Natural Pozzolans in Concrete: Pozzolans can be combined with Portland cement to create blended cements that can be used in place of pure Portland cement in building materials such as concrete and bricks.
Natural pozzolans are used in a variety of civil engineering applications, including structural concrete, precast and prestressed components.
The article discusses the advantages of using natural pozzolans in these applications.
Table of Contents
What are natural pozzolans?
A pozzolan is a siliceous substance with negligible cementitious properties on its own. When finely divided and exposed to moisture, it reacts with portlandite [Ca(OH)2] to primarily produce calcium silicate hydrate. It can be used in concrete mixtures in place of cement. Today, the most frequently used natural pozzolans in concrete applications are calcined clay, calcined shale, and metakaolin. Among the other natural pozzolans that are less often used in modern applications are volcanic ash and rice husk ash.
Natural pozzolans are derived from mineral and volcanic occurrences. While some minerals, such as clay or shale, need heat treatment to become pozzolans, others, such as volcanic ash, show pozzolanic activity with little processing.
Applications of Natural Pozzolans in Concrete
1. Concrete for Structural Purposes
Natural pozzolans are used in concrete structures either as cement substitute materials or at a defined rate of addition.
Natural pozzolans boost the plastic properties of concrete, increase the mixture’s cohesion and workability, thus reducing segregation and facilitating convergence, decreasing permeability, and increasing longevity.
2. Concrete Elements That Have Been Precast and Prestressed
Natural pozzolans aid in the development of high strength at early ages and durability in precast/prestressed concrete components. These are critical criteria when precast and prestressed concrete components are used in the design of bridges, homes, and parking garages.
The high initial strength enables the formwork to be removed quickly. However, structures exposed to mild to extreme conditions need a high degree of durability.
Precast and prestressed concrete structures are typically exposed to mild to extreme conditions. Extreme reactivity Metakaolin is a naturally occurring pozzolan that is used in the manufacture of precast and prestressed concrete units.
3. Massive Concrete Elements
Nowadays, concrete used to construct large dams includes natural pozzolans.
It decreases the amount of heat generated during hydration, thus reducing the thermal stresses inside the concrete that may lead to the development of cracking.
Additionally, it enhances sulfate tolerance and reduces the possibility of alkali-silica reactions expanding.
4. Pipes made of concrete
The application of a natural pozzolan in the production of concrete pipe has a number of advantages. It conserves cement while maintaining the workability needed for pipe manufacturing.
Natural pozzolans increase the unit weight of concrete pipes while decreasing their permeability.
Finally, the reduced heat hydration of natural pozzolan-containing concrete results in a low probability of hairline crack growth.
5. Masonry Units made of concrete
To manufacture concrete masonry units, natural pozzolans are used. It increases the plasticity and cohesion of the concrete used in the manufacture of masonry units, thus aiding in its compaction. Since natural pozzolans degrade the toughness of concrete, they inhibit forming of salt efflorescence on concrete brick units.
6. Low-strength Materials
Ordinary Portland cement, water, natural pozzolan and sand are combined to create a managed low-strength fill content that can be used in place of compacted soil. Compaction is not needed to accomplish the required unit weight and load-bearing capability.
The managed low-strength materials are primarily used to replace compacted granular materials in situations where the setting up and subsequent settlement may be problematic.
Moreover, low strength materials have been used to backfill trenches, pipe bedding, and foundation sub-bases, etc.
7. Mortar and Grout
Natural pozzolans are used in grouts to improve workability, reduce hydration heat, reduce alkali-silica reaction expansion, reduce permeability, and improve sulfate resistance, among other benefits.
Natural pozzolans can have an effect on the bonding strength, setting time, and other critical characteristics of mortar.
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