Response of alkali activated fly ash mortars to microwave curing

Volumetric heating provided by microwave curing results in faster property development as compared to conventional heat curing that relies on heat conduction from the skin to the core. This paper discusses the compressive strength and microstructure development of microwave cured NaOH activated fly ash mortars, and relates them to the microwave energy absorption by the material which is a function of its dielectric properties. Microwave curing parameters are chosen so as to eliminate the effects of thermal runaway. Strengths that are comparable to or greater than those of mortars heat cured for 48 h at 75 °C are obtained in less than 120 min of microwave curing. The rate of energy absorption by the mortars is found to be relatively constant for a considerable fraction of the microwave curing duration, attributable to the compensation for the drop in dielectric loss factor as a result of moisture loss by the increase in internal electric field. Compressive strength is shown to be related to the microwave energy absorbed by the specimens, especially during the time when free water is present in the system.     

Sagittal plane lumbar loading when navigating an obstacle and carrying a load

The current study quantified lumbar loading while carrying an anterior load mass and navigating an obstacle. Eight healthy male participants walked down a walkway and crossed an obstacle under three randomised LOAD conditions; empty-box (2 KG), five kilogram (5 KG) and ten kilogram (10 KG). Each walk was assessed at two events: left foot mid-stance (LMS) and right toe-crossing (TC) to characterise any changes from approach to crossing. Measures of interest included: trunk pitch, L4/L5 joint moment, compression, joint anterior–posterior shear and erector spinae activation. Findings demonstrate that obstacle crossing extended posture by 50, 41, 44%, respectively for each carried load magnitude. Further, these results indicate that shear rather than compressive loading may be an important consideration during crossing due to increase by 8, 9, 22% from LMS to TC for each load magnitude tested. These results provide insight into sagittal lumbar loading when navigating an obstacle while carrying a load.

Practitioner Summary: The risk of carrying while navigating obstacles on the lumbar spine is not completely understood. The forces at the lumbar spine while simultaneously carrying and obstacle crossing were analysed. Data indicate that carrying and obstacle crossing influence lumbar shear loads, thereby moderately increasing the relative risk at lumbar spine.