Clause 7.2.2 (Revised): All concrete used in toboggan construction must be comprised of at least 30% cementing materials by mass. Cementing materials are any materials having cementing properties or contributing to the formation of silicate compounds. Examples include portland cement, hydraulic cement, fly ash, slag, silica fume, and metakaolin.
If we have two concrete mixes do they both need to be 30% Portland cement by mass or can the sum of both mixtures total 30%?
All concrete mixes must comply with the requirements. Therefore if you make two concrete mixes, each mix must have at least 30% Portland cement content by mass.