Augercast grout and sample size.

[Jabson]

Can anyone either show me or tell me where to find the reason why augercast grout sample sizes are 2x2 or 2x4? I have an out of state engineer who requires 6x12 cylinders for augercast grout. And he informes me that unless I can show why 2x2 or 2x4 break more accuratly and consistently than 6x12, our special inspectors will be making 6x12's. Washington state has used 2x2 and 2x4's exclusively for over the 10 years I have been here.

 

[concretemasonry]

What do the job specifications say about the the sampling and testing procedures?

What procedure was used in the mix designs for submittals?

When you test 2x2 samples, you will different results than the same grout in a 6x12 cylinder due to the different aspect ratios of the samples, not including the different factors for curing and sample preparation.

With a 2x2, you are getting close to confined compression failure whereas you will get a shear failure in a 6x12 sample. Specifications must be in accordance with testing procedures. That is why there is an ASTM.

Dick

 

[Jabson]

Not sure of the specifications, this is coming from a testing agency asking me about this. As for sizes used for mix design, The supplier did qualify thier mix using 2x4 cylinders.

And since we are looking at piles, would we not want confined compression results, instead of shear, since the grout is confined by its surrounding soils?

 

[concretemasonry]

Confinement by soil is not really confinement of the MATERIAL itself in a laboratory even if it might provide some laterial support for the MEMBER in the field. - I also said a cube failure is "close to comfined compression", but it is not actually the same.

The testing procedure is a standard method to test the properties of a material. The specification for the material should include the testing method.

Concrete is used with reinforcement, but concrete is never tested in a laboratory with reinforcement since the purpose of the lab test is to determine the quality of the material irregardless of the field loading or construction - that is why there are engineers.

If the supplier's sumittal was approved based on 2x4 cylinders, that should be the standard by which they should be tested and approved. I assumed the of state engineer was the one that approved the supplier initially.

Dick

 

[henri2]

The engineer probably thinks grout is tested the same way as concrete in so far as strength is concerned.

Even masonry grout specimens are smaller than standard 6 x 12 in concrete specimens.

Grout strength specimens for: base plate grout, for precast post-tensioned concrete, auger cast piles etc are typically 2 inch cubes. I have seen 2 x 4 in molds used as well.

When you use 6 x 12 in specimens, you will almost certainly get lower test results than you will with 2 in cubes or 2 x 4 in cylinders.

The influence of size and type of specimen on compresive strength of cement grout (for auger cast piles) is examined in this study

http://www.dot.state.fl.us/statemat...nce/grip/2006/auger-castpilegroutresearch.pdf

 

[Jabson]

Henri2 - Thanks, that is a big help! Especially when they compared 2x's to 6x's. I will forward that link and see where it leads regarding the engineer.

 

[GeoPaveTraffic]

One reason for using 2x2 cubes for grout is that you get better consoidation of the samples when they are made. You tend to get more voids in the 6x12's due to the consistancy of the material.

 

[civilperson]

Most auger cast piles use concrete or a grout with coarse aggregate. I use cylinders to check the concrete and allow a unlimited height freefall of the mix.