Abstract
The need for non-toxic radiation-shielding composites has increased because conventional lead-based and heavyweight shielding solutions raise environmental, handling and structural-load concerns. This study aimed to evaluate whether thermally treated colemanite, a naturally occurring boron-rich mineral, can improve photon and neutron attenuation in a cement-based matrix while clarifying the associated mechanical penalty. Portland-cement composites containing 0, 1, 5 and 10 wt.% colemanite were prepared and tested for X-ray/gamma-ray mass attenuation, neutron attenuation, 7-day compressive strength, SEM morphology and XRD phase identification. Colemanite addition modified photon attenuation in an energy-dependent manner, with the strongest average low-energy improvement observed for the 5 wt.% mixture (+5.5% relative to the control). The effective linear neutron attenuation coefficient increased from 0.248 cm-1 for the control to 0.346 cm-1 for the 5 wt.% composite, whereas the highest density-normalized neutron attenuation value was obtained at 10 wt.% colemanite. This shielding benefit was accompanied by severe strength loss: 29.3%, 93.0% and 98.0% at 1, 5 and 10 wt.% colemanite, respectively. SEM and XRD findings indicate that colemanite was incorporated as a crystalline particulate phase, but heterogeneous dispersion and hydration interference governed the shielding-mechanical trade-off. The composites are therefore more suitable for non-load-bearing radiation-protective panels, partitions and surface layers than structural concrete applications.