California_Boulevard_Pavement_Report_ST26PW11.pdf

NCE Project No. 1126.09.55

May 2, 2025

Jessica Lowe, P.E.

Deputy Public Works Director Public Works, City of Napa 1600 First Street, Napa, CA 94559

RE: California Boulevard Pavement Design – Draft Report Revised

Dear Jessica:

NCE is pleased to present this draft letter-report for the pavement rehabilitation of California Boulevard from First

Street to Trancas Street.

Background

NCE was hired by the City of Napa to provide pavement rehabilitation recommendations for California Boulevard as shown in Figure 1. The City has currently put together a set of plans for rehabilitation of California Boulevard from Lincoln Avenue to Industrial Way. California Boulevard is a predominantly two lanes, partially divided north-south running arterial. The portion of California Boulevard this project entails is from 1st Street to Trancas

Avenue, approximately 1.7 miles long. Stripped vehicle parking areas along both curb lines and adjacent Class II bike lanes are present intermittently along the length of the section. There is an approximately 1,100 ft. long four

(4) lane section between G Street and Merced Street, serving the commercial area around Lincoln Avenue.

Figure 1 Site Map of California Boulevard Project

The pavement condition varies in level of distress over the length of the section, often with frequent changes over short lengths. Portions of the street are new asphalt concrete (AC) and connect to heavily alligator cracked failing sections. Transverse thermal cracks and random longitudinal cracks of varying severities up to and including near potholes are present.

Passenger car traffic is relatively heavy throughout these 30 to 35 mph corridors. Based upon the City’s 2022

Standard Specifications, Table 3-1, with this street section being considered a Minor Arterial, the Traffic Index used for design should be 9.0, equivalent to approximately 1.0 million equivalent single axle loads (ESALs) over 20 years.

Overall, the condition of the street generally ranges from fair to good. Northbound from First Street to Pueblo

Avenue the current Pavement Condition Indexes range from 63 to 71 and north of Pueblo to Trancas from 41 to

59. Southbound the street is in poorer condition with PCIs ranging from 63 to 40 between Clay Street and Central

Avenue and 41 to 59 from Pueblo Avenue to Trancas Street. The section between Central Avenue to Pueblo

Avenue is largely failed with a PCI of 17

Field Investigation

Pavement Condition Survey

NCE performed a walking and driving pavement condition survey of California Boulevard for the purpose of evaluating the existing pavement distresses, ride quality, and associated failure mechanisms. The pavement condition is highly varied over the length of the section and consists of a mix of replaced lanes (inlays, failing and not failing), high severity and pumping alligator cracked areas, intermittent block and thermal cracking, utility cuts and reflective cracking from cuts, and numerous pavement surface changes. It appears, though it can’t be confirmed, that many lane replacement inlays were done without base repairs prior to their placement – whether done by utilities or City projects – hence their showing frequent premature localized failures.

Table 1 presents generalized distresses and severities (H High, M Medium, L Low) present (not a complete list) over the length of the section. Pavement Condition Index surveys performed in fall 2024 are presented where appropriate. Sectionalization and limits vary slightly from that in the table.

Table 1 California Boulevard Distresses by Block

Section Northbound Northbound

PCI (2024)

Southbound Southbound

PCI (2024)

First to Clay New AC Newer AC, Alligator – H, M, L Raveling and weathering Thermal cracking (shoulder)

Clay to E Alligator – M and H Patches Longitudinal and transverse cracking

71 63 E to F Alligator – M and H

Thermal cracking Alligator cracking (M), longitudinal cracking Thermal cracking (shoulder)

F to G Alligator – M and H Block Cracking

New AC inlay Alligator – H Thermal Cracking

G to H Alligator – M and H Longitudinal and transverse Block Cracking

Alligator – H and M Block Cracking

H to Lincoln Block Cracking, Rutting Block Cracking

Alligator – H and M Rutting – H Lane 2

Lincoln to Lone Oak Alligator – H Block Cracking

Alligator – H and M Failed inlay/lane Block cracking 40

Lone Oak to Central Alligator – H and L Weathering

Inlay/lane - Longitudinal and Alligator H, M

Central to Park Alligator – H and M Patching/Utility cut

Failed inlay/lane Thermal cracking

Park to Menlo Alligator – H and M Patching

Failed Inlay/lane

Menlo to Myrtle Alligator – H and L Patching

Failed Inlay/lane

Myrtle to Pueblo Weathering Longitudinal and Transverse

Failed Inlay/lane Thermal cracking

Pueblo to #3031 Alligator – H – intersection Localized alligator, longitudinal, and patching

Block Cracking Thermal Cracking Failed Utility Cut

#3031 to Industrial New AC

Longitudinal and Transverse Thermal Cracking Block Cracking

Industrial to Trancas Alligator – H and M

Weathering Block Cracking

Longitudinal and Transverse Thermal Cracking Block Cracking

Common distresses and typical pavement conditions seen on California Boulevard are shown in Figure 2 through

Figure 9. They are present in multiple areas over the length of California Boulevard.

Figure 2 Block and longitudinal cracking NB between F

St. and G St.

Figure 3 Severely failed patch NB between

Lincoln St. and Lone Oak Ave

Figure 4 Reflective cracking (premature) from utility trench NB between Lone Oak Ave and Central Ave

Figure 5 More severe cracking adjacent to utility near Pueblo Ave

Figure 6 - Load related, thermal, and utility cut cracking SB near Pueblo Ave

Figure 7 High severity alligator cracking and pumping on new overlay SB near Industrial Way

Figure 8 High severity alligator and pothole cracking SB between Menlo Ave and Park Ave

Figure 9 Severe thermal cracking in new inlay SB near

Permanente Way

Additional photos are presented in the Appendix.

Pavement Coring

NCE performed pavement coring on March 20, 2025 to help interpret the nature of the distresses, material conditions, and the thickness of the pavement. A total of 12 cores were obtained, including 2 bulk samples for subgrade assessment. A map of the coring locations is shown in Figure 10.

For each core sample, the surface material type was identified, and layer thicknesses were measured and recorded. Additional structural materials such as aggregate base were also measured and recorded, if possible, and the presence of pavement fabric was observed and recorded if present. AC thicknesses generally ranged from about 4 inches to 6 inches, with half the cores between 4.5 inches and 5.25 inches. Two cores exceeded these typical values with thicknesses of 7.75 inches and 15 inches. In the two bulk core locations, the aggregate base

(AB) was measured at 14.5 inches and 18.5 inches. The complete coring results are summarized in Table 2.

Given the high prevalence of thermal and environmental cracking exhibited, NCE performed much of the coring on these cracks. The goal of this process is to assess whether these cracks are top-down, bottom-up (full depth), or formed in another way. And based on these findings, milling depths and rehabilitation strategies can be developed with more knowledge than just by thickness cores alone.

An example core is shown in Figure 11 where the environmentally driven block cracking initiated at the surface

(left side) and is progressing into the pavement. In time, this crack will likely propagate through the entire

Figure 10 Pavement Core Locations thickness of the layer. Ideally, catching these cracks early in their life can mean thinner mill and fill depths or fewer base repairs or inlays during rehabilitation.

Figure 11 Core with top-down cracking

DCP Testing

Dynamic Cone Penetrometer (DCP) testing was performed at 8 core locations on California Boulevard. The DCP is a simple device often used to for the in-situ characterization of shallow soils, especially for pavement design purposes, where the number of repeated blows from a slide hammer correlates to an R-value or California

Bearing Ratio (CBR), both of which are used to represent the “strength” of the soil. These values are estimated from the number of blows per inch of depth of the penetration cone and can also be used to estimate the AB thickness. The stiffer AB layer requires more blows per inch than a soft subgrade. Typical AB has a CBR of between 80 and 100. As shown in Figure 12 the estimated CBR drops dramatically a depth of 17 inches, which represents an AB thickness of 11 inches, since the first point at 6 inches is the bottom of the AC/top of the AB.

Not all DCP plots are this clear and interpretation is often needed. In some cases, the DCP reaches a point of

“refusal” where due to hitting a large rock for example, the DCP can no longer penetrate the soil.

Figure 12 DCP Plot

Overall, of the DCP tests that were not refusal, estimated AB thicknesses range from 12 inches to 18 inches.

Pavement Deflection Testing NCE performed deflection testing in March 4, 2025 on California Boulevard in both lanes where present and both directions in accordance with California Test Method (CTM) 356 to evaluate the structural capacity of the existing pavement and to aid in overlay and rehabilitation design. In general, deflection testing was performed in the inner wheel path to allow traffic to flow around the right of the testing vehicle. A nominal 9,000-pound falling load was applied while measuring the resulting deflection at seven geophones radially displaced from the point of contact.

A total of 219 data points were collected in both directions at an average spacing of 100 ft, with a 50 ft. stagger where adjacent lanes exist. Greater variability in deflections were observed to correspond with the locations of fatigue cracking in both directions. The deflection data for California Boulevard northbound is shown in Figure 13.

Due to the wide variability, this data is broken up into “design sections.” Details are presented further in the

Pavement Design section and Appendix.

Figure 13 Deflection data for California Boulevard northbound

Laboratory Testing

BSK Associates in Livermore, CA performed laboratory testing on the bulk samples obtained during coring. This testing was done to support potential reconstruction design decisions of select sections and to evaluate the soil characteristics for in advance of construction, specifically soil preparation and compaction. The laboratory tests determined in-situ moisture content, Atterberg Limits (liquid limit, plastic limit, and plasticity index), and R-Value.

These test results provide good indications of subgrade strength and drainage potential. A subgrade with high R-value and low moisture content is desired for pavement. The plasticity index gives a good indication of subgrade expansion/contraction potential. The greater the PI, the greater the soil expansion/contraction potential.

Bulk subgrade samples were taken at core locations CA-4 and CA-6. The laboratory testing results showed that the in-situ moisture content of the subgrade ranged from 14% to 17.7%. Both subgrade samples were assessed as low plasticity clays (CL) and were plastic to similar degrees with Plasticity Index (PI) values of 27 and 28. The R-values of the subgrade beneath the street were both measured at 5. The laboratory testing results are included in the

Appendix.

Pavement Design

California Boulevard exhibits a considerable range of conditions along the length of the street, ranging from brand new to complete failure and other states in between. A major consideration for pavement design for California

Boulevard is whether to fully rehabilitate the portions of the street that are in current need of repair or to develop a strategy that effectively unifies the appearance of the street over the entire 1.7 miles, but perhaps does not address all pavement distress. Meaning costly deep lift repairs where necessary perhaps at the expense of shallow repairs and a surface seal to cover the street. Cost can be impacted dramatically by these options. The

City has developed a plan set showing a mix of mill and overlay lane resurfacing along with potential surface seal.

Caltrans Empirical Design

Pavement design was conducted using the Caltrans empirical method. Caltrans methods can be used to calculate pavement mill and overlay depths for large sections of pavement. A typical minimum is 21 data points or about

2,100 feet in this case. It does not discriminate between areas that have been repaired or not – that is the designer’s choice but for broad general treatments. The deflection testing method is helpful for assessing overall structural capacity. The Caltrans method (Section 630, 2020 Highway Design Manual) is designed to provide suitable 20 year mill and overlay designs based upon a formal combination of Traffic Index (TI), deflection testing results, and core thicknesses.

In the Caltrans method, the design is based on the premise that pavements deflect under traffic loading. The

Highway Design Manual (HDM) identifies the Tolerable Deflection at the Surface (TDS) of a pavement as the maximum deflection it should have for a given AC thickness to achieve its full pavement design life. For example, it is expected that thicker pavements will have lower TDS than thinner pavements due to a more robust structure.

If a thick pavement and thin pavement have the same deflection results, one could surmise that the thicker pavement is more in need of rehabilitation as it is “underperforming” in terms of deflection than the thin pavement. Deflection testing results and core thicknesses for given sections of pavement are compared to TDS to calculate appropriate overlay or mill and overlay needs.

The parameters used for the Caltrans design are:

• Design Life: 20 years

• TI: 9 (provided by the City)

• Existing Pavement Conditions: Deflection test results, core thicknesses, laboratory subgrade testing.

Engineering Judgement Designs

Design recommendations were also developed using engineering judgement. Engineering judgement methods rely on NCE experience following an assessment of core thicknesses, cracking patterns, deflection testing results, ride quality, available treatments, and cost, and may or may not be “designed” to achieve a 20-year expected life.

Factors considered included pavement distress levels and extent, deflection data, AC and AB lift and total thicknesses and conditions, cracking patterns, types, and depths, among others. While these designs are not based upon a formal design procedure, with no expected “design life” they are made with respect to practical considerations present on California Boulevard and concerns for budget and constructability.

Rehabilitation Recommendations

Based on the deflection data, as exemplified in Figure 13 and the coring and condition data, the project limits were segmented to comprise areas with common properties. High/outlier deflection points are removed from the analysis as they indicate areas of significant cracking or weakness that will be addressed through base repairs or digouts in addition to a resurfacing. For northbound California Boulevard, the design process was divided into

4 locations based upon consistency and values of deflection testing and distress conditions. These limits are:

• Clay Street to G Street

• G Street to Lone Oak Avenue

• Lone Oak Avenue to Pueblo Avenue

• Pueblo Avenue to Trancas Street

For southbound California, a similar process yielded:

• Trancas Street to ~800 feet south of Trancas Street (pavement change)

• ~800 feet south of Trancas Street to Merced Street

• Merced Street to ~ G Street

• ~ G Street to Clay Street

Even within these divisions, there are variations in conditions due to the nature of how the street has been rehabilitated over the years. And these will need to be addressed through plan details that identify specific repair locations.

As part of the design process, NCE explored traditional engineering solutions, such as mill-and-overlay, reconstruction, and base repair and seal treatments. NCE also looked at value and sustainable engineering solutions, including cold-in-place recycling and rubberized hot mix asphalt and proposed those options as appropriate. Detailed descriptions and advantages of the value and sustainable engineering options are provided.

NCE considered multiple rehabilitation options for California Boulevard. This is a major corridor for the City and no treatment is going to be free of disturbance to the residents of Napa. If the elected treatments involve more than surface seals and base repairs, night paving may be the best way to minimize the construction impact.

Given the relative thickness of the AC (5 to 7 inches) and aggregate base (17 inches), the high prevalence of environmentally driven thermal and block cracking, some of which is top down, along with intermittent and sometimes high severity fatigue cracking, several main strategies emerged as the most suitable and there are options within each:

• Mill and Overlay (Potentially in all lanes to varying degrees) o Conventional AC Overlay o Fiberized AC Overlay o RHMA-G Overlay o Any of the above options with Warm Mix Asphalt Technology o Any of the above options with a rubberized Stress Absorbing Membrane Interlayer (SAMI-R)

• Full Depth Reclamation

• Cold In-Place Recycling

• Deep Lift AC in areas of high severity cracking, pumping, and rutting

• Microsurfacing or double Microsurfacing seal treatments with base repairs, if sufficiently conducted may offer a suitable surfacing for the medium term, tying the project together visually. Micromilling could potentially be used in conjunction with Microsurfacing to enhance pavement smoothness, as seal treatments by themselves have minimal impacts on existing pavement surface roughness. However, cracks that are not addressed under the seal will reflect through the seal sooner than they will an overlay.

• Like Microsurfacing, Rubberized Cape Seal may provide satisfactory service as a value treatment. The rubber chip seal portion of this product will help mitigate crack propagation with the Microsurfacing surface adding smoothness. With the relatively slow speeds on California Boulevard, there is potential for this treatment to work if the City maintains the Microsurfacing layer to ensure the rubber chip seal does not become exposed, leading to chip loss. This treatment does not have the overall smoothness of the others, but would be enhanced through prior micromilling and rolling during chip seal and microsurfacing placement.

Rehabilitation treatment recommendation summaries are presented in Table 1 in the Appendix. The following section discusses particulars of each option.

Treatment Discussion

Mill and Overlay

A common theme seen on California Boulevard is the high rate of failure of what appears to be relatively new AC lane replacements/inlays. In some cases, the failures are on older pavements. To address this, a smooth ride may be restored with a mill and overlay treatment, however failed areas must be addressed with base repairs prior to the AC overlay and/or thicker overlays should be used.

Caltrans method recommends various mill and overlay depths for different lanes, directions, and sections of

California Boulevard.

• For the northbound and southbound between 1st Street and G Street, there is no overlay thickness that can be placed that is thinner than the existing AC that provides adequate service. In other words, these sections have very high deflections and will require significant base repairs to yield a well performing pavement. An overlay to unify the appearance and provide a smooth riding surface will work well here.

• For northbound and southbound between G Street and Lone Oak Avenue/Merced Street, Caltrans design shows that following base repair of the failed sections, no additional structure is required and a modest mill and overlay treatment will suffice to provide sound service.

• For northbound between Lone Oak Avenue and Pueblo, like between 1st Street and G Street, there is no overlay thickness that can be placed thinner than the existing AC that provides adequate service.

Significant base repairs on the fatigued areas need to be performed and an overlay will unify and smooth the surface.

• For southbound between Merced Street and ~800 feet south of Trancas Street, a deeper overlay is required than that milled away, meaning that a deep treatment or significant base repairs are required for structural adequacy. An overlay that provides a consistent surface will cover these base repairs.

• For northbound between Pueblo Avenue and Trancas Street, following localized base repairs of failed areas, no additional structure is required and a modest mill and overlay treatment will provide adequate surface.

• For Southbound for the last 800 feet up to Trancas Street no structural overlay or additional thickness is required, but base repairs if needed should be conducted and an overlay will provide smoothness.

The Caltrans method does not take into account visible environmental and structural cracking as part of the recommendation – but rather based upon structural performance. A pavement section may have considerable environmental cracking, but perform well from a vehicle load carrying capacity.

Whether the street is technically structurally sound or not, treatment is needed in the areas of environmental cracking – and recommendations can come from engineering judgement. These recommendations are not part of an official Caltrans or other design approach, but are based upon what is present in the field and what is available practically to rehabilitate the pavement.

While performing base repairs and placing shallow mill and fill layers may provide adequate service based upon

Caltrans methods, engineering judgement design adds that in order to mitigate the recurrence of existing block and thermal cracking, mill depths need to be sufficient to go below these top down cracks. Considering Figure 11 and other cores taken that show cracking either through the entire core or down through most of it, it is wise to consider milling depths that are 3 inches or more or in some cases using “surface reconstruct” techniques to mill out all the AC, compact the AB, and replace AC in full thickness.

Another option is to utilize the shallower mill depth and to place a Stress Absorbing Membrane Interlayer (SAMI) as specified by Caltrans underneath the overlay. This consists of a rubberized chip seal made with 3/8-inch aggregate to act as a crack retardation material to aid in keeping cracks that are still present following milling, or are approaching from below unseen, from eventually reflecting through the pavement.

Place a new AC overlay on the SAMI. This overlay, whether on the SAMI or not, can be made of a number of different material options, each of which has definite pros and cons.

o Conventional AC using PG 64-10 is the industry and regional standard but does not offer any significant performance benefits in terms of rutting or reflective cracking performance on top of the frequently present environmental cracks on Trancas Avenue. It is straightforward to pave and known to contractors.

o Fiberized conventional AC using PG 64-10 offers further crack retarding potential at a modest cost increase. It is not as well known or utilized as conventional AC by contractors but certainly is constructable.

o RHMA-G, noted for its reflective cracking performance could be utilized. Currently it is only recommended by Caltrans for thicknesses up to 2.5 inches (though NCE understands that this may change in the near future). Going with a 2.5 inch mill and overlay would leave cracked areas beneath the overlay and some areas that could potentially remain as “scabs” or unmilled thin layers.

o Given the cracking seen on the pavement and the inability of fabrics to retard these cracks, they are not recommended as a strategy for California Boulevard.

o Warm Mix Asphalt (WMA) technology, whether chemical or foam allows an AC mix to be compacted down to lower temperatures, giving the contractor a significantly longer time window to achieve proper compaction. Given potential night paving on California Boulevard, this is an option to consider to help maximize density and overall performance.

Regardless of the various treatment options available, performing a consistent treatment throughout the street would be simpler for bidding and construction, and allow the City to know what is present on the street when future work is needed. A deeper than perhaps structurally necessary mill and overlay would mitigate against the significant amount of block and transverse cracking present on the street.

Base Repair and Seal Treatments

This strategy performs base repairs on structurally failed sections, cracks seals or mastic fills cracks of varying widths and places a seal treatment on the pavement as a wearing and appearance unifying surface. The seal treatments can be Microsurfacing, two layers of Microsurfacing (aka Double Microsurfacing), and a Rubber Cape

Seal. The performance of these treatments cannot be expected to match that of the overlay treatments, but may well provide satisfactory service for up to 10 years if properly constructed. Given the high level of traffic, but slower speeds, the Microsurfacing layer should be monitored over time and repaired if the material wears to the point that the lower chip seal layer becomes visible. Micromilling may be performed following base repairs and ahead of the seal treatments to address any surface roughness that may be present.

Cold In-Place Recycling (CIR)

While CIR may well address much of the environmental cracks seen on California Street, given that so much of the street is structurally inadequate, and suffers from base failure, and that the size of the project is too small to warrant, CIR is not advised for California Boulevard.

Value and “Green” Treatment Descriptions

To help save budget and extend paving dollars, throughout the design process, NCE explored value engineering options as efficient and cost-saving alternatives to traditional reconstruction or mill and overlay. These value engineering options included cold-in-place recycling (CIR), full-depth reclamation (FDR), and rubberized hot mix asphalt (RHMA). Some of these treatments are advised and some are not. Summaries of these processes follow.

Full Depth Reclamation

Full Depth Reclamation techniques can be considered a value engineered reconstruction method, as off haul of materials are minimized and the materials are recycled in place – often at a considerable cost reduction over traditional reconstruction. For a similar structural performance, FDR sections require relatively less HMA than comparable “mill and overlay” or “remove and replace” options. And it will provide California Boulevard with a stable base platform well into the future, meaning that costly base repairs will be minimized as future maintenance. One major benefit of this design is that it allows considerable flexibility in developing overall grading design for the street should that be necessary and will address any roughness issues due to the presence of failing AC. However, depths of utilities and other constructability issues should be checked before deciding on

FDR.

Full depth reclamation on California Boulevard would involve blending of existing AC, AB, and native clay subgrade into a uniform material, followed by removal of necessary “dirty” material and grading to a height required to allow for the new AC surface. The incorporated AC material will give additional structure and strength to the fat clay subgrade present on California Boulevard. The in-place material would then be blended with either cement, lime, or a lime/cement mixture depending upon the final mix percentages of AC, AB, and native subgrade, and allowed to mellow/cure, and then compacted to grade. An AC overlay, or potentially an RHMA-G surfacing is placed on this surface.

This method addresses the poor subgrade support by creating a firm, moisture insensitive and volumetrically stable layer to support the new AC surfacing. Presently this poor subgrade has been addressed with multiple AC lane width patches that are not always providing adequate support for California Boulevard’s traffic. Construction wise, challenges with this method include opening up the street for multiple days during which the reclamation process occurs, however traffic can be allowed once stabilized and cured. There is enough width on California

Boulevard to potentially do the street half at a time width wise to keep traffic flowing – but it should be discussed with an FDR contractor to ensure this is feasible. Potentially utilities may need to be lowered as well, which should be researched as part of the decision making process.

Given the widespread level of structural and environmental distress found on California Boulevard, FDR is recommended as a design alternative. A structural section of 5 inches AC over 18 inches FDR meets Caltrans 20-year design requirements.

Cold In-Place Recycling (CIR) Asphalt Concrete

CIR is a process in which all or part of the asphalt pavement layers are pulverized, mixed with an asphalt emulsion or a foamed asphalt binder, and repaved in place. CIR can take place within the roadway and can use up to 100 percent of the recycled asphalt pavement (RAP) generated during the process. Typical treatment depths are 3 to 4 inches for emulsion methods and up to 5 inches for foam methods. The CIR process commonly uses asphalt binder (emulsion or foam), cement, water, and a mixing unit; either a single vehicle for foam methods or milling and mixing vehicles for emulsion methods. Pavers and rollers are used to spread and compact the recycled material.

CIR is generally used on pavements with high frequency and high severity, non-load associated distresses (thermal cracking, block cracking, raveling, etc.). Cracked pavements that are structurally sound and have well-draining bases are ideal candidates. However, CIR can also be used to address load-related distress when used in conjunction with an asphalt overlay, and base repairs to increase the pavement’s structural capacity, which is a pavement’s ability to carry traffic loads while maintaining minimal structural distresses.

The advantages of CIR include:

• Reduction of public inconvenience and project duration by up to 30%

• Construction of a brand-new asphalt bound layer utilizing the existing materials

• Removal the existing crack patterns

• Rejuvenation of the previous pavement surface

• Maintenance of bridge clearances and curb heights

• Minimization of offsite hauling of excess milled materials

Given that so much of California Boulevard suffers from structural failure, CIR is not recommended.

Rubberized Hot Mix Asphalt (RHMA)

RHMA is asphalt material that includes recycled tires that have been ground up and added into the asphalt binder.

The primary technique used today for combining recycled rubber and asphalt is the asphalt rubber process, also known as the “wet process.” The terminal blend process had been used in California but is largely unused today.

Both processes involve blending ground tire rubber and asphalt binder, either in a blending unit at the hot mix plant (AR process) or at a refinery (terminal blend process), and then adding the blended mixture to the specified aggregate gradation to produce the final mix. Caltrans Standard Specification Sections 39 and 92 address AR binders.

RHMA-G is generally used as overlays on pavements that are susceptible to reflective cracking. Numerous laboratory studies, field installations, and accelerated pavement testing programs, have identified advantages of properly designed and constructed AR pavements. Such advantages include:

• Resistance to reflective cracking

• Reduction in pavement noise

• Improved driving safety

• Increased structural capacity

• Reduced environmental impact in terms of waste material

Since RHMA-G provides a higher resistance to reflective cracking than traditional HMA, RHMA would be a suitable treatment for the mill and overlay strategy. The main concern in the mill and overlay method would be the how well top down cracks would be addressed with a 2.5 inch thick overlay, the thickest currently allowed by Caltrans.

It is important to fully remove the AC down to a solid surface and if needed to remove the top down cracks. Any thin layers or “scabs” could potentially lead to delamination of the overlay. Given that RHMA-G can only be placed to a thickness of 2.5 inches based upon Caltrans guidance, proper and precise milling during construction would need to be performed. One option would be to mill to 3 inches, place a SAMI-R and then RHMA.

Construction Considerations

Base Repairs

Base repairs should be completed in areas where moderate to high severity fatigue cracking is present to mitigate reflective cracking in the new surface overlay. With HMA overlays, areas with severe structural distresses should receive base repairs before placement of the overlay. If used in conjunction with mill and overlay, base repairs should be 4 or 6 inches deep depending on the remaining AC, and as measured from the top of the milled surface.

The base repair shall then be filled with full-depth HMA in lifts of up to 3 inches.

Base repairs serve several functions. When an overlay is designed using deflection testing per Caltrans methods, they allow the required overlay thickness to be reduced. Deflection measurements from areas of high distress are naturally higher than in areas of minimal distress. By repairing the weakest pavement areas, overall pavement performance is improved.

Due to the prevalence of high plasticity and low R-Value subgrades, it can be expected that overexcavation may be required in order to achieve compaction of the AC base repair. The following language is recommended for inclusion in the technical specifications:

The Contractor should remove existing asphalt concrete pavement and base material at areas marked in the field by grinding or removing to the specified depth. The Contractor should scarify, grade, and compact the top of any base material encountered. Any import base material needed to meet the requirement for this work should be compacted to ninety-five percent (95%) minimum modified proctor. The Contractor should place asphalt concrete that conforms to the 3/4-inch HMA Type A aggregate gradation specified in Section 39 “Aggregate” of the

California Standard Specifications. If adequate compaction is not achievable with aggregate base along, installation of geogrid shall be performed prior to aggregate base. The Contractor should apply a tack coat (SS-1h emulsion) to the edges of the existing asphalt pavement and to the base material prior to asphalt placement.

Full Width Milling

When removing a portion of the existing pavement structural section by milling, it is important to ensure that sufficient AC remains below the milling plane to support placement of new HMA or RHMA-G (assuming all HMA is not going to be removed). NCE suggests a minimum remaining AC thickness between 2 -3 times the thickness of the existing maximum HMA aggregate size. For example, for an existing HMA mix with ¾-inch aggregate, at least 1

½-inches of AC should remain below the milling plane. If this minimum thickness cannot be maintained, then the entire AC section should be removed, and the exposed aggregate base or subgrade material should be compacted before the new AC layer is placed. The exception to this minimum remaining AC thickness is if pavement-reinforcing fabric is present in the section. In this case, a minimum AC thickness of 2-3 times the existing maximum HMA aggregate size should remain above the fabric if the existing fabric will not be removed, regardless of how much AC exists below the fabric.

The CIR and mill and overlay designs will require removal of portions of the AC thickness. Removal of AC thickness must be performed in accordance with Section 39of Caltrans Standard Specifications.

Crack Sealing

Crack sealing on cracks greater than ¼-inch prior to overlay treatments allows future protection against infiltration of water into aggregate base and subgrade and therefore affords additional preservation of the pavement. Crack sealing underneath Microsurfacing provides similar benefits. Crack sealing beneath rubberized chip seals may result in crack seal bulking or movement.

If crack sealant is applied excessively it will bulk (or expand) when the hot mix asphalt or rubberized surface seal is placed on top and can produce a bump in the final paving surface. Therefore, it is recommended that the crack sealant not be allowed to collect on the pavement and should only be applied in the crack itself and should be recessed ⅛ to ¼ - inch below the paving surface to allow room for it to expand. If that is not feasible, crack sealing should be performed with a shoe applicator that results in a minimal amount of side band surrounding the crack, and less than 1/16 in. in thickness. Adequate cure time (at least six months for conventional rubberized sealants) should also be allowed prior to any overlay or pavement treatment to allow for proper curing and hardening of crack sealing material, which leads us to recommend against rubberized sealants.

However, we understand for pavement surfaces that are to be milled, proper curing and hardening of conventional rubberized crack sealant will not be achievable. Napa may elect to use a non-rubberized crack sealant (such as Crafco Superflex HT Polymer Modified or those made by Main Street Materials) to shorten the cure time for the planned construction time frame.

Wide cracks from 1 to 4 inches may be filled with an asphalt mastic product such as Crafco Mastic One or Maxwell

Products Gap Mastic. This material will help maintain smoothness on surface sealing sections where conventional crack sealant materials are inadequate.

Closure

We trust this letter report provides the necessary information at this time. If you have any further questions, please contact us at (510) 215-3620.

Yours very truly, Nichols Consulting Engineers, Chtd.

Prepared by:

James Signore, PhD, PE Principal

Jakrit Saint Yoojaroen Staff Engineer

NCE

1003 W. Cutting Blvd., Suite 110 Richmond, CA 94804 510-215-3620

APPENDIX

Pavement Design Tables

Table 1 – Pavement Rehabilitation Recommendations

Table 2 – Pavement Layer Thicknesses and Lab Results Summary

Pavement Core Photos

Deflection Testing Results

DCP Testing Results

Laboratory Test Results

Appendix A - Pavement Design Tables

City of Napa

California Boulevard

Table 1. Rehabilitation Design

No. Street Name Begin Location End Location No. of

Lanes (1)

Functional

Class (1)

Length

(ft)

Width

(ft)

Approx.

Area

(sf)

Surface

Type (1)

No. of

Cores (2)

Existing AC

Thickness from Core

(in.)

(2)

Existing AB

Thickness (in.)

(3)

Subgrade

RV

PI

MC

Soil Type (4)

Recommended Design (5)

Recommended Design (5)

Alternate Design (6)

Alternate Design (7)

1 CALIFORNIA BLVD (NB) 1ST ST G ST 1 A 2,430 18 43,740 AC 2 3.75" - 5.00" 14.50"

CL

17.7

5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

2 CALIFORNIA BLVD (NB) G ST LONE OAK AVE 1 A 1,570 18 28,260 AC 1 5.00" 18.50"

CL

5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

3 CALIFORNIA BLVD (NB) LONE OAK PUEBLO AVE 1 A 2,040 18 36,720 AC 1 5.25" Present - 5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

4 CALIFORNIA BLVD (NB) PUEBLO AVE TRANCAS ST 1 A 2,810 18 50,580 AC 1 15.00" Present - 5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

5 CALIFORNIA BLVD (SB) TRANCAS ST 773' S/O TRANCAS ST 1 A 773 18 13,914 AC 2 7.75" Present - 5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

6 CALIFORNIA BLVD (SB) 773' S/O TRANCAS ST MERCED ST 1 A 4,347 18 78,246 AC 2 4.25" - 4.50" 12.00" - 5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

7 CALIFORNIA BLVD (SB) MERCED ST

805' S/O LINCOLN ST (G

ST)

1 A 1,150 18 20,700 AC 3 5.00" 18.00" -

5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

8 CALIFORNIA BLVD (SB)

805' S/O LINCOLN ST (G

ST)

1ST ST 1 A 2,580 18 46,440 AC 4 6.00" 14.00" -

5 inch AC overlay, 18 inch FDR (Cement/Lime)

3 inch mill, base repairs, SAMI-R, and 2.5 inch AC overlay

2 inch mill, base repairs, and 2 inch AC overlay

Base repairs with double

Microsurfacing or Cape Seal.

Optional micromilling.

(1) The functional classes were provided by the City StreetSaver.

(2) Pavement coring and laboratory testing data is summarized in Table 2.

(3) The aggregate base (AB) thickness were measued at bulk sample locations

(4) RV: R-Value, PI: Plasticity Index, MC: Moisture Content %, CL: Low Plasticity Clay

(5) RHMA-G may be substituted. Treatment not conducted in areas already rehabilitated by City unless exhibiting high deflections and premature failure.

(6,7) Treatments will provide unifying visual appearance but are not anticipated to provide the same level of service as the recommended treatment.

California Boulevard Rehabilation Porject

Table 2 Summary

Aggregate

Base (AB)

Layer

Layer1 Layer2 Layer3 Layer4 Layer5

CA-1 NB No Fabric 4.00 - - - - 4.00 Present - - - - - -

CA-2 OPT NB No Fabric 3.75 - - - - 3.75 Present - - - - - -

CA-4 BULK NB No Fabric 4.00 5.00 - - - 5.00 14.50 CL 5 17.7 28 49 37.75

CA-6 BULK NB No Fabric 3.00 5.00 - - - 5.00 18.50 CL 5 14 27 48 42

CA-7 NB No Fabric 2.25 5.25 - - - 5.25 Present - - - - - -

CALIFORNIA BLVD (NB) PUEBLO AVE TRANCAS AVE 1 CA-9 NB No Fabric 2.75 5.50 15.00 - - 15.00 Present - - - - - -

CA-11 SB No Fabric 2.25 5.00 7.75 - - 7.75 Present - - - - - -

CA-12 SB No Fabric 4.50 - - - - 4.50 12.00 - - - - - -

CA-14 SB No Fabric 2.00 4.50 - - - 4.50 Present - - - - - -

CA-15 SB No Fabric 1.75 4.25 - - - 4.25 12.00 - - - - - -

CA-16 SB No Fabric 2.25 3.50 5.00 - - 5.00 18.00 - - - - - -

CA-17 SB No Fabric 2.25 4.50 6.00 - - 6.00 14.00 - - - - - -

PUEBLO AVE

CALIFORNIA BLVD (NB) 1ST ST LINCOLN AVE

Core ID DirectionStart End Lot Location No. of Core

Asphalt Concrete (AC) or Aggregate Treated Base

(ATB) Layer Subgrade Layer

Depth from Surface to the bottom of layers (in.)

Total

Thicknes s (in.)

Presence /

Thickness

From Core

(in.) (2)

Types of

Soil R-Value

Moisture

Content

Fabric Depth (in.)

Liquid limit

Depth Moisture

Sample Taken (in.)

Plasticity

Index

(PI) (3)

CALIFORNIA BLVD (SB) LINCOLN AVE 1ST ST

CALIFORNIA BLVD (SB) TRANCAS AVE PUEBLO AVE

CALIFORNIA BLVD (SB) PUEBLO AVE LINCOLN AVE

CALIFORNIA BLVD (NB) LINCOLN AVE

Appendix B - Pavement Core Photos

Core Photo Log

Pavement Design Memo April 2025

CA -1 CA -2

CA-4 CA-6

CA-7

CA-9

Core Photo Log

Pavement Design Memo April 2025

CA-11 CA-12

CA-14 CA-15

CA-16 CA-17

Attachment C – Deflection Testing Results

California Boulevard Rehabilation Project

FWD Testing Summary

1s t S t

C la y St

D S t

E St

F St

G S t

CA-1 CA-2 OPT

CA-4 BULK

0+00 5+00 10+00 15+00 20+00

AC

T hi ck ne ss

(i n)

D ef le ct io n

(m ils

Project Stationing (ft)

California Blvd NB 1st St (Sta 00+00) to G St (Sta 24+30)

Cross Street Northbound Lane 1 Northbound Lane 2 Core Information

FWD Testing Summary

G S t

H S t

L in c o ln

A v e

L o n e O a k

A v e

CA-6 BULK

24+30 26+30 28+30 30+30 32+30 34+30 36+30 38+30

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd NB G St (Sta 24+30) to Lone Oak Ave (Sta 39+00)

Cross Street Northbound Lane 1 Northbound Lane 2 Core Information

FWD Testing Summary

L o n e O k

A v e

C e n tr a l A v e

P a rk

A v e

M e n lo

A v e

M yr tl e A v e

P u e b lo

A v e

CA-7

39+00 44+00 49+00 54+00 59+00

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd NB Lone Oak Ave (Sta 39+00) to Pueblo Ave (Sta 59+40)

Cross Street Northbound Lane 1 Core Information

FWD Testing Summary

P u e b lo

A v e

S ta d iu m A v e

In d u s tr ia l W a y

P e rm a n e n te

W a y

T ra n c a s S t

CA-9

59+40 64+40 69+40 74+40 79+40 84+40

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd NB Peublo Ave (Sta 59+40) to Trancas St(Sta 88+50)

Cross Street Northbound Lane 1 Core Information

FWD Testing Summary

T ra n c a s S t

O ld

C a lif o rn ia

W y

CA-11

0+00 1+00 2+00 3+00 4+00 5+00 6+00 7+00

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd SB Trancas St (Sta 00+00) to 773' S/O Trancas St (Station 7+73)

Cross Street Southbound Lane 1 Core Information

FWD Testing Summary

P u e b lo

A v e

M yr tl e A v e

M e n lo

A v e

P a rk

A v e

C e n tr a l A v e

M e rc e d S t

CA-12 CA-14 CA-15

7+73 12+73 17+73 22+73 27+73 32+73 37+73 42+73 47+73

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd SB 773' S/O Tracas St (Sta 7+73) to Merced St (Sta 51+20)

FWD Testing Summary

M e rc e d S t

L in c o ln

A v e

CA-16

51+20 53+20 55+20 57+20 59+20 61+20

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd SB Merced St (Sta 51+20) to 805" S/O Lincoln St (Sta 62+70)

Cross Street Southbound Lane 1 Southbound Lane 2 Core Information

FWD Testing Summary

F S t

E S t

D S t s t S t

CA-17

62+70 67+70 72+70 77+70 82+70 87+70

A C

T h ic k n e s s in

D e fl e c ti o n m ils

Project Stationing (ft)

California Blvd SB 805" S/O Lincoln St (Sta 62+70) to 1st St (Sta 88+50)

Attachment D – DCP Testing Results

Sheet Number 1 OF 2

Operator

DCP LOG Test Date

Job #

Client Hammer Weight X 8 Kg 4 Kg

Facility Depth of Zero 170 mm

Location

Reading # of Blows

Scale Reading

(cm)

Pen.

Between Readings

(mm) Pen. Per blow Hammer Factor*

DCP Index (mm/blow) CBR

Depth, inches

0 20.5 6.7

1 5 21.7 12 2.4 1 2.4 110 7.2

2 5 22.1 4 0.8 1 0.8 375 7.3

3 5 22.4 3 0.6 1 0.6 517 7.4

4 5 22.5 1 0.2 1 0.2 1771 7.5

5 10 23.2 7 0.7 1 0.7 435 7.8

6 10 23.5 3 0.3 1 0.3 1125 7.9

7 10 23.9 4 0.4 1 0.4 815 8.0

8 10 24.3 4 0.4 1 0.4 815 8.2

9 10 24.4 1 0.1 1 0.1 3849 8.2

10 10 24.42 0.2 0.02 1 0.02 23347 8.2

11 10 24.44 0.2 0.02 1 0.02 23347 8.2

12 10 24.5 0.6 0.06 1 0.06 6821 8.3

13 10 24.6 1 0.1 1 0.1 3849 8.3

14 10 25.1 5 0.5 1 0.5 635 8.5

15 10 25.1 0 0 1 0 #DIV/0! 8.5

16 10 25.1 0 0 1 0 #DIV/0! 8.5

17 10 25.1 0 0 1 0 #DIV/0! 8.5

18 10 25.1 0 0 1 0 #DIV/0! 8.5

* Enter 1 for 8 kg. Hammer, 2 for 4.6 mm hammer

Napa, CA

California Blvd

CA-1

ME & KF

20-Mar-25

1126.12.55

Sheet Number 2 OF 2

DCP LOG Test Date

Job #

Client Hammer Weight X 8 Kg 4 Kg

Facility Depth of Zero 170 mm

Location Latitude: 38.30036 Longitude: -122.3004

Napa, CA

California Blvd

CA-1

ME & KF

20-Mar-25

1126.12.55

0 200 400 600 800 1000 1200 1400 1600 1800 2000

D e p th

, I n ch e s

CBR

DCP LOG Test Date

Job #

Client Hammer Weight X 8 Kg 4 Kg

Facility Depth of Zero 143 mm

Location

Reading # of Blows

Scale Reading

(cm)

Pen.

Between Readings

(mm) Pen. Per blow Hammer Factor*

DCP Index (mm/blow) CBR

Depth, inches

0 17.6 5.6

1 3 19.2 16 5.333333 1 5.3333333 45 6.3

2 3 20.8 16 5.333333 1 5.3333333 45 6.9

3 3 22.1 13 4.333333 1 4.3333333 57 7.4

4 3 23.2 11 3.666667 1 3.6666667 68 7.8

5 3 24.4 12 4 1 4 62 8.3

6 3 25.4 10 3.333333 1 3.3333333 76 8.7

7 3 26.4 10 3.333333 1 3.3333333 76 9.1

8 3 27.2 8 2.666667 1 2.6666667 97 9.4

9 3 28.2 10 3.333333 1 3.3333333 76 9.8

10 3 29.1 9 3 1 3 85 10.2

11 3 29.9 8 2.666667 1 2.6666667 97 10.5

12 3 30.6 7 2.333333 1 2.3333333 113 10.7

13 3 31.5 9 3 1 3 85 11.1

14 3 32.4 9 3 1 3 85 11.5

15 3 33.3 9 3 1 3 85 11.8

16 3 34.3 10 3.333333 1 3.3333333 76 12.2

17 3 35.2 9 3 1 3 85 12.6

18 3 36.1 9 3 1 3 85 12.9

19 3 36.7 6 2 1 2 134 13.1

20 3 37.4 7 2.333333 1 2.3333333 113 13.4

21 3 38.1 7 2.333333 1 2.3333333 113 13.7

22 3 38.9 8 2.666667 1 2.6666667 97 14.0

23 3 39.6 7 2.333333 1 2.3333333 113 14.3

24 3 40.5 9 3 1 3 85 14.6

25 3 41.2 7 2.333333 1 2.3333333 113 14.9

26 3 41.9 7 2.333333 1 2.3333333 113 15.2

27 3 42.7 8 2.666667 1 2.6666667 97 15.5

28 3 43.4 7 2.333333 1 2.3333333 113 15.8

29 3 44.1 7 2.333333 1 2.3333333 113 16.1

30 3 44.8 7 2.333333 1 2.3333333 113 16.3

31 3 45.4 6 2 1 2 134 16.6

32 3 46 6 2 1 2 134 16.8

33 3 46.6 6 2 1 2 134 17.0

34 3 47.3 7 2.333333 1 2.3333333 113 17.3

35 3 48.1 8 2.666667 1 2.6666667 97 17.6

36 3 48.8 7 2.333333 1 2.3333333 113 17.9

37 3 49.6 8 2.666667 1 2.6666667 97 18.2

38 3 50.2 6 2 1 2 134 18.5

39 3 51.1 9 3 1 3 85 18.8

40 3 51.7 6 2 1 2 134 19.1

41 3 52.5 8 2.666667 1 2.6666667 97 19.4

42 3 53.2 7 2.333333 1 2.3333333 113 19.6

43 3 53.7 5 1.666667 1 1.6666667 165 19.8

44 3 54.4 7 2.333333 1 2.3333333 113 20.1

45 3 55.1 7 2.333333 1 2.3333333 113 20.4

Napa, CA

California Blvd

CA-2

ME & KF

46 3 55.9 8 2.666667 1 2.6666667 97 20.7

47 3 56.7 8 2.666667 1 2.6666667 97 21.0

48 3 57.5 8 2.666667 1 2.6666667 97 21.3

49 3 58.3 8 2.666667 1 2.6666667 97 21.7

50 3 59.2 9 3 1 3 85 22.0

51 5 60.6 14 2.8 1 2.8 92 22.6

52 5 62.2 16 3.2 1 3.2 79 23.2

53 5 64.2 20 4 1 4 62 24.0

54 5 66.8 26 5.2 1 5.2 46 25.0

55 2 74.1 73 36.5 1 36.5 5 27.9

56 1 75.7 16 16 1 16 13 28.5

57 1 77.2 15 15 1 15 14 29.1

58 1 78.7 15 15 1 15 14 29.7

59 1 80.1 14 14 1 14 15 30.2

60 1 81.4 13 13 1 13 17 30.7

61 1 82.7 13 13 1 13 17 31.3

62 1 84.2 15 15 1 15 14 31.9

63 1 85.7 15 15 1 15 14 32.4

64 1 87.6 19 19 1 19 11 33.2

65 1 89.3 17 17 1 17 12 33.9

66 1 91.6 23 23 1 23 9 34.8

67 1 94.4 28 28 1 28 7 35.9

* Enter 1 for 8 kg. Hammer, 2 for 4.6 mm hammer

DCP LOG Test Date

Job #

Client Hammer Weight X 8 Kg 4 Kg

Facility Depth of Zero 143 mm

Location Latitude: 38.30183 Longitude: -122.30077

Napa, CA

California Blvd

CA-2

ME & KF

20…