Concrete Pad in Iraq 4

[IraqEngineer]

I'm working on putting a Scope of Work together to construct a 450'x70'concrete pad with overhead cover in Iraq. This pad will need to hold up to having 10K Fork Lifts driving on it on a regular basis. I'm trying to get some information on how thick it should be, the PSI rating, and the slump? I appreciate the help.

 

[Ron]

The thickness will depend, to some degree, on the subgrade support soils. The design needs to support your forklift traffic in a fully loaded condition. Design for the front wheel loads of the forklift and check for the back wheels. The counterweight condition can sometimes prevail.

Make sure the control joints are cut into the slab the same day as placement. I would use a minimum compressive strength of 4000 psi. This will afford reasonable durability and strength to resist the loads. Use the largest coarse aggregate you can practicably use, preferably at least No. 57 stone, but larger if you can. I would keep the slump below 5 inches and the water-cement ratio in the 0.45 to 0.50 range..no higher.

When you do the analysis, you'll likely find that the thickness will be in the 7 to 9 inch range. A thickness of 8 inches will likely be serviceable for the conditions you noted, assuming reasonable subgrade support.

Wet cure the concrete and use hot weather placement procedures (assuming it will placed in the summer in a hot climate).

Consider using dowels for load transfer at the joints. This will make the slab more serviceable and require less maintenance. You can use round dowels, plate dowel baskets, or other proprietary systems.

The Portland Cement Association(PCA) design procedures can be used or you can use an elastic layer analysis approach. The PCA and ACI both have good publications for concrete slabs on grade, including pavement slabs.

 

[concretemasonry]

Make sure you are aware of the capabilities of the ready-mix plan regarding admixtures and controls.

From my experience some plants are reliable if the systems and aggregates have have been maintained. With any new facilities, the history must be evaluated.

the front end wheels in a critically loaded condition with virtually no load on the rear should be considered. Impact and turning is based on the anticipated operations, especially in a repeated operation.

Moist cure is the only viable method even if you might see the cold evening temperatures that do not directly relate to the concrete temperatures, but the humidity will be be low.

dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

IraqEngineer...Dick raises some significant points. Check those. This is not as easy as just forming and "pouring" concrete. It requires a concerted design process.

Thanks, Dick...good points.

Ron

 

[Zambo]

Is it really only 70' wide - it seems narrow only about 20m compared to over 140m long.

I would aim to pour it in 3 sections each about 45 x 20m. This would have to be checked with the batching plant and also whether pumps are available.

What is a 10K forklift, what load can it carry?

 

[IraqEngineer]

Thanks for all the information. I used the 10K forklift as the standard just because that will be the heaviest equipment that's used on the pad. The 10K just refers to the lift capacity but the actual forklift is over 20,000 lbs. The reason the pad is the size it is has more to do with the space we have to utilize more than anything else. The big issue here is that in our desire to put money back into the local economy we have to contract out these projects to local companies. Time and time again I'm reminded that the construction standards here pale in comparison to those in the States.

 

[dik]

My $.02...

I would deep the slump below 4" and preferably 3". Water:Cement ratio about 0.4 max and sawcutting within about 6 or 8 hours after finishing, even if cutting into the night. As soon as the concrete is hard enough to work. If available, consider using a sofcut type of saw. A good slab requires good quality control at the batch plant... the recommendation on history of operations is critical.

Dik

 

[BarryEng]

I will not comment on the structural issues, but as far as concrete quality is concerned, you may be interested in a joint publication of CIRIA & the Concrete Society: -

Guide to the construction of reinforced concrete in the Arabian peninsular
CIRIA publication C577
Concrete Society special publication CS136
ISBN 0 946691 93 4
232 p, 2002 (original was 1985 I think)

I have found the principles in this book very useful to me because I design many structures in a similar environment (but 35 deg south).

 

[concretemasonry]

The two biggest concerns of the job are not the design of the slab and jointing.

They are 1) Quality of the plants producing the concrete and 2) the quality of the aggregates available. The following is a bit of clarification depending on what I have seen in developing or re-developing countries. Much depends on the particular area of Iraq.

1. You could encounter a wide range of quality and quality control depending on the location and age of the facilities. In the major metropolitan areas you count encounter some very new high-tech plants and some very old and traditional limited plants. In the more remote areas, you could encounter almost any level of older plants unless there is a new plant supplied from the U.S. or Germany IF there is some spomsored rebuilding. The newer plants are what you would find in any western or developed middle esat country, but they may too new for there to be a reliable developed history of uniformity. It is important to know where the concrete will come from since there can be some political or military reasons.

2. The aggregate is a major problem. You specifications for aggregate may be meaningless if there are not the deposits OR the processing procedures and equipment to produce the aggregate. Just like new ready mix plants, the processing equipment can be flown in easily, but the aggregate desposit and the processing methods cannot be relocated. You may specify a specific aggregate, but it may be several hundred miles away and difficult to ship because of the roads, accessibility and distance. The specified aggregate could cost $100 to $200 per ton delivered to the site (I have seen this in Africa). After the logistics are established, I would concentrate on the soundness of the aggregate because of the temperature variations in part of the country. The most common problem will be be cleanliness and dust in the aggregate because of the reliance on water for washing/processing. If you are processing near a river, water is less of a problem. Get more than a test report and get a sample secured by someone you can rely on.

Once you get into a project, the specifications can become meaningless if the materials cause the limitations in quality.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BigH]

Further to concretemasonry, there is also a question as to the quality of cement and that the cement doesn't get "doctored" on the way to the site if, in fact, you can verify that the cement manufactured is "good." Would suggest that your site lab to a few tests (strength, setting time) of the cement on delivery. Aggregates need to ensure that they are not subject to alkali reactivity.
Then again, how long is it expected that your structure be "active"? How much expense are you looking at - there is always a budget. 450' x 70' x 0.8' = slightly less than 1000 yard3. Much is said of plants but to be honest, you might very well have this done by portable site mixers - did all our bridges in central Laos with them.
Need to pay attention to time of year (cold weather concreting - winter, or hot weather concreting). In hot weather, You might need an ice plant or chillers for the water; shading and wetting of the aggregate for cooling; use of misters and wind breaks in hot weather at placement - to minimize plastic shrinkage cracking - Even if you use a curing membrane, I would strongly suggest the use of wet burlap or a "short bund" and puddled water for curing. Moistening the base onto which the concrete will be placed just before placing so that the water in the mix doesn't get sucked out by the underlying soil . . .

 

[jheidt2543]

A very good reference on the structural design of slabs-on-grade is "Designing Floor Slabs on Grade" by Ringo and Anderson. They cover design for forktruck and storage rack loading. There is a lot of good information on subgrade support, many good design tables for subgrade parameters and slab thickness design.