Effects of calcium-carbonate-based aggregates on alkali-free accelerators

Alkali-free flash setting accelerators are widely used in the area of underground construction as they allow a very rapid hardening of cementitious systems. These admixtures are particularly used for wet-mix shotcrete, which involves pneumatically pumping a previously prepared concrete to a nozzle, where liquid accelerator is added. Compressed air is used to ‘shoot' the mixture onto the receiving surface. The resulting concrete layer acts as a consolidating shield that helps to avoid the tendency of the excavated section to squeeze (convergence) or collapse. The accelerator's efficiency is related to many parameters such as cement class, environmental conditions (humidity, temperature), concrete mix design and aggregate type. A limited number of papers have been published on the effects of these factors on the accelerating properties of alkali-free accelerators. In this paper, the influence of the aggregates chemical nature is studied. Setting time and mechanical strength development of mortar samples con...