Development of lightweight and low-crystalline artificial aggregate using cementless fly ash binder for thermal neutron shielding concrete manufacture

Abstract

This study developed artificial lightweight aggregates (CNF aggregates) using a Ca(OH)2-Na2CO3-activated fly ash (CNF) binder system and boron compounds (H3BO3 and Na2B4O7) for thermal neutron shielding through cold-bonding pelletization. The study demonstrated that the CNF aggregates having 5 wt% H3BO3 and Na2B4O7 were lightweight and adequate for structural use, satisfying ASTM C 330, Korean CSD, and KS F2527. The CNF aggregates were safe from heavy metal toxicity and did not noticeably lose boron due to leaching. In addition, these aggregates had only a small amount of quartz and thus had considerably lower risks of neutron-induced volumetric aggregate expansion in PC concretes than crushed (or natural) aggregates. The use of the CNF aggregates in PC concrete production was excellent in increasing the thermal neutron shielding performance of PC concrete. The thermal neutron shielding efficiencies of the PC concretes with CNF aggregates having 5 wt% H3BO3 and Na2B4O7 were 96.6 % and 99.3 %, respectively. In addition, the compressive strengths of PC concrete with these CNF aggregates were high enough (29.2-30.2 MPa) to satisfy the structural lightweight aggregate concrete requirement (>17 MPa) according to ACI 213.