Concrete questions

Focus2005

Hi all
Mind if I ask you these questions please.. which I have been wondering about, for example:
1) if the concrete mix ends up too dry how can you improve workability? (cannot add water!! or it changes water/cement ratio)
2)what should one do if its starts raining whilst casting a concrete slab or beam?
3)can you cast a concrete slab or beam in 2 or 3 phases? i think not due to the joint created does not allow 1 monolithic cast
4) how would you know if the concrete has reached the desired strength?
5) what to do if a lot of aggregate appears on the surface?

thanks!!
Philip

pipeguy

I'm not sure whay you mean by "winds up" too dry. If you mean it sets up in the form beyond the point of being workable then the answer is there is nothiong you can do to improve workability if casting water on it is not acceptable.
Plasticizers and superplasticizers may be added to a mix, prior to placement in the form, to improve workability. A ready-mix supplier is a good source of information about these 'add mixtures'.

Providing for such a contingency beforehand is the first step. If rain is encountered then implement the concrete's protection from the weather and complete the finishing process allowing for a proper construction joint if additional pours are required to complete the work.


An engineer can best tell you if a 'cold joint' is allowable in your particular design. It's my experience that joints are frequently found in slabs and rarely (if at all) found in beams. Beams are frequently precast monolithically and hoisted into place by crane.


A testing laboratory can prepare 'cylinder samples' during the pouring process for the purpose of conducting periodic testing to determine the properties of the particular concree batch as it ages (7 day, 14 day, etc.) To determine the properties of the concrete that is actually poured int the forms, one can coredrill samples from the in place concrete and have them tested.


aggregate will only appear if it is improperly finished. If this happens then you likely have a concrete that is substandard throughout (not just at the surface) due to a high water to cement ratio.