There are many test methods used in the laboratory to detect potential alkali-aggregate reactions (AAR). However, up to now, there is no consensus if they are reliable and efficient. This work presents the development of a new and accelerated concrete prism test called ABCPT (accelerate Brazilian concrete prism test) as an attempt to create a reliable and fast test that can analyze and classify the potential reactivity of aggregates in the laboratory. For this research, six aggregates from different lithotypes were used. The methods CPT, ACPT and ABCPT were carried out with all the aggregates and a comparative analysis among all tests was performed. ABCPT seems to have a great potential to analyze and classify aggregates in the laboratory, although it needs further testing with other lithotypes to be confirmed as feasible.Keywords: alkali-aggregate reaction, test methods, concrete prism test (CPT), accelerated Brazilian concrete prism test (ABCPT).Existem muitos métodos de ensaio de laboratório utilizados na prevenção da reação álcali-agregado, entretanto, até o momento não existe consenso no que tange confiabilidade e eficiência destes. Este trabalho apresenta a tentativa de desenvolvimento de um novo método de ensaio acelerado denominado ABCPT (método acelerado brasileiro de prismas de concreto), com o intuito de que este possa, de maneira rápida e confiável, analisar e classificar agregados mediante a sua potencial reatividade em laboratório. Para o desenvolvimento desta pesquisa, foram utilizados seis litotipos diferentes de agregados. Os métodos CPT (método de prismas de concreto), ACPT (método acelerado de prismas de concreto) e ABCPT foram realizados com todos os agregados e após, uma análise comparativa foi realizada. Os resultados indicam que o ABCPT demonstra grande potencial para utilização na análise e classificação de agregados em obras correntes de engenharia. No entanto, para a sua real comprovação, torna-se muito importante a realização do ensaio com um maior número de amostras de diferentes litotipos.Palavras-chave: reação álcali-agregado, métodos de ensaio, método de prismas de concreto (CPT), método acelerado brasileiro de prismas de concreto (ABCPT). Using the accelerated Brazilian concrete prism test (ABCPT) to evaluate alkali aggregate reaction (AAR)Uso do método acelerado brasileiro de prismas de concreto (ABCPT) para avaliação da reação álcali-agregado (RAA) Abstract Resumo
Delayed Ettringite formation (DEF) is an internal expansive reaction that can damage concrete. DEF is strongly influenced by the temperature, above about 60-65°C, and other factors involving cement chemistry especially, but also its physical characteristics. The exposure environment over time also promotes a condition to increase deterioration from DEF. Expansions results from secondary ettringite formation are progressive and can lead concrete to microcracking impacting its performance and durability over time. Several concrete structures are pointed to be severely attacked by DEF, and test method as well a better comprehension on this pathology is necessary to promote specific and proper preventive measures to avoid future damages. Furthermore, compared to alkali-silica reaction, DEF occurs more readily and aggressively, and sometimes prematurely, depending on several factors, such as type of cement, concrete mix design, exposure conditions, among others. This paper involves an overall analysis of the behavior of concretes with two types of Portland cements (High early-strength cement and a Portland pozzolanic cement, with fly-ash) in relation to DEF process. Several data from a laboratory study where DEF was induced through a specific thermal curing procedure are presented and discussed. The analyses involved the assessment of physical, mechanical, and expansive properties besides microstructural monitoring of samples from concretes over time. These experiments allowed detecting high values of expansions from DEF (up to 1.2%) in the concrete without fly ash. The mechanical properties were severely impacted from this deleterious process; as expansions increased, losses in the mechanic and elastic properties were verified. Expansion levels in the order of 0.5% prompted remarkably high reductions and, at about 1% the losses were relevant for both strengths (tensile and compressive) and modulus of elasticity, of 60% and 80%, respectively, in the presence of cement without fly-ash. Concrete microstructure has indicated massive formations of ettringite as well as micro-cracking and the fragility of the cement matrix because of DEF. On the other hand, expansion up to 0.2% did not promote important negative effects on the properties of concrete, especially with the pozzolanic cement tested. Furthermore, an overall approach with several correlations between physical and mechanical properties was taken to obtain different levels of deterioration for a concrete presenting DEF.
Neste estudo objetivou-se alertar a comunidade técnico-cientifica local com relação à investigação do grau de reatividade potencial, quanto à Reção Álcali-Agregado (RAA), de 11 areias extraídas no Estado do Paraná. Foram investigados os aspectos geológicos e ascaracterísticas físico-químicas dos agregados estudados. Com relação aos resultados, 73% das amostras apresentaram expansões superiores ao previsto pela norma NBR 15577-1:2018. Além disso, os teores de finos foram compreendidos fora da zona ótima indicada pela NBR 7211:2009, induzindo a dificuldades para o alcance de trabalhabilidades desejadas em concretos e argamassas. Os grãos apresentaram tipologias diferenciadas e diferentes fases minerais associadas. Quanto ao grau de expansibilidade, concluiu-se que os agregados da Formação Ponta Grossa não apresentaram reatividade potencial. Já os agregados com potencial reativo foram os dos depósitos aluvionares, com fontes em rochas migmatíticas e gnáissicas, em rochas areníticas e conglomeráticas (Grupo Itararé) e os de origem eólica (Formação Caiuá).
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