Limitations of casting reinforced concrete slab

[Khyzer Ahmed]

We are looking for some reference for placement of concrete in tunnel. What is the maximum horizontal length of placement of concrete and at what interval we can place the next adjacent pour of concrete.?

Is there any code limitation on this or we can go to the next pour placement.?

[EngrUzair]

Refer to "ACI 224.3R-95 Joints in Concrete Construction", Chapter 7 at the following link, for your required information:-

http://xa.yimg.com/kq/groups/2173108/199513267/name/2243r_95.pdf

 

Regards.

[abdulqadeer29]

10 hours ago, engruzair said:

Refer to "ACI 224.3R-95 Joints in Concrete Construction", Chapter 7 at the following link, for your required information:-

http://xa.yimg.com/kq/groups/2173108/199513267/name/2243r_95.pdf

 

Regards.

THIS paper is good for joints but there is no mention of time duration between pouring of successive concrete especially  in massive concrete.

[EngrUzair]

16 hours ago, abdulqadeer29 said:

THIS paper is good for joints but there is no mention of time duration between pouring of successive concrete especially  in massive concrete.

There are two aspects of this question:

a. When the concrete is to be placed in single layer, as in a tunnel construction (what IMO OP has asked for)

Recommendations regarding maximum horizontal length of concrete pour for this case, are given in ACI Standard referred in my previous post.

When the concrete is reinforced properly, to withstand applied loads as well as thermal cracking, next or adjacent layer of concrete may be cast both sooner (the same day) as well as later (e.g., next morning), depending upon availability of concreting party. Proper construction joint should however be provided at the face of concrete common between the two pours.

When the the concrete is to be cast in panels, separated by expansion joints (as in the case of concrete pavements), casting is generally done in alternate panels at one time.

b. When the Mass Concrete is to be laid in multiple-layers

Guidance regarding Mass Concrete is given in ACI 207.1R-05. AFAIK, no specific time duration has been given by ACI for placement of successive layers in a mass concrete. However, last paragraph of ACI 309R-05 Section 7.2 provides general guidance in this regard, in following words:

"When the placement consists of several layers, concrete
delivery should be scheduled so that each layer is placed
while the preceding one is still plastic to avoid cold joints. If
the underlying layer has stiffened just beyond the point
where it can be penetrated by the vibrator, bond can still be
obtained by thoroughly and systematically vibrating the new
concrete into contact with the previously placed concrete;
however, an unavoidable layer line will show on the surface
when the form is removed."

Ways and means are available for execution of large mass concrete works in a single casting operation. Following link gives details of such a mass concreting job, involving casting of 5.5 m (18 ft) thick concrete slabs at 70 m (230 ft) depth belo ground level, carried in one-go using self-compacting concrete.

http://www.silicafume.org/pdf/reprints-201407.pdf

Regards.

[UmarMakhzumi]

17 hours ago, abdulqadeer29 said:

THIS paper is good for joints but there is no mention of time duration between pouring of successive concrete especially  in massive concrete.

I will add to what Uzair has said. For mass concrete, recommendations of ACI 207 are used to reduce heat of hydration during curing. This involves replacing cement with a recommended percentage of fly ash and water with crushed ice. The temperature inside foundation is monitored using thermocouples. Generally, contractor has to ensure that no part of concrete mass is allowed to become cooler than the hottest part by more than 20^oC (68^oF).

Thanks.

[abdulqadeer29]

On 5/2/2016 at 0:30 AM, engruzair said:

 

When the concrete is reinforced properly, to withstand applied loads as well as thermal cracking, next or adjacent layer of concrete may be cast both sooner (the same day) as well as later (e.g., next morning), depending upon availability of concreting party. Proper construction joint should however be provided at the face of concrete common between the two pours.

 

 

Thanks for your valuable guidance.Can you provide a reference which allows us to pour successive slab within 24 hours in case of concrete tunnel linings.?

As our project specifications don't provide any guideline related to concrete tunnel linings but still our consultant restrict us for 72 hours until next pour, applying the limit of mass concrete as carried out in weir structures.

[UmarMakhzumi]

There should be no problem for pouring successive slab within 24 hours if you meet temperature requirements. Roughen the existing and pour the new as long as you stay within the temperature. Use thermocouples are stated above.

[EngrUzair]

6 hours ago, abdulqadeer29 said:

As our project specifications don't provide any guideline related to concrete tunnel linings but still our consultant restrict us for 72 hours until next pour, applying the limit of mass concrete as carried out in weir structures.

1. According to ACI Concrete Terminology 2013, Mass Concrete is

   "any volume of concrete in which a combination of dimensions of the
   member being cast, the boundary conditions can lead to undesirable
   thermal stresses, cracking, deleterious chemical reactions, or reduction in
   the long-term strength as a result of elevated concrete temperature due to
   heat from hydration."

   Now, first of all it is necessary to check whether your concrete really comes under the definition of Mass Concrete or not. ACI 207.1R-05 does  provide basic information & general guidance about mass concrete, but it does not specify any minimum dimensions of concrete to qualify as 'Mass Concrete'.  Following links however suggest some critical dimensions of concrete to consider it 'mass  concrete', as well as useful information regarding placement of mass concrete and recommended practice for effective control of heat of hydration & thermal cracking in mass concrete.

a. https://www.concrete.org/tools/frequentlyaskedquestions.aspx?faqid=650

b. http://people.wallawalla.edu/~larry.aamodt/engr325/concrete_heating.pdf

c. http://www.nrmca.org/aboutconcrete/cips/42p.pdf

d. https://www.structurepoint.org/publication/pdf/pdh-Mass-Concrete-Structures.pdf

e. ACI 301-05, Section 8 Mass Concrete (Includes required concrete placement temperatures, among others)

f. http://people.ce.gatech.edu/~kk92/massconcrete.pdf

g. http://www.agcia.org/documents/Mass Concrete Thermal Control.pdf

In case your concrete tunnel lining actually falls within definition of Mass Concrete, you will need to adopt suitable measures (including installation of thermocouples, as advised above by Umar) to keep the concrete temperatures within limits recommended for mass concrete.

2. Alternately, you may ask your consultant to provide you the calculations to prove that concreting you are doing is mass concrete, and also to provide you the reference that requires waiting for 72 hours, to start the next pour.

3. You may possibly do such calculations yourself too, provided you have relevant temperature values and other required information. Guidance is available in following document:-

http://www.oea.org.lb/Library/Files/Arabic/Downloads/Reports/ندوات ومؤتمرات/Presentation Mass Concrete OEA dec 20.pdf

 

8 hours ago, abdulqadeer29 said:

Can you provide a reference which allows us to pour successive slab within 24 hours in case of concrete tunnel linings.?

I don't have some reference now. However, if the tunnel lining concrete does not qualify for mass concrete, in the light of documents referred earlier, or (as already said earlier) the concrete reinforcement design & placement is adequate to counter both the applicable loads as well as thermal cracking, 72 hour restriction might not be applicable. In such a case, you can start next pour earlier.

Regards.

[abdulqadeer29]

On 5/6/2016 at 2:05 AM, engruzair said:

 

 

I don't have some reference now. However, if the tunnel lining concrete does not qualify for mass concrete, in the light of documents referred earlier, or (as already said earlier) the concrete reinforcement design & placement is adequate to counter both the applicable loads as well as thermal cracking, 72 hour restriction might not be applicable. In such a case, you can start next pour earlier.

Regards.

Thanks a lot Sir, for providing these valuable information.......