BY Fazal Wadood Class no. 38 UET Peshawar Jalozai campus

ADMIXTURES

DEFINITION:

Need of Admixture: Retard or accelerate the time of initial setting. Increases workability To ensure the quality of concrete during mixing , transporting and placing etc

Effectiveness FACTORS EFFECTING RESULTS OF USE: Type & amount of cement: Chemistry effects due to portland components MIXING TIME: Effects of admixtures are dependent on time allowed to react.

Types Of Admixtures:

Types of chemical admixtures: Type A: water reducing Type B: Set Retarding Type C: Set accelerating Type D: water reducing + Set Retarding Type E: water reducing + Set accelerating Type F: High range water reducing Or Super plasticizers Type G: High range water reducing and retarding.

Water-Reducing Admixtures: Internal lubricant Allows for reduction of w/c ratio while maintaining workability. Can reduce water requirement at least 5-10% Obtain higher slump without adding water Dosage: 4-10 oz per cwt of cement

Retarding Admixtures: Slow curing rate Used to counteract hot weather conditions that cause increase rate of hardening. Examples of Retarders: Sugar carbohydrate derivatives Soluble zinc salt methanol etc.

Accelerating Admixtures Increase curing rate for achievement of high early strength. Used for speeding curing rate in cold weather concreting. Dosage: 16-64 oz/cwt of cement High dosages increase acceleration rate. Examples: Calcium chloride Triethanolamine

Pozzolans By Abbas Ali Class no.16

Mineral Admixtures Pozzolanic (Low-calcium FA) Cementitious (Granulated iron. blast-furnace slag) Both pozzolanic and cementitious (Hihg calcium FA) Natural materials (Volcanic Ash) By-product Material

Definition: siliceous and aluminous materials which in themselves possess little or no cementitious value but will, in finely divided form and in the presence of moisture, chemical react with Ca(OH)2 at ordinary temperatures to form compounds possessing cementitious properties.

The Pozzolanic Reaction CH+S+aq CSH Portland Cement Hydratio C3S + aq CSH + CH The pozzolanic reaction is slow, so the rate of the strength development and the heat of hydration associated with this reaction are low. It may be noted that the pozzolanic reactions can be accelerated by temperature.

Fly Ash Fly ash is a by-product of the combustion of pulverized coal in thermal power plants. The dust collection system removes the fly ash, as a fine particulate residue, from the combustion gases before they are discharged into the atmosphere

Effect on Heat of Hydration Replacement of cement by fly ash results in a reduction in the temperature rise in fresh Concrete. This is particular importance in mass concrete where cooling, following a large temperature rise, can lead to cracking.

Blast-Furnace Slag Blast furnace slag is a by-product of pig iron manufacture. When quenched rapidly with water or air to a glassy state and finely ground, it develops the property of latent hydraulicity. Blast furnace slag has chemical component similar to that of Portland cement. Due to hydraulicity, therefore, its use contributes not only to improvement in concrete performance, but also to resource and energy savings.

Hardened concrete The strength development is greatly affected by the quality and replacement ratio of blast furnace slag, and curing condition. Heat of hydration of concrete containing slag powder decreases with the increase in the slag power content. Concrete containing slag as a mineral admixtures generally offers better chemical resistance due to improved water tightness, since the concrete texture becomes dense.

Silica Fume Silica fume is an industrial by-product consisting of ultrafine particle(0.01μm). It is recovered from electric furnace by means of dust collectors from the waste gas emitted during the production of ferro-silicon metal.  Silica fume is a highly pozzolanic materials. Difficult to handle so necessary to use (high range) water-reducing admixture

Rice Husk Ash Rice husk ash is obtained by burning rice husk. Highly pozzolanic characteristic. The properties are greatly affected by the burning conditions. The large amount of unburnt carbon due to the incomplete combustion exist and make the color of rice husk ash is black, whereas, the burning is done under enough air supply condition the rice husk ash become gray and white. The white rice husk ash has better quality compared to the black rice husk ash due to the existence of carbon affecting adversely on the reactivity.

PLASTICIZER AND SUPER PLASTICIZER By Hamza Marjan CLASS NO.31

PLASTICIZER AND SUPER PLASTICIZER PLASTICIZING ACTION

PLASTICISING ACTION The action of palsticizer is mainly to fluidify the mix and improve workibility of concrete. MECHANISM; DISPERSION: Flocculation Repulsive Force:Zeta potential

Plasticizers and Super Plasticizers Plasticizers or water reducers, and superplasticizer or high range water reducers, are chemical admixtures that can be added to concrete mixtures to improve workability. The strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is added which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants.

USED Plasticizers are also often used when pozzolanic ash is added to concrete to improve strength. This method of mix proportioning is especially popular when producing high-strength concrete and fiber- reinforced concrete.

MADE OF Plasticizers are commonly manufactured from pop lignosulfonates, a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonatednaphthalene condensate or sulfonated melamine formaldehyde, although newer products based on polycarboxylic ethers are now available.

Ligno sulfonate & sulfonated milamine formaldehyde

EFFECTS Adding 1-2% plasticizer per unit weight of cement is usually sufficient. Adding an excessive amount of plasticizer will result in excessive segregation of concrete and is not advisable. Depending on the particular chemical used, use of too much plasticizer may result in a retarding effect. Fluidize the mortar or concrete. Reduces water requirment by 5-15%. Improve workability. Increase slump from 30-150 mm. May entrain air at a small percentage(1-2%). Increase concrete strength 10- 20 %. Small effect on dry shrinkage.