Institute for Transportation

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.

About the research

This project investigated helical pile foundation implementation for bridges, resulting in a design and construction guide. The simplicity and speed of helical pile installation, along with the ability to work within areas of limited size with smaller, more maneuverable equipment, can accelerate the construction of bridge structure foundations.

The guide provides bridge engineers and designers with direction and specifications for this substructure foundation option, which can be advantageous on any bridge project, but particularly for low-volume roads where budgetary considerations tend to be a specific priority.

The guide includes many useful design specification reference tables and also useful construction and installation documentation tools as examples and as table forms that can be used for helical pile bridge foundations.

About the research

Unpaved roads make up almost 80% of roadway miles within the State of Iowa. These unpaved roads have lower traffic volumes but still account for many of the fatal and serious injury crashes throughout the state. Since these crashes tend to be more widespread and not concentrated to a single area, low-cost systemic countermeasures would be the ideal way to improve safety on these roads. Most research and guidance materials available related to low-cost systemic countermeasures focus on applications along paved roads. This project would help to address this gap by focusing on low-cost safety improvements for unpaved roads. Additionally, local road owners desire a toolbox of strategies for improving safety on unpaved roads.

The objectives for this research project include the following:

• Develop a toolbox of strategies for improving safety on unpaved rural roads based on
  available research and guidance
• Identify demonstration projects for innovative (possibly untested) safety improvement
  concepts for unpaved roads
• Identify information gaps and develop research problem statements to address those gaps
• Identify field research needed to develop crash modification factors (CMFs) or surrogate
  safety metrics to determine the effectiveness of various rural road safety strategies on
  unpaved rural roads

About the research

In the past, the Iowa Department of Transportation (DOT) has had a number of pavements placed from 1986 to 1994 that exhibit vibrator trails. Many of these pavement sections exhibited cracking in the vibrator trails and investigation shown high air loss in those areas. Research was conducted on vibration in concrete pavement placements. The research found that at 12,000 vibrations per minute (vpm), aggregate distribution and air content was greatly affected. This research led to specification changes on vibration, reducing the vibration from a minimum of 7000 vpm to 5000 to 8000 vpm. Another research project led to the implementation of vibration monitoring on projects greater than 50,000 square yards. Newer paving machines have a tablet based system for inspectors to monitor vibration during the project. Older paving equipment typically have the old system of vibration monitoring, which requires occasional checks of the vibrators on the paving equipment.

This research was conducted on concrete mix designs with only coarse and fine aggregates and likely were gap graded. Since 1999, the Iowa DOT has been utilizing well graded aggregate combinations on quality management concrete (QMC) mix designs. It is not known what effect vibration has on well-graded aggregate mix designs. Perhaps, these mix designs may allow a higher tolerance on vibration or perhaps less is required. The Iowa DOT has been experimenting with reduction in cement content in QMC mixes, validated with the performance engineered mix (PEM) testing procedures.

Even with research conducted in the past, we do not have a full understanding of the vibration energy impact on durability and consolidation. Frequently, it has been noted that there are still a fair amount of voids found in concrete pavement cores. Iowa State University has conducted a small study on the effect of vibration on concrete mixtures. The study noted localized changes in w/c ratio and air movement within the concrete. It is not known if this could lead to localized durability issues. This project will investigate the impact of vibration on concrete pavement mix designs. In particular the QMC mixes and those reduced cement content mixes validated with PEM test procedures. Lab research will be validated on a concrete paving project.

About the research

This research aims to develop, test, and implement a cost-effective ultra-high performance concrete (UHPC) mixture design tailored to equip new bridge decks with a protective layer against environmental and mechanical stressors. For this purpose, utilizing the ingredients available from local resources and regional suppliers in Iowa, the non proprietary UHPC mixture design developed for Iowa bridges will be further optimized, especially to achieve the expected balance between flow and viscosity. With completing a set of laboratory investigations, the outcome will provide a UHPC mixture design enabled with thixotropic properties required for bridge deck and overlay applications. In the next step, laboratory trials will be performed to determine the most optimal surface preparation and curing regime. This will directly assist contractors with the field implementation of non proprietary UHPC for target applications. In the proposed project, the developed thixotropic non-proprietary UHPC will be used (as overtop) to construct the deck of a new bridge structure identified by the Iowa Department of Transportation’s Bridges and Structures Bureau. This candidate bridge deck will provide a unique testbed to apply and further evaluate the performance of the developed UHPC mixture in a real field setting. The scope of field work will involve both short- and long-term studies. The short-term investigations will cover the practical aspects and considerations that must be figured out to successfully add a layer of non-proprietary UHPC to the normal concrete substrate. On the other hand, the long-term investigations will closely monitor the integrity and overall condition of this new bridge deck system over time. For this purpose, a dense array of instrumentation will be utilized, while regular inspections will be performed in parallel. The outcome is expected to benefit from the superior strength and durability of UHPC to address the long-standing issues associated with the deterioration of bridge decks.

About the research

The project aligns with the Iowa Department of Transportation’s (DOT’s) focus areas of sustainability and technology. Maintenance and rehabilitation of granular-surfaced roads consumes significant portions of counties’ annual budgets, as well as large amounts of natural resources in the form of virgin aggregates. By assessing the performance of different test sections constructed with and without the Perma-Zyme stabilization product through two winter-spring cycles, the Iowa DOT and county engineers will better understand the life-cycle costs and relative advantages of using the enzymatic stabilizer as well as the different construction methods (i.e., compaction by sheepsfoot vs. smooth-drum roller during construction).

Most importantly, the project would establish a new Granular Surfaced Roads Test Facility comprising several miles of granular-surfaced roads at Camp Dodge, through a cooperative relationship with the Iowa Army National Guard. The facility would enable long-term research on unpaved roads with great efficiency by reducing travel time compared to locating test sections in several counties around the state and by enabling many different projects on an ongoing basis in one central location. Overall, the long-term benefits of the project will be to improve the quality, longevity, and state of good repair of Iowa roadways, which constitute a vital component of Iowa’s infrastructure.

About the research

In recent years, various proprietary bio–based fog sealers or rejuvenators have been introduced and marketed as potentially cost–effective and environmentally friendly alternatives to traditional petroleum–based sealers for preserving asphalt roads. The RePLAY Agricultural Oil Seal and Preservation Agent, as one such bio–based fog sealer, and its performance, has been evaluated on a 3.3–mile pilot testing section located in Clinton County, Iowa, for five consecutive years (i.e., summer 2016 through summer 2021). This study has important insights about RePLAY and its first–level field implementation in Iowa. However, further research is needed to identify the frequencies and benefits of the reapplication of RePLAY and further evaluate and validate its cost effectiveness. In addition, Clinton County has interested in evaluating the reapplication of RePLAY at the same project site for extending its use on other project sites. This research will be performed in response to such a research need and interest and will be achieved through the execution of the following primary tasks: (1) developing and executing a detailed field experimental plan, (2) evaluating and validating cost effectiveness, (3) executing subsequent technology transfer and information dissemination activities and developing implementation plans with recommendations, and (4) publishing final research project documents.

This research project will be highly helpful to the Iowa Department of Transportation and Iowa counties in better understanding the benefits of the reapplication of RePLAY while facilitating their decision making in selecting cost–effective application frequency options.

About the research

Curling and warping behavior due to temperature and moisture variation has been widely considered an influential factor affecting the smoothness of jointed plain concrete pavement (JPCP). In recent decades, while extensive efforts have been made to quantify the impact of curling and warping-related deflections on the smoothness of JPCP, a standardized method for characterizing the effects of environmental factors on JPCP smoothness is still unavailable. A Phase I study examined curling and warping conditions at six sites using a stationary light detection and ranging (LiDAR) system and developed recommendations to minimize curling and warping based on literature review findings. However, the data collection effort in the Phase I study was limited and was insufficient to validate the recommendations derived from the literature review.

The Phase II study described in this report aimed to evaluate and quantify the impact of curling and warping on Iowa concrete pavements and determine the factors that most influence curling and warping behavior. A high-speed profilometer and a LiDAR device were utilized to execute a large-scale field data collection plan for JPCP sites in Iowa, including Long-Term Pavement Performance (LTPP) Program highways, non-LTPP highways, and county roads and city streets. The variables evaluated in this study included temperature and moisture gradients, seasonal and diurnal effects, slab geometry, pavement structural design, mix design, and construction conditions. A validated MATLAB-based algorithm with two different curve-fitting models was coded to evaluate the degrees of curling and warping in multiple ways. This study also used statistical analyses to select the variables that significantly affect curling and warping behavior. The proposed actionable pavement design and construction recommendations will help minimize curling and warping and correct curling and warping-related performance issues.

About the research

Iowa has three classes of public roads: state primary highways, county (secondary) roads, and city streets. Among these, Iowa county roads serve rural Iowa transport needs by assuring a public road connection (i.e., to local access roads) for serving as conduits that channel the flow of people and commodities to and from towns and terminals (i.e., farm-to-market roads). Many Iowa county pavement systems are multilayered structures that have experienced multiple cycles of construction and renewal that make it more complex to estimate pavement structures’ current structural capacities.

This study developed a Microsoft Excel macro and Visual Basic for Applications (VBA)-based automated Pavement Structural Analysis Tool (PSAT) with three analyzing options—asphalt concrete (AC) pavement systems with 1 to 10 layers on a (1) stabilized base, (2) granular base, and (3) stabilized base and granular base—to estimate the current structural capacities of in-service pavement systems by following consecutive sections within the user-friendly platform. To address this aim, a systematic approach to develop a highly realistic annotated synthetic database was created for use in artificial neural network (ANN)-based pavement response prediction models that required inputs of pavement materials and structural features and outputs of pavement responses, deflections, and strains at critical locations within the pavement structure. In addition, the equivalent layer theory (ELT) concept was integrated into the PSAT to simplify multilayered pavement systems into three-layered systems—an asphalt layer, a base layer, and a subgrade layer. Thus, it could make it easier for an Iowa county engineer to understand the current structural capacities of in-service county pavements. Mechanistic- and empirical-based approaches were also integrated into the tool to estimate the remaining service life (RSL) associated with two types of major failures for flexible pavements, namely fatigue and rutting failures, by relating pavement responses predicted by the ANN models through transfer functions. The PSAT is expected to be used as part of routine pavement analysis, design, and asset management practices for better prioritization and allocation of resources, as well as to support effective communication related to pavement needs both with the public and with elected officials.