Production of geopolymeric binder from blended waste concrete powder and fly ash

Recycling and utilization of waste concrete is a significant contribution to environment and sustainable development. In current practice, the recycling of waste concrete is mainly limited to the use of crushed aggregates in low-specification applications. Few researchers have investigated complete recycling of waste concrete. These complete recycling methods, however, need to re-clinker the hydrated cement using the standard cement kiln procedures and thus consume significant amount of energy and release large quantity of CO2. To completely recycle and utilize waste concrete in a sustainable and environmentally-friendly way, a method that does not need re-clinkering at high temperature should be used. This paper studies the production of geopolymeric binder from ground waste concrete (GWC) powder mixed with class F fly ash (FA), which can then be used with recycled concrete aggregates to produce new concrete. Specifically, the effect of composition and concentration of the alkaline solution and the content of GWC on the unconfined compressive strength (UCS) of the produced geopolymeric binder is investigated. SEM/EDX, XRD, and FTIR analyses are also performed to investigate the micro/nano-structure, morphology and phase/surface elemental compositions of the produced geopolymeric binder and the effect of calcium (Ca) on them. The results indicate that utilization of GWC together with FA can increase the UCS of the geopolymeric binder up to 50% GWC content. Further increase of GWC decreases the UCS of the geopolymeric binder. So with proper combination of GWC and FA, the geopolymeric binder with required strength can be produced.

► Studied geopolymer binder produced from waste concrete powder (WC) and fly ash (FA).
► Inclusion of WC increases the UCS of geopolymer binder until 50% WC content.
► Low Ca semi-crystalline CSH gel coexists with the geopolymer gel.
► Ca+ incorporated into the geopolymer network acts as charge balancing cation.
► WC can be recycled and used together with FA to produce geopolymer binder.