ACI 530.1 Specs for Masonry Structures

[RedHorseEngineer]

ACI 530.1-05 (Specification for Masonry Structures) Table 2 (Compressive strength of masonry based on the compressive strength of concrete masonry units and type of mortar used in construction) specifies the “net area compressive strength of CONCRETE MASONRY UNITS” and the “net area compressive strength of MASONRY.” It is my understanding that using 4800 psi CMU with Type M mortar will provide a constructed wall compressive strength of 3000 psi. Pls confirm my understanding.

Additionally, if 3000 psi masonry is required, what is the turnaround time to have these specially constructed 4800 psi CMU’s fabricated & tested?

 

[JAE]

Yes, per ACI 530, the 4800 psi for the units corresponds to f'm = 3000 psi for the masonry assembly for type M mortar.

Not sure about turn around time on the unit testing - you might check with local CMU suppliers on that. They may have on-going test records that back up their units.

 

[concretemasonry]

RedHorse -

You certainly read that conservative table correctly.

There is always the option of testing actual hollow masonry prisms. This will give you different (usually lower) block unit strength requirement, especially with Type N mortar, since mortar has a minor effect on prism strength.

DEFINITELY check with the most probable local supplier to find out what knowledge they have that is based on their particular units and materials.

I worked for a block producer that had testing back-up based on several series of prism tests, so the units could be produced and made available for delivery in as little as 7 to 14 days (depending on the level of business). He had the 3000 psi prism as a standard product line. We also had the formulas and testing for 4500 psi prisms, but engineers could never find a need for them since most of the loadbearing was less than 10 or 12 stories. We made the 8500 psi block for the 4500 psi prisms because the f'm table could not be legally extrapolated beyond 3000 psi. You could have a hard time finding a testing lab that can or will test such a high strength unit, since they may only have cylinder testing machines without the correct platens.

Keep in mind that most of the block business is based on controls, automation and controlled curing. The volume of a single 7 to 10 story building can be produced in a day if the units are not in inventory. The block are only in the plant for 24 to 48 hours before they are ready for delivery. There is no such thing as 28 days in the ASTM C90 and C140 requirements, since the curing is usually a part of the automated curing process and is not dependent on the site curing conditions.

DEFINITELY check with a good local supplier since the materials (aggregate make-up/geology and particle shape) can vary by region geographically. Nationally, cement is very uniform no matter where you are, but some plants may use a "product" or Type III for some production.

Dick

 

[RedHorseEngineer]

I typically specify a lesser-required compressive strength, but need the higher compressive strength on this project to accommodate the flexural strength & bending imposed by the roof trusses (high lateral loads due to hurricane force winds & seismic activity). Due to the higher strength requirement, these CMUs are being specially made for this project & the contractor is advising that it will be mix design time + 28 days for testing: potential project construction delay. I’ve personally conducted concrete testing, but unfortunately, I’ve done the testing on CMUs and thus looking for guidance on this.

On the Portland Cement Association’s website (

http://www.cement.org/masonry/ds_compressive_strength.asp),

they note that after curing in bags for the prism test “Then [the units] are further cured, removed from the bags two days prior to compressive strength testing, and tested in compression at an age of 28 days or another designated test age.” Could this be a Standard Test Method for Compressive Strength of Masonry Prisms, ASTM C 1314, requirement?

 

[RedHorseEngineer]

typo...I've never done CMU testing & thus looking for guidance. Thanks