Percorrer por autor "Hawreen, A."
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- 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.
- Evaluation of alkali-silica reaction in recycled aggregates: The applicability of the mortar bar testPublication . Santos, Miguel Barreto; Brito, Jorge de; Silva, António Santos; Hawreen, A.Alkali-silica reaction (ASR) is considered one of the most concrete degrading agents causing expansion due to a gel formation that swells in contact with water. In this regard, this study investigates ASR through an expansion test of mortars produced with recycled aggregates (RA). The RA were prepared by crushing source concrete (SC) mixes that were previously produced with alkali reactive natural aggregates (NA). SC mixes were exposed to different environments to accelerate ASR. The mortars were tested using the ASTM C1260 accelerated mortar bar test (AMBT). For comparison purposes, the aggregates were also tested using the RILEM AAR-3 concrete prism test (CPT). As for mortars with NA, changes were needed to optimize the mix production procedure to obtain a mouldable mortar and more trustworthy values. For this purpose, RA-mortars were produced with RA obtained from primary or secondary crushing, different water adjustment types, including the addition of constant volumes of water to maintain a mouldable slump, the addition of 50% of the total absorption water, and pre-saturation of RA. The results showed that the adjustment type of RA absorption water in the mix highly influenced the expansion results. The addition of constant volumes of water to maintain a mouldable slump led to the more trustworthy values. The expansion limits of ASTM C1260 seems be too high for fine RA's evaluation.