Unconsolidated High Lift CMU

[reviest54]

Hello all

Our firm designed a 3 story structure with fully grouted CMU bearing/shear walls. The mason did his grouting in high lifts 8-12 feet with 100% cleanouts according to the inspection reports. No issues were reported in the inspection reports.

After several mistakes the mason was fired after completing the second story, and a new mason was hired. The first thing the new mason did was check the previous work and he found several hollow blocks throughout the structure.

Here is the only repair I can see:

1. Prism tests of wall to see what the strength of the "well constructed" portions is.
2. Locate all of the unconsolidated grout locations (non-destructive and/or destructive testing).
3. Demo a sufficient distance beyond each unconsolidated area to provide new fully developed reinforcing that is epoxied into acceptable CMU.
4. Infill with CMU or concrete depending on the extent.

Does anyone have a more clever approach or see an issue with mine?

Thanks.

 

[concretemasonry]

revist -

What kind of prism tests do you propose to use, considering that you have solid grouted walls. The ACI 530 code and specifications suggests making block hollow prisms (h/t =2)with full mortar bedding as a basic moisture strength (f'm) for design and quality control. The behavior of masonry walls is generally based on the strength of panels and not localized situations.

The strength of the mortar does not control the wall strength and I have seen controls on excessive grout strength. I have seen 2 block (8x8x16) high hollow masonry prisms (mortar that was 2200 psi) that that had an masonry f'm of about 5000 psi. The failure mode is a diagonal shear failure.

"Unconsolidated grout" is rare if the grout has and 8" to 11" slump and the appropriate shape units are used. Most CMU suppliers have many different shapes available for the common block types (1 core, 2 core and 3 core).

If your design or construction controls require prism to be tested, be aware that the weight and transporting is prohibitive and that damaged samples are quite common.

Dick

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

 

[reviest54]

Thanks for the response regarding the prism tests. I will look into them.

Our plans call for a solid grouted wall. It seems some areas did not get grouted. These areas are located seemingly at random. I assumed they occurred because of the high lifts and lack of consolidation.

The destructive/non-destructive testing sequence will still need to be worked out.

I was more curious about the repair to guide these investigative efforts.