Este artigo investigou a influência do teor de aditivo superplastificante e da adição mineral - sílica ativa e filer basáltico - na retração plástica ena fissuração de argamassas do concreto auto-adensável (CAA). Numa primeira fase foi realizada a análise do comportamento reológico dasfases pasta e argamassa das composições de CAA. Em seguida, foram mensuradas as deformações das argamassas pelo efeito da retração plástica e avaliada sua fissuração. Tanto na retração plástica quanto na fissuração, a composição com adição de sílica ativa apresentouresultados superiores, independente da ação do vento e teor de superplastificante. No entanto, no assentamento plástico, a composição comsílica ativa apresentou resultados superiores somente nos ensaios com ventilação imposta. O comportamento reológico afetou diretamente aretração plástica e fissuração nas primeiras idades, fato confirmado pela análise das pressões capilares das argamassas ensaiadas.

The perennial rhizomatous grass Arundo donax L. (Poaceae), the giant reed, is an exotic invasive species in several countries of Europe that is rapidly spreading in the savannas of Central Brazil, locally known as Cerrado. Allelopathy could facilitate the successful invasion of this species by hampering or suppressing the regeneration of the native vegetation. However, information on the phytotoxicity of A. donax extracts is limited.  We investigated the allelopathic potential of A. donax leaf and rhizome extracts, screened them for phytochemicals by thin-layer chromatography (TLC) and nuclear magnetic resonance (1H-NMR), and tested the extracts for antioxidant activity, antimicrobial activity, and cytotoxicity against Artemia salina. Aqueous and methanolic extracts were initially tested in germination and seedling growth bioassays using Lactuca sativa L. (Asteraceae). The aqueous extracts were then tested on five Cerrado tree species and on Megathyrsus maximus, an invasive, alien grass in the Cerrado. Extracts negatively affected germination and seedling growth of the target species. Leaf extracts were more inhibitory. Extracts did not show antioxidant and cytotoxic activity and had very low antimicrobial activity. Flavonoids, and other phenolics were detected mostly in leaves. Terpenes, which were also present in the leaves, were the main secondary metabolites in rhizomes. Alkaloids were detected by TLC in leaf methanolic extracts. However, 1H-NMR revealed the presence of indole alkaloids in methanolic extracts from rhizomes and leaves. We confirmed the allelopathic potential of this species and caution against weed control methods relying on cutting the plant back to soil level for favouring release of allelochemicals.

This is a repository copy of Extraction of tricalcium aluminate for research applications by selective dissolution of portland cement clinker.