In Construction, What Is Aggregate?

Also known as "aggregate". Granular material that acts as a skeleton and a filler in concrete and mortar. There are two types of fine aggregate and coarse aggregate. The diameter of the fine aggregate particles is between 0.16 and 5 mm. Generally, natural sand is used, such as river sand, sea sand, and valley sand. When natural sand is lacking, artificial sand can also be ground by hard rocks. The diameter of coarse aggregate particles is greater than 5 mm. Gravel and pebble are commonly used Under the same conditions, the strength of crushed stone concrete is higher than that of pebble concrete, but crushed stone is crushed from rock and the cost is higher than that of pebble. Coarse aggregates commonly used in lightweight aggregate concrete include natural porous rocks such as pumice, and artificial porous aggregates such as ceramsite and expanded slag. ^[1]

Aggregates with a particle size greater than 4.75 mm are called coarse aggregates, commonly known as stones. There are two types of gravel and pebble. Crushed stone is made of natural rock or rock by mechanical crushing and sieving, and the particle size is larger than 4.75 mm. Pebble is a rock particle with a particle size greater than 4.75 mm formed by natural weathering, water transport and sorting, and accumulation. Pebble and crushed stone particles are longer than the average particle size of the corresponding particle size of 2.4 times the needle-like particles; thickness less than 0.4 times the average particle size is flaky particles (average particle size refers to the upper and lower limit of the size Diameter). Construction pebbles and crushed stones should meet the technical requirements of the national standard GB / T 14685-2001 "Construction Pebbles and Crushed Stones".

Aggregates with a particle size of less than 4.75 mm are called fine aggregates and are commonly called sand. Sand is divided into natural sand and artificial sand according to the source of production. Natural sand is rock particles with a particle size of less than 4.75 mm formed by natural weathering, water transport, sorting, and accumulation, but does not include particles of soft rocks and weathered rocks. Natural sand includes river sand, lake sand, mountain sand, and desalinated sea sand. Artificial sand is a collective name for machine-made sand and mixed sand treated with soil removal.

Fine aggregate

1. The fine aggregate should be hard, clean and well graded; the fineness modulus of artificial sand should be in the range of 2.4 to 2.8, and the fineness modulus of natural sand should be in the range of 2.2 to 3.0. The use of mountain sand, coarse sand, corresponding experimental demonstration should be taken.

2. During the mining process, fine aggregates shall be tested for alkali activity regularly or according to a certain amount of mining. During periods of potential harm, corresponding measures shall be taken and verified by special tests.

3. The moisture content of the fine aggregate should be kept stable, and the moisture content of the artificial sand saturated surface should not exceed 6%. If necessary, accelerated dehydration measures should be taken.

Aggregate, as the main raw material in concrete, plays a skeleton and supporting role in buildings. During mixing, the cement becomes thin when mixed with water. If no aggregate is added, it will not be formed and will not be usable. Therefore, aggregate is a very important raw material in construction.