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 °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: αV0 = 4.50(10)·10−5 K−1. The loss of structural H2O occurs at least from ∼240 °C, and at T > 325 °C an irreversible amorphization occurs, followed by a complete dehydration. The potential implications on the use of colemanite as concrete-aggregate are discussed.