Concrete admixture- concrete admixture refers to an ingredient other than water, cement and aggregate that when added to concrete will change its properties depending on the user needs.
There are five major categories of concrete admixtures:
- Water reducing admixtures
- Retarding admixtures
- Accelerating admixtures
- Super plasticizers
- Corrosion inhibiting admixture
WATER REDUCING ADMIXTURES:
This admixture is useful when one requires a higher strength concrete with less amount of water used during its formation. This type of admixture tends to reduce the water cement ratio by about 5% to 10%. They also improve the concretes plastic (wet) and hardened properties.
RETARDING ADMIXTURES
Slows down the setting of concrete, mainly used to counteract the accelerating effect of the hot humid temperature that increases setting of the concrete. They delay the setting of the cement and have little or no effect. Retarding plasticizing admixtures not only delay the setting of the cement but are also efficient plasticizing water-reducers. Most commercially available retarders are of this type
ACCELERATING ADMIXTURE:
Mainly used to increase the rate of early strength developments while reducing the time period for curing, they also function by increasing either the rate of stiffening or setting of the concrete or the rate of hardening and early strength gain to allow earlier form work striking and demoulding. Most accelerators achieve one rather than both of these functions. Hardening accelerators are most effective at low temperature. Accelerators can be used with super plasticisers where early age strength is required, especially at lower temperatures. Concrete containing an accelerator will set faster than the equivalent plain concrete. The reduction in setting time is typically 1–2 hours but is affected by accelerator type, dose and temperature.
SUPER PLASTICISERS
Also known as High-range water reducers (HRWR), When used properly, they can increase the strength of the concrete and provide greatly increased workability without adding more water. HRWR are commonly used to produce flowing, self-consolidating, or high-performance concrete. They should reduce the water requirement by at least 12%—with ACI reporting possible reductions as high as 30%—and meet the requirements of ASTM C 494 for Type F and G water-reducing admixtures or ASTM C 1017. While the effects are often less with low- and mid range water reducers, super plasticizers' uses in different types of concrete projects demonstrate the important role of water-reducing admixtures.Super plasticizers can be effective, for example, when making high-strength concrete (6000 psi or more) and are added to mixes with water-cement ratios below 0.35 to ensure control of the water and again in the field for placing purposes. HRWR's effect of early strength gain in concrete and easy placement has been recognized by the pre-cast industry. They are also commonly found in self-consolidating concrete. Added to architectural concrete mixes, they increase the concrete's workability and prevent bug holes.
CORROSION INHIBITING ADMIXTURE
Corrosion-inhibiting admixtures can significantly reduce maintenance costs of reinforced concrete structures throughout a typical service life of 30 to 40 years. Although corrosion-inhibitors can raise the corrosion threshold, they are not an alternative to impermeable durable concrete.
Corrosion-inhibiting admixtures have little effect on strength at either early or later ages. The function of this type of admixture is to enhance the long term durability of reinforced concrete by enhancing passivation to the cathodic and/or anodize areas of embedded steel. Structures built in the 1970s with calcium nitrite still contain the original level of nitrite and show no signs of deterioration. The addition of corrosion-inhibiting admixtures based on calcium nitrite or amino alcohol does not affect the long-term durability of the base concrete but can offer extended life to the overall structure.
At East African Flooring we guarantee our clients for the best supplies and services.
we are also experts in identifying the best admixture for your concrete.
feel free to reach to us on:
telephone:0202001038
mobile:0774299636
email:info@eastafricanflooring.co.ke
website:www.eastafricanflooring.co.ke
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