Grout Throughout: A Prison Case Study
Masonry Home > Application:
Public Buildings > Justice Center Expansion, Douglas County, Colorado
Grout Goes Straight
on Prison Project
by Tom Cummings, Lafarge Construction Materials*
 Reinforced
masonry can be used beneficially on many types of building projects.
Perhaps one drawback has been the sometimes difficult task of grouting
cells, especially small/tight cores that contain heavy reinforcement.
With conventional grouts, this can be a slow process, as they wend
their way through numerous zig-zag paths. Ensuring that grout spaces
are properly filled requires thorough inspection plus consolidation
and reconsolidation, but the process can be time consuming and costly.
New fourth generation superplasticizing admixtures(polycarboxylates)
have the potential to change that (Ref. 1). These materials coat
cement particles and prevent the stickiness associated with particle
flocking but don’t lead to segregation. Simply stated, self-consolidating
grouts (SCGs) are free flowing and cohesive, two traits necessary
to fill the long, small, absorptive spaces within or between masonry
units. On the Justice Center expansion project for Douglas County
(Colorado), easy material placement is the real hero, leading to
increased security and safety, cost savings, and better quality
of construction.
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(Left) Self-consolidating
grout moves freely in tight
spaces, as seen through the
clear plastic face on this
demonstration panel. |
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| This close-up of the panel to the left shows
the leading front of the grout as it travels over a projection
into the core, flowing around obstructions to fill the cells
completely. |
Security
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| Reinforced masonry with fully grouted cells
creates solid confinement for prisoners. |
County officials stressed the importance of 100% solid grouting for
the prisoner housing areas. SCGs have high fluidity, and they maintain
flow during placement better than grout with water alone. As a result,
SCGs have a superior capacity for filling cores. Grouting contractor
Central Masonry's Dennis Jasken said “The self-consolidating
grout worked just like they said it would. But don't put it where
you don't want solid grouting, because it's going to find its way
everywhere.” The SCG formulation provided good assurance that
there would be no voids in any of the walls, pleasing designers, builders,
and the owner.
Cost Savings
With the county watching its budget, it wasn't obvious that SCGs
would be cost effective. In addition to the costly admixtures, these
grouts are frequently formulated with higher cementitious materials
contents. In the Denver market, the grout mix itself commands a
premium of 8% to 11%. But off-loading trucks and getting the grout
in place has been faster: production numbers on Central Masonry's
jobs in the Denver area are averaging half the time it takes to
place conventional grouts. This allows the ready-mix producer to
keep his fleet productive. Otherwise, the extra time would have
to be built into the cost of the grout.
The contractor saves in two ways. If walls contain reinforcement,
it's cheaper to use a little more grout and grout everything than
to pick out certain cells and increase labor costs. Also, there's
no need for an extra laborer on top of the wall to run the vibrator.
That person can be assigned to other duties, speeding up the construction
project and further decreasing the cost of putting the grout in
place.
Improved Quality with Reduced Surveillance
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| Cleanouts are used to assure that grout spaces
are free of debris prior to grouting. |
Ultimately, where the technology is paying the biggest dividends
for the county is in the quality of the finished walls. Because
the SCG moves virtually unrestricted, there is much less likelihood
of developing voids or partially filled cores. Grout flows well,
even around wide mortar fins. In fact, the grout supplier cautioned
the contractor that he'd better strongly brace the cleanouts if
he wanted grout to remain in the wall during placement. Holes or
openings will be quickly located if present, because this type of
grout will find them and keep flowing. Small openings like unmortared
cross webs may be able to prevent excessive grout loss across units,
but it's better to fully mortar them if you want to keep grout out
of adjoining cores.
Reinforced masonry has the strength to resist impact. For the prison,
that was an important design constraint. Lab testing for this SCG
mix showed compressive strength averaged 5020 psi, well above the
minimum of 2000 psi at 28 days required by ASTM C 476, Standard
Specification for Grout for Masonry. These tests were done on cored
specimens drilled from the grouted wall, according to a variation
permitted by ASTM C 1019, Standard Test Method for Sampling and
Testing Grout.
The Learning Curve
Designers were not familiar with SCGs and were reluctant
to specify them, but the contractor saw the benefit of faster, easier
placement. A demo panel was built to teach the testing agency how
to test this material. Flow, not slump, is checked by measuring
the spread of material placed into a standard slump cone (see “Characteristics
of Self-Consolidating Grouts”). Grout spread was about
26 in. without any segregation of materials—no bleed water
or poorly distributed aggregates. This meant that the grout was
properly designed and mixed to do the job.
Criminals Are the Only Losers
Self-consolidating grouts offer a win-win-win option for designers,
builders, and owners of this prison. Designers were assured that
their grouted walls would be strong and completely filled. Builders
are saving time and increasing productivity. The owner sees his
project moving ahead of schedule, with excellent results. During
construction, there may be an occasional breach because this type
of grout is very fluid and can leak through any opening. The intended
occupants, however, won't be so lucky. Once this job is finished,
there won't be any breakouts.
*Tom Cummings, Lafarge Construction Materials,
New Products Commercialization Manager, Denver; 303.657.4327;
Tom.Cummings@lafarge-na.com
References
- Yelton, Rick, “Flowing without Loss,” Masonry Construction,
Hanley-Wood, LLC, Addison, Illinois, September 2004.
- Building Code Requirements for Masonry Structures, ACI 530-02/ASCE
5-02/TMS 602-02, Masonry Standards Joint Committee, 2002.
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