Jushak Rahman Chukkan’s Post

I encountered a similar issue on a project, and I resolved it by deviating from the specifications, submitting supporting calculations and references, which were ultimately accepted.

Please make sure the lifting strength is achieved in first 12 to 14 hrs . If the object is lifted without any damage then please proceed. No need to wait for 72 hrs. The middle east ambinent temp (where the actual object is casted ) is high which will help us to accelerate the strenght and we should take benefit of it. Its contradicting that the cubes are kept at 20 to 21 degree curing where as the objecti is cured at ambinet temp of 35 to 45 degree.

Delayed demoulding always delay the whole process which eventually affects the site progress. What I encountered that some consultants can’t differentiate between cast at site and precast units and they are treating same like cast at site structures . In this case i think we normally have meetings with the consultant and try to convince them that we can avoid this as we are complying specifications in terms of strength, finish , color etc

We faced a similar situation with a huge client. Long story short what we did is: 1. Proved early strength was sufficient for demoulding - by QC & design calcs 2. Wrote contractual letters claiming EOT as the 72hrs is nowhere mentioned in the project specs (they were in a hurry) 3. Offered to water cure the elements post demoulding for 7 days (up from 3 days) After nearly 1-2 months of struggle, got it approved. Design was on-going in parallel so this didn’t impact the schedule much. End of the day if the client wants it, he wants it… they just have to pay for the prolongation (EOT) Good luck!

Hii Sir, It is very true that delay in demoulding will affect execution of the project, it will increase utilization of casting area and so on. I have been part of projects with similar conditions. Specification demands lifting of elements only after attaining strength of 30MPa which will take around 3 days (may vary depending on various factors including climate), removal of side shutters after 36hrs etc. What we did is we tried to convince the client to follow our standard i.e. demoulding immediately after attaining 10MPa and lifting after 15-18MPa, highlighting the cost impact if we need to go with the specification. Some clients will accept but some are very particular to stick with the specifications without any deviation. I think for the case you mentioned, specification will be for cast in situ concrete where the elements should be ready to take up loads after deshuttering which will not be the case for precast elements.

The 72-hour demolding requirement seems excessive for non-prestressed precast elements, especially when typical practice is to demold after reaching sufficient strength, like 13.8 MPa, in 10 to 14 hours. Some possible reasons for this could be: • Overly conservative specifications. • Special environmental conditions requiring longer curing times. • Extra caution for durability or load handling.

It could also be a conservative approach to ensure quality and safety. To manage this situation, it is advisable to discuss with the project engineer or client to understand the rationale behind the specification and explore potential adjustments based on technical data and industry standards like PCI MNL 116

We have faced similar challenges with several projects in the UAE and Qatar. A classic example was the Dubai Expo project. During the project, we sat across the table with the consultant, architect, and project management consultant to ensure informed decisions were made. To gain a comprehensive understanding of our solutions, we demonstrated mock-up production. This involved showcasing the demolding of precast elements after reaching the required strength, typically between 10 to 14 hours. The final step in demonstrating our capabilities was the actual installation of the precast elements. Additionally, we conducted joint inspections at the factory stock-yard and on-site. The specification and compliance statement was submitted in accordance with the manufacturers guidelines, accompanied by supporting documents. One of the projects we were working on recently in Saudi Arabia had similar challenges. The precast manufacturer also went through the same exercise.

It is a common deliberation between the precast manufacturer and the end user (client). With respect to project specification the client has the right to implement of what it seems is written. As a precast manufacturer we have the lieu to demonstrate our own standard practice in line with the PCI standard. The following are the essential steps to convince the client about the early stripping criteria. 1. Submit substantial design calculation considering the capacity of lifting anchor againts the weight of precast elements. 2. Conduct initial assessment of stripping strength based on a certain time interval, ie starting after 10, 12,14 hrs depending on the weather condition. 3. Demonstrate the actual testing of cube specimen once you had established the time where as the desired stripping strength can be achieved. 4. Apply steam curing if possible. 5. Qualify early stripping in your submitted production program. Yet there are several client which doesn’t respect the PCI standard practice. But it is a matter of how are you going to convince them in a technical way.

I believe we should: Submit the reference of the MNL to the consultant. Submit a letter of undertaking that the required strength has been achieved. Provide evidence of the sample test results. That should help in convincing the Engineer to waive the specifications requirement.