What factors need to be considered in the selection of aggregates used for building mortar?

The selection of aggregates for building mortar is crucial as it directly influences the properties and performance of the mortar. Several factors need to be considered when choosing aggregates:

1. Particle Size Distribution: Aggregates should have a well-graded particle size distribution to ensure proper packing and minimize voids in the mortar mix. A balanced distribution of coarse, fine, and filler particles helps improve workability and strength.
2. Particle Shape: The shape of aggregates affects the workability, cohesiveness, and strength of the mortar. Angular or rough-surfaced aggregates provide better mechanical interlocking and improve bond strength compared to rounded or smooth-surfaced aggregates.
3. Surface Texture: The surface texture of aggregates influences the bond between the aggregate particles and the mortar matrix. Aggregates with a rough surface texture offer increased bond strength and adhesion compared to smooth-surfaced aggregates.
4. Absorption and Moisture Content: Aggregates should have low absorption to prevent excessive water absorption from the mortar mix, which can lead to reduced workability and strength. Excessive moisture content in aggregates can also cause volume changes and affect the performance of the mortar.
5. Particle Density and Specific Gravity: Aggregates with higher particle density and specific gravity contribute to denser and stronger mortar mixes. Lightweight aggregates can be used to reduce the weight of the mortar and improve thermal insulation properties.
6. Cleanliness and Contamination: Aggregates should be free from organic materials, clay, silt, dust, and other contaminants that can adversely affect the properties of the mortar. Contaminated aggregates can lead to poor bond strength, durability issues, and surface staining.
7. Durability: The durability of aggregates is essential to ensure the long-term performance of the mortar. Aggregates should be resistant to weathering, chemical attack, and freeze-thaw cycles to maintain the integrity of the mortar over time.
8. Availability and Cost: Consider the availability and cost of aggregates, especially for large-scale construction projects. Locally sourced aggregates are often preferred to minimize transportation costs and environmental impact.

By considering these factors, builders and engineers can select suitable aggregates that meet the specific requirements and performance criteria for building mortar applications.