Aggregates are granular minerals that when mixed with portland cement concrete will result. Judging from the origin of the material, the aggregate consists of two kinds, namely aggregate natural stone and artificial aggregates. For natural rock aggregate, based on its size divided into 2 types, namely fine aggregate (sand) and coarse aggregate (gravel or kricak / crushed stone).
In the concrete, aggregates a neutral filler with 70-75% of the composition of the concrete. The purpose of the use of aggregate in the concrete mix at levels;
1 Conserve the use of portland cement.
2 Generate a large force on the concrete.
3 Reducing shrinkage in hardening concrete.
4 With a good aggregate gradation can be achieved solid concrete.
5. workable properties (workability) can be checked on the concrete with good gradation.
The nature of workable concrete mix can be cultivated by adjusting gradation of aggregate. Good aggregate gradation will result in solid concrete. The composition of solid concrete will produce a large force on the concrete. Good aggregate should be hard, strong and resilient. Strength exceeds the strength of the hardened cement paste. Aggregate containing closed pores but does not add to the nature of water penetrating the concrete. The more aggregate in the concrete decreases shrinkage of concrete in the hardening process.
1 Fine Aggregate (Sand)
The sand is soft rock material, composed of grains with a size of 0.14 to 5 mm, obtained from natural rock disintegration basil (natural sand) or by splitting (artificial sand). As the mortar material, both for the species and concrete, the fine aggregate should be checked field.
The things that can be done in the examination of fine aggregate in the field is;
a. Fine aggregate consists of particles of sharp and hard. Grains of fine aggregate must be lasting, arlinya not broken or crushed by weather influences.
b. Fine aggregate mud does not contain more than 5% (determined on dry weight). If the sludge levels exceed 5%, then the fine aggregate should be washed.
c. Fine aggregate shall not contain organic ingredients too much, it can be observed from the color of fine aggregate.
d. Aggregates from the sea should not be used as fine aggregate for all species and concrete mortar.
2 Coarse Aggregate (gravel / Stone Broken)
Coarse aggregate divided into two kinds, namely gravel (from natural rock) and kricak (from natural rocks were broken). According to its origin can be distinguished on the gravel; excavated gravel, river gravel and gravel beach. Gravel excavation baisanya contain substances such as clay, silt, sand and organic substances.
River gravels and gravel beaches are usually free of substances are mixed, smooth surface and a more rounded shape. This is due to the influence of water. Grains of coarse gravel nature will ensure better bonding mortar. Crushed stone (kricak) is a coarse aggregate obtained from broken natural stone, measuring 5-70 mm. Panggilingan / solving is usually done with a stone crusher (Jaw breaker / crusher). According to its size, gravel / kricak can be distinguished;
a. Grain size: 5-1 0 mm called gravel / kricak smooth,
b. Grain size: 10-20 mm are called gravel / kricak being,
c. Grain size: 20-40 mm are called gravel / kricak rough,
d. Grain size: 40-70 mm are called gravel / kricak rude.
e. Grain size> 70 mm are used for concrete construction Cyclops (cyclopen concreten).
In general, the meaning of coarse aggregate is aggregate with a grain size of more than 5 mm. As the concrete material, the coarse aggregate should be examined in the field. The things that can be done in the examination of fine aggregate in the field is;
a. Coarse aggregate must consist of grains of hard and non-porous.
Coarse aggregate containing flat grains can only be used, if the number of lamellar grains does not exceed 20% of the weight of the whole aggregate. Grains of coarse aggregate should be
eternal, meaning not broken or destroyed by weather influences.
b. Coarse aggregate should not be me pregnant with mud more than 1% (determined on dry weight). If the sludge levels exceed 1%, then the coarse aggregate should be washed.
c. Coarse aggregate shall not contain substances that can damage the concrete, such as substances that are relatively alkaline.
d. The maximum aggregate grain size should be no more than the fifth smallest distance between the side areas of the mold, one third of the slab thickness or 3/4 of the minimum clearances reinforcement rods.