Interfacial bond behavior of adhesively-bonded timber/cast in situ concrete (wet bond process)

The goal of this research was to study the strength of the interfacial bond between cast-in-situ concrete and engineered timber (cross-laminated timber (CLT)). Double lap specimens were manufactured using fresh concrete that was cast between two CLT blocks. Polyurethane and epoxy adhesives were used to bond the wet concrete with the CLT blocks. The shear strength of wet-bond specimens was compared with the specimens prepared under dry conditions (prefabricated concrete cube glued to CLT blocks). The statistical analysis (T-test) of bond strength showed that the shear strengths of wet- and dry-bond specimens using epoxy and polyutrthane adhesives were no significantly different for the tested C25 plain concrete and the CLT. The failure mode of dry-bond specimens were concrete failure near the interface, however, debonding at interface was the dominant failure for the wet-bondspecimens

Influence of nanoclays on water uptake and flexural strength of glass-polyester composites

Fiber-reinforced polyester composites have received significant attention in a variety of applications due to their considerable potential due to such characteristics as high strength, stiffness, and modulus. However, one of the most important concerns about polymeric composites is their sensitivity to moisture attack. This work has been conducted to investigate the effects of nanoclay addition on reinforcing glass/polyester composites against water absorption and the resultant deterioration of flexural strength. Therefore, chopped strand mat and woven fiberglass polyester specimens were fabricated by using the hand lay-up technique with varying weight percentages of Cloisite 20A nanoclays (0, 1.5, and 3 wt%) and immersion in water for a time duration of 21 days. The specimens were weighed for the water absorption test. The results showed a remarkable drop in water absorption of the composite samples with the increase of nanoclay content. Moreover, although all the pure and nanocomposite specimens underwent degradation in flexural strength due to the water absorption, the strength was found to significantly increase with increasing the percentage of nanoclay at all immersion periods. The experimental results were confirmed by scanning electron microscopy (SEM). SEM images indicated that the presence of nanoclay protected the fiber/matrix interfaces