From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
Date: Mon, 28 Feb 2000 10:30:54 -0600
The prism testing should indicate if you have good bond and should be the
"proof" to you and the owner that you need. The purpose of the unit testing
is to serve as an indicator of what the prism strength will be. Prism
testing is the important criteria.
The mistake that I have seen on grout testing is plastic cylinders or
plastic cube molds in lieu of the procedure in ASTM C1019.
Be careful in specifying high strength grouts (higher than 2000). Grout
needs to be very "wet" (8" t 11" slump) to get proper bond to the masonry
units. Masonry will absorb a tremendous amount of water from the grout.
Focus on the prism strength. As a guide, grout strengths should be designed
for 25% greater strength than the specified f'm. But again, it is the prism
strength that should be the focus.
If the prism tests are acceptable, I would not worry about it. If they are
not, then the contractor is going to be busy.
"Getting A Good Grout", Masonry Construction, January 1998.
"Designing Grout Mixes", Masonry Construction, June 1991.
NCMA-TEK 23A "Grouting for Concrete Masonry Walls".
"Grout.. The Third Ingredient", Masonry Industry Magazine, June 1980.
> -----Original Message-----
> From: Brian K. Smith [SMTP:smitheng(--nospam--at)dos.net]
> Sent: Friday, February 25, 2000 3:04 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Grout Strength
> Thanks Harold for your input. I guess I am somewhat worried because the
> states the minimum grout strength shall be 2000 psi. Additionally,
> indicates the 2000 psi minimum is specified to insure bond between the
> blocks as well as to the reinforcement. If the test was done incorrectly,
> how do I prove to myself as well as the owner that what we have in the
> is okay?
> > -----Original Message-----
> > From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> > Sent: Friday, February 25, 2000 2:05 PM
> > To: seaint(--nospam--at)seaint.org
> > Subject: RE: Grout Strength
> > Brian,
> > Masonry is a composite material composed of masonry units, mortar, and
> > grout. What you are ultimately after is the f'm of the composite. The
> > testing methodology is best described in the ACI 530 as opposed
> > to the UBC.
> > There are 2 ways of compression testing masonry (1. Prisms or 2 Unit
> > Strength). The prism test has been recognized as the method that is
> > allowed, even if the unit testing fails.
> > I guess I don't understand why you have a problem is the f'm works in a
> > prism test.
> > It is legitimate to have f'm of 3000 psi and grout strengths of 2000
> > If you want to really get worried check the compressive strength of a
> > cylinder of mortar. The point is that it doesn't matter what the unit
> > strengths are. It is the prism that is critical.
> > Keep in mind that even for concrete, you are allowed to have individual
> > tests less than the specified f'c.
> > I have had more problems with how the unit tests are performed. Make
> > that they did the grout testing per ASTM C1019.
> > The problem with testing a core is that you can not extrapolate
> > cylinders to
> > prisms well at all. If you do anything, I would suggest cutting grout
> > prisms from the cores, but again, I would focus on the prism testing.
> > Regards,
> > Harold Sprague
> > > -----Original Message-----
> > > From: Brian K. Smith [SMTP:smitheng(--nospam--at)dos.net]
> > > Sent: Friday, February 25, 2000 9:42 AM
> > > To: seaint(--nospam--at)seaint.org
> > > Subject: Grout Strength
> > >
> > > I have a project currently under construction in which we have low
> > > grout
> > > strength. I specified a grout strength of 3000 psi; however, we are
> > > getting
> > > 28 day strengths just over 2000 psi. One break had a 28-day strength
> > > 1970 psi which is lower than the 2000 psi minimum specified by UBC.
> > > Masonry
> > > prisms were specified, however, I have not seen the results. Even if
> > > surpass the f'm=2000 psi specified, I still do not meet the UBC
> > >
> > > The problem is, as always, the wall is partially in place. I would
> > > like to
> > > determine what strength we actually have before the wall is completed.
> > > The
> > > wall is partially grouted, 32"oc. However, I specified the bottom 4'
> > > wall to be grouted solid. Can I core this section of wall, and
> > then run a
> > > compressive test on the core? Do they need to saw off the face shells
> > > prior
> > > to the test?
> > >
> > > Any help will be appreciated.
> > >
> > > Brian K. Smith, P.E.
> > >