Long-Term Performance of Epoxy Adhesive Anchor Systems (2013)

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E-1 A P P E N D I X E Adhesive-Alone Tests—University of Florida

E-2 ADHESIVE-ALONE TESTS—UNIVERSITY OF FLORIDA This chapter presents the test program conducted at the University of Florida to investigate the isolated sustained load and short-term creep behavior of the adhesive alone. Test apparatus This section describes the test apparatus used for the dogbone and DMTA and creep testing. Dogbone Short-term Testing Apparatus The short-term testing was done on an INSTRON 5582 load frame (Figure 1) with a load cell capacity of 2250 pounds. The temperature of the sample was controlled by an oven accessary (Figure 2). Figure 1: INSTRON tensile testing machine. Figure 2: The oven, which pulls forward around the INSTRON, used to keep the samples at temperature. Dogbone Sustained Load (Creep) Testing Apparatus The sustained load creep tests were done on custom built test frames (Figure 3). The sample was suspended from the frame by an eyehook. The load was applied to the sample through a 24” long lever arm with a 10:1 ratio and was transferred to the dogbone sample

E-3 through a hook on the lever arm as well. The self-weight of the lever arm resulted in around 80 pounds of base load on the sample and additional weight could be added to the end of the lever arm. Each test frame had two grips used to clamp the dogbone sample shown in Figure 4. A jig was used to ensure a consistent clamping position of the dogbone. In addition, 60 grit sandpaper was inserted between the grip and the dogbone to increase the friction and prevent slippage between the dogbone and the grips. Once the dogbone sample was clamped by hand tightening the screws on the grips, the sample was then inserted into the test frames between the two hooks mentioned above. Prior to loading, the upper eyehook’s height was adjusted until the lever arm was horizontal. With the lever arm supported, the lower hook would become disengaged. Such a design ensured the dogbone sample would not be subjected to a load prior to testing. During testing, as the dogbone elongated during creep, the lever arm would gradually displace downwards. Figure 3: Test frames for sustained load dogbone testing. Figure 4: Dogbone specimen loaded in grips.

E-4 DSR Machine The DMTA and creep tests were performed on a TA Instrument’s AR-EX2000 DSR machine with a rectangular torsional grips and an environmental test chamber (ETC). The heating of the ETC was achieved through a peltier element and the ETC was air cooled by a Thermo Cube is 10-300A-1-AR system. Figure 5 shows the DSR machine with the ETC open for sample loading. Figure 5: DSR machine. Specimen fabrication This section describes the fabrication of specimens used for the dogbone and DMTA and creep testing. Adhesive The same three adhesives identified earlier were used in this portion of the project. The three adhesive products were stored in an environmentally controlled room maintained within the temperature and humidity range specified by the manufacturers prior to installation. Dogbone Sample The silicone molds (Figure 6) for the dogbone samples were made from Dow Corning Silastic E RTV Silicone Rubber with dogbone shaped steel blanks. The steel dogbones were machined according to the Type I dogbone shape specified in ASTM D638. Once the silicone was cured, the steel dogbones were removed.

E-5 Figure 6: Silicon molds for casting dogbone specimens. The dogbone samples were cast into the pre-made silicone molds directly from the tube. Due to the viscosity difference between the three adhesive, there was a slight difference in preparing the exposed smooth surface. Adhesives A and B were allowed to overflow the mold and a razor blade was used to screed the excessive adhesive in one pass thereby leaving a smooth surface. Later it was decided that such a procedure resulted in too rough a surface for Adhesive A and the procedure was modified as follows. Once overfilled, a piece of glass was pressed against the mold to squeeze the excessive adhesive out. Since Adhesive A showed almost no adhesion to glass, the glass was detached easily after the sample cured. Adhesive C was too sticky for any overfill-screed processing. Fortunately it was found that Adhesive C would slowly flow before gelation and the final procedure for making Adhesive C was to carefully control the amount of the adhesive injected into the mold and let the adhesive flow under gravity and form the smooth surface. Specimens for DMTA and Creep Testing The specimens for DMTA and creep testing (Figure 7) on the DSR machine were rectangular thin sheets with a thickness ranging around 0.039” (1.00mm), width of approximately 0.35” (9mm) and a length of approximately 2” (50mm). These sizes were chosen based on recommendations from the DSR equipment manufacturer. The precise control of the thickness of the specimen was very important for the accuracy of the measurement and every

E-6 effort was made to ensure the sample thickness variation was within ±0.0008” (±0.02mm) throughout the sample length. A thin sheet was first made by casting a quantity of adhesive into an aluminum plate and placing spacers of 0.039” (1.00mm) thickness (glass slides were used) around edges of the plates. Another aluminum plate was placed on top of adhesive and pressed to squeeze out the excess adhesive. When the adhesive sheet was cured, the specimens were cut into small rectangular strips by a precision diamond saw. Again due to the different adhesion behavior of samples, the processing of the thin sheets was slightly different. For Adhesive A, it was found that it did not adhere to the aluminum plate and they were therefore directly placed onto the aluminum plate. For Adhesives B and C, the aluminum plate was coved by a thin cyclic olefin copolymer sheet prior to casting the adhesives. Figure 7: DMTA and DSR creep specimens. Instrumentation This section describes the instrumentation used for the dogbone and DMTA and creep testing. Measurement Strain. The creep of the dogbone sample was measured with strain gauges. All strain gauges were purchased from Micro-Measurement. The gauge designation was C2A-XX-250LW- 350 for Adhesives A and C while adhesive B used EP-08-250-BF-350. Both types of strain gauges had an initial resistance of 350 ohm and a gauge factor slightly larger than 2 (2.09 for B

E-7 and 2.12 for A and C). The strain gauges used for Adhesive B could detect strain up to 20% while for Adhesives A and C the strain gauges had a limit of 3%. The measurement of the strain gauge resistance was through a quarter-bridge setting. The strain of the short-term tests was measured by an INSTRON 2630-115 extensometer attached to the sample surface along the loading direction. Load. The tension in the dogbones was measured indirectly from a relationship to the load applied to the end of the lever arm. For the short-term tests, the loads were measured directly by a load cell. Temperature. Ambient air temperature in the test chamber was measured by a Cincinnati Sub-Zero EZT-560i Environmental Chamber Controller installed in the Cincinnati Sub-Zero Model WM-STH-1152-2-H/AC Walk-In Stability Chamber. Analog cards installed in the Cincinnati Sub-Zero EZT-560i Environmental Chamber Controller provided an analog signal output allowing the ambient air temperature to be monitored by the data acquisition system. Humidity. Relative humidity in the test chamber was measured by a Cincinnati Sub-Zero EZT-560i Environmental Chamber Controller installed in the Cincinnati Sub-Zero Model WM- STH-1152-2-H/AC Walk-In Stability Chamber. Analog cards installed in the Cincinnati Sub- Zero EZT-560i Environmental Chamber Controller provided an analog signal output allowing the humidity to be monitored by the data acquisition system. Time. Time was measured using the computer’s internal clock. Instrument Calibration Strain. The extensometer was automatically calibrated with the built-in function of the measurement software. Load. The INSTRON 5582 calibrated its load cell electronically by the built-in software function before every set of tests. The load cell was allowed to warm up for 15 minutes before calibration. Each test frame lever arm was calibrated with an Omega Engineering, Inc. Model ICCA-10K 10-kip load cell in order to determine the load applied to a dogbone specimen due to the addition of load on the end of the lever arm. The load cell was calibrated on an INSTRON System 3384 150 kN universal testing machine. Temperature. The National Semiconductor LM35 Precision Centigrade Temperature Sensors factory calibration was validated in June 2010 against a high quality mercury

E-8 thermometer over a temperature range of 100°F to 120°F (43°C to 49 °C). The temperature sensor in the test chamber was calibrated by the factory. Humidity. The humidity sensor in the test chamber was calibrated by the factory. DSR Machine. The system inertial and rotational friction mapping was done with the built-in function of the DSR machine software daily before every set of experiments. The stiffness of the DSR machine geometry was provided by the manufacture. Environmental control This section describes the environmental control for the dogbone tests. The environment for the DMTA and creep tests was controlled via the testing device. Standard Temperature An air conditioned space was used to store and condition the adhesive and the dogbone specimens at 75ºF ±10ºF (24ºC ±5ºC) and 50% ±10% relative humidity. Temperature was controlled by a Frigidaire air conditioner. Elevated Temperature A 12’ by 12’ by 8’ tall Cincinnati Sub-Zero Model # WM-STH-1152-2-H/AC Walk-In Stability Chamber was used to condition and test at the elevated testing temperature of 110ºF +10ºF/-0ºF (43ºC +5ºC/-0ºC)and below 40% relative humidity for the sustained load (creep) test. The chamber was purchased and installed in the fall of 2009. The chamber had a temperature range of -20°C to 60°C (-4°F to 140°F) and a relative humidity range of 10% to 95%. The chamber was equipped with a CSZ EZT-560i Touch Screen Controller to monitor and control the temperature and humidity. The dogbone test specimens were placed in test frames located on shelves 5 feet high in order to provide space for anchor testing below (Figure 8 and Figure 9).

E-9 Figure 8: Left side of testing chamber. Figure 9: Right side of testing chamber. Data management and acquisition During the testing and conditioning of the test slabs to the elevated temperature, a Microsoft compatible computer ran several National Instruments LabVIEW 8.6 software programs developed by the author to collect, record, and display the data. Measured values included load, displacement, temperature, humidity, and time. Data acquisition was performed with a National Instruments NI cDAQ-9172 chassis with several National Instruments NI 9219

E-10 modules and a NI 9205 module to interface with the instrumentation. Data acquisition for the DSR creep tests was conducted directly by the DSR machine. Data Sampling Program A LabVIEW 8.6 program (Figure 10) was developed to centrally sample data for every test. This program provided a half-second time averaged record sampled at 2000 Hz. Global variables for each of the sixteen sustained load test frames were updated every half second to the computer memory to be read when needed by the separate LabVIEW programs for each test frame. Each global variable included a timestamp, strain, and environmental chamber temperature and humidity. Figure 10: Data sampling LabVIEW program. Long Term (Creep) Test Program A LabVIEW 8.6 program (Figure 11) developed for this project was used for the sustained load (creep) test. Strain, temperature, and humidity readings were recorded at one of the following two conditionings: If the difference between the last recorded strain and current reading was larger than 2E-6. Every ten minutes if no change in strain larger than 2E-6 occurred.

E-11 A strain versus time curve (Figure 12) for each dogbone specimen was displayed on the screen for real-time feedback. The latest data readings were displayed on the screen and each data reading was automatically recorded in a Microsoft Excel spreadsheet. Figure 11: Sustained load test LabVIEW program (main screen).

E-12 Figure 12: Sustained load test LabVIEW program (strain plot). Specimen preparation procedure The standard specimen preparation procedure is described below for the dogbone specimens and the DMTA and creep specimens. Dogbone Specimen Preparation To prepare the dogbones for strain gauges, the center of the dogbone was first degreased using isopropyl alcohol, and then polished successively using 120 and 300 grit sandpaper in the presence of the conditioning solvent from Micro-Measurement. After polishing, neutralizing solvent was applied to adjust the pH of the dogbone surface for optimal strain gauge adhesion. The strain gauge was attached to the degreased and polished dogbone along the principle strain direction using adhesive tape first for easy handling of the strain gauge. Extra care was taken during the handling of the strain gauges to ensure the strain gauges were never touched directly by fingers. After partly peeling away the adhesive tape along with the strain gauge, a thin layer of the M-bond 10 adhesive from Micro-Measurement was applied underneath the strain gauge to permanently attach it to the dogbone sample. The M-bond 10 adhesive was allowed to cure in the test chamber for two hours before the dogbone specimens were loaded.

E-13 DMTA and Creep Specimen Preparation For samples A and B, the thin sheets made for DMTA and creep testing were cut into the specimen strips after proper curing. For sample C, small white spots due to improper mixing were commonly present and care was taken to ensure that the final specimen strips were free of these imperfections. Specimen conditioning This section discusses the specimen conditioning for the dogbone and DMTA and creep test specimens. Dogbone Short-Term Testing The short-term testing specimens were conditioned the same as the sustained load testing specimens as described below. Dogbone Sustained Load (Creep) Testing Upon completion of the seven day adhesive curing period, the test specimens for test series 21 were placed into the 110ºF (43ºC) 35% humidity environmental test chamber for conditioning. The temperature of the environmental chamber as well as the humidity in the environmental chamber were monitored and recorded. Testing began upon completion of the 24 hour conditioning period in the environmental test chamber. DMTA and Creep Testing The conditioning of the DMTA and creep testing samples and the sustained load (creep) test samples were all at 24 hours. After 12 hours of conditioning inside the environmental test chamber the DMTA and creep testing samples were removed and cut into small specimen strips. After cutting, the specimens were returned to the environmental test chamber for the remaining 12 hours of the 24 hour conditioning duration. Testing began after the completion of conditioning. Testing procedure The standard testing procedures for the short-term tests, sustained load (creep) tests, and DMTA and creep tests are described below.

E-14 Dogbone Short-Term Test Procedure Once the samples were conditioned, the area where the sample was clamped by the grip was roughed by sand paper and the samples were moved into the oven of the INSTRON for several minutes to reach 110°F (43°C). The samples were clamped between the grip with sand paper for increased friction and a stable grip during test. An extensometer was then clipped onto the sample. Once the samples were loaded, they were allowed to equilibrate with the temperature for an additional five minutes. The extensometer was calibrated and both the extensometer and the load cell were zeroed. After entering the test speed and sample dimensions of the dogbone in the testing software, the test was started. Dogbone Sustained Load (Creep) Test Procedure Once the dogbone specimens were conditioned and the strain gauges were attached, they were placed in the testing frame without additional weight placed on the lever arm and the lever arm was immediately supported so that no load was applied to the dogbone sample. The top eyehook was adjusted so that the initial position of the lever arm was horizontal as confirmed by a tubular spirit level. While still supported, additional steel weights as determined from the calibration factors were applied to the lever arm. Subsequently, the strain gauge was connected to the data acquisition hardware. Finally, the testing began as one person removed the support underneath the lever arm while another person started the data acquisition process in LabVIEW. DMTA and Creep Test Procedure After the torsional grip was mounted in the DSR machine, calibration tests for the system inertial and rotational friction mapping were performed. The grips were then brought to within 0.1” (3mm) of each other and the software was allowed to determine the zero position of the grip gap, which corresponded to the length of the sample during testing. The dimension of the conditioned test strip was first measured and inputted into the DSR machine software and then placed into the grip and tightened to 5.3 in-pounds (60 cm-N) using a torque screwdriver. A 0.03” (0.75mm) spacer was used to align the specimen per recommendations of the DSR machine manufacturer. Next, the ETC was closed and the temperature inside set to the desired experimental temperature through the DSR machine software. Once the temperature stabilized, the specimen would be conditioned at the temperature for 10 minutes before testing. Based on a preliminary test, the dynamic storage modulus of the specimen became stable after 10 minutes of

E-15 conditioning at the test temperature, which indicated the 10 minutes condition time is sufficient for the relatively thin specimen strips to reach the stable test temperature. Throughout the test, a 0.07±0.4 pound (0.3±0.2 N) tension force was applied to the specimen to compensate for any thermal expansion. Each creep test was 30 minutes in duration. The test specimen dimensions were entered into the DSR software and the shear stress was precisely controlled by the DSR software. The DSR machine recorded the radial displacement of one end of the strip in relation to the other end and automatically calculated the conversion of strain and compliance.