Presentation by Mustafa

Cement

Kardan UniversityUploaded By: Engr.Ahmad Sameer

- Materials other than cement, water & aggregates added to the concrete mix to modify & to improve specific properties of concrete.

ADMIXTURE

Materials used as admixtures included milk and lard by the Romans; eggs during the middle ages in Europe; polished glutinous rice paste, lacquer, tung oil, blackstrap molasses, and extracts from elm soaked in water and boiled bananas by the Chinese; and in Mesoamerica and Peru, cactus juice and latex from rubber plants. The Mayans alsoused bark extracts and other substances as set retarders to keep stucco workable for a long period of time.

History of Admixture

1.    To improve workability of fresh concrete.2.    To improve durability by entrainment of air.3.    To reduce the water required.4.    To accelerate setting & hardening to produce

high early strength 5. To aid curing. 6.     To improve water proofing property. 7.   To cause dispersion of the cement particles

when mixed with H2O.

     

PURPOSE OF ADMIXTURE?

8.   To retard setting.9.     To improve hardness .10.     To reduce shrinkage during setting & hardening.11.     To cause expansion of concrete and automatic prestressing

of steel.12.   To aerate mortar / concrete to produce a light – weight product.   13. To impart color.14.    To reduce some chemical reaction.15. To reduce bleeding.16. To reduce the evolution of heat .

        

Continued….

Chemical Admixtures

“a material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing.”

Chemical definition of Admixtures

1. Air-Entraining Admixtures2. Water-reducing admixtures 3. Retarding admixtures4. Accelerating admixtures 5. Super plasticizers6. Corrosion-inhibiting admixtures

Common Types of Chemical Admixtures

Air-entraining admixtures are used to stabilize microscopic air bubbles in concrete. Proper air-entrainment, with appropriate volume and spacing factor, will dramatically improve the durability of concrete exposed to moisture during of freezing and thawing.

Entrained air also improves concrete’s resistance to surface scaling caused by chemical deicers.

Air-Entraining Admixtures

Air-Entraining Admixtures

MB-AE™ 90 MB-AE 90 air-entraining admixture is for use in concrete mixtures. It meets the requirements of ASTM C 260, AASHTO M 154 and CRD-C 13.

Features Ready-to-use – in the proper concentration for rapid, accurate dispensing  Benefits

Improved resistance to damage, from cyclic freezing and thawing Improved resistance to scaling from, deicing salts Improved plasticity and workability Reduced permeability – increased water tightness Reduced segregation and bleeding

Air-Entraining Admixtures

Water-reducing admixtures usually reduce the required water content for a concrete mixture by about 5 to 10 percent. Consequently, concrete containing a water-reducing admixture needs less water to reach a required slump than untreated concrete. The treated concrete can have a lower water-cement ratio. This usually indicates that a higher strength concrete can be produced without increasing the amount of cement.

Water-reducing admixtures

Recent advancements in admixture technology have led to the development of Mid-range water reducers. These admixtures reduce water content by at least 8 percent and tend to be more stable over a wider range of temperatures. Mid-range water reducers provide more consistent setting times than standard water reducers.

Continued…

Water-reducers are used to increase slump of concrete without adding water and are useful for pumping concrete and in hot weather to offset the increased water demand.

Water-reducing admixtures are used to improve the quality of concrete and to obtain specified strength at lower cement content. They also improve the properties of concrete containing marginal- or low-quality aggregates and help in placing concrete under difficult conditions. Water reducers have been used primarily in bridge decks, low-slump concrete overlays, and patching concrete.

Water-reducing admixtures

SEMI CONCRETE BOND is a normal plasticizer, water reducing admixture confirming ASTM C 494. type A

FEATURES AND BENEFITS Increases workability. Lower water requirement for given workability. Easier placing, better compaction and finishing. Lower cement content for specified strength. Increases strength and durability of concrete. Higher cohesion. Reduces risk of segregation and bleeding. Improves slump and reduces permeability.

Super Plasticizers Water Reducing Admixture - Normal Plasticizer

SEMI CONCRETE BOND can be used to reduce

cement content to the extent of 8 to 10% by

maintaining the original strength specified

and workability and reducing water content required for the given mix.

Can be used in precast concrete work, Mass concrete

work , Structural R.C.C. construction , Heavy

industrial construction

TECHNICAL INFORMATION

Color: Brown

Density: 1.18+0.02 GM/c.c at 30o c.

PH: 7-8

Dose: 150 to 250 gm. / 50 kg cement

Packing: 1,5,20,50,200 liters

AREAS OF APPLICATION

Retarding admixtures, which slow the setting rate of concrete, are used to counteract the accelerating effect of hot weather on concrete setting. High temperatures often cause an increased rate of hardening which makes placing and finishing difficult. 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.

Retarders should meet the requirements for Type B or D in ASTM C 494.

Retarding admixtures

Retarding admixtures

Accelerating admixtures increase the rate of early strength development, reduce the time required for proper curing and protection, and speed up the start of finishing operations. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.

Accelerating admixtures

pozzolith® 122 HE 

Pozzolith 122 HE ready-to-use, liquid admixture is designed to make more uniform and predictable quality concrete while accelerating setting time and strength development. Pozzolith 122 HE admixture meets ASTM C 494 requirements for Type C, accelerating, and Type E, water-reducing and accelerating, admixtures.

Features

Increased early and ultimate strengths – compressive and flexural

Reduced water content required for a given workability

Accelerated setting time characteristics

Accelerating admixtures

1. Improved workability 2. Superior finishing characteristics for flatwork and

cast surfaces 3. Earlier finishing of slabs – reduced labor costs 4. Reduced protection time in cold weather 5. Earlier stripping and reuse of forms 6. Earlier structural use of concrete, as in lift-slab, tilt-

up, paving and floors 7. Easy to disperse in concrete mixtures, avoiding

many of the problems associated with flake calcium

Benefits

Super plasticizers, also known as plasticizers or high-range water reducers (HRWR), reduce water content by 12 to 30 percent and can be added to concrete with a low-to-normal slump and water-cement ratio to make high-slump flowing concrete. Flowing concrete is a highly fluid but workable concrete that can be placed with little or no vibration or compaction. The effect of super plasticizers lasts only 30 to 60 minutes, depending on the brand and dosage rate, and is followed by a rapid loss in workability. As a result of the slump loss, super plasticizers are usually added to concrete at the jobsite.

Super plasticizers

Corrosion-inhibiting admixtures fall into the specialty admixture category and are used to slow corrosion of reinforcing steel in concrete. Corrosion inhibitors can be used as a defensive strategy for concrete structures, such as marine facilities, highway bridges, and parking garages, that will be exposed to high concentrations of chloride. Other specialty admixtures include shrinkage-reducing admixtures and alkali-silica reactivity inhibitors. The shrinkage reducers are used to control drying shrinkage and minimize cracking, while ASR inhibitors control durability problems associated with alkali-silica reactivity.

Corrosion-inhibiting admixtures

Rheocrete® 222+ 

Rheocrete 222+ patented state-of-the-art corrosion-inhibiting admixture is formulated to prevent the corrosion of steel reinforced concrete. Rheocrete 222+ admixture provides two levels of corrosion protection, making it the most effective corrosion-inhibiting admixture available.

Features

Inhibited corrosion at its most critical points

Reduces the rate at which chlorides and moisture enter the concrete

Adsorbed onto the reinforcing steel to form a corrosion-resistant protective film

Corrosion-inhibiting admixtures

Extended service life of reinforced concrete structures

Premium corrosion protection by slowing the ingress of chlorides and moisture into the concrete and forming a strong, durable protective film on the reinforcing steel

Effective in cracked concrete where the elements that cause corrosion have direct access to the reinforcing steel

Increased sulfate resistance Normal set product that is easily used in

elevated temperatures

Benefits

Chemical Admixtures

-by adding to a hydraulic binder , gives very high workability and allows a large decrease in water content for a given workability.

1-enhances the hydration process      2-allows the particles to be more workable 3-prevent from segregation and bleeding. Note: commonly used superplasticizer are

napthalene based, amino sulphuric acid,poly carboxylate super plasticizer

Super plasticizer

1- Prolong/delay the setting time of cement paste in concrete2- used in hot weather to reduce any premature stiffening of the concrete & consequent loss of workability. 4- Consist of the general chemical types: Calcium, sodium, potassium, or ammonium

salts of lignosulphonic acid Hydroxyls

Retarding Admixture

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