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

The selection of aggregates for building mortar depends on several factors, including:

1. Particle size distribution: The particle size of the aggregates affects the workability, strength, and porosity of the mortar. Aggregates with a wide range of particle sizes can improve the packing density and reduce the porosity of the mortar, leading to improved strength and durability.
2. Shape and texture: The shape and texture of the aggregates affect the bonding between the mortar and the substrate. Aggregates with angular or rough surfaces can provide better interlocking and adhesion, while smooth or rounded aggregates may result in weaker bonding.
3. Density: The density of the aggregates affects the weight and volume of the mortar. Lightweight aggregates can reduce the overall weight of the structure, while high-density aggregates can increase the strength and durability of the mortar.
4. Porosity: The porosity of the aggregates affects the water-cement ratio and the drying shrinkage of the mortar. Aggregates with low porosity can reduce the water demand and drying shrinkage, leading to improved durability and reduced cracking.
5. Chemical composition: The chemical composition of the aggregates can affect the setting time, strength, and durability of the mortar. Aggregates with high levels of organic matter or sulfates can interfere with the cement hydration process and lead to reduced strength and durability.
6. Availability and cost: The availability and cost of the aggregates can vary depending on the location and demand. Local availability of aggregates can reduce transportation costs and environmental impacts, while high-quality aggregates may increase the cost of the mortar.