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12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

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A LARGE-SCALE MOCK-UP…WHAT CAN WE LEARN? A CASE STUDY OF THE PERFORMANCE OF BEDFORD LIMESTONE

IN THE MAIN GROUP BUILDINGS AT MIT

John Speweik,1 Gary Tondorf-Dick, 2 Mark Liebman3 and Battle Brown 4

1Speweik Preservation Consultants, Inc. ([email protected])

2Program Manager, Department of Facilities, MIT ([email protected])

3Case Forensics Corporation ([email protected])

4Manassas Consulting ([email protected])

Abstract

The neoclassical Main Group buildings at the Massachusetts Institute of Technology campus in Cambridge were the site of this study. The buildings were built in 1913-32 by noted architect William Welles Bosworth (1868-1966). There are a total of eleven buildings linked together by corridors and hallways. The buildings were constructed of cast-in-place structural concrete columns and spandrel beams with ashlar Indiana Bedford limestone cladding throughout. Cracking, flaking, blistering, and loss of structural integrity of the stone façade and lintels have been occurring for years around the façade, parapets and window openings.

In 2009, a plan was conceived to develop a methodology to restore the windows and stonework to their original condition by performing large-scale mock-ups at a corner of Building 2. Three window bays were selected for investigation and repair. The investigation focused on the condition of the stone and masonry backup during the deconstruction process and what could be learned from the building’s existing conditions. Factors contributing to the stone deterioration, included water infiltration, inappropriate pointing mortar, rusted ferrous anchors, and stresses inadvertently introduced to the stone cladding by the thermal freeze-thaw cycle and settlement/shrinkage of the concrete structure over time. The initial conditions were documented using a proprietary PhotoDrawing technique, followed by a nondestructive forensic investigation. The ultimate objective was to develop a set of restoration standards and procedures that would respect the building’s historic character and result in a solution that would last for another 100 years. The initial plan called for an extensive rehabilitation that involved rebuilding a section of the limestone façade and parapet at the mock-up location.

The project was completed in 2011. This paper will present the details of the documentation and technical investigation, discuss the challenges of the program, and describe the methodology and workmanship utilized to remediate the stone, windows, and façade. The onsite training program for the masons who performed the work will also be discussed.

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Keywords: limestone, training, cracking, structural integrity, nondestructive forensic investigation, preservation, rehabilitation, mock-up, historic masonry, lime mortar, workmanship standards, quality assurance 1. Introduction

The 2010 project was based on empirical exploration and scientific testing using a “mock down / mock-up” method. Four vertical bays of the façade that wrap around the southeast corner of Building 2 were selected because of their complete representation of façade issues. They were then mocked down – systematically deconstructed from the parapet to the sills of the first floor windows. In the process, the current condition, failure modes, materials, and construction techniques used for each component were analyzed, tested, and documented. Those data explained how and why the window wall had failed in selected areas. Once the mock down was completed, solutions to the many individual problems were developed, alternatives were tested, and the best were employed to completely rebuild the façade test bays. This was called the mock-up, and it was used to test assembly methods, construction techniques, and visual appearance. The mock-up / mock down process served as the basis for cost and time estimates and implementation strategies for the whole Main Group. The following principles were laid out prior to the development of the work scope.

• Rationale: To ensure that present and planned future historic repair, rehabilitation, and restoration treatments to this property are appropriate and deemed necessary, are based on historic building performance data, and U.S. Department of the Interior Preservation Standards

• Objective: To gather quantifiable information on the original building materials by establishing reliable data on lifecycle performance from controlled, highly-supervised removal of historic materials during the deconstruction work in each specification division

• Goal: To develop historic rehabilitation treatment recommendations and certified project specifications sensitive to the historic integrity of this property - supported by the actual installation of those recommendations into the facade masonry and window wall - establishing the workmanship quality standard for installation

• Proposed Solution: Exterior facade, limestone masonry, and window evaluation survey and restoration standards development

2. Project Scope Details

The work included a complete exterior survey of the façade; documentation of all existing historic masonry and window conditions; the use of non-destructive investigation technologies; remove and replace/rehabilitate/repair/restore windows; rebuild brick back-up wall systems at select locations; evaluation of cracks to determine natural flex points of building; identify deterioration patterns; removal of non-original materials; re-installation of original materials and proposed replacement products;

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Dutchman repair; redress insitu; remove and replace limestone; remove redress limestone and return to the same location; limestone cleaning; limestone repointing; parapet reconstruction; material repair performance as influenced by environment; building movement; workmanship methods and approach with life-cycle-performance projections; complete on-site work-in-progress site inspections; and create and deliver a project specific historic masonry certificate training program. 2.1 Overview

The Main Group became the iconic representation of MIT when the first six buildings were constructed in 1916. The complex formed a monumental presence on the Charles River, a unique blend of restrained Beaux Arts design within a grand campus plan, and the best lab and industrial design of the day. The Main Group was designed to embody and enable MIT’s pedagogical mission, the free exchange and nurturing of ideas among different academic disciplines. The Main Group has always housed MIT’s core functions while also serving as the historic center of Institute culture. To this day, it continues to be remarkably successful at doing both. Main Group buildings are essentially cast-in-place industrial loft buildings with floor-to-floor heights and abundant natural light, which comprise a little more than one million sq. ft. of education and research space. The buildings have proven their strength and adaptability throughout the years and have been successfully modified and renovated to serve changing academic and research requirements. The Main Group will continue to be the emblematic and functional center for MIT as it completes its second century of education and research and looks beyond. However, ninety-five years on a New England urban coastal river bank has had a predictable effect on the complex’s exterior. The Institute’s sesquicentennial seems a fitting point at which to assess and respond to the condition of one of the Institute’s greatest and most visible assets.

A recently completed assessment of the Main Group façade revealed a group of problems that must be addressed. The problems are divided on a roughly 60%/40% basis between the masonry wall and the window systems. The primary problems include corrosion and deformation of the window systems; and cracking, spalling, and shifting of the composite limestone masonry walls. The problem causes include the logical consequences of a century of use, some constraints in the original technology, issues linked to extreme weather during part of the original construction, and, in a very few cases, minor flaws in the design which were revealed by the passage of time. The financial, occupant comfort, and building performance consequences of the façade condition require a prompt and reasoned response. A recently completed detailed study has developed a strategy that could both prepare the Main Group for its next 100 years and make a substantial improvement to building thermal performance and the Institute’s sustainability mission.

In 2011, the Main Group Window Wall Restoration Pilot Project in the southeast corner of Building 2 in the MIT Main Group was completed. This study was an insitu mock down and mock-up process conducted by MIT in association with the consulting team of EinhornYaffee Prescott Architects, Stephen Wessling Architects, Robert Silman Engineers, Speweik Preservation Consultants, and Shawmut Design and Construction.

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This pilot project resulted in the development of Restoration Standards for the Main Group Facades. 2.2 Background

There had been a large study by EinhornYaffee Prescott completed in 1998, that had studied the Main Group Windows and Exterior Envelope. While the study was comprehensive in nature and identified a rational approach to restoring the windows and façade, the total cost of the project was overwhelming and implementation was put on hold. When Payette Associates took on the Main Group Master Plan, it was understood that the windows and envelope could be restored independently from the façade. Idealistically, the buildings would be vacated and the exterior envelope and interior renovation work could be done simultaneously with the least amount of disruption to the building occupants and the quickest turn around for the work.

However, with over 1,000,000 square feet and the understanding that major upgrades to the buildings would be done incrementally and strategically with a programmatic imperative, it became apparent that a systematic full renovation of the Main Group building by building was unlikely to ever occur. 2.3 Main Group Master Plan Principles

The Main Group Master Plan was conceived with a set of principles that are still relevant to the William Welles Bosworth 1913-1916 Main Group vision and plan and still seem to provide a solid foundation for future interventions in the Main Group. His design theme was “The Elegant Warehouse” drawing from Industrial Architecture and adhere to the William Welles Bosworth’s Four Principles of the 1915 Main Group Design:

� A Flood of Window Light � A Flood of Fresh Air � Avoidance of Lost Motion � Psychology of Student Life

• Preserve the historic fabric of the original buildings • Conserve the original planning principles of the complex and in particular, the

connectivity and character of the corridor network • Upgrade and organize building systems for future adaptability • Provide for future program flexibility • Encourage a more effective use of public spaces with increased transparency and

day lighting of the corridors 2.4 Fixed Principles

The Main Group building exterior envelope (window, wall, and parapet) will be retained and restored in compliance with the Main Group Façade Restoration Standards established in the 2011 Window Wall Restoration Pilot Project. The architectural features of the building’s iconic exterior are to be preserved and made long-lasting; therefore, every effort shall be made to work within the existing volume and envelope.

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Principles include: maximum retention of the historic fabric; minimum intervention;integrated (simultaneous) window wall restoration; improve occupant comfort and energy efficiency;rebuild in accordance to the original design - 20th Century Main Group Building technology restored in a 21st Century design and construction technology context;conformance with Cambridge Historical Commission Guidelines; conformance with U.S. Department of the Interior Standards for Rehabilitation.

3. Documentation

Existing conditions at the southeast corner of Building 2 for both east and south facades were documented using PhotoSurvey inspection tool and PhotoDrawing blueprint substitutes.

The PhotoDrawing tool is a patented process resulting in a scaled pen and ink style rendering showing full surface texture of the façade.

The PhotoSurvey inspection tool provides imagery at a selection range of resolution developed in a software based photogrammetric process from multiple images. These images are converted to web browser zoom capable imagery and allow for desktop inspection of the building facade.

The use of the PhotoSurvey

inspection tool allowed for close inspection of the existing condition. A sample of the zoom capability is demonstrated in Figure 2 below.

4. Training A historic masonry training program was incorporated into the project construction

phase and followed the framework of the new ASTM E2659-09 Standard Practice for Certificate Programs. Each training event was carried out at the project site with the masons performing the work. The training program allowed MIT and the architects to identify qualified masons based upon delivering acceptable test panels of each specified

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stone treatment. Each mason met certain criteria and passed a written test defined in the training program plan in order to receive an ASTM E2659-09 project certificate. An oversight committee was formed representing the primary stakeholders. The primary stakeholders were MIT, the architect, and general contractor.

The project training program plan was developed by Speweik Preservation

Consultants in collaboration with MIT and the project architect during the design development stage. ASTM E2659-09 Training Summary Reports were issued for each training component for the project. The training program supported the quality assurance of the overall project. The project training program plan was submitted to the oversight committee for review and approval. The Speweik Preservation Consultant certificate issuers were qualified historic masonry specialists having designated authority charged to administer the training.

The oversight committee required all masons and supervisors to participate in a series of learning events designed to assist in achieving the learning outcomes within a defined scope prior to working on the project.

The ASTM E2659-09 Project Certificate Training Program helped to ensure delivery of the highest quality craftsmanship and maximum life-cycle performance of the stone and brick repairs. All learning events in each training component complied with project goals and objectives. The training program preserved the historic integrity of the building by assuring quality applications and installations.

5. Wall Description

MIT Building 2 is constructed from reinforced cast-in-place structural concrete and limestone cladding with clay masonry back-up. The building is designed with a composite wall system. The wall is comprised of exterior ashlar-cut Indiana Bedford limestone measuring 4 to 8 inches in thickness. The limestone is set in coursings of 24 x 36 inch blocks.

The limestone is attached with ferrous anchors to concrete structural beams and 6 to 12 inches of clay masonry back-up in the façade depending upon the location of the structural beam (see Figure 4). The clay masonry back-up, as well as the unexposed side

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of the limestone, was coated in a black asphaltic product (a type of waterproofing material). The plinth course of the building is smooth-faced granite. The interior finish is a three-coat gypsum/lime plaster 1 inch in thickness over metal lath mechanically attached to the clay masonry units. The exterior limestone was laid in mortar joint tolerances of less than ¼ inch in width. The total wall thickness is 16-1/2 inches.

Steel plates were set into the limestone mortar beds in 1913-1916 to anchor the windows at every course. These steel plates corroded and rust-jacked over time and were removed. Several brick back-up coursings had to be dismantled and the back of the limestone was notched-out at the joint area to remove the corroded material. The pressure from the steel corrosion caused blistering, flaking, and cracking of the limestone units at these locations. A new replacement stainless steel anchoring design was installed in place of the original corroded steel. Stone treatments were completed after careful evaluation of the most appropriate approach was identified.

6. Replacement Materials The area selected for the large-scale mock-up was a corner of the building that was

constructed over an ancient river bed. Building movement has occurred at this location over the past 95 years resulting in cracked limestone, debonded mortar joints, and shelf-angle shifting. In an effort to accommodate future movement of the materials, the team decided to utilize lime-based technology in the reconstruction and repair design. The hard cement-based repointing mortar in the limestone was removed to a depth of 2.5

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times the width of the joint and replaced with a mortar formulation consisting of one part lime putty and two and one half parts sand. The back-up brick walls and parapets were reconstructed using a Type O mortar, a formulation consisting of one part portland cement, two parts hydrated lime, and eight parts sand. Surface cracks in the limestone units were injected using a dispersed hydrated lime (DHL) from Germany. A lime spachtel surface treatment was applied to the injection areas and color matched to the exterior of the stone surfaces. The Dutchman repairs were attached using a natural hydraulic lime mixed with equal parts of limestone dust and bank sand supported by a stainless steel anchor, where specified. The final joint was finished with a lime spachtel material. Where stone was specified to be replaced it was matched in color, density, absorption, strength, and stone type confirmed through ASTM test methods for performance comparison. Dutchman repair pieces were obtained from harvested stone on the same elevation.

7. Forensic Investigation

In support of the pilot program deconstruction and mock-up process, a number of state-of-practice nondestructive investigation technologies were utilized to gather information on both the mode of construction and the condition of the materials. These technologies included ground penetrating radar (GPR), ferrous metal detection, ultrasonics, field microscopy, and water uptake measurement. In addition, minimally invasive drill resistance technology was included in the forensic investigation program.

To ascertain dimensional, material condition and embedded reinforcement information for the wall cross-section consisting of the limestone cladding, brick substructure and concrete columns and beams, a MALA CX GPR unit with 1.6 GHz antenna was used to scan the interior and exterior walls. The resulting data revealed that the structural columns were nominally 0.305 meters x 0.305 meters and that these columns contained both horizontal and vertical reinforcing bar. The structural beams were determined to be nominally 0.95 meters in height by 0.305 meters wide, and that horizontal and vertical embedded reinforcement was present. The presence of metal lath in the interior plaster limited the effectiveness of the GPR during the interior scanning process. Most of the substantive data was acquired during the exterior scanning.

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The MALA GPR unit and Schoenstedt ferrous metal detection equipment were also employed to attempt to detect vertical bars used to attach the coping stone to the parapet wall, the parapet wall to the corona stone, and the corona stone to the underlying limestone clad brick wall. While no discernible pattern of placement was revealed, some ties between the coping stone and parapet and parapet to corona stone, consisting of approximately 0.025 meter diameter threaded iron rods, were detected. The available angle of attack precluded gathering significant data regarding the corona stone to the underlying wall attachment and limited the ability to delineate the parapet to corona stone depth of embedment or nature of the attachment.

An Arborsonic ultrasonic unit employing 54 KHz transmitter and receiver transducers was used to gather baseline and relative data on the condition of the limestone. The velocity measurements at the coping stone ranged from 2790 meters per second (m/s) to 1880 m/s at the cladding stone from 2820 m/s to 1930 m/s, and at the cornice stone from 2630 m/s to 1880 m/s. Based on the uniformly lower time of flight measurements at the top and face of the coping stone, the stone appears to be naturally bedded. The variation in the data appeared representative for naturally occurring, heterogeneous material. While it appears, based on the ultrasonic data, that the stone used in the structure would fall in the mid to lower end of the density spectrum for limestone, it does not appear the stone is experiencing significant deterioration.

The field microscopy was performed using a Peak 60x field microscope. The

microscopy revealed the residual presence of a surface coating on the limestone that appeared to have been lost to weathering in some areas but remained in others. It is a matter of speculation as to when this coating was applied as no records documenting this occurrence were discovered. The field microscope was also employed to examine the separation of the mortar and stone, a fact likely attributable to the stiffness of the original mortar utilized and the dimensional changes in the materials due to thermal cycles. The separation of the original mortar from the limestone, particularly along the head joints, was documented and the more frequent separation of subsequent repointing mortars from the stone was also noted. It is feasible that concrete creep at the time of construction has imparted unanticipated loads in the wall system, as reflected in the nature of the cracking of the stone. These cracks were also examined with the microscope and appeared to have been in existence for a considerable length of time.

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To ascertain additional information on the stone and mortar, a SINT DRMS drill resistance tool was employed at select locations. This tool was developed in Florence, Italy for use on the Leaning Tower of Pisa and the Cathedral of Florence. A 3mm drill bit is programmed for rate of rotation and rate of advance, and a graph is generated based on the resistance of the material being assessed to the penetration by the bit. While some deterioration of the surface of the limestone was evident in the drill resistance graphs, the resistance to penetration increased significantly beyond a depth of 2mm indicative of the fact that the stone is largely intact beneath the surface. It is likely that the coating has played a role in the deterioration at the surface of the stone. Drill resistance testing of the mortar revealed characteristics of a high cement content and high compressive strength, both in the original and later repointing mortars. The use of this type of mortar would be expected for buildings of this era, but may have played a detrimental role in not accommodating creep related concrete shrinkage. The more recent dense, inflexible repointing mortars also appear to have been unable to accommodate thermal cycles in the structure and, while intact, have debonded from the stone in numerous locations.

As part of the long term monitoring program for the pilot program mock-up, Omega temperature/relative humidity and dew point sensors were in installed at six locations along the walls at varying elevations. The sensors employed were Omega iTHX-SD units capable of continuous data acquisition and data transmission to a remote data acquisition system via an Ethernet connection. The sensors employed a 0.125 meter probe that was positioned at the midpoint of the wall between the limestone cladding and brick wythes.

The nondestructive and minimally invasive forensic investigation program provided significant information on the dimensions and condition of the materials, the mode of construction, and presence of embedded reinforcement and metal connections in the wall system.

8. Summary

The work and information gathered from the 2011 Window Wall Restoration Pilot Project will help to develop an implementation plan in synchronization with program initiatives. The plan is for the gradual installation of restored limestone facades and parapets and replicated windows meeting established performance standards.

Implement limestone, window and roof restoration, replication and maintenance using compatible materials and to ensure that future maintenance practices are not escalating the deterioration of the building envelope. Train restoration masons and maintenance teams regarding best practices for historic building repairs. Until the 1980s, there was a team of trades people who focused on maintaining the Main Group. Since the demise of this manner of providing maintenance, the buildings have deteriorated substantially. Many of the recent repairs have been done with incompatible materials and have accelerated the deterioration of the limestone.

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9. References Manassas Consulting LLC 2010. Sheet number ‘2E01.00’ titled Building 2, East Face

Masonry Window Investigation and Restoration Demonstration 2010’ of drawing set Building 2 Test Panel Installation For Window Restoration.

Speweik, J. 2011. ‘ASTM E2659-09 SPC Historic Masonry Preservation Training Summary Reports’. Speweik Preservation Consultants Inc.

Tondorf-Dick, G., Stephen Wessling Architects, Inc., and Torrance Steel Windows, Inc. 2012. ‘Steel Window Replication Standards and Specifications, March 2012.

Wessling, S., Mobraten, J. 2011. ‘Building 2 Window Wall Restoration Standards-Limestone Façade and Steel Window Replication’. Replacement and Masonry Wall Restoration: Mockup Summary Report, June 2011. Stephen Wessling Architects, Inc.

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