a- What are the main differences between plasticizers and superplasticizers? b- What is pozzolanic material; what benefits can be achieved by using Pozzolana with cement in concrete?

 

Q#

a-      What are the main differences between plasticizers and superplasticizers?                                  

b-      What is pozzolanic material; what benefits can be achieved by using Pozzolana with cement in concrete?                                                                                                                                  

 

Solution#

Answer A

Plasticizer super plasticizer

Both are different things Plasticizers are the chemicals used to increase plasticity or fluidity of a material they are added to. For example moulding clay.
Superplasticizers(water reducers) are the chemicals used in concrete to increase its usability or workability for example less water should be used to make stronger concrete but this affects its workability because it makes concrete difficult to mix now since strength is inversely proportional to the amount of water added,thereby for this purpose both plasticizers and superplastizers are used which makes the concrete much efficient.

 

Plasticizer

1.      A plasticizer is an additive used to improve the plasticity of a certain substance.

2. Increase the plasticity of polymer materials such as PVC & as a water reducer in concrete admixtures.

3. Also called water reducers.

4. Can reduce the need for water by 5-15%

5. Added 0.1 – 0.5% by weight of cement

6. Plasticizers are usually based on lignosulphonate, which is a natural polymer

Superplasticizer

 

1.  Superplasticizer is a water-reducing admixture capable of producing large water reduction or great flowability without causing undue set retardation or entrainment of air in mortar or concrete.

2. Further increase the water requirement for concrete mixtures, increasing the strength & durability of concrete.

3. Also called high range water reducers.

 

pozzolanic material

 

   A pozzolan is a siliceous or siliceous and aluminous material that in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties.

 

what benefits can be achieved by using Pozzolana with cement in concrete?                     

Pozzolanic reaction begins immediately after hydration of cement and continues for a long time thereby increasing strength. Concrete attained its maximum strength at a pozzolana replacement of 30%; corresponding to an increase of 19% in the 28-day strength compared to the control concrete. Similarly, the 7-day, 14-day, and 21-day compressive strengths respectively show increases of 3%, 11% and 24% compared to the compressive strength of the control concrete 

Concrete derives its strength from the pozzolanic reaction between silica in pozzolana and the calcium hydroxide liberated during the hydration of OPC. At low percentages of replacement, the quantity of silica is low, therefore, only a limited quantity of C-S-H can be formed, though a large quantity of calcium hydroxide is liberated due to the relatively large quantity of portland cement. However, at high percentage replacement, the quantity of pozzolana in the mix increases. C-S-H formed reduces due to liberation of a small quantity of calcium hydroxide from the hydration of the relatively small quantity of portland cement available. The strength of concrete at both low and high percentage replacement is therefore low. An optimum level of replacement exists at which compressive strength is the highest. It can also be concluded that the strength of concrete depends on the relative proportions of silica in pozzolana and ordinary portland cement available.

CONCLUSION

At the end of the study, the following conclusions are drawn:\• Replacement of cement with pozzolana significantly increased the strength of concrete

• Replacement of 30% of the mass of cement with pozzolana achieved the maximum value of compressive strength.

• The 7-day, 14-day,21-day and 28-day compressive strengths at 30% replacement respectively showed increases of 3%, 11%,24% and 19% compared to the compressive strength of the control concrete at those ages

• Increase in pozzolana replacement decreased the workability of concrete