Institute for Transportation

About the research

The main purpose of this research is to develop a comprehensive asphalt recycling strategy for high RAM mix up to 50% in consultation with surrounding state departments of transportation (DOTs), along with cities and counties, by performing the following tasks:

• Evaluate existing and new high RAP projects and test sections
• Select a cracking test procedure as a performance test
• Conduct performance tests of high RAP mixtures up to 50%
• Develop an approval process for rejuvenators
• Evaluate warm mix asphalt (WMA) with a high RAM content
• Develop a comprehensive asphalt pavement recycling strategy

About the research

The main purpose of the proposed research is to develop a mix design procedure for high RAM mixtures with both rejuvenators and fractionated RAM materials for the Iowa Department of Transportation (DOT) and local public agencies by thoroughly understanding complex interactions between fractionated RAM and rejuvenators. The main objectives of this research are to: (1) examine the effects of various rejuvenators and different methods of RAP stockpile fractionation on the volumetric mix design properties, (2) evaluate long-term oven aging of both laboratory and field rejuvenated/fractionated high RAM mixtures and (3) develop specifications for evaluating asphalt mixtures with rejuvenators and high fractionated RAM contents.

About the research

An electrically conductive concrete (ECON) heated pavement system (HPS) utilizes the inherent electrical resistance of concrete to maintain the pavement surface at above-freezing temperatures and thus prevent snow and ice accumulation on the surface. Such a sustainable concrete pavement system can improve its infrastructure resiliency by allowing it to be safe, open, and accessible during even harsh winter storms. The primary objective of this project is to to enhance the practicality of the ECON mix design and ECON HPS field implementation by conducting necessary tests to establish a defined range of electrical conductivity compliant with national electrical safety specifications for executing the construction of the Iowa City Bus Stop Enhancement Project. This will be achieved through execution of the following primary tasks: (1) project management; (2) formulating robust production, transportation, and quality control/assurance (QC/QA) protocols; (3) determining electrical safety protocols; (4) developing implementation plans with recommendations; and (5) producing a final project report. The outcomes of this project will include both best-practice guidance on the steadfast and uniform quality of ECON mixture production as well as a defined range of electrical conductivity for the ECON HPS, ensuring both performance and safety. Such outcomes could result in successful implementation of the ECON HPS for the Iowa City Bus Stop Enhancement Project.

About the research

The Iowa secondary road system has a large number of scour-susceptible bridges or bridges with unknown foundation conditions. These structures are commonly required to have a plan of action (POA) to close them during flood events, or have countermeasures installed to keep them open. In the case of unknown foundations, countermeasures must be installed.

Among the many different countermeasures available is a potentially viable technique known as a partially grouted revetment. Partially grouted revetment construction involves the placement of rock, stone, and/or recycled concrete on a filter layer that is compatible with the subsoil. The voids of the matrix are then partially filled with a portland cement-based grout material.

Partially grouted revetment appear to achieve a desirable balance between full and no grouting of revetment. Specifically, partial grouting increases the stability of the system without eliminating the flexibility of a looser matrix. In addition, a partially grouted revetment system allows for the use of smaller (and less expensive) rock, stone, and/or recycled concrete, which also results in decreased layer thickness. The ideal system adheres adjoining pieces together while leaving relatively large voids between the stones.

The final project report presents background information on countermeasure types and their frequency of use, including a field review of existing countermeasures to determine quality of performance. These efforts were followed by several pilot installation sites on county infrastructure in Iowa using partially grouted riprap. These pilot installations are described and their performance documented after years of service.

About the research

State and federal legislators regularly request increases to the axle or gross weight limits for commercial vehicles. The question that is always asked is, “What is the impact on the life expectancy of a bridge when heavier loads are allowed on some vehicles?” There is no past or present method to determine how heavier loads affect the life of Iowa highway bridges. Bridge owners need a method of quantifying the effects of heavier loads or any load on a bridge’s life expectancy. The objective of this research is to qualify the relationship between increased legal loads and reduced bridge service life for Iowa bridges. To achieve the proposed objective, a 36-month research plan was developed, which includes conducting a comprehensive literature review, collecting Iowa-specific data, estimating bridge costs and life reduction due to truck weight limitation increases, and performing the laboratory test for the validation of bridge life reduction prediction. The result of this project will help the bridge owner make reasonable assumptions on the life of a bridge when subjected to increased truck loads.

About the research

Roller-compacted concrete (RCC) is a no-slump concrete having same basic ingredients as ordinary Portland cement concrete (PCC). While RCC has been used in commercial areas and for local streets and highways, its use for paving shoulders has not been studied in Iowa. The primary objective of this project is to develop mix design, construction, and maintenance/preservation specifications for using RCC in Iowa pavement applications. This will be achieved through execution of the following primary tasks: (1) literature review; (2) comprehensive laboratory assessment; (3) field demonstration construction and evaluation; (4) life-cycle cost analysis (LCCA) for quantifying cost effectiveness of various shoulder options; (5) facilitation of three workshops on RCC maintenance and preservation, life expectancy, recycling, and potential Iowa transportation infrastructure application types; and (6) Iowa RCC specification development. The successful outcomes of this research will be of great benefit when providing justification on the proper use of RCC as an alternative durable and strengthened material for the paving of shoulders and other applicable areas in Iowa transportation systems.

About the research

Iowa has over 110,000 miles of roads, and they frequently support local residential vehicles as well as heavy trucks. Traditional bituminous surface treatments (BST) could be employed to maintain these roads properly, but these treatments typically require high-quality materials and standard construction equipment. Otta seal is a relatively new BST that allows for the use of more economical local aggregates and commonly available equipment. To evaluate the feasibility of Otta seal implementation, a Phase I study was launched to design and construct Iowa’s first Otta seal-surfaced road in Cherokee County in 2017. The successful construction of the first Otta seal road in Iowa provided valuable experience and knowledge for local public agencies, and a follow-up Phase II study was initiated in 2018. The Phase II study described in this report aimed to establish the recommended specifications through comprehensive laboratory evaluation and characterization and additional field implementation projects. In the Phase II study, more than 50 Otta seal sites constructed since 2017 were evaluated. These sites had various local aggregate and binder types, as well as various application rates. Five consecutive years of field measurements were executed in this Phase II study, including lightweight deflectometer-derived elastic modulus, International Roughness Index, dust generation, and skid resistance. The field evaluation in 2023 indicated that all Phase II Otta seal sites still exhibit satisfactory performance. A detailed laboratory investigation was conducted to establish a rational methodology for designing Otta seal road surfaces utilizing locally available materials. Four distinct aggregate types were considered in this study: limestone, recycled concrete aggregate (RCA), slag, and river aggregates. The McLeod method was modified to determine optimal rates for aggregate and binder application. The laboratory study primarily assessed Otta seal performance through a sweep test exploring the impact of material type, aggregate gradation, binder type, and application rate on aggregate loss. Key findings include the significance of aggregate gradation in reduced aggregate loss, the comparable performance of HFMS-2s and MC 3000 binders, the suitability of recycled materials (especially slag), and the effectiveness of the modified McLeod method. A life-cycle cost analysis revealed that the lowest cost was associated with Otta seal designed using the modified McLeod method. These findings contribute to a more efficient Otta seal design, enhancing road surface longevity while utilizing locally sourced materials.

About the research

Pavement roughness serves as a critical indicator of the overall ride quality of road surfaces. Elevated levels of pavement roughness can give rise to concerns regarding driving safety, fuel consumption, and exhaust gas emissions. The International Roughness Index (IRI) stands as the globally accepted standard for quantifying road surface roughness. Although one of the primary responsibilities of local public agencies (LPAs) involves monitoring and maintaining appropriate IRI levels for the local road system, existing techniques used to collect IRI data, such as using high-speed and walking profilometers, typically entail high annual costs for network-level inspection. Consequently, LPAs are in need of a cost-effective IRI data collection system that enables them to gather pavement performance data annually. Smartphones come equipped with an array of sensors, including multi-axis accelerometers and global positioning systems (GPS), that present an efficient and economical approach for collecting vehicle suspension data, specifically vertical acceleration. These data can then be harnessed to estimate pavement profiles and roughness. This study endeavored to develop a low-cost, smartphone-based, nonproprietary data collection system designed for use by LPAs to gather pavement roughness data on an annual basis. This adaptable system can be implemented on Android phones, iPhones, or custom-developed smart boxes that incorporate accelerometers and GPS units. All data gathered in this way can be seamlessly transferred to a cloud-based server and subsequently processed using a Python-based algorithm to compute the IRI. The accuracy of such a system was assessed using four distinct smartphones, one custom-developed smart box, and a Class 1 high-speed profilometer that was used to establish reference IRI values. The field data collection program encompassed 24 Story County sites selected to validate the accuracy of IRI measurements. The results demonstrate that the smartphone-based and smart box systems developed offer a dependable, low-cost, and user-friendly solution for LPAs to use in assessing local road roughness. A prototype smartphone application for detecting road surface distress through captured videos and images was also developed and evaluated.

About the research

Joint sawing is a critical part of concrete pavement construction, as the jointing system plays an important role in concrete pavement performance and service life. To ensure successful construction, it is important to understand the basic principles of the joint sawing process. These principles include proper timing, depth, and spacing of saw cuts, as well as the many factors related to materials, climate, and equipment that affect the sawing window. Understanding the fundamentals of joint sawing is even more important today thanks to the changing construction workforce and ongoing changes to mixtures and materials used in concrete pavements. The objectives of this research are to perform a comprehensive literature review on joint sawing of concrete pavements; to conduct a survey of agencies, contractors, and equipment providers to establish today’s typical practices and the most common problems related to joint sawing in Iowa; and to perform a field investigation that diagnoses these problems and tests out potential solutions on Iowa pavement construction projects. The results of each of these components will be combined and summarized in a guide culminating the best practices for joint sawing concrete pavements.

About the research

Integral and semi-integral abutment bridges have become increasingly popular in Iowa and across the country because they eliminate joints at the bridge ends. Expansion joints in bridge decks allow water to seep in and corrode bearings along with other structural elements in conventional bridge construction. An integral abutment connects the bridge deck and girders with the substructure in one piece to reduce maintenance and increase service life. The abutment moves with the rest of the bridge, and this movement introduces new issues with water drainage, soil settlement, soil erosion, and concrete cracking. The objective of this research was to evaluate improved bridge end details to increase service life and investigate limitations placed on the use of semi-integral abutment bridges. Research methods include a literature review, visual inspections, field monitoring, and finite element simulations.

The extensive literature review identified research relevant to improving the performance of bridge ends. Abutments, approach slabs, geotechnical aspects, drainage, and expansion joints were evaluated in detail. It was found that innovative bridge abutments allow for the elimination of conventional bearings and attempt to reduce issues associated with integral construction. Semi-integral abutment bridges and those with approach slabs attached to the abutment were inspected across the state of Iowa to assess the performance of current design methods. The condition and performance of tied joints was found to be unsatisfactory in some instances, with measured openings much larger than those built during initial construction. Joints between wingwalls and approach slabs were also found to be in poor condition. Four bridges were outfitted with a multitude of sensors, including strain gauges and displacement transducers, to measure concrete expansion and bridge displacement. Finite element models were also created to investigate the movement of approach slabs on the soil below. Simulated bridge expansion provided insights into approach slab behavior and tie bar stresses due to friction. Parametric studies were completed on various approach slab properties, including friction with soil, soil stiffness, tie bar style, and bridge skew.