Cement production is one of the more highly energy intensive manufacturing processes, and concrete is a huge component of the building industry worldwide.
Established solutions exist to reduce the amount of cement in concrete by using alternatives as partial cement replacement.
Slag, a waste product from steel production, and flyash, a waste product from burning coal, are together considered Supplementary Cementiitous Materials (SCMs) - alternatives to cement.
These SCMs can be substituted for 10-60% of Portland cement. The upper end of this substitution rate can be specified for non structural paving concrete without significant issues. For structural applications, the substitution should always be subject to the structural engineers approval.
In all jobs, ask the question, and ensure you are getting logical answers. Using SCMs delivers the huge double environmental benefit of reduced energy consumption in raw material production (reduced cement), and also creating a market for waste products from other industries (slag and flyash).
The strength of concrete that incorporates SCMs is similar or greater than concrete with Portland cement, and the price is similar and equal with many suppliers.
The established Green Star ESD rating tool has been rewarding developments that use SCMs for over a decade (See GS Design and As Built credit 19) so the material is well established in the industry. You just need to ask for it.
Better concrete mixes
Earth Friendly Concrete (EFC) from Wagners uses no portland cement, just SCMs.
Installing under-slab insulation to a slab on ground
Installing insulation under a slab on ground has its challenges. Some options are detailed in the excellent Mullum Creek Ground Slab Insulation Guide
Wafflepod slabs are a simpler solution to underslab insulation as teh wafflepod sits on top of the ground, and each of the wafflepods provides both the formwork for the slab beams and insulation combined. Rigid insulation board is also required to be placed at the bottom of the beams between the pods, and also around the perimeter of the slab. See image below courtesy of Greenyflats.com.au