Evaluating As-Built Prope rties of Masonry Wall Systems Using Investigative Laboratory and In-Situ Testing Tec hniques Kenrick J. Hartma n, LEED AP BD +C and Thomas C. Kuczynsk i Wiss, Jann ey, Elstner Associates, Inc. 1350 Broadway, Suite 910, New York, NY 10018 Phone: 212-760-2540 • Fax: 212-760-2548 E-mail: khartman@wje.com and tkuczynski@wje.com S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 4 7 ABSTR ACT When diagnosing failures in masonry wall systems, it is often advantageous to determine the as-built conditions of the subject structure as well as the chemical and/or physical properties of the wall’s components. Defining the source(s) of an encountered failure mode based exclusively on assumptions and visual observations repeatedly leads to improper and misdiagnosed repairs. However, various investigative laboratory and in-situ testing techniques can be implemented to determine the existing properties of a wall assembly and its materials, allowing for effective repair design. This study examines, in detail, the best practices for investigating existing masonry wall systems using forensic techniques that include ground-penetrating radar (GPR), petrography, mortar tensile bond-strength testing, and strain-relief testing. Information is collected from technical literature and standardized testing methods, as well as from the authors’ project experiences. Additionally, case studies are presented that illustrate the implementation and advantages of the discussed techniques and how the as-built wall performances compare with historic and current design standards. SPEAKER S Kenrick J. Hartman — Wiss, Jann ey, Elstner Associates, Inc. Kenrick J. Hartman specializes in the evaluation and repair of building envelope systems. He has experience with a variety of materials including terra cotta, brick, concrete, steel, glass, and various roofing and waterproofing products. Hartman performs field testing, moisture infiltration investigations, building envelope evaluations, and repair design for modern and historic structures. Thomas C. Kuczynski — Wiss, Jann ey, Elstner Associates, Inc. Thomas Kucz ynski participates in investigative and repair projects involving structural testing, analysis, instrumentation, repair design, condition assessment, and cost estimation. He has worked with various building typologies, including both residential and commercial towers. These projects involve brick masonry, concrete, steel, stone, and precast panel elements. 4 8 • Ha r t m a n a n d K u c z y n s k i S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 INTRODUCTION When evaluating or repairing an existing masonry structure, it is often important to determine, within a reasonable degree of engineering certainty, the physical and chemical properties of the building materials in their current state. Age, moisture infiltration, temperature cycling, and many other factors can deteriorate common building materials, leading to potentially costly repairs. In order to provide the appropriate repair for a given condition, an engineer/ architect will often require information about the as-built conditions that cannot be visibly identified, such as compressive and flexural tensile strength of a wall assembly, potential presence and condition of embedded wall elements (e.g., wall ties and steel reinforcement), and physical and chemical properties of wall assembly materials. Several tests exist that will better enable an engineer or architect to effectively diagnose the cause of failure and, in turn, formulate repair recommendations. These tests range from physical tests of masonry wall assemblies performed in the field to the petrographic evaluation of an individual wall material sample as performed in a laboratory setting. In-situ tests include but are not limited to compressive stress-and-strain relief testing, flexural tensile bond-strength testing, and nondestructive wall scanning using ground-penetrating radar (GPR). Laboratory tests include mortar petrography and mortar proportion analyses, determination of the bricks’ future durability via testing to determine saturation coefficient, absorption, freeze/thaw durability, and many more. IN-SITU TESTING Compressive Stress-and-Strain Relief Testing For masonry structures and façades, two types of ASTM International (ASTM) “strain-relief” flatjack tests exist that can be used to estimate the compressive properties of the masonry. Flatjack testing requires custom-fabricated, pillow-shaped steel bladders that, when deflated, are inserted into saw-cut mortar bed joints and pressurized to induce loads within a masonry wall. Reduction factors, calibrated based on the flatjack used, are applied to the measured flatjack gauge pressure to determine the actual compressive load induced on the surrounding masonry. Performing flatjack testing is a partially nondestructive test method in that, depending on the as-built conditions and in particular the thickness of the mortar joints, the test can be performed so as not to damage any masonry units, making the repair following the test a simple masonry joint repointing. Flatjack testing may be performed destructively if desired; however, repair or replacement of the masonry units would likely be required. The advantage of performing flatjack testing destructively is in the greater accuracy in the results, specifically when estimating compressive strength. When performing the test nondestructively, compressive strengths are estimated analytically. ASTM C1196, Standard Test Method for In-Situ Compressive Stress Within Solid- Unit Masonry, Estimated Using Flatjack Measurements, is one test that can be performed to determine the in-situ compressive stresses, if any, that exist within a given localized masonry section. Engineers and architects will specify this test when conditions arise that could potentially be caused by excessive localized compressive stresses such as spalled, bowing, or cracked masonry veneer. One cause of such conditions, for example, is a lack of or insufficient performance of brick veneer shelf angles, which can result in a stacking effect where loads from multiple floors of veneer are concentrated at the bottommost support point. Another common cause of such distress is unaccommodated expansion of clay masonry veneer, coupled with shortening of a cast-in-place concrete structure. These loads have the potential to locally overcome the compressive-strength capacity of the masonry material, resulting in distress as the loads release. Performing the ASTM C1196 test allows the engineer or architect to quantify the remaining in-service compressive stresses in order to subsequently recommend an appropriate repair. In performing the ASTM C1196 test to determine in-situ compressive stress, a series of gauge point pairs (typically four) are fixed to the wall at a set spacing vertically (typically 10 in.) and horizontally (typically between 3 and 4 in.). The vertical distance between each set of gauge points is accurately measured. Once the baseline Evaluating As-Built Prope rties of Masonry Wall Systems Using Investigative Laboratory and In-Situ Testing Tec hniques S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 4 9 Figure 1 – ASTM C1196 test setup sketch (ASTM C1196 [2009]). “stressed” measurement is taken, a horizontal slot is cut in the masonry between the pairs of gauge points, “relieving” any compressive stresses that may have been present in the masonry above the test area. The vertical distance between each set of gauge points is again accurately measured. If significant compressive stresses were present above the test area, the top gauge point in each pair will displace downwards under load when the slot is cut, bringing the gauge point pair closer together. Finally, the deflated flatjack is inserted into the sawed slot and pressurized incrementally with a hydraulic fluid, and gauge-point measurements are monitored until the initial presaw-cut measured distance between the gauge points is achieved. Figure 1 shows the test setup sketch from the ASTM publication, and Figure 2 shows a photograph of the test setup in the field. The corresponding calculated compressive stress applied by the flatjack to achieve the initial presaw-cut state is theoretically equal to the preexisting in-situ compressive stress. A second type of flatjack “relief” test is ASTM C1197, Standard Test Method for In-Situ Measurement of Masonry Deformability Properties Using the Flatjack Method. This test can be performed to estimate the compressive strength and compressive elastic modulus of an existing masonry structure or façade. It provides similar results to that of a brick prism compressive test; however, with the added advantage of being performed in the field where the removal of an intact prism is not an option. This is often the case on older structures with mass walls or significantly deteriorated masonry that cannot be removed in one piece. Engineers and architects will specify this test when the strength and deformability properties of a new repair material such as grout are to be specified such that the desired strength performance of the repaired wall, whatever that may be, is achieved or if additional loads from a building addition or renovation are to be applied to the load-bearing wall. The ASTM C1197 test is similar to the ASTM C1196 test; however, two flatjacks are used. The gauge-point pairs are located between the flatjacks, above and below. Figure 3 shows the test setup sketch from the ASTM publication, and Figure 4 shows a photograph of the test setup in the field. After the two slots are cut, the flatjacks are pressurized incrementally with gauge-point measurements taken between each increment. The gauge-point distances—converted to a strain measurement—and corresponding calculated compressive stress applied by the flatjacks are then plotted, providing the compressive stress-strain curve for the tested wall assembly. The ASTM C1196 and ASTM C1197 tests involve a similar procedure to obtain different results. It is important to note the differences between the two and to understand that neither test is a substitute for 5 0 • Ha r t m a n a n d K u c z y n s k i S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 Figure 2 – Flatjack installed in the field per ASTM C1196. Figure 3 – ASTM C1197 test setup sketch (ASTM C1197 [2009]). Figure 4 – Flatjack installed in the field per ASTM C1197. the other. ASTM C1196 estimates stresses within the wall, while ASTM C1197 estimates the strengths of the materials that make up the wall. Flexural Tensile Bond-Strength Testing Flexural tensile (bond) strength of the mortar in an existing masonry assembly is another physical property that may be required by an engineer or architect. The flexural tensile strength of a brick veneer assembly (specifically the tensile strength of the mortar bond to the masonry units) can be determined using ASTM C1072, Standard Test Methods for Measurement of Masonry Flexural Bond Strength. The procedure, per the test standard, calls for the use of a loading apparatus to be used on masonry prisms assembled during new construction. The loading apparatus as published in the ASTM standard is shown in Figure 5. The loading apparatus applies a flexural load to a single masonry unit to failure of the horizontal mortar bed joint. The measured failure moment is used to calculate the flexural tensile load at which the failure occurred. This is a laboratory test. However, when confronted with an existing structure, the test can also be performed in-situ because the removal and subsequent transport to an off-site laboratory of an intact prism of masonry from an old or deteriorated wall may be difficult. The test can be performed in-situ using an alternate modified approach to ASTM C1072. In the modified version of the test, the masonry bed joint and unit selected for testing are isolated on all but the bottom face; the masonry unit to be tested is held in place by only the bed joint. A custom clamp is affixed to the unit. A calibrated torque wrench, attached to the clamp, is then used to apply a moment to the unit, stressing the bed joint in flexure. The moment measured by the torque wrench at the point of failure of the bed joint is used to calculate the flexural tensile load at which the failure occurred. This modified methodology is beneficial in that it can be performed in-situ (shown in Figure 6). However, depending on the asbuilt conditions, obstructions to affixing the clamp on the tested unit are not uncommon, especially with a mass masonry wall or veneers with no cavity or grouted collar joints. These conditions restrict access to isolating the unit on five sides, and precautions have to be taken not to disturb the bed joint to be tested. Because of the complexity of performing this test and the inherent variability of material properties throughout a single given masonry wall assembly, a number of tests should be performed for statistical purposes. GROUND-PENETRATING RADAR (GPR) GPR is a nondestructive testing method for the evaluation of structural elements and materials. It is used to locate structural components, anomalies, and voids, and to approximate material thicknesses. A GPR control unit (shown in Figure 7) typically consists of an antenna that passes over the surface of the scanned area. The antenna emits electromagnetic waves through the material, which subsequently reflect from material interfaces of differing dielectric properties. The unit receives the reflected signals, which are then processed by a receiver and displayed to the user for visual interpretation. GPR is commonly used on concrete to determine the depth and spacing of steel reinforcing bars, to verify slab thickness, or to locate voids. But GPR can also be used on concrete masonry unit (CMU) walls to deter- S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 5 1 Figure 5 – ASTM C1072 test setup sketch (ASTM C1072 [2013]). Figure 6 – Modified ASTM C1072 setup in field. mine if the cells are grouted or ungrouted; and, if grouted, to determine the grout and/ or reinforcing spacing. GPR can be used on masonry or concrete to locate other embedded objects, such as electrical conduits or plumbing pipes. In the authors’ opinion, GPR often provides more reliable results than thermal imaging when used for locating voids or ungrouted masonry cells. Figure 8 shows a representative horizontal GPR scan of the interior face of an ungrouted (full-of-voids) CMU block wall. The y-axis represents depth (interior face of CMU measured at a 0-in. depth and increasing, moving to the exterior), while the x-axis is the distance scanned (moving laterally across the interior face of the CMU wall). In Figure 8, the consistent solid band across the top 7/8 in. of depth represents the thickness of the outer-face shell of the CMU. The repeating pattern of dark spots represents the air-filled voids in the CMU block (i.e., the cells). As shown in this scan, each CMU block has three ungrouted cells. At greater depths in this case, due to the obstructive large air voids, little information is known beyond the depth of the CMU cells, and the apparent wave-like features shown on the readout are simply reflections or “noise.” GPR is a useful tool for a quick evaluation of an unknown structure. While the GPR itself is purely nondestructive, it is important to verify results for calibration purposes, which can entail destructive probing at select scanned locations. Because of the nature of the technology in its utilization of radar waves, embedded objects can cause interference, which may inhibit the depth of the GPR’s visibility. For example, plaster wall or ceiling finishes reinforced with tight-knit wire mesh will restrict the visibility of anything deeper than the metal mesh, as the radar waves will simply reflect back and forth between the GPR and the metal lath. LABORATORY TESTING Mortar Analysis Petrography is the initial step in mortar compositional analysis and is conducted prior to chemical analysis in order to identify constituents of the mortar or conditions such as chemical alteration that may bias or interfere with the chemical analysis. Petrographic analysis of mortar commonly refers to the examination of thin sections of mortar using a polarized-light microscope. Using this method, one can determine the general composition and microstructure of the mortar sample. Petrographic studies are conducted in accordance with the petrographic examination portion of ASTM C1324, Standard Test Method for Examination and Analysis of Hardened Masonry Mortar, using the appropriate methods and procedures outlined in ASTM 5 2 • Ha r t m a n a n d K u c z y n s k i S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 Figure 7 – GPR control unit. Figure 8 – Horizontal GPR scan of the interior face of the CMU block. C856, Standard Practice for Petrographic Examination of Hardened Concrete. Masonry prisms can also be assessed for mortar-to-brick bond and other characteristics using the methods and procedures described in ASTM C856, Standard Practice for Petrographic Examination of Hardened Concrete, which also generally applies to brick and mortar. During this procedure, the quality of the bond is judged by the ease with which the brick is removed from the adjacent mortar. Cracks and discolorations in the brick masonry, filling of joints, and the condition of the mortar also may be visually observed. Following the petrographic analysis, the chemist uses several analytical techniques, as appropriate, to determine the proportions of constituents of the mortar. Example chemical analysis methods are as follows: • X-Ray Diffraction (XRD): XRD is used to determine the crystalline components of the mortar. The x-ray diffraction pattern of a crystalline substance is like a fingerprint that can be used to identify and determine the relative amounts of the components of a material that consists of a mixture of substances. • Acid Digestion: This procedure dissolves out the binders in the mortar to obtain the amount of acidinsoluble materials; typically, this is the fine aggregate content. The petrographic examination guides the chemist in determining whether any components of the fine aggregate are acid-soluble. If acid-soluble materials such as limestone are present, the resulting fine-aggregate content of the mortar is likely to be underreported. • Atomic Absorption Spectroscopy (AA or AAS): This procedure is used to determine the amount of a given element within the sample. In mortar analysis, AA is used to determine the amounts of specific elements in the dissolved or extracted binder. This information can help determine the amount of cement, lime, and sand in the mortar. • Loss on Ignition (LOI): A sample of mortar is heated to specific temperatures until no mass loss is detected at said temperatures. This procedure is used to determine the free water, combined water, carbonates, and carbonation. • Thermal Gravimetric Analysis or Thermogravimetric Analysis (TGA): TGA measures the change in mass from dehydration, decomposition, and oxidation reactions with time and temperature. Specific materials exhibit characteristic curves that can be used to identify the materials and determine how much of the material is present in a sample. This information can be useful for identifying components of a mortar that elude other analytical methods of analysis. • Chloride Content: Chloride content can be determined using either the water-soluble chloride analysis method given in ASTM C1218, Standard Test Method for Water-Soluble Chloride in Mortar and Concrete, or the acid-soluble chloride analysis method in ASTM C1152, Standard Test Method for Acid-Soluble Chloride in Mortar and Concrete. Mortars with high chloride content are more likely to cause corrosion of embedded metals, such as steel reinforcement and steel wall ties. The acid-soluble chloride content is the amount of chloride in the mortar from all sources: aggregates, mixing water, and cementitious materials; and any external sources such as deicing compound exposure. The water-soluble chloride content is the amount of chloride that is readily available to cause corrosion. The amount of chloride in a mortar can change throughout its service life due to absorption from the surroundings and potential changes in solubility and leaching. Obtaining accurate mortar composition can be not only a beneficial tool to diagnosing causes of masonry failures, but it can also be an aid in repair design. Repair mortars are typically designed to match the existing mortars’ chemical and physical properties so as to not cause undue stress to the adjacent masonry or to the new and existing mortar. By accurately determining the properties of the existing mortar, the repair designer is able to better specify mortar for repair work. While the tests and methods presented above are common tools for discerning mortar properties and characteristics, they comprise only a small sample of the tests available. A qualified laboratory should be consulted when mortar analysis is desired to determine the specific tests that are beneficial to the project. BRICK MASONRY ANALYSIS The properties of brick masonry units can greatly affect the performance of masonry wall assemblies. Often, brick specifications stipulate the grade of the brick units to be used. During masonry failure investigations, it is often advantageous to verify the properties of the installed brick. The most commonly performed laboratory tests used to determine brick unit properties are described in ASTM C67, Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile. Since it is difficult to remove all of the mortar within the pore structure of an existing brick unit, and the units have already weathered, current tests are not designed for brick taken from service. However, the test results are useful as a tool to determine the existing properties of the brick and also as a tool to help predict future durability. The tests that are most used are described as follows: • Absorption and Saturation Coefficient: These tests can be used to predict the brick’s durability. The 24-hour and five-hour boil absorption is found by submerging five half-brick units in cold (approximately room temperature) water for 24 hours and in boiling water for five hours, respectively. The saturation coefficient is then found by taking the ratio of the saturated weight of each brick from the 24-hour coldwater test (subtracting the unit’s dry weight) to the saturated weight of the corresponding brick from the five-hour boiling test (again, subtracting the unit’s dry weight). The saturation coefficient is generally defined as the ratio of easily filled to total fillable pore space in the tested material. Different grades of brick have different values for maximum acceptable absorption and saturation coefficient. • Freeze/Thaw: Another test that can be used to predict durability is the freeze/thaw test. Five half-brick units are subjected to cycles of freezing and thawing. One cycle consists S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 5 3 of the brick unit being soaked for approximately four hours in water and then moved to a freezer for approximately 20 hours. The test may be concluded at 50 cycles or when the brick unit develops cracks, breaks, or visually appears to have lost more than 3 percent of its original weight due to disintegration. The test is a measure of the brick’s durability under cyclic freezing and thawing conditions. ASTM C67 outlines other test methods, including compressive and shear-strength tests, elongation capabilities, and efflorescence potential. As with mortar analysis, a qualified laboratory should be consulted for test recommendations when brick analysis is desired. CASE STUDIES Two Mass Masonry Buildings, Southern United States In-situ testing and laboratory analysis were used on two large historic mass masonry structures in the southern United States. A representative photograph of one of the buildings can be seen in Figure 9. Some parts of the structures are over 100 years old. These structures had additions constructed in later years using different brick and mortar materials. The two structures were to be structurally upgraded to meet modern code requirements. Deterioration over time has led to significant voids throughout the mass wall system. The high amount of voids contained within the walls required extensive grout injection. The repair material was to be specified to meet the specific strength and material properties of the existing system. These existing material properties, being unknown, were determined via a combination of laboratory and field tests. GPR was also used to verify that the installation material—in this case a fluid-injection grout—was reaching the open voids within the walls. Strain-Relief Testing The ASTM C1197 test was performed on both structures, henceforth referred to as Building #1 and Building #2. The purpose of the test in this case was to estimate the compressive strength of the existing building materials. Five successful tests were performed on each structure, ten in total. Since both buildings had multiple dates of construction, tests were performed in areas representing each date of construction for the original walls and the additions. The stress-strain plots resulting from the ASTM C1197 tests for Building #1 are shown in Figure 10, including the three ages of the wall assemblies tested. The stress-strain plots for Building #2 are shown in Figure 11, including the two ages of the wall assemblies tested. As shown in Figures 10 and 11, it is clear that the physical properties of the brick masonry vary greatly, based on the time of construction. From these stressstrain curves, if the test were to have been performed destructively, the compressive strength of the masonry would be estimated using the stress at the failure section of the stress-strain curve. If the masonry is not brought to failure, as is the case with the tests shown in Figures 10 and 11, the compressive strength is estimated analytically. Typically, if the compressive strength is unknown but the elastic modulus is known, compressive strength can be estimated by dividing the elastic modulus by 550, as given in ASCE 41-06, Seismic Rehabilitation of Buildings. The compressive elastic modulus is estimated using the slope at the linear portion of the stress-strain curve. The compressive strength results from the 1900-era construction averaged approximately 300 psi, the 1930 results averaged approximately 500 psi, and the 1998 results averaged approximately 4,000 psi. This approximation, while not exact, is accurate enough for the purposes of this scenario. The measured or calculated compressive-strength data were then used by the consulting engineer in order to specify the target strength range of the custom-manufactured grout material appropriate for these specific walls for all dates of construction. Ground-Penetrating Radar GPR was used on the mass masonry walls to determine the extent of voids and to locate any potential embedded objects within the walls. Locating embedded objects such as conduits was important in order for the installation of wall anchors to proceed without encountering unseen obstacles. Voids were mapped prior to an extensive injection grout installation in order to verify the depth of grout penetration and the filling of major voids to within an established tolerance. 5 4 • Ha r t m a n a n d K u c z y n s k i S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 Figure 9 – Representative view of subject buildings. GPR was successful in verifying the depth of grout penetration and for locating power conduits. The mass masonry walls were scanned with GPR prior to the installation of the injection grout, and again scanned with the GPR after the repair injection grout installation. Laboratory Studies Clay brick samples from Building #1 and Building #2 were also analyzed in the laboratory to determine the existing material properties. Absorption tests for saturation coefficient were conducted in accordance with ASTM C67. Compressive strength tests of the brick units were also performed. Per the project’s specifications, the repair material was to match (within a reasonable tolerance) the moistureperformance properties of the existing wall to be repaired. The information gathered via the lab studies was invaluable for the specification of the repair grout material in order for the repaired wall to meet these predetermined moisture-performance requirements. Petrographic analysis on mortar samples from both buildings was also performed in accordance with ASTM C1324 in order to provide information on the quality, composition, and raw proportions of the existing mortar. To summarize, the analyses found that the mortars at both buildings contained Portland cement and hydrated lime paste/binder. The mortars were also analyzed chemically and with X-ray diffraction, again following the ASTM C1324 standard. These tests determine ratios of the minerals and elements that make up the mortar. This ratio data was then used to calculate an estimated original strength of the mortar. Contribution of In-Situ and Laboratory Tests Combining the laboratory tests with the in-situ testing, the consulting engineer was able to recommend a series of repair grout options for mock-up testing. The laboratory testing on the mortar provided information on mix ratios and moisture performance properties of the existing mortar. From a strength perspective, the flexural bond strength of the mortar and the compressive strength of the brick-and-mortar assembly were determined in the field. Compressive strength of the mortar was estimated using the laboratory chemical and x-ray diffraction studies, and compressive strength of the brick units was also measured in the laboratory. This wide range of tests provided invaluable information to the consulting engineer in recommending an appropriate repair grout for injection into the void-filled mass walls. Mock-up testing and further laboratory testing of the recommended repair grouts S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 5 5 Figure 10 – Stress-strain plot of the ASTM C1197 tests for Building 1. Figure 11 – Stress-strain plot of the ASTM C1197 tests for Building 2. were performed to ensure the recommended products met the predetermined specifications provided to the consulting engineer. Residential Building Complex, Northeastern U.S. The subject buildings are residential apartments composed of four adjoining sixstory apartment buildings located in the northeastern U.S., constructed in 1952. A representative photograph of the buildings is shown in Figure 12. Each building’s façade consists of a mass masonry wall composed of one (exterior) wythe of brick and one wythe of CMU. Header courses of the outside wythe of brick are laid into the CMU backup course. Each building has punched window fenestrations. The roofs consist of a modified-bitumen membrane over a wood deck and wood framing with a three-wythe brick masonry parapet at the roofs’ perimeters. In 2007, repairs to the buildings were performed by the contractor based on design documents provided by the architect of record. Repairs included the rebuilding of the masonry parapets. Subsequent to completion of the repairs, a third-party consultant hired by the building owners alleged that the parapets were structurally deficient. The claims included that the brick-to-mortar bond and the mortar strength were insufficient. This allegation was made by the consultant following his visual observations of how the mortar completely separated from the brick units as probes were being made. Flexural Tensile-Bond Strength Testing Initially, flexural tensile-bond strength tests were performed. Testing was employed utilizing techniques outlined in ASTM C1072, Standard Test Method for Measurement of Masonry Flexural-Bond Strength, modified for field applications. A total of 12 flexural tensile-bond strength tests were performed at two discrete locations. During the bond wrench testing, it was typical for the removed brick to fully separate from the mortar, frequently leaving the mortar bed in the wall. This was consistent with the allegations that initiated the investigation. However, the measured average flexural tensile-bond strength of the brick mortar joints was 190 psi at the first test and 254 psi at the second test location. Table 1 below includes the results of each test. Laboratory Studies Laboratory studies were conducted on brick masonry prisms sampled from the two probes to determine brick and mortar characteristics. The scope of the laboratory studies included petrographic examination of the brick-mortar interface in the new brick construction and compositional analyses of two samples of the new mortar. Petrographic studies of the brick-mortar bond were conducted using methods described in ASTM C856, Standard Practice for Petrographic Examination of Hardened Concrete, which also applies to other construction materials. The petrographic studies were conducted in accordance with the petrographic examination portion of ASTM C1324, Standard Test Method for Examination and Analysis of Hardened Masonry Mortar. Mortar samples from the probes were analyzed using the appropriate analytical methods outlined in ASTM C1324. 5 6 • Ha r t m a n a n d K u c z y n s k i S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 Figure 12 – Representative view from street elevation of the subject buildings. Table 1 – Results of ASTM C1072 tests. The bond between the brick and mortar was also judged to be strong via the petrographic examination. Contribution of In-Situ and Laboratory Tests Based on flexural tensile-bond strength testing, the flexural tensile strength of the mortar bed joints at the reconstructed parapet walls is very strong when compared to the governing design code in effect when the repairs were performed. The measured flexural- bond strength values may also be used during structural evaluation of the parapets in lieu of the assumed values suggested in applicable design references. The measured flexural bond strength far exceeded that required by governing code and thus proved that the mortar-to-brick bond strength did not decrease the structural capacity (per the original design) of the parapet. This contradicted the claims that initiated the investigation. Furthermore, the laboratory analysis confirmed the strong mortar-to-brick bond. Both the in-situ and the laboratory tests were very useful in this case study to substantiate the true flexural bond strength of the masonry, via scientific data rather than by visual observation. SUMMARY When diagnosing failures and as-built conditions of masonry wall systems, it is often advantageous to determine the asbuilt conditions of the subject structure as well as the chemical and/or physical properties of the wall’s components through both in-situ and laboratory testing. In-situ tests include compressive stress and strainrelief testing, flexural tensile bond-strength testing, and wall scanning using GPR. Material samples may also be collected and sent for laboratory testing, including mortar petrography; mortar proportions analyses; and determination of the brick’s future durability via testing to determine the saturation coefficient, absorption, freeze/thaw durability, etc. The discussed testing techniques and procedures can be implemented to determine the existing properties of a wall assembly and its materials, allowing for effective failure diagnoses and providing critical information required to properly design a repair. The combination of field and laboratory testing can be used to corroborate findings and substantiate test data. SOURCES American Society of Civil Engineers (ASCE). Seismic Rehabilitation of Existing Buildings (41-06). Reston, VA, 2007. ASTM International (ASTM) Standard C67, 2012, Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C0067-12 ASTM Standard C270, 2012a, Standard Specification for Mortar for Unit Masonry, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C0270-12A ASTM Standard C856, 2011, Standard Practice for Petrographic Examination of Hardened Concrete, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C0856-11 ASTM Standard C1072, 2013, Standard Test Methods for Measurement of Masonry Flexural Bond Strength, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/ C1072-13 ASTM Standard C1152, 2014 (2012), Standard Test Method for Acid- Soluble Chloride in Mortar and Concrete, ASTM International, West Conshohocken, PA, 2003, DOI: 1 0 . 1 5 2 0 / C 1 1 5 2 _ C 1 1 5 2 M – 04R12E01 ASTM Standard C1196, 2009, Standard Test Method for In Situ Compressive Stress Within Solid Unit Masonry Estimated Using Flatjack Measurements, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C1196-09 ASTM Standard C1197, 2009, Standard Test Method for In Situ Measurement of Masonry Deformability Properties Using the Flatjack Method, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C1197-09 ASTM Standard C1218, 1999 (2008), Standard Test Method for Water- Soluble Chloride in Mortar and Concrete, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C1218_C1218M-99R08 ASTM Standard C1324, 2010, Standard Test Method for Examination and Analysis of Hardened Masonry Mortar, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C1324-10 S y m p o s i u m o n B u i l d i n g E n v e l o p e T e c h n o l o g y • No v e m be r 2 0 1 3 H a r t m a n a n d K u c z y n s k i • 5 7
