Task 6: Material Thermal Input for Iowa Materials, May 2008

The present research project was designed to determine thermal properties, such as coefficient of thermal expansion (CTE) and thermal conductivity, of Iowa concrete pavement materials. These properties are required as input values by the Mechanistic-Empirical Pavement Design Guide (MEPDG). In this project, a literature review was conducted to determine the factors that affect thermal properties of concrete and the existing prediction equations for CTE and thermal conductivity of concrete. CTE tests were performed on various lab and field samples of portland cement concrete (PCC) at the Iowa Department of Transportation and Iowa State University. The variations due to the test procedure, the equipment used, and the consistency of field batch materials were evaluated. The test results showed that the CTE variations due to test procedure and batch consistency were less than 5%, and the variation due to the different equipment was less than 15%. Concrete CTE values were significantly affected by different types of coarse aggregate. The CTE values of Iowa concrete made with limestone+graval, quartzite, dolomite, limestone+dolomite, and limestone were 7.27, 6.86, 6.68, 5.83, and 5.69 microstrain/oF (13.08, 12.35, 12.03, 10.50, and 10.25 microstrain/oC), respectively, which were all higher than the default value of 5.50 microstrain/oF in the MEPDG program. The thermal conductivity of a typical Iowa PCC mix and an asphalt cement concrete (ACC) mix (both with limestone as coarse aggregate) were tested at Concrete Technology Laboratory in Skokie, Illinois. The thermal conductivity was 0.77 Btu/hr•ft•oF (1.33 W/m•K) for PCC and 1.21 Btu/hr•ft•oF (2.09 W/m•K) for ACC, which are different from the default values (1.25 Btu/hr•ft•oF or 2.16 W/m•K for PCC and 0.67 Btu/hr•ft•oF or 1.16 W/m•K for ACC) in the MEPDG program. The investigations onto the CTE of ACC and the effects of concrete materials (such as cementitious material and aggregate types) and mix proportions on concrete thermal conductivity are recommended to be considered in future studies.

Investigation into Shrinkage of High-Performance Concrete Used for Iowa Bridge Decks and Overlays, TR-633, 2013

High-performance concrete (HPC) overlays have been used increasingly as an effective and economical method for bridge decks in Iowa and other states. However, due to its high cementitious material content, HPC often displays high shrinkage cracking potential. This study investigated the shrinkage behavior and cracking potential of the HPC overlay mixes commonly used in Iowa. In the study, 11 HPC overlay mixes were studied. These mixes consisted of three types of cements (Type I, I/II, and IP) and various supplementary cementitious materials (Class C fly ash, slag and metakaolin). Limestone with two different gradations was used as coarse aggregates in 10 mixes and quartzite was used in one mix. Chemical shrinkage of pastes, free drying shrinkage, autogenous shrinkage of mortar and concrete, and restrained ring shrinkage of concrete were monitored over time. Mechanical properties (such as elastic modulus and compressive and splitting tensile strength) of these concrete mixes were measured at different ages. Creep coefficients of these concrete mixes were estimated using the RILEM B3 and NCHRP Report 496 models. Cracking potential of the concrete mixes was assessed based on both ASTM C 1581 and simple stress-to-strength ratio methods. The results indicate that among the 11 mixes studied, three mixes (4, 5, and 6) cracked at the age of 15, 11, and 17 days, respectively. Autogenous shrinkage of the HPC mixes ranges from 150 to 250 microstrain and free dying shrinkage of the concrete ranges from 700 to 1,200 microstrain at 56 days. Different concrete materials (cementitious type and admixtures) and mix proportions (cementitious material content) affect concrete shrinkage in different ways. Not all mixes having a high shrinkage value cracked first. The stresses in the concrete are associated primarily with the concrete shrinkage, elastic modulus, tensile strength, and creep. However, a good relationship is found between cementitious material content and total (autogenous and free drying) shrinkage of concrete.

Laboratory Study of Slurry Seal Coats, HR-185, Revised, 1978

Extensive programmed laboratory tests involving some 400 asphalt emulsion slurry seals (AESS) were conducted. Thirteen aggregates including nine Iowa sources, a quartzite, a synthetic aggregate (Haydite), a limestone stone from Nebraska, and a Chat aggregate from Kansas were tested in combination with four emulsions and two mineral fillers, resulting in a total of 40 material combinations. A number of meetings were held with the Iowa DOT engineers and 12 state highway departments that have had successful slurry seal experiences and records, and several slurry seal contractors and material and equipment suppliers were contacted. Asphalt emulsion slurry seal development, uses, characteristics, tests, and design methods were thoroughly reviewed in conjunction with Iowa's experiences through these meetings and discussions and through a literature search (covering some 140 articles and 12 state highway department specifications). It was found that, while asphalt emulsion slurry seals (when properly designed and constructed) can economically improve the quality and extend the life of existing pavement surface, experiences with them had been mixed due to the many material, slurry, and construction variables that affect their design, construction, and performance. The report discusses those variables identified during the course of the project and makes recommendations concerning design procedures, design criteria, specifications and the means of evaluating them.

Evaluation of Cover Aggregate Stripping Characteristics, HR-182, 1979

The purpose of Research Project HR-182 was to identify those aggregate types which would perform satisfactorily as seal coat aggregates. Aggregates were chosen from across the State to represent the various types normally encountered and were used with two different types of binder bitumens. A water spray treatment was also included to simulate the effects of rainfall. The evaluation was based upon aggregate retention. Due to the influence of unexpected variables upon the field samples, the laboratory data are reliable for only the most general observations. Namely, that gravels as a group appear to be retained better than carbonates and rain-fall shortly after seal coat placement can affect aggregate retention. The subsequent field observations and analysis of skid resistance data permit the following conclusions: 1. Aggregate retention is influenced by lithologic type with the gravels, quartzite, haydite, dolomites, and medium grained limestones performing best. 2. Aggregate retention is not influenced by binder bitumen type. 3. Friction values of seal coats are influ-enced by aggregate retention and/or lithologic type. The following recommendations have been determined: The aggregate used for cover aggregate/seal coat projects should be Type 4 or better skid resistance as identified in Iowa DOT Materials Instructional Memorandum T-203. This will result in maximizing the possibility of good aggregate retention and skid resistance.

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.

Polymerized Asphalt Cement, HR-533, 1989

In 1986, a 0.34 mile experimental section of polymerized asphalt cement (PAC30) concrete was placed in the westbound driving lane of Interstate 80 in western Iowa. It was used in a 2" asphalt concrete inlay using 20% recycled asphalt pavement. The virgin aggregate included 41% crushed gravel, 25% crushed quartzite and 14% natural sand. The evaluation of the project was severely limited when a 1987 reconstruction project extended into the experimental section leaving only 395 feet. Rut depths under a 4-foot gage were taken for a period of two years. No significant rutting occurred in the experimental polymerized section. The frequency of transverse cracking in the polymerized AC section was the same as that of the comparative AC-20 section. The asphalt paving mixture made with polymerized AC cost 120% of the cost of the conventional mix.

Maintenance of Pavement Skid Resistance (Open Graded Asphalt Friction Courses), Progress Report, HR-170, 1976

This project involved the evaluation of several aggregates previously rated poor to excellent with respect to skid resistance and certain mix design parameters. An open graded asphalt friction course was evaluated using 4 comparably graded aggregates: quartzite, fine grained limestone, coarse limestone and lightweight expanded shale. The performance investigations involved the verification of observations of the quartzite test sections, evaluation of the effect of blending the superior quartzite with a typical coarse grained-textured limestone, and the evaluation of the limestone. The effects of traffic on the aggregates used in the test sections were studied, as well as the relationship between asphalt content levels and traffic with respect to performance. The bond of the open graded friction course mixture was also evaluated. The SN performance of all test sections after sixteen months of exposure was found to be satisfactory in that none of the material combinations had polished to the point where unacceptable SN levels developed. When material combinations were compared, significant differences were noted.

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 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.

Identification of Laboratory Techniques to Optimize Superpave HMA Surface Friction Characteristics, TR-450, 2010

Wet pavement friction is known to be one of the most important roadway safety parameters. In this research, frictional properties of flexible (asphalt) pavements were investigated. As a part of this study, a laboratory device to polish asphalt specimens was refined and a procedure to evaluate mixture frictional properties was proposed. Following this procedure, 46 different Superpave mixtures, one stone matrix asphalt (SMA) mixture and one porous friction course (PFC) mixture were tested. In addition, 23 different asphalt and two concrete field sections were also tested for friction and noise. The results of both field and laboratory measurements were used to develop an International Friction Index (IFI)-based protocol for measurement of the frictional characteristics of asphalt pavements for laboratory friction measurements. Based on the results of the study, it appears the content of high friction aggregate should be 20% or more of the total aggregate blend when used with other, polish susceptible coarse aggregates; the frictional properties increased substantially as the friction aggregate content increased above 20%. Both steel slag and quartzite were found to improve the frictional properties of the blend, though steel slag had a lower polishing rate. In general, mixes containing soft limestone demonstrated lower friction values than comparable mixes with hard limestone or dolomite. Larger nominal maximum aggregate size mixes had better overall frictional performance than smaller sized mixes. In addition, mixes with higher fineness moduli generally had higher macrotexture and friction.