Application of basalt fibre reinforced polymer (BFRP) bar reinforced seawater sea-sand concrete structures in marine and coastal buildings could bring both environmental and economic benefits. As BFRP bar reinforced seawater sea-sand concrete members are likely to be exposed to temperature variations during their service life, the bond durability between BFRP bar and seawater sea-sand concrete should be well understood. This paper investigated the effects of thermal cycling, such as target temperature (i.e. amplitude of variation) and cycling times, bar diameter and concrete strength on the bonding behavior of BFRP bars in seawater sea-sand concrete by pullout test. It is found that target temperature and cycling times lead to a significant reduction of BFRP bar-to-seawater sea-sand concrete bonding, which is mainly attributed by the degradation of BFRP under thermal cycles. Through the method of scanning electron microscopy, microstructure of BFRP is examined and the bond mechanism considering the effect of temperature variations is clarified. Finally, theoretical model is proposed to predict the bond stress-slip relationship of BFRP bars in seawater sea-sand concrete. Accuracy of the predictions is validated by the experimental results.
Herein
we describe a sequential metalation process at an sp3 carbon
center from μ2- to μ3- to the first
benzyl hypercoordinated carbon (HC)-centered μ4-gold(I)
cluster. Starting with a gem-dimetalated
precursor, attachment of two gold atoms on the ipso carbon enables the formation of an electron-rich silicon center,
and the resulting stable C–Si bond is even resistant to the
attack of fluoride. Addition of the third Au(I) ion results in an
HC-centered [Au3–C(Ar)–Si]+ transition
state, which facilitates the formation of unique Au–Si agostic
bonding and accordingly promotes the electrophilicity of the silicon
center. The subsequent facile C–Si bond cleavage drives further
metalation of the trimetalated benzyl carbon to constitute an HC-centered
tetrametalated structure. This biased polymetalation effect in every
elementary step along with the escalation of the nuclearity has been
thoroughly deconvoluted via detailed structural analysis and kinetic
and theoretical studies.
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