Vladimir,

If we have a job in which curing is specified to be done by “Fog Curing” and we have a lot of concrete and a limited amount of Fog Curing equipment then our pours can be limited by the availability of this resource.

Curing is an activity that must start almost immediately after concrete pouring, usually starts before the end of big pours. Therefore, the link between concrete pouring and curing must be a “strong link”.

Take a look at the following schedules:

1. The first schedule screen is from a sample job before leveling.
2. The second is from a leveled schedule without using strong links.
3. The third is from a leveled schedule using strong links. In Spider Project Strong Link option prohibits increasing lag between activities in resource constrained scheduling.

I believe this was one of the wishes from our friend David Kelly, a very relevant wish. Spider Project got a solution that yields a workable solution that in occasions can be near optimal or even optimal but in others will not. Seems like a very complicated resource-leveling issue that the more activities you add to the train it becomes exponentially more difficult to solve, maybe a compromise to limit the model to two continuous activities will help to solve most of the issues (a single strong link per activity) very close to optimal.

Although not used frequently "strong links" are very useful functionality when you need it, I would like to see this functionality also on logic links.

Because we do not use fog curing here I do not need to resource load the curing activity, as a matter of fact we use a FS lag for these purposes even when not considered to be a "good practice" by many, here even people out of the construction business know concrete must be cured and need no further explanation for the lag when they look at the schedule. With Spider Project this is even easier as we can define the lag calendar to be Calendar days while preceding and succeeding activities use other calendars of their own while other software complicate such simple thing.

Regards,

Rafael

You can define that activity as a "Level of Effort" activity.

Valdimir,

To reinforce my comments check this scenarios;

Scenario 1:

For Car park Slab ; there is no superstructure on it . with the curing the activity is completed.

Scenario 2:

For Ground floor Slab; the continuous curing for 7 days must start immediately after concrete casted & wait till ground slab to take load of form works for 1st floor. You will definitely have Zero Float for this.

Scenario 3:

If you make concrete cube sample casted on site & make curing with the structure in actual condition , and you tested the cube in 3 or 4 or 5 or 6 days as proof of sufficient concrete strength was gained at site to stop curing then & go to next activity (which is the best practice specially for precast slabs, still can be used to other areas of concrete )

Scenario 4:

Don't show the curing activity separately just say 'Concrete Casting & Curing' as one activity & make sure successor activity based on this will have lag 7 days. Hope this is very simple Not a Problem of Float.

Rizwan.

Valdimir,

To understand CASTING OF CONCRETE-FS-CURING ACTIVITY link, you better have an idea about Concrete Technology & Practice.

Technology says; 

After concrete poured in place, it will start setting withing 3 hours of time (initial setting) & finish setting by 10 hours.

you must start curing immediately after initial setting time of concrete finished.

 

Practice is;

If slab this is possible, but for columns & walls its already covered so you can cure only top part which is very small area.

Concrete will gain more than 66% of strength in seven days & 100% of strength in 28 days. As long as the concrete can take (3 to 7 days) enough strength the form work can be removed & the start curing immediately.

So, in case of wall if you say curing for seven days it will consume total 10 days if you wait for striking form works in columns after 3 days. so, leaving form works in column also is one type of curing as it not allowing to dry columns.

So the FS is correct irrelevant to other activities for ASTING OF CONCRETE-FS-CURING ACTIVITY link.

Rizwan.

Kumar
If you really need zero float on curing you need to date constrain and in my mind this flys directly in the face of good planning
Clive

Kumar,

I hope I understand your querry correctly:

P3 is set to Early Start for activities thus curing commences the day after you pour your concrete (in P3). Using FS from pour/cast -> cure -> de-shutter(strip forms) -> waterproofing etc. would give cure the same Total Float as cast/pour (assuming no other influencing links in this sequence) - do you agree with this so far?

Now if deshutter has, say 100days float, then curing will also have at least that much float (depending on how soon you plan to deshutter) So if deshutter starts on Day 8 (7-day cure) then "curing" would also have 100 days float, if there is a delay in de-shutter, then "curing" would have even more float --- correct?

So is your point that: since curing by nature occurs once concrete is mixed/set/poured (unless you freeze it) you want to show it curing with zero float???

If the preceding is a correct interpretation, then I (unfortunately) do not have a great solution to your issue.

However, I don’t agree that this 100 day float on curing is incorrect. Based on the successors, the curing would not technically NEED to finish any differently than the free-float and total-float would indicate in P3. Though, by nature, it would finish much earlier. Also, if you are using early dates in P3 (as most of the world wuold) then your timing for the cure would always be correct as well.

Why do you find it neccessary to show TF=0 on curing? When I have done P3 work on concrete jobs I have usually added an FS lag (1 to 4 weeks depending on concrete strength requirements for successors) after the cast/place activities. If someone wanted to see a curing activity I added one, but we didn’t get hung up on the float. The curing would always be after the pour/cast.

Doing winter concrete work in northern climates at times requires testing with maturity meters or breaking of cast cylinders/cubes to determine when formwork/shuttering, removing shoring supports and loading activities can commence and thus the duration may not be fixed either. I know of one project in Canada where concrete froze in a bridge deck pour. This delayed further activities by months and the curing did not continue until the concrete temperature was raised above 10 degrees centigrade again. I’d sure be glad to have float in that situation.

I’m not sure if this has been any help, but I hope I interpreted your question correctly. Could you explain the importance of showing TF=0 for curing?

Cheers,

Charles H

Hello,

What kind of thread is this? Kumar, the float should be the same.

How it comes different was due to the logic and network of the succesors activities that you done which we dont have access in the first place.

The onus is with you to make sure that the float should be the same, hence, you need to re-visit what have you done in your logic, predecessor-successor realtionship.

Regards,

Charlie

If casting and curing have a FS relationship, they should have the same float. The only two possibilities which could cause the float to differ are:

• a disjoint between working calendars (ie. between the casting task and the curing task’s successor - assuming that curing is a 24 hour calendar)
• the casting task has some other successors with a lessor float path than the curing task

Either way, I really don’t see what the problem is. The early start, early finish and float should all be calculated correctly given the defined parameters. Any additional hours on the curing task’s float (beyond the casting task’s float) should not impact the critical path should the casting task be delayed to it’s late start.

Stacy
Project Management Knowledge Base

The time for concrete to cure (or paint to dry or fibreglass to go off) is not an activity/task at all because it is not something which someone or something has to do, is it? It is the time between the end of pouring concrete and the earliest that we can begin to strip formwork. It’s lag on the FS link between pouring and stripping.