Concrete Mix Adjustments for Surface Water

[S28]

Given the attached information...

If asked the volume of coarse aggregate for batch #3....

Wouldn't this be found by:

WCA x (1+SSD Moisture Content) = 146 x (1+.008) = 147.168 (Adjusted SSD Weight)

Volume = (147.168 lbs) / (62.4 x 2.65) = 0.89 CF.

The answer in the book uses a different equation, but I think the book makes the mistake of thinking the coarse aggregate is wet, when it is clearly labeled "dry"...

I just want to make sure I'm not completely missing something here with adjusting CA/FAs.

ConcMix.pdf

 

[desantmf]

S28, Where did you get that equation from? I am sorry but I am not sure how to solve this problem with the information given. I am interested in other peoples comments too. I don't think a question like that will be on the exam though.

Also I don't think you are right either since you are dividing by the SSD SG not the Dry SG.

 

[S28]

It came from passpe.com's Construction Engineering for Civil PE License Practice Problems Book (By Dr. Mansour). The more I look at some of these questions, I think they have alot of errors in the concrete mix problems, as well as many other portions of this book. Now that I went and looked at the other concrete mix questions, he has two equations he lists to get wet or dry aggregates to SSD Condition.

If the material is dry, he lists WSSD = WDRY(1+SSD moisture content)

If the material is wet, he lists WSSD = [Wwet/(1+Moisture content)] x (1+SSD moisture content)

In the problem I asked about, they give you the dry weight of the coarse aggregate, so you have to adjust it and make it so it is SSD before you can go ahead and calculate the volume. So I think the way I wrote it above makes sense, I thinkt he book just used the wrong formula for that specific problem I asked about.