Microwave processing of glass-fiber reinforced composites—Modification of the microstructure

The present article deals with the influence of microwave treatment on the properties of glass-fiber reinforced composites. The cement used in the matrices of the composites was either plain ordinary portland cement or metakaolin-blended cement. Two levels of microwave power were investigated: 40 W and 80 W for 1 hour 30 minutes. The behavior of such composites was compared to that of specimens cured at ambient conditions (20°C) and at 60°C and 90°C. The mechanical behavior was assessed by means of three-point flexure tests. The microstructure was investigated using differential thermal analysis, infrared spectrometry, and scanning electron microscopy. The results obtained show that microwave treatment enhanced the pozzolanic reaction between ordinary portland cement and metakaolin and the bond between the fibers and the matrix. Interfaces between fibers and matrix were also modified. The mechanical performances of the microwave-processed composites were very interesting at early ages, but microwave heating degraded some long-term properties, such as work of fracture and toughness.