Institute for Transportation

About the research

Longitudinal joints are thought to provide relief from expansion and contraction of the bridge deck resulting from temperature change, shrinkage, and live loads. Historically, however, these joints have been known to leak, allowing chloride-laden water to reach the bottom of the deck overhang and even the exterior girders.

One of the primary conclusions from the previous Phase I project was that the development of cracking in bridge decks appears to be less dependent on the total width of the deck and more dependent on restraint of the abutment to temperature changes and, in particular, temperature gradients. Based on the results of that research, a 115 ft long, 228 ft wide, bridge in Black Hawk County, Iowa was selected and designed to incorporate a thermal isolation barrier.

The objective of this research was to follow and document the design, construction, and performance of the bridge in Black Hawk County with a specific focus on the success of the deck crack mitigation efforts. To achieve this objective, the newly constructed bridge on Viking Road over IA 58 was selected for this study.

A nearly two-year-long monitoring period enhanced by multiple bridge inspections was conducted. In addition, an analytical study was conducted to investigate the efficacy of the isolation barrier on resisting the cracking at the end of the deck for an integral abutment bridge.

The results confirmed the findings from the Phase I research that development of cracking in bridge decks seems less dependent on the total width of the deck. The finite element model results indicated the maximum deck strain to be 46% greater without the effects of the thermal isolation barrier. This indicated that, without the thermal isolation barrier, the Viking Road Bridge could see cracking at the end of its deck.

The researchers recommend the use of a thermal isolation barrier between the abutment and backfill soils for wide integral abutment bridges as one way to lengthen the service life of these bridge decks while reducing maintenance, rehabilitation, and/or replacement costs as well.

About the research

This study investigated the utilization of eggshell powder (ESP) as a bio-based cementitious material for soil stabilization in Iowa, a state recognized as the leading egg producer in the United States. The prominence of egg production in Iowa results in substantial eggshell waste, a byproduct that, despite its high calcium carbonate content, remains largely underutilized. Eggshells, constituted of nearly 95% calcium carbonate, present an environmentally friendly opportunity to repurpose agricultural waste into beneficial construction materials. Addressing the dual challenges of waste management and soil stabilization, this study explored the potential of ESP derived from ground eggshells to enhance the properties of subgrade soils. Through a series of treatments—no treatment, oven drying, and calcination—the study assessed the effectiveness of ESP in improving soil engineering properties. Laboratory experiments with two types of Iowa soils mixed with up to 12% ESP demonstrated that calcination significantly optimized ESP’s performance, particularly when the soil was combined with 3% additional water and cured at 40°C. The optimal addition rate for maximizing unconfined compressive strength (UCS) was identified as 6% to 8% ESP, which provided over a tenfold increase in UCS compared to soil without ESP. This enhancement was especially notable in loess soils, which exhibited marked strength improvements. Field simulations using the dynamic cone penetration (DCP) test further validated the laboratory results, indicating that the inclusion of calcined ESP substantially enhanced the tested soil’s California bearing ratio (CBR). The findings underscore ESP’s potential as an innovative and sustainable additive for soil stabilization, offering a practical solution to managing eggshell waste while contributing to the development of eco-friendly construction practices in Iowa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that adding calcined ESP (1,830°F or 1,000°C) to soils resulted in a denser and more solid soil structure due to the formation of hydration products. This research not only addresses environmental concerns associated with eggshell waste but also highlights the broader application of agricultural byproducts in civil engineering, promoting sustainability in construction materials.

About the research

Several state and county engineers are facing the daunting task of maintaining an inventory of corroding steel structures. Capitalizing on the superior strength and durability properties of ultra-high performance concrete (UHPC), an innovative solution will be developed, tested, and demonstrated through this research project. This will lead to substantial advances in the repair and retrofit of steel bridges subjected to corrosive environments. The use of UHPC is believed to introduce a broad spectrum of benefits in both the short and long term. Specifically, UHPC offers a workable repair that can be applied in the field with minimum equipment requirements. This significantly expedites the repair process, resulting in minimized road closures and traffic disruptions. When repaired using UHPC, steel girders will not only regain their lost structural capacity but will also be protected against corrosive environments by a strong yet passive layer. This is an important feature, which will greatly extend the expected service life of steel bridge girders without having to repeat maintenance actions every few years.

To achieve the ultimate goal of this research project, a holistic set of research tasks and activities have been planned, including conceptual designs, numerical simulations, laboratory investigations, and a field demonstration. With the development of supporting technology transfer materials, the outcome of this project is expected to pave the way to utilizing the advantages of this repair solution for future use and implementation in various state- and county-owned steel bridges.

About the research

A significant amount of waste ash in the United States does not meet the necessary specifications for construction and other uses, and power plants are searching for a way to dispose of surplus waste ashes.

To address this issue, this research aimed to treat waste ashes using CO₂ injection in order to modify their properties and enable their beneficial use in concrete. The main tasks of the study were to (1) optimize the carbon treatment procedure (pressure, moisture, and time) for the selected waste ashes, (2) determine the effects of the carbon treatment on the properties of the ashes (surface chemistry, morphology, pore structure, etc.), (3) evaluate the effects of carbon-treated ashes on the properties of cement composites such as paste and mortar (set time, flowability, hydration, strength, etc.), and (4) quantify CO₂ sequestration and assess the benefit-to-cost potential of the carbon-curing treatment. Findings indicate that certain types of waste ashes can increase the decarbonation of cement and concrete providing a use for the waste ashes and promoting sustainability.

About the research

Plastic waste is one of the greatest environmental challenges in not only Iowa but also other states. Recent bans on imported plastic waste into developing countries has forced many US cities and states to take issues related to plastic waste more seriously. In addition, fiberglass-based (also known as glass-reinforced plastic or glass-fiber-reinforced plastic) wind turbine blades from wind powered generators in Iowa are being heaped up in piles in landfills instead of recycled.

The objectives of this research are to determine the structural benefits and environmental suitability of using recycled plastics as a base stabilization agent and then to develop a practitioner’s guide to document best practices to implement such a solution in Iowa’s gravel road network. This will be achieved through the execution of the following primary tasks: (1) characterization of recycled plastic materials, including recycled wind turbine blade materials, (2) identification of innovative solutions of using recycled plastics to stabilize granular roads through comprehensive laboratory assessment, (3) construction and assessment of pilot test sections employing identified solutions through a set of field tests and surveys, (4) determination of the structural benefits and environmental suitability, (5) cost-effectiveness evaluation, and (6) development of best practice guidance documents and implementation recommendations. The successful outcomes of this research will not only help reduce landfill waste but also provide an innovative and less expensive alternative to strengthen the bases of Iowa’s granular roads.

About the research

The goal of this project was to identify effective and economical methods for stabilizing Iowa granular-surfaced roads to reduce freeze-thaw-related damage using materials and construction equipment that are readily available to county engineer’s offices. To study a range of representative Iowa aggregate sources, subgrade soil types, and weather conditions, 31 test sections were constructed and/or monitored in four counties across Iowa. The test sections included one control section in each county and several mechanical and chemical stabilization methods.

The performance of the stabilized and control sections was evaluated over two years using extensive field and laboratory tests, as well as digital image surveys and surface condition rating reports completed by the grader operators. The field tests included falling weight deflectometer (FWD), lightweight deflectometer (LWD), dynamic cone penetrometer (DCP), and nuclear density gauge (NDG) tests. Samples of the surfacing materials were collected on several occasions before and after each winter and were evaluated through laboratory tests including sieve analysis, Atterberg limits, compaction, shear strength, and durability tests. The construction costs and maintenance costs were tracked with the assistance of the county engineers, and an economic analysis was conducted to compare the relative cost effectiveness of the different stabilization methods.

Among the stabilization methods examined, the most economical and potentially effective were optimized gradation with clay slurry (OGCS), 4 in. cement-treated surface course, and the liquid chemical stabilizers BASE ONE, EMC SQUARED, and Claycrete.

About the research

Prolonged road/lane closures associated with the rehabilitation or replacement of bridges lead to congested traffic conditions, which, among other consequences, pose an increased risk of safety for both construction workers and the traveling public. In an attempt to minimize these concerns, sophisticated procedures, combining the use of prefabricated bridge components, high performance characteristics of unconventional construction materials, and careful planning, are being developed to expedite bridge projects from conception to delivery. These novel techniques can drastically reduce abridge on-site construction time while enhancing both the quality and durability of the completed structure, and have promoted accelerated bridge construction (ABC) among the bridge design community.

Effective ABC methods require easy-to-fabricate and lightweight modules that can be transported to the site and assembled relatively quickly with commonly used equipment. Moreover, the connections of the system must be properly designed and detailed to facilitate assembly and enable the overall structure to achieve a performance that is comparable, if not superior, to that of a similarly cast-in-place (CIP) system. The Iowa DOT has invested in the development of abutment connection details to facilitate implementation of ABC techniques in its practice.

Building on previous research, this project will advance the accelerated bridge construction method for integral bridge abutments supported on steel piles and constructed using prefabricated and in-situ concrete along with other advanced construction techniques (3D printing) and materials as appropriate.

About the research

Prestressed concrete structures have become a popular choice for transportation infrastructure applications. According to the National Bridge Inventory, the percentage of bridges built with prestressed concrete technology has been rapidly increased from 15.0% to 23.5% over the past two decades. Specifically, precast prestressed concrete beams (PPCBs) are extensively used for bridge superstructures, owing to a number of favorable attributes, including great quality control on material and workmanship from one side, and fast, economic, and energy-efficient construction from the other side. The bridge superstructures are, however, known to be vulnerable to continuous deterioration. As a consequence, a problem commonly observed in the PPCB that supports the bridge superstructure is that the beam ends experience a faster (and more severe) deterioration compared to the rest of the beam. This is not surprising considering the fact that the beam end regions are subjected to a harsher exposure condition. To minimize serviceability issues and avoid catastrophic failures, effective maintenance and repair efforts are essential. The ultimate goal of this research project is, therefore, to develop feasible and cost-effective preservation strategies to extend the service life of the PPCB used in bridges in service.

About the research

Building on previous research, the proposed project will advance the accelerated bridge construction method for bridge substructures using steel piles and precast pile caps and columns. The weight of the precast members will be reduced using hollow sections, which in turn will improve both construction tolerances and constructability. The hollow sections will be filled with in-situ concrete. The piles will be designed with temporary collars, which will eliminate the need to wait for the concrete to cure before continuing with the superstructure construction.

The research will include a large-scale test unit that will incorporate both vertical and battered steel piles. The testing of the system will incorporate service level and extreme loads and ensure dependable performance of the new system and its components. As part of the testing program, the performance of the column and pile foundations will be examined systematically. Analytical models will be developed to realize the observed performance of the test unit and the components. Using previously discovered analytical and experimental observations and findings, appropriate design recommendations will be developed for improving bridge construction.

About the research

The goal of this project was to investigate the performance of granular road sections stabilized with quarry fines byproducts and perform a benefit-cost analysis (BCA) to find the most beneficial quarry fines options for stabilization.

Five sources of quarry fines were selected among 19 quarries across Iowa to build 3 test sections in Jones County, Iowa, and 4 sections in Boone County, Iowa. These two sites are among the most populated roads with relatively stiff subbase and subgrade layers, and they suffer from heavy traffic loads and freeze-thaw effects during winter and spring seasons. Construction and maintenance procedures for the test sections are detailed, and the associated costs of aggregate, hauling, and equipment are also documented in this report.

Extensive laboratory and field tests were performed before and after construction, as well as after one seasonal freeze-thaw period from 2019 to 2020, to evaluate and monitor the performance of the constructed sections. A BCA was performed using the documented construction and maintenance costs for service life scenarios of 20, 30, 40, and 50 years. A benefit-cost ratio (BCR) was calculated for each test section for different scenarios based on various performance measures including gravel content change, average fines content, total breakage, gravel-to-sand ratio, stiffness, shear strength, surface roughness, and dust emission. Performance measures were categorized into three overall mechanistic performance-based groups, and their BCRs were compared.

Overall, the results of this study showed that stabilization by quarry fines improved performance by providing binding between the surface aggregates, reducing dust emission and gravel loss, and increasing the stiffness and strength of the surface layers. Stabilization could be cost-effective by reducing the maintenance frequency depending on the material, hauling, and labor costs. The Limestone and Moscow Mine sections in Jones County, and Moscow and Ames Mine sections in Boone County had the best performance and cost-effectiveness among all stabilized sections. Although the Clay Slurry material was helpful to reduce dust emission compared to the rest of the sections, sections with the Clay Slurry were among the average-performance sections, and the increased construction costs made them a less cost-effective option for both counties.