Set times of concrete

What would be the ideal set time and cure time of a quick cure concrete for marine applications? I'm not concerned with the final material properties (insufficiencies) at this point, only with general timing issues that would allow for adequate pouring and finishing.
Also, are there any concretes that can be poured into water and still cure? What is their std. set and cure time?

Thanks.

 

[ishvaaag]

Reference to marine grouts with portland cement is given in the document

ISO/CD 19902

in chapter 18

Search for this pre-standard thing as pdf document.

Construction of Prestressed Copncrete Structures
Chapter 14 Bottom Founded Concrete Sea Structures
Ben C. Gerwick Jr.
Wiley

Good on general description.

Says special curing almost never feasible.

There must be more reference in the off-shore publications or pdfs.

 

[RiBeneke]

Re your last 2 questions :
Concrete cures by reaction of cement powder with water, so all cement-based concretes will cure very well under water.
However, the mixed concrete must be prevented from being diluted by too much water and also the salt content of sea water can have undesirable effects.
Common set times are from 1 to 3 hour to produce the initial soft gel, and cure times are from 5 to 10 days to reach 50% of designated strength, depending on conditions.

 

[kay]

Joe,
For some materials on set/cure times see BS 8110,Structural Use of Concrete, one of the Appendices at the end.
Set and cure times are also reflected in minimum times required before striking the form work.

There is a requirement especially for marine structures to prevent the ingress of water during the hydration process, hence the use of water tight materials for shuttering, and blinding concrete for a foundation structural base.

 

Please forgive me as in, as I learn, I also am able to better phrase the questions:

Although RiBeneke listed TYPICAL set times as 1-3 hours, what would be IDEAL (Christmas-wish-list) set times and cure times to achieve (first) some initial integrity and (then) the 50% designated strength.

I know this sounds strange, but what if there was an additive that:
1) sped up the initial set time without detrimental long-term effects on structural integrity;
2) acted as an osmotic barrier to slow and regulate the hydration process so as to not dilute the concrete;
3) prevent salt infultration into the cement;

Basically, a form would be sunk, the concrete mixture would be poured into it, displacing the water (no need for isolating the form and pumping water out first), and setting would take place within XXX time, allowing the forms to be stripped. Final curing would occur in YYY time. The questions are, what is the XXX and YYY times that would be desirable?

 

[poki]

I reckon that the initial setting time for ordinary protland cement (time required for complete hydration of cement with evolution of heat) is 50minutes. The time required for hardening (final seeting time) is 10hours.

 

[kieran1]

you could look at the publication Concrete in Maritime works by the cement & concrete association
ISBN 0 7210 1235 3
It says admixtures are seldom required in maritime works, although water-reducing mixtures are sometimes helpful to aid placing and compaction and that there is no problems with curing times although works may be governed by tidal waters
Kieran
BEng(hons),CEng, M.I.Struct.E, M.I.E.I.

 

[RiBeneke]

I do not think that it would normally be desirable to reduce the initial setting time as this would create placing problems.
There are additives and variations on cement type and mix design that will reduce curing (strength gain) time.
I suggest you log on to the concrete engineering forum in eng-tips and read the many posts there.

 

[maniskov]

Joe M,

Your question can have many ideal answers depending on location of works and the scope of the work. With significant water flows, or wave action for example, a fast set is desirable, but must accomodate concrete batching, loading, delivery and offloading time. In many of our cases, delivery time is a crucial element.

The YYY time at which forms can be stripped I think is not of great concern because re-use of materials is limited to the forms alone (ie. there is no re-use of sheet pile cofferdams, pumping equipment, etc), further substructure work could commence with the footing forms left in place (ie. pier shafts), and there is not significant savings to be had here by stripping the forms quickly if this is a project where there are say, four or more locations to be worked on. Stripping non-floating forms (not wood!) would be done by divers likely, and would add significantly to the cost. Assess whether it is cheaper to leave the forms in place if they can remain securely fastened--perhaps stainless steel form ties.

There are cementitious products available for underwater works, though used mainly in patching type work. In a concrete pour of large volume with especially rapid set, be wary of "burning" the concrete by heat resulting from the hydration process. My experience says not to exceed concrete temperatures of 70C or the concrete strengths after both initial cure, and at 28 days will be less than required. Cool waters may aid in maintaining the proper temperature. One underwater product is from CPD at

http://www.cpd.ca

and is called CPD Aquacrete. Similar products are Fastcrete, Redcrete, etc and have variable working life times.