Discuss NCARB PDD Exam Topic 2 Question 5

Which of the following admixtures is used to greatly increase the slump of concrete?

AAir-entraining agent

BWater-reducing agent

CCalcium chloride

DSuperplasticizer

Suggested Answer: D

Comprehensive Detailed Explanation with all NCARB ARE 5.0 Project Development and Documentation (PDD) Study Guide Reference:

In concrete technology, admixtures are used to modify properties of fresh or hardened concrete:

Air-entraining agents: Introduce microscopic air bubbles to improve freeze-thaw resistance; they do not increase slump.

Water-reducing agents: Reduce water content while maintaining slump; increase workability but only moderately.

Calcium chloride: An accelerator, speeds up setting time; does not increase slump.

Superplasticizers (also called high-range water reducers): Significantly increase the slump (workability) of concrete without adding extra water, making the mix more flowable and easier to place.

Thus, to greatly increase slump while maintaining water-cement ratio, the superplasticizer is the correct choice.

Supporting Reference:

NCARB ARE 5.0 Review Manual, Materials and Assemblies section

Portland Cement Association publications on admixtures

ACI (American Concrete Institute) guidelines on admixtures

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14 comments · newest first

Herman 10 months ago

Air-entraining agents are for air, not slump!

Lashandra 10 months ago

Superplasticizer is the way to go!

Marylyn 10 months ago

Definitely D) Superplasticizer!

Anisha 10 months ago

I thought it was B) Water-reducing agent?

Lavina 10 months ago

Wait, are you sure about that? Sounds too good to be true.

Jestine 11 months ago

I feel like calcium chloride is more about accelerating curing, not really about increasing slump. So, I’d lean towards D as well.

Jovita 11 months ago

I’m a bit confused. I know air-entraining agents are for freeze-thaw resistance, but I can't recall how they affect slump.

Mozell 11 months ago

I remember practicing a question about admixtures, and I think water-reducing agents also help with slump, but not as much as superplasticizers.

Shannon 11 months ago

I think the answer might be D) Superplasticizer, but I'm not entirely sure. We talked about it in class.

Markus 12 months ago

D) Superplasticizer, for sure. That's the admixture designed to increase the workability and slump of concrete without adding more water. I'm confident that's the right answer here.

Nguyet 12 months ago

I'm a bit confused on this one. I know the different admixtures have different effects, but I can't quite recall which one is used to boost the slump. I'll have to review my notes before answering.

Tamekia 12 months ago

Okay, let me walk through this step-by-step. Superplasticizers are high-range water reducers that can dramatically increase the slump of concrete without adding more water. That's the key thing I remember from my concrete materials course. So I'm pretty sure the answer is D.

Lazaro 1 year ago

Hmm, I'm not totally sure about this one. I know air-entraining agents and water-reducers can affect concrete properties, but I'm not confident which one specifically increases the slump. I'll have to think this through carefully.

Winifred 1 year ago

I think the answer is D) Superplasticizer. That's the one that's used to increase the slump of concrete, right?

NCARB PDD Exam - Topic 2 Question 5 Discussion