Thermal stability and high-temperature behavior of the natural borate colemanite: An aggregate in radiation-shielding concretes

Colemanite is a natural borate that can be used as an aggregate in neutron-radiation shielding concretes. In this study, we report its thermal behavior, up to 500 degrees C, by describing: 1) its dehydration mechanisms and 2) its thermo-elastic parameters. The thermal expansion of colemanite is significantly anisotropic. The refined volume thermal expansion coefficient at ambient conditions is: alpha(V0) = 4.50(10).10(-5) K-1. The loss of structural H2O occurs at least from similar to 240 degrees C, and at T > 325 degrees C an irreversible amorphization occurs, followed by a complete dehydration. The potential implications on the use of colemanite as concrete-aggregate are discussed. (C) 2019 Elsevier Ltd. All rights reserved.