Boron Rich Mortars for Neutron Shielding, Mechanical and Attenuation Properties

Boron thanks to his high neutron cross section is an effective absorber of thermal neutrons. Mortar manufacturing with a useful boron contents is particularly relevant for neutron shielding applications. The use of natural boron rich minerals or synthetic boron compounds as sands is an affordable route for boron charged mortars. Nowadays, a largely available boron rich mineral is colemanite, which is a calcium borate hydrate with an atomic boron content of 15.78 wt%. Nonetheless, colemanite in contact with cement pore solution is partially soluble and releases boron species harmful to C3S hydration. We investigated the effect of inserting colemanite in normal portland cement mortars by varying the grain size of colemanite sand and evaluating the mechanical and neutron attenuation properties of mortar samples. Additionally, we tested danburite that is a boron rich silicate mineral as an insoluble mineral alternative. Danburite is certainly less available than colemanite, but it can be produced via hydrothermal synthesis starting from colemanite and a reactive silica source. The results shown that a 3.2% of atomic boron on total weight of mortar can be achieved without compromising the mechanical properties with selected colemanite grain size.