The aggregate is a component in the mortar with the largest dosage and the lowest cost. It has relatively good volume stability and high strength. Some aggregates also have good thermal insulation properties. The performance of aggregate can affect the effects of other components. Therefore, the rational use and giving full play to aggregate are of important significance to improve the performance of mortar and reduce the cost.
The aggregate has the following roles:
- . Role of framework
The aggregate typically has relatively high strength. These high-strength particles can play the role of framework in the hardened mortar. When the mortar is under stress, the aggregate often bears greater load. Therefore, the mechanical property of aggregate has a greater effect on the mechanical property of mortar.
(2) Role of stabilizing volume deformation
In the hardening process of mortar, the aggregate is generally not involved in chemical reactions and will not produce a change in the volume resulting from chemical reactions. The main component that produces shrinkage in the hardened mortar is the cement component. The dry shrinkage of aggregate is relatively small and can limit the shrinkage of cement stone. In addition, the thermal expansion coefficient of aggregate is lower than that of hardened cement stone, so its thermal stability is better than that of cement stone.
- Improving the durability of mortar
The aggregate has better adaptability to environmental conditions. Under the condition of freeze-thaw cycles, the cement stone usually gets damaged, while the aggregate rarely gets damaged. Under the condition of sulfate attack, the cement stone also gets damaged, and the aggregate rarely gets damaged. But some aggregates can react with the alkali, causing damage to the material or structure. However, for most non-reactive aggregates, this reaction won’t occur.
- Affecting the performance of mortar
The performance of aggregate can have an impact on the water requirement, mechanical properties, dry shrinkage performance and temperature deformation properties of mortar.
The dry shrinkage and temperature deformation are the main reasons for the cracking of mortar. When the aggregate gradation is inappropriate, the greater voidage and smaller fineness modulus will increase the water requirement of mortar and cause the decrease in the mortar strength, or increase the shrinkage and temperature deformation of mortar and result in the decrease of crack resistance. Therefore, the rational design of cement-sand ratio and adjustment of aggregate gradation can improve the performance of mortar.
- Thermal insulation
Some lightweight aggregates such as polystyrene particles, expanded perlite and expanded rainbow stone, have a thermal insulation effect. They are commonly used for the formulation of thermal insulation mortar.
Some colored aggregates have decorative effects, and compared with the pigment, has the following characteristics: 1) various colors, aggregates of different colors are mixed together, colorful and not intermingled; 2) permanency of colors.
- Reducing costs
In the constituent materials of mortar, the aggregate is the cheapest. Giving full play to aggregates can effectively reduce the cost of mortar.