About the research
The aim of the work described in this report was to investigate the impacts of internally cured (IC) concrete paving on warping in test pavements built in Iowa. The study involved both laboratory investigations and field implementation of internally cured concrete for Iowa pavement systems.
The primary objective of this research was to perform a full-scale field demonstration using IC technology and to investigate its performance in rural roadways. Two overlay construction projects were identified for the field demonstration. Samples of the mixtures were taken at the time of placement and sent to the laboratory for parallel testing with laboratory prepared mixtures.
A number of sensors were embedded in the concrete slabs to monitor moisture and temperature over time. Periodic measurements were taken throughout the year to observe and evaluate the dimensional stability of the slabs.
To assess the value proposition of using internal curing in concrete overlays, life-cycle cost analyses were conducted using reported costs from the projects. Because little structural benefit is expected from the IC mixtures, the assessment was based on a predicted reduction in maintenance costs of the sections due to improved permeability determined in the laboratory tests. Both the net present value (NPV) and equivalent annual annuity (EAA) calculation results indicate a net savings over time with the use of IC technology.
Based on the field and laboratory results, using lightweight fine aggregate (LWFA) improved the concrete hydration for about one month after placing. The biggest challenge appears to be related to obtaining and preconditioning the LWFA.
In summary, the technique does appear to be of benefit for reducing the potential for early-age cracking, improving ride and increasing the longevity of relatively thin overlays. Assuming that the challenges of transportation and storage can be overcome, this is a viable technique to help improve the performance of such pavements.
About the research
It is common practice to put additional longitudinal reinforcement (b2 bars) over intermediate supports to resist any negative moment induced by the superimposed dead loads and live loads on bridges. However, little research has been conducted on the performance of the additional negative reinforcing steel. Requirements for the termination of the additional negative moment reinforcing steel have largely been based on engineering judgement, previous performance, and existing practice.
The main objective of this research was to evaluate the effect of different amounts of b2 bar on resisting the negative moment over the pier on a continuous prestressed concrete girder bridge when it is subject to the live load-generated moment and secondary moment. To achieve this objective, a live load field test was performed on a bridge designed with different amounts of b2 bars to allow for comparison of the varying levels of negative moment reinforcement present.
A full-scale finite element model was developed and validated against the field-collected data to study b2 bar performance subjected to live loads. An evaluation was performed utilizing an analytical approach by calculating the time-dependent secondary moment using mRESTRAINT and loading the beam-line finite element model with the maximum negative moment.
It was found that the negative moment induced by the live load and secondary moment does appear through the service life of the bridge. The high differential shrinkage rate between the fresh deck concrete and the girder concrete is the main source of the negative moment over the supports. The magnitude of the secondary moment was found to be highly influenced by the time when the continuity is established.
The results also indicated that the additional longitudinal reinforcing steel provides minimal effect on resistance to the negative moment prior to the formation of deck cracking, regardless of whether the negative moment was induced by live loads or by the secondary moment. The current design approach determines the b2 bar requirement for the strength level based on the live load, while it may be necessary to include the secondary moment in the design.
About the research
The opportunity to produce a high-value material derived from vegetable oil from the Midwest creates a tremendous economic opportunity to replace a dangerous and carcinogenic material in butadiene, which is derived from crude oil petroleum. The majority of butadiene is imported to use for subsequent production of polymers or is contained in polymers imported to the US. Development of the biopolymer technology for asphalt paving was sponsored by the Iowa Highway Research Board (IHRB) under a special funding mechanism for high-risk/high-potential-pay-off research. The biopolymers developed by Iowa State University were found to be an excellent alternative to the polymers currently used.
Since the conclusion of the first phase of this study in April 2014, a ton-per-day pilot plant was designed and built at Iowa State University’s BioCentury Research Farm, west of Ames, at a cost of more than $6 million. The pilot plant was installed in late 2015, winterized for the 2015–2016 winter, and reopened in Spring 2016.
The research team worked since the completion of the Phase I IHRB project in getting the pilot plant working and correctly calibrated. The Bio-Polymer Processing Facility underwent rigorous troubleshooting and upgrades during 2016 and became capable of producing biopolymers in sufficient quantities to conduct field demonstration paving projects. Research done during this work led to optimized formulations of biopolymer and furthered the march toward the implementation of biopolymer for field demonstration projects.
Due to the high number of mix designs that include reclaimed or recycled asphalt pavement (RAP), the biopolymer was transformed with a rejuvenator into a liquefied state to perform easier and more efficient blending with neat binders. From this new biopolymer/rejuvenator combination, called BioMAG, one test section and two demonstration projects were paved at the National Center for Asphalt Technology (NCAT) Test Track at Auburn University in Alabama and two sites in Iowa. The section at the NCAT Test Track is performing well against rutting and cracking.
Currently, additional data are being collected about other distresses. For the two demonstration projects in Iowa, mix and binder were collected from the Altoona, Iowa site. Full mix and binder characterization have shown that BioMAG performs well in RAP mix designs and improves resistance against low temperature cracking and rutting.
About the research
Internal curing is the practice of providing small, well-distributed reservoirs of water throughout a concrete section such that the w/cm of the mixture can be kept low, but the water can later be delivered to hydrating cement as the system dries out. Internal curing has been reported to be effective in reducing shrinkage cracking, improving potential durability of concrete mixtures, and most notably, reducing warping and associated cracking in pavements and slabs on grade.
Currently, the use of light-weight fine aggregate (LWFA) is the most common practice in the US to produce internally cured concrete. This method, however, necessitates pre-saturation of aggregate at concrete batch plants in accordance with a set timeline. This may increase costs related to stockpile management in addition to the costs and emissions associated with production and hauling the LWFA.
The use of superabsorbent polymers (SAP) as a means of internal curing can address such problems, while still promoting hydration and reducing the risk of early age cracking. However, there has been relatively little work conducted in the US on these materials. The aim of the work is to conduct laboratory work to address some remaining questions:
- How should SAP products be specified?
- How much is needed?
- Can SAPs be dry batched with additional water in the mixture without compromising performance?
- How are mixtures affected by their use?
About the research
The Iowa Highway Research Board funded a study (IHRB Project TR-761) to determine the feasibility of an Iowa Public Works Service Bureau. As a part of that study, a questionnaire was emailed to representatives of all cities with a population exceeding 250 people to determine if there was interest in developing a public works service bureau. The questions dealt with a city’s interest in web applications including elements such as a database of city contacts, asset management, organizational charts, job descriptions, pay levels, sample ordinances, sample policies, and communications with the Iowa Department of Transportation (DOT). Over 80% of the respondents indicated that they were highly or somewhat likely to use those applications.
With that indication of interest, potential organizational structures and funding were evaluated. Based on those evaluations, a majority of the Technical Advisory Committee recommended pursuing a project to establish the Iowa Public Works Service Bureau within the Statewide Urban Design and Specifications program with permanent funding from the street construction portion of Iowa’s Road Use Tax Fund. Due to the time required to work with the Governor’s office and the legislature to establish the permanent funding, a two-year Phase 2 project was recommended with funding from the IHRB. This project will involve creating the website elements, hiring two programmers to establish the applications, establishing a permanent advisory committee, and working to establish permanent funding with a Road Use Tax off-the-top allocation.
About the research
A life-cycle cost analysis (LCCA) tool for bridges was successfully developed as part of the Phase I project and takes into consideration the deterioration rates specific to Iowa bridge decks at two-year time intervals and aims to predict the agency and user costs associated with preserving, rehabilitating, and repairing the bridge decks. This offers a unique advantage over Iowa’s current system, which selects projects based on the lowest bid or estimated initial cost. In addition, the developed tool is extendable to cover various bridge elements, if needed. However, the initial tool did not take into consideration various sources of uncertainty or include an optional choice to consider indirect costs in the calculations. In addition, feedback from potential users of the tool will be necessary to further enhance the tool.
Phase II seeks to enhance the usability of the tool. Specifically, this tool will deliver firsthand information about how the timing, frequency, and procedure used for the maintenance of a set of similar bridges can lead to different service life extensions and future needs. This can be immediately employed to identify the most promising maintenance and management strategies for the bridges in service.
About the research
This study investigated the differences between the American Railway Engineering and Maintenance-of-Way Association (AREMA), American Association of State Highway and Transportation Officials (AASHTO), and Iowa Department of Transportation (DOT) concerning vehicular collisions. The researchers evaluated the performance of common Iowa bridges and their components when an 80 kip tractor-semitrailer collides into them. The researchers also performed a parametric study on a frame pier and T-pier that experience vehicular collision.
The frame pier with two 3.5 ft column diameters with a spiral of #5 rebar and 4 in. pitch experiences minor damage when impacted by a tractor-semitrailer at an impact velocity of 50 mph. There is, however, severe damage and failure for the impact velocity of 70 mph and 90 mph, respectively. The T-pier commonly used in Iowa does not collapse under any of the three impact velocities. The minimum requirements for a crash wall specified by the Iowa DOT were able to keep the frame pier from failure when it was struck by a tractor-semitrailer traveling at each of the three impact velocities. The Iowa DOT’s 54 in. tall concrete barrier successfully redirects a tractor-semitrailer and therefore prevents it from hitting the frame pier it is set up to protect.
The frame pier with two column diameters of 4 ft with at least 1.0% longitudinal reinforcement, #5 spiral rebar at a 4 in. pitch, and Grade 60 steel, did not collapse under any of the three impact velocities. The T-pier with no ties experiences minor damage when impacted at the 50 mph impact velocity. However, ties spaced at 24 in. and 12 in. are required for minor damage at a 70 mph and 90 mph impact velocity, respectively.
The damage ratio index (DRI) values and damage description for the frame pier accurately predicted the damage observed in the frame pier due to vehicular collision. The DRI damage state description for the frame pier did not accurately describe the damage for the T-pier. Therefore, a DRI damage state description table was developed for the T-pier.
About the research
The early-age thermal development in mass concrete has a significant impact on the performance and long-term serviceability of mass concrete structures, such as bridge foundations. Great efforts have been made on predicting and controlling the thermal development in mass concrete. The free computer software ConcreteWorks (CW) has been developed and increasingly used for this purpose. In the recent IHRB Project TR 712 (Phase I), the CW software was modified to include features that are suitable for Iowa’s use, particularly for the prediction of the thermal behavior of mass concrete elements with a smallest dimension of 6.5 ft or less. During this Phase I study, two related research areas were identified by the research team and the Technical Advisory Committee (TAC) for further research, and they are:
- Improving the thermal prediction for mass concrete containing slags, and
- Predicting the temperature profile of seal coat concrete slabs of bridge foundations.
About the research
Low-volume rural roads are generally low funding priorities compared to the roads that are part of the National Highway System (NHS). Therefore, low-volume rural roads tend to deteriorate to a point where traditional pavement preservation and maintenance techniques no longer have the desired effect or sufficient funding is not available.
As a potential solution, the Iowa Department of Transportation (DOT) constructed 10 test sections with various base and surface treatments on a 13 mi low-volume asphalt road segment in northeast Iowa in 2013, which were studied as part of the first phase of this research project. The aim of the project was to develop holding strategies beyond pavement preservation as a solution to low-volume roads that are in poor condition when there are not resources available for a complete rehabilitation. Due to the success of this first phase, a second phase was proposed in 2018.
This second phase study focused on surface treatments and was intended to treat highly distressed composite pavements that have asphalt overlays on portland cement concrete (PCC) pavements. Eight test sections were constructed on US 65, between Hubbard and Zearing in Iowa. The holding strategies evaluated were a combination of cold in-place recycling with various surface mixes, 1 in. profile milling with various surface courses, 2.5 in. profile milling with interlayer and surface course, and double coats of microsurfacing with and without additional spot grinding.
Based on the evaluation of the test sections and follow-up surveys, recommendations are given regarding the selection of the most advantageous strategy for the conditions of the studied pavement.
About the research
Selecting the right treatment for the right pavement at the right time has been a fundamental principle to pavement preservation success. The objective of this project is to develop “Iowa’s Pavement Preservation Guide,” a document tailored to serving the needs of Iowa practitioners who have active pavement preservation programs or plan to implement a pavement preservation program.This proposal outlines a research approach based on national-best practices for pavement preservation program implementation. Many states have developed pavement preservation manuals. The research addresses six areas including: (1) project selection, (2) anticipated benefit/costs of pavement preservation treatments at the network-and project-level, (3) implementing pavement preservation into system-wide strategic planning, (4) preservation treatment considerations, (5) construction/specifications, and (6) materials training. It is important that pavement preservation guidance include project-level and system-level selection strategies project-level decisions have a network-wide impact. Practitioners who use this guidance will be able to communicate pavement preservation benefits at the project-and network-levels, identify candidate roadways for preservation treatments, and utilize the guide to enhance project delivery of pavement preservation treatments.