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- Métodos de evaluación de las reacciones álcali-sílice en hormigones con áridos recicladosPublication . Barreto Santos, Miguel; Brito, Jorge; Silva, António SantosAlkali-silica reactions (ASR) are one of the causes of chemical degradation of concrete with natural aggregates (CNA) that compromise its durability. The introduction of recycled aggregates (RA) in concrete creates changes in their properties and differences in the results of the evaluation tests of ASR. Existing bibliography emphasizes special care in the evaluation of RA and concrete with recycled aggregate (CRA) for ASR and changes are proposed to the existing test methods. There are proposals to change the accelerated test of mortar and concrete with RA to accelerate the reactions and recommendations to prevent changes in the characteristics of the RA, during the preparation of samples. Some articles recommend the pre-saturation of the AR, due to its absorption of water, to avoid significant variations in the results of expansion of concrete samples from early ages. This article aims to briefly describe the characteristics of CRA and ASR presenting comments from existing bibliography to the evaluation methods of ASR in CRA and CNA. Las reacciones álcali-sílice son una de las causas químicas de la degradación de los hormigones con áridos pétreos (HAP) que comprometen su durabilidad. La introducción de áridos reciclados (AR) en los hormigones produce alteraciones en sus propiedades y diferencias en los resultados de los ensayos de evaluación de las RAS. Se encuentran en la bibliografía algunos cuidados en la evaluación de los AR y de los hormigones con áridos reciclados (HAR) en cuanto a la RAS, así como propuestas de modificación de las metodologías de ensayo existentes. Existen propuestas de modificación del ensayo acelerado de mortero y hormigón con AR para acelerar las reacciones y recomendaciones para evitar alteraciones en las características del AR grueso, durante la preparación de probetas. Algunos artículos recomiendan la pre-saturación del AR, debido a su absorción de agua, para evitar variaciones en los resultados de expansión de probetas de hormigón a edades prematuras. El presente artículo pretende describir sucintamente las características de los HAR y de las RAS presentando observaciones de la bibliografía en cuanto a los métodos de evaluación de las RAS en HAR y en HAP.
- 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.
- Study of ASR in concrete with recycled aggregates: Influence of aggregate reactivity potential and cement typePublication . Santos, Miguel Barreto; Brito, Jorge de; Silva, António Santos; Ahmed, Hawreen HasanThe incorporation of recycled aggregate (RA) in structural concrete requires deep knowledge of this material's potential and limitations by assessing its effect on the concrete properties. Alkali-silica reaction (ASR) is one of the most concerning degradation agents in concrete produced with natural aggregates, and more expectedly in recycled aggregate concrete (RAC), which motivated this study. ASR was analysed through expansion evolution in concrete mixes produced with different replacement levels of coarse natural aggregates (CNA) with reactive and non-reactive coarse recycled aggregates (CRA). In addition, concrete mixes were naturally and artificially aged to simulate the reaction at different ages. The influence of cement type on ASR development in RAC was also evaluated. The results showed that the incorporation of 20% of reactive RA did not affect concrete's expansion behaviour. The highest expansions were obtained when 100% of reactive RA and a higher strength class cement were used.