Large Foundation India

[Zambo]

We are planning to cast a 10,000m3 foundation in India in a single pour. It will take about 8 weeks to get the formwork and rebar in place and then we will proceed with casting in about 4 or 5 days, assuming we can get enough resources together i.e batching plants, trucks and concrete pumps.

Does anyone know of any documentation on similar works in India? There may even be a text book on the subject as India does have a prolific technical publishing industry.

 

[hokie66]

Nothing about India, but the big mat pours of that size I know about have all been made in 12-24 hours. Keeping the face fresh over longer times is problematic.

 

[Zambo]

Agreed about keeping the face fresh. But that's a lot of concrete to pour in 24 hours, the plant may not be available. Will know more after my site visit end of this month.

 

[hokie66]

Yes, the ones I have heard reported were in the US and in Dubai, so large capacities of batching, trucks, and pumps available. Even in those places, takes a lot of planning to make it happen.

 

[Ron]

Agree that placement should be done quickly. The obverse issue with that is an increase heat of hydration and thermal problems in the concrete. Suggest you monitor in place temperatures and consider using cooling methods as well as retarding admixtures.

As hokie66 noted, this takes a lot of planning and coordination. The mix designs have to be right on, the production has to be continuous with backup...and on and on...

 

[Zambo]

Ron and hokie66

thanks for the interest.

The first thought is to cast one time, of course the fall back plan is to cast in sections - but maximum of 4.

During my visit I will assess the batching plant availability in the area. Next pumps to support the batching plants. After that the distance from the batching plants to site and decide on the number of trucks. Once that is known then I can look at the pump placement and how to keep the concrete face live throughout the pour. If the plant resources aren't sufficient then Plan B.

The reason I am looking for documentation of previous projects in India is that it will start to show where success and failure have been found before. I need to know the availability of cement replacement such as PFA, are water cooling plants frequently used, countries sometimes have particular ways of working which are of interest.

If we decide to go for more than one pour then there is a decision needed on whether the construction joints are horizontal or vertical. I do not favour horizontal construction joints (i.e pour the section in layers) but there would be advantages in this with regard to controlling the heat. Vertical construction joints on the otherhand give a massive section and problems of heat, plus additional shoring strength for the formwork. Ron and hokie66 - your thoughts?

 

[hokie66]

Yes, a lot of decisions to be made, and I hope you can get it done in one casting, although I have a preconceived notion that it won't happen in India.

If this were a mat on piles which has to be broken into pieces, I would want to break it with vertical construction joints, centred on the piles, provided that the weather is not severe and the concrete temperature as placed can be kept low. If a ground supported mat as I imagine it is, then I would look closely at casting it in layers to attempt to deal with the thermal issues. I think any horizontal shear issues can be overcome with sufficient roughness, reinforcement, and keying if necessary.

 

[Zambo]

It's an annulus on piles. If we cast 24 hours (or even my thought of 4 or 5 days) then I guess the weather will be severe in that we cannot use the cool part of the day. Usually I like to start casting about 6a.m when the aggregates are at their coolest.

 

[hokie66]

At least with an annulus, the faces are well defined, but you have two to keep going at the same time if a construction joint is to be avoided. I think I would live with a construction joint, preferably centred on a row of piles. How thick is it? The thickness, along with the ambient temperatures and temperature of concrete as placed, all must come into the decision.

 

[Ron]

Zambo...on mass placements like this, I would start at 10:00 or 11:00 pm. Make sure aggregate stockpiles are kept damp and the temperature will decline enough after sundown to be less of an issue.

I would tend to go with horizontal joints for this quantity of placement as you will have a significantly increased cooling surface area that will help. With the use of admixtures, roughness (I don't recommend raking for roughness...to much opportunity for unfilled voids), bonding agents, dowels or any combination of such will overcome the horizontal shear issues, which are not likely to be high anyway.

Mix cooling can be done in a variety of ways...using ice for mixing water replacement (partial only), using cooled water, or using liquid nitrogen injection into the transit mixer.

 

[SlideRuleEra]

Zambo - For what it is worth, I'll offer some observations. You can do quite a bit of the preliminary planning before your upcoming return trip to India. Then, you can ask the right questions while there. For example:

To place 10,000 m^3 in 5 days (120 hours) will require an uninterrupted delivery and placement of 84 m^3 per hour. If a typical truck transports 6 m^3 per load then this is a truck arriving \ unloading every 4 minutes (average time). As hokie66 pointed out, with two working faces on the annulus, each of the two construction crew, will need to handle a truck every 8 minutes.

With this basic calculation you can continue with informed questions about concrete pumping capacity, etc.

Also, the above math also indicates that traffic control will be an issue that requires thought.

Interesting to note that even if four separate placements are made (assuming 1 1/4 days for each), the math above is identical, along with the same considerations. Four placements may minimize some technical problems, but the logistical problems remain the same.

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[BigH]

zambo - depends where you are in India; are you talking pre-existing batch plants or project purpose plants? You might be able to get enough plants in Mumbai or Delhi - but probably not elsewhere unless you set up plants to produce this amount of concrete. Two project ready plants of 60m3/hr would probably be enough.

Ron hinted at the "timing" of the placement. In the big cities - Calcutta (oops, Kolkata), Mumbai, and Delhi - you might have to consider hot weather concreting all year round. As you know, these major cities have temperatures in the low to upper 40s (Celcius) in the daytime and it doesn't get that much cooler at night - exceptions (at least in Calcutta - January and February). So you will need to plan for hot weather conditions - ice plants, cooling pipes, misters for ensuring no plastic shrinkage cracking. You will need to assess the work force - they might have the plant capability, trucks and pumps but will they have enough experienced skilled labourers to be able to place and consolidate the concrete? This needs to be assessed (as we have learned in Indonesia) - there might be local labour requirements you will have to contend with. (When I was in India, they have special hardhats with a plastic ring on top - why? Even though a Miller (transit mixer) brings the concrete to the site, the local labourers take the concrete to the placement location by small pans - which, of course, they place on top of their heads - hopefully, you will not have to worry about this). Off line I could probably hook you up with a very very knowledgeable concrete man out of Mumbai.

As SRE says, do your homework ahead of time - historical temperatures, humidity, how much retarder will you use (we are using enough for 10 hours), local manpower conditions (and skills) - etc.

 

[hokie66]

BigH mentioned consolidation, which is a big issue not mentioned before. I did read about a big placement like this where "self-consolidating concrete" was used, but I don't have any experience with it.

 

[concretemasonry]

Zambo -

Getting as much information before you get there will help you better formulate your questions and planning the possible the possible design/construction. This leads to the specifications and the enforcement. Usually, the contractor is identified and advance and there is a local engineering firm that is involved in similar work/problems there.

Find out if your design project is located on or near or a newer or project that may have some equipment available. I was at a auto plant near one of the major cities that had 4 plants and material stockpiles on site because of the transportation, weather and material supplies. - This concept is very common since the ready-mix industry has not developed the same as elsewhere despite the high level of professional technical of people involved. Even in 7 to 20 story apartments in Delhi site plants are common and it is not uncommon common to see rebar delivered on bicycles to get through the traffic even in the outer areas.

The sooner you find a local engineer, you can formulate some questions in advance for preparation for your trip.

Aggregates can be problematic because the weather can halt the supply of fine aggregate and even some of the coarse aggregates. Sand can require more attention in the areas along the coast (up to 50 miles away)because much of the land can be lower and they are subject to flooding of brackish water. Because of this, the testing becomes more important because the salt content can be variable.

Dick





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

 

[JAE]

I just heard a presentation on the Trump Tower in Chicago - big mat pour (I think it was 5000 cy done in 20 hours or so.

They used Self-Consolidating Concrete (SCC).

This allowed the trucks to offload at full spin. The pumps and/or conveyors never had to move (the concrete just flowed away from the discharge point), the water cement ratio was low (lower heat), etc.

I could get you the name of the guy who designed the mix if you want.

 

[BigH]

Large pours are not uncommon . . . a friend of mine in Bangkok was involved with one over 24,000 m3. India is aware of SCC - when I was there back in 2001-2005, I attended an presentation by the India Chapter of PCA regarding SCC. They'll have designers who can do it there if that is what you want. As indicated by concretemasonry, the quality of the materials will also have to be controlled very closely (he also has the experience of working there I remember).

 

[concretemasonry]

Zambo -

The biggest factor is where the project is (in a city, just outside a city or in the country) because the problems causing design and construction options are based on what is available, and not what is necessary or specified. What can be done reliably can be done well in Delhi, but not possible in Agra (a short drive east). It is just one of those places where almost anything is possible or impossible - In other words, "If it does not make sense, it must be true" and an advanced trip is very wise on a major project to determine since the country is so large and has the options. The traffic and exploding use of cars is even worse than China because the cities are dense and confined and the road system was not developed because of the superb train/rail system.

The geographic location is required to recognized what cannot be changed. The weather (especially the predictable monsoons) and soil (highly variable) through the country control the site, accessibility of materials and the operations, since this project may just be one of many. That is why portable plants for major pours and developments are common because materials can be stockpiled and many of the variables, even for a single 10 story apartment building can be minimized. When you are building a 120+ acre auto plant facility with housing and schools there is no question that you cannot rely on exterior logistics and some items, but a design with construction alternates may be good for your project since there is technology skilled engineers and a ready labor supply. The people are hard working and follow instructions if there is proper instruction and transportation to the project and meals (Indian tradition/obligation).

I spent about 12 trips of 1-2 weeks looking at construction in India and I was always learning. - I considered moving to an area near the coast south of Chennai (Madras at one time) because of the engineering people I met.

Just make sure you get as much information as possible before your trip, so you are prepared what to look for. This will let you get a clearer picture quicker, since things do not always happen as quick as you wish.

Dick

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

 

[Zambo]

BigH, concretemasonry, JAE, hokie66, SRE and Ron. Thanks for all the input. It'll take a while to digest everything and get some more project detail. Then I'll come back with some more thoughts on how this could best be carried out.