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Old Posted Dec 5, 2010, 6:48 AM
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South end of 1.15 raft

Looking down through 11 layes of 32mm bar in 1.15

Insisde the raft 1.15. Notice the carry bar is under the standee supports!

The other direction


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New update by Loony: a world record

World Trade Center Raft Foundation Pour

By Loony, on December 3rd, 2010

After months of digging, chipping, waterproofing, casting of blinding slabs and walls and placing rebar, the big day was finally here. December 1st would be the day the big pour would go. The estimated volume was 16,000 meters. The largest continuous raft ever done was 16,000 cubic meters at the Landmark Hotel in Abu Dabi in 2009. We were hoping to surpass that number if even by 1 meter! In any event, it has been very exciting for me to have been involved in the process of executing this monster placement.

What we look for:
While on site, I focus my attention in several areas:

Watch for a continuous flow of concrete to each pump.
Make sure the concrete flows properly and does not segregate. Segregation occurs when the aggregate is separated from the paste of the mix.
Monitor consolidation by vibration to make sure the crews are paying attention to all areas equally and not over vibrating.
Watch the concrete in areas that are not close to the pump hose. Those areas can dry out and begin to set which is a cold joint, or bleed water may start coming to the top. The bleed water is ok in small amounts but when we get excessive amounts, we need to figure out why. We want the concrete to set just way it was delivered.
We are also interested in temperature monitoring. The contractor placed multiple probes in the raft to allow for periodic verification of the concrete temperature during placement and after. The concrete during curing should stay under 70c with upper tolerance of possibly 75c.
We are also interested in the testing and sampling stations. They must do the tests correctly and maintain proper records.


The Pour:
The pour was scheduled to begin at 10 pm. A prepour meeting would be held at 8pm for final coordination. The players involved in the placement were as follows:

Dar Al Riyadh…………………………………………… Site Supervision Consultant
Saudi Binladin Group…………………………………. General Contractor
Saudi Readimix………………………………………… Concrete and pump supplier
Al Bustan………………………………………………… Concrete and pump supplier
Premco…………………………………………………… Concrete and pump supplier

There were 10 pumps setup and deployed on three sides of the project. Five pumps from Saudi Readimix on the East side, 3 from Al Bustan on the North side and 2 from Premco on the West side reaching in from the cut and cover tunnel that will loop the Financial District.

The goal was to supply about 80 cubic meters (about 102 cubic yards) per hour to each pump. Some pumps would allow for two trucks to back up and discharge side by side while others would only have room for one truck at a time. The concrete mix design is a flowable mix that is nearly self-consolidating but would require minimal consolidation by using vibrators. Holes were cut through the raft top layers of steel at 7 to 10 meter intervals to allow for the pump hoses to be lowered to near the top of the bottom layers of reinforcing. Rolls of plastic were placed on top of the raft to keep concrete from collecting and drying on top of the raft. All very good planning and preparation.

Testing of the concrete would be done at stations setup above the hole next to the entry ramp on the Northeast side and also on the West side. Trucks that were to be tested would be directed to stop at the testing station and samples would be taken to test slump spread and to cast sample cylinders before sending the truck to the site.

Placement began on schedule at 10:00 pm. Trucks began rolling down the ramp into the hole and were directed by a flagger toward their respective pumps. The trucks here are impressive. In the states, trucks are limited in size and weight by Department of Transportation (DOT) rules. Concrete trucks in the states have typically 10 or 11 cubic yard capacity (7.6 M3 or 8.4M3). The restrictions are due to the weight of the concrete and the number of tires the trucks have to put on the ground to spread out the load. Normal weight concrete weighs about 150 lbs/cuft on average which is approximately 4000 lbs. A cubic meter of normal weight concrete weighs in at about 5200 lbs (about 2400 kg). The trucks here have a capacity of either 10 or 12 cubic meters. That is about 13 cubic yards and about 15.6 cubic yards respectively. As you can see, the numbers add up pretty quickly. Trucks with loads of that size would find themselves over the limit and subject to fines in the states unless they had enough wheels on the ground and were long enough to spread the load.

For our purposes here, the larger capacity trucks are quite nice and greatly enhance the speed of delivery. Saudi Readimix and Al Bustan both have batch plants just across the street in the zone 6 area. Premco has a plant a bit down the road but the distance did not seem to hinder their ability to deliver.

I stayed on site all of the first night and watched the bottom of the raft being covered. The concrete looked good and the supply was never ending. Trucks were lined up all the way from the bottom of the Financial District hole to the top and at times, down the street. I would walk back to our office occasionally but the distance is about 1 km each way and the safety boots I wear on site are not exactly of the high mileage variety and they are quite heavy. I do this on a regular basis during the course of a normal day but it is very tiring and a little nerve racking when you have weave your way through a bunch of concrete trucks backing up or driving out. I usually made my way out the west side so I had to carefully walk past the truck and trailer dump trucks hauling loads of rock out of a nearby hole that is being chipped 24 hours a day. All this is not to mention the dust. I pretty much always wear a dust mask and did so when walking to and from the office.

At midnight dinner was served in the SBG site office complex. I had been walking the site with Joe, the project manager for DAR, so we both walked up to get some food. We were quite surprised to find a rather formal affair with servers and a large platter of food in the middle of both tables. Attending the dinner were VIP’s from SBG. I knew one of the gentlemen at the table but not the others. I was asked to join at the table with the VIP’s and was introduced to the Saudi gentlemen there. One of them is a member of the Binladin family, a sheik in fact. I was quite impressed. After the meal, the group and I went to the site to show the VIP’s’ the raft and observe the pour. We took pictures on the raft and they all headed out. All in all a very interesting evening I thought.

I stayed on site until about 5 am before heading back to our office to rest a bit. I had to figure out how to turn the AC units into heaters as I was getting cold. The temperature had dipped down into the low 50’s at this point. I took about a 1 hour nap on the couch then got up and waited for Mohammed to deliver Mark to the site so I could get a ride back home.

I took a nap for a few hours at home then had Mohammed take me back to the site when he brought the Meinhardt folks home from work. I joined Joe again and we walked the site then went back to the office and waited for lunch to be brought in. Lunch was served in the conference room and consisted of shawarma sandwiches. Very good. I stayed a while before calling it a day and had Mohammed drive me home. Things were looking pretty good at this point and the concrete supply was continuing nonstop.

In the end, a total of 16,200 cubic meters ( 21,188 cubic yards) of concrete was placed. This surpasses the Abu Dabi Landmark hotel for the world’s record. Now is our time to enjoy bragging rights and all the fame and fortune that goes with it (Not!) For me, sleep and a day off would be fine.

What was in it for me? I felt a lot of energy surge inside me when my research showed that this would at least match the biggest ever done. I don’t know if this is something that I would say was on my bucket list but it is now and it has been checked off. If you participate in this line or work, monitoring large scale construction, you have to have a passion for it. You have to find things like concrete and steel entertaining and even awe inspiring. You measure yourself against the project and see just how far into the thing you can go. I feel like I went pretty far this time. I could leave Saudi now satisfied that I did something worthwhile after all the sweat and all the miles of walking and climbing up and down in the dust and heat.

The future here for me is, at least for now, short term. I leave Saudi on the 15th to go home in time to meet my new baby girl early next month. I will keep blogging until then but after that, well If I return in a couple months I will take it up again.

All set

Getting Closer

Plastic being laid down on the top of the raft to protect it from concrete spills

All ready on the western front

Here we go!

Testing to do too!

Close to midnight and going strong.

The next day and still going strong

Almost to the top

Temperature probes

Shift change

Looking Northwest at sundown

Trucks and pumps still going

The Saudi Readimix side

Blogger Mo proves that he was there (Loony)

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