below strength mortar

[jpier99463]

I am building a stone and mortar perimeter wall around a military base. All of the mortar is testing good at 7 days as I wait for the 28 day results. That is except for the first days mortar where the strenth is 500psi at 7 days vs 900-1100 psi at seven days for subsequent day's samples. The section of wall where the mortar was used is obviously at the bottom of the place where we began constructing the wall. Specs call for 1850 psi at 28 days. Won't make it with the first day's mortar cubes. How do you test in-place mortar in the stone wall to see if it eventually achieves design strength? Can you core drill into such a wall? Should I hold my final mortar cube til 45 days to then test and verify if it reaches strength. I'm certainly open to suggestions.

 

[concretemasonry]

You cannot accurately test in-place 3/8" mortar for comparison to a standard 2x2x2 mortar cube.

The curing conditions are difficult and the sample size/shape make any correlation difficult or impossible.

What is the actual use for the mortar? Is the strength actually important or is it a specification requirement? Is is a proportion or performance specification, since the two cannot be used in combination. - One or the other, but it is a very common mistake in specifying.

ASTM C270 specifications, in the appendix, recommends the use of the lowest strength mortar possible to carry the structural loads. This is because workability, bond, flexibility and other concepts far overshadow the vertical compressive strength factors. - I have seen 4800 psi block prisms made with 1800 psi mortar.

Dick