Composite Pavement Systems, Volume 2: PCC/PCC Composite Pavements (2013)

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82 Note on Versions of the MEPDG MEPDG version 1.014:9030A (03/11/2009) was the first build of MEPDG tailored to the R21 project. Results from 1.014:9030A initially were compared with MEPDG version 1.003, which was the public release build of the MEPDG for many years until late in the MEPDG’s life span (just before the release of DARWin-ME). In December 2010, a second build tailored to the SHRP 2 R21 project was released. This second build was designated as 1.206:R21. After continued analysis of this version of the MEPDG and its performance predictions for the factorial of R21 PCC/PCC cases, v. 1.3000:R21 was devel- oped and released in May 2011. This was the final build tailored to the R21 project, and it is the last build examined by the R21 research team. Note that before DARWin-ME can be used to design PCC/PCC composite pavements in its present form (version 1.0.18), even using “Bonded PCC over JPCP”, all of the R21 modifications must be made to the program because it may not produce correct results. The revisions made to the MEPDG models included in the MEPDG (v. 1.3000:R21) were done in such a way as to not require any changes to the underlying MEPDG and EICM framework. These modifications were 100% compatible with the MEPDG and the EICM that existed before the R21 proj- ect: No additional coding was required for R21, only modi- fications to existing source code. The R21 recommended modifications have made the MEPDG more robust in terms of the different pavement types that it can assist engineers in designing and understanding. Guidelines and Design Procedure Using AASHTO MEPDG One of the major successes of the SHRP 2 R21 project is that the AASHTO MEPDG is able to be used for newly constructed PCC/PCC design and performance analysis with no impact on the way the user previously interacted with the MEPDG. The user needs only to accept the use of a “Bonded PCC Overlay of JPCP” project as a modeling simplification for the newly con- structed PCC/PCC pavements addressed by the R21 research. Once the user has selected a Bonded PCC Overlay of JPCP project, the remaining steps of the MEPDG design process to characterize the pavement system are identical to those for other rigid pavement projects. Here the user will characterize two PCC layers, and the remainder of the pavement input proceeds as in any other design. Design recommendations for use of R21-modified MEPDG (v. 1.3000:R21) to design PCC/ PCC composite pavements are provided below: 1. General use of MEPDG for composite pavements a. Design Type: Select “PCC Overlay”. As detailed above, this Project Type represents a PCC/PCC pavement for the purposes of design and analysis with the MEPDG. b. Pavement Type: • Select “Bonded PCC/JPCP”. • Select “Bonded PCC/CRCP”. c. Design Life: Select desired life of structural design until major rehabilitation is needed. Composite pavements are appropriate for a long structural life, exhibiting little structural deterioration over many years. MEPDG can design pavements for a design life as long as 100 years. To design a long-life pavement, select a life of more than 40 years. The PCC surface can be renewed as needed through diamond grinding, but the PCC slab will remain over the long design life with little structural fatigue damage. 2. Trial Design: Select all design inputs for a trial design. The inputs for a PCC/PCC composite pavement are as follows: a. Design reliability and performance for composite pavements: • Design reliability should be based on traffic level of the highway. Higher traffic levels warrant higher C H A P T e r 4 PCC/PCC Design Guidelines

83 reliability levels. For example, interstate, freeways, and divided highways warrant 95% to 99% and other highways and urban collectors/arterials war- rant 90% to 94%. Local residential and farm-to- market roads warrant 75% to 89%. • Structural fatigue cracking and punchouts: 1. JPCP: 10% slabs (range: 5 to 15) transverse fatigue cracking. 2. CRCP: 10 punchouts per mile (range: 5 to 15). • Smoothness, Terminal International Roughness Index (IRI) should be based on traffic level of the highway. Higher traffic levels warrant lower terminal smoothness levels. 1. Interstate, freeways, divided highways: 150 in./mi; 2. Other highways and urban collectors/arterials: 160 in./mi; and 3. Locals and farm-to-market: 175 in./mi. • Joint faulting: 0.15 in. • Initial IRI: The initial IRI for PCC/PCC composite pavements can be very low because of the multiple layering of the pavement. Initial IRI values as low as 50 in./mi have been achieved. b. Type of PCC surface layer. The type depends on the design objectives. • If a design objective is to reduce noise levels to a minimum, then either an EAC can be used or spe- cial diamond grinding (such as the next-generation grind that showed the lowest noise level of all sur- faces at MnROAD) of the PCC surface can be done. • If a design objective is durability against polishing and long life of the surface, then use of the high- est quality, hard, nonpolishing aggregate possible is required. The next-generation grind may also be useful in this situation. • If neither of these objectives is applicable, a more conventional texturing of the surface that includes the hard aggregates would be sufficient. c. Thickness of PCC surface layer. Layer thickness should be the minimum possible to provide durability and surface characteristics desired for a given truck traffic and climate. Thicknesses ranging from 1.5 in. to 3 in. have been built successfully. d. Type (JPCP or CRCP) and thickness of the lower PCC layer. This is the load-carrying capacity layer for the composite pavement. The trial design should start with an estimate based on the total required for a one-layer slab minus the surface layer thickness. If the pavement is being designed to last for a long time period, during which multiple surface renewals (e.g., diamond grind- ing) will be needed, the designer may consider adding a small increment to the lower layer thickness design (e.g., 0.25 in./renewal). e. Joint design for JPCP. Joint design includes joint spac- ing and joint load transfer. • Joint spacing is considered directly in the MEPDG analysis and affects transverse fatigue cracking as well as joint faulting. A shorter joint spacing requires a thinner slab to control fatigue cracking. • Joint load transfer requirement is similar to one- layer JPCP design in that dowels of sufficient size are required to prevent erosion and faulting for any sig- nificant level of truck traffic. The greater the dowel diameter, the higher the joint LTE and the more truck loadings the pavement can carry to the termi- nal faulting level. 1. Simplified dowel design: the dowel diameter should be at least ¹⁄8 the slab thickness. For exam- ple, a total PCC thickness of 12 in. requires a dowel diameter of at least 12/8 = 1.5 in. For exceptionally heavy truck traffic highways, it may be necessary to add 0.25 in. diameter. 2. Low-volume roadways where dowels would not normally be used for one layer JPCP do not require dowels for composite pavement. f. Lower PCC layer recommendations. The formed concrete to be used for the lower layer of a PCC/PCC composite pavement can vary widely, as described here: • Typical concrete used in one-layer JPCP can be used with no changes. There are no special requirements different from those for one-layer pavement. • Lower cost concrete based on local aggregates or recycled concrete. The strength, modulus of elas- ticity, CTE, and drying shrinkage of the concrete can be varied as it is a direct input to the MEPDG software. 1. The MnROAD experimental PCC/PCC clearly showed that properly recycled concrete from a local roadway can be used for the lower layer. 2. The MnROAD experiment PCC/PCC also showed that a local aggregate source can be used success- fully for the lower layer. • Both of these alternatives provide for substantial sustainability advantages and cost savings yet show adequate durability. • Certainly attention must be paid to good construc- tion practices to locate dowels and tie bars properly and to saw all joints to the greater of one third of the total PCC thickness and the thickness of the upper layer plus ½ in. g. Base layer and other sublayers should be selected that are similar to those used for one-layer JPCP designs, based on minimizing erosion, construction ease, and

84 cost effectiveness. No attempts should be made to reduce the friction between the slab and the base. Good friction also helps control erosion and pumping and reduces stress in the slab. 3. MEPDG Design Output Interpretation a. Run the trial design using MEPDG (v. 1.3000:R21) and examine the outputs. Transverse fatigue cracking, IRI, and faulting must all meet the design reliability require- ments for a trial design to be feasible. b. If any of these do not “Pass” at the reliability level, a modification in the design is required. Some guidelines for making modifications are as follows: • Excess transverse cracking: increase slab thickness, shorten joint spacing, add a tied PCC shoulder or 1-ft widened slab, use a stabilized base course, increase PCC strength (with appropriate change in the modulus of elasticity), or use a different aggre- gate source (one with lower CTE). • Excess IRI: reduce transverse cracking or require a smoother initial pavement. Two-layer PCC/PCC composite pavements can be constructed with exceptionally low initial IRI (e.g., 50 in./mi). Include incentive smoothness specifications with significant incentives so that the initial IRI is reduced. Smooth- ness incentives have been used with great success over several decades to improve initial IRI. Illustrative Designs PCC/JPC Composite Design for Interstate Highway: Albertville, Minnesota a. Initial project detail • Design life: 20 years. • Design reliability: 90%. • Construction details. 1. Existing pavement: May 2010. 2. Pavement overlay: May 2010. 3. Traffic open: June 2010. • Project type: bonded PCC over JPCP. b. Analysis parameters • Initial IRI: 63 in./mi. • Rigid pavement analysis. 1. Terminal IRI: 172 in./mi, 90% reliability. 2. Transverse cracking: 15% cracked slabs, 90% reliability. 3. Mean joint faulting: 0.12 in., 90% reliability. c. Traffic • Two lanes in each direction. • Initial two-way average annual daily truck traffic (AADTT): 2,000 (directional distribution = 50%; lane distribution: 90%). • Growth rate: 4% compound (MEPDG default). • Use site-specific MEPDG defaults for other traffic inputs. d. Climate • A virtual weather station was created for this site using the three closest stations. e. Structure, design features • Permanent curl and warp efficiency temperature dif- ference: -10°F. • Joint design: joint spacing, 15 ft; dowel diameter, 1.25 in.; dowel spacing: 12 in. • Base properties: erodibility index, 3 = erosion resistant; PCC-base interface, full friction contact; loss of friction, 360 months. f. Structure, Layer 1 PCC properties • General: thickness, 3 in.; unit weight, 150 lb/ft3; Poisson’s ratio, 0.2. • Thermal specification: CTE, 5.5 × 10-6/°F; thermal conductivity, 1.25 Btu/[(ft)(hr)(°F)]; heat capacity, 0.28 Btu/[(lb)(°F)]. • Mix design: cement content, 675 lb/ft3; water-cement ratio: 0.42; coarse aggregate type: basalt. • Strength properties: 28-day modulus of rupture, 750 psi. g. Structure, Layer 2 PCC properties • General: thickness, 6 in.; unit weight, 150 lb/ft3; Pois- son’s ratio, 0.2. • Thermal specification: CTE, 5.5 × 10-6/°F; thermal conductivity, 1.25 Btu/[(ft)(hr)(°F)]; heat capacity, 0.28 Btu/[(lb)(°F)]. • Mix design: cement content, 550 lb/ft3; water-cement ratio, 0.42; coarse aggregate type, chert. • Strength properties: 28-day modulus of rupture, 625 psi. h. Structure, base/subbase properties • Type: granular, A-1-a. • Thickness: 8 in. • Strength properties: modulus of elasticity, 40,000 psi. i. Structure, subgrade properties • Type: soil, A-6. • Thickness: semi-infinite. • Strength properties: modulus of elasticity, 14,000 psi. j. Rigid rehabilitation inputs • Existing distress: before, 0; after, 0. • Foundation support: dynamic modulus of subgrade reaction, not available. According to MEPDG performance predictions, the PCC/PCC constructed at Albertville, Minnesota, will perform well within its 20-year design life, as illustrated in Table 4.1. Furthermore, the performance predictions suggest it will perform adequately well beyond the specified 20-year design life.

85 MEPDG Design Comparisons The following subsections describe the development of com- posite PCC/PCC projects in MEPDG (v. 1.3000:R21), based on sections in the R21 PCC/PCC database, and determine a single-layer JPCP alternative for these pavements. Each of the following comparisons is for 20 years of service, and the projects being compared differ only in the composition of the concrete slab: either it is a single, homogeneous PCC lift (JPCP) or it is two heterogeneous PCC lifts (PCC/JPC). PCC properties of the slabs differ as indicated below. PCC/PCC Composite Design for Interstate Highway, Albertville, Minnesota (MnROAD Test Section) a. Design reliability and performance requirements • Design life: 20 years. • R: 90%. • Transverse slab cracking: 15% maximum. • Transverse joint faulting: 0.12-in. • IRI: 172 in./mi (initial IRI assumed 63 in./mi). b. Materials • Upper PCC: cement content 675 lb/yd3, and 28-day flexural strength is 750 psi. • Lower PCC: cement content 550 lb/yd3, and 28-day flexural strength is 625 psi. • Aggregate base course: AASHTO A-1-a is used to simulate Minnesota DOT Class 5 aggregate; MEPDG defaults are used for base material properties. c. Site conditions • Traffic. 1. Two lanes in each direction 2. Initial two-way AADTT: 2,000 (directional distribu- tion = 50%, lane distribution = 90%). 3. Growth rate: 4% compound. 4. Use site-specific MEPDG defaults for other traffic inputs. • Subgrade: assume subgrade soil A-6 and other MEPDG defaults. • Climate: a virtual weather station was created for this site using the three closest stations. d. Trial composite design • Upper PCC: 3-in. thickness. • Lower PCC: 6-in. thick JPCP layer with a 15-ft joint spacing and dowel diameter of 1.25-in. • Base: 8-in. thickness placed directly on the fine-grained, prepared and compacted subgrade. e. Output results for composite design • Total number of trucks in design lane over 20 years: 10.3 million. • Transverse cracking of JPCP: R > 90%, Pass. • IRI: R > 90%, Pass. • Faulting: R > 90%, Pass. f. Final composite design • 3-in. PCC upper lift. • 6-in. JPCP (containing recycled PCC from existing roadway). • 8-in. dense-graded aggregate base. This design passes all of the requirements for slab fatigue transverse cracking, faulting (and thus good joint LTE), and IRI. The PCC surface may need to be rehabili- tated after 10 to 20 years because of various weathering problems that occur in this harsh climate. g. Comparative single-layer JPCP design Given the design obtained for the composite pavement, what would be an equivalent design for a single-layer JPCP at this location and for these traffic levels? The MEPDG was run for a single-layer JPCP with PCC properties of cement content 550 lb/yd3 and 28-day flexural strength of 650 psi; all other inputs were identical to the composite design. The JPCP thickness design shown in Table 4.2 was required. Table 4.1. Performance Predictions for PCC/JPC Constructed at Albertville, Minnesota, at 90 Percent Reliability Location IRI in./mi (Limit: 172) Percent Slabs Cracked (Limit: 15%) Mean Joint Faulting, in. (Limit: 0.12) Bottom-up Cracking Damage Top-down Cracking Damage Albertville, Minnesota 121.9 2.2 0.052 0.139 0.044 Table 4.2. Equivalent PCC/PCC and Single- layer JPCP Designs Modeled Using MEPDG for MnROAD Test Section Design PCC/PCC Pavement JPCP PCC Surface 3-in. PCC None JPCP H = 6 in. Dowels = 1.25 in. H = 8.75 in. Dowels = 1.25 in. Base 8-in. Untreated aggregate 8-in. Untreated aggregate Reliability >90% >90% Note: MEPDG (v. 1.3000:R21); H = PCC thickness.

86 For this level of reliability, the MEPDG suggests a mini- mum of 8.75-in. JPCP thickness to function as an equally performing single-layer alternative to the PCC/PCC. Given that there are cost savings both in terms of materials used in the PCC/PCC layers and over the course of the life span of the pavement, the PCC/PCC pavement is a viable option in situations in which quality aggregates are in short supply, supplementary cementitious materials (SCMs) are available for high levels of cement replacement, or any other readily available alternative materials can be used in the lower lift of the PCC/PCC. In addition, the comparison here does not consider the benefits in durability and texturing options offered by the high-quality surface PCC. Note that the thick- ness of the JPCP is lower than the total thickness of the two layers of the PCC/PCC composite pavement. The difference arises from the material properties of the JPCP relative to the lower PCC layer (especially PCC flexural strengths: 650 psi for JPCP versus 625 psi for the lower lift of the PCC/PCC). PCC/PCC Composite Design for Interstate Highway, Abilene, Kansas a. Design reliability and performance requirements • Design life: 20 years. • R: 90%. • Transverse slab cracking: 15% maximum. • Transverse joint faulting: 0.12-in. • IRI: 172 in./mi (initial IRI assumed 63 in./mi). b. Materials • Upper PCC: cement content 650 lb/yd3 and 28-day flex- ural strength is 750 psi. • Lower PCC: cement content 548 lb/yd3 and 28-day flex- ural strength is 620 psi. • Aggregate base course: cement stabilized granular base, MEPDG defaults used for base material properties. c. Site conditions • Traffic 1. Two lanes in each direction. 2. Initial two-way AADTT: 4,000 (directional distribu- tion = 50%, lane distribution = 90%). 3. Growth rate: 4% compound. • Use site-specific MEPDG defaults for other traffic inputs. • Subgrade: assume subgrade soil A-6 and other MEPDG defaults. • Climate: a virtual weather station was created for this site using the three closest stations. d. Trial composite design • Upper PCC: 1.5-in. (40-mm) thickness. • Lower PCC: 11.8-in. (300-mm) JPCP layer with a 15-ft joint spacing and dowel diameter of 1.5 in. (40 mm). • Base: 6-in. thickness. This will be placed directly on the fine-grained, prepared and compacted subgrade. e. Output results for composite design • Total number of trucks in design lane over 20 years: 20.7 million. • Transverse cracking of JPCP: R > 90%, Pass. • IRI: R > 90%, Pass. • Faulting: R > 90%, Pass. f. Final composite design • 1.5-in. PCC upper lift. • 11.8-in. JPCP (containing recycled PCC from existing roadway). • 6-in. cement treated granular base. This design passes all of the requirements for slab fatigue transverse cracking, faulting (and thus good joint LTE), and IRI. g. Comparative single-layer JPCP design Given the design obtained for the composite pavement, what would be an equivalent design for a one-layer JPCP at this location? The MEPDG was run for a single-layer JPCP with PCC properties of cement content 525 lb/yd3 and 28-day flexural strength is 650 psi. All other inputs are identical to the composite design. The JPCP thickness design shown in Table 4.3 was required. For this level of reliability, the MEPDG suggests a minimum of 13-in. JPCP thickness to function as an equally performing single-layer alternative to the PCC/PCC. Given that there are cost savings both in terms of materials used in the PCC/PCC layers and over the course of the life span of the pavement, the PCC/PCC pavement is a viable option in situations in which quality aggregates are in short supply, SCMs are available for high levels of cement replacement, or any other readily avail- able alternative materials can be used in the lower lift of the PCC/PCC. In addition, the comparison here does not con- sider the benefits in durability and texturing options offered by the high-quality surface PCC. Note that the thickness of the JPCP is lower than the total thickness of the two layers of the PCC/PCC composite pavement. The difference arises from the material properties of the JPCP relative to the lower PCC layer (especially PCC flexural strengths: 650 psi for JPCP versus 620 psi for the lower lift of the PCC/PCC). Table 4.3. Equivalent PCC/PCC and Single-layer JPCP Designs Modeled Using MEPDG for Interstate Highway in Abilene, Kansas Design PCC/PCC Composite JPCP Surface 1.5-in. PCC None JPCP H = 11.8 in. Dowels = 1.5 in. H = 13 in. Dowels = 1.5 in. Base 8-in. Untreated aggregate 8-in. Untreated aggregate Reliability >90% >90% Note: MEPDG (v. 1.3000:R21); H = PCC thickness.

87 Sensitivity Analysis Influence of Upper-lift PCC Flexural Strength in PCC/PCC Performance The upper-lift PCC flexural strength was varied to deter- mine what effect it would have on performance of the PCC/ PCC composite pavement. The only parameter changed was the flexural strength and corresponding moduli of elasticity because these are inherently related PCC properties. All other parameters were kept constant across all trials. A performance comparison of two PCC/PCC composite pavements with upper-layer flexural strength varying from 650 psi to 300 psi is presented in Table 4.4. It was expected that a decrease in the modulus of rupture of the upper PCC layer would lead to an increase in predicted top-down cracking without much effect on the predicted faulting or bottom-up cracking. These results meet expectations in that the top-down crack- ing fatigue damage increases dramatically when the flexural strength of the upper lift of the PCC/PCC is reduced. Influence of Lower-Lift PCC Flexural Strength in PCC/PCC Performance The lower-lift PCC flexural strength was varied to determine what effect it would have on performance of the PCC/PCC composite pavement. The only parameter changed was the flexural strength and its corresponding moduli of elasticity because these are inherently related PCC properties. All other parameters were kept constant across all trials. A performance comparison of two PCC/PCC composite pavements with lower-layer flexural strength varying from 650 psi to 300 psi is presented in Table 4.5. It was expected that a decrease in the modulus of rupture of the lower lift PCC would lead to an increase in predicted bottom-up cracking without much effect on the predicted faulting or top-down cracking. Once again, the results meet expectations as the bottom-up cracking fatigue damage increases dramatically because of the reduc- tion in flexural strength of the lower-lift PCC. Influence of CTE in PCC/PCC Pavement Performance CTE was varied from 5.3 × 10-6/°F to 10.0 × 10-6/°F in the upper-layer PCC, and the results were compared as shown in Table 4.6. The expectation that accompanied this modifica- tion is that performance in all aspects would become worse. The performance predicted because of the change in the CTE met expectations. Influence of Modulus of Elasticity in PCC/PCC Pavement Performance The PCC modulus of elasticity was reduced from 4,000,000 to 2,000,000 psi in both the upper- and lower-layer PCC and compared. The expectation that accompanied this modifica- tion was that faulting in a doweled pavement is improved less by a decrease in the elastic modulus of the upper layer than it would be improved by a decrease in the elastic modu- lus of a thicker lower layer. This is because in a PCC pave- ment, reduced stiffness improves the ability of the dowels to transfer a load from one slab to the other. For these tri- als, the upper and lower PCC thicknesses are 3 and 6 in., respectively, but the sections were modified to use reduced dowel thickness, increased dowel spacing, and a higher base erodability to exaggerate faulting. The comparison is pre- sented in Table 4.7. Table 4.4. Sensitivity of Pavement Performance to Flexural Strength of the Upper PCC Layer Using MEPDG Flexural Strength of Upper PCC Layer (psi) IRI, in./mi (Limit: 172) Percent Slabs Cracked (Limit: 15) Mean Joint Faulting, in. (Limit: 0.12) Bottom-up Cracking Damage Top-down Cracking Damage 650 68.6 0.4 0.006 0.0427 0.0439 300 88.7 100 0.007 0.0433 359.0657 Note: MEPDG (v. 1.3000:R21). Table 4.5. Sensitivity of Pavement Performance to Flexural Strength of the Lower PCC Layer Using MEPDG Flexural Strength of Lower PCC Layer (psi) IRI, in./mi (Limit: 172) Percent Slabs Cracked (Limit: 15) Mean Joint Faulting, in. (Limit: 0.12) Bottom-up Cracking Damage Top-down Cracking Damage 650 68.6 0.4 0.006 0.0427 0.0439 300 151 100 0.007 97.6881 0.0439 Note: MEPDG (v. 1.3000:R21).

88 For doweled pavements, reductions in the modulus of elasticity for either PCC layer result in a relatively minor improvement in overall faulting, so the performance in fault- ing predicted by MEPDG met expectations. This trial is one of many reasons the JPCP faulting model was not modified because the existing model appears to capture composite slab faulting behavior adequately. Furthermore, this trial shows that doweling is as important to the performance of composite pavements as it is to conventional JPCP. Table 4.7 also shows that changing the modulus of elasticity of a layer affects the PCC damage and amount of cracking. Lowering the modulus of the surface increases the amount of cracking. Thus, a higher modulus for the upper-layer PCC is desirable, which will always be the case for PCC/PCC composite pave- ments, as defined for this SHRP 2 R21 project. PCC Surface Material and Texture Design Options The designer has several options to consider for the thin top lift of PCC/PCC and the type of texture to be performed. These options are listed as follows with their advantages and disadvantages. Option 1: EAC Mixture and Exposed Aggregate Surface This is a PCC material conforming to a high quality EAC mixture that includes hard nonpolishing aggregates. The surface texture would be an exposed aggregate surface. This is the traditional European PCC/PCC composite pavement design that has performed very well over 20 years. Advantages and disadvantages of this approach are as follows: • Advantages: The EAC mixture is very durable because no deterioration was observed in cold climate Europe for as long as 20 years with this layer under heavy traffic. The EAC mix- ture does not polish significantly, even in heavy snow and icy highways. When the mixture is properly designed and con- structed, the noise level is relatively low and comparable with dense-graded HMA, and the surface remains smooth. • Disadvantages: The brushing technique can be challeng- ing to achieve the proper texture depth but can be mas- tered by construction crews. The construction process is more complicated than that for conventional concrete and requires greater effort to perform all tasks properly. Option 2: High-Quality PCC with Highly Durable Aggregate Concrete and Conventional Texturing or Diamond Grinding This is a PCC material conforming to a high-quality PCC mixture that includes hard, nonpolishing aggregates. The surface texture could be conventional texturing or diamond grinding of some type. Advantages and disadvantages of this approach are as follows: • Advantages: The high quality PCC mixture would be very durable. The diamond grinding or the conventional textur- ing would polish less than with softer aggregates and should have a long life, even for highways with heavy snow and Table 4.6. Sensitivity of Pavement Performance to CTE of the Upper PCC Layer Using MEPDG CTE of Upper PCC Layer (1026/F) IRI, in./mi (Limit: 172) Percent Slabs Cracked (Limit: 15) Mean Joint Faulting, in. (Limit: 0.12) Bottom-up Cracking Damage Top-down Cracking Damage 5.5 68.6 0.4 0.006 0.0427 0.0439 10 153.7 100 0.012 0.0045 69.8954 Note: MEPDG (v. 1.3000:R21). Table 4.7. Sensitivity of Pavement Performance to PCC Elastic Modulus Using MEPDG Elastic Modulus of Upper PCC Layer (psi) Elastic Modulus of Lower PCC Layer (psi) IRI, in./mi (Limit: 172) Percent Slabs Cracked (Limit: 15%) Mean Joint Faulting, in. (Limit: 0.12) Bottom-up Cracking Damage Top-down Cracking Damage 4,000,000 4,000,000 90.0 0.4 0.047 0.0433 0.0438 2,500,000 4,000,000 94.6 8.3 0.043 0.0119 0.2968 4,000,000 2,500,000 85.5 0.0 0.039 0.0076 0.0000 Note: MEPDG (v. 1.3000:R21).

89 ice. The noise level is relatively low for the diamond grind (and next-generation grind is even lower, as demonstrated at MnROAD). The high-quality PCC top lift and either dia- mond grinding or conventional texturing is relatively easy to construct. • Disadvantages: The conventional textured surface (even longitudinal tining) would have good but not exceptional low noise characteristics as compared with the diamond grinding or EAC texture. The diamond grinding texture (particularly the next-generation grind) may be expensive because of the hardness of the aggregate. Option 3: Normal-Quality PCC and Conventional Texturing or Diamond Grinding This is a PCC material conforming to a conventional quality PCC mixture used for PCC paving. The surface texture could be conventional texturing or diamond grinding of some type. Advantages and disadvantages of this approach are as follows: • Advantages: The only advantage is that the top lift would be the typical conventional mixture used in a state and thus would be lower in cost than the EAC or high-quality PCC layer described above. The surface could be convention- ally textured or diamond ground (either conventional or next-generation). The conventional PCC top lift and either diamond grinding or conventional texturing are relatively easy to construct. • Disadvantages: The conventional textured surface (even lon- gitudinal tining) would have good but not exceptional low noise characteristics, as would diamond grinding or EAC texture. In harsh climates, its durability would not be as good as the EAC or high-quality concrete and aggregate surfaces. Cost Analysis and Pavement Type Selection PCC/PCC composite pavements have not been constructed widely in the United States. Therefore, guidelines on pave- ment type selection and cost analysis will be helpful to state highway agencies and others. When engineers and contrac- tors in the Netherlands, Germany, and Austria were asked the question “Are PCC/PCC pavements cost effective in your country,” they all responded “yes they are” and explained why. The main reason was that high-quality aggregates are very expensive, and if their use can be restricted to the top 2- to 3 in. of a PCC pavement and use lower-cost aggregates in the thicker lower portion of the PCC pavement, there could be significant savings to pay for the additional manpower and equipment needed for PCC/PCC construction. Although the performance of these PCC/PCC composite pavements has been excellent, particularly in Europe, few agencies in the United States typically consider them in their pavement selection procedures. This may be because of the perception that they are more expensive to build than con- ventional PCC pavements. However, given the need to con- sider pavement alternatives that not only have long-term structural load-carrying capacity (e.g., long life) but also have long-term excellent surface characteristics, a competitive life- cycle cost, and can be rapidly rehabilitated in the future as needed, the interest in and use of PCC/PCC composite pave- ments may increase at both state and local highway agencies. The information and technology assembled and devel- oped under the SHRP 2 R21 project gives highway agencies much additional information related to PCC/PCC composite pavements: 1. Performance of this type of composite pavement on inter- states and other major highways: The PCC/PCC compos- ite pavement could certainly be used on lower-volume highways or urban streets for long life pavement with major sustainability benefits if the costs were competitive. 2. Validation of a rational mechanistic-based AASHTO design procedure (e.g., MEPDG v. 1.3000:R21). 3. Construction guidelines and recommendations for build- ing quality composite pavements. This section of the report provides recommendations for pavement selection procedures and life-cycle cost analysis (LCCA) of PCC/PCC pavements. This information will aid highway agencies in including composite pavements in their routine pavement selection process and conducting the LCCA process properly. NCHRP Report 703 (Hallin et al. 2011) is recommended as a good process for addressing the selection process and the LCCA of composite pavements. Below is a step- by-step process that focuses on PCC/PCC composite pavements and closely follows the NCHRP report recommendations. Step 1 Establish LCCA Framework • Analysis period. The analysis period for PCC/PCC com- posite pavements should reflect the time over which the highway agency wants the pavement to perform without major structural damage (e.g., transverse fatigue cracking in PCC/JPC or punchouts in PCC/CRC) at a desired level of reliability. The surface of a high-quality EAC or a diamond- ground, high-quality PCC surface should last well beyond 20 years. Thus, the longer a PCC/PCC composite pave- ment is designed to exhibit low structural damage, the more cost-effective and sustainable it will likely be because small increases in structural design capacity result in long-term extension of fatigue damage (e.g., slightly thicker lower slab). The design could be made for only 20 years; however, this would result in reduced cost competitiveness and reduced sustainability benefits. Thus, a structural life of 40 years or more is recommended. The PCC/PCC composite design

90 becomes essentially a long-life pavement with rapid surface renewal at intermediate times. One PCC/JPC composite pavement located on US-45 in Florida was constructed in 1978 and received no surface rehabilitations (grinding or overlay) or structural repairs for 30 years, but at 30 years, it was in need of a rapid renewal through diamond grinding. This pavement exhibited almost no transverse fatigue cracks after carrying 8 million heavy trucks in the outer lane with- out a single slab replacement. The ideal analysis and design period for this project should have been about 40 to 50 years because it will not exhibit significant structural distresses and likely will need only one surface retexturing during that time period. • Discount rate. Long-term real discount rate values pro- vided in the latest edition of the Office of Management and Budget (OMB) Circular A-94, Appendix C, should be used. • Economic analysis technique. The net present value (NPV) method using constant or real dollars and a real discount rate in NPV computations is recommended. • LCCA computation approach. There are two approaches to NPV analysis: deterministic and probabilistic. Either one could be used for PCC/PCC composite pavements. Estimation of the variabilities involved in the probabilis- tic approach is a major challenge. In either approach, the service life must be estimated with sufficient accuracy and also the standard deviation and distribution must be esti- mated for the probabilistic approach. Recommendations for PCC/PCC composite pavement: 1. Service life (PCC layer structural life). As part of this SHRP 2 R21 project, PCC/JPC composite pavements were analyzed and found that they fit into the nation- ally calibrated MEPDG fatigue damage models for JPCP (using v. 1.3000:R21) so that the prediction of structural life until the terminal level of cracking is reached can be obtained from the software output. The mean 50% prediction curve should be used as the life estimate when it crosses the critical transverse cracking limit. If this does not occur during the analysis period, the slab should be considered as having a long life and would have a significant remaining life at the end of the analysis period. 2. Service life (PCC top layer functional life). Chapter 2 included several examples of numerous EAC pave- ments in Europe and the Florida conventional PCC upper layer that have performed from 20 to more than 30 years without renewal. There are two main perfor- mance indicators that would result in terminal life for the thin PCC type of surface. • Wearing of the surface in wheelpath from studded tires or chains: The long A1 motorway across Austria is subject to harsh winter ice and snow but did not show much polish or wear over 18 years. Thus, the hard durable aggregates in the surface course are expected to last well over 20 years. • Raveling: This must be estimated by the local highway agency because it cannot be predicted. Very little of this was observed on the EAC surfaces over many years. 3. Survival curves. Often the best way to estimate the mean service life of a pavement is to use survival analysis. Unfor- tunately, there are not enough older PCC/PCC pavements constructed with sufficient survival history to do that at this time. However, additional construction and monitor- ing of their performance will allow that in the future. The 50th percentile should be used as the mean life and the standard deviation for the probabilistic approach. Step 2 Estimate Initial and Future Costs • Initial construction costs. This includes the cost of the pave- ment structure, including the PCC top layer consider- ing the selected form of texturing (e.g., EAC, diamond grinding, conventional texture), PCC bottom layer, and base and other embankment layers. Information from the Kansas I-70 project with all of the above mentioned types of surface texturing is available for consideration. A cost com- parison example using the MnROAD data is provided later in this chapter. • Future rehabilitation and maintenance costs. Future costs include some routine maintenance and the rapid renewal of the PCC surfacing through some type of diamond grinding. New and innovative techniques to be developed into the future will make this operation even more cost effective and produce even better surface characteristics. • Salvage costs. Estimated cost of the pavement at the end of the design analysis period. • Initial and future highway (extra) user costs. There are sev- eral components of extra highway user costs. The word “extra” is used to indicate that these are in excess of those obtained for smooth pavements because of increased roughness, accidents, and lane closures for maintenance and rehabilitation. The FHWA RealCost program includes estimates of most of these extra costs and reasonable pro- cedures to estimate them. The timing of the surface reha- bilitation and its duration must be estimated. • Develop expenditure stream diagrams. Basically, for PCC/ PCC composite pavements, there will be the initial construc- tion, future routine maintenance, and future rehabilitation of the surface layer (typically removal and replacement with a better product at the time). An example is shown in Table 4.8, where the design analysis period is 40 years and, given the climate and traffic, a 20-year life is expected for the PCC surface layer texture. Some user delay and other user costs are expected every time lane closures are programmed, even if they are done during off peak traffic hours.

91 Step 3 Compute Life-Cycle Cost Analysis The FHWA’s RealCost EXCEL spreadsheet software is con- venient and efficient for entering all of the above costs and properly computing an NPV cost estimate for a composite pavement. RealCost also will compute highway user’s cost for project conditions. RealCost can use deterministic and probabilistic approaches for conducting the LCCA. Step 4 Select Preferred Pavement Alternative A composite pavement can be compared directly with conven- tional HMA or PCC pavement alternatives in terms of costs (e.g., NPV) and noneconomic selection factors. Although the NPV can be computed from all of the associated direct and indirect costs, it can be evaluated separately as follows: • Initial construction cost; • Highway user’s costs during initial construction; and • Future direct cost to highway agency for lane closures such as 4 Maintenance; 4 Rehabilitation; and 4 Salvage. • Future highway user’s costs during maintenance and reha- bilitation lane closure activities; and • Total costs NPV. The non-economic factors are important and include the following, based on NCHRP Report 703. In some cases, a composite pavement has advantages over conventional asphalt or concrete. • Roadway/lane geometrics: PCC/PCC composite pavement would be similar to any other PCC pavements in terms of dealing with lane widths, shoulders, turning movements, and so forth, but may have some advantages with respect to some conventional HMA with regard to total thickness of all pavement layers. • Continuity of adjacent pavements: If this is desired, then wherever the adjacent pavement is PCC, a PCC/PCC com- posite would be appropriate because the user would see the same type of surface. • Continuity of adjacent lanes: When widening is being designed, it is usually good design practice to continue the widening with similar materials. When the existing pavement is PCC that is in an acceptable condition, a PCC/PCC composite for the additional lanes has distinct advantages. The main advan- tage is ease to the driver in maintaining consistency across all lanes. There is also advantage in connecting the existing and new traffic lanes together so that they will not separate. • Availability of local materials and experience: A PCC/PCC pavement can be built using recycled concrete aggregate (RCA) or recycled asphalt pavement (RAP) from the exist- ing or nearby old highway, or from a local pit with some types of substandard aggregates (such as softer aggregates susceptible to polishing). The PCC surfacing will provide a smooth and durable surface for traffic. • Conservation of materials/energy: PCC/PCC offers signifi- cant advantage in conservation of materials and energy. See Sustainability for PCC/PCC advantages. • Local preference: There could be local preference for long-life PCC pavement but with low noise and low maintenance/ rehabilitation needs. The PCC/PCC composite pavement can provide low noise with the EAC surface or with a special diamond-ground surface that will last a long time because of the high-quality aggregates in the surface layer. • Stimulation of competition: A PCC/PCC composite pavement with low life-cycle costs stimulates increased competition. • Noise issues: PCC/PCC can be designed with an EAC sur- face or with a diamond-ground surface that will provide low noise levels for many years. Either of these surfaces can be renewed easily and rapidly into the near future. • Safety considerations: The EAC surface provides long-term high friction. The diamond-ground, high-quality aggregate surface provides high friction over a longer time period than is seen with conventional aggregates: It also provides lower probability for hydroplaning. Table 4.8. Example of Expenditure Stream Table for Performing LCCA Time, Years 0 5 10 15 20 25 30 35 40 User (U) $ Delay, etc. $ 0 $ 0 $ U 0 $ U $ 0 $ U $ U $ 0 Maintenance (M) $ Routine $ 0 $ 0 $ M 0 $ M $ 0 $ M $ M $ 0 Renewal (R) $ Surface Layer $ 0 $ 0 $ 0 $ 0 $ R $ 0 $ 0 $ 0 $ 0 Initial (I) $ Salvage (SAL) $ $ I $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ SAL

92 • Experimental features: Building a PCC/PCC composite pavement with distinct experimental features and sustain- ability benefits is a good way to get one built in a state or local highway agency. • Future needs: A PCC/PCC can be designed to have a very long structural life with only the retexturing of the thin surface every 20 years (or longer). • Maintenance capability: Little surface routine mainte- nance has been needed on the older EAC/PCC in Europe. The high quality concrete surface can be renewed rapidly through diamond grinding. • Sustainability: This is where PCC/PCC has several distinct advantages over conventional pavements: 4 The lower PCC layer can be designed for a very long fatigue damage life, such as 40 to 100 years with mini- mal fatigue cracking repair. This results in a concrete slab that will remain structurally sound over decades while requiring only that the high-quality PCC surface be retextured every 20 to 40 years. Thus, there will be minimal, if any, full-depth slab replacements, which are expensive and require days to replace. 4 This renewal of the surface through some form of dia- mond grinding will provide excellent surface charac- teristics, including smoothness, low noise, and good friction. The hard aggregates will not polish as easily as often occurs with conventional softer aggregates. 4 This composite pavement design will thus reduce the amount of lane closures over the long design life of the pavement. This has a major sustainability impact because of the reduction in emissions caused by the extra congestion due to lane closures for maintenance and rehabilitation. 4 Reduction of the use of natural resources also contrib- utes to improved sustainability. Recycled concrete was successfully used in the lower PCC slab at MnROAD. The existing concrete from I-94 was recycled as 50% of the coarse aggregate. There may be many projects for which such recycling of existing old PCC and old HMA/PCC pavements into new composite pavement would result in a major reduction in the haul distances involved, which would then result in lower energy use and costs. Use of recycled concrete results in a savings of natural aggregates. 4 Increased use of fly ash contributes to a substantial reduc- tion in portland cement content in the lower PCC slab. The lower layer of the two MnROAD PCC/PCC compos- ite sections contained 40% and 60% fly ash replacement, respectively. This reduces the carbon dioxide emissions and improves the sustainability of construction. 4 There exist highways in certain states where studded tire wear is the major cause of deterioration and needed rehabilitation. A highly durable wearing surface such as EAC could be used for a PCC/PCC composite pave- ment. If wear-down occurs over time, the surface can be renewed through diamond grinding. Various methods are available for weighting economic and noneconomic factors. These include alternative-preference screening matrix, as described in NCHRP Report 703. Example Cost Analysis of PCC/PCC Pavement Initial Cost Analysis An illustrative example of LCCA for a PCC/PCC composite pavement with EAC texture was prepared by the MnROAD paving contractor on behalf of this SHRP 2 R21 research. This also includes a direct comparison with a conventional JPCP at the same site. The composite paving, or wet-on-wet paving, is a process that involves paving the roadway in two lifts. The first lift being one thick, lower-cost layer of concrete using recycled concrete as the main aggregate with lower percentages of higher-quality aggregates in the mix design. The second lift is a fairly thin (2 to 3 in.) high-quality layer that has high-quality aggregate (with none of the recycled material present) and higher cement content with less SCMs. The benefit of com- posite paving is expected to be in areas where high-quality aggregates are of a high cost or low supply (typically these are interrelated), and low-quality materials throughout one layer is not an option because of their polishing tendencies or durability as a surface material. Composite paving allows the lower layer to be produced using less expensive recycled material, allowing the higher-priced or scarce high-quality aggregates to be used in the upper layer. The recycled material in the lower layer is not expected to affect the structural qual- ity of the slab as a whole, and this may require an increased thickness if strength is lower. This project (used for the example LCCA) is based on an actual project located in Minnesota, in an area not readily accessible to high-quality aggregates. This situation com- monly exists in many locations in the United States. The original conventional pavement bid is compared with the expected costs of paving had it been bid using composite pav- ing techniques. The extra cost of two paving operations as well as two batch plants are compared with the expected costs for the aggregates using recycled material instead of Class A material for the lower layer. The objective is to find what the savings on the recycled material would have to be to break even in comparison with the conventional method. General InformatIon The project was concrete paving along U.S. Highway 14 near Waseca, Minnesota. The project involved 90,000 cubic yards of concrete, 80,000 cubic yards of which was for paving 310,000 square yards of mainline pavement and 10,000 cubic yards of which was for crossroads and ramps. The project totaled 19.5 miles of paving. Twenty-two days of mainline

93 paving were scheduled. The pavement was 27 ft wide, with a thickness of 9 in. For this project, the closest Class A aggregate source was New Ulm Quartzite. That source was a 2-hour round-trip haul from the project site. ComparIson A comparison of the crew and equipment used for a conven- tional JPCP paving operation and the crew and equipment that would be necessary for composite PCC/PCC paving (with EAC texture) is shown in Table 4.9. Note the assumption of two pav- ing operations and two PCC plants for the PCC/PCC paving operation. Table 4.10 shows the expected differences in the extra cost to place the pavement compared with the savings in produc- ing the structural concrete. Table 4.11 details the difference in the amount of aggregates used, as well as the cost differential between Class A aggregates and RCA. The composite PCC/PCC showed comparable costs (dif- ference of $44,800 or 0.7% of the total cost of approximately $6.7 million), while having substantial advantages. Also note that had a conventional texture been used (rather than the EAC texture) the costs would be even closer or actually lower for the PCC/PCC composite pavement. The price dif- ferential between the composite and the conventional pave- ment is mainly attributable to the increased costs of placing the two-layer concrete. Placement costs for the PCC/PCC composite paving increased $0.72 compared with conven- tional JPCP as a result of the increased costs to run an extra paver, belt placer, and larger crew size. However, the savings from the concrete aggregates was equal to $2.23 per cubic yard. This savings was due entirely to the use of recycled aggregate. These savings are achieved by crushing concrete on or near the site and using the recycled material as the main aggregate source in the thick lower layer. By substituting RCA instead of Class A as the course aggregate material, the amount of high-quality Class A aggregates needed for the job is reduced. The cost savings per ton of the RCA is between $5 and $6. In addition, the haul time for high-quality aggre- gates was a 2-hr round trip, but by crushing concrete on-site, Table 4.9. Comparison of Conventional JPCP with Composite PCC/PCC with EAC Texture Conventional Composite 1 Boom truck 1 Boom truck 1 Paver 2 Pavers 1 Belt placer 2 Belt placers 1 Cure/texture 2 Cure/texture 1 Skid steer 1 Skid steer 1 Pickup truck 1 Pickup truck 1 Service truck 1 Service truck 1 Water truck 1 Water truck 1 Steel bristle broom 13 Crew members 18 Crew members Assumed mainline paving production of 0.90 mi/day Assumed identical production of 0.90 mi/day Unit cost to pave/tie/green saw: $2.98/square yard, or a total of $923,800 Unit cost to pave/tie/green saw: $3.70/square yard, or a total of $1,147,000 Mobilize and operate 1 plant Mobilize and operate 2 plants. Marginal cost to mobilize second plant of $50,000 or a $.55/cubic yard premium Plant operations cost $1.60/cubic yard to batch mix; cost includes plant operator, loader, and operator. Operations cost of running 2 plants of $3.82/cubic yard to batch mix; cost includes 2 plant operators, loader, and operator. Table 4.10. Example of Conventional versus Composite Paving Costs for U.S. Highway 14 near Waseca, Minnesota Conventional Paving Composite Paving Pave, Tie, Green Saw Square yards 310,000 310,000 $ per Square yard $2.98 $3.70 Total cost $923,800 $1,147,000 Structural Concrete Cubic yards 80,000 80,000 $ per Cubic yard $71.54 $69.31 Total cost $5,723,200 $5,544,800 Total Conventional cost $6,647,000 $6,691,800

94 Fig ure 4.3, respectively. As evident in these figures, the per- formances of these structurally equivalent pavements are nearly identical. Considering the comparable initial costs (and potential initial cost savings if conventional texture was used), this suggests that the use of composite paving can pro- vide cost benefits over the design life of a project with no sacrifice in performance. Conclusions These examples were prepared using a real-life project and the numbers it took to be a low bidder. The examples have shown that in the areas of the state where Class A aggregates are not readily available or are very expensive, PCC/PCC composite paving is a viable alternative to conventional pav- ing. The heavier the truck traffic, the thicker the lower layer of lower cost concrete would become and the greater the dif- ference in cost between the conventional and the compos- ite PCC/PCC pavement. Although this example was a case of having no readily available Class A concrete aggregates, it has shown that it is possible for an alternative technique such as composite paving to compete essentially equally with the costs of a conventional paving process. The MEPDG performance prediction of both sections illus- trates the ability of PCC/PCC to equal its single-layer JPCP structural equivalent in performance and service life. Note that a life-cycle cost comparison of these two alternatives would have to assume that the future maintenance and rehabilitation were the same, at least over the first 20 years because of the pre- dictions from the MEPDG. However, from 20 years on, the per- formance may be different, depending on how the surfaces of each pavement would perform in the harsh climate where this project would be constructed. It is expected that the PCC/PCC composite alternative would show better durability to harsh climate conditions because of the top high-quality PCC surface. Table 4.11. Example of Aggregate Comparisons for U.S. Highway 14 Near Waseca, Minnesota Type Tons Conventional Aggregates ¾ in. Class A 34,270 1½ in. Class A 37,213 Total tons 71,483 Class A Material $/ton $12.78 Trucking (2 hour) $7.46 Total $ per ton $20.24 Composite Aggregates ¾ in. Class A 11,310 1½ in. Class A 12,280 Recycled aggregate 47,893 Total tons 71,483 Recycled Material $/ton $7.00 Trucking (2 hour) $1.45 Total $ per ton $8.45 Table 4.12. PCC Properties Used in Comparison of Conventional JPCP with Composite PCC/JPC Pavement for US-14 Section Using MEPDG Design Feature Conventional JPCP Composite PCC/JPC Slab thickness 9 in. 3-in. high-quality concrete (granite aggregate) 6-in. low-cost concrete (50% RCA, 60% fly ash substitution) Joint spacing and load transfer 15 ft 1.25-in. dowels at 12-in. spacing 15 ft 1.25-in. dowels at 12-in. spacing Base course 8-in. unbound crushed aggregate 8-in. unbound crushed aggregate Shoulders HMA HMA Note: MEPDG (v. 1.3000:R21). the haul time could be reduced to a 20-min round trip. This results in a savings of just over $6 per ton in trucking costs. Had this project been on the interstate with much heavier truck traffic, the lower layers would have been much thicker and the cost difference in favor of the PCC/PCC composite pavement. Even a difference of 1 to 3 in. (for a total PCC thickness of 10 to 12 in.) would tilt the cost advantage sub- stantially in favor of the PCC/PCC composite pavement in this example. MEPDG Performance Comparison In addition to the initial construction cost, a performance anal ysis of the US-14 section using MEPDG (v. 1.3000:R21) was conducted. This analysis involved a comparison of the conventional JPCP with a PCC/JPC composite pavement. The designs are shown in Table 4.12. The inputs for this compari- son used the same climate, traffic, and subgrade. The initial truck traffic was two-directional AADTT of 1,020. This traffic value was prescribed for heavy commercial traffic along US-14 in the vicinity of Waseca by the Minnesota DOT 2006 Trunk Highway Traffic Volume Map. Performances for these sections with respect to fault- ing, cracking, and IRI are illustrated in Figure 4.1 through

95 0 0.02 0.04 0.06 0.08 0.1 0.12 0 5 10 15 20 Fa ul ti ng (i n) Pavement Age (yr) US-14 PCC/JPCP US-14 JPCP Figure 4.1. Joint faulting performance of the US-14 JPCP and its PCC/JPCP structural equivalent over a 20-year design life predicted using MEPDG (v. 1.3000:R21). Figure 4.2. Percent cracked slabs for the US-14 JPCP and its PCC/JPCP structural equivalent over a 20-year design life predicted using MEPDG (v. 1.3000:R21). 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 Pavement Age (yr) Pe rc en t C ra ck ed S la bs US-14 PCC/JPCP US-14 JPCP Figure 4.3. IRI predictions for the US-14 JPCP and its PCC/ JPCP structural equivalent over a 20-year design life using MEPDG (v. 1.3000:R21). 60 70 80 90 100 110 120 130 140 0 5 10 15 20 IR I ( in /m i) Pavement Age (yr) US-14 PCC/JPCP US-14 JPCP