The reaction of CO2 gas with OPC, OPC-BFS and OPC-PFA composite cement systems were studied using XRD, SEM and TG to investigate the applicability of these materials to immobilise carbon arising from graphite waste. XRD results suggested that calcite formed in OPC system after the carbonation reaction, whereas calcite and vaterite were observed in OPCBFS and OPC-PFA systems. In OPC system, nearly half of Ca(OH)2 was consumed to form CaCO3. In OPC-BFS and OPC-PFA systems, the amount of CaCO3 formed, corresponded to the consumption of greater than 100% of Ca(OH)2 initially present, suggesting that other hydration products e.g. C-S-H were also consumed, either directly or indirectly during the carbonation process. The OPC-BFS system became more porous after carbonation. OPC-PFA system indicated a high efficiency on the conversion of Ca in the system into CaCO3.