Ultrasonic testing and microscopic analysis on concrete under sulfate attack and cyclic environment

The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder(W/B) ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity(RDME) and the surface damage layer thickness of concrete were measured.Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete.The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.

Mechanical characterization of rose bengal and green light crosslinked collagen scaffolds for regenerative medicine

Collagen is one of the most important biomaterials for tissue engineering approaches.Despite its excellent biocompatibility,it shows the non-negligible disadvantage of poor mechanical stability.Photochemical crosslinking with rose bengal and green light(RGX)is an appropriate method to improve this property.The development of collagen laminates is helpful for further adjustment of the mechanical properties as well as the controlled release of incorporated substances.In this study,we investigate the impact of crosslinking and layering of two different collagen scaffolds on the swelling behavior andmechanical behavior inmicro tensile tests to obtain information on its wearing comfort(stiffness,strength and ductility).The mechanical stability of the collagen material after degradation due to cell contact is examined using thickness measurements.There is no linear increase or decrease due to layering homologous laminates.Unexpectedly,a decrease in elongation at break,Young’s modulus and ultimate tensile strength are measured when the untreated monolayer is compared to the crosslinked one.Furthermore,we can detect a connection between stability and cell proliferation.The results show that with variation in number and type of layers,collagen scaffolds with tailored mechanical properties can be produced.Such a multi-layered structure enables the release of biomolecules into inner or outer layers for biomedical applications.