures. Nowadays, the use of pozzolanic mineral additions is recommended to mitigate this type of degradation. Moreover, their effect depends on their chemical and mineralogical composition and also on the cement content replacement ratio. Glass is a common material with some environmental problems regarding recycling and landfilling. Some studies exist about its use as fine powder, like a pozzolan, in cement-based materials. However, there are also some problems related to its use as coarse aggregate in cement–based materials due to ASR development. This paper presents the results obtained in mortars exposed to 1M NaOH solution prepared with crushed glass as aggregate and as addition in cement substitution. The results reveal that ASR is reduced with the incorporation of glass as aggregate or addition, and its efficiency depends on its replacement content. This study shows that an incorporation of glass aggregates up to 20% in mass will generate no significant expansion when compared with concrete made with natural aggregates.
- Effect of the source concrete with ASR degradation on the mechanical and physical properties of coarse recycled aggregatePublication . Santos, M. Barreto; Brito, J. de; Silva, A. Santos; Hawreen, A.Knowing the aggregates' properties is fundamental for the correct design and performance prediction of concrete. The incorporation of coarse recycled aggregate (CRA) in concrete requires a deep understanding of CRA's capacity and limitations. CRA properties are mainly conditioned by the type of natural aggregates (NA), the interstitial transition zone (ITZ), and the adhered mortar's quality. All these conditions are restricted by the chemical, physical, and mechanical properties of the source concrete (SC). The potential alkali reactivity of CRA raises the alkali-silica reaction (ASR) issue when CRA incorporation in concrete is an option. The heterogeneity of CRA affects the reactive silica and alkali content present in NA and in the adhered mortar, respectively, depending on the characteristics of the SC. This makes it difficult to analyse the influence of CRA's heterogeneity when ASR-effected SC is used. This work intends to investigate modifications of CRA properties due to ASR level in the SC. For this purpose, several tests including ASR evaluation, particle size distribution, density and bulk density, water absorption, shape index, flatness index and fragmentation resistance were performed on NA (fine and coarse) and CRA under natural and accelerated aging conditions. The results shown that the use of ASR-effected CRA does not change its mechanical and physical properties. In fact, these properties are more dependent on the corresponding characteristics of NA, ITZ, and the adhered mortar than on the ASR level in the SC.