University of California Pavement Research Center

This technical memorandum evaluates the half-life performance of three long-life jointed plain concrete pavements (JPCPs), a combined total of 260 lane-miles, that were built in Southern California in the early 2000s. The pavements were designed for a 40-year life, which was twice the standard 20-year design life used for JPCP at that time. The projects are located in or close to the Mojave Desert on heavily trafficked interstate highways with 2022 annual average daily truck traffic levels between 2,800 to 5,100. The performance of the pavements has been evaluated based on data from the Caltrans pavement management system (PMS) databases (with software system PaveM), including pavement condition surveys with data about lane-based cracking, transverse joint faulting, and smoothness data, and the as-built database that includes all maintenance, rehabilitation, and reconstruction activities conducted on the Caltrans road network. The PMS databases were complemented with an in-situ evaluation of the projects in 2022 that included an inertial profiler evaluation and a road closure of one mile per project for visual inspection, coring, and falling wight deflectometer testing. Overall, the performance of the projects has been excellent so far. The third-stage cracking (slabs with two or more cracks) is essentially zero in all lanes, the faulting is also essentially zero, and the smoothness as measured by the International Roughness Index has been stable since the construction of the projects. The load transfer efficiency of the doweled transverse joints was high, from 80% to 85%, and it was also very uniform along the sections, with minimal diurnal variation (morning versus afternoon). Mechanistic-empirical modeling with AASHTOWare Pavement ME Design (version 2.5.5) supports the excellent performance of the projects and the lack of transverse cracking, in particular. Further, none the JPCP long-life projects has required any maintenance or rehabilitation activity (e.g., individual slab replacement or grinding) since their construction. The only concern with the performance of the projects is the presence of longitudinal cracking, affecting to 4% to 7% of the slabs, in some truck lanes. The longitudinal cracking may be related to the dry environment and, potentially, the use of widened slabs in one of the projects.

Fatigue cracking due to repeated truck traffic loads is the leading cause of failure of asphalt concrete pavement in many locations. Rest periods, referring to the time intervals between successive trucks, may allow for partial or full recovery from fatigue damage and in turn extend pavement fatigue life. This study examines the characteristics of rest periods using traffic data from 40 weigh-in-motion (WIM) stations installed on California state highways and evaluates their effects on pavement performance using a mechanistic-empirical simulation program, CalME. Truck traffic data were extracted from these WIM stations at selected periods throughout 2015. Rest periods, the probability distribution of rest periods, and quantiles of cumulative rest periods were calculated. Regression and statistical analyses of the 0.5 quantiles (i.e., median) of rest periods were also performed for different spectrum groups and seasons. It was found that rest periods are strongly correlated with the truck traffic volume regardless of the WIM station location or season. The actual rest periods based on the nonuniform truck traffic measured from the WIM data were found to be slightly shorter than the corresponding theoretical average rest periods for uniform traffic (ARP-UT), currently assumed in CalME, likely due to truck-following. This theoretical value assumes an equal time interval between trucks at all times. After comparing pavement performance with and without rest periods using CalME, it was found that rest periods have significant influence (a 30% difference) on pavement cracking. CalME simulations also show that the difference in pavement performance caused by the difference between the actual rest periods and the ARP-UT is minimal. Continued use of the ARP-UT is therefore recommended to account for the effect of rest periods in pavement design.

This technical memorandum summarizes a study that investigated the use of a confined compressive strength (CCS) test to replace the R-value test currently used for some pavement design and for quality control/quality assurance in California. The report covers a literature review, development of an alternative test, and a comparison of the results from the proposed test with R-value results.

The following are conclusions made based on the findings. First, California Test 216 needs revision. The compaction density reported by the test method is lower than the physical density of the compacted specimen in the CT 216 apparatus. The reported CT 216 density is approximately 88% of Modified Proctor density. Second, the proposed specimen compaction procedure, using Modified Proctor as the reference density, produced unbound specimens that could be handled and tested in a triaxial cell. Third, there is no correlation between the R-value test and the CCS test for the materials tested to date because the limited range of R-values produced by the 22 base and one subbase materials is too small to define a relationship with the CCS test. Most of the R-values of the materials tested were just above the minimum specified value of 78 for Class 2 aggregate base. Fourth, the suggested preliminary CCS criteria for replacement of the R-value specification for Class 2 aggregate base are minimum 101 psi peak stress at 5 psi confinement and minimum 144 psi peak stress at 10 psi confinement.

The following interim recommendations are made based on the testing, the documented low test precision of the R-value test, and the limitations of developing a correlation between R-value and the CCS test. First, additional testing of four or five subbase materials with R-values between 40 and 60 should be completed to refine the CCS test criteria. If these materials are not available from producers, they can be manufactured in the UCPRC laboratory by blending available materials. Second, material properties, including gradation, flakiness, crushed faces, sand equivalence, Atterberg limits, and moisture sensitivity (i.e., shape of the optimum moisture content curve) should be considered when analyzing any correlations.

Current Caltrans Standard Specifications for rubberized hot mix asphalt–gap-graded (RHMA-G) do not allow the inclusion of reclaimed asphalt pavement (RAP). This report summarizes the research conducted by the UCPRC in support of the Caltrans-industry initiative “10% RAP in RHMA-G,” whose goal is to evaluate the use of up to 10% RAP (by aggregate replacement) in RHMA-G mixes, provided that the research does not identify significant potential problems for durability. Five pilot projects were built by Caltrans as part the initiative. In each of the pilots, a control RHMA-G (without RAP) and an RHMA-G with 10% RAP were placed. The mixes were sampled during production and tested using performance-related tests at the UCPRC laboratory. The results of the testing of the mixes—including stiffness, four-point bending fatigue resistance, and rutting resistance—indicate that the addition of 10% RAP had minor effects on the mechanical properties of the RHMA-G. With just a few exceptions related to changes in the total binder content of the mix, the effect of the RAP addition was negligible compared with project-to-project differences. Modeling with CalME software based on four-point bending testing results indicated that the impact of the RAP addition on the cracking performance of the pavement was either negligible or comparable to project-to-project differences. From the constructability point of view, the addition of the RAP did not create any problems. The life cycle assessment presented in this report indicates that the addition of 10% RAP to the RHMA-G can reduce the greenhouse gasses emissions associated with the RHMA-G production (cradle-to-gate) by up to 5%.

This report is a comprehensive review of natural and human-made materials with the potential to reduce cement content in concrete by partially replacing portland cement or as additives. The review aims to reveal possible source materials as alternative supplementary cementitious materials (ASCMs) to coal-burned fly ash and ground granulated blast furnace slag as these SCMs supplies rapidly decline. Information required to estimate supplies of each ASCM was gathered, and ASCM candidates with enough abundance to support California’s concrete paving sector were identified for further laboratory evaluation. In addition, the required chemical, thermal, and mechanical treatments of the source materials were gathered so the environmental and economic impacts of the processes could be considered. A review of scientific literature on the technical performance of the studied materials in cement paste, mortar, or concrete was also conducted when that information was available.

The reviewed feedstock material categories include biomass sources, construction and demolition wastes, natural pozzolans (volcanic and sedimentary materials), and post-consumer waste. As part of the biomass category, biopolymer-based nanomaterials were also included in the review for their promise to reduce cement content from added strength. The following information was included for each material considered in this report: feedstock description, the potential mechanism of performance in concrete, physical and chemical properties, feedstock supplies and processing method, technology readiness level (TRL), a summary of technical performance in cementitious systems based on the scientific literature, environmental impacts of the production phase, and cost considerations.

Based on the comprehensive information gathered, several materials present potential as ASCMs, fillers, and admixtures for the California paving industry. However, most materials identified are at TRL 3 or 4, requiring more research and development to move toward implementation. In addition, some of these ASCMs may not fully satisfy the current regulations for SCMs. For example, biomass ash from some sources may contain a high alkaline content and a greater than 6% unburnt carbon content. Furthermore, some natural pozzolans impose a high water demand and have slow strength gain. In addition, the reported performance in the literature for the biobased nanomaterials studied is conflicting and performance data in concrete is scarce. Finally, some reviewed materials were not selected for more advanced laboratory evaluation because a supplier was not found in California. These materials include municipal solid waste ash, wastewater treatment sludge, and seashell waste. In addition, ground glass, harvested coal-burnt fly ash, and fines from carpet recycling were not chosen for laboratory evaluation because they are being investigated in other Caltrans and non-Caltrans research contracts.

This report presents the initial performance of the Woodland SR 113 thin concrete overlay on asphalt (COA) project built in 2018-2019.The project comprises approximately four miles of a two-lane highway. The COA had 6 ft. transverse joint spacing, a slab thickness of 6in., and an asphalt base that was overall in very poor condition. The performance of the project between the date of construction andOctober 2020 is presented in this report. The performance was evaluated by different means, including periodic visual inspections andlongitudinal profiler evaluations; falling weight deflectometer (FWD) testing; real load testing (RLT), where the concrete strains undertruck loading were recorded; and continuous monitoring of slab temperatures and drying shrinkage deformations. Overall, the projectperformed as expected. Visual inspection of the COA did not indicate any cracking, faulting, or other structural distress. FWD and RLTevaluations indicate that the COA structure has remained stable since the construction. While the smoothness varied considerably during the period evaluated in this report, the variation was caused by changes in slab curvature due to thermal gradients through the slab depthand concrete drying shrinkage.

Full depth recycling (FDR) has emerged as a feasible rehabilitation alternative in California. This study focuses on addressing the economic feasibility of example FDR structures using life cycle cost analysis (LCCA) that included probabilistic and deterministic life cycle agency costs and deterministic life cycle road user costs. Two LCCA case studies were performed to provide an initial understanding of the agency cost variation. Estimating roadway construction costs plays a key role in pavement LCCA and long-term planning. Materials costs per functional unit are the major input values affecting pavement cost and total construction cost, and they are dependent on project scale, market, region, risk, climate, and economic circumstances. Publicly available contract cost data from past roadway construction activities on the California state highway network were used in this study. Economies of scale suggest that high quantities of materials would have lower unit costs. Unsupervised machine learning techniques were employed to divide the available data into four volume categories (low, medium, high, very high) based on material quantities in a project to accomplish the probabilistic LCCA. Work zone delay road user costs were estimated in RealCost-CA and incorporated into the life cycle cost of each alternative. Case studies were conducted for rehabilitation of two California highways, State Route 113 (SOL 113) and State Route 84 (YOL 84), for a 60-year design life. Two different pavement rehabilitation alternatives were considered for the project, an FDR structure and a hot mix asphalt HMA reconstruction, along with their respective maintenance and rehabilitation sequences. Two different pavement structural design methods were also included in the study to enable comparison: R-value and CalME.

A pilot project for the inclusion of recycled asphalt shingles (RAS) in hot mix asphalt (HMA) was built on State Route 49 in El Dorado County in November 2021. Four mixes were included in short test sections: (1) a control mix with no RAS or recycled asphalt pavement (RAP), (2) a typically used mix with 10% RAP that was also used for construction of the rest of the overall project, (3) a mix with 3% RAS, and (4) a mix with 10% RAP and 3% RAS. This technical memorandum presents the laboratory test results from plant mix produced for job mix formula (JMF) verification and from two quality assurance (QA) samples taken during test section construction as well as observations of plant production and construction. The results showed that the mixes submitted for JMF verification and tested as part of QA all met the two performance-related specifications. Most of the QA samples had binder and mix testing results that were similar to or better than those of the JMF verification samples, though there were exceptions. There were no major problems during production or placement of the mixes. The existing roadway has highly variable thicknesses of remaining HMA after milling, and the remaining original HMA has transverse, wheelpath, and block cracks.

This technical memorandum summarizes the construction and instrumentation of a test track to study the behavior of cold central plant recycled (CCPR) layers in a pavement structure. Two recycling agents will be tested including emulsified asphalt from two different producers and foamed asphalt from one binder supplier. The pavement structure includes an aggregate subbase, an aggregate base, the recycled layer, and a gap-graded rubberized hot mix asphalt (RHMA-G) surfacing. The structure was constructed on prepared subgrade. Material properties and construction procedures met all relevant Caltrans specifications. Instrumentation includes multi-depth deflectometers, strain gauges, pressure cells, and moisture sensors. The test track was considered to be representative of a highway project and was approved for Heavy Vehicle Simulator testing.

In late 2015, Caltrans requested that 26 recently constructed concrete projects be tested for smoothness in terms of the International Roughness Index (IRI). The stated purpose was to observe measured IRI on projects accepted after a standard special provision (SSP) change that Caltrans made in 2013 and that was incorporated into the 2015 Construction Contract Standards. The projects provided 52 test sections for evaluation, consisting of three types of paving work: (1) diamond grind on existing pavement, (2) new continuously reinforced concrete pavement, and (3) new jointed plain concrete pavement. The project plans had completion dates from May 2010 to December 2014, and contract acceptance dates from April 2014 to October 2015. Caltrans did not identify which projects had the new SSP or specification change in its contract documents. The IRI data were collected from October 2016 to December of 2016. The IRI data collected included the effects of paving, any corrective grinding required to meet contract acceptance, and the increased roughness caused by traffic over post-construction periods of one to more than two and a half years. At the time of testing in 2016, the UCPRC test vehicle was equipped with a point laser in the left wheel path and a wide spot laser in the right wheel path. The data presented in this technical memorandum are primarily from the wide spot laser because the current standards require the wide spot laser. In general, the IRI measured by a point laser can be unduly increased due to the surface texture of the pavement, which is part of the reason for moving toward a wide spot laser. The construction specification considers both wheel paths and not just the right wheel path tested in this project. The IRI data using the wide spot laser in the right wheel path alone showed that 22% of the 0.1 mi. long sections met the construction standard of 60 in./mi. when measured one to two and a half years after construction. Based on the results from the right wheel path and the wide spot laser, 67% of the right wheel path sections are in good condition with IRI values between 60 and 94 in./mi., 28% are in acceptable condition with IRI values between 95 and 170 in./mi., and 5% are in poor condition with IRI values of 170 in./mi. or greater. Although Caltrans did not identify which projects included the new specification, a trend was observed that projects completed later had lower IRI values than those completed several years earlier.