Concrete is the result of mixing cement, sand, coarse aggregate and water using a predetermined formula to produce an appropriate density.
The final concrete product can be batched at a central location and delivered for placement or mixed on site either in large truck drums or portable mixers.
The importance of air should be carefully considered as it tends to improve durability in certain situations and environments.
Indeed, regulatory compliance governs the specific amounts of required air content at the point of placement or pumping when used to construct and repair municipal roads and highways.
The loss of air can be controlled by slowing down the dispersing of the concrete in the pumping pressure.
The effective flow of concrete is referred to as a measure of slump.
Concrete's consistency is its ability to flow smoothly and with a predetermined speed.
The higher the slump the wetter the concrete mix.
Additional water will increase the slump and reduce the strength, durability and permeability of concrete and result in segregation of the elements.
Admixtures are water reducers and used in lieu of water to create a higher slump.
The coarse aggregates of the mix will absorb large amounts of water when being pumped.
This frequently causes blockage and can literally shut down the pump itself.
This necessitates soaking the aggregate for a long period of time to achieve a dryness effect.
Lightweight aggregate is porous with higher absorption values.
The resultant concrete is lightweight by design and weighs from 90 to 120 pounds per cubic foot.
This compares with normal concrete at 135 to 150 pounds per cubic foot.
The higher absorption value requires the aggregate to be saturated in water to minimize severe slump loss.
Block fill is used to fill voids in various masonry units.
It is either a fine or coarse grout substance and will generally pump easily.
It tends to set quickly unless the material is kept moving or turning.
Temperature plays a large part in concrete sensitivity.
Hot weather can cause difficulties in controlling the air and create premature settling.
Adding additional water to compensate can alternatively cause decreased strength and durability.
Accelerators are used to reduce the setting time and early strength of hardened concrete.
Calcium chloride is widely used in non-structural concrete.
It has been known to enhance the corrosion of reinforcing steel.
Non-chloride accelerators are used in structural concrete because they do not contribute to corrosion.
It is best to be extremely cautious when purchasing accelerating admixtures because it is common for the manufacturer not to identify whether the product contains calcium chloride or not.
Fly ash makes concrete more slippery without the addition of water.
This, then, increases the pumping action of concrete.
The small, spherical shape of fly ash is the physical characteristic that makes it useful.
Their particles range from the cement size to 20 times smaller.
The smaller size and shape improve the pumping process.