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Methyl methacrylate (MMA) material is considered to be a suitable material for repairing concrete crack, provided that its large volume shrinkage during polymerization is resolved. This study was dedicated to investigating the effect of low shrinkage additives polyvinyl acetate and styrene (PVAc + styrene) on properties of the repair material and further proposes the shrinkage reduction mechanism based on the data of FTIR spectra, DSC testing and SEM micrographs. The results showed that PVAc + styrene delayed the gel point during the polymerization, and the formation of two-phase structure and micropores compensated for the volume shrinkage of the material. When the proportion of PVAc + styrene was 12%, the volume shrinkage could be as low as 4.78%, and the shrinkage stress was reduced by 87.4%. PVAc + styrene improved the bending strength and fracture toughness of most ratios investigated in this study. When 12% PVAc + styrene was added, the 28 d flexural strength and fracture toughness of MMA-based repair material were 28.04 MPa and 92.18%, respectively. After long-term curing, the repair material added with 12% PVAc + styrene showed a good adhesion to the substrate, with a bonding strength greater than 4.1 MPa and the fracture surface appearing at the substrate after the bonding experiment. This work contributes to the obtaining of a MMA-based repair material with low shrinkage, while its viscosity and other properties also can meet the requirements for repairing microcracks.

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In this work, the formation of tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate for CO2 capture was studied by conducting experiments in a kinetic setup coupled with high-pressure in situ Raman spectroscopy. The impacts of TBAB concentration and operating temperature on CO2 incorporation into TBAB semiclathrate hydrates were investigated from the macroscopic and microscopic perspectives. It was found that the structure transition of TBAB semiclathrates from type A to type B occurred in the presence of CO2 and could be identified by the splitting of the Raman peak at 1447 and 1465 cm–1 (C–C stretching vibration mode in TBA+). CO2 consumption increased substantially upon the occurrence of hydrate structure transition, indicating that a larger amount of CO2 is incorporated into the TBAB semiclathrate of type B. The structure transition of the TBAB semiclathrate occurring at 2.57 mol % TBAB is faster than that at 0.29 and 3.72 mol % TBAB, and CO2 consumption obtained at 2.57 mol % TBAB is greater. When the temperature is reduced from 282.15 to 279.15 K, the structure transition of the TBAB semiclathrate occurs faster, but the amount of CO2 trapped in the hydrate is reduced. Therefore, the TBAB semiclathrate formed at 2.57 mol % TBAB and 282.15 K is a suitable system for CO2 capture using TBAB semiclathrate hydrates.

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