Pozzolans are silica rich minerals which can be used as a substitute for cement. In NZ, the pozzolans we know well are Fly Ash and Microsilica and they have been used succesfully for many years, but each have their limitations. Overseas, most cements are blended cements so the technology is very common and well understood.
It has been recognised since the 1950s that silica-rich volcanic ash deposits in NZ's Central Plateau have superb potential as pozzolans but until now it has been uneconomic to use them. ECO-CEM uses up to 25% of these Natural Pozzolans to create a GB type blended cement that is a marked improvement on those currently available - it won't add cost*, with performance that is much better than normal GP cement, and with lower embodied carbon.
* For projects in the upper North Island, ECO-CEM should be the same price as GP type cement. Outside of this area, there could be a small increase in cartage costs.
The Pozzolanic Reaction
When normal cement reacts, the main binding component produced is Calcium Silica Hydrate (C-S-H), but a weak by-product of around 25% Calcium Hydroxide (C-H) also results.
The silica (S) from the pozzolan utilises this C-H with a secondary reaction to make more C-S-H. This reaction is a little slower so strength development is different and 56 day testing is required.
A strong history of Pozzolanic Cements
– globally and in NZ
The Romans understood pozzolans well, mixing silica rich volcanic ash with burnt lime to create the early cement used throughout the empire, including for the Pantheon and the Pont du Gard which still stand today.
In NZ in the 1950s, pozzolans form the nearby Central Plateau were used in the concrete to build the Waikato dam and other associated projects. This followed extensive DSIR trials, and the Atiamuri, Waipapa and Ohakuri projects are testament to their longevity.
ECO-CEM creates a lower porosity concrete that is harder & denser than regular concrete, making it more resistant to chemical attack. Structures will last longer and require fewer long term repairs.
Fast early strength
Initially Eco-cem gains strength fast but overtime this becomes a little slower than normal cement, so typically a 56 day not 28 day test is used, as shown below:
In normal cement, the water soluble Calcium Hydroxide dissolves forming voids which allow chemical attack from chlorides, sulphates and acids. Because the pozzolanic reaction uses up the Calcium Hydroxide in the cement, far fewer voids form and as a result there are fewer routes for chemicals to take into the concrete - consequently it has better resistance to chemicals such as chlorides and sulphates.
Durability testing is not yet complete, but in the meantime ECO-CEM can be used for Exposure Classification A & B as described in NZS3101.
For the same reasons that the concrete has low porosity, pozzolanic cements also have lower shrinkage performance.
Using ECO-CEM instead of regular cement on a typical house floor will save roughly 1.5T of CO₂. Afamily car produces around 4 Tonnesper year, .
Development of ECO-CEM began in 2017 and is on-going. A thorough testing and data gathering program is underway and ECO-CEM will be launched as soon as we are able.
It will be readily available in the Upper North Island but its availability could be limited in other areas due to logistical challenges - get in touch and we can discuss your needs.
Please get in touch:
Cameron Greig | Sales Director