Fly ash is an important ingredient used for the production of cement-based materials like concrete, mortar, etc. One primary application of fly ash is in concrete pavement construction, where a certain percentage of cement is replaced with fly ash to provide significant economic benefits.
Its widespread application in pavement construction and embankment has gained acceptance by the Federal Highway Administration(FHWA). It is an innovative supplementary cementitious material useful for low-cost rural road construction.
This article briefly explains the significance and features of using fly ash for rigid pavement construction.
1. Introduction of Fly Ash for Concrete Pavement
The application of fly ash in concrete pavement dates back to more than 2000 years. Canada used to construct its roadways and highways using fly ash in the early ‘50s and ’60s. They were constructed in every type of climate, without any constraints.
The Federal Highway Administration promoted the application of fly ash in concrete pavements with its Notice N 5080.4 in January 1974. As per the notice, the states were allowed to perform partial substitution of fly ash for concrete pavement in feasible situations.
FHWA indicated that the replacement of cement by fly ash in the order of 10 to 25% provides concrete with equal or better strength and durability than conventional concrete.
2. Significance of Using Fly Ash in Concrete Pavement Construction
Fly ash is a useful resource rather than a waste product, considering the benefits it imparts for the strength and durability of concrete pavements. Its unique filling properties give compact concrete with improved chemical and strength gain characteristics.
The effective use of fly ash in concrete pavement construction can reduce the thermal power industry’s disposal and storage costs. It reduces the cement consumed and related carbon dioxide emissions. Hence, it facilitates the production of “green concrete,” especially for low-cost rural roads.
Few important properties of using fly ash for concrete pavement construction are explained below:
2.1 Physical Properties
The use of fly ash in concrete pavement mix helps to place the concrete at a lower slump value without altering the required workability. The mix requires less handwork for the contractor and a better surface finish.
2.2 Compressive Strength
As per FWHA, a properly proportioned quantity of fly ash can provide required compressive strength for concrete pavement. Substitution of 25% of cementitious material with fly ash can give equivalent compressive strength in all ages (7-day test, 14-day test, and 28-day test).
2.3 Denser Concrete
The use of fly ash in concrete results in denser concrete with greater ultimate strength and durability. Fly ash provides good-quality hydration products, which reduces the amount of non-hydrated cement in the concrete. It reduces the amount of air voids, making the concrete more dense and impermeable.
3. Advantages of Fly Ash in Concrete Pavement
- Fly ash concrete pavement has more resistance to sulfate attack compared to conventional concrete pavement.
- It is more resistant to freezing and thawing actions.
- The chances of an alkali-aggregate reaction are less in fly ash concrete pavement.
- Fly ash improves the compressive strength and ultimate strength of concrete.
- Compared to asphalt pavement, fly ash concrete pavement has a lower cost.
The effective use of fly ash in concrete pavement construction can reduce the thermal power industry’s disposal and storage costs. It facilitates the production of “green concrete,” especially for low-cost rural roads. It reduces the cement consumed and related carbon dioxide emissions.
1. Fly ash concrete pavement has more resistance to sulfate attack than conventional concrete pavement.
2. It is more resistant to freezing and thawing actions.
3. The chances of the alkali-aggregate reaction are less in fly ash concrete pavement.
4. Fly ash improves compressive strength and ultimate strength of concrete.
5. Compared to asphalt pavement, fly ash concrete pavement owns an initial competitive cost.
Long Term Properties of Geopolymer Concrete with Low Calcium Fly Ash