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Structure
Characteristics
The structure was
constructed with reinforced concrete slab beams and columns. The
in-fill between four exterior columns one at each corner of the
tower and two intermediate is 8 inch concrete masonry units (CMU).
The exterior façade is comprised of a setting bed overlaid with
ceramic tile. The original building plans indicate that the tile
setting bed should be 5/8 inches. Test results using impact echo
have found the setting bed varying from 1.7 to 2.7 inches. The total
façade thickness varied due to the inconsistency in the setting bed
thickness.
Problems that
Prompted Repair
Significant areas
of mosaic tile were unbonded from the grout base. In limited and
random sections tile fell leaving gapping holes in the façade.
Furthermore damage with regard to the structural integrity of the
façade was evidenced by the loss of bond of the grout base to the
CMU in-fill and the concrete columns. This loss of grout bond
resulted in profile protuberance throughout the entire face of the
both tower mosaics.
In isolated areas the grout matrix was compromised and
disintegrated causing a build up in the protruded areas making it
impossible to reestablish a level surface profile. Grout
joints on both towers were severely weathered and on the greater
portion of the surface area the grout was missing disintegrated and
or friable.
The façade’s poor condition increased the probability that the tile
and grout could loosen the mechanical bond and sections would shear
from the face of the tower posing grave concern for public safety.
Inspection /
Evaluation Methods
Prior to Balvac’s
involvement in the project a January 2002 condition assessment of
the mosaic tile involved a physical inspection including a
delamination survey and destructive testing of the façade. The
delamination survey was performed by sound with a hammer. The
destructive testing entailed opening an area of the wall at the
handrail anchorage and a hollow area on the north tower. A 4 inch
core was taken to evaluate the composite construction of the façade.
Subsequently Balvac
made a condition assessment specifically to evaluate the extent of
damage and deterioration of the tile grout base and setting bed
using non-destructive impact echo technology. Structural engineers
Tadjer Cohen Edelson and Associates
www.tadjerco.com provided an
objective assessment of this analysis and also considered the Balvac
vacuum process as a viable and cost effective means of restoring the
integrity of the tile façade.
Test Results
Findings of the
2002 report indicated advanced deterioration of the mortar setting
bed in addition to voids and debonding of the tile throughout the
façade. The 2002 report also indicated that substrate could not
receive any additional dead load. The conclusion was removal and
replacement of the entire façade.
The condition
assessment conducted by Balvac found tile exhibiting varying degrees
of visible deterioration and previous repairs. Impact echo testing
in these areas was prohibited as test results would only verify
visually observable and known conditions. Therefore testing
modifications were made to avoid these areas to determine the
general soundness of the façade.
Observations of the cores and impact echo findings revealed a
wide range of construction total thickness. The physical properties
and composition of tile setting bed concrete and CMU substrate
changed the actual wave speed during the impact echo analysis.
Experience with multiple layers of construction of this type has
revealed a variance of 5 to 15% in the wave speed. Therefore the
depth of recorded readings reflected the variable thickness of the
setting bed.
Causes of
Deterioration
Stainless steel mechanical anchors were installed on a
two-foot grid pattern over the entire surface of both towers. It
was necessary to install the anchors after the damaged and missing
tile areas were restored to secure the composite façade and realign
the profile of the façade where possible.
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