University of California Pavement Research Center

This technical memorandum presents the results of a visual assessment of five pilot projects constructed by Caltrans between 2022 and 2023 as part of a Caltrans-industry initiative aimed at evaluating the feasibility of using 10% reclaimed asphalt pavement (RAP), by aggregate replacement, in rubberized hot mix asphalt–gap-graded (RHMA-G) mixes, which is currently not permitted under Caltrans standard specifications. Each pilot project included a section constructed with RHMA-G incorporating 10% RAP while the remainder of the project was built with a conventional RHMA-G containing no RAP. The visual assessments were conducted between October 2025 and January 2026, when the projects had been in service for approximately 2.4 to 3.1 years. The assessment included, for each pilot project, a 0.4-0.6 miles long section built with RHMA-G with 10% RAP and an adjacent section, either immediately upstream or downstream, built with conventional RHMA-G without RAP. Overall, both RHMA-G mixes—with and without RAP—performed satisfactorily across the five pilot projects. In three projects, no significant distresses were observed in either of the two mixes. In the remaining two projects, cracking was observed; however, the extent of cracking was greater in the sections without RAP than in the sections with RAP. The satisfactory preliminary performance of the mixes with RAP across the five pilot projects supports the continued use of 10% RAP in RHMA-G.

Samples from various material groups including biomass ashes, biochars, natural pozzolans, and construction and demolition waste (C&DW) were evaluated as supplementary cementitious materials (SCMs) for concrete. C&DW included rock dust (baghouse fines) from asphalt plants, rock dust from aggregate quarries, recycled concrete aggregate fines, crushed concrete aggregate fines, and concrete wash pond sludge. Characterization covered chemical and physical properties. Cementitious reactivity (pozzolanic or latent hydraulic) was measured based on ASTM C1897. Materials identified as pozzolanic reactive with equivalent total alkalis >5% or equivalent available alkalis >1.5% were further assessed for alkali-silica reactivity (ASR) by ASTM C1567 using a standard mortar with highly reactive sand and 20% cement replacement by each SCM. For SCMs that mitigated ASR expansion but did not meet Caltrans’s 0.1% limit, testing was repeated at replacement levels >20% when possible.

A multicriteria approach was used to choose the materials to advance to the concrete-phase evaluation. Criteria were 7-day and 28-day strength activity index (SAI) >80% or 90-day SAI >80%, calorimetry heat release >90 J/g SCM, calcium hydroxide consumption >50 g/100 g SCM, water requirement <115% of control, grinding/milling <5 minutes, foam index test: >0.40 mL air-entraining admixture demand, and ASR performance <50% of control with highly reactive aggregate. Based on these criteria, recommended SCMs for further evaluation include 15 biomass ash samples, a few biochar samples, 28 natural pozzolans, rock dust from asphalt plants, and minimally ground wash pond sludge from the C&DW group. Beyond next-phase concrete testing, additional actions were identified: expand rock dust sampling from more asphalt plants and estimate available supply in California, establish rock dust availability from aggregate quarries in California and neighboring states, and collect more wash pond sludge from concrete plants with supply estimates. Finally, to update Caltrans specifications, it was recommended to require ASTM C1897 testing for SCM acceptance (acceptance levels as above) and to revise ASTM C618 SAI from 75% at 7 days and28 days to 80% at 7 days and 28 days or 80% at 90 days and replace prescriptive compositional requirements for SCMs such as equivalent total and available alkalis with performance criteria such as ASR expansion evaluation.

In January 2022, the Caltrans Pavement Program asked the University of California Pavement Research Center (UCPRC) to provide a quick high-level estimate of the effects of gross vehicle weight limit increases for trucks on pavement performance and the associated impact on the costs of pavement maintenance (Maintenance budget) and rehabilitation (SHOPP budget). Caltrans is considering increasing the limit from current 80 kips to 88 kips. This technical memorandum was delivered in February 2022. It was updated based on Caltrans comments in the same month and used internally by Caltrans but was not published. In September 2024 the Pavement Program requested that the UCPRC publish the technical memorandum. The results show that the high-level estimate is that the Maintenance and SHOPP budgets for pavement will need to increase by approximately 6% over the current projected 10-year total cost of $20.2 billion, resulting in a 10-year total increase of approximately $1.2 billion.

This study evaluates the performance of recycled and virgin fibers in fiber-reinforced concrete (FRC), with a focus on workability, concrete production, and mechanical properties. Fibers were directly sourced from manufacturers and used at dosages recommended by manufacturers and supported by the literature. All fibers improved the modulus of rupture of plain (control) concrete. The fibers investigated included plastic, steel, composite, glass, and basalt fibers. Across most fiber types—regardless of whether they were virgin or recycled—FRC demonstrated improved post-cracking load-carrying capacity, resulting in enhanced residual strength and ductility. Plastic fibers exhibited the best post-cracking performance, with high residual strength, toughness, and effective flexural strength ratios, though they reduced workability. Recycled plastic fibers performed comparably to virgin plastic fibers in terms of post-cracking behavior. Steel fibers had minimal impact on workability and provided good residual strength and toughness; recycled steel fibers performed similarly to the best-performing steel fiber and outperformed other steel fibers. The improved performance of random-shaped and twisted steel fibers was attributed to enhanced fiber–matrix bonding. Recycled glass fiber-reinforced polymer composite fibers from decommissioned wind turbine blades showed some improvement in post-cracking performance, particularly for larger fiber sizes; however, further testing is needed to optimize fiber size and dosage. In contrast, glass and basalt fibers exhibited limited post-cracking performance compared to plastic, steel, and composite fibers. Most fibers increased compressive strength, while improvements in the modulus of elasticity were negligible. Fibers generally reduced drying shrinkage, with a maximum reduction of 21% at 56 days. Overall, FRC performance was strongly influenced by fiber characteristics, including length, surface texture, chemical surface groups, and dosage. Recycled fibers demonstrated comparable performance to virgin fibers and showed potential for reducing greenhouse gas emissions, depending on recycling processes and treatments. These results indicate that recycled fibers are suitable for rigid pavement applications in California. Based on comparative performance, the following fibers are recommended for further evaluation: BarChip R50, BarChip 48, MAC Matrix, Strux 90/40, and Ferro-Green plastic fibers; Flexo and Helix steel fibers; and Recon XL composite fibers.

This technical memorandum describes the design and construction of a full-scale test track and the construction quality control/quality assurance testing of the different materials, including subgrade, aggregate base, and asphalt mixes. Construction of the test track and the Heavy Vehicle Simulator (HVS) and laboratory testing that followed are part of the Caltrans balanced mix design (BMD) implementation effort led by the Pavement and Materials Partnering Committee (PMPC) BMD Working Group. The main goal of the test track evaluation was to compare the rutting performance of surface mixes under the HVS with laboratory rutting test results. A secondary goal was to compare the reflective cracking performance of the same mixes with laboratory cracking test results. The test track includes four lanes, each 177 ft. long, and each with a variation of a control hot mix asphalt (HMA) surface mix, with two sections in each lane for evaluation of either rutting or reflective cracking performance. The rutting evaluation sections had an asphalt long-life pavement structure designed and built to test the rutting performance of the surface layer under the HVS. The reflective cracking evaluation sections were an asphalt overlay on a jointed plain concrete pavement. The test track asphalt surface can be evaluated and replaced in successive testing rounds. Following PMPC BMD Working Group directions, the first round of testing focused on HMA Type A with plain binder, used in the construction documented in this document. The control mix, used for paving Lane 1 of the test track, was an HMA with 3/4 in. maximum aggregate size, 25% reclaimed asphalt pavement content (percent by aggregate replacement), and virgin binder graded as PG 58-22. Three alternative mixes were used for paving Lane 2, Lane 3, and Lane 4. The alternative mixes were intentionally designed to make the mixes susceptible to rutting. The construction of the subgrade, aggregate base, concrete slabs, and asphalt mixes went as expected, with no incidents to report. Overall, the asphalt mixes used for the construction matched the design expectations, and the field compaction was as expected.

A pilot project for the inclusion of high percentages of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in hot mix asphalt (HMA) was built on State Route 26 in San Joaquin County in September 2022. Six mixes were included in short test sections: (1) a control mix with no RAS or RAP, (2) a mix with 25% RAP and recycling agent (RA) (3) a mix with 30% RAP and RA, (4) a mix with 35% RAP and RA, (5) a mix with 40% RAP and RA, and (6) a mix with 25% RAP, 3% RAS, and RA. A seventh mix, which was a typically used mix with 12% RAP and no RA, was used for construction of the rest of the overall project. This technical memorandum presents the laboratory test results from plant mix produced for job mix formula verification and from one or two quality assurance (QA) samples, depending on the test, taken during test section construction, as well as observations of plant production and construction. None of the mixes passed the Delta Tc specification, which is not uncommon for polymer-modified binder mixes. There is FHWA guidance and past UCPRC experience with other polymer-modified Caltrans mixes that indicate Delta Tc may not be a good parameter to use with modified binders. The mixes with 40% RAP and 25% RAP/3% RAS and one of the two QA samples for the mixes with 30% and 35% RAP and RA did not meet the performance grade (PG) specification low temperature limit. All mixes passed high and intermediate temperature PG specifications, and the other QA samples passed the low temperature PG specification. The 25% RAP with RA mix and one of the two QA sublots of the 30% RAP with RA mix missed the IDEAL cracking tolerance (IDEAL-CT) index number by a small amount, and one of the sublots for the 35% and 40% mixes missed by a wider margin. Results are presented for volumetric tests, flexural and axial dynamic modulus tests, repeated load triaxial tests, flexural fatigue tests, and Hamburg Wheel-Track tests. IDEAL-CT tests were done with both reheated and medium-term oven-aged samples, and results are reported for the IDEAL-CT index and indirect tensile strength for both aging conditions.

Three pilot projects were constructed using hot mix asphalt (HMA) with higher percentages of recycled asphalt pavement (RAP) (25% to 40%) and recycled asphalt shingles (RAS) used at 0% or 3%. The three projects were paved between 2021 and 2022 on State Route 49 in El Dorado County (ED 49), State Route 215 in San Bernardino County (SBD 215), and State Route 26 in San Joaquin County (SJ 26). Two and a half to three years later, pavement condition surveys were conducted to observe surface distresses. On ED 49, the 3% RAS mix exhibited 6% low-severity wheelpath alligator cracking, often with mild pumping. The other mixes on ED 49 exhibited lower levels of alligator and total cracking. No alligator cracking was observed on SBD 215, which includes a cement-treated base not present in the other pilot projects. On SJ 26, all test sections exhibited some form of cracking, though mostly of low severity. Among the mixes, the 25% RAP/3% RAS mix showed the most alligator cracking on SJ 26 (around 7% of the wheelpath), while the 0% RAP/0% RAS control mix showed the most transverse cracking and the highest total cracking.

The first asphalt concrete long-life (AC Long Life) project was constructed in Los Angeles County on Route 710 (LA-710) near Long Beach in 2001/2004 and is now over 20 years old. Four more AC Long Life projects have been completed in California since then, three between 2011 and 2014 (TEH-5, SIS-5, SOL-5), and one in 2021/2022 (SAC-5). The goal of these AC Long Life projects was to achieve design lives of 30 years or 40 years (the standard Caltrans asphalt pavement design life was 20 years at the time). Measures taken to achieve those lives included the use of performance-related specifications for job mix formula approvals, higher compaction requirements, and the use of a three-layer asphalt concrete system for structural capacity. These measures required additional costs. Calculations indicate that the longer lives will result in life cycle cost reductions if they achieve the design lives. Hence, periodic performance evaluations are important, which is the purpose of this technical memorandum. Extensive material sampling and structural evaluation were conducted regularly on the LA-710 and TEH-5projects. This technical  memorandum reviews the available performance data, summarizes the material testing and structural evaluation data for the LA-710 and TEH-5 projects, and compares the as-built materials with statewide medians. The cracking, patching, roughness (IRI), and rutting data revealed that these projects had all performed very well in general at respective 10- to 20-year milestones. No rehabilitation and only one minor maintenance activity has been performed on LA-710, and no maintenance/rehabilitation activity has been performed on the 10-year-old projects. Analysis of the LA-710 and TEH-5 deflection data suggests some densification (not to the extent of crushing) and aging in the asphalt-bound layers but no signs of traffic-induced damage. Laboratory test data on between-wheelpath specimens from the TEH-5 project indicate that the as-built materials in general have better fatigue performance, lower stiffness, and lower permanent deformation performance than the statewide median materials tested during mix design. Given the fact that only minor rutting has been observed in these projects, the as-built materials are believed to be good examples of mixes with balanced performance, with a few exceptions.

A pilot project for the inclusion of high percentages of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) was built on State Route 215 in San Bernardino County in September 2022. Five mixes were included in short test sections: (1) a control mix with no recycled asphalt shingles (RAS) or RAP, (2) a mix with 25% RAP and recycling agent (RA), (3) a mix with 30% RAP and RA, (4) a mix with 35% RAP and RA, and (5) a mix with 40% RAP and RA. A sixth mix, which was a typically used mix with 23% RAP, was used for construction of the rest of the overall project. This technical memorandum presents the laboratory test results from plant mix produced for job mix formula verification and from one or two quality assurance (QA) samples, depending on the test, taken during test section construction as well as observations of plant production and construction. Only the control mix binder consisting of the virgin PG 64-28M base binder and the mix with PG 58-34M, 25% RAP, and RA passed the delta Tc specification. There is FHWA guidance and past UCPRC experience with other polymer-modified Caltrans mixes that indicate delta Tc may not be a good parameter to use with modified binders. The mixes with 30%, 35%, and 40% RAP and RA and the mainline mix did not meet the PG specification low temperature limit. All the mixes easily passed the IDEAL-CT (cracking tolerance) index number. Construction QA sampled binder test results indicated that the PG 58-34M binder was used for the control mix with no RAP instead of the specified PG 64-28M binder. Results are presented for volumetric tests, flexural and axial dynamic modulus tests, repeated load triaxial tests, flexural fatigue tests, Hamburg Wheel-Track tests, and IDEAL-CT tests with reheated and medium-term oven aged samples reported in terms of the IDEAL-CT index and indirect tensile strength.

Research has demonstrated the multiple benefits of fibers for the early and late-age performance of concrete pavements and bridge decks. Many research studies have also shown that the expected enhancements in properties of concrete with recycled fibers could be commensurate with those of concrete reinforced with virgin fibers. However, compared with virgin polymeric fibers and steel fibers from primary steel, recycled fibers and fibers from natural sources are not as commonly implemented in construction due to several barriers. Some of these obstacles include a lack of research on recycled fibers, leading to gaps in technical performance data, case studies, test tracks, and pilot projects. The primary reason for the lack of research is related to gaps in information regarding the quality of recycled fibers compared to virgin fibers. To help overcome some of these barriers, this study included a comprehensive survey of concrete fiber suppliers. Those suppliers with recycled fiber and natural fiber manufacturing lines were identified and interviewed. The categories of fibers included in this report are recycled polymeric fibers, natural fibers mainly from cellulose, recycled steel fibers, carbon and glass fiber-reinforced polymer composites (for example, from end-of-life windmill blades), recycled carbon fibers, and glass and basalt fibers. The information gathered from the manufacturers is summarized in this report and includes the feedstock material, recycling process, geometric properties of fibers, recommended load for concrete flatwork applications, performance data (if available), cost, and environmental product declaration, if available. In addition to manufacturers’ surveys, a synthesis of performance in concrete is provided based on published technical literature for each fiber type. The topics included in the literature review are fiber dispersion and the impacts of fibers on the workability of concrete, plastic and drying shrinkage, strength and post-cracking performance, and durability of concrete. Based on this comprehensive review, many fibers from recycled and natural sources were identified for each source material. These fibers are already available on a large scale in the market, and several have been successfully implemented in concrete applications. In the case of steel and carbon fibers, recycled fibers are available at a fraction of the cost of virgin fibers, making this product more feasible in construction. Cellulosic fibers appear to have great potential to reduce plastic shrinkage cracking in concrete. Glass and basalt fibers are from natural silica sources and offer many structural advantages to the performance of concrete. These fibers are recommended for laboratory testing in the next phase of the project.