CMA

46 Only chloride that is “free” (in the pore solution of concrete) and unbound by clinker minerals can cause corrosion, and thus some researchers have noted that appropriate clinker compositions may fix chloride within the mineralogical composition of the cement to prevent chloride migration. Stable chloride containing minerals that may form during the clinkerization process, such as calcium- chloroaluminate or chlorellastadite, fix chloride within the lattice microstructure, a concept often used to manufacture high chloride containing eco-cements with low chloride leachability (Ashraf et al., 2019). Similarly, raw materials containing high alkali content may be limited to mix designs that contain lower alkaline traditional raw materials and high sulfur fuels may be required to maintain an equilibrium between the alkalis and SO3. Sulfur (though not a major input from MSWI ash) and alkali cycling in cement manufacturing operations is a highly complex system, but generally the stoichiometric balance between sulfur (mostly supplied by the fuel source) and alkalis in the raw material is controlled such that the volatility of the resulting alkali sulfates is low and will not accumulate in and circulate between the kiln and preheater tower. 4.2 Clinker composition Viable compositions for ordinary cement are dominated by the minerals alite (tricalcium silicate, critical for early age strength development) and belite (dicalcium silicate, responsible for late age strength development), among other important phases such as aluminate and ferrite. Higher MSWI replacements in the raw meal created cements with more SiO2 and belite, but lower CaO and alite. Studies has shown lower alite and higher belite proportions in cement with increasing addition of MSWI fly ash from 5% to 35%, and that clinker containing up to 6% MSWI fly ash might not have sufficient CaO content to form alite; washing the ash resulted in cements with higher alite content which may highlight the influence of trace elements on clinker formation. 2–6% bottom ash clinkers had relatively constant alite content but decreased with 8% addition which is attributed to trace elements present in the ash inhibiting phase formation. Clinkers created with up to 10% MSWI bottom ash and pelletized clinker with up to 15% bottom ash replacement required addition of extra calcium oxide; several studies reported that increasing MSWI ash addition contributed to this issue. Clavier et al. (2019) reported 10% higher alite in ash-amended cements containing 2.8% MSWI bottom ash. 4.3 Cement performance Pan et al. (2008) found that fly ash (1.75%) and bottom ash (3.50%) additions to cement production were associated with an increase in setting time but no changes in compressive strength of the cement. Bogush et al. (2020) reported that up to Alternative Fuels Hot meal Clinker Raw mix Raw meal Coal Oil Figure 2. Chlorine circulation in the lower part of the preheater indicated by the circle