Cement is one of the most used construction materials today. Construction without cement is no longer imaginable, although several alternative materials have been introduced.
Higher cement content in concrete can lead to high heat of hydration, higher construction cost, formation of ettringite due to increased heat in the concrete core, etc. For this reason, fly ash was introduced as a substitute for concrete.
Fly ash replacement is limited to a maximum of 35% and offers more advantages than disadvantages. Most of the time, an increase in the time to reach strength is observed and, at the same time, a significant reduction in the heat of hydration of the cement when higher quality concrete is used.
As it is a material added to concrete or mixed with cement, the quality of fly ash must be checked. To ensure material consistency, frequent testing must be performed in accordance with regulations or project specifications.
Test and Limit Values: Physical Properties
| Test/Units | Specification in accordance with BS EN 450-1:2012 |
| Fineness /% | Category N: must not exceed 40% and must not deviate from the specified values by more than ±10 percentage points. Category S: must not exceed 12% |
| Particle density / kg/ m3 | It cannot deviate by more than 200 kg/m 3 from the value specified by the manufacturer. |
| Force /mm | Should not be greater than 10 mm |
| Activity index / %28 days90 days | Not less than 75, not less than 85 |
Test and limit values: Chemical properties
| Test/Units | Specification in accordance with BS EN 450-1:2012 |
| Loss of ignition/% by mass | Cannot be greater than 5.0 |
| Silicon dioxide (SiO 2 ) /% by weight | The sum of the contents cannot be less than 70 |
| Aluminum oxide (Al 2 Ó 3 ) /% by weight | The sum of the contents cannot be less than 70 |
| Iron oxide (Fe 2 Ó 3 )/% by weight | The sum of the contents cannot be less than 70 |
| Total calcium oxide (CaO*)/% by mass | – |
| Chloride content (Cl – ) / % by weight | Should not be more than 0.10 |
| Total alkaline equivalent as Na 2 O/mass% | Must not exceed 5.0 |
| Sulfate (SO 3 ) / % by weight | Cannot be greater than 3.0 |
Note: If the total calcium oxide content does not exceed 10% by mass, the reactive calcium oxide requirement is considered met.
