Comparison of Creep and Resilient Modulus Laboratory Results with Field Cores, HR-311, Part 3, 1993

This is Part 3 of a study of creep and resilient modulus testing of hot mix asphalt concrete. The creep and resilient modulus testing in Part 1 showed the improved load carrying characteristics of crushed particles. Cores from pavements drilled in Part 2 exhibited a poor correlation with rutting and creep/resilient modulus on pavement with a range of rut depths. The objective of Part 3 was to determine the relationship of creep and resilient modulus for 1) Marshall specimens from laboratory mixing for mix design; 2) Marshall specimens from construction plant mixing; and 3) cores drilled from the hot mixed asphalt pavement. The creep and resilient modulus data from these three sources exhibited substantial variations. No meaningful correlations of the results from these three sources were obtained.

Field Data Collection and Reporting Study, HR-377, 1997

A review of the Iowa Department of Transportation's field data collection and reporting system has been performed. Included were several systems used by the Office of Construction and Local Jurisdictions. The entire field data collection and reporting systems for asphalt cement concrete (ACC) paving, portland cement concrete (PCC) paving, and PCC structures were streamlined and computerized. The field procedures for materials acceptance were also reviewed. Best practices were identified and a method was developed to prioritize materials so transportation agencies could focus their efforts on high priority materials. Iowa State University researchers facilitated a discussion about Equal Employment Opportunity (EEO) and Affirmative Action (AA) procedures between the Office of Construction field staff and the Office of Contracts. A set of alternative procedures was developed. Later the Office of Contracts considered these alternatives as they developed new procedures that are currently being implemented. The job close-out package was reviewed and two unnecessary procedures were eliminated. Numerous other procedures were reviewed and flowcharted. Several changes have been recommended that will increase efficiency and allow staff time to be devoted to higher priority activities. It is estimated the improvements in ACC paving, PCC paving and structural concrete will by similar to three full time equivalent (FTE) positions to field construction, field materials and Office of Materials. Elimination of EEO interviews will be equivalent to one FTE position. It is estimated that other miscellaneous changes will be equivalent to at least one other FTE person. This is a total five FTEs. These are conservative estimates based on savings that are easily quantified. It is likely that total positive effect is greater when items that are difficult to quantify are considered.

Crack and Seat PCC Pavement Prior to Resurfacing US 59 - Shelby County, HR-527, 1993

Asphalt concrete resurfacing is the most commonly utilized rehabilitation practice used by the Iowa Department of Transportation. The major problem with asphalt concrete resurfacing is the reflective cracking from underlying cracks and joints in the portland cement concrete (PCC) pavement. Cracking and seating the PCC prior to an asphalt overlay was the construction method evaluated in this project. There was cracking and seating on portions of the project and portions were overlaid without this process. There were also different overlay thicknesses used. Comparisons of crack and seating to the normal overlay method and the different depths are compared in this report. Cracking and seating results in some structural loss, but does reduce the problem of reflection cracking.

Recycling of Portland Cement Concrete Roads in Iowa, MLR-77-6, 1977

We are depleting the once seemingly endless supply of aggregate available for concrete paving in Iowa. At the present time, some parts of our state do not have locally available aggregates of acceptable quality for portland cement concrete paving. This necessitates lengthy truck and rail hauls which frequently more than doubles the price of aggregate. In some parts of the state, the only coarse aggregates available locally are "d-cracking" in nature. Iowa's recycling projects were devised to alleviate the shortage of aggregates wherever they were found to have an economic advantage. We completed our first recycling project in 1976 on a 1.4 project in Lyon county. The data collected in this project was used to schedule two additional projects in 1977. The larger of these two projects is located in Page and Taylor county on Highway #2 and is approximately 15 miles in length. This material is to be crushed and re-used in the concrete paving, it is to be reconstructed on approximately the same alignment. The second project is part of the construction of Interstate I-680 north of council Bluffs where an existing 24 foot portland cement concrete roadway is to be recycled and used as the aggregate in the slip form econocrete subbase and the portland cement concrete shoulders.

The Effects of Crushed Particles in Asphalt Mixtures, HR-311 and MLR-88-16, 1990

One of the most serious impediments to the continued successful use of hot-mix asphalt (HMA) pavements is rutting. The Iowa Department of Transportation has required 85% crushed particles and 75-blow Marshall mix design in an effort to prevent rutting on Interstate roadways. Relationships between the percent of crushed particles and resistance to rutting in pavement through the use of various laboratory test procedures must be developed. HMA mixtures were made with 0, 30, 60, 85, and 100% crushed gravel, crushed limestone, and crushed quartzite combined with uncrushed sand and gravel. These aggregate combinations were used with 4, 5, and 6% asphalt cement (ac). Laboratory tests included Marshall stability, resilient modulus, indirect tensile, and creep. A creep resistance factor (CRF) was developed to provide a single numeric value for creep test results. The CRF values relate well to the amount of crushed particles and the perceived resistance to rutting. The indirect tensile test is highly dependent on the ac with a small effect from the percent of crushed particles. The Marshall stability from 75-blow compaction relates well to the percent of crushed particles. The resilient modulus in some cases is highly affected by grade of ac.

Durability Study of Type II Cements, MLR-71-03 and R-247, 1971

A study of type II cements at the Iowa State Highway Commission concluded that the amount of tricalcium aluminate in the cement appears to have an inverse effect on concrete durability. This conclusion agrees with the results of the Kansas Highway Department's study to determine the combination of cement and aggregate which would produce the best possible durability factor. This study is a result of the questions raised following the completion of the project at the Iowa State Highway Commission. This project is being conducted on a larger scale so. that more definite conclusions can be drawn. The purpose of this project is to determine if the amount of tricalcium aluminate in type II cements has an inverse effect on the durability of concrete.

Portable School Stop Signs and Other Non-Uniform School Stop Control Devices, HR-190, 1978

Portable (roll-out) stop signs are used at school crossings in over 300 cities in Iowa. Their use conforms to the Code of Iowa, although it is not consistent with the provisions of the Manual on Uniform Traffic Control Devices adopted for nationwide application. A survey indicated that most users in Iowa believe that portable stop signs provide effective protection at school crossings, and favor their continued use. Other non-uniform signs that fold or rotate to display a STOP message only during certain hours are used at school crossings in over 60 cities in Iowa. Their use does not conform to either the Code of Iowa or the Manual on Uniform Traffic Control Devices. Users of these devices also tend to favor their continued use. A survey of other states indicated that use of temporary devices similar to those used in Iowa is not generally sanctioned. Some unsanctioned use apparently occurs in several states, however. A different type of portable stop sign for school crossings is authorized and widely used in one state. Portable stop signs similar to those used in Iowa are authorized in another state, although their use is quite limited. A few reports in the literature reviewed for this research discussed the use of portable stop signs. The authors of these reports uniformly recommended against the use of portable or temporary traffic control devices. Various reasons for this recommendation were given, although data to support the recommendation were not offered. As part of this research, field surveys were conducted at 54 locations in 33 communities where temporary stop control devices were in use at school crossings. Research personnel observed the obedience to stop control and measured the vehicular delay incurred. Stopped delay averaged 1.89 seconds/entering vehicle. Only 36.6 percent of the vehicles were observed to come to a complete stop at the study locations controlled by temporary stop control devices. However, this level of obedience does not differ from that observed at intersections controlled by permanent stop signs. Accident experience was compiled for 76 intersections in 33 communities in Iowa where temporary stop signs were used and, for comparative purposes, at 76 comparable intersections having other forms of control or operating without stop control. There were no significant differences in accident experience An economic analysis of vehicle operating costs, delay costs, and other costs indicated that temporary stop control generated costs only about 12 percent as great as permanent stop control for a street having a school crossing. Midblock pedestrian-actuated signals were shown to be cost effective in comparison with temporary stop signs under the conditions of use assumed. Such signals could be used effectively at a number of locations where temporary stop signs are being used. The results of this research do not provide a basis for recommending that use of portable stop signs be prohibited. However, erratic patterns of use of these devices and inadequate designs suggest that improved standards for their use are needed. Accordingly, nine recommendations are presented to enhance the efficiency of vehicular flow at school crossings, without causing a decline in the level of pedestrian protection being afforded.

Improved Asphalt Surfaces and Asphalt Resurfacing Performance through Crack Maintenance, HR-213, 1987

In 1980, a Vanguard High Pressure Water Blaster capable of providing 10 gallons of water per minute at 2000 psi was purchased to evaluate water blasting as a crack cleaning method prior to crack filling on asphalt concrete pavements. Afer some iniital trials demonstrated its effectiveness of removing dirt, debris and vegetation, it was included in joint and crack maintenance research on Iowa 7 in Webster County. The objective of the research was to evaluate six crack preparation methods and seven "sealant" materials. The cleaning and sealing was performed in the spring of 1983. Visual evaluations of the performance were made in the fall of 1983 and spring of 1985. Compressed air and/or high pressure water did not adequately prepare cracks less than 3/8 inch wide. Routing or sawing was necessary to provide a sealant reservoir. The water blaster was more effective than compressed air in removing dirt, debris and vegetation but this did not yield significant improvement in sealant adhesion or longevity. Periodic crack filling is necessary on ACC surfaces throughout the remaining life of the pavement.

Alternatives for Rural Roads, HR-242, 1989

Much of the nation's rural road system is deteriorating. Many of the roads were built in the 1880s and 1890s with the most recent upgrading done in the 1940s and 1950s. Consequently, many roads and bridges do not have the capacity for the increased loads, speed, and frequent use of today's vehicles. Because of the growing demands and a dense county road system (inherited from the land settlement policies two centuries ago), revenue available to counties is inadequate to upgrade andmaintain the present system. Either revenue must be increased - an unpopular option - or costs must be reduced. To examine cost-saving options, Iowa State University conducted a study of roads and bridges in three 100 square mile areas in Iowa: • A suburban area • A rural area with a large number of paved roads, few bridges, and a high agricultural tax base and •A more rural area in a hilly terrain with many bridges and gravel roads, and a low agricultural tax base. A cost-benefit analysis was made on the present road system in these areas on such options as abandoning roads with limited use, converting some to private drives, and reducing maintenance on these types of roads. In only a few instances does abandonment of low traffic volume roads produce cost savings for counties and abutting land owners that exceed the additional travel costs to the public. In this study, the types of roads that produced net savings when abandoned were: • A small percentage (less than 5 percent) of the nonpaved county roads in the suburban area. However, net savings were very small. Cost savings from reducing the county road system in urbanized areas are very limited. • Slightly more than 5 percent of the nonpaved county roads in the most rural area that had a small number of paved county roads. • More than 12 percent of the nonpaved roads in the rural area that had a relatively large number of paved county and state roads. Converting low-volume roads to low-maintenance or Service B roads produces the largest savings of all solutions considered. However, future bridge deterioration and county liability on Service B roads are potential problems. Converting low-volume roads to private drives also produces large net savings. Abandonment of deadend roads results in greater net savings than continuous roads. However, this strategy shifts part of the public maintenance burden to land owners. Land owners also then become responsible for accident liability. Reconstruction to bring selected bridges with weight restrictions up to legal load limits reduces large truck and tractor-wagon mileage and costs. However, the reconstruction costs exceeded the reduction in travel costs. Major sources of vehicle miles on county roads are automobiles used for household purposes and pickup truck travel for farm purposes. Farm-related travel represents a relatively small percent of total travel miles, but a relatively high percentage of total travel costs.

Engineering Study for the Evaluation of Public Road Administration and Maintenance Alternatives, Executive Summary for HR-265, 1985

Iowa's public road system of 112,000 miles is one of the largest and the best in the nation. It represents a considerable financial investment of taxpayer revenues over the years. And, it requires a sustained investment to preserve an economical level of transport service into the future. In 1982, a Governor's Blue Ribbon Transportation Task Force evaluated the effectiveness of Iowa's entire transportation system. Four important Task Force recommendations dealt with public road administrative issues in Iowa. These issues were related to: 1. design criteria and levels of maintenance 2. consistency in the use of standards among jurisdictions 3. consolidation of maintenance operations at one jurisdictional level and 4. jurisdictional authority for roads. The issues formed the background for Research Project HR-265.

Development of an Economic Dust Palliative for Limestone Surfaced Secondary Roads, HR-297, 1990

This research project was directed at laboratory and field evaluation of sodium montmorillonite clay (bentonite) as a dust palliative for limestone surfaced secondary roads. It had been postulated that the electrically charged surfaces of the clay particles could interact with the charged surfaces of the limestone and act as a bonding agent to agglomerate fine (-#200) particulates and also to band the fine particulates to larger (+#200) limestone particles. Laboratory testing using soda ash dispersed bentonite treatment of limestone fines indicated significant improvement of compressive strength and slaking characteristics. It was recommended that the project proceed to field trials and test roads were constructed in Dallas and Adair counties in Iowa. Soda ash dispersed bentonite solutions can be field mixed and applied with conventional spray distribution equipment. A maximum of 1.5% bentonite(by weight of aggregate)can be applied at one time. Higher applications would have to be staged allowing the excess moisture to evaporate between applications. Construction of higher application treatments can be accomplished by adding dry bentonite to the surfacing material and then by dry road mixing. The soda ash water solution can then be spray applied and the treated surfacing material wet mixed by motor graders to a consistency of 3 to 4 inch slump concrete. Two motor graders working in tandem can provide rapid mixing for both methods of construction. Calcium and magnesium chloride treatments are 2 to 3 times more effective in dust reduction in the short term (3-4 months) but are prone to washboarding and potholing due to maintenance restrictions. Bentonite treatment at the 2-3% level is estimated to provide a 30-40% dust reduction over the long term(18-24 months). Normal maintenance blading operations can be used on bentonite treated areas. Vehicle braking characteristics are not adversely affected up to the 3.0% treatment level. The bentonite appears to be functioning as a banding agent to bind small particulates to larger particles and is acting to agglomerate fine particles of limestone. This bonding capability appears recoverable from environmental effects of winter, and from alternating wet and dry periods. The bentonite appears to be able to interact with new applications of limestone maintenance material and maintains a dust reduction capability. Soda ash dispersed bentonite treatment is approximately 10 times more cost effective per percent dust reduction than conventional chloride treatments with respect to time. However,the disadvantage is that there is not the initial dramatic reduction in dust generation as with the chloride treatment. Although dust is reduced 30-40% after treatment there is still dust being generated and the traveling public or residents may not perceive the reduction.

Bentonite Treatment for Economical Dust Reduction on Limestone Surfaced Secondary Roads, HR-351, 1995

This research project was directed at laboratory and field evaluation of sodium montmorillonite clay (Bentonite) as a dust palliative for limestone surfaced secondary roads. It was postulated that the electrically charged surfaces (negative) of the clay particles could interact with the charged surfaces (positive) of the limestone and act as a bonding agent to agglomerate fine (-#200) particulates, and also to bond the fine particulates to larger (+#200) limestone particles. One mile test roads were constructed in Tama, Appanoose, and Hancock counties in Iowa using Bentonite treatment levels (by weight of aggregate) ranging from 3.0 to 12.0%. Construction was accomplished by adding dry Bentonite to the surfacing material and then dry road mixing. The soda ash/water solution (dispersing agent) was spray applied and the treated surfacing material wet mixed by motor graders to a consistency of 2 to 3 inch slump concrete. Two motor graders working in tandem provided rapid mixing. Following wet mixing the material was surface spread and compacted by local traffic. Quantitative and qualitative periodic evaluations and testing of the test roads was conducted with respect to dust generation, crust development, roughness, and braking characteristics. As the Bentonite treatment level increased dust generation decreased. From a cost/benefit standpoint, an optimum level of treatment is about 8% (by weight of aggregate). For roads with light traffic, one application at this treatment level resulted in a 60-70% average dust reduction in the first season, 40-50% in the second season, and 20-30% in the third season. Crust development was rated at two times better than untreated control sections. No discernible trend was evident with respect to roughness. There was no evident difference in any of the test sections with respect to braking distance and braking handling characteristics, under wet surface conditions compared to the control sections. Chloride treatments are more effective in dust reduction in the short term (3-4 months). Bentonite treatment is capable of dust reduction over the long term (2-3 seasons). Normal maintenance blading operations can be used on Bentonite treated areas. Soda ash dispersed Bentonite treatment is estimated to be more than twice as cost effective per percent dust reduction than conventional chloride treatments, with respect to time. However, the disadvantage is that there is not the initial dramatic reduction in dust generation as with the chloride treatment. Although dust is reduced significantly after treatment there is still dust being generated. Video evidence indicates that the dust cloud in the Bentonite treated sections does not rise as high, or spread as wide as the cloud in the untreated section. It also settles faster than the cloud in the untreated section. This is considered important for driving safety of following traffic, and for nuisance dust invasion of residences and residential areas. The Bentonite appears to be functioning as a bonding agent.

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.

Longitudinal Grinding and Transverse Grooving to Improve Frictional and Profile Properties, HR-1035, 1983

There are many miles of portland cement concrete pavement in Iowa that due to normal wear, and in some cases accelerated wear from studded tires, the surface has become polished resulting in less than desirable friction values. Retexturing the surface may be an economical way to re-establish desirable friction values. Retexturing by grinding with diamond blades and transverse grooving with diamond blades are two methods of rehabilitating p.c.c. surfaces. MU Inc. of Lebanan, Tennessee proposed to provide without charge to the Iowa Department of Transportation, one 1500 ft x 12 ft section each of three methods of texturing. They are longitudinal grinding, transverse grooving and longitudinal grinding followed by transverse grooving. A section of 1500 feet is needed to properly evaluate a texturing method. It was decided by Iowa DOT personnel that due to possible differential friction it would be undesirable to texture only one lane. The decision was made to do test sections of 1500 ft x 24 ft with the cost of the additional texturing paid by the Iowa DOT. Iowa also has areas where the p.c.c. pavement has faulted at the joints and cracks which results in poor riding quality. Methods of correcting the faulting are to underseal the pavement where needed and/or grinding the surface to eliminate the faulted areas. It was decided to include in this research project a section for profiling by grinding.

Iowa D.O.T's Experience with Recycling Portland Cement Pavement and Asphalt Cement Pavement, MLR-77-4, 1977

This report provides details of IADOT's experience removing and crushing asphaltic concrete and portland cement concrete for recycling. The recycled material was used on interstate highways for the subbase and shoulders. The major problem IADOT encountered on this project was the removal of reinforcing steel from the broken concrete. The contractor used hydraulic powered shears to clip off all protruding steel during the removal and loading of the concrete on the grade. This project took place in 1977.