Concrete Admixtures
Concrete Admixtures are those ingredients or additives (other than aggregates, cement, water) added to the concrete during the time of mixing to enhance or alter its mechanical and material properties. The desired characteristics such as high workability, high compressive strength, setting time, and durability parameters can be altered by the addition of admixtures.
Admixtures are selected according to the site conditions and desired strength characteristics that are to be achieved. When concreting in special circumstances such as freezing environmental conditions, hot weather, increased wear or exposure to salts or chemicals, admixtures are helpful.
Types of Concrete Admixtures
In the following section, I’ve tried to briefly cover major concrete admixtures used in Construction Industry and especially in India. The approximate cost and indicative dosage of concrete admixtures are also discussed. However, these dosages must be confirmed with the admixture supplier specifications and instruction. Incorrect dosage or admixtures can lead to strength loss and undesired outcomes. Detailed information about admixtures are available here.
Air-entraining admixtures
These admixtures are generally used in concrete to achieve good workability, increased durability in freeze-thaw and alkali reactive environment, and reduce bleeding. The admixture entertains air bubbles inside the concrete and hence helps to achieve these desired qualities. Salts of wood resins, some synthetic detergents, teepol, salts of petroleum acids, and sulfonated lignin are commonly used air-entraining admixtures.
Dosage: The dosage rates of Air-entraining admixtures can vary from 16-131ml/100kg of cementitious material. (The mentioned dosage is an approximate value. Field tests should be required to find the exact value of admixtures for concrete.)
Price: 30/- per kg (As per current Indian market. Price may changes according to time and locations)
Water reducing admixture
These admixtures used to reduce the water content needed in concrete. The water-cement ratio can considerably reduce for concrete of given consistency. Lingnin sulfonic and metallic salts are commonly used water-reducing admixtures.
Dosage: The dosage varies from 88.5-354ml/ 45 kg of cementitious materials used.
Price: 75/- per kg
Superplasticizers
The addition superplasticizers can reduce 20% – 30% of water requirement for concrete. This will not affect the workability of concrete. Superplasticizers also used to make flowing concrete with a sump of 175mm to 200mm which can effectively use in high dense reinforced structures. Lignosulfonates, polycarboxylates, sulphonated malanie- formaldehyde condensates (SMF), sulponated naphthalene- formaldehyde condensates (SMF) are commonly used superplasticizers.
Dosage: Typical dosage of superplasticizers taken by 0.7-1% of weight by cement. This may changes according to the site condition and required strength of concrete.
Price: 105/- per kg
Accelerating admixture
Accelerating admixtures are used to gain an early setting of concrete and early strength development. This admixture is commonly used for the concreting in cold weather conditions. Calcium chloride is the most common accelerator in concrete, but it causes corrosion in steel reinforcement. Calcium formate, calcium nitrite, calcium nitrate are also used as accelerators.
Dosage: Normally varies from 520- 2080ml/100kg of cementitious material. Dosage can change according to the site conditions
Price: 71/- per kg
Retarding Concrete admixtures
Retarders are added to increase the setting time of concrete. Some retarding admixtures also act as water reducers. These admixtures are helpful when concrete has to be transported to a long distance by mixers and concreting at high temperatures. Lignin, Borax, Sugars, Sodium and ammonia salts, oxides of lead, zinc, phosphate are the retarders commonly used.
Dosage: 128ml/100kg of cementitious materials are typically taken.
Price: 3500/- per barrel (1 barrel= 50kg)
Hydration control admixtures
Hydration control admixtures slow down the hydration process and also reduce slump loss and air loss. In other words, these are advanced set retarders. Carboxylic acid, phosphorus-containing organic acid salts are used as hydration control admixtures.
Dosage: For normal application, 130-520ml/100kg of cementitious materials is preferred. For longer periods, the dosage can be increased.
Price: 452/- per liter. (changes applicable)
Corrosion inhibitors
Corrosion inhibitors used to prevent the risk of corrosion in steel bars in a chloride rich environment. This admixture slows down corrosion by increasing anodic or cathodic polarization behavior. Calcium nitrite, sodium nitrite, sodium benzoate are used as corrosion inhibitor.
Dosage: Usually taken 10-25L/m3 of concrete.
Price: 450/- per 4 litre
Shrinkage reducers
Used to reduce the drying shrinkage in concrete. This admixture blocks the capillary pore water(by forming crystals inside the capillaries) which is the major cause of drying shrinkage.
Dosage: Recommended dosage is 1-2.5% by weight of cementitious materials.
Price: 45/- per kg
Alkali silica reactivity inhibitor
This is used to reduce alkali aggregate reactivity expansion. The alkali silica reaction commonly called as concrete cancer and it leads to swelling. Barium salts, lithium nitrate, lithium carbonate, lithium hydroxide are used as alkali silica reactivity inhibitors.
Dosage: As per the experiments conducted, a dosage over 10% by weight of cementitious materials is effective in preventing Alkali silica reactivity.
Price: 800/- kg
Alkali-Silica reaction (www.youtube.com/civil engineering)
Coloring Concrete admixtures
Coloring admixtures are added to get various shades of colored concrete. Colored concrete is adopted for an aesthetic or uniform appearance. Modified carbon black, iron oxide, chromium oxide, titanium oxide, cobalt blue, etc. are some coloring admixtures.
Dosage: Dosage is estimated according to intensity of color needed and site condition.
Price: 130/- per kg
Anti-washout admixtures
This admixture is used in underwater concrete construction. Anti washout admixtures make concrete cohesive and prevent washout of cement and fines when placed in water. Cellulose, acrylic polymer are often used as anti washout admixtures.
Dosage: The recommended is 07- 1L/100kg of cementitious materials. It may varies according to the concrete strength required and site condition.
Price: 150/- per kg
Waterproofing Concrete Admixtures
Waterproof admixtures used to prevent the water penetration to the hardened concrete which later causes chemical attacks and corrosion to steel reinforcement. The admixture creates small crystal particles, which later fills up the pores in concrete. Chemical admixtures like silicate soda, aluminum and zinc sulphates, aluminum and calcium chloride are used as waterproofing admixtures.
Dosage: 256-328ml/525kg of cementitious materials is commonly preferred. (May changes according to the site conditions)
Price: 640/- per Litre
Miscellaneous admixtures like Pozzolanic admixtures, grouting admixtures, bonding admixtures, gas forming admixtures are also used.
*Dosage mentioned here can changes according to site condition and strength requirements of the concrete.
Concrete Admixture Suppliers and Market in India
As per the report in “India Naphthalene and PCE based Admixtures Market Forecast and opportunities 2019”, the growth achieved by the Indian admixtures market during 2014- 19 is CAGR of 12%. BASF, FOSROC India, SIKA India are the major manufacturers and distributors in India and holds around 60% of the market.
The construction industry in India is growing faster. The vertical construction and infrastructure development created a positive impact on admixture demand (especially in superplasticizers and retarders) and supply. This also because of the increase in demand for ready mix concrete too. For the next five years, an annual growth of 20% is expected in the consumption of ready-mix concrete in India.
The admixtures market likely to cross a turnover of $683 million by the end of 2021 (The current impact of the pandemic situation may affect this growth). So the demand for admixtures is likely to increase in the coming years.