How can "cast-in-place" concrete be precast?

Question

How can "cast-in-place" concrete be precast? That don't make sense to me, but my teacher said I got it wrong on the exam. He says that "cast-in-place" concrete can be precast. Can someone explain this to me?

Answer 1

your teacher must be dreaming.. the terms are obviously in opposition to each other.

give him/her some coffee.

Answer 2

Actually I don't think you all should be so quick to judge the teacher.  I don't believe that the teacher was suggesting the two forms of construction had any chance of being substituted for each other, that would just be goofy.  After all, by definition, cast in place cures on the job site, precast cures elsewhere.

I am thinking that the teacher was trying to get the students to look into the reasons why one form is chosen over the other.  In other words, maybe the question could have been asked this way, "When can precast design be substituted for cast-in-place design?" or "When can a precast cross-section work as well as a cast-in-place section?"

I am believing this is what he was after.  If not, then I guess he is a knucklehead after all.

Answer 3

I agree.  Ask your teacher to explain the difference (This I gotta hear. :-) ) and please post the answer.

Precast concrete is an ancient type of construction material made with concrete cast in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place.

Cast-in-place concrete is transported in an unhardened state, primarily as ready-mix, and placed in forms. Ready mixed concrete is proportioned and mixed off the project site. The concrete is delivered to the site in a truck agitator (often incorrectly called a “cement truck”) but can also be delivered in a non-agitating truck. Specialized paving equipment may be used to mix and spread concrete for pavement.

Now I understand why Frank Loyd Wright built "Fallingwater" without reinforcing steel. (and it is crumbling as a result of that failure to understand Structural Engineering)  Your teacher needs to go back and take more Structures.

Cast-in-place means that the object cast stays at the exact spot where it was poured.  As soon as you move it it is "Pre-cast."  It cannot be both.  Project specifications must be un-ambigious.  If the specs say that a wall is to be cast-in-place, then the contractor is to build the forms and pour the wall in the exact location where the wall is to be.  If he chooses to build molds and make or buy pre-cast wall sections without the Project Engineer or Project Manager's approval, he can be required to tear the work down and do it over.  The two fabrication methods are NOT the same, NOT interchangeable, and the final results are NOT the same.