www.concreteinternational.com | Ci | MAY 2019 51
deterioration by the letter/number designation and the
corresponding photograph, if available. We documented
508 cracks (16 pages), 17 delaminations (one page), 214 areas
of efflorescence (seven pages), 22 cases of previous repairs
(one page), 661 spalls (20 pages), 321 instances of
deterioration on the piers (11 pages), and 97 cases of
deterioration on the benches (four pages). In total, we found
1840 deterioration events and provided 60 pages of tabulations
with photo references and the location, width, depth, and
height above finished grade for each event.
Because the project was done for the National Park
Service and since there is never enough money to do
everything, the next step was to create an evaluation matrix
to rationalize the process of deciding what should be done
first. We evaluated 88 deficiency categories across five
impact/value-of-repair factors. Each deficiency category was
given a 1 to 10 score in each of the five factors. We tallied the
scores and assigned the highest priority to the highest score.
To develop the five impact/value-of-repair factors, we
developed a repair philosophy.
Safety is a major determinant of repair priorities in any
public place. In this case, the two major areas of concern were
tripping hazards (places where paving had heaved or settled)
and the potential for pieces of concrete to fall from overhead.
The visibility of a feature and its importance to the park’s
integrity—in other words, the severity of a deficiency’s threat
to the historic fabric—were other factors we used to establish
repair priorities. Thus, some forms of deterioration needed
immediate attention, while some could wait for later repair
The Park Service decided to make repairs to slow down the
rate of deterioration of the historic fabric; remove tripping
hazards and improve accessibility (repairs to the stairs); and
improve appearance by replacing severely deteriorated piers,
making repairs to the fountain bowls, and cleaning (general
cleaning and removal of calcium and graffiti).
Testing Repair Methods
We documented instances of surface soiling, organic
growth, calcium deposits (in some areas very threedimensional),
and graffiti in the park. Cleaning the concrete
was important not only to improve appearance but also so
repairs would match clean existing fabric.
We experimented with test cleaning of the vertical surfaces
first, beginning with the gentlest means possible (water,
detergent, and bristle brushes). From there, we worked our
way up through cold and hot pressure washes and various
concrete cleaners, stain removers, and herbicides.
Crack and spall repairs
We had identified narrow and wide cracks on vertical
surfaces, spalls on vertical surfaces, and cracks in paving
(horizontal surfaces). Further, crack types were identified as
independent and network. We considered a trial repair to be
successful when the anticipated method was feasible and it
resulted in a good match with the adjacent historic concrete.
We found that vertical cracks were successfully repaired
using injection grout and mortar, spalls were successfully
repaired using a combination of injection grout and repair
mortar, and horizontal cracks were successfully repaired using
full-penetration injection with low-viscosity vinyl-ester and
topping them with flexible acrylic resin.
We had observed that the most damage to walls seemed to
correlate with locations at which the tops had a number of
hairline cracks, so we tested a clear breathable sealer for the
top horizontal surfaces—wall copings and pier caps—to
provide some protection against future water infiltration.
We identified major deterioration to four piers at the north
entrances to the park, parts of the fountains, and in some of
the walks. These areas needed partial or complete replacement.
We worked with Bob Armbruster, The Armbruster Company,
to develop appropriate mixture designs and find sources of
materials to make these major repairs. We selected 12 of the
most widely used mixtures in the park, some precast, some
cast-in-place, one troweled as a thin surface (stucco on the
ceiling at the 16th Street entrance), and some pavement for the
Petrographic examination, per ASTM C856,2 of cores
from a severely deteriorated pier and from a section of the
wall in good condition helped us describe the general
composition of the concrete and identify the possible cause(s)
of deterioration. All of the 1922-era concrete samples,
predating air entrainment, were of similar composition. The main
cause of deterioration in the test pier appeared to be freezing
and thawing. While we also found some evidence of alkalisilica
reaction and corrosion of the embedded steel, these were
identified as “opportunistic and contributory in nature.”
The concrete at Meridian Hill Park is gap-graded.
Armbruster used acid digestion and sieve analysis on all the
target mixtures to identify aggregate sizes. Once target
aggregates were found, petrographic examination allowed
comparison of the new stone to the historic.
The original specification called for white sand throughout
the park but did not give the size, type, or gradation. The
petrographic analysis revealed that the sand in all mixtures was
mostly white quartz with small amounts of clear and light
brown quartz and fractional amounts of other minerals. Acid
digestion and sieve analysis determined the gradation of the
sand used in each mixture.
The Earley Studio used white cement from the Atlas
Portland Cement Company. This product is now produced by