Effect of Superabsorbent Polymer (SAP) Size on Microstructure and Compressive Strength of Concrete.

Superabsorbent polymers (SAPs) are hydrophilic, polymeric network materials renowned for their ability to enhance various properties of cementitious materials. This investigation examines the impact of SAP size on the hydration degree, porosity, and compressive strength of cement pastes and concrete under diverse curing conditions and ageing periods. The findings reveal that SAP addition stimulates the hydration of the C2S phase, particularly during the early curing stages, thereby favouring early strength development. However, the effect of SAPs on hydration promotion diminishes as their size increases. Conversely, the size of SAPs affects the hydration range of their action, and the 400 µm SAP demonstrates the most extensive range of hydration enhancement, reaching up to 105 µm. Additionally, SAPs effectively reduce porosity in small pores (4 nm-10 µm), with 200 µm and 400 µm SAPs exhibiting the highest efficacy. While analysing the effects of SAPs on larger pores (>10 µm), the results show that although larger SAPs result in larger average porosity, the total porosity is effectively reduced, particularly in samples incorporating 400 µm SAP. The compressive strength of cement paste, even after 28 days, is slightly reduced following the introduction of SAPs. However, the strength of concrete, due to the naturally occurring pores eliminating the negative effects of the pores produced by SAPs, is significantly increased following the introduction of SAPs, especially 400 µm SAP.

PCy3-catalyzed ring expansion of aziridinofullerenes with CO2 and aryl isocyanates: evidence for a two consecutive nucleophilic substitution pathway on the fullerene cage.

A PCy3-catalyzed ring-expansion reaction of aziridine-fused fullerenes (aziridinofullerenes) through the insertion of CO2 and aryl isocyanates is disclosed. The reaction allows for CO2 fixation by aziridinofullerenes, producing oxazolidinone-fused fullerenes (oxazolidinofullerenes) in high yields, whereas treatment with aryl isocyanates led to a new fullerene family-imidazolidinone-fused fullerenes (imidazolidinofullerenes)-in good to high yields. Furthermore, a mechanistically related unprecedented fullerenyl phosphonium salt was successfully isolated. Using the isolated salt, mechanistic studies were also investigated.