Characteristics of Iowa Fine Aggregate, MLR-92-6, 1996

The objective of this research was to evaluate the quality (angularity, mortar strengths and alkali-silica reactivity) of fine aggregate for Iowa portland cement concrete (PCC) pavements. Sands were obtained from 30 sources representative of fine aggregate across Iowa. The gradation, fineness modulus and mortar strengths were determined for all sands. Angularity was evaluated using a new National Aggregate Association (NAA) flow test. The NAA uncompacted void values are significantly affected by the percent of crushed particles and are a good measure of fine aggregate angularity. The alkali-silica reactivity of Iowa sands was measured by the ASTM P214 test. By P214 many Iowa sands were identified as being reactive while only two were innocuous. More research is needed on P214 because pavement performance history has shown very little alkali-silica reactivity deterioration of pavement. Six of the sands tested by P214 were evaluated using the Canadian Prism Test. None were identified as being reactive by the Canadian Prism Test.

Permeability of Granular Subbase Materials, MLR-90-4, 1991

The purpose of this research was to evaluate the materials Iowa uses as a granular subbase and to determine if it provides adequate drainage. Numerous laboratory and in-situ tests were conducted on the materials currently being used in Iowa. The follow conclusions can be made based on the test results: 1. The crushed concrete that is used as a subbase material has a relatively low permeability compared to many other materials used by other states. 2. Further research and tests are needed to find the necessary parameters for crushed concrete to make sure it is providing its optimum drainage and preventing premature damage of the pavement. 3. We have definitely made improvements in drainage in the past few months, but there are many areas that we can improve on that will increase the permeability of this material and insure that the pavement system is safe from premature damage due to water. The current gradation specification for granular subbase material at the start of this study was: Sieve # % Passing 1” 100 #8 10-35 #50 0-15 #200 0-6

Correlation of the IJK Roadmeter to the International Roughness Index, MLR-91-5, 1992

The Iowa Department of Transportation has been determining a present serviceability index (PSI) on the primary highway system since 1968. A CHLOE profilometer has been used as the standard for calibrating the Roadmeters that do the system survey. The current Roadmeter, an IJK Iowa DOT developed unit, is not considered an acceptable Roadmeter for determining the FHWA required International Roughness Index (IRI). Iowa purchased a commercial version of the South Dakota type profile (SD Unit) to obtain IRI. This study was undertaken to correlate the IRI to the IJK Roadmeter and retire the Roadmeter. One hundred forty-seven pavement management sections (IPMS) were tested in June and July 1991 with both units. Correlation coefficients and standard error of estimates were: r' Std. Error PCC pavements 0.81 0.15 Composite pavements 0.71 0.18 ACC pavements 0.77 0.17 The correlation equations developed from this work will allow use of the IRI to predict the IJK Roadmeter response with sufficient accuracy. Trend analysis should also not be affected.

PC Concrete Texturing, R-246, 1975

Skid resistance is a major concern of the safety engineer since wet pavement conditions are present for approximately 18% of the total accidents in Iowa according to studies by the Traffic and Safety Department. Many of these accidents may be influenced by the low skid resistant quality of the pavement. The size, shape, type, and arrangement of the concrete's particles interrelate with each other in a complex manner to give us frictional resistance. The purpose of this investigation was to determine which method of texturing provides the best skid resistance properties on portland cement concrete pavement.

Evaluation of the Argentine Nondestructive Test for Determining Concrete Compressive Strength, R-269 and MLR-75-2, 1975

The compressive strength of concrete is an important factor in the design of concrete structures and pavements. To assure the quality of the concrete placed at the project, concrete compressive cylinders are made at the jobsite. These cylinders undergo a destructive test to determine their compressive strength. However, the determination of concrete compressive strength of the concrete actually in the structure or pavement is frequently desirable. For this reason, a nondestructive test of the concrete is required. A nondestructive test of concrete compressive strength should be economical, easily performed by field personnel, and capable of producing accurate, reproducible results. The nondestructive test should be capable of detecting the extent of poor concrete in a pavement or structure due to improper handling, placement, or variations in mixing or materials.

Cracking and Seating to Retard Reflective Cracking - Fremont County, HR-279, 1993

The concept of cracking and seating a portland cement concrete (pcc) pavement prior to laying an asphalt cement concrete (acc) surface in order to reduce reflection cracking has been around since the 1950s. With the advent of improved cracking equipment, this method gained renewed interest in the 1970s and 1980s. This project incorporated six test sections of which four were cracked and seated prior to being overlaid. Fremont County decided to utilize only a 0.9 m (3 ft) cracking pattern based on a 30 m (100 ft) trial test section. Pavement cracking appeared to be effective in reducing primarily longitudinal reflectance cracking, but only marginally successful in the reduction of transverse reflective cracking.

Iowa Development of Roller Compacted Concrete, HR-300, 1989

Roller compacted concrete (RCC) is a zero slump portland cement concrete mixture that has been used since the early 1970's in massive concrete structures. Iowa Highway Research Board project HR-300 was established to determine if this type mix could be used to pave roads on the Iowa road system. Manatt's Inc. of Brooklyn, Iowa agreed to pave an 800 ft. x 22 ft. x 10 in. section of RCC pavement in their Ames construction yard. This report discusses the construction of the test slab and interprets test results conducted during and after construction. It was observed that RCC can be placed with conventional asphalt paving equipment. However, there are several problems with RCC paving which must be resolved before RCC can become a viable paving alternative on Iowa's roadway system.

Bond Enhancement Techniques for PCC Whitetopping, HR-341, 1996

This research was initiated in 1991 as a part of a whitetopping project to study the effectiveness of various techniques to enhance bond strength between a new portland cement concrete (PCC) overlay and an existing asphalt cement concrete (ACC) pavement surface. A 1,676 m (5,500 ft) section of county road R16 in Dallas County was divided into 12 test sections. The various techniques used to enhance bond were power brooming, power brooming with air blast, milling, cement and water grout, and emulsion tack coat. Also, two sections were planed to a uniform cross-section, two pavement thicknesses were placed, and two different concrete mix proportions were used. Bond strength was perceived to be the key to determining an appropriate design procedure for whitetopping. If adequate bond is achieved, a bonded PCC overlay technique can be used for design. Otherwise, an unbonded overlay procedure may be more appropriate. Conclusions are as follows: (1) Bond Strength Differences - Milling increased bond strength versus no milling. Tack coat showed increased bond strength versus no tack coat. Planing, Air Blast and Grouting did not provide noticeable improvements in bond strength; nor did different PCC types or thicknesses affect bond strength significantly. (2) Structure - Structural measurements correlated strongly with the wide variation in pavement thicknesses. They did not provide enough information to determine the strength of bonding or the level of support being provided by the ACC layer. Longitudinal cracking correlated with PCC thicknesses and with planing. (3) Bond Over Time - The bond between PCC and ACC layers is degrading over time in the outside wheel path in all of the sections except tack coat (section 12). The bond strength in the section with tack coat was lower than the others, but remained relatively steady.

Dynamic Deflections to Determine Roadway Support Ratings, HR-245, 1983

The Benkelman Beam structural test of flexible pavements was replaced in 1976 by dynamic deflection testing with a model 400 Road Rater. The Road Rater is used to determine structural ratings of flexible pavements. New pavement construction in Iowa has decreased with a corresponding increase of restoration and rehabilitation. A method to determine structural ratings of layered systems and rigid pavements is needed to properly design overlay thickness. The objective of this research was to evaluate the feasibility of using the Road Rater to determine support values of layered systems and rigid pavements. This evaluation was accomplished by correlating the Road Rater with the Federal Highway Administration (FHWA) Thumper, a dynamic deflection testing device. Data were obtained with the Road Rater and Thumper at 411 individual test locations on 39 different structural sections ranging from 10" of PCC pavement and 25" of asphalt pavement to a newly graveled unpaved roadway. A high correlation between a 9000 pound Thumper deflection and the 1185 pound Road Rater deflection was obtained. A Road Rater modification has been completed to provide 2000 pound load inputs. The basin, defined by four sensors spaced at 1 foot intervals, resulting from the 2000 pound loading is being used to develop a graph for determining relative subgrade strengths. Road Rater deflections on rigid pavements are sufficient to support the potential for this technique.

A Nondestructive Method for Determining the Thickness of Sound Concrete on Older Pavements, HR-250, 1983

The primary purpose of this project was to assess the potential of a nondestructive remote sensing system, specifically, ground penetrating subsurface interface radar, for identification and evaluation of D-cracking pavement failures. A secondary purpose was to evaluate the effectiveness of this technique for locating voids under pavements and determining the location of steel reinforcement. From the data collected and the analysis performed to date, the following conclusions can be made regarding the ground penetrating radar system used for this study: (1) steel reinforcement can be accurately located; (2) pavement thickness can be determined; (3) distressed areas in pavements can be located and broadly classified as to severity of deterioration; (4) voids under pavements can be located; and (5) higher resolution recording equipment is required to accurately determine both the thickness of sound pavement remaining over distressed areas and the depth of void areas under pavements.

Special Surface Preparation Prior to Bituminous Overlays, HR-231, 1987

Research project HR-231, "Special Surface Preparation Prior to Bituminous Overlay", was initiated in 1982 to study the effectiveness of three different crack fillers in extending pavement life. In particular, this project was designed to determine if any of the fillers could substantially reduce the rate of subsurface deterioration and general deterioration of an asphalt pavement at crack locations. This project also sought to determine the effects of the various crack filling procedures on different thicknesses of bituminous overlays. The three fillers, a fly ash slurry, an emulsion, and a rubberized asphalt mixture, were used along with a control section with no crack filler material on a 2.5 mile section of Cerro Gordo Trunk Route S-25 south of the town of Thornton. This report discusses the construction and performance of each filler material and makes recommendations concerning future use of any of the materials used.

Reducing the Problem of Transverse Cracking, HR-232, 1985

The Iowa Department of Transportation (DOT) is continually improving the pavement management program and striving to reduce maintenance needs. Through a 1979 pavement management study, the Iowa DOT became a participant in a five state Federal Highway Administration (FHWA) study of "Transverse Cracking of Asphalt Pavements". There were numerous conclusions and recommendations but no agreement as to the major factors contributing to transverse cracking or methods of preventing or reducing the occurrence of transverse cracking. The project did focus attention on the problem and generated ideas for research. This project is one of two state funded research projects that were a direct result of the FHWA project. Iowa DOT personnel had been monitoring temperature susceptibility of asphalt cements by the Norman McLeod Modified Penetration Index. Even though there are many variables from one asphalt mix to another, the trend seemed to indicate that the frequency of transverse cracking was highly dependent on the temperature susceptibility. Research project HR-217 "Reducing the Adverse Effects of Transverse Cracking" was initiated to verify the concept. A final report has been published after a four-year evaluation. The crack frequency with the high temperature susceptible asphalt cement was substantially greater than for the low temperature susceptible asphalt cement. An increased asphalt cement content in the asphalt treated base also reduced the crack frequency. This research on prevention of transverse cracking with fabric supports the following conclusions: 1. Engineering fabric does not prevent transverse cracking of asphalt cement concrete. 2. Engineering fabric may retard the occurrence of transverse cracking. 3. Engineering fabric does not contribute significantly to the structural capability of an asphalt concrete pavement.

Effect of Mix Times on PCC Properties, HR-1066, 1998

The objectives of this research were the collection and evaluation of the data pertaining to the importance of concrete mixing time on air content and distribution, consolidation and workability for pavement construction. American Society for Testing and Materials (ASTM) standard C 94 was used to determine the significance of the mixing time on the consistency of the mix being delivered and placed on grade. Measurements of unit weight, slump, air content, retained coarse aggregate and compressive strength were used to compare the consistency of the mix in the hauling unit at the point of mixing and at the point placement. An analysis of variance was performed on the data collected from the field tests. Results were used to establish the relationship between selected mixing time and the portland cement concrete properties tested. The results were also used to define the effect of testing location (center and side of truck, and on the grade) on the concrete properties. Compressive strength test concepts were used to analyze the hardened concrete pavement strength. Cores were obtained at various locations on each project on or between vibrator locations to evaluate the variance in each sample, between locations, and mixing times. A low-vacuum scanning electron microscope (SEM) was used to study air void parameters in the concrete cores. Combining the data from these analysis thickness measurements and ride in Iowa will provide a foundation for the formulation of a performance based matrix. Analysis of the air voids in the hardened concrete provides a description of the dispersion of the cemtitious materials (specifically flyash) and air void characteristics in the pavement. Air void characteristics measured included size, shape and distribution.

Evaluation of Preformed Neoprene Joint Seals, HR-318, 1994

Most pavement contraction joint seals in Iowa, in general, have been performing in less than a satisfactory manner. The effective life of the seals, in maintaining a watertight joint, has been only from two to five years. In search of improvements, research was proposed to evaluate preformed neoprene joint seals. The performance of those seals was to be compared mainly with the hot poured rubberized asphalt sealants and cold applied silicone sealants or other sealants commonly used at the time this research began. Joint designs and methods of sawing were also investigated. All evaluations were done in new portland cement concrete (PCC) pavements. Three projects were initially selected and each included a research section of joint sealing. Some additional sites were later added for evaluation. Several joint sealants were evaluated at each research site. The various sites included high, medium and low levels of traffic. Evaluations were done over a five-year period. Neoprene joint seals provided better performance than hot or cold field formed joints.

Measurement of Ice Scraping Forces on Snow-Plow Underbody Blades, HR-372, 1997

In this study, several new cutting edges for removal of ice from the roadway were tested in a series of closed road tests. These new cutting edges consisted of a variety of serrated shapes. The study also included measurement of ice scraping forces by in-service trucks. These trucks were instrumented in a similar manner as the truck used in the closed-road tests. Results from the closed-road and in-service tests were analyzed by two parameters. The first parameter is the scraping effectiveness, which is defined as the average horizontal force experienced by a cutting edge. The amount of ice scraped from the roadway is directly proportional to the magnitude of the scraping effectiveness. Thus an increase in scraping effectiveness indicates an increase in the amount of ice being scraped from the roadway. The second parameter is force angle, which is defined as tan to the -1 power [vertical force/horizontal force]. A combination of a minimal force angle and a maximized scraping effectiveness represents a case in which the maximal amount of ice is being removed from the pavement without an exceptionally large vertical force. Results indicate that each cutting edge produced a maximal scraping effectiveness with a testing configuration of a 15 deg blade angle and a 23,000 lb. download force. Results also indicate that each cutting edge produced a minimal force angle with a testing configuration of a 15 deg blade angle and a 10,000 lb. download force. Results from the in-service trucks produced similar data and also similar trends within the data when compared to the results of the closed-road tests. This result is most important, as it suggests that the closed-road tests do provide an accurate measure of ice scraping forces for a given blade and configuration of that blade. Thus if the closed-road tests indicate that certain blades perform well, there is now excellent reason to conduct full scale tests of such blades.