Potential CO2 reduction and cost evaluation in use and transport of coal ash as cement replacement: A case in the Philippines.

Coal ash can potentially be utilized as partial replacement for cement in concrete and mortar formulations. The use of coal ash can lessen the cost and energy production, and reduce the impact on the environment. At present, the annual coal ash generation amounts to ~2.78 Mt and may reach to ~13.02 Mt by 2035 in the Philippines. If coal ash is utilized as clinker replacement in the production of cement at a clinker-to-cement ratio of 0.7, GHG emissions can potentially be reduced to at least ~1.26 Mt CO2_eq in 2018 and could further be reduced by ~5.89 Mt CO2_eq by 2035 when surplus coal ash is utilized as partial cement replacement in concrete mixtures in concrete batching plants. As transport of coal ash can also result in GHG emission owing to fuel combustion, a critical distance is calculated in order to achieve positive net reductions. Critical distance is obtained by comparing the emission on coal ash transportation with that of cement production, while taking into consideration the emissions of the return trip. Thus, transporting the coal ash is limited to a distance of ~2841 km. Existing concrete batching plants are situated within 2,000 km from existing coal-fired power plants, where the transport of coal ash to these plants would not result in additional emissions but instead result in annual net reduction of GHG. Further, the cost of coal ash per bag varies according to the distance travelled and is much lower than the cost of cement per bag.