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Conservation Solutions, in collaboration with the project architect and conservation consultant Martin Weaver, designed these two new anchoring systems for the cornice. The design for the dismantled section (above) uses AISI Type 316, non-corroding
stainless-steel rods in a grout-injection system by CINTEC. Small injection tubes are positioned in the joints between the terra-cotta units for inflation with grout after assembly. The stabilizing anchors (below) are designed to be installed
in-situ by means of a different type of CINTEC grout-injection system, also using AISI Type 316 stainless-steel rods.
Most importantly, we disassembled approximately 6 feet of the cornice to reveal its construction and anchoring system. We also exposed a portion of the parapet decking to determine the condition of the underlying
concrete substructure. In collaboration with the architect and Martin Weaver, a new anchoring system was designed. We also worked with the noted terra-cotta manufacturer, Gladding, McBean to determine which sections of terra-cotta would need to be
replaced.
Finally, after our investigative work was done, CSI made the opening in the cornice watertight.
Following observation of severe cracking and movement at the corners of the main terra-cotta cornice of the octagonal lower drum of the dome, it was jointly decided to erect scaffolding and to carefully make an exploratory opening into the
terra-cotta work.
The purposes of this intervention were to establish if the cracking and movement were evidence of a dangerous situation, to establish the types, locations, and conditions of the hidden steel support structure and anchors, and to establish the type,
location, and condition of the reinforced concrete sub-structure.
We selected the southeast corner of the octagonal lower drum, apparently the area of the cornice with the worst conditions, and the best site for our investigations. Pablo Quinones and Martin Weaver had noted what appeared to be evidence of severe
damage in this same area in 1998.
As the careful cutting away commenced a the cornice's upper level, we found that the cornice was backed-up by a mass of "clinker concrete" or "cindercrete". This material is based on a aggregate of furnace ash and large fragments
of clinker. Its use has been suspended for many years because the large quantities of sulfur compounds present in the ash and clinker have been found to cause severe corrosion of adjacent steel in the presence of moisture.
After removal of the cindercrete from the adjacent area, the cutting-out proceeded and it was noted that the movement of the terra-cotta was beginning to accelerate. The terra-cotta mass at the corner -- probably weighing in excess of 500 lbs. --
was pulling away from the main mass of the cornice by active diagonal cracks propagating down on either side of the corner. The unstable mass was immediately secured by ropes and temporary supports and was carefully cut apart and removed. |
Water had penetrated down into the cornice, and all its steel structural supports and anchors had been totally destroyed by corrosion. The total failure of the structural-support steel and
anchor system had led to the structural failure of the cantilevered, and now unreinforced, terra-cotta cornice. The only reason that it had not collapsed was a combination of the cohesive and frictional effects of the mortar and brick fragments used
as back-up to the hollow terra-cotta units.
Moisture had entered via open joints and cracks and, to a lesser extent, through leaks in the roof above and behind the cornice. The reason for the extreme corrosion of the steel was a combination of chlorides from sea spray and the sulfuric acid
formed when saline moisture saturated and then passed through the contaminated cindercrete. The corrosion had been so severe that it was no longer possible to establish the exact dimensions of any of the former steel elements. Some had disappeared
totally, leaving only rusty stains in the terra-cotta work.
It should be noted that any corrosion of embedded steel is associated with massive expansion of the corrosion products. In the case of the Capitol Building, this expansion had resulted, and will continue to result, in the shattering of the
immediately adjacent terra-cotta. Thus, all stabilization, conservation, and restoration work must involve the removal of all corroding steel and/or the prevention of any further corrosion and associated expansive effects. All new steelwork must be
AISI Type 316 stainless steel, which is non-corroding in the chloride-rich maritime environment present here. AISI Type 304 stainless steel is attacked by chlorides and cannot be used here under any circumstances because it will corrode.
On the basis of our observations, we concluded that in any and all locations where the terra-cotta cornices show evidence of cracking and movement, with open joints and possibly rust staining on the lower surfaces, then this terra-cotta work has had
all, or most, of its structural-support steel and anchoring system so severely corroded that it is either totally gone or is so seriously deteriorated that the whole cornice, or pars thereof, are liable to become dangerous and could collapse
suddenly and without further evidence of failure.
The extreme nature of the deterioration process was such that it will inevitably lead to catastrophic failure, with collapse of the terra-cotta onto, and possibly through, the openings in the roof below. Accordingly, we recommended that all cracked
and deformed areas of the cornice should be carefully dismantled as soon as possible. Shattered terra-cotta units should be replaced with high-quality matching new units from a well-established manufacturer such as Gladding, McBean of California.
This firm has been in continuous practice since before the erection of the Capitol and is known for the high quality of its architectural terra-cotta.
The dismantled corners should be rebuilt using AISI Type 316, non-corroding stainless-steel rods in a grout-injection anchor system by CINTEC, specially designed with small injection tubes positioned in the joints between the terra-cotta units for
inflation with grout after assembly.
Undamaged areas of terra-cotta may be stabilized in-situ by means of a different type of CINTEC grout-injection anchor system, also using AISI Type 316 stainless-steel rods. It will be necessary to open up a series of areas in the terra-cotta work
at random locations to determine if, in fact, the apparently undamaged terra-cotta can be safely stabilized in this way.
Once the ware has been prevented from getting into the top of the cornices and other details, and the CINTEC in-situ stabilization system has been applied in diamond-tipped core-drilled holes, the crucial factor then will be whether any existing
embedded steel can be left in-situ. All in-situ stabilization work must involve dry-drilling with advanced air-cooled drilling equipment. Under no circumstances can water-cooled drilling systems be used because of the danger of water causing further
deterioration.
It was recommended that a complete condition survey of all the terra-cotta work should be carried out as soon as possible to locate any other dangerous areas which may already exist.
Joseph Sembrat is President and Head Conservator of Conservation Solutions, Inc., District Heights, MD. The firm specializes in the conservation of historic structures, monuments, sculpture, and fountains in such
materials as metal, stone, and terra-cotta.
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