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Low compressive strength for grout

Low compressive strength for grout

Low compressive strength for grout

I have a low 56-day grout break. What investigative services can be done other than windsor probe (which is not exactly deependable)?

RE: Low compressive strength for grout

First check to see if you really need the grout strength specified for your appication.

Too often, a high grout strength can end up being specified since someone erroneously thinks stronger is better.

There are applications where the grout strength should be lower than the compressive strength of the masonry units.

What sampling and testing procedure was used? -  ASTM C1019?


RE: Low compressive strength for grout

The specified grout strength is 3000 psi for load bearing walls (with pilasters). The mix itself was a job site mix not a ready mix. The grout was tested in accordance with ASTM C1019 (using the cardboard grout boxes-not the old school block strategy).The compressive strength were 53% at 7-day, 75% at 28-day and only went 80% at 56-day.

RE: Low compressive strength for grout

what's the f'm for the total masonry package and the mortar used? (mortar types M,S,N?)

do you have submitted breaks for the CMU's by the supplier?

Are you the testing firm, contractor, grout supplier, egr?

What state are you located in?

RE: Low compressive strength for grout

Was there an f'm or was there just material specs required?

You may be faced with trying to acheive 3000 psi grout in a 1900 psi (net) block strength where the gorout is only intended to bond the rebar to the masonry, since the compression strength of the block is probably the critical item.

Mortar strengths are a minor factor in the compressive strength of most masonry. If you use higher strength grout to acheive a required prism strength, someone is making a very big error.

Cardboard forms can give misleading results with some different types of masonry units (unit density and absorption can vary widely).

If you are just testing the materials, give the results to the engineer, so he can decide if the materials are adequate for the design in the big picture.

RE: Low compressive strength for grout

For engineered masonry in essential and nonessential facilities, IBC Sec 2105.2 and MSJC Spec Article 1.4B provide two methods for verifying compliance with f'm. IBC 1708 deals with level of QA and frequency of testing.

The first method dealt with in 2105.2, is the unit strength method and the second method is the prism test method.

In addition to testing masonry units, compliance with f'g is required when the unit strength method is used. The f’g must be equal to f’m but must not be less than 2,000 psi. It seems that the unit strength method is the approach you followed. No?

If compliance with f'm is by the unit strength method, what are the f'm, type of mortar used, and the required net area compressive strength of the CMUs? Do you have test results for compressive strength of the masonry units?

Well, what are the options if compliance with f’m is not achieved with either the UNIT STRENGTH METHOD or the PRISM TEST METHOD? The code (IBC 2105.3) does permit for determining compliance with f'm by testing prisms cut from masonry. If you want to utilize an NDT method as an alternate, it will be prudent to first discuss this approach with the EOR and AHJ/BO in order to seek approval of the NDT method proposed.

RE: Low compressive strength for grout

F'm is 2000 with type S mortar and 3000 psi grout. The NDT method is not good due to the reinf. steel in the block. Only the reinf. cells are grouted. I know that the SER must approve or disapprove the components in place. The contractor wants to know what tests may be done for the grout to determine the in place strength. There has been one other grout test for the project and it made strength at 28-days.

RE: Low compressive strength for grout

F'm = 2000psi has a grout with min 2000psi.  i don't think there is a problem.

of course the SER is god in the issue since it's his/her spec.

Watch out for NDT on the walls. just b/c there is an ASTM test for saw-cutting and compression testing the sample doesn't mean it is easy or that your break machine can handle the load.  Windsor probing is not meant for what you're doing.  

As far as the rebar and the grout spacing goes, this has been a problem with this test every time it's been done NDT, would you agree. I had to take samples to the university to break them.  The samples were truly pains in but to cap too (had to build molds and it was still awkward ~1 hr per sample.  There is an old Uniform Building Code method that involves horizontal coring the wall and testing the core that appears easy to perform.

I've been using NDT loosely here, obviously coring or saw-cutting samples are DT.  I am unaware (and very skeptical of it if one exists) of any true NDT test for masonry construction in this application, but i don't see a problem with what you've presented anyway.


RE: Low compressive strength for grout

ignore the "bottom" don't know how it got there

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