Concrete Pavement Mixture Design and Analysis (MDA): Assessment of Air Void System Requirements for Durable Concrete, TPF-5(205), 2012

Concrete will suffer frost damage when saturated and subjected to freezing temperatures. Frost-durable concrete can be produced if a specialized surfactant, also known as an air-entraining admixture (AEA), is added during mixing to stabilize microscopic air voids. Small and well-dispersed air voids are critical to produce frost-resistant concrete. Work completed by Klieger in 1952 found the minimum volume of air required to consistently ensure frost durability in a concrete mixture subjected to rapid freezing and thawing cycles. He suggested that frost durability was provided if 18 percent air was created in the paste. This is the basis of current practice despite the tests being conducted on materials that are no longer available using tests that are different from those in use today. Based on the data presented, it was found that a minimum air content of 3.5 percent in the concrete and 11.0 percent in the paste should yield concrete durable in the ASTM C 666 with modern AEAs and low or no lignosulfonate water reducers (WRs). Limited data suggests that mixtures with a higher dosage of lignosulfonate will need about 1 percent more air in the concrete or 3 percent more air in the paste for the materials and procedures used. A spacing factor of 0.008 in. was still found to be necessary to provide frost durability for the mixtures investigated.

Assessment of Weathering Steel Bridge Performance in Iowa and Development of Inspection and Maintenance Techniques, RB17-012, 2013

Weathering steel is commonly used as a cost-effective alternative for bridge superstructures, as the costs and environmental impacts associated with the maintenance/replacement of paint coatings are theoretically eliminated. The performance of weathering steel depends on the proper formation of a surface patina, which consists of a dense layer of corrosion product used to protect the steel from further atmospheric corrosion. The development of the weathering steel patina may be hindered by environmental factors such as humid environments, wetting/drying cycles, sheltering, exposure to de-icing chlorides, and design details that permit water to pond on steel surfaces. Weathering steel bridges constructed over or adjacent to other roadways could be subjected to sufficient salt spray that would impede the development of an adequate patina. Addressing areas of corrosion on a weathering steel bridge superstructure where a protective patina has not formed is often costly and negates the anticipated cost savings for this type of steel superstructure. Early detection of weathering steel corrosion is important to extending the service life of the bridge structure; however, written inspection procedures are not available for inspectors to evaluate the performance or quality of the patina. This project focused on the evaluation of weathering steel bridge structures, including possible methods to assess the quality of the weathering steel patina and to properly maintain the quality of the patina. The objectives of this project are summarized as follows:  Identify weathering steel bridge structures that would be most vulnerable to chloride contamination, based on location, exposure, environment, and other factors.  Identify locations on an individual weathering steel bridge structure that would be most susceptible to chloride contamination, such as below joints, splash/spray zones, and areas of ponding water or debris.  Identify possible testing methods and/or inspection techniques for inspectors to evaluate the quality of the weathering steel patina at locations discussed above.  Identify possible methods to measure and evaluate the level of chloride contamination at the locations discussed above.  Evaluate the effectiveness of water washing on removing chlorides from the weathering steel patina.  Develop a general prioritization for the washing of bridge structures based on the structure’s location, environment, inspection observations, patina evaluation findings, and chloride test results.

MEPDG Work Plan Task No. 5: Characterization of Unbound Materials (Soils/Aggregates) for Mechanistic-Empirical Pavement Design Guide, 2009

The resilient modulus (MR) input parameters in the Mechanistic-Empirical Pavement Design Guide (MEPDG) program have a significant effect on the projected pavement performance. The MEPDG program uses three different levels of inputs depending on the desired level of accuracy. The primary objective of this research was to develop a laboratory testing program utilizing the Iowa DOT servo-hydraulic machine system for evaluating typical Iowa unbound materials and to establish a database of input values for MEPDG analysis. This was achieved by carrying out a detailed laboratory testing program designed in accordance with the AASHTO T307 resilient modulus test protocol using common Iowa unbound materials. The program included laboratory tests to characterize basic physical properties of the unbound materials, specimen preparation and repeated load triaxial tests to determine the resilient modulus. The MEPDG resilient modulus input parameter library for Iowa typical unbound pavement materials was established from the repeated load triaxial MR test results. This library includes the non-linear, stress-dependent resilient modulus model coefficients values for level 1 analysis, the unbound material properties values correlated to resilient modulus for level 2 analysis, and the typical resilient modulus values for level 3 analysis. The resilient modulus input parameters library can be utilized when designing low volume roads in the absence of any basic soil testing. Based on the results of this study, the use of level 2 analysis for MEPDG resilient modulus input is recommended since the repeated load triaxial test for level 1 analysis is complicated, time consuming, expensive, and requires sophisticated equipment and skilled operators.

MEPDG Work Plan Task No. 7: Existing Pavement Input Information for the Mechanistic-Empirical Pavement Design Guide, 2009

The objective of this study is to systematically evaluate the Iowa Department of Transportation’s (DOT’s) existing Pavement Management Information System (PMIS) with respect to the input information required for Mechanistic-Empirical Pavement Design Guide (MEPDG) rehabilitation analysis and design. To accomplish this objective, all of available PMIS data for interstate and primary roads in Iowa were retrieved from the Iowa DOT PMIS. The retrieved data were evaluated with respect to the input requirements and outputs for the latest version of the MEPDG software (version 1.0). The input parameters that are required for MEPDG HMA rehabilitation design, but currently unavailable in the Iowa DOT PMIS were identified. The differences in the specific measurement metrics used and their units for some of the pavement performance measures between the Iowa DOT PMIS and MEPDG were identified and discussed. Based on the results of this study, it is recommended that the Iowa DOT PMIS should be updated, if possible, to include the identified parameters that are currently unavailable, but are required for MEPDG rehabilitation design. Similarly, the measurement units of distress survey results in the Iowa DOT PMIS should be revised to correspond to those of MEPDG performance predictions. *******************Large File**************************

Stream Stabilization in Western Iowa: Structure Evaluation and Design Manual, HR-385, 1998

Stream degradation is the action of deepening the stream bed and widening the banks due to the increasing velocity of water flow. Degradation is pervasive in channeled streams found within the deep to moderately deep loess regions of the central United States. Of all the streams, however, the most severe and widespread entrenchment occurs in western Iowa streams that are tributaries to the Missouri River. In September 1995 the Iowa Department of Transportation awarded a grant to Golden Hills Resource Conservation and Development, Inc. The purpose of the grant, HR-385 "Stream Stabilization in Western Iowa: Structure Evaluation and Design Manual", was to provide an assessment of the effectiveness and costs of various stabilization structures in controlling erosion on channeled streams. A review of literature, a survey of professionals, field observations and an analysis of the data recorded on fifty-two selected structures led to the conclusions presented in the project's publication, Design Manual, Streambed Degradation and Streambank Widening in Western Iowa. Technical standards and specifications for the design and construction of stream channel stabilization structures are included in the manual. Additional information on non-structural measures, monitoring and evaluation of structures, various permit requirements and further resources are also included. Findings of the research project and use and applications of the Design Manual were presented at two workshops in the Loess Hills region. Participants in these workshops included county engineers, private contractors, state and federal agency personnel, elected officials and others. The Design Manual continues to be available through Golden Hills Resource Conservation and Development.

Investigation of Two Bridge Alternatives for Low Volume Roads, Volume 1 of 2 Concept 1: Precast Steel Beam Units, HR-382, 1997

Recent reports have indicated that 23.5% of the nation's highway bridges are structurally deficient and 17.7% are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86% of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement. In a recent investigation (HR-365 "Evaluation of Bridge Replacement Alternatives for the County Bridge System") several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69%) have the ability and are interested in utilizing their own forces to design and construct short span bridges. In reviewing the results from HR-365, the research team developed one "new" bridge replacement concept and a modification of a replacement system currently being used. Both of these bridge replacement alternatives were investigated in this study, the results of which are presented in two volumes. This volume (Volume 1) presents the results of Concept 1 - Steel Beam Precast Units. Concept 2 - Modification of the Beam-in-Slab Bridge is presented in Volume 2. Concept 1, involves the fabrication of precast units (two steel beams connected by a concrete slab) by county work forces. Deck thickness is limited so that the units can be fabricated at one site and then transported to the bridge site where they are connected and the remaining portion of the deck placed. Since Concept 1 bridge is primarily intended for use on low-volume roads, the precast units can be constructed with new or used beams. In the experimental part of the investigation, there were three types of static load tests: small scale connector tests, "handling strength" tests, and service and overload tests of a model bridge. Three finite element models for analyzing the bridge in various states of construction were also developed. Small scale connector tests were completed to determine the best method of connecting the precast double-T (PCDT) units. "Handling strength" tests on an individual PCDT unit were performed to determine the strength and behavior of the precast unit in this configuration. The majority of the testing was completed on the model bridge [L=9,750 mm (32 ft), W=6,400 mm (21 ft)] which was fabricated using the precast units developed. Some of the variables investigated in the model bridge tests were number of connectors required to connect adjacent precast units, contribution of diaphragms to load distribution, influence of position of diaphragms on bridge strength and load distribution, and effect of cast-in-place portion of deck on load distribution. In addition to the service load tests, the bridge was also subjected to overload conditions. Using the finite element models developed, one can predict the behavior and strength of bridges similar to the laboratory model as well as design them. Concept 1 has successfully passed all laboratory testing; the next step is to field test it.

Investigation of Two Bridge Alternatives for Low Volume Roads - Phase II Volume 1 of 2 Concept 1: Steel Beam Precast Units, TR-410, 2000

This project continues the research which addresses the numerous bridge problems on the Iowa secondary road system. It is a continuation (Phase 2) of Project HR-382, in which two replacement alternatives (Concept 1: Steel Beam Precast Units and Concept 2: Modification of the Benton County Beam-in-Slab Bridge) were investigated. In previous research for concept 1, a precast unit bridge was developed through laboratory testing. The steel-beam precast unit bridge requires the fabrication of precast double-tee (PCDT) units, each consisting of two steel beams connected by a reinforced concrete deck. The weight of each PCDT unit is minimized by limiting the deck thickness to 4 in., which permits the units to be constructed off-site and then transported to the bridge site. The number of units required is a function of the width of bridge desired. Once the PCDT units are connected, a cast-in-place reinforced concrete deck is cast over the PCDT units and the bridge railing attached. Since the steel beam PCDT unit bridge design is intended primarily for use on low-volume roads, used steel beams can be utilized for a significant cost savings. In previous research for concept 2, an alternate shear connector (ASC) was developed and subjected to static loading. In this investigation, the ASC was subjected to cyclic loading in both pushout specimens and composite beam tests. Based on these tests, the fatigue strength of the ASC was determined to be significantly greater than that required in typical low volume road single span bridges. Based upon the construction and service load testing, the steel-beam precast unit bridge was successfully shown to be a viable low volume road bridge alternative. The construction process utilized standard methods resulting in a simple system that can be completed with a limited staff. Results from the service load tests indicated adequate strength for all legal loads. An inspection of the bridge one year after its construction revealed no change in the bridge's performance. Each of the systems previously described are relatively easy to construct. Use of the ASC rather than the welded studs significantly simplified the work, equipment, and materials required to develop composite action between the steel beams and the concrete deck.

Manual for Evaluation, Rehabilitation and Strengthening of Low Volume Bridges, HR-323, 1993

This report contains an evaluation and design manual for strengthening and replacing low volume steel stringer and timber stringer bridges. An advisory panel consisting of county and municipal engineers provided direction for the development of the manual. NBI bridge data, along with results from questionnaires sent to county and municipal engineers were used to formulate the manual. Types of structures shown to have the greatest need for cost-effective strengthening methods are steel stringer and timber stringer bridges. Procedures for strengthening these two types of structures have been developed. Various types of replacement bridges have also been included so that the most cost effective solution for a deficient bridge may be obtained. The key results of this study is an extensive compilation, which can be used by county engineers, of the most effective techniques for strengthening deficient existing bridges. The replacement bridge types included have been used in numerous low volume applications in surrounding states, as well as in Iowa. An economic analysis for determining the cost-effectiveness of the various strengthening methods and replacement bridges is also an important part of the manual. Microcomputer spreadsheet software for several of the strengthening methods, types of replacement bridges and for the economic analysis has been developed, documented and presented in the manual. So the manual, Chp. 3 of the final report, can be easily located, blue divider pages have been inserted to delineate the manual from the rest of the report.

Effects of Deicing Salt Trace Compounds on Deterioration of Portland Cement Concrete, HR-271, 1987

A study was made of the detrimental effects of trace amounts of calcium sulfate (occurring naturally in halite deposits used for deicing) on portland cement concrete pavements. It was found that sulfate introduced as gypsum with sodium chloride in deicing brines can have detrimental effects on portland cement mortar. Concentrations of sulfate as low as 0.5% of the solute rendered the brine destructive. Conditions of brine application were critical to specimen durability. The mechanisms of deterioration were found to be due to pore filling resulting from compound formation and deposition. A field evaluation of deteriorating joints suggests that the sulfate phenomena demonstrated in the laboratory also operates in the field. A preliminary evaluation was made of remedies: limits on sulfates, fly ash admixtures, treatment of existing pavement, and salt treatments. This report gives details of the research objectives, experimental design, field testing, and possible solutions. Recommendations for further study are presented.

Validation of Design Recommendations for Integral Abutment Piles, HR-292, 1989

Since integral abutment bridges decrease the initial and maintenance costs of bridges, they provide an attractive alternative for bridge designers. The objective of this project is to develop rational and experimentally verified design recommendations for these bridges. Field testing consisted of instrumenting two bridges in Iowa to monitor air and bridge temperatures, bridge displacements, and pile strains. Core samples were also collected to determine coefficients of thermal expansion for the two bridges. Design values for the coefficient of thermal expansion of concrete are recommended, as well as revised temperature ranges for the deck and girders of steel and concrete bridges. A girder extension model is developed to predict the longitudinal bridge displacements caused by changing bridge temperatures. Abutment rotations and passive soil pressures behind the abutment were neglected. The model is subdivided into segments that have uniform temperatures, coefficients of expansion, and moduli of elasticity. Weak axis pile strains were predicted using a fixed-head model. The pile is idealized as an equivalent cantilever with a length determined by the surrounding soil conditions and pile properties. Both the girder extension model and the fixed-head model are conservative for design purposes. A longitudinal frame model is developed to account for abutment rotations. The frame model better predicts both the longitudinal displacement and weak axis pile strains than do the simpler models. A lateral frame model is presented to predict the lateral motion of skewed bridges and the associated strong axis pile strains. Full passive soil pressure is assumed on the abutment face. Two alternatives for the pile design are presented. Alternative One is the more conservative and includes thermally induced stresses. Alternative Two neglects thermally induced stresses but allows for the partial formation of plastic hinges (inelastic redistribution of forces). Ductility criteria are presented for this alternative. Both alternatives are illustrated in a design example.

Thin Maintenance Surfaces - Phase II, TR-435, 2003

In recent years there has been renewed interest in using preventive maintenance techniques to extend pavement life and to ensure low life cycle costs for our road infrastructure network. Thin maintenance surfaces can be an important part of a preventive maintenance program for asphalt cement concrete roads. The Iowa Highway Research Board has sponsored Phase Two of this research project to demonstrate the use of thin maintenance surfaces in Iowa and to develop guidelines for thin maintenance surface uses that are specific to Iowa. This report documents the results of test section construction and monitoring started in Phase One and continued in Phase Two. The report provides a recommended seal coat design process based on the McLeod method and guidance on seal coat aggregates and binders. An update on the use of local aggregates for micro-surfacing in Iowa is included. Winter maintenance guidelines for thin maintenance surfaces are reported herein. Finally, Phase One's interim, qualitative thin maintenance surface guidelines are supplemented with Phase two's revised, quantitative guidelines. When thin maintenance surfaces are properly selected and applied, they can improve the pavement surface condition index and the skid resistance of pavements. For success to occur, several requirements must be met, including proper material selection, design, application rate, workmanship, and material compatibility, as well as favorable weather during application and curing. Specific guidance and recommendations for many types of thin maintenance surfaces and conditions are included in the report.

Modification of Ca-Montmorillonite by Low-Temperature Heat Treatment, HR-106, 1964

Objectives of this investigation were to measure the effects of moderate heat treatments (below the dehydroxylation temperature) on physical and chemical properties of a calcium-montmorillonite clay. Previous workers have noted the reduction in cation exchange capacity and swelling property after heating in the range 200 to 400°C, and have suggested several possible explanations, such as hysteresis effect, increased inter-layer attractions due to removal of inter-layer water, or changes in the disposition of inter-layer or layer surface ions. The liquid limits of Ca-montmorillonite were steadily decreased with increased temperature of treatment, levelling at about 450°C. The plastic limit decreased slightly up to 350°C, above which samples could no longer be rolled into threads. The gradual change is in contrast with sudden major changes noted for weight loss (maximum rates of change at l00°C and 500°C), glycol retention surface area (520°C), and d001 diffraction peak intensity (17.7 A spacing) and breadth after glycolation (530°C). Other properties showing more gradual reductions with heat treatment were amount of exchangeable calcium (without water soaking), cation exchange capacity by NH4AC method, and d001 intensity (21 A spacing) after storing at 100% r.h. one month and re-wetting with water. Previous water soaking allowed much greater release of fixed Ca++ up to 450°C. Similar results were obtained with cation exchange capacities when samples were treated with N CaCl2 solution. The 21.0 A peak intensity curve showed close similarity to the liquid limit and plastic index curves in the low temperature range, and an explanation is suggested.

Investigation of Two Bridge Alternatives for Low Volume Roads Volume 2 of 2 Concept 2: Beam In Slab Bridge, HR-382, 1997

Recent reports have indicated that 23.5% of the nation's highway bridges are structurally deficient and 17.7% are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86% of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement. In a recent investigation (HR-365 "Evaluation of Bridge Replacement Alternatives for the County Bridge System") several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69%) have the ability and are interested in utilizing their own forces to design and construct short span bridges. After reviewing the results from HR-365, the research team developed one "new" bridge replacement concept and a modification of a replacement system currently being used. Both of these bridge replacement alternatives were investigated in this study, the results of which are presented in two volumes. This volume (Volume 2) presents the results of Concept 2 - Modification of the Beam-in-Slab Bridge. Concept 1 - Steel Beam Precast Units is presented in Volume 1. Concept 2 involves various laboratory tests of the Beam-in-Slab bridge (BISB) currently being used by Benton County and several other Iowa counties. In this investigation, the behavior and strength of the BISB were determined; a new method of obtaining composite action between the steel beams and concrete was also tested. Since the Concept 2 bridge is primarily intended for use on low-volume roads, the system can be constructed with new or used beams. In the experimental part of the investigation, there were three types of laboratory tests: push-out tests, service and ultimate load tests of models of the BISB, and composite beam tests utilizing the newly developed shear connection. In addition to the laboratory tests, there was a field test in which an existing BISB was service load tested. An equation was developed for predicting the strength of the shear connection investigated; in addition, a finite element model for analyzing the BISB was also developed. Push-out tests were completed to determine the strength of the recently developed shear connector. A total of 36 specimens were tested, with variables such as hole diameter, hole spacing, presence of reinforcement, etc. being investigated. In the model tests of the BISB, two and four beam specimens [L=9,140 mm (30 ft)] were service load tested for behavior and load distribution data. Upon completion of these tests, both specimens were loaded to failure. In the composite beam tests, four beams, one with standard shear studs and three using the shear connection developed, were tested. Upon completion of the service load tests, all four beams were loaded to failure. The strength and behavior of the beams with the new shear connection were found to be essentially the same as that of the specimen with standard shear studs.

Non-Grouted Bonded PCC Overlay City of Oskaloosa, HR-528, 1993

Based upon the success the Iowa Department of Transportation has had using thin bonded, low slump, dense portland cement concrete on bridge decks for rehabilitation, it was decided to pursue research in the area of bonded portland cement concrete resurfacing of pavements. Since that time, in an effort to reduce costs, research was conducted into eliminating the grouting operation. On this project a non-grouted overlay was used to modernize an existing urban street. This research project is located in the City of Oskaloosa on 11th Avenue from South M Street to South Market Street. Construction of the project went well and the non-grouted overlay has performed very well to date.

Reinforced Slope with Geogrids, HR-548, 1997

The objective of this research study is to evaluate the performance, maintenance requirements and cost effectiveness of constructing reinforced slope along a concrete bikeway overpass with a Geogrid system such as manufactured by Tensar Corporation or Reinforced Earth Company. This final report consists of two separate reports - construction and performance. An earlier design report and work plan was submitted to the Iowa DOT in 1989. From the Design Report, it was determined that the reinforced slope would be the most economical system for this particular bikeway project. Preliminary cost estimates for other design alternatives including concrete retaining walls, gabions and sheet pile walls ranged from $204/L.F. to $220/L.F. The actual final construction cost of the reinforced slope with GEDGRIDS was around $112/L.F. Although, since the reinforced slope system was not feasible next to the bridge overpass because of design constraints, a fair cost comparison should reflect costs of constructing a concrete retaining wall. Including the concrete retaining wall costs raises the per lineal foot cost to around $122/L.F. In addition to this initial construction cost effectiveness of the reinforced slope, there has been little or no maintenance needed for this reinforced slope. It was noted that some edge mowing or weed whacking could be done near the concrete bikeway slab to improve the visual quality of the slope, but no work has been assigned to city crews. It was added that this kind of weed whacking over such steep slope is more difficult and there could possibly be more potential for work related injury. The geogrid reinforced slope has performed really well once the vegetation took control and prevented soil washing across the bikeway slab. To that end, interim erosion control measures might need to be considered in future projects. Some construction observations were noted. First, there i s no specialized experience or equipment required for a contractor to successfully build a low-to-medium geogrid reinforced slope structure. Second, the adaptability of the reinforced earth structure enables the designer to best fit the shape of the structure to the environment and could enhance aesthetic quality. Finally, a reinforced slope can be built with relatively soft soils provided differential settlements between facing are limited to one or two percent.