A recent study comparing concrete slabs with and without high-reactivity metakaolin (HRM), a high-performance mineral admixture that yields results comparable to silica fume, found that HRM improves concrete properties while offering good workability and finishability. According to the concrete supplier and contractor involved in the experiment, the non-pozzolanic control concrete and the HRM-modified concrete had similar properties. However, the concrete containing HRM had a creamier texture, set somewhat faster, and generated less bleedwater.
The results of the 1993 study conducted by Construction Technology Laboratories Inc., Skokie Ill., show that the compressive and flexural strength development of HRM mixes is significantly greater than that of a nonpozzolanic control mixture and similar to that of silica-fume mixtures. The study also found that HRM concrete:
- Requires 25% to 30% less super-plasticizer than silica-fume concrete to achieve a comparable slump (at water-cementitious materials ratio above 0.35)
- Has a very low chloride permeability, similar to that of silica-fume concrete
- Exhibits less drying shrinkage than conventional portland-cement concrete, and drying shrinkage similar to that of silica-fume concrete
Though HRM concrete is similar in price to silica-fume concrete, it can offer economic benefits to the contractor resulting from its easy finishability and quick cleanup.