It is possible to completely eliminate Portland cement, PC, and with a very similar "process" produce concrete with even greater strength.  The aggregates are the same but the PC  is replaced by a geopolymer cement.   There are many routes to a geopolymer cement, my favorite is 75% class f fly ash, 15% ground granulated blast furnace slag (GGBFS), 10% Agsil (a potassium silicate "water-glass" powder sold as a fertilizer).  Just like Portland cement concrete the ingredients  are dry mixed then as little water as possible is mixed in, it is placed, compacted finished and cured.  The cured strength is reduced by excess water and some of the super-plastizers used with Portland cement work similarly with geopolymers.  When prepared with minimal water geopolymers are stronger than Portland concrete, compressive strengths of 80 MPa are typical at 28 days.  Curing begins in hours and is essentially complete in 24 hours but strength continues to improve.  Some geopolymers have been shown to be rather remarkable insulators, one grout (fine sand+geopolymer cement) tested  r 2.88/".   Unfortunately the only "paper" that documents the thermal conductivity of an geopolymer used an "obsolete" formula that required use of very hostile caustic solutions.  I personally am planning on testing this aspect of grouts prepared by the "user friendly" recipe given above.

Libeler: are any existing plants able to supply this, or are these experiments for future use?

Bob,
     Most all batch plants use fly ash, some use GGBFS, none, at this time use Agsil, it would have to be added from bags but it is 10% of the weight of what would otherwise be Portland cement.  I've had a local, to me, transit mixed concrete supplier say they are willing to mix it.  In Florida there may be plants set up to deliver a "proprietary" geopolymer being sold as " Blue World Crete".  I've contacted this company and their answers are vague at best.  They verbally claim they have a grout that demonstrates r 3.5/".
Another advantage of geopolymer concrete is it doesn't shrink in curing.