What is a pozzolan?
Pozzolan definition, according to the American Concrete Institute [1][2]:
A pozzolan is a siliceous or siliceous and aluminous material that in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties.
A natural pozzolan is a raw or calcined pozzolan that is found in natural deposits. A material is referred to as “calcined” when it has been heated below the temperature of fusion to alter its composition or physical state. A raw pozzolan is a natural material that has pozzolanic properties, such as volcanic tuffs or pumicites […]
The benefits of using natural pozzolan for construction
There are quite a few different materials that can be a pozzolan, but not all are natural. Some pozzolan have to be fired (calcined) to become reactive, and that firing has an additional intensive energy/emissions footprint.
Amazingly, natural volcanic pozzolan is reactive without additional firing because it was calcined by Mother Nature. It does not contain the heavy metal content of fly ash, the carbon footprint of calcined pozzolans such as Metakaolin or Expanded Shale/Clay, and ours is 100% Made in USA.
The many benefits of using natural volcanic pozzolan in your hempcrete and concrete mixes:
- Enhances Compressive Strength and Durability
- Mitigates Alkali Silica Reaction (ASR)
- Reduces Heat of Hydration (especially useful for Mass Concrete)
- Resists Chloride Attack
- Resists Sulfate Attack
- Protects Steel Reinforcement
- and more
Historic use of natural volcanic pozzolan
Our American Hydraulic Lime™ is based in part on the most magnificent, long-standing structures of human history. Notably, the Roman Pantheon, still standing proud after nearly 2,000 years. The Pantheon is a marvel of engineering, as the worlds largest unreinforced (e.g. no “steel rebar”) concrete dome, at 142 feet in diameter. And the foundation of Roman concrete, was the combination of volcanic ash pozzolan and powdered, calcined (fired) limestone.
Practical applications with natural pozzolan in the mix design
- Make Hempcrete Binder by mixing natural pozzolan with hydrated lime
- Precast Concrete
- Glass Fiber Reinforced Concrete Panels (GFRC)
- Stone Veneer
- Mass Concrete
- Architectural Concrete
- Industrial & Infrastructure
- Oil Well Cementing
- Ready Mix Concrete
- Lightweight Concrete
- Decorative Concrete
- Type IP Cements and Green Cement
Bagged pozzolan for hempcrete
As described on our Hempcrete Binder product page, pozzolan is a key ingredient when making hempcrete binder. And the beautiful hempcrete projects displayed on our Gallery Page feature this natural pozzolan.
Hempcrete binders are lime based, meaning composed of a limestone product such as hydrated lime (calcium hydroxide aka slaked lime/air lime) with the addition of reactive minerals. The reactive silica and alumina minerals in natural pozzolan react with hydrated lime to form Calcium Silicate Hydrate (CSH) and CASH if you include the aluminum oxides. CSH is the bonding gel that makes concrete materials stick together. CSH is also what makes a really good hempcrete binder.
To make your own hempcrete binder, you can mix natural pozzolan with hydrated lime powder — such as Type S (Special Autoclaved) Hydrated Lime. Typical proportions for industry are to use 10-25% pozzolan by weight in the total portion of lime binder.
Example using the common mix ratio of 50 lbs. lime binder to 33 lbs. hemp hurd to make 4.5 cubic feet of hempcrete:
Instead of using 50 lbs. of pure lime, that total portion of 50 lbs. would be divided to 40 lbs. lime, 10 lbs. pozzolan (50 lbs. total, with 20% pozzolan input).
Another commonly used practice is to add the pozzolan right on top of the full 50 lbs. lime bag.
Example: 1 full 50 lbs. bag of lime + 5-10 lbs. of pozzolan addition. That 5 to 10 lbs. would be a 9%-16% addition of pozzolan in the mix.
With this approach (1) 50 lb. bag of Natural Pozzolan can be used for up to 10 hempcrete batches, costing just $3.65 per 4.5 ft3 batch for the pozzolan addition.
Questions about these natural building materials? Want to talk about placing your volume order? Contact Hemp and Block for more information.
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