Relationship of Carbonate Aggregates to Concrete Aging, HR-116, 1967

HR-116 is concerned with the relationship of carbonate aggregate to aging of highway concrete. The ultimate purpose of the research is to provide the Materials Department with better criteria for selection of carbonate aggregates for use in highway concrete. The research stems from the problem in Iowa which relates durability of highway concrete to use of certain aggregates. Service records of certain highways have shown that concrete deterioration is related to the source of coarse carbonate aggregate. Research on this problem in projects HR-15 and HR-86 helped define three broad areas of the problem in more detail: 1. The problem of evaluation of rocks which pass current specifications but have poor service records 2. The basic problem of how rocks contribute to distress in concrete 3. The problem of how concrete ages or weathers.

Evaluation of Gap-Graded Asphalt Concrete Mixtures, Vol. 1. Physical Properties (Part I: Mechanical Properties), HR-157, Volume 1, 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper-combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100(d/D)^n is not justified. It is recommended that the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Evaluation of Gap-Graded Asphalt Concrete Mixtures Part II: Statistical Design and Analysis, HR-157, 1973

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3, 960 Marshall and Hveem specimens were examined. The main thrust of the statistical analysis conducted in this experiment was in the calibration study and in Part I of the experiment. In the former study, the compaction procedure between the Iowa State University Lab and the Iowa Highway Commission Lab was calibrated. By an analysis of the errors associated with the measurements we were able to separate the "preparation" and "determination" errors for both laboratories as well as develop the calibration curve which describes the relationship between the compaction procedures at the two labs. In Part I, the use of a fractional factorial design in a split plot experiment in measuring the effect of several factors on asphalt concrete strength and weight was exhibited. Also, the use of half normal plotting techniques for indicating significant factors and interactions and for estimating errors in experiments with only a limited number of observations was outlined,

Evaluation of Gap-Graded Asphalt Concrete Mixtures Vol. 3. Appendix, HR-157, Volume 3 (Part 3), 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100 (d/D)n is not justified. It is recommended that. the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Mission-Oriented Dust Control and Surface Improvement Processes for Unpaved Roads, HR-194, 1981

Six subject areas prompted the broad field of inquiry of this mission-oriented dust control and surface improvement project for unpaved roads: • DUST--Hundreds of thousands of tons of dust are created annually by vehicles on Iowa's 70,000 miles of unpaved roads and streets. Such dust is often regarded as a nuisance by Iowa's highway engineers. • REGULATIONS--Establishment of "fugitive dust" regulations by the Iowa DEQ in 1971 has created debates, conferences, legal opinions, financial responsibilities, and limited compromises regarding "reasonable precaution" and "ordinary travel," both terms being undefined judgment factors. • THE PUBLIC--Increased awareness by the public that regulations regarding dust do in fact exist creates a discord of telephone calls, petitions, and increasing numbers of legal citations. Both engineers and politicians are frustrated into allowing either the courts or regulatory agencies to resolve what is basically a professional engineering responsibility. • COST--Economics seldom appear as a tenet of regulatory strategies, and in the case of "fugitive dust," four-way struggles often occur between the highway professions, political bodies, regulatory agencies, and the general public as to who is responsible, what can be done, how much it will cost, or why it wasn't done yesterday. • CONFUSION--The engineer lacks authority, and guidelines and specifications to design and construct a low-cost surf acing system are nebulous, i.e., construct something between the present crushed stone/gravel surface and a high-type pavement. • SOLUTION--The engineer must demonstrate that dust control and surface improvement may be engineered at a reasonable cost to the public, so that a higher degree of regulatory responsibility can be vested in engineering solutions.

Effects of Special Aggregate on Bridge Deck Overlay Frictional Properties, HR-205, 1986

The Iowa DOT has been using the "Iowa Method" thin bonded low-slump dense Portland Cement Concrete (PCC) bridge deck overlay for rehabilitation of delaminated decks since 1963. In time, continued use of studded tires will wear away the transverse grooved texture. The objective of this research was to evaluate the benefit of incorporating a hard durable aggregate into a dense PCC overlay to provide frictional property longevity. The project included three overlays on I-35 near Ankeny. The texture and friction properties of two overlays, one constructed with crushed granite and the other with crushed quartzite coarse aggregate, were compared to an overlay constructed with locally available crushed limestone. There were no construction problems resulting from the use of crushed granite or quartzite. There was no significant frictional property benefit from the crushed granite or crushed quartzite through six years.

The Relationship of Ferroan Dolomite Aggregate to Rapid Concrete Deterioration, HR-266, 1987

Some of Iowa's 13,200 miles of portland cement concrete (pcc) pavement have remained structurally sound for over 50 years while others have suffered premature deterioration. Research has shown that the type of coarse aggregate used in the pcc is the major cause of this premature deterioration. Some coarse aggregates for concrete exhibit a nonuniform performance history. They contribute to premature deterioration on heavily salted primary roadways while providing long maintenance-free life on unsalted secondary pavements. This inconsistency supports the premise that there are at least two mechanisms that contribute to the deterioration. Previous research has shown that one of these mechanisms is a bad pore system. The other is apparently a chemical reaction. The objective of this research is to develop simple rapid test methods to predict the durability of carbonate aggregate in pcc pavement. X-ray diffraction analyses of aggregate samples have been conducted on various beds from numerous quarries producing diffraction plots for more than 200 samples of dolomitic or dolomite aggregates. The crystalline structures of these dolomitic aggregates show maximum-intensity dolomite/ankerite peaks ranging from a d-spacing of 2.884 angstroms for good aggregates to a d-spacing of 2.914 angstroms for nondurable aggregates. If coarse aggregates with known bad pore systems are removed from this summary, the d-spacing values of the remaining aggregates correlate very well with expected service life. This may indicate that the iron substitution for magnesium in the dolomite crystal is associated with the instability of the ferroan dolomite aggregates in pcc pavement.

The Effects of Crushed Particles in Asphalt Mixtures, HR-311 and MLR-88-16, Part 1, 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. The objective of this research and report is to develop relation~hips between the percent of crushed particles and resistance to rutting in pavement through the use of various laboratory test procedures. 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 testing 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.

Relating Creep Testing to Rutting of Asphalt Concrete Mixes, HR-311, Part 2, 1991

The Iowa Department of Transportation began creep and resilient modulus testing of asphalt concrete mixtures in 1989. Part 1 of this research reported in January 1990 was a laboratory study of hot mix asphalt (HMA) mixtures made with O, 30, 60, 85 and 100% crushed gravel, crushed limestone and crushed quartzite combined with uncrushed sand and gravel. Creep test results from Marshall specimens related well to the percent of crushed particles and the perceived resistance to rutting. The objective of this research, part 2, was to determine if there was a meaningful correlation between pavement rut depth and the resilient modulus or the creep resistance factor. Four and six inch diameter cores were drilled from rutted primary and interstate pavements and interstate pavements with design changes intended to resist rutting. The top 2 1/2 inches of each core, most of which was surface course, was used for creep and resilient modulus testing. There is a good correlation between the resilient modulus of four and six inch diameter cores. Creep resistance factors of four and six inch diameter cores also correlated well. There is a poor correlation between resilient modulus and the creep resistance factor. The rut depth per million 18,000 pound equivalent single axle loadings (ESAL) for these pavements did not correlate well with either the resilient modulus or the creep resistance factor.

Investigation of Rapid Thermal Analysis Procedures for Prediction of the Service Life of PCCP Carbonate Coarse Aggregate, HR-337, 1993

The major objective of this research project was to use thermal analysis techniques in conjunction with x-ray analysis methods to identify and explain chemical reactions that promote aggregate related deterioration in portland cement concrete. Twenty-two different carbonate aggregate samples were subjected to a chemical testing scheme that included: • bulk chemistry (major, minor and selected trace elements) • bulk mineralogy (minor phases concentrated by acid extraction) • solid-solution in the major carbonate phases • crystallite size determinations for the major carbonate phases • a salt treatment study to evaluate the impact of deicer salts Test results from these different studies were then compared to information that had been obtained using thermogravimetric analysis techniques. Since many of the limestones and dolomites that were used in the study had extensive field service records it was possible to correlate many of the variables with service life. The results of this study have indicated that thermogravimetric analysis can play an important role in categorizing carbonate aggregates. In fact, with modern automated thermal analysis systems it should be possible to utilize such methods on a quality control basis. Strong correlations were found between several of the variables that were monitored in this study. In fact, several of the variables exhibited significant correlations to concrete service life. When the full data set was utilized (n = 18), the significant correlations to service life can be summarized as follows ( a = 5% level): • Correlation coefficient, r, = -0.73 for premature TG loss versus service life. • Correlation coefficient, r, = 0.74 for relative crystallite size versus service life. • Correlation coefficient, r, = 0.53 for ASTM C666 durability factor versus service life. • Correlation coefficient, r, = -0.52 for acid-insoluble residue versus service life. Separation of the carbonate aggregates into their mineralogical categories (i.e., calcites and dolomites) tended to increase the correlation coefficients for some specific variables (r sometimes approached 0.90); however, the reliability of such correlations was questionable because of the small number of samples that were present in this study.

Sprinkle Treatment (Bristowes Spreader), HR-512

Safety is an important aspect of highway design. Texture and frictional properties are important characteristics in providing safe roadways. Longevity of desirable frictional properties is highly dependent on the aggregate within asphalt pavement. Iowa unfortunately has areas of the State where the locally available aggregate will not give long lasting desirable frictional properties. Iowa has utilized sprinkle treatments to improve the safety of many new asphalt concrete pavements.

Foamed Asphalt Shoulders City of Muscatine, HR-529, 1993

Foamed asphalt shoulders were placed on an Industrial Connector road at the south edge of Muscatine. The foamed asphalt was produced by injecting 1 to 2 percent water into hot asphalt cement in a patented foaming chamber. A foam develops which is 10 to 15 times the original volume. of the asphalt cement. A 3/8" limestone aggregate was used in the foamed asphalt mixture. This foamed asphalt was placed on the shoulders and in the radii on the Industrial Connector road in May 1987. The radii were later replaced due to reconstruction, but the shoulders remain and performed fairly well with some recent stripping and potholing. The performance appeared to be lower than expected from conventional hot mix on projects with similar traffic.

Recycling of Asphalt Concrete From I-80 in Cass County, HR-1011, 1978

Approximately 40,000 tons of deteriorated asphalt concrete has been removed from Interstate 80 in Cass County and stockpiled. Laboratory tests indicate that this material has considerable value when upgraded with new aggregate and asphalt cement. This report documents the procedures used and results obtained on an experimental recycling project. It was demonstrated that present drum mixing-recycling equipment and procedures can be used to utilize this material with satisfactory results. Laboratory analyses of material components and mixtures were performed; these analyses indicate mixture can be produced that is uniform, stable, and very closely resembles mixture produced with all virgin material. A 1700 foot long test section was constructed on US 169 in Kossuth County wherein salvaged asphalt concrete from I-80 in Cass County was utilized. The salvaged mix was blended with virgin aggregate and recycled through a modified drum mixing plant, the reprocessed mixture was satisfactorily placed 1 1/2 inches thick as a resurfacing course on an old PCC pavement. An inspection of the test section was made in December of 1978 to evaluate the performance after one full year of service. There was no evidence of rutting or shoving from traffic. The surface does, however, have a very dry and somewhat ravelled appearance. This can be related to a low asphalt content in the mix and some temperature control problems which were difficult to get fully corrected on such a short project and with a short supply of readily available materials.

Factors Relating to Aggregate Durability in Portland Cement Concrete, HR-2022, Interim Report, 1983

Over the past several years we conducted a comprehensive study on the pore systems of limestones used as coarse aggregate in portland cement concrete (pee) and their relationship to freeze-thaw aggregate failure. A simple test called the Iowa Pore Index Test was developed and used to identify those coarse aggregates that had freeze-thaw susceptible pore systems. Basically, it identified those aggregates that could take on a considerable amount of water but only at a slow rate. The assumption was that if an aggregate would take on a considerable amount of water at a slow rate, its pore system would impede the outward movement of water through a critically saturated particle during freezing, causing particle fracture. The test was quite successful when used to identify aggregates containing susceptible pore systems if the aggregates were clean carbonates containing less than 2% or 3% insolubles. The correlation between service record, ASTM C666B and the pore index test was good, but not good enough. It became apparent over the past year that there were factors other than the pore system that could cause an aggregate to fail when used in pee. The role that silica and clay play in aggregate durability was studied.

Air Content and Permeability of PCC Pavements: 1909 to 2006, MLR-05-02, 2007

Portland cement concrete pavements have given excellent service history for Iowa. Many of these pavements placed during the 1920’s and 1930’s are still in service today. Many factors go in to achieve a long term durable concrete pavement. Probably the most important is the durability of the aggregate. Until the 1930’s, pit run gravel was the most predominant aggregate used. Many of these gravels provided long term performance and their durability is dependent upon the carbonate fraction of the gravel. Later, limestone (calcium carbonate) and dolomite (calcium, magnesium carbonate) sources were mined across Iowa. The durability of these carbonate aggregates is largely dependent upon the pore system which can cause freeze thaw problems known as D-cracking, which was a problem with some sources during the 1960’s. Also, some of these carbonate aggregates are also susceptible to deterioration from deicing salts. Geologists have identified the major components that affect the durability of these carbonate aggregates and sources are tested to ensure long term performance in Portland cement concrete. Air entrainment was originally put in concrete to improve scaling resistance. It is well known that air entrainment is required to provide freeze thaw protection in concrete pavements today. In Iowa, air entrainment was not introduced in concrete pavements until 1952. This research investigates properties that made older concrete pavements durable without air entrainment.