vaporation rate of concrete surface 1

[SPR Baker]

hello Everyone
why we need calculate the evaporation rate of surface ? when we know it what will we do at site? (attachment file)
thank you

 

[Ron]

The evaporation rate is critical to controlling plastic shrinkage cracking, which often connects to full depth cracking of the concrete. These cracks occur before control joints can be cut.

Evaporation also affects surface curing which can lead to scaling and dusting....conditions you do not want in a floor slab.

 

[SPR Baker]

Ron after we know that w=0.88kg/m^2/hr, what do we do at site?

 

[r13]

SPR,

 

[r13]

SPR,

Note that, IMO, the evaporation rate is most important during initial setting stage, in which the concrete temperature is very high due to heat of hydration, and the difference between the concrete and the air temperature is huge. Without proper measures and care, the result will be as indicated by Ron.

Evaluation of evaporation rate is very important during concrete curing period as well.

 

[SlideRuleEra]

When we know it what will we do at site?

Appendix A, is extracted from ACI 305.1 Hot Weather Concreting. Per other paragraphs of ACI 305.1 take the following steps:

These steps are good requirements and should be followed... however, note that there are no enforceable time limits or other conditions specified.

The following are my opinions:

For a qualified Contractor, calculating the evaporation rate is a worthless, academic exercise, for the following reasons:

1) It is in a Contractor's best interests to place and finish concrete "as quickly as conditions will permit." (Saves labor costs)

2) Attempts to "control concrete surface bleed-water evaporation" during concrete placement tend to slow down placement and finishing. This contradicts Item 1, because...

...using proper planning, there are measures a Contractor can take to minimize evaporation. Examples are:
Use cold water or even 100% shaved ice for concrete mix.
Use large-scale water sprinklers (for cooling) on stockpiles of aggregate well before concrete mixing takes place.
Start concrete placement in early morning or even at night (Usually cooler air temperatures).

3) If concrete curing has been properly specified in the bid documents/contract, the Contractor has included money to comply. In that case, getting concrete curing started quickly and correctly is in the Contractor's best interest (Minimize labor costs).

The intent of proper curing is to reduce moisture loss, by evaporation and otherwise, to essentially zero (0.00).

http://www.SlideRuleEra.net

 

[Ron]

@SPR Baker.....put up wind breaks and keep the surface of the concrete wet

 

[SPR Baker]

Thank you all
Ron it means when curing stage we watered the concrete more than w=0.88kg/m^2/hr ? Right?