Eric Wirquin

Assessment of the surface permeation properties of recycled aggregate concrete

The water permeability, air permeability and surface permeability of recycled aggregate concrete (RAC) are compared with those of a control concrete made with natural aggregate. The study shows that the permeation properties of RAC depend on mix-design, conditions of curing and drying of samples. Relationships between permeability and other physical characteristics of concrete such as water absorption capacity and diffusivity are discussed. According to the criteria existing for ordinary concrete made with natural aggregate, RAC could be classified as being of moderate quality rather than poor quality. The testing methodology shows that some of the techniques used to measure the permeability of RAC need to be modified in order with the distinctive characteristics of this material.

Methodology to Couple Time-Temperature Effects on Rheology of Mortar

Cement-based material rheological property evolution during the cement hydration dormant period depends on coupled temperature and time effect. To facilitate construction there has been increasing use of highly flowable concrete. To account for workability changes at different temperatures during transportation and placement, there should be optimization of such concrete. A methodology is presented by the authors which combines time and temperature influence on cement-based material rheologicial property variations. The expression of such variation is done as a function of calorimetric measurement-deduced relative time scale. There was preparation of four micromortars at temperatures of 10 to 30 degrees Celsius (50 to 86 degrees Fahrenheit) and testing for evolution of rheological property determination over the cement hydration dormant period. Variation in linear fashion of apparent plastic viscosity and yield stress is shown with the relative time scale combining time and temperature during the tested micromortar dormant periods.