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Basic Facts/Info

Regular concrete

Regular concrete is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 1450 psi to about 5800 psi, depending on the purpose, ranging from blinding to structural concrete respectively. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

Typically, a batch of concrete can be made by using 1 part Portland cement, 2 parts dry sand, 3 parts dry stone, 1/2 part water. The parts are in terms of weight – not volume. For example, 1-cubic-foot (0.028 m³) of concrete would be made using 22 lb (10.0 kg) cement, 10 lb (4.5 kg) water, 41 lb (19 kg) dry sand, 70 lb (32 kg) dry stone (1/2" to 3/4" stone). This would make 1-cubic-foot (0.028 m³) of concrete and would weigh about 143 lb (65 kg). The sand should be mortar or brick sand (washed and filtered if possible) and the stone should be washed if possible. Organic materials (leaves, twigs, etc) should be removed from the sand and stone to ensure the highest strength.

High-strength concrete

High-strength concrete has a compressive strength generally greater than 6,000 pounds per square inch 5800 psi. High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.

Precast
 
Precast concrete is concrete cast elsewhere than its final position. Precast construction can be used to produce a wide variety of structural elements such as wall panels, bridge girders, pipes, poles, crash barriers, lift stations, etc. The concrete can be reinforced, lightly prestressed or prestressed depending upon its requirements. Precast concrete elements are typically transported from the plant to the job site through highways, rail, or barges. Tilt-up concrete is a form of precast concrete and is generally referred to as site precasting.

Tilt-Up
 
Tilt-Up construction is "a construction technique of casting concrete elements in a horizontal position at the jobsite and then tilting and lifting the panels to their final position in a structure". The greatest advantage of tilt-up construction over cast-in-place concrete is the ease and speed of construction. Generally the concrete should attain a high early age flexural strength to facilitate lifting and handling. Tilt-up concrete is a form of precast concrete and is generally referred to as site precasting.

Flowable Fill
 
Flowable also known as constrolled low-strength material (CLSM) is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. The compressive strengths must be lower than 1200 psi and often is lower than 200 psi. Since the material flows into place no compaction is required which is a significant advantage over compacted back fill. Flowable fill can be made with very high amounts of non-standard materials.