Investigation of hierarchical porous cold bonded lightweight aggregates produced from red mud and solid-waste-based cementitious material

Here, solid-waste-based cementitious material (SCM) and red mud (RM) were innovatively applied to produce cold bonded lightweight aggregate (CBLAs) via synchronous pelletizing and foaming process. To integrally demonstrate the feasibility of developing the acceptable CBLAs, the following were investigated: (1) the effects of the production parameters on the pelletizing efficiency of CBLAs was investigated, and the results showed that SCM and RM exhibited the best compatibilities for CBLAs with a pelletizing efficiency of 91.9 %; (2) the effects of SCM and the addition of a novel hydrogen peroxide (HP, a foaming agent) on the properties of CBLAs was investigated, and the results revealed that the coordination of SCM with HP promoted synchronous pelletizing and foaming, thereby generating unified hierarchical pores on CBLAs and significantly decreasing their density. Viable CBLAs with low loose bulk density of 680 kg/m3, crushing strength of 3.1 MPa and water absorption of 20.7 % were obtained; (3) two surface modification methods of organosilicon waterproofing agent (OWA) spraying and SCM coating were carried out to further reduce water absorption of the prepared CBLAs, and the results indicated that the spraying of an OWA can effectively reduce the water absorption to 8.7 %. Additionally, the durability and environmental impact of CBLAs were evaluated acceptable employing the frost resistance and leaching tests. This work offers a new method for producing CBLAs from 100 % solid wastes and is a promising approach for the large-scale recycling of RM.