Percorrer por autor "Brito, Jorge de"
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- 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.
- A Review on Alkali-Silica Reaction Evolution in Recycled Aggregate ConcretePublication . Santos, Miguel Barreto; Brito, Jorge de; Silva, António SantosAlkali-silica reaction (ASR) is one of the major degradation causes of concrete. This highly deleterious reaction has aroused the attention of researchers, in order to develop methodologies for its prevention and mitigation, but despite the efforts made, there is still no efficient cure to control its expansive consequences. The incorporation of recycled aggregates in concrete raises several ASR issues, mainly due to the difficult control of the source concrete reactivity level and the lack of knowledge on ASR's evolution in new recycled aggregate concrete. This paper reviews several research works on ASR in concrete with recycled aggregates, and the main findings are presented in order to contribute to the knowledge and discussion of ASR in recycled aggregate concrete. It has been observed that age, exposure conditions, crushing and the heterogeneity source can influence the alkalis and reactive silica contents in the recycled aggregates. The use of low contents of highly reactive recycled aggregates as a replacement for natural aggregates can be done without an increase in expansion of concrete. ASR expansion tests and ASR mitigation measures need to be further researched to incorporate a higher content of recycled aggregates.
- 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.