Civil Engineering - Concrete Technology - Discussion

The incorrect statement is **Admixtures give high strength**.

Here's why:

*Admixtures:* These are materials added to concrete *during mixing* to modify its properties.

*How Admixtures Work:* Admixtures primarily affect the *workability*, *setting time*, *durability*, and other characteristics of concrete. They don't directly "give" high strength in the sense of fundamentally changing the cement's inherent strength potential.

*Indirect Strength Effects:* Some admixtures, like water reducers, can *indirectly* lead to higher strength by allowing for a lower water-cement ratio. A lower water-cement ratio generally results in stronger concrete. However, the admixture itself isn't providing the strength; it's facilitating a mixed design that allows for higher strength development from the cement.

The other statements are generally true:

*Admixtures accelerate hydration:* Accelerators speed up the chemical reactions of cement hydration, leading to a faster setting and early strength gain.
*Admixtures make concrete waterproof:* Some admixtures, like waterproofing admixtures, reduce the permeability of concrete, making it more resistant to water penetration.
*Admixtures make concrete acid-proof:* Certain admixtures can improve concrete's resistance to chemical attack, including some acids.

Therefore, while admixtures can *influence* strength indirectly, they don't directly "give" high strength. The primary strength of concrete still comes from the cement hydration process.

Admixtures can have an effect on the hydration of concrete, but typically they do not increase hydration.

Admixtures reduced the water contents and it give strength for the structure. It also accelerate or retired hydration. Therefore the correct answer is E.

Functions of Admixtures.

-Retard or reduce heat generation during early hardening.

-Accelerate the rate of strength development.

-Increase the strength of concrete or mortar (Compressive, tensile, or flexural). This function is conducted mainly water-reducing and retarding admixtures, high range water reducing admixtuers.

-Reduce scaling caused by deicing salts.

-Increase resistance to freezing and thawing such as air entrainment admixture.

-Decrease the capillary flow of water.

-Decrease the permeability to liquids for instance high range water reducing admixtures.

-Control the expansion caused by the reaction of alkalis with certain aggregate constituents, such as Lithium admixtures.

-Produce cellular concrete.

-Increase the bond of concrete to steel reinforcement. High range water reducing and Bonding admixtuers.

-Increase the bond between old and new concrete such as Bonding admixture.

-Improve impact resistance and abrasion resistance.

-Inhibit the corrosion of embedded metal which is play by Corrosion-inhibiting admixtures.

-Produce colored concrete or mortar.

-Reduce drying shrinkage and curling which is performed by Shrinkage-reducing admixtures.

So what makes setting faster?

As per my knowledge, markplast admixture causes the rapid setting and gaining strength and super plasticize the concrete.

Option D is the right answer. Please explain me.

Admixture may affect the acceleration or retardation effects in scence of setting time (having any form or shape) rather than hydration (gaining strength).

Yes, B is the correct answer.

D is the correct answer. No any admixture gives strength. Its only used for initial purposes.

Many chemical admixtures are known to retard cement hydration.