Full-Scale Field Testing for Injected Foam Stabilization of PCC Repairs

Transcription

1 Full-Scale Field Testing for Injected Foam Stabilization of PCC Repairs Lucy P. Priddy, PE Research Civil Engineer U.S. Army Engineer Research and Development Center 0 Halls Ferry Rd Vicksburg, MS 10 Lucy.P.Priddy@usace.army.mil Phone: 01-- Fax: Sarah R. Jersey, PE Research Civil Engineer U.S. Army Engineer Research and Development Center 0 Halls Ferry Rd Vicksburg, MS 10 Sarah.R.Jersey@usace.army.mil Phone: 01-- Fax: Cody M. Reese, PE Research Mechanical Engineer U.S. Naval Facilities Engineering Command, Engineering Services Center 10 rd Ave Port Hueneme, CA, 0 Cody.Reese@navy.mil Phone: 0-- Fax: 0--1 Words:, Figures: Tables: Equivalent Words:, Page 1 TRB 0 Annual Meeting CD-ROM

2 Abstract A series of foam-injected repairs were performed on a portland cement concrete (PCC) test section at the U.S. Army Engineer Research and Development Center. Repairs consisted of uncompacted backfill overlaid by a -in. rapid-setting cementitious cap. A series of injection tubes were inserted through the cap into the uncompacted debris backfill, and a two-component rigid polyurethane foam was injected into the underlying backfill. The test matrix compared the performance of three different repairs using various volumes of injected foam. A fourth repair was constructed without injected foam as a control item. Three hours after cap construction, the repairs underwent simulated aircraft traffic using an F-1E load cart. The performance of the four repairs was measured in terms of passes to failure. The results of traffic testing were used to evaluate foam-injection technology for rapid repair of PCC pavements. The performances of foam-injected repairs were also compared with poured foam and traditional full-depth backfill repairs, each capped with rapid-setting materials. Comparisons were in terms of pavement performance, costs, and total duration required installing the repair. Results showed that injection of excessive foam was detrimental to repair surface, inducing cracking prior to traffic application, potentially leading to the premature development of FOD. However, repairs using moderate amounts of foam and pure backfill sustained the required traffic levels, defined by the research sponsor, of 00 passes within hours of initiating the pavement repair. In terms of cost and repair duration those repairs that did not include foam were more effective. Page TRB 0 Annual Meeting CD-ROM

3 INTRODUCTION Due to short construction and rehabilitation windows, new rapid repair techniques are required for deteriorated portland cement concrete (PCC) pavements on airfields. For military and civilian runways, construction windows may be as short as hr. To complete rehabilitation with the allotted timeframe, many local and federal agencies have adopted the use of rapid-setting cementitious materials in lieu of traditional PCC. The development of laboratory testing protocols to reduce the selection of inferior repair products has improved construction techniques and long-term performance and durability of repair efforts (1,,,,). However, selection of an appropriate repair product is not the only issue that individuals tasked with conducting pavement repairs must address. Repair materials can be used directly on the existing subgrade surface when deterioration of these materials has not occurred. In scenarios where the subgrade has weakened due to water infiltration through the deteriorated pavement or from drainage or environmental conditions, the sublayer materials must be removed and replaced. In these situations, time required to remove or replace a weakened subgrade will either increase the total repair time or reduce the time available for the rapid-setting material to cure. As a result, new rapid backfill technologies must also be investigated. Priddy et al. (,) investigated the applicability of using pourable polyurethane foam as a backfill replacement material. Several rigid, polyurethane foams, typically used for architectural molding and insulation, were evaluated under laboratory and field conditions. Foams were mixed and placed by hand or with specially developed equipment. When compared to the equipment required to place and compact traditional pavement materials, the use of foams reduced repair logistics. After curing, in as little as 1 minutes, these foams exhibited compressive strengths similar to compacted soil or aggregate. Although results of field and laboratory tests were favorable for this technology, the mixing and dispensing equipment required significant improvements before application of this technique for repair volumes greater than yd (). Priddy et al. () also investigated the use of concrete rubble (1 to ft in diameter) as a rapid backfill material. The use of uncompacted concrete rubble was advantageous due to reduced logistical requirements. The debris generated when deteriorated PCC slabs were removed could be reused immediately without the need for crushing and compacting aggregate. This also reduced the amount of material required for disposal. Concerns about settlement of the debris under traffic can be alleviated by filling the voids. This can be accomplished with flowable fill or foam. Tests indicated that pourable foam was not appropriate for debris stabilization due to the expulsion of concrete rubble during foam expansion. Confinement of the debris was required to resist the lifting action of the foam. Additionally, pressure injection was required for foam to penetrate and fill the voids. In response to this need, an investigation into a technology typically used for raising in-place slabs, known as slab jacking, was initiated. RESEARCH OBJECTIVES The primary objective of this study was to quantify the benefits of foam-injection technology for conducting rapid repairs of PCC pavements. The scope of this work included construction of full-scale repairs and simulation of traffic using an F-1E load cart. This paper summarizes the construction, trafficking, monitoring, and performance of each repair, including passes to failure. Results of traffic tests of the completed repairs were compared to performances of previous full-depth PCC repairs with traditional backfill materials such as compacted stone or aggregate. Additionally, comparisons of the foam-injected repairs to poured foam and traditionally backfilled repairs are provided. Pertinent conclusions from the testing are summarized, and recommendations for future investigations are provided. Page TRB 0 Annual Meeting CD-ROM

4 METHODOLOGY The experimental program consisted of testing a foam-injection system for conducting rapid PCC repairs on a simulated airfield pavement. Four full-depth patches were repaired in an experimental test section at the U.S. Army Engineer Research and Development Center (ERDC). After a short cure time, approximately three hours, each repair was trafficked until failure under simulated F-1E aircraft traffic. During trafficking, limited instrumentation measurements were recorded, and physical damage to all repairs and passes-to-failure rates were determined. BACKGROUND Many state departments of transportation and airfields have used slab jacking techniques for slab stabilization (). Slab jacking is a quick and often economical method to raise a settled area to the desired elevation by injecting cement grouts, mud-cements, or polyurethane foams under the slabs, filling the voids. By raising the settled area, the ride quality of the section improves, and the risk of failure of the section under repeated trafficking is reduced. In 00, the U.S. Navy developed a small foam-injection system by partnering with a slab jacking company. The goal of the investigation was to determine if foam injection could increase the bearing capacity of uncompacted soil and fill voids under disturbed pavements. Reese () indicated that the repair concept could be used to stabilize debris backfill in small-scale field and laboratory tests. No quantifiable measurements of strength before and after foam injection were conducted during these experiments; the primary focus of the study was proof of concept. Following the small-scale tests, a proprietary expeditionary injectable-foam system was developed for full-scale field testing. This expeditionary injection system was housed in a tri-con-sized container that could be loaded and transported on the back of a flatbed truck or military cargo aircraft. The C- 10 transportable container housed most of the items necessary for a foam injection operation: component supply pumps, two heated metering injection pumps, one air compressor, shielded heated injection hoses for each metering pump, two injection guns, injection tubes, gun connector fittings, a hammer drill, drill bits, hand tools, and spare equipment parts. The two-component polyurethane liquids that combine to generate the foam and a 1-kW generator were not housed with the injection system. FOAM INJECTION Foam Materials The foam selected for all repairs was generated from a two-component liquid system consisting of isocyanate and polyol precursor liquids. The mixing of the two components in specific ratios produces polyurethane foam. This is a standard lifting material for slab jacking operations. Although this specific polyurethane foam formulation is proprietary due to its moisture tolerance, most polyurethane foams have the same general chemistry, consisting of isocyanate component and a polyol component. For this experiment, the components were housed in 0 gal totes. The mixing ratio for the two components of this foam was 1:1 by volume. The mixing in this system was automatically controlled with pumping/metering equipment selected by the manufacturer. Once the components were combined at the mixing head, an exothermic reaction began that resulted in the generation of carbon dioxide and subsequent formation of closed cells (bubbles) as well as the polymerization of the liquids into hardened form. The foam creation became visibly noticeable after approximately 0 seconds. Page TRB 0 Annual Meeting CD-ROM

5 Immediately after mixing and before the foaming action was noticeable, the liquid was forced through steel injection tubes into the ground where the cells expanded and hardened rapidly into a rigid solid with a lb/ft density in the unconfined or free-rise condition. General Injection Methodology A four-man team was used for the injection process. Steel injection tubing was used to direct the injected foam into the backfill at desired depths. The injection tubing was stored within the tri-con container (in lengths up to ft). Prior to foam injection, the tubing was cut to lengths proportional to the desired injection depth. Each injection tube had an inside diameter of 1/ in. and an outside diameter of / in. with an attachable. degree cone tip, which aids in driving the tubes into the backfill. An operator drilled through the pavement layers using a hammer drill fitted with a / in.- diameter drill bit to provide adequate room to insert the injection tubing. Again using the hammer drill, the injection tubes were then forced into the pre-drilled holes. Once the tubing was inserted to the desired depth, excess tubing remained above the pavement surface or was saw cut and ground to recess the tubing below the pavement surface. The injection tube tip was then removed by placing a steel rod inside the placed injection tube to force the tip from the tubing. The tip was removed immediately prior to the injection of that site, as early removal of tips might have resulted in foam or debris entering the tubing, prohibiting injection of that site. Once the tubing was inserted, the injection process began. For alignment, a laser level system was set up on both the surrounding (parent) pavement and the cap surface next to the injection hole to be filled. This laser system alerted the operator when the repaired cap surface had reached a cumulative surface deformation of 0.1 in. due to pressure from the subsurface foam injection. Failure to stop the injection after the received warning could have resulted in excessive injection, cracking the surrounding pavement and destroying the repair cap. The injection gun and hose were then placed into the first injection tube. During injection, the foam flowed through the system. First, supply pumps fed the foam components from the totes into the metering injection pumps. The pumps metered, heated, and pumped the individual foam components into heated gun supply hoses, which ran to an injection gun with a mixhead for mixing the foam components. To inject the foam, the gun tip was forced into the top of the first injection tube. While the gun was held in place, the trigger was squeezed and released in a 1 to 0 sec cycle, allowing the foam to flow and expand. This process was repeated until the laser level receiver warning indicated surface movement of 0.1 in. After that point, the operator moved the laser receivers to the next injection site and repeated the process until all tubes were injected. Once all injections were complete, any excess tubing protruding from the surface was removed. The tubes were ground, recessed, and sealed with epoxy. FULL SCALE FIELD TESTING Test Section Description The test section consisted of 1 in. of PCC over a compacted subgrade with a modulus of subgrade reaction, k, of 1 psi/in. The full-scale concrete test section consisted of a 0-ft wide by 10-ft long section divided into three lanes of slabs each 0-ft wide and 0-ft long. The test section was exposed to the environment and was originally designed to withstand 0,000 passes of an F-1E aircraft. Soils testing conducted at the time of construction revealed the subgrade material was sandy, lowplasticity clay with a Unified Soil Classification () of CL. The percentages of gravel, sand, and fines in the soil were 0., 1., and. percent, respectively. The soil s liquid limit and plasticity index Page TRB 0 Annual Meeting CD-ROM

6 were and 1 percent, respectively (1). With modified Proctor compaction (1), this soil had an optimum moisture content and a maximum dry density of approximately. percent and lb/ft, respectively. During concrete placement, beams and cylinders were cast onsite and were tested for flexural and compressive strength to ensure the concrete met specifications (1, 1). After days of curing, the compressive and flexural strengths were measured as,1 psi and 0 psi, respectively. Rapid Repair Procedures After days of curing, square repair test items of varying sizes were prepared in the PCC pavement. Each item was located on the interior section of the original pavement slabs. The repair items were prepared by saw cutting the PCC. Repair Items 1 through were simulated by saw-cutting three -ft by -ft squares within the exterior lane of slabs to simulate a full-depth PCC repair. Item was reused following all field tests as Item. The concrete was broken and removed using a skid-steer with breaker attachment, and the subgrade material was removed to a total repair depth of. ft using a mini-excavator and hand shovels. Foam components were stored onsite to allow the materials to equilibrate to ambient air temperatures before repairs were conducted. Dynamic cone penetrometer (DCP) tests were then performed to determine the strength of the repair subgrade (1), for which no compactive efforts were used. Moisture and density measurements were performed with a nuclear gauge (1, 1). Three replicates were conducted per repair. Table 1 summarizes average density, moisture, and strength data obtained at the subgrade surface. TABLE 1. Moisture, density, and CBR strength measurements for uncompacted subgrade Nuclear Gage Measurements DCP Item Depth (ft) Material Dry Density (pcf) Wet Density (pcf) Moisture Content (%) Estimated Strength, CBR (%) 1. Sandy Clay.... Sandy Clay Sandy Clay Sandy Clay The excavated PCC and subgrade materials were reused as debris backfill for the repairs. The PCC rubble was mixed with the excavated subgrade material. Samples were collected from the debris to characterize the grain size distribution (Figure 1). The debris material was placed in each repair by a skid steer with a bucket attachment. Materials were not compacted aside from densification associated with pluviation of the backfill during the repair process. When backfill reached a depth of in. from the PCC pavement surface, the debris was manually spread across the surface of the backfill to prevent penetration of the rapid-setting capping material into the voids in the backfill and to provide a relatively smooth surface for construction of the surface cap. Due to the makeup of the backfill, traditional tests such as DCP or plate bearing were not conducted to determine the uncompacted backfill strength. Following the placement of the debris base, a four-man team placed -in.-thick caps consisting of a commercially available, rapid-setting concrete mix. Following manufacturer mixing instructions, a single batch was mixed for each repair in a prototype portable concrete mixer with a capacity of yd. The capping material was a high-early strength cementitious-type material with hr compressive strengths of,000 psi or greater. Each repair cap was struck level and hand troweled immediately following placement. Curing compound was not used, nor was the repair moist cured. Each repair was cured for 1 hr prior to foam injection activities. The repairs were surveyed prior to foam injection to quantify relative changes in elevation due to the injection process. Page TRB 0 Annual Meeting CD-ROM

7 To obtain information to validate observations from previously conducted full-scale testing, limited instrumentation was placed in the repairs. Earth pressure cells (EPCs) were placed in the center of each repair atop the exposed subgrade prior to placement of the repair materials. EPCs were placed to monitor the distribution of stress at the interface between the repair materials and the subgrade. The EPCs were in.-diameter, hydraulic-oil-filled, stainless steel devices with a range of 0 psi. These sensors were installed by leveling the surface of the subgrade with a 1 in. layer of sand. The sensor and wires were covered with additional sand to protect the instrumentation. Despite this effort, the EPC used for Item 1 was damaged during foam injection, and no data was available for review. A series of temperature sensors were also placed in the surface cap to monitor the temperature generation during curing of the rapid-setting material at depths of 1 in.,. in., and in. below the surface of the -in. thick cap. These sensors were mounted on wooden dowels and were hammered into the backfill just prior to cap placement. EPCs and temperature sensors were not placed in the control repair. The four test items were designed to test different repair procedures. Although the injection method had been used extensively for fully cured PCC pavements to raise in-place slabs, no injections had been conducted under young, recently placed pavements. The test matrix investigated the number of foam injection sites and injection depths. Figures and show the general repair procedures used in this study. Table summarizes the foam volume and the time required to perform foam injection for each test item. Items 1 through were constructed on three consecutive days. Each item underwent initial traffic testing (00 passes) hours after construction. The remaining traffic testing of each test item was performed once all test items were complete. After construction and traffic testing of Items 1,, and was completed, Item was re-excavated for subsequent construction and traffic testing of a control item (Item ). Item was backfilled using reserved debris generated during excavation of Items 1 through. This repair was constructed in a similar manner as the previous test items, excluding the foam injection process. Significant cracking occurred during the injection of Item 1 due to the high number of injection sites and the high volume of injected material (Figure ). Due to the resulting cracking in the rapidsetting cap and surrounding slabs, both the number of injection sites and the quantity of foam were greatly reduced for Items and. Traffic Testing Procedures For each item, a simulated normally distributed traffic pattern consisting of 1 passes was applied in a.-ft-wide traffic lane. These lanes were designed to simulate the traffic distribution pattern, or wander width, of the main landing gear wheel of an F-1E aircraft on the concrete surface when taxiing on an active runway. The F-1E aircraft generates one of the worst-case damage scenarios to a repair due to its, lb being distributed over three tires, with the main gear tires having a tire pressure of psi. Traffic was applied by driving a specially designed single-wheeled load cart. The pass-to-coverage ratio for this traffic pattern was.0. Each repair was trafficked until failure occurred. The repair surface was periodically inspected for damage; however, maintenance was not conducted during or after the traffic testing process. Repair failure was expected to occur due to surface deterioration or crushing of the foam backfill under the heavy vehicle traffic. Visual inspections were performed at selected traffic intervals to identify specific distresses associated with high foreign object damage (FOD) potential such as cracking, spalling, or scaling. Cracking was considered minor unless spalled material accumulated, the repair was divided into or more pieces by intersecting cracks (shattered), or if crack widths exceeded 1 in. When distresses posed high FOD potential or tire hazards were identified, the repair was considered failed. Page TRB 0 Annual Meeting CD-ROM

8 TABLE. Total injected foam weight and time required for foam injection of repairs Number of Foam Injected Time Required Item Injections (lb) (min) 1 1, U.S. Standard Sieve Sizes " " " 1" # # #1 #0 #0 #0 # Percent Finer by Weight Percent Coarser by Weight Cobbles Grain Size in Millimeters Gravel Sand Coarse Fine Coarse Medium Fine FIGURE 1. Grain-size distribution for the debris backfill. Page TRB 0 Annual Meeting CD-ROM

9 FIGURE. Clockwise from top left: backfilling with debris; debris backfill surface; rapidsetting cap; typical injection tube layout FIGURE. Clockwise from top left: laser level setup and injection; injection tubing recessing; completed repair with excessive cracking (Item 1); close-up of spalling of cracks at failure. RESULTS AND DISCUSSION Data collected during traffic testing included periodic surface condition assessments (distress data), heavy weight deflectometer (HWD) readings, instrumentation results, and pavement elevation readings. Condition assessments, HWD tests, and elevation surveys were performed at 0,, 1, Page TRB 0 Annual Meeting CD-ROM

10 ,00, and,000 passes, corresponding to 0,, 1,, and 00 coverages. Instrumentation response data were obtained more frequently. Based on the Navy s expedient pass criterion a repair was considered successful when it remained serviceable after 00 passes (,1). These tests were also conducted at repair failure. Surface Condition Data During trafficking, all items were monitored for any changes in surface condition. Item 1 was monitored closely due to cracks that occurred during the injection process. During trafficking, additional cracking between injection points was monitored. As trafficking progressed, small pieces of the repair cap rocked under traffic, and spalling along the cracks and edges of the cap became progressively worse. A close-up view of the intersecting cracks and spalling at failure is presented in Figure. Following 1,00 passes, Item 1 was considered failed due to cracking (shattered cap) and FOD potential. During trafficking of Items,, and, spalled material accumulated along the edges of the cap. Failure of these items was due to high-severity FOD potential on the repair edges at 1,; 1,00; and 1,00 passes, respectively. HWD Data Deflections measured with the HWD were normalized to an applied force of 0,000 lb. These values represent the deflection under the load plate, which was located at the center of the repair. Figure shows the degradation of pavement stiffness during traffic testing. This figure indicates increased deflections in the control item relative to the foam-injected items. The deflections associated with the control repair were much higher than those observed in the foam-injected test items at failure. Excessive foam backfill material and the resulting surface cracking observed in Item 1 may have led to the increased deflections relative to Item under the initial traffic testing. The 0% reduction in foam backfill by volume between Items and resulted in increasing measured deflection by more than %. As mention previously, failure was due to high-severity FOD generation for all repairs except Item 1 that failed due to shattered repair cap and FOD. The reduced deflections in the foam-injected repairs indicate that these repairs may have sustained extended traffic if spalling had not occurred. Temperature Sensor Data Temperatures were measured 1-in from the cap surface, in the center, and 1-in. from the cap bottom during the repair process. Data was recorded starting immediately after placement of the cap. Figure presents average temperatures generated in the cap during the -hour period following cap placement. The injection process began an hour after cap placement. An inflection point is present in the temperature curves, corresponding to injection. The presence of foam in the backfill increased measured surface temperatures at this time due to the exothermic reaction of the foam. The rate of temperature reduction can be attributed to the volume of foam. Increased volumes simultaneously provided increased temperatures after injection and insulation, delaying the return to ambient temperatures. Temperature sensors were not placed in the control repair. It was expected that heat generation in the control repair would follow trends observed in historical testing of these repair materials (, ). Page TRB 0 Annual Meeting CD-ROM

11 Item 1 Item Item Item (Control) 1 Normalized Deflection, mils , ,00 1,00 0 1, , , ,000 1,00 1,00 1,00 1,00 Passes FIGURE. Increase in measured normalized deflections under aircraft traffic. 10 Item 1 Item Item Temperature, F Surface Deformations Time, hr FIGURE. Average temperature generation in rapid-setting cap. Surveys were performed along the repair surface at periodic intervals, including before-foam injection, after-foam injection, and throughout traffic testing. Figure shows the profiles taken along the center of the traffic lane for Items 1 and. The data at a -ft offset represent the edge of the repair as well as the edge of the parent material. A larger volume of foam was injected into Item 1 than into Items and. The figure indicates that the quantity of foam injected into Item 1 induced measureable movements in the repair surface. This phenomenon was not observed in Items and, in which less foam was used. The surface Page TRB 0 Annual Meeting CD-ROM

12 deformation data are further supported by cracking that was visually identified prior to traffic. As the repairs deteriorated under traffic loading, spalled edges produced FOD, which was removed. FOD production and removal was evident in Item 1 along the edges of the repair after 1,00 passes, as Figure shows. Item 1 Item Elevation, ft Surface Pre-Foam Inj. Surface Post-Foam Inj. Surface Passes Surface 1 Passes Surface 1,00 Passes Surface 1,00 Passes Elevation, ft Surface Pre-Foam Inj. Surface Post-Foam Inj. Surface Passes Surface 1 Passes Surface 1,00 Passes Surface 1,00 Passes Offset (ft) Offset (ft) FIGURE. Measured surface elevations along center of traffic lane (Items 1 and ). BENEFITS OF FOAM INJECTION RELATIVE TO HISTORICAL TESTS In 00, two-component polyurethane foams of two densities were used to fill excavated repairs and to provide a suitable surface to place the cap. These repairs had the same geometry, used the same materials during capping, and were trafficked and monitored for deterioration in the same manner as the foam-injected repairs presented in this study. An additional repair conducted using clay gravel during this time is also presented to compare foam backfill to a traditional backfill material when capped with the same material and cap thickness. Results of tests from 00 testing validated that pourable, rigid polyurethane foams, were viable options for backfilling repairs without the need for quality backfill materials. These repairs did not, however, sustain as many passes prior to failure as the clay gravel repair (). Table includes critical results from the injectable foam, the full-depth, pourable foam, and a clay gravel backfill options. No data is available for peak temperature or peak stress for Item. Due to instrumentation failure, no EPC (i.e. peak stress) data is available for Item 1 and Item F from 00. As Table shows, these repairs sustained 1,0 to,000 passes before failing. The measured passesto-failure met or exceeded both U.S. Air Force (0 to 1,00 passes) and U.S. Navy (00 passes) requirements for expedient repairs. The repair sustaining the most passes was the clay gravel backfill repair sustaining,000 passes prior to failure with the debris backfill repair sustaining 1,00 passes. Repair Time The time required to conduct repairs should be considered as part of the selection process when investigating repair alternatives. Figure presents a summary of the time required to conduct the repair from the beginning of backfilling to the onset of traffic testing. As this figure shows, the injectablefoam process did not increase the total repair time, as the injection process and the cap curing were performed concurrently. For the three foam-injected repairs, differences in total repair times were due to the placement time required for the caps. Item 1 required an additional 0 min due to a very stiff mix used for that repair cap. Additionally, the repair speed increased as the crew gained experience Page 1 TRB 0 Annual Meeting CD-ROM

13 with using the rapid-setting material and mixer. An increased amount of water was used in Items and to reduce the labor and time required to complete the cap (with minimal impact to the repair strength). The time to mix and place the repair cap may also be reduced if mixing equipment with larger batch capacities is used. Figure also indicates that the backfill time can greatly be reduced by using only debris or by using foam injection with debris. Reducing the time spent on backfilling is the most effective method for reducing overall repair time. It should be noted, however, that overall repair durations would decrease for all repair methods as users become increasingly familiar with the equipment. Test Year Item Backfill Type Failure Mode 0 1 Foam/ FOD debris ( Potential inj. Sites) 0 Foam/ FOD debris ( Potential inj. Sites) 0 Foam/ FOD debris ( Potential inj. Sites) 0 Debris FOD (Control) Potential 0 F1 1-lb Foam FOD Potential 0 F -lb Foam FOD Potential 0 G Clay FOD Gravel Potential TABLE. Summary of Repair Failures Failure Detail High-severity joint spalls/ shattered slab High-severity joint spalls High-severity joint spalls High-severity joint spalls High-severity joint spalls High-severity joint spalls High-severity joint spalls Passes- to- Failure # Peak Temp. ºF Peak Deflection mils Passes at Peak Deflection # Peak Stress psi 1,00 1 1,00 No data Passes at Peak Stress # 1, 1 1,00. 1,11 1, 1, ,00 No 1,00 No data data 1,00 1 1, , 1,0 10 1,0 No data, ,1 Repair time comparison Backfilling Capping Foam Injection Cap Curing Repair Time, hr ,000 Passes 1,0 Passes 1,00 Passes Cap mixing time increased due to failure of mixer Total cure time = Cap curing + Foam Injection ( hr) 1,00 Passes 1, passes 1, Passes1,00 Passes 0.00 FY0 Repair: Clay Gravel FY0 Repair: -lb Foam FY0 Repair: 1-lb Foam Current Repair: Injections- Foam/Debris Current Repair: Injections- Foam/Debris Current Repair: Injections- Foam/Debris Current Repair: Debris 1 Backfill Option 1 FIGURE. Comparison of required repair times. Page 1 TRB 0 Annual Meeting CD-ROM

14 1 1 1 Repair Costs The costs associated with a repair technique play an important role in the selection process, since materials with excessive costs may not be feasible, regardless of the increase in structural capacity. The material costs for the foam-injected, poured-foam, clay gravel, and pure debris backfill repairs were compared. Manpower costs were excluded from this comparison as -man teams were utilized all repair efforts; however, costs associated with labor can be extrapolated from the time required to complete each repair, as shown in Figure. Additionally, equipment costs were not included as the studies utilized prototype equipment not commercially available. As Figure shows, the debris backfill option was the least expensive with the only expense being the rapid-setting cap. Because the 1-lb density poured-foam repair had a lower expansion ratio resulting in increased material requirements, it was the most expensive option. These costs provide an additional means for selecting the appropriate repair alternative. Repair material cost comparison Actual Backfill Cost Ave. Cap Cost Repair Cost, $,00,000,00,000,00,000,00,000,00,000 1,00 1, ,000 Passes FY0 Repair: Clay Gravel 1,0 Passes FY0 Repair: -lb Foam SUMMARY AND CONCLUSIONS 1,00 Passes FY0 Repair: 1-lb Foam 1,00 Passes Current Repair: Injections- Foam/Debris Backfill option 1, Passes Current Repair: Injections- Foam/Debris 1, Passes Current Repair: Injections- Foam/Debris FIGURE. Cost comparison for different repair methods. 1,00 Passes Four full-repairs were constructed and tested during this study. Repairs included removal and replacement of subgrade materials followed by placement of a rapid-setting cementitious cap. After capping, foam was injected into the backfill to improve the structural stability of the repair. The test matrix compared repairs, which used three different foam volumes as well as a control repair, as they underwent testing using normally distributed simulated F-1E aircraft traffic. Traffic was applied three hours after construction. Results from these tests were compared to those for poured foam and a traditional backfill material. The following conclusions were derived: 1. The use of foam-injection for backfill stabilization met the Navy s pass-to-failure requirement of 00 passes.. Repair failures generally were due to FOD production.. The foam-injected repairs provided more passes prior to failure and were generally less Current Repair: Debris Page 1 TRB 0 Annual Meeting CD-ROM

15 expensive and time consuming than the pourable foam repairs of 00.. Despite early cracking due to excessive injection, Item 1 sustained 1,00 passes prior to failure, and the cracking did not result in a significant tire hazard for the aircraft. This repair sustained pass-tofailure levels on the same order as the debris and clay gravel backfilled repairs.. The foam-backfilled repairs (injected or pourable) repairs were not cost effective options.. The use of debris backfill eliminated the requirement for compaction compared to the clay gravel repair reducing the overall repair time.. The use of debris backfill provided similar pass-to-failure numbers as traditional backfill materials such as clay gravel. In terms of cost, this repair was the most economical solution and provided reuse of pavement debris to conduct repairs.. Based on the repair costs and durations associated with the foam-injected backfill methods, the debris backfill method was more economical. However, the foam injection methods may be more suitable in scenarios where quantities of high-quality debris backfill, similar to that used in this investigation, are not available. The foam injection technology used in this study may also be beneficial in expeditionary slab-jacking scenarios.. Prior to repair technique implementation, construction and trafficking of replicates for all repairs are needed to validate repair performance benefits observed during this research. ACKNOWLEDGEMENTS The tests described and the resulting data presented herein were obtained from research sponsored by Headquarters, Air Combat Command and Headquarters, Department of the Navy by the Office of Naval Research, Rapid Technology Transition Office. This work was conducted at the U.S. Army Engineering Research and Development Center, Waterways Experiment Station. Permission was granted by the laboratory director to publish this information. REFERENCES 1. Vaysburd, A.M., P.H. Emmons, J.E. McDonald, R.W. Poston, and K.E. Kesner. Performance Criteria for Concrete Repair Materials, Phase II Summary. Technical Report REMR-CS-. U.S. Army Waterways Experiment Station, 1.. Shoenberger, J.E., W.D. Hodo, C.A. Weiss, P.G. Malone, and T.S. Poole. Expedient Repair Materials for Roadway Pavements. ERDC-GSL Technical Report 0-0. U.S. Army Engineer Research and Development Center, 00.. Air Force Civil Engineering Support Agency (AFCESA). Engineering Technical Letter (ETL) 0-0: Testing Protocol for Rigid Spall Repair Materials, Tyndall AFB, FL, 00.. National Transportation Evaluation Program Accessed July 1, 00.. Priddy, L. P., S. R. Jersey, and R. B. Freeman, Full-Scale Traffic Tests and Laboratory Testing Protocol for Determining Rapid-Setting Material Suitability for Expedient Pavement Repairs. Transportation Research Record: Journal of the Transportation Research Board, Transportation Research Board of the National Academies, Washington, D.C., 00 (in press).. Priddy, L. P., J. S. Tingle, T. J. McCaffrey, and R. S. Rollings. Laboratory and Field Investigations of Small Crater Repair Technologies. ERDC/GSL TR-0-. U.S. Army Engineer Research and Development Center, 00.. Priddy, L.P., C. Moore, and E. Padilla. Advanced Airfield Damage Repair Technologies-Phase I. ERDC/GSL TR-0-. U.S. Army Engineer Research and Development Center, 00. Page 1 TRB 0 Annual Meeting CD-ROM

16 Tingle, J.S., L.P. Priddy, C. Gartrell, M. Edwards, and T.J. McCaffrey. Critical Runway Assessment and Repair (CRATR) Technology Demonstration: Tyndall Air Force Base, Florida. ERDC Technical Report GSL-0-1. U.S. Army Engineer Research and Development Center, 00.. Soltesz, S. Injected Polyurethane Slab Jacking. Final Report SPF 0-1. Oregon Department of Transportation, 00.. Reese, C.M. Foam Injection Airfield Damage Repair System: Using Injectable Foam to Stabilize Crater Backfill-Phase I Conceptual Testing. Test Report. Naval Facilities Engineering Command Engineering Services Center, 00.. American Society for Testing and Materials (ASTM). Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System. Designation D -0. West Conshohocken, PA, ASTM. Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. Designation D West Conshohocken, PA, ASTM. Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. Designation C -. West Conshohocken, PA, ASTM. Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading). Designation C -. West Conshohocken, PA, ASTM. Standard Test Method for the Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications. Designation D 1-0. West Conshohocken, PA, ASTM. Standard Test Method for Water Content of Soil and Rock in Place by Nuclear Methods (Shallow Depth). Designation D West Conshohocken, PA, ASTM. Standard Test Method for Density of Soil and Rock in Place by Nuclear Methods (Shallow Depth). Designation D -0. West Conshohocken, PA, Headquarters, Naval Facilities Engineer Command Engineering Services Center. Airfield Damage Repair: Using Injectable Polyurethane Foam to Compact Fill within Airfield Craters. Draft TTP, Port Hueneme, CA, 00. Page 1 TRB 0 Annual Meeting CD-ROM