1. Aggregate size and gradation: Mass concrete requires reasonable aggregate size and good gradation. The particle size of coarse aggregate should not be too large to reduce the internal stress concentration of concrete and improve the crack resistance. At the same time, good gradation can ensure the close accumulation of aggregate, reduce the dosage of cement and reduce the hydration heat, thus preventing the occurrence of temperature cracks.
2. Aggregate quality and silt content: Aggregate quality directly affects the strength and durability of concrete. High-quality aggregate should be strong, wear-resistant and clean. Mud content is an important index to evaluate aggregate quality. Excessive mud content will reduce the strength and durability of concrete. Therefore, the silt content of aggregate for mass concrete must be strictly controlled.
3. Alkali activity and harmful substance content of aggregate: Alkali activity refers to the ability of aggregate to react chemically with alkali in concrete. Aggregates with alkali activity may cause concrete expansion, cracking and even destruction. Therefore, aggregate with alkali activity should be avoided in mass concrete.
Relevant knowledge of aggregate
1. Types and characteristics of aggregate: Aggregate is the main component of concrete, including coarse aggregate and fine aggregate. Coarse aggregate refers to aggregate with particle size greater than 5mm, such as gravel and pebbles; Fine aggregate refers to aggregate with particle size less than 5mm, such as sand. Different types of aggregates have different physical and chemical properties, such as density, hardness and wear resistance.
2. Quality requirements of aggregate: The quality of aggregate has an important influence on the performance of concrete. Generally speaking, high-quality aggregate should have the following characteristics: uniform particles, cleanliness, firmness, no weathering, no cracks and so on. In addition, the mud content, clay content, mica content, light matter content and chloride ion content of aggregate also need to meet the requirements of relevant standards.
3. Aggregate mix design: In concrete mix design, aggregate mix is an important link. Reasonable aggregate mixture ratio can ensure that concrete has good working performance and mechanical properties. Generally speaking, when determining the concrete mixture ratio, it is necessary to comprehensively consider the concrete strength grade, construction conditions, engineering requirements and other factors, and determine the best aggregate mixture ratio through experiments.