High Strength Concrete (HSC) is a relatively recent development in concrete technology which has grown in demand over the last 10 to 15 years. It has been made possible by the introduction of efficient high range water-reducing admixtures and high strength cementitious materials.
The perception of what level of compressive strength constitutes HSC has been continually revised upwards and is likely to continue to rise in the near future. The design of NZ Concrete Structures code, NZS 3101:2006, limits the use of HSC to 70 MPa for seismic design requirements (ductility). Other structures can however be designed using concrete strengths up to 100 MPa.
The key drivers of the development of high strength concrete are the long term use of concrete construction, the design of much taller buildings and the requirement to have thinner column or wall elements allowing for more useable space.
HSC is produced by making optimal use of raw materials that make up normal strength concrete. Most producers of HSC understand the factors that affect compressive strength and have the knowledge to engineer those factors to achieve the required strength.
The selection of raw materials is of utmost importance before they can be optimised into the required mix design:
- High Quality Portland Cement
- Supplementary Cementitious Materials (SCMs)
HSCs are more sensitive to changes in constituent material properties than conventional concretes and therefore a greater degree of quality control is required for the successful production of HSC.
Consistently manufactured EverSure will meet the high quality cement requirements for the production of HSC. The inclusion of Microsilica SF and EverPlus Class C fly ash will provide the additional properties required from a SCM for HSC.
The inclusion of Microsilica SF improves the concrete strength and durability through a pozzolanic reaction producing additional calcium silicate hydrates, fine powder packing mechanism and the improvement of bond at the aggregate paste interface. There will also be an improvement in bond at the concrete/reinforcement interface.
The inclusion of EverPlus Class C Fly Ash improves long term concrete strength and durability through a pozzolanic reaction producing additional calcium silicate hydrates. The primary benefits are however realised through the spherical particle shape of the EverPlus Class C Fly Ash as this will assist with controlling water content and improving mix rheology and concrete pump ability.