An Evaluation of the Troxler 3241-B Nuclear Asphalt Gauge, MLR-85-11, 1986

The Troxler 3241-B Asphalt Content Gauge is intended for rapidly determining the bitumen content of bituminous paving mixtures. A 300 Millicurie Americuium 241: Beryllium source emitts neutrons which are affected by the hydrogen in the mix. The affected neutrons are detected by Helium 3 detectors, counted and computed into a percentage bitumen of the asphalt mix. The current methods of determining the bitumen content of bituminous paving mixtures requires the use of potentially hazardous chemicals and several hours of testing time. When extracted aggregates are not needed, determination of the bitumen content of a paving mixture by the nuclear method may be easier, quicker and potentially safer. The objective of the project is to study the accuracy of the Troxler 3241-B Nuclear Asphalt Content Gauge in measuring the asphalt cement (AC) content of asphalt concrete mixtures produced with different asphalt cements and different aggregates.

Laboratory Evaluation of Roller-Compacted Concrete, MLR-86-6, 1988

Fine limestone aggregate is abundant in several areas of the state. The aggregate is a by-product from the production of concrete stone. Roller compacted concrete (RCC) is a portland cement concrete mixture that can be produced with small size aggregate. The objective of the research was to evaluate limestone screenings in RCC mixes. Acceptable strength and freeze/thaw durability were obtained with 300 pounds of portland cement and 260 pounds of Class C fly ash. The amount of aggregate passing the number 200 sieve ranged from 4.6 to 11 percent. Field experience in Iowa indicates that the aggregate gradation is more critical to placeability and compactibility than laboratory strength and durability.

Gradation Analysis of Cold Feed and Extracted Bituminuous Mix Samples, MLR-88-2, 1988

Since 1987, the Iowa Department of Transportation has based control of hot asphalt concrete mixes on cold feed gradations. This report presents results of comparisons between cold feed gradations and gradations of aggregate from the same material after it has been processed through the plant and laydown machine. Results are categorized based on mix type, plant type, and method of dust control, in an effort to quantify and identify the factors contributing to those changes. Results of the report are: 1. From the 390 sample comparisons made, aggregate degradation due to asphalt plant processing was demonstrated by an average increase of +0.7% passing the #200 sieve and an average increase in surface area of +1.8 sq. ft. per pound of aggregate. 2. Categories with Type A Mix or Recycling as a sorting criteria generally produced greater degradation than categories containing Type B Mixes and/or plants with scrubbers. 3. None of the averages calculated for the categories should be considered unacceptably high, however, it is information that should be considered when making mix changes in the field, selecting asphalt contents for borderline mix designs, or when evaluating potential mix gradation specification or design criteria changes.

Fly Ash Affect on Alkali-Aggregate Reactivity, MLR-88-7, 1989

Cement-aggregate reactions were first reported in the 1940's. Depletion of quality aggregate, changes in cement and the use of fly ash make cement-aggregate reactions a problem still today. This latest research into alkali-aggregate reactivity was initiated to evaluate the new ASTM style test containers and evaluate the effect of Class C fly ash on the expansive reaction. Three aggregates were tested in combination with three cements and three fly ashes available in Iowa. Thirty-six combinations were made and tested over a six-month period. The conclusions were: (1) the new style ASTM containers were much more effective than the containers used by the Iowa DOT in the past; (2) some mixes with 15 percent Class C fly ash had increased expansion over comparative mixes without fly ash; and (3) the Oreapolis #8 pit did not appear to have an alkali-silica reaction problem based on this testing and earlier reported testing.

Evaluation of Alternative Methods to Obtain Specific Gravity of Coarse Aggregate, MLR-89-7, 1990

AASHTO has a standard test method for determining the specific gravity of aggregates. The people in the Aggregate Section of the Central Materials Laboratory perform the AASHTO T-85 test for AMRL inspections and reference samples. Iowa's test method 201B, for specific gravity determinations, requires more time and more care to perform than the AASHTO procedure. The major difference between the two procedures is that T-85 requires the sample to be weighed in water and 201B requires the 2 quart pycnometer jar. Efficiency in the Central Laboratory would be increased if the AASHTO procedure for coarse aggregate specific gravity determinations was adopted. The questions to be answered were: (1) Do the two procedures yield the same test results? (2) Do the two procedures yield the same precision? An experiment was conducted to study the different test methods. From the experimental results, specific gravity determinations by AASHTO T-85 method were found to correlate to those obtained by the Iowa 201B method with an R-squared value of 0.99. The absorption values correlated with an R-squared value of 0.98. The single operator precision was equivalent for the two methods. Hence, this procedure was recommended to be adopted in the Central Laboratory.

Evaluation Study of Pit Run Gravel Asphalt Treated Base Mixtures with Various Percentages of Crushed Limestone, R-217, 1968

In November of 1966, an investigation of the rigid Class I asphalt treated base specification, requiring 70 per cent crushed limestone, was initiated. It was felt that it might be possible to modify the need for crushed particles, in the construction of basis on heavy duty roads, at a savings, by using more local materials, without sacrificing strength and/or durability. This is a short study on typical sources of pit run gravel, with various percentages of limestone. It is conducted with an eye open to the possibility that our specifications may be modified. The possibility that further investigation may be desirable is not ignored.

Evaluation of Cohesion and Swell Characteristics of Asphalt Treated Base Mixtures, R-223, 1968

This study was undertaken to evaluate the suitability of various stones which play an important role in the properties of compacted mixtures in asphalt treated bases. The determination of the effect of water temperature on the cohesion of the mixes is investigated. A number of stones were prepared for the test. Attention is paid to the particular source of stone with the corresponding test results. A preliminary study of the effect of lime when added to mixed aggregate was also conducted. The purpose of this study is to provide needed information on the cohesive characteristics of asphalt treated bases using a wide range of stones. This study is also to evaluate the suitability of the various stone sources.

Determination of the Optimum Base Characteristics for Pavements, TR-482, 2004

In recent years, it has become apparent that the design and maintenance of pavement drainage extends the service life of pavements. Most pavement structures now incorporate subsurface layers. Part of the function of these subsurface layers is to drain away excess water, which can be extremely deleterious to the life of the pavement. To assure the effectiveness of such drainage layers after they have been spread and compacted, simple, rapid, in-situ permeability and stability testing and end-result specification are needed. This report includes conclusions and recommendations related to four main study objectives: (1) Determine the optimal range for in-place stability and in-place permeability based on Iowa aggregate sources; (2) Evaluate the feasibility of an air permeameter for determining the permeability of open and well-graded drainage layers in situ; (3) Develop reliable end-result quality control/quality assurance specifications for stability and permeability; and (4) Refine aggregate placement and construction methods to optimize uniformity.

Freeze-Thaw Durability of Concretes with Infilling of Ettringite in Voids, Phase 2, MLR-94-9, 1997

Examination of field portland cement concrete cores, from Iowa pavements with premature deterioration, reveals extensive infilling of calcium sulfate aluminum (CSA) compound in their air voids. A previous study (Phase I) has shown some evidence of the correlation between freeze-thaw durability of concretes and ettringite infilling. To further verify the previous observation, a more extensive experimental program was conducted in this Phase 2 study. A total of 101 concrete mixes were examined. Seven cements, six fly ashes, two water reducers and three coarse aggregates were used in the concrete mixes. Specimens were under moist curing for up to 223 days before being subjected to the freeze-thaw cycling. An environmental treatment consisting of three consecutive wet [70 deg F (21 deg C) in distilled water]/dry [120 deg F (49 deg C) in oven] cycles was applied to some specimens. Immediately prior to the freeze-thaw cycling, most specimens were examined by a low-vacuum scanning electron microscope (SEM) for their microstructure. The results obtained further demonstrate the correlation between concrete freeze-thaw response and CSA compound infilling in the air voids. The extent of the infilling depends on the period of moist curing as well as the wet/dry treatment. The extent of the infilling also relates to materials used. Concrete mixes with extensive infilling are more vulnerable to the freeze-thaw attack. Based on the obtained results, material criteria on cements and fly ashes for mainline paving were proposed for minimizing potential infilling of CSA compound in concrete.

Durability of P.C. Concrete as Affected by Aggregate Size, Curing and Proportions, R-214, 1968

The durability of concrete is a most important aspect in pavement life. Deterioration of the interstate portland cement concrete pavement has prompted various studies of factors which may contribute to the durability. Studies of cores taken from deteriorated areas indicated that the larger particles of coarse aggregate may contribute greatly to the problem. This indication was mainly due to the analysis of the cracking pattern which showed that most of the cracks passed through the larger aggregates and the larger aggregate particles were more cracked than the smaller particles. The purpose of this project is to determine if the size of the coarse aggregate has a bearing on the durability of freeze and thaw beams. A secondary purpose of this project is to determine what effect the method of curing and proportions have on the durability of freeze and thaw beams.

An Investigation of Portland Cement Concrete Utilizing 70% Class V Aggregate and 30% Calcareous Coarse Aggregate, R-255, 1973

The main sources of coarse aggregate for secondary slip form paving in Southwest Iowa exhibit undesirable "D" cracking. "D" cracking is a discoloration of the concrete caused by fine, hairline cracks. These cracks are caused by the freezing and thawing of moisture inside the coarse aggregate. The cracks are often hour glass shaped, are parallel to each other, and occur along saw joints. The B-4, a typical secondary mix, utilizes 50% fine aggregate and 50% coarse aggregate. It has been proposed that a concrete mix with less coarse aggregate and more fine aggregate might impede this type of deterioration. The Nebraska Standard 47B Mix, a 70% fine aggregate, and 30% coarse aggregate mix, as used by Nebraska Department of Roads produces concrete with ultimate strengths in excess of 4500 psi but because of the higher cost of cement (it is a six bag per cubic yard mix) is not competitive with our present secondary mixes. The sands of Southwest Iowa generally have poorer mortar strengths than the average Iowa Sand. Class V Aggregate also found in Southwest Iowa has a coarser sand fraction, therefore it has a better mortar strength, but exhibits an acidic reaction and therefore must be·used with limestone. This illustrates the need to find a mix for use in Southwest Iowa that possesses adequate strength and satisfactory durability at a low cost. The purpose of this study is to determine a concrete mix with an acceptable cement content which will produce physical properties similar to that of our present secondary paving mixes.

Characteristics of Chemical Treated Roadway Surfaces, HR-33, 1963

Iowa Highway Commission Project HR-33, "Characteristics of Chemically Treated Roadway Surfaces", was investigated at the Iowa Engineering Experiment Station under Project 375-S. The purpose of the project as originally proposed was to study the physical and chemical characteristics of chemically treated roadway surfaces. All chemical treatments were to be included, but only sodium chloride and calcium chloride treated roadways were investigated. The uses of other types of chemical treatment were not discovered until recently, notably spent sulfite liquor and a commercial additive. Costs of stabilized secondary roads in Hamilton County averaged $4300.00 per mile even though remanent soil-aggregate material was used. The cost of similar roads in Franklin County was $4400.00 per mile. The Franklin County road surfaces were constructed entirely from materials that were hauled to the road site. Costs in Butler County were a little over $3000.00 per mile some eight years ago. Chemical investigations indicate that calcium chloride and sodium chloride are lost through leaching. Approximately 95 percent of the sodium chloride appears to have been lost, and nearly 65 percent of the calcium chloride has disappeared. The latter value may be much in error since surface dressings of calcium chloride are commonly used and have not been taken into account. Clay contents of the soil-aggregate-chemical stabilized roads range from about 6 to ll percent, averaging 8 or 9 percent. The thicknesses of stabilized mats are usually 2 to 4 inches, with in-place densities ranging from 130 to 145 pcf. Generally the densities found in sodium chloride stabilized roads were slightly higher than those found in the calcium chloride stabilized roads.

Studies on Soil-Aggregate-Sodium Chloride Stabilized Roads in Franklin County, Iowa, HR-33

This investigation was conducted to study the performance characteristics of low cost roadway surfaces of soil-aggregate-sodium chloride mixtures. Many roads have been successfully stabilized with sodium chloride. However, little information is available on either the properties of the road materials or the effects of sodium chloride on the materials. The performance of some of the sodium chloride stabilized roads in Franklin County, Iowa, and the performance of some near-by nonchemically treated roads has been studied. The study of sodium chloride stabilized roads was restricted to the roads in which the binder soil used in construction came from the same source. The effects of sodium chloride on some of the engineering properties of the soil and soil-aggregate mixtures used were studied in the laboratory.

Factors Influencing Stability of Granular Base Course Mixes, Progress Report, HR-99, 1965

The problems of laboratory compaction procedures, the effect of gradation and mineralogy on shearing strength, and effect of stabilizing agents on shearing strength of granular base course mixes are discussed. For the materials tested, a suitable laboratory compaction procedure was developed which involves the use of a vibratory table to prepare triaxial test specimens. A computer program has been developed to facilitate the analysis of the test data of the effect of gradation and mineralogy on shearing strength of soils. The effects of the following materials have been selected for evaluation as stabilizing agents’ portland cement, sodium and calcium chloride, lime organic cationic waterproofer, and asphaltic materials.

Factors Influencing Stability of Granular Base Course Mixes, Progress Report, HR-99, 1964 (April)

The problems of laboratory compaction procedures, the effect of gradation and mineralogy on shearing strength, and effect of stabilizing agents on shearing strength of granular base course mixes are discussed. For the materials tested, a suitable laboratory compaction procedure was developed which involves the use of a vibratory table to prepare triaxial test specimens. A computer program has been developed to facilitate the analysis of the test data of the effect of gradation and mineralogy on shearing strength of soils. The effects of the following materials have been selected for evaluation as stabilizing agents’ portland cement, sodium and calcium chloride, lime organic cationic waterproofer, and asphaltic materials.