www.sefindia.org

[sspawar]

Dear Sefians,

Minimum time for stripping out of shuttering is well described in codes and specifications.
But is there any restriction for longer time of shuttering enveloped the concrete elements like column beam slab foundation etc.
At many incidences shuttering are not removed till longer periods.
Curing of concrete will be affected or not.
If yes then what should be the limitations and norms.

Regards
S S Pawar

[vikram.jeet]

Generally rcc columns forms / rcc walls forms  are removed after 24 - 48 hrs , even slip forms are moved after final set /24 hrs and curing is done  for 14 days on concrete wrapped by Hessian cloth/gunny  bags.

In case forms are kept longer , curing is still needed . Earlier wooden forms are are heat resistant and protect concrete from direct radiation of sun(keeping forms longer could be beneficial) , but summer months still need curing . In case of steel forms , no protection from rising day temperatures and keeping forms in position , will still require Hessians cloth to be kept moist nearby to forms in position to have cooling due to evaporation from cloth . The additional arrangement to hang cloths need to be provided and to be  kept moist .

But it is seen that forms are struck early possible  by construction agencies for reuse in upper lifts /floors .

For slab  concrete , curing is effected from top thru ponding and keeping shuttering longer is immaterial .

[suraj]

Keeping forms in position for more than required time does not  pose any problem to an extent temperature of concrete vicinity is maintained, between 20 to 27 deg Celcius
As, rightly stated by other expert engineer, about when evaporation is reduced by such arrangement of no exposition of concrete to weather directly, but only exposed area be formally cured
In fact, indirectly, instead of water curing, thermal curing to some extent is effected
In higher temperature zone, water sprinkling can be done on forms itself & direct water applied on exposed surfaces
If evaporation is prevented by whatever means, it is an automatic type of thermally induced curing
Formally, on certain massive blocks, no formal water curing is permitted, but only thermal curing for a couple of days, till surface can accept application of curing compound
Steam curing is also, conducted in certain pre-casting yards
we must think beyond old specifications, included within codes & other virtually, obsolete documents
On columns & wall surfaces, water evaporation is prevented by forming a vertical membrane of curing compound wax based or water based
Moreover, when GGBS / PFA etc. being used, curing requires extended time, for it impacts on normal setting of concrete, but in long run, ultimate strength remains same

[suraj]

World
Buildings Practice Facilities Plants/Petrochemicals
Chapter 22
Project Execution Method EPC 225 MW Combined Cycle Power Project
Owner:
Project Execution Method-(Project Implementation Strategy)-Civil, Buildings & Plant Installations-An Overview
1     Document for General / Specific Directives for EPC Contractor, Subcontractors,
2     Design Engineers & Project Organisation Managers & Informative to Employer & Engineer
3     In Compliance to Article …………. EPC Contract

EPC Contractor……………………….

https://www.facebook.com/pesuraj/posts/5271973676152094 Part 01

[vikram.jeet]

Yes , very rightly reminded by Sri Suraj  saheb , the removal of shuttering time prescribed in IS 456 is for OPC , but now a days PPC is being used ,for which longer period is needed for Strickling the shuttering /scaffolding.  Strength gain is comparatively slow in PPC  , though final strength is same.