Which retarder used in concrete?
10.2. 2.2 Set Retarders
|Field of application
|Gelatin, casein, gum arabic
|PSI, PASP (0.01–1 wt%)
|PSI (0.05–1.0 wt%)
Which is commonly used retarder?
Some commonly used retards are: Organic retardants include unrefined calcium, sodium, NH4, salts of lignosulfonic acids, hydrocarboxylic acids, and carbohydrates. Inorganic retardants include oxides of lead and zinc, phosphates, magnesium salts, Calcium Sulphate, Gypsum, fluorates and borates.
Why retarders are used in concrete?
Retarders for concrete are used to delay the initial setting time of the concrete upto an hour. They are generally used in the hot weather condition to counter the rapid hardening due to high temperature, thus allowing the time for mixing, transporting and placing.
Can you put too much retarder in concrete?
Also, if too much retarder is added to concrete used for a slab it can lead to crusting, where the surface sets but the concrete below is still soft. This can really reduce your flatness and even lead to delamination of the surface.
How is concrete admixture calculated?
MIX CALCULATION :
- Volume of concrete = 1m^3.
- Volume of cement = (373/3.15)x1/1000 = 0.118 m^3.
- Volume of water = ( 149/1)x1/1000= 0.149 m^3.
- Volume of admixture = ( 7.6/1.145)x1/1000 = 0.006.
- Volume of coarse aggregate and fine aggregate = a – ( b + c + d) = 1-( 0.118 + 0.149 + 0.006 )= 0.727 m^3.
What can be added to concrete to make it set slower?
Water reducers, retarders, and superplasticizers are admixtures for concrete, which are added in order to reduce the water content in a mixture or to slow the setting rate of the concrete while retaining the flowing properties of a concrete mixture.
What is cement retarder?
1. n. [Well Completions] A chemical agent used to increase the thickening time of cement slurries to enable proper placement.
How does retarder affect concrete?
Retarding admixtures, which slow the setting rate of concrete, are used to counteract the accelerating effect of hot weather on concrete setting. Retarders keep concrete workable during placement and delay the initial set of concrete. Most retarders also function as water reducers and may entrain some air in concrete.
Is the most commonly used in concrete?
The most commonly used mix is cement, aggregates and water in the proportion 1:2:4. The density of this concrete is between 2200 and 2500 kg/cubic metre, whereas its compressive strength is in the range of 200 to 500 kg/square centimetres.
Why are admixtures used in concrete?
Air Entraining Admixture. These are generally used to improve workability,ease of placing,increased durability,better resistance to frost action and reduction in bleeding.
Which admixture increase the strength of concrete?
Water-reducing admixtures are called “plasticising admixtures” when they are used to increase the consistence or workability of concrete. When the water-cement ratio is low in concrete, this leads to greater compressive strength. Water-reducing admixtures allows the concrete strength to be increased whilst maintaining workability.
What is a retarder for concrete?
Retarders for concrete are used to delay the initial setting time of the concrete upto an hour. They are generally used in the hot weather condition to counter the rapid hardening due to high temperature, thus allowing the time for mixing, transporting and placing. Retarders also acts as water reducers.
What is the percentage of admixture in concrete?
Gas forming admixtures are also used to prepare light weight concrete. For settlement and bleeding resistance purpose, small quantity of gas forming admixtures which is generally 0.5 to 2% by weight of cement is used. But for making light weight concrete larger quantity generally 100 grams per bag of cement is recommended.