Effect of Delay in Testing Asphalt Concrete Specimens for Marshall Stability, MLR-86-08, Draft, 1986

The Central Laboratory has been delaying the mix design testing of 2 1/2" X 4" Marshall specimens for stability, until the next day after molding. For example, if the mixes are made and samples molded on Friday a man would have to come in and work on Saturday to test these specimens. The reason for this is that the ASTM-01559 "Resistance to Plastic Flow of Bituminous Mixes Using Marshall Apparatus," states that "the specimens after being molded shall be carefully transferred to a smooth, flat surface and allowed to stand overnight at room temperature, before being weighed, measured and tested." The AASHTO procedure, AASHTO Designation T-245-82 "Resistance to Plastic Flow of Bituminous Mixtures using Marshall Apparatus," does not say when the specimens shall be tested for stability. The IDOT Lab. Specifications, Test Method No. Iowa 502-8 and test method No. Iowa 506-C "compacting asphaltic concrete by the Marshall Method" and "Resistance to Plastic Flow of Bituminous Mixtures Using the Marshall Apparatus," respectively, only state that the specimens shall be cooled before testing. Due to the above conflict in specifications, a number of mix samples were tested, in the Central Lab, for stability on different days. This should furnish enough information to allow us to change the procedure and to test for stability the same day molded, or be able to delay the testing for 3 days or more.

Early Strengths of Class F, C, and B Portland Cement Concrete, MLR-87-07, 1987

Fast track concrete has proven to be successful in obtaining high early strengths. This benefit does not come without cost. Type III cement and insulation blankets to accelerate the cure add to its expense when compared to conventional paving. This research was intended to determine the increase in time required to obtain opening strength when a fast track mix utilized conventional Type I cement and also used a conventional cure. Standard concrete mixes also were tested to determine the acceleration of strength gain when cured with insulation blankets. The goal was to determine mixes and procedures which would result in a range of opening times. This would allow the most economical design for a particular project and tailor it to that projects time restraint. Three mixes were tested: Class F, Class C, and Class B. Each mix was tested with one section being cured with insulation blankets and another section without. All used Type I cement. Iowa Department of Transportation specifications required 500 psi of flexural strength before a pavement can be opened to traffic. The Class F mix with Type I cement and using insulation blankets reached that strength in approximately 36 hours, the Class C mix using the blankets in approximately 48 hours, and the Class F mix without covers in about 60 hours. (Note: Class F concrete pavement is opened at 400 psi minimum and Class F bonded overlay pavement at 350 psi.) The results showed a significant improvement in early strength gain by the use of insulation blankets. The Type I cement could be used in mixes intended for early opening with sacrifices in time when compared to fast track but are still much sooner than conventional pavement. It appears a range of design alternatives is possible using Type I cement both with and without insulating blankets.

A Study of Fine Sand from Nine Mile Island at Dubuque, MLR-88-08, 1988

The specifications for concrete sand in Iowa have been used for many years with very good results. In several locations of the state, it is becoming more difficult to produce concrete sand consistently at a reasonable cost. Both ASTM and AASHTO have specifications for concrete sands that allow a finer, poorer graded sand than the Iowa specification. The ASTM and AASHTO specifications are based on the use of trial mix testing prior to construction. Iowa does not currently use the trial mix procedure.

Evaluation of PCC Specification Changes Impact on Durability: 1992 - 1997 Core Study, MLR-98-06, 2005

In 1990, early distress had shown up on US 20 in Hamilton/Webster counties, three years after paving. Since that time, over a dozen more projects, constructed between 1984 and 1994, have been found to exhibit similar early distress. Several changes to the concrete and Portland cement specifications occurred in 1994 and 1996. This study was undertaken to investigate in place concrete pavements before and after specification changes were implemented. The objective of this research is to evaluate the impact of Portland cement and concrete specification changes made in 1994 and 1996 on PCC durability. Cores were obtained in 1998 and 2003 from projects constructed in 1992, before specification changes, and 1997 after specification changes. The following is a brief summary of the conclusions: 1. The pavements in the study constructed under the new specifications are performing much better after 5 years of service than the pavements constructed under the old specifications. 2. According to ISU, micro-cracking is evident in all concrete that has been in service, due to thermal stresses and loading stresses. Also, the low vacuum SEM will desiccate the concrete enough to cause micro-cracking. The SEM should not be used as a tool to indicate micro-cracking. 3. Use of Type II cement (C3A <8%) and a 3.0% SO3 limit does not completely eliminate ettringite infilling in air voids, as indicated in the bottom of the 1997 cores. 4. In areas of high moisture (bottom of the core), infilling is present in most of the 1997 cores. 5. Low air content and high spacing factor in the top of 1992 cores apparently causes F/T cycling cracking and then increased moisture paths from cracking causes infilling. 6. Use of ground granulated blast furnace slag (GGBFS) and fly ash reduces ettringite infilling either by diluting the aluminate (C3A) or lowering permeability, which slows ingress of moisture. 7. The specification changes that made the biggest impact on pavement durability are the limits on vibration and increase in air content in September 1994. 8. Investigations of cores from pavements placed in 2002 and 2003 indicate improved air contents and spacing factors. In-place air content and spacing factors should be monitored to determine if appropriate air void parameters are being met.

Development of Bridge Load Testing Process for Load Evaluation, TR-445, 2003

Recent reports indicate that of the over 25,000 bridges in Iowa, slightly over 7,000 (29%) are either structurally deficient or functionally obsolete. While many of these bridges may be strengthened or rehabilitated, some simply need to be replaced. Before implementing one of these options, one should consider performing a diagnostic load test on the structure to more accurately assess its load carrying capacity. Frequently, diagnostic load tests reveal strength and serviceability characteristics that exceed the predicted codified parameters. Usually, codified parameters are very conservative in predicting lateral load distribution characteristics and the influence of other structural attributes. As a result, the predicted rating factors are typically conservative. In cases where theoretical calculations show a structural deficiency, it may be very beneficial to apply a "tool" that utilizes a more accurate theoretical model which incorporates field-test data. At a minimum, this approach results in more accurate load ratings and many times results in increased rating factors. Bridge Diagnostics, Inc. (BDI) developed hardware and software that are specially designed for performing bridge ratings based on data obtained from physical testing. To evaluate the BDI system, the research team performed diagnostic load tests on seven "typical" bridge structures: three steel-girder bridges with concrete decks, two concrete slab bridges, and two steel-girder bridges with timber decks. In addition, a steel-girder bridge with a concrete deck previously tested and modeled by BDI was investigated for model verification purposes. The tests were performed by attaching strain transducers on the bridges at critical locations to measure strains resulting from truck loading positioned at various locations on the bridge. The field test results were used to develop and validate analytical rating models. Based on the experimental and analytical results, it was determined that bridge tests could be conducted relatively easy, that accurate models could be generated with the BDI software, and that the load ratings, in general, were greater than the ratings, obtained using the codified LFD Method (according to AASHTO Standard Specifications for Highway Bridges).

Design Guide for Improved Quality of Roadway Subgrades and Subbases, TR-525, 2008

The performance of a pavement depends on the quality of its subgrade and subbase layers; these foundational layers play a key role in mitigating the effects of climate and the stresses generated by traffic. Therefore, building a stable subgrade and a properly drained subbase is vital for constructing an effective and long lasting pavement system. This manual has been developed to help Iowa highway engineers improve the design, construction, and testing of a pavement system’s subgrade and subbase layers, thereby extending pavement life. The manual synthesizes current and previous research conducted in Iowa and other states into a practical geotechnical design guide [proposed as Chapter 6 of the Statewide Urban Design and Specifications (SUDAS) Design Manual] and construction specifications (proposed as Section 2010 of the SUDAS Standard Specifications) for subgrades and subbases. Topics covered include the important characteristics of Iowa soils, the key parameters and field properties of optimum foundations, embankment construction, geotechnical treatments, drainage systems, and field testing tools, among others.

The Utilization of Agriculturally Derived Lignin as an Antioxidant in Asphalt Binder, TR-557, 2008

Oxidation is the primary cause of long-term aging in asphalt pavements. As a pavement oxidizes, it stiffens and can eventually crack. The use of an antioxidant as a performance enhancer in an asphalt binder could delay aging, thus increasing the life of an asphalt pavement. Lignin is a highly available and well-studied antioxidant. A wet-mill ethanol plant produces several co-products, some of which contain lignin. The use of lignin from ethanol production could provide a benefit to asphalt pavements and also give more value to the co-products. The following research examined the effects of lignin on asphalt pavements. Three lignin-containing co-products were separately combined with four asphalt binders in varying amounts to determine the optimum amount of co-product that would provide the greatest benefit to the asphalt binders. The asphalt binder and co-product blends were evaluated according to Superpave specifications and performance graded on a continuous scale. The data indicated a stiffening effect on the binder caused by the addition of the co-products. The more a co-product was added, the more a binder stiffened. Binder stiffening benefited the high temperature properties and the low temperature binder properties were negatively affected. However, the low temperature stiffening effects were small and in many cases not significant. The co-products had an overall effect of widening the temperature range of the binders. This result suggests some antioxidant activity between the binder and the lignin. Testing with a fourth co-product with no lignin supported the idea that lignin acts as an antioxidant. The samples with no lignin aged significantly more than the samples with lignin. Infrared spectrometry also supported the idea that lignin acts as an antioxidant by observing decreases in some oxidative aging products.

Embankment Quality: Phase III, TR-401, 2002

This report describes test results from a full-scale embankment pilot study conducted in Iowa. The intent of the pilot project was to field test and refine the proposed soil classification system and construction specifications developed in Phase II of this research and to evaluate the feasibility of implementing a contractor quality control (QC) and Iowa DOT quality assurance (QA) program for earthwork grading in the future. One of the primary questions for Phase III is “Was embankment quality improved?” The project involved a “quality conscious” contractor, well-qualified and experienced Iowa Department of Transportation field personnel, a good QC consultant technician, and some of our best soils in the state. If the answer to the above question is “yes” for this project, it would unquestionably be “yes” for other projects as well. The answer is yes, the quality was improved, even for this project, as evidenced by dynamic cone penetrometer test data and the amount of disking required to reduce the moisture content to within acceptable control limits (approximately 29% of soils by volume required disking). Perhaps as important is that we know what quality we have. Increased QC/QA field testing, however, increases construction costs, as expected. The quality management-earthwork program resulted in an additional $0.03 per cubic meter, or 1.6%, of the total construction costs. Disking added about $0.04 per cubic meter, or 1.7%, to the total project costs. In our opinion this is a nominal cost increase to improve quality. It is envisioned that future contractor innovations have the potential for negating this increase. The Phase III results show that the new soil classification system and the proposed field test methods worked well during the Iowa Department of Transportation soils design phase and during the construction phase. Recommendations are provided for future implementation of the results of this study by city, county, and state agencies.

Fly Ash Soil Stabilization for Non-Uniform Subgrade Soils, Volume I: Engineering Properties and Construction Guidelines, TR-461, 2005

Soil treated with self-cementing fly ash is increasingly being used in Iowa to stabilize fine-grained pavement subgrades, but without a complete understanding of the short- and long-term behavior. To develop a broader understanding of fly ash engineering properties, mixtures of five different soil types, ranging from ML to CH, and several different fly ash sources (including hydrated and conditioned fly ashes) were evaluated. Results show that soil compaction characteristics, compressive strength, wet/dry durability, freeze/thaw durability, hydration characteristics, rate of strength gain, and plasticity characteristics are all affected by the addition of fly ash. Specifically, Iowa selfcementing fly ashes are effective at stabilizing fine-grained Iowa soils for earthwork and paving operations; fly ash increases compacted dry density and reduces the optimum moisture content; strength gain in soil-fly ash mixtures depends on cure time and temperature, compaction energy, and compaction delay; sulfur contents can form expansive minerals in soil–fly ash mixtures, which severely reduces the long-term strength and durability; fly ash increases the California bearing ratio of fine-grained soil–fly ash effectively dries wet soils and provides an initial rapid strength gain; fly ash decreases swell potential of expansive soils; soil-fly ash mixtures cured below freezing temperatures and then soaked in water are highly susceptible to slaking and strength loss; soil stabilized with fly ash exhibits increased freeze-thaw durability; soil strength can be increased with the addition of hydrated fly ash and conditioned fly ash, but at higher rates and not as effectively as self-cementing fly ash. Based on the results of this study, three proposed specifications were developed for the use of self-cementing fly ash, hydrated fly ash, and conditioned fly ash. The specifications describe laboratory evaluation, field placement, moisture conditioning, compaction, quality control testing procedures, and basis of payment.

Field Instrumentation, Testing, and Long-Term Monitoring of High-Mast Lighting Towers in the State of Iowa, TR-518, 2006

As a result of the collapse of a 140 foot high-mast lighting tower in Sioux City, Iowa in November of 2003, a thorough investigation into the behavior and design of these tall, yet relatively flexible structures was undertaken. Extensive work regarding the root cause of this failure was carried out by Robert Dexter of The University of Minnesota. Furthermore, a statewide inspection of all the high-mast towers in Iowa revealed fatigue cracks and loose anchor bolts on other existing structures. The current study was proposed to examine the static and dynamic behavior of a variety of towers in the State of Iowa utilizing field testing, specifically long-term monitoring and load testing. This report presents the results and conclusions from this project. The field work for this project was divided into two phases. Phase 1 of the project was conducted in October 2004 and focused on the dynamic properties of ten different towers in Clear Lake, Ames, and Des Moines, Iowa. Of those ten, two were also instrumented to obtain stress distributions at various details and were included in a 12 month long-term monitoring study. Phase 2 of this investigation was conducted in May of 2005, in Sioux City, Iowa, and focused on determining the static and dynamic behavior of a tower similar to the one that collapsed in November 2003. Identical tests were performed on a similar tower which was retrofitted with a more substantial replacement bottom section in order to assess the effect of the retrofit. A third tower with different details was dynamically load tested to determine its dynamic characteristics, similar to the Phase 1 testing. Based on the dynamic load tests, the modal frequencies of the towers fall within the same range. Also, the damping ratios are significantly lower in the higher modes than the values suggested in the AASHTO and CAN/CSA specifications. The comparatively higher damping ratios in the first mode may be due to aerodynamic damping. These low damping ratios in combination with poor fatigue details contribute to the accumulation of a large number of damage-causing cycles. As predicted, the stresses in the original Sioux City tower are much greater than the stresses in the retrofitted towers at Sioux City. Additionally, it was found that poor installation practices which often lead to loose anchor bolts and out-of-level leveling nuts can cause high localized stresses in the towers, which can accelerate fatigue damage.

Revision to the SUDAS Traffic Signal Design Guide, TR-546, 2009

Changes in technology have an impact on standard practice, materials, and equipment. The traffic signal industry is constantly producing more energy-efficient and durable equipment, better communications, and more sophisticated detection and monitoring capabilities. Accordingly, this project provides an update to the traffic signal content within the Statewide Urban Design and Specifications (SUDAS) Design Manual and Standard Specifications. This work was completed through a technical advisory committee with a variety of participants representing contractors, the Iowa Department of Transportation, cities, consultants, vendors, and university research and support staff.

Wind Loads on Dynamic Message Cabinets and Behavior of Supporting Trusses, TR-612, 2013

Large Dynamic Message Signs (DMSs) have been increasingly used on freeways, expressways and major arterials to better manage the traffic flow by providing accurate and timely information to drivers. Overhead truss structures are typically employed to support those DMSs allowing them to provide wider display to more lanes. In recent years, there is increasing evidence that the truss structures supporting these large and heavy signs are subjected to much more complex loadings than are typically accounted for in the codified design procedures. Consequently, some of these structures have required frequent inspections, retrofitting, and even premature replacement. Two manufacturing processes are primarily utilized on truss structures - welding and bolting. Recently, cracks at welding toes were reported for the structures employed in some states. Extremely large loads (e.g., due to high winds) could cause brittle fractures, and cyclic vibration (e.g., due to diurnal variation in temperature or due to oscillations in the wind force induced by vortex shedding behind the DMS) may lead to fatigue damage, as these are two major failures for the metallic material. Wind and strain resulting from temperature changes are the main loads that affect the structures during their lifetime. The American Association of State Highway and Transportation Officials (AASHTO) Specification defines the limit loads in dead load, wind load, ice load, and fatigue design for natural wind gust and truck-induced gust. The objectives of this study are to investigate wind and thermal effects in the bridge type overhead DMS truss structures and improve the current design specifications (e.g., for thermal design). In order to accomplish the objective, it is necessary to study structural behavior and detailed strain-stress of the truss structures caused by wind load on the DMS cabinet and thermal load on the truss supporting the DMS cabinet. The study is divided into two parts. The Computational Fluid Dynamics (CFD) component and part of the structural analysis component of the study were conducted at the University of Iowa while the field study and related structural analysis computations were conducted at the Iowa State University. The CFD simulations were used to determine the air-induced forces (wind loads) on the DMS cabinets and the finite element analysis was used to determine the response of the supporting trusses to these pressure forces. The field observation portion consisted of short-term monitoring of several DMS Cabinet/Trusses and long-term monitoring of one DMS Cabinet/Truss. The short-term monitoring was a single (or two) day event in which several message sign panel/trusses were tested. The long-term monitoring field study extended over several months. Analysis of the data focused on trying to identify important behaviors under both ambient and truck induced winds and the effect of daily temperature changes. Results of the CFD investigation, field experiments and structural analysis of the wind induced forces on the DMS cabinets and their effect on the supporting trusses showed that the passage of trucks cannot be responsible for the problems observed to develop at trusses supporting DMS cabinets. Rather the data pointed toward the important effect of the thermal load induced by cyclic (diurnal) variations of the temperature. Thermal influence is not discussed in the specification, either in limit load or fatigue design. Although the frequency of the thermal load is low, results showed that when temperature range is large the restress range would be significant to the structure, especially near welding areas where stress concentrations may occur. Moreover stress amplitude and range are the primary parameters for brittle fracture and fatigue life estimation. Long-term field monitoring of one of the overhead truss structures in Iowa was used as the research baseline to estimate the effects of diurnal temperature changes to fatigue damage. The evaluation of the collected data is an important approach for understanding the structural behavior and for the advancement of future code provisions. Finite element modeling was developed to estimate the strain and stress magnitudes, which were compared with the field monitoring data. Fatigue life of the truss structures was also estimated based on AASHTO specifications and the numerical modeling. The main conclusion of the study is that thermal induced fatigue damage of the truss structures supporting DMS cabinets is likely a significant contributing cause for the cracks observed to develop at such structures. Other probable causes for fatigue damage not investigated in this study are the cyclic oscillations of the total wind load associated with the vortex shedding behind the DMS cabinet at high wind conditions and fabrication tolerances and induced stresses due to fitting of tube to tube connections.

Iowa Mass Concrete for Bridge Foundation Study - Phase II, Final Report, 2014

The early-age thermal development of structural mass concrete elements has a significant impact on the future durability and longevity of the elements. If the heat of hydration is not controlled, the elements may be susceptible to thermal cracking and damage from delayed ettringite formation. In the Phase I study, the research team reviewed published literature and current specifications on mass concrete. In addition, the team observed construction and reviewed thermal data from the westbound (WB) I-80 Missouri River Bridge. Finally, the researchers conducted an initial investigation of the thermal analysis software programs ConcreteWorks and 4C-Temp&Stress. The Phase II study is aimed at developing guidelines for the design and construction of mass concrete placements associated with large bridge foundations. This phase included an additional review of published literature and a more in-depth investigation of current mass concrete specifications. In addition, the mass concrete construction of two bridges, the WB I-80 Missouri River Bridge and the US 34 Missouri River Bridge, was documented. An investigation was conducted of the theory and application of 4C-Temp&Stress. ConcreteWorks and 4C-Temp&Stress were calibrated with thermal data recorded for the WB I-80 Missouri River Bridge and the US 34 Missouri River Bridge. ConcreteWorks and 4C-Temp&Stress were further verified by means of a sensitivity study. Finally, conclusions and recommendations were developed, as included in this report.

Investigation of Negative Moment Reinforcing in Bridge Decks, TR-660, 2015

Multi-span pre-tensioned pre-stressed concrete beam (PPCB) bridges made continuous usually experience a negative live load moment region over the intermediate supports. Conventional thinking dictates that sufficient reinforcement must be provided in this region to satisfy the strength and serviceability requirements associated with the tensile stresses in the deck. The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications recommend the negative moment reinforcement (b2 reinforcement) be extended beyond the inflection point. Based upon satisfactory previous performance and judgment, the Iowa Department of Transportation (DOT) Office of Bridges and Structures (OBS) currently terminates b2 reinforcement at 1/8 of the span length. Although the Iowa DOT policy results in approximately 50% shorter b2 reinforcement than the AASHTO LRFD specifications, the Iowa DOT has not experienced any significant deck cracking over the intermediate supports. The primary objective of this project was to investigate the Iowa DOT OBS policy regarding the required amount of b2 reinforcement to provide the continuity over bridge decks. Other parameters, such as termination length, termination pattern, and effects of the secondary moments, were also studied. Live load tests were carried out on five bridges. The data were used to calibrate three-dimensional finite element models of two bridges. Parametric studies were conducted on the bridges with an uncracked deck, a cracked deck, and a cracked deck with a cracked pier diaphragm for live load and shrinkage load. The general conclusions were as follows: -- The parametric study results show that an increased area of the b2 reinforcement slightly reduces the strain over the pier, whereas an increased length and staggered reinforcement pattern slightly reduce the strains of the deck at 1/8 of the span length. -- Finite element modeling results suggest that the transverse field cracks over the pier and at 1/8 of the span length are mainly due to deck shrinkage. -- Bridges with larger skew angles have lower strains over the intermediate supports. -- Secondary moments affect the behavior in the negative moment region. The impact may be significant enough such that no tensile stresses in the deck may be experienced.

Revision to the SUDAS Traffic Signal Standards - Phase 2, 2012

This report provides a summary of the updates to the traffic signal content within the Iowa Statewide Urban Design and Specifications (SUDAS) Design Manual Chapter 13 and Standard Specifications Division 8. Major focal points included pole footing design, cabinets and controllers, monitoring systems, communications systems, and figure updates. This work was completed through a project task force with a variety of participants (contractors, Iowa Department of Transportation, city traffic engineers, consultant, vendors, and University research and support staff).