Abstract In recent years, the use of ASTM C595 Type IL portland-limestone cement (PLC) has continued to gain momentum in the concrete industry. In the Southeast United States, PLC ground to fineness levels exceeding 500 m2/kg have demonstrated useful synergies with some fly ash sources. In 2014, the Mississippi Department of Transportation (MDOT) approved use of PLC and they have a specification that allows up to 35 % fly ash with PLC but only up to 25 % fly ash with ASTM C150 Type I ordinary portland cement (OPC). The primary objective of this paper is to assess the use of PLC in Mississippi in the context of MDOT’s new specification for both MDOT and non-MDOT projects. The authors documented several case study projects including residential-light commercial, highway barriers, slabs, a multistory hotel, and a wastewater facility with sulfate exposure conditions, in addition to evaluating data from several dozen laboratory-produced concrete mixes to make assessments. Class C and Class F fly ashes were considered, mostly at 20–35 % replacement rates. Overall, Type IL PLC was found to be a better cement for use in the marketplace for Mississippi than Type I OPC, and MDOT’s existing specifications were successfully vetted.