Rapid Slab Repair and Replacement of Airfield Concrete Pavement (2021)

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19   Partial-Depth Repair As defined in Chapter 1, PDR refers to the removal of small areas of damaged pavement contained within the top half of a concrete slab and replacement with a cementitious, polymeric, or other specialty repair material. PDR is a common practice to maintain and preserve concrete airfield pavements. When correct materials are selected and proper construction techniques are employed, PDR can be a cost-effective, long-term solution for concrete pavement repair needs. This chapter discusses the appropriate distresses, materials, design, and construction for a PDR project and presents an assessment tool to help users evaluate the considerations necessary to complete a successful PDR. Introduction to Partial-Depth Repair At airports, PDR is typically used to address concrete surface defects that can lead to FOD, which can damage aircraft or inhibit the safe passage of aircraft (Speer 2007, Hammons and Saeed 2010). However, PDR is also very important for preservation of concrete pavement. Spalling at joints, cracks, and midslab locations is the most common candidate for PDR [FAA 2014b, U.S. Department of Defense (DOD) 2018]. Spalling typically occurs when pieces of concrete are dislodged from a transverse crack or joint (or midslab). Figure 8 shows examples of spalling at joints and cracks and midpanel. Candidate Distresses and Conditions PDR is appropriate for addressing distresses that are confined to the top half of the slab and to relatively small surface areas. Distresses that have been successfully corrected with PDR include • Spalling caused by the intrusion of incompressible materials into the joints; • Spalling or raveling caused by poor consolidation or improper joint formation; • Surface delamination or spalling caused by weak concrete, clay balls, or reinforcing steel located too close to the surface; and • Spalling caused by lightning strikes and isolated to the top half of the slab. PDR is not a long-term solution for correcting surface deterioration resulting from the following causes (Smith et al. 2014, U.S. DOD 2018): • Improper finishing and curing during construction (e.g., shrinkage, map cracking), • Environmental deterioration [e.g., freeze–thaw damage, durability cracking (D-cracking), scaling], and • Undesirable chemical reaction (e.g., alkali–silica reactivity, alkali–carbonate reaction). C H A P T E R 3

20 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Source: Nichols Consulting Engineers, Chtd. Figure 8. Candidate spalling conditions for partial-depth repair: (a) joint spalls, (b) crack spalls, (c) midslab spalls, and (d) deterioration of previous spall repairs.

Partial-Depth Repair 21   There are, however, situations where these distresses present an immediate safety hazard (e.g., FOD or depression) and temporary PDRs have been effectively used as a stopgap measure until a long-term treatment can be planned and executed. In these cases, the primary purpose in addressing these conditions is to quickly restore pavement serviceability and to ensure overall safety. Material Selection Several materials are available for use with PDR, and, in general, PDR material specifications vary between agencies. FAA AC 150/5380-6C (FAA 2014b) and AC 150/5370-10H (FAA 2018) provide limited guidance on PDR patching materials. The U.S. Army Engineer Research and Development Center (ERDC) conducts extensive assessment of various proprietary PDR repair materials. Recent findings are detailed in Evaluation of Concrete Spall Repair Materials (Falls 2019) and Evaluation of Rapid-Setting Cementitious Materials and Testing Protocol for Airfield Spall Repair (Ramsey et al. 2020). FAA AC 150/5380-6C (FAA 2014b) references use of P-501 cement concrete pavement, as well as state department of transportation (DOT) specifications for allowable materials. The U.S. DOD Unified Facilities Criteria for operations and maintenance (O&M), the O&M Manual: Asphalt and Concrete Pavement Maintenance and Repair (U.S. DOD 2018), classifies materials in three categories: cementitious, polymeric, and bituminous (generally regarded as a tempo- rary repair material for concrete pavements). Cementitious materials are commonly based on ASTM C150 (Standard Specification for Portland Cement) Portland Cement Type I, but ASTM C150 Portland Cement Type III is allowed when the repair needs to be opened to traffic within 1 to 3 days after placement. Smith et al. (2014) list the following materials as possible options for PDR: • Most repair material is produced with either ASTM C150 Portland Cement Type I (with set- accelerating admixture) or Portland Cement Type III. In addition to strength, consideration must be given to the following material properties that affect short- and long-term performance: coefficient of thermal expansion (CTE), elastic modulus, shrinkage, and bond strength. Some agencies have standard HES concrete mixtures for PDR, but there are also several commercially available proprietary mixtures. • Modified hydraulic cement concrete includes concrete made with modified cement, gypsum- based cement, calcium aluminate cement, calcium sulfoaluminate (CSA) cement, and other hydraulic cement–based mixes, most of which meet ASTM C1600 requirements. • Gypsum-based cements have very quick set times, are resistant to deicing chemicals, and typically require dry installation conditions. • CSA cements are a modified derivative of portland cement clinker; they exhibit rapid strength gain, good durability, low shrinkage, and high sulfate resistance. • Calcium aluminate cements are similar to CSA, having rapid strength gain, good bonding properties, and good resistance to freeze–thaw cycles and deicing chemicals and exhibit- ing low shrinkage. However, concrete made from calcium aluminate cements undergoes a phenomenon called conversion, during which a portion of the concrete strength is lost. The mix design should be evaluated with a conversion test to ensure the converted strength exceeds the specified strength (Adams 2015). • Polymer-based and resinous concrete are combinations of polymer resins, an initiator, and, often, aggregate. The aggregate is added as a filler and reduces costs, provides a durable wearing surface, and makes the thermal characteristics (as assessed by CTE) more consis- tent with that of concrete. Polymers exhibit faster strength gain than typical cementitious materials but can be expensive and sensitive to temperature and moisture. Some of these

22 Rapid Slab Repair and Replacement of Airfield Concrete Pavement repair materials are very flexible and can be placed across joints and cracks without the need to reestablish the joint. Urethane resins and epoxies are common polymers used for pavement repair applications. • Polyurethanes are two-component materials that are very flexible and typically exhibit rapid strength gain. However, these materials are known to have very high CTE values, can be very sensitive to mixing and moisture, and exhibit large initial shrinkage. • Epoxy polymer concretes typically have very good adhesive capabilities and are impermeable. However, these products have a wide range of bonding capabilities, setting times, applica- tion temperatures, and strengths. They also exhibit high CTE values, and compatibility with concrete needs to be considered. • Magnesium-phosphate concrete is a very rapid-setting material with HES gain. Materials are impermeable but very sensitive to water (in the mix or on the repair surface). Clean, dry surfaces are needed for bonding. Workability can be a challenge in hot weather due to short set times, but some of the products are specially formulated for hot-weather applications. • Conventional or modified bituminous materials are low-cost, short-term, bituminous-based materials. They are easily applied and widely available and can be opened to traffic very quickly. Polymer-modified bituminous materials have shown better performance than unmodified materials but have a higher cost. These materials are typically considered to be temporary for PDR of concrete pavement, and the U.S. DOD O&M Manual (2018) does not allow bituminous materials for concrete airfield pavement PDR. For this reason, bituminous PDR materials are not considered further in this report. The selection of repair materials for long-term PDR applications is based on several factors, including the specific application, environment, performance history, and facility opening-to- traffic requirements. Opening-to-traffic requirements are often the most important factor; however, products with very early opening times are more expensive. Factors to consider for PDR material selection include the following (Smith et al. 2014): • Time available for construction and strength gain (i.e., closure time), • Ambient conditions during and after placement, • Repair material properties (e.g., CTE, shrinkage, bond strength), • Material and installation costs, • Handling and workability, • Compatibility with the existing concrete pavement, • Repair size and depth, • Alignment of material performance capabilities and performance requirements (expectations) of the repair, and • Project size or number of anticipated repairs. Other factors not specifically mentioned by Smith et al. (2014) include • Equipment requirements (and capabilities) for mixing and material application; • Complexity of mixing and material application; • Long-term durability, especially in harsh environments; • Agency maintenance and contractor employee exposure and safety (i.e., hazards associated with materials); and • Agency maintenance and contractor employee experience with the material. Ultimately, three major factors need to be considered when a PDR material is being selected for airport pavement repairs: (1) closure time (minimizing operational delays), (2) compatibility with the surrounding concrete, and (3) long-term durability, especially in harsh environments.

Partial-Depth Repair 23   As there are numerous commercial (and sometimes proprietary) products available for constructing PDRs, a material selection screening process that includes the following steps can be used: • Assess the products on the basis of project needs and conditions by reviewing product literature and talking with manufacturer representatives. • Obtain airport references from the manufacturer and speak with previous users of the product. It is often best to contact similarly sized airports and inquire about products used, lessons learned, and recommendations. • Request that the manufacturer provide a demonstration by installing the materials in non- critical areas before they are used in operation-critical locations. One airport agency commented that the materials used for PDR do not necessarily need to be the most expensive or the newest on the market. Rather, it is important to identify and use the product that best suits the needs of the airport and the knowledge and skills of the personnel who will mix, handle, and install the product. HES materials can be difficult to handle and install. Even if construction crews have experience, they should demonstrate their ability to properly install the materials off-site or start work on the least critical areas (e.g., aprons) before moving to critical areas (e.g., runways). These materials can be very sensitive to weather conditions during installation and curing; manufacturer’s recommendations should be followed. Design PDR projects may or may not use detailed plans and specifications. The design process differs depending on the extent and nature of the PDR (i.e., emergency versus nonemergency). Emergency repairs generally rely on standard details and materials on hand. For larger PDR projects, plans and specifications can be used (particularly for bidding), but the use of stan- dard details is more common. Following are some considerations, particularly for larger PDR projects: • Material requirements: FAA AC 150/5380-6C references the use of P-501 cement concrete pavement or state DOT materials for PDR (FAA 2014b). Proprietary material specifications are often provided by the manufacturer. PDR material requirements commonly focus on strength gain and final strength, bond strength, shrinkage, CTE, and other important properties. • Provisions for disincentives when repairs affect critical airport operations: Provide incen- tives for early completion. Penalties for not returning pavement to service are generally much more severe for runways (e.g., $500/minute) but can be applied to other areas if they are critical to operations. Small PDRs are likely to be completed within the allotted closure, especially if an appropriate material is selected. • Plan details: Design should include plan dimensions and depth details, but requirements can vary by product. Design efforts also need to consider contingencies in case some of the PDR locations are determined during construction to be better candidates for FDR. • Quality control/quality assurance (QC/QA): Because batch sizes are generally quite small, extensive material testing is not practical. QC/QA for PDR is more often based on observations of means and methods, such as verifying preparation steps, material mixing and handling, finishing, and curing methods. • Opening-to-traffic requirements: Opening to traffic is often based on time. This is because material testing is commonly less extensive for PDR than FDR or other large concrete place- ments. Often a prescriptive number of hours or days is used as the opening criterion when

24 Rapid Slab Repair and Replacement of Airfield Concrete Pavement work is being done within certain specified temperature conditions. The required times can be established during the mix design stage for cementitious products or established by the manufacturer. • Provision for a preconstruction conference: It is advisable to hold a preconstruction meet- ing prior to closing pavement areas and allowing construction work to proceed. Confirming work methods, personnel responsibilities, site safety, and security are significant factors in the success of PDR projects. • Requirement for just-in-time training: This training should cover product specifics and include a provision for a product installation demonstration on a noncritical pavement area (or off-site). This is especially important when new repair materials are being used, especially early-strength materials. Construction In general, steps for PDR construction are provided by Hajek et al. (2011), Frentress and Harrington (2012), Smith et al. (2014), FAA (2014b), the U.S. Air Force (USAF 2017), and the U.S. DOD (2018) and are as follows: 1. Determine and mark repair boundaries (confirm design plans). 2. Demolish and remove concrete. 3. Clean and prepare repair area. 4. Reestablish joint, as needed. 5. Place and consolidate repair material. 6. Finish and cure repair. 7. Reseal joints, as needed. 8. Open to traffic. Each step of the PDR construction process is further described in the following sections. Boundary Selection and Marking Aside from visual characterization of distress, the limits of deteriorated concrete can be determined by the sounding method, which consists of striking the concrete with a solid steel rod or a hammer and listening to the resulting sound. A dull sound is heard if the concrete is weak or delaminated, whereas a ringing sound is indicative of sound concrete. For larger areas, a chain drag or delamination detection tool can be used. Figure 9 shows examples of the sounding method. Once the distressed area is identified, the repair boundary is established as follows for conventional cementitious repair materials (Wilson et al. 2001, Frentress and Harrington 2012, USAF 2017, U.S. DOD 2018): • The boundary should extend at least 3 inches beyond the unsound concrete on all sides. • The minimum repair length is 15 inches (the U.S. DOD recommends 6 inches). • The minimum repair width is 10 inches (the U.S. DOD recommends 6 inches). • The minimum repair depth is 2 inches and should extend 0.5 inch into visually sound concrete. • Repair boundaries should be kept square or rectangular; irregular shapes are to be avoided. Dimensions for PDRs that use a proprietary material should be in accordance with the manufacturer’s recommendations. The proximity of patches to one another should also be considered. FAA guidance suggests that spall repairs less than 1.5 feet apart should be combined into one repair (FAA 2014b). The

Partial-Depth Repair 25   U.S. DOD (2018) provides similar guidance but indicates combining repairs if they are within 24 inches. Repairs that are greater than half the thickness of the pavement are not candidates for PDR on an airport. If load-transfer devices are observed in the damaged area while marking boundaries, FDR is the appropriate repair option (see Chapter 4). Concrete Demolition and Removal Once the repair area has been identified and marked, the damaged concrete within the repair boundaries is removed. Figure 10 shows schematic examples of different types of PDRs, and Table 9 provides basic descriptions and photos of each repair type. Source: (a) Nichols Consulting Engineers, Chtd., and (b) Applied Pavement Technology, Inc. Figure 9. Sounding method using (a) hammer and (b) steel rod. Source: Nichols Consulting Engineers, Chtd. Type 1 Mid Panel and Corner Type 2 Transverse Joint Type 2 Longitudinal Joint Type 1 Joint Type 2 Crack Figure 10. Types of partial-depth repairs.

26 Rapid Slab Repair and Replacement of Airfield Concrete Pavement There are four general PDR removal methods: (1) saw and chip out, (2) chip out, (3) mill out, and (4) clean out (Smith et al. 2014). 1. Saw and chip out: A diamond-bladed saw is used to outline the repair boundaries (Figure 11). The depth of the cut usually extends to 2 inches. A light jackhammer (typically 15 pounds maximum weight, but up to 30 pounds if no damage to sound concrete is observed) is used to remove the concrete. The jackhammer can be carefully used to slightly chip the vertical polished saw cut edge to provide a rough surface to promote bonding between the patch repair material and the sound concrete. PDR Type Description Example 1 Spot repairs (less than 6 feet in length). These are used to repair spalling at joints, corners, and slab interior. Applicable to repairs at transverse joints when load- transfer devices are still functional and not exposed. 2 Repairs of extended length along a longitudinal or transverse joint or a crack longer than 6 feet. Source: Frentress and Harrington (2012) and Smith et al. (2014). All images provided by Applied Pavement Technology, Inc. Table 9. Description of distress and appropriate PDR types. Source: Nichols Consulting Engineers, Chtd. Figure 11. Saw and chip out.

Partial-Depth Repair 27   2. Chip out: A light jackhammer (typically 15 pounds maximum weight, but up to 30 pounds if no damage is observed) is used to remove the damaged concrete, starting from the center of the repair area. The boundary edges are then removed at a slight angle with hand tools or a light jackhammer to avoid damaging sound concrete (Figure 12). 3. Mill out: A milling machine with a 12- to 18-inch-wide head is operated along the spalled area (Figure 13). The milling depth must be adjusted to remove all the damaged concrete material. This method is cost-effective, with the highest production rate of any method, and produces rough, uniform surfaces that promote bonding between the repair material and the existing concrete. Strong bonds result in good performance. 4. Clean out: Used only for emergency repairs, this method typically consists of removing the loose concrete with hand tools or a light jackhammer. The repair area is cleaned with stiff brooms. FAA AC 150/5380-6C includes the use of saw and chip out (FAA 2014b). The U.S. DOD O&M Manual (2018) suggests both saw and chip out and mill out. Hammons and Saeed (2010) assessed expedient removal techniques and found that mill out (i.e., cold planer) achieved rapid preparation of the repair area. Source: Nichols Consulting Engineers, Chtd. Figure 12. Chip out. Source: Frentress and Harrington (2012). Figure 13. Mill out.

28 Rapid Slab Repair and Replacement of Airfield Concrete Pavement As previously stated, distresses that extend deeper than half the pavement thickness are not appropriate for PDR, particularly if load-transfer devices are exposed during concrete demolition and removal. If this occurs during construction, the load-transfer device should be cut through at the joint and a temporary PDR completed. This repair should be identified for future replacement with FDR (see Chapter 4). Cleaning Prior to placement of the PDR material, clean the exposed faces and bottom of the repair area to remove all loose particles, oil, dirt, dust, previous patch materials, and other contaminants. Thoroughly clean the area around the PDR with a power broom, vacuum sweeper, or hand broom to prevent debris from reentering the repair zone. Any contamination of the surface will reduce the bond between the PDR material and the existing concrete. FAA AC 150/5380-6C (FAA 2014b) indicates removing all loose material by hand, vacuuming, and cleaning the PDR area with high-pressure water. The U.S. DOD O&M Manual states, “as a minimum, air- blow with compressed air, wash with high-pressure water, and air-blow again” (2018, p. 102). Ensure the repair area is completely dried if high-pressure water is used to clean the repair area. Always follow the product manufacturer’s recommendations, as they differ by the type of repair product. Once the PDR area has been cleaned, the surface is prepared in accordance with the recom- mendations of the manufacturer of the repair material. For some cementitious materials, this may require applying a grout prior to placing the PDR material. If used, the grout must not set before the repair material is placed; otherwise, the repair will not bond to the substrate. Prepackaged materials may or may not require application of a liquid bonding agent. If a bond- ing agent is required, the manufacturer’s recommendations must be followed. Reestablishing the Joint PDRs that abut working joints or cracks that extend the full depth of the slab usually require that the crack or joint be reformed to prevent the repair material from contacting the abut- ting concrete and to ensure the repair material does not flow into the joint or crack. Failure to reestablish the joint or crack or allowing repair material to flow into it can cause stress points that may damage or dislodge the repair. A compressible insert or other bond-breaking medium is commonly inserted into the joint or crack to reform it and ensure that the repair material does not enter (Figure 14). As an alternative, the joint or crack can first be caulked to prevent material from entering and the compressible insert tacked into place to reestablish the joint or crack. Regardless of approach, the insert needs to be the full depth of the repair to avoid failure. Although reestablishing the joint or crack may not be required for some flexible proprietary materials, caulk should still be used to prevent the materials from entering. Some agencies have established additional preparation requirements. One airport that participated in this study uses reinforcement in its PDRs. The detail includes tie bars arranged in a grid pattern that are drilled and grouted into the sound concrete (Figure 15). Material Placement and Consolidation Production of PDR materials is different from that of materials produced for larger projects, such as slab replacements, because the quantity of material required per repair is much smaller (potentially 0.5 cubic feet or less). Transit mix trucks and other large equipment cannot effi- ciently produce such small quantities and would decrease the quality and result in waste of

Partial-Depth Repair 29   material (U.S. DOD 2018). Because of the small quantity of material needed, it is common to mix cementitious PDR material on-site with a small drum or paddle mixer. For proprietary materials, the manufacturer’s material preparation and placement instructions should be followed, particularly with regard to the size of repair and temperature. Some products are mixed in the container that they were shipped in. If material packaging is damaged, it should not be used. Source: Nichols Consulting Engineers, Chtd. Figure 14. Compressible insert at a joint (retrofitted electrical conduit shown; not a dowel bar). Source: John Rone. Figure 15. Reinforcing steel used in partial-depth repair.

30 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Following are recommendations for placing repair materials (Frentress and Harrington 2012, Smith et al. 2014): • Follow the manufacturer’s recommendations for proprietary materials. Some materials must be placed in lifts, and some materials may be self-consolidating. • For small patches, consolidate the material by rodding or tamping by hand. • Work and float the material from the center of the patch toward the edges for better bonding with repair edges. • Monitor air temperature and maintain compliance with material placement requirements (many materials should be used with air temperatures between 50°F and 90°F). Material for large patches may be consolidated by using small spud vibrators. Vibrators greater than 1 inch in diameter are not recommended (U.S. DOD 2018). Finishing and Curing The surface of the repaired area must match the profile of the surrounding slabs. Texture should match that of the existing adjacent pavement; burlap drag and tined surfaces are common. Over-finishing the repair surface can weaken it and make it susceptible to scaling and durability problems. One airport that participated in this study installed the repair material slightly higher than the surrounding concrete and then ground the repair flush after it hardened, finding that this approach mitigates material settlement. Curing is very important for PDR, since the ratio of the surface area to volume of the repair is typically large, and moisture can be rapidly lost through evaporation. Curing recommendations include the following (Frentress and Harrington 2012, Smith et al. 2014, USAF 2017): • For cementitious materials, curing is often done by applying an ASTM C309 white-pigmented curing compound immediately after water from the surface has evaporated. Poly-alpha- methylstyrene (PAMS) resin curing compounds have been found to be highly effective. • Curing material application rates are higher for PDRs than for full slabs or larger areas, usually 1½ to 2  times the normal application rate. • Other effective curing methods include moist burlap or polyethylene sheeting. Insulating blankets can be used in cold weather conditions or to accelerate strength gain but should be used cautiously in warm weather conditions. Some proprietary materials do not require curing. For these materials, the manufacturer’s recommendations should be followed. Joint Resealing Following curing—if it was necessary to reestablish the joints—remove the joint/crack insert or reforming material at the surface so that the joint or crack can be properly prepared (i.e., cleaned). Then create the reservoir and place the appropriate joint/crack sealant. Opening to Traffic The new PDR must be protected from traffic until the material has achieved the required strength. The time to opening can vary considerably and depends on the PDR material used and other environmental factors. Portland cement–based materials may take days to gain sufficient strength, while some HES and proprietary materials may reach the required strength in a matter of minutes or hours. For cementitious materials, mix design testing can help establish strength gain properties (since field testing is not likely with the small batch quantities). Alternative methods for estimating strength gain (e.g., maturity meters) for PDRs have not been widely

Partial-Depth Repair 31   used. Manufacturers’ recommendations for opening to traffic should be followed for proprietary materials. Figure 16 shows examples of completed PDRs. Partial-Depth Repair Assessment Tool Figure 17 and the associated tables (Tables 10–12) present a framework for assessing some of the key variables considered during planning for and constructing PDRs. This tool provides users with practical guidance on the feasibility of concrete pavement repair techniques for a variety of facilities and closure times. Note: See Figure 10 and Table 9 for explanation of the types of partial-depth repair. Source: Nichols Consulting Engineers, Chtd. Figure 16. Examples of completed partial-depth repairs: (a) Type 1 joint, (b) Type 1 joint that used a flexible repair material that did not require reestablishing of the joint, (c) Type 1 corner, and (d) Type 2 joint.

32 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Figure 17 presents a decision tree for identifying the location of the planned PDR. 1. Select the facility on which the PDR will be completed (i.e., runway, taxiway, or apron). 2. Identify the relative operational priority of the repair area (e.g., runway intersection, runway safety area). 3. Determine how much time is available to do the work. Closure time is divided into three groups: – Less than 8 hours (equivalent to an overnight closure), – 8 to 24 hours (equivalent to a 1-day closure), and – 24 to 60 hours (equivalent to a weekend closure). In many instances, work can be scaled to fit into the available closure time. That is, if a closure of less than 8 hours is the only available option for a given material and preparation method, the number of repairs may be limited in a given closure window to ensure all repair areas have achieved the required strength at the time of opening. Similarly, with a longer closure time, a more conventional repair material can be used. Longer closure times also permit a higher production rate, as more time is available to work under a single mobilization. Each set of decisions leads to a table that summarizes the planning and construction con- siderations associated with the resulting box in Figure 17; see Table 10 for PDR 1, Table 11 for PDR 2, and Table 12 for PDR 3. Note: See Table 10, Table 11, and Table 12 for PDR 1, PDR 2, and PDR 3, respectively. Source: Nichols Consulting Engineers, Chtd. Figure 17. Partial-depth repair decision framework.

Partial-Depth Repair 33   PDR 1 (<8 hours) Preparation Repair types and location • Type 1: Spot repairs from 15 inches to 6 feet along the length of a joint. • Type 2: Extended-length repairs along a longitudinal or transverse joint or cracks longer than 6 feet. • Consider closure time and placement rate in selecting the quantity of repairs and ensure the final repair placed during closure will be able to achieve the required strength at the time of opening. Material selection considerations • Allowable closure time: VHES proprietary materials are likely needed, although some highly accelerated portland cement–based mixtures may be acceptable. • Minimum strength requirements. • Workability time. • Necessary batching equipment. • CTE. • Ambient temperature and climatic conditions. • Cost. • Material performance. • Size of the repair area. Repair boundaries • Extend at least 3 inches beyond unsound concrete on all sides of the repair. • Minimum repair length (along the joint) of 15 inches. • Minimum width (away from the joint) of 10 inches. • Minimum depth of 2 inches or according to manufacturer’s recommendation. • Keep repair boundaries square or rectangular and avoid irregular shapes. Demolition/Removal Removal method • For Type 1: Saw and chip out. • For Type 2: Mill out. • Mill out will be faster than saw and chip out. Cleanup • Dry sweeping. • Light sandblasting. • Compressed air blasting. • High-pressure water. Joint preparation • Insert a polystyrene, polyethylene, or asphalt-impregnated fiberboard strip or other compressible joint-/crack-reforming material into the joint or working crack. Some proprietary flexible repair materials can be placed without reestablishment of the joint (check manufacturer’s recommendations), but the joint or crack must still be taped or caulked to prevent infiltration. • Caulk can be used in the joint or crack to prevent infiltration of repair material. Material Mixing and Placement Bonding agent • For cementitious materials, a bonding agent is not required, but HES epoxy bonding agents have been used. • Follow manufacturer’s recommendations for proprietary materials. Mixing and placement • Use a small drum or paddle-type mixer with a capacity of up to 2 cubic feet. • Follow the manufacturer’s recommendations for proprietary materials. • Ensure proper consolidation. Finishing • A stiff board can be used for small repairs. • Work the material toward the perimeter of the repair. • For cementitious repair materials, place grout around the circumference of the repair and into any saw cut overruns. • Texture to match surrounding slab. Table 10. Summary of PDR 1 decisions. (continued on next page)

34 Rapid Slab Repair and Replacement of Airfield Concrete Pavement PDR 1 (<8 hours) Curing • Apply a white-pigmented curing compound for cementitious materials that meet ASTM C309. PAMS curing compounds have been found to be highly effective. • Follow the manufacturer’s recommendations for proprietary materials. Joint sealing • Make sure transverse and longitudinal joints are well formed or sawed. • Ensure joints are clean and dry. • Install approved sealant in joint (and in overruns if not previously filled with grout). Note: Resealing is often performed in a separate closure in compliance with the sealant manufacturer’s recommendations. Opening to Traffic Compressive strength • Demonstrated as part of mix design, typically 3,100 psi. Note: Some VHES polymeric materials cannot be tested by using compressive strength, and a time-based opening criterion is used according to the manufacturer’s recommendations. Flexural strength • Flexural strength is rarely specified for PDR materials. Other • Timing per manufacturer’s recommendations. • Maturity monitoring. • Consider whether direct traffic loadings will be likely (i.e., only require strength for an emergency loading as opposed to continuous traffic). Note: psi = pounds per square inch. Table 10. (Continued). PDR 2 (8–24 hours) Preparation Repair types and location • Type 1: Spot repairs from 15 inches to 6 feet along the length of a joint. • Type 2: Extended-length repairs along a longitudinal or transverse joint or cracks longer than 6 feet. • Consider closure time and placement rate in selecting the quantity of repairs and ensure that the final repair placed during the closure will be able to achieve the required strength at the time of opening. Material selection considerations • Allowable closure time: accelerated portland cement–based mixtures may work, but consider proprietary materials. • Minimum strength requirements. • Workability time. • Necessary batching equipment. • CTE. • Ambient temperature and climatic conditions. • Cost. • Material performance. • Size of the repair area. Repair boundaries • Extend 3 inches beyond unsound concrete on all sides of the repair. • Minimum repair length (along the joint) of 15 inches. • Minimum width (away from the joint) of 10 inches. • Minimum depth of 2 inches (or according to the manufacturer’s recommendation). • Keep repair boundaries square or rectangular and avoid irregular shapes. • Avoid saw cut overrun. Table 11. Summary of PDR 2 decisions.

Partial-Depth Repair 35   Curing • Apply a white-pigmented curing compound for cementitious materials that meet ASTM C309. PAMS curing compounds have been found to be highly effective. • Follow the manufacturer’s recommendations for proprietary materials. Joint sealing • Make sure transverse and longitudinal joints are well formed or sawed. • Ensure joints are clean and dry. • Install approved sealant in joint (and in overruns if not previously filled with grout). Note: Resealing is often performed in a separate closure in compliance with the sealant manufacturer’s recommendations. Opening to Traffic Compressive strength • Demonstrated as part of mix design, typically 3,100 psi. Note: Some HES polymeric materials cannot be tested by using compressive strength, and a time-based opening criterion is used according to the manufacturer’s recommendations. Flexural strength • Flexural strength is rarely specified for PDR materials. Other • Timing per manufacturer’s recommendations. • Maturity monitoring. • Consider whether direct traffic loadings will be likely (i.e., only require strength for an emergency loading as opposed to continuous traffic). Demolition/Removal Removal method • Type 1: Saw and chip out. • Type 2: Mill out. • Mill out will be faster than saw and chip out. Cleanup • Dry sweeping. • Light sandblasting. • Compressed air blasting. • High-pressure water. Joint preparation • Insert a polystyrene, polyethylene, or asphalt-impregnated fiberboard strip or other compressible joint-/crack-reforming material into the joint or working crack. Some proprietary flexible repair materials can be placed without reestablishment of the joint (check manufacturer’s recommendations), but the joint or crack must still be taped or caulked to prevent infiltration. • Caulk can be used in the joint or crack to prevent infiltration of repair material. Material Mixing and Placement Bonding agent • For portland cement concrete materials, a bonding agent is not required. A grout made with cement and water (and at times sand) has been used. • Follow the manufacturer’s recommendations for proprietary materials. Mixing and placement • Use a small drum or paddle-type mixer with a capacity of up to 2 cubic feet. • Follow the manufacturer’s recommendations for proprietary materials. • Ensure proper consolidation. Finishing • A stiff board can be used for small repairs. • Work the material toward the perimeter of the repair. • Place grout around the circumference of the repair and into any saw cut overruns. • Texture to match surrounding slab. PDR 2 (8–24 hours) Table 11. (Continued).

36 Rapid Slab Repair and Replacement of Airfield Concrete Pavement PDR 3 (24–60 hours) Preparation Repair types and location • Type 1: Spot repairs from 15 inches to 6 feet along the length of a joint. • Type 2: Extended-length repairs along a longitudinal or transverse joint or cracks longer than 6 feet. • Consider closure time and placement rate in selecting the quantity of repairs and ensure that the final repair placed during the closure will be able to achieve the required strength at the time of opening. Material selection considerations • Allowable closure time: Lightly accelerated portland cement–based concrete mixtures are suitable. • Minimum strength requirements. • Workability time. • Necessary batching equipment. • CTE. • Ambient temperature and climatic conditions. • Cost. • Material performance. • Size of the repair area. Repair boundaries • Extend 3 inches beyond unsound concrete on all sides of the repair. • Minimum repair length (along the joint) of 15 inches. • Minimum width (away from the joint) of 10 inches. • Minimum depth of 2 inches, or according to the manufacturer’s recommendations. • Keep repair boundaries square or rectangular and avoid any irregular shapes. • Avoid saw cut overrun. Demolition/Removal Removal method • Type 1: Saw and chip out. • Type 2: Mill out. • Mill out will be faster than saw and chip out. Cleanup • Dry sweeping. • Light sandblasting. • Compressed air blasting. • High-pressure water. Joint preparation • Insert a polystyrene, polyethylene, or asphalt-impregnated fiberboard strip or other compressible joint-/crack-reforming material into the joint or working crack. Some proprietary flexible repair materials can be placed without reestablishing the joint (check manufacturer’s recommendations), but the joint or crack must still be taped or caulked to prevent infiltration. • Some proprietary flexible repair materials can be placed across a joint (check manufacturer’s recommendations). Material Mixing and Placement Bonding agent • For portland cement concrete materials, a bonding agent is not required. A grout made with cement and water (and at times sand) has been used by some. • Follow the manufacturer’s recommendations for proprietary materials. Mixing and placement • Use a small drum or paddle-type mixer with a capacity of up to 2 cubic feet. • Follow the manufacturer’s recommendations for proprietary materials. • Ensure proper consolidation. Finishing • A stiff board can be used for small repairs. • Work the material toward the perimeter of the repair. • Place grout around the circumference of the repair and into any saw cut overruns. • Texture to match surrounding slab. Table 12. Summary of PDR 3 decisions.

Partial-Depth Repair 37   PDR 3 (24–60 hours) Curing • Apply a white-pigmented curing compound for cementitious materials that meet ASTM C309. PAMS curing compounds have been found to be highly effective. • Follow the manufacturer’s recommendations for proprietary materials. Joint sealing • Make sure transverse and longitudinal joints are well formed or sawed. • Ensure joints are clean and dry. • Install approved sealant in the joint (and in overruns if not previously filled with grout). Note: Resealing is often performed in a separate closure in compliance with the sealant manufacturer’s recommendations. Opening to Traffic Compressive strength • Typically 3,100 psi. Flexural strength • Flexural strength is rarely specified for PDR materials. Other • Timing per manufacturer’s recommendations. • Maturity monitoring. Table 12. (Continued).