Evaluation of the Chemical Durability of Iowa Fly Ash Concretes, HR-327, 1993

The major objective of this research project was to investigate how Iowa fly ashes influenced the chemical durability of portland cement based materials. Chemical durability has become an area of uncertainty because of the winter application of deicer salts (rock salts) that contain a significant amount of sulfate impurities. The sulfate durability testing program consisted of monitoring portland cement-fly ash paste, mortar and concrete test specimens that had been subjected to aqueous solutions containing various concentrations of salts (both sulfate and chloride). The paste and mortar specimens were monitored for length as a function of time. The concrete test specimens were monitored for length, relative dynamic modulus and mass as a function of time. The alkali-aggregate reactivity testing program consisted of monitoring the expansion of ASTM C311 mortar bar specimens that contained three different aggregates (Pyrex glass, Oreapolis and standard Ottawa sand). The results of the sulfate durability study indicated that the paste and concrete test specimens tended to exhibit surface spalling but only very slow expansive tendencies. This suggested that the permeability of the test specimens was controlling the rate of deterioration. Concrete specimens are still being monitored because the majority of the test specimens have expanded less than 0.05%; hence, this makes it difficult to estimate the service life of the concrete test specimens or to quantify the performance of the different fly ashes that were used in the study. The results of the mortar bar studies indicated that the chemical composition of the various fly ashes did have an influence on their sulfate resistance. Typically, Clinton and Louisa fly ashes performed the best, followed by the Ottumwa, Neal 4 and then Council Bluffs fly ashes. Council Bluffs fly ash was the only fly ash that consistently reduced the sulfate resistance of the many different mortar specimens that were investigated during this study. None of the trends that were observed in the mortar bar studies have yet become evident in the concrete phase of this project. The results of the alkali-aggregate study indicated that the Oreapolis aggregate is not very sensitive to alkali attack. Two of the fly ashes, Council Bluffs and Ottumwa, tended to increase the expansion of mortar bar specimens that contained the Oreapolis aggregate. However, it was not clear if the additional expansion was due to the alkali content of the fly ash, the periclase content of the fly ash or the cristobalite content of the fly ash, since all three of these factors have been found to influence the test results.

Freeze-Thaw Durability of Concretes with and without Class C Fly Ash, MLR-94-9 Phase I, 1997

The freeze-thaw resistance of concretes was studied. Nine concrete mixes, made with five cements and cement-Class C fly ash combinations, were exposed to freeze-thaw cycling following 110 to 222 days of moist curing. Prior to the freeze-thaw cycling, the specimens were examined by a low-vacuum scanning electron microscope (SEM) for their microstructure. The influence of a wet/dry treatment was also studied. Infilling of ettringite in entrained air voids was observed in the concretes tested. The extent of the infilling depends on the period of moist curing as well as the wet/dry treatment. The concretes with 15% Class C fly ash replacement show more infilling in their air voids. It was found that the influence of the infilling on the freeze-thaw durability relates to the air spacing factor. The greater the spacing factor, the more expansion under the freeze-thaw cycling. The infilling seems to decrease effective air content and to increase effective spacing factor. The infilling also implies that the filled air voids are water-accessible. These might lead to concrete more vulnerable to the freeze-thaw attack. By combining the above results with field observations, one may conclude that the freeze-thaw damage is a factor related to premature deterioration of portland cement concrete pavements in Iowa.

Low Cost Fly Ash - Sand Stabilized Roadway Des Moines County, HR-259, 1991

The objectives of this research were to develop a low cost fly ash-sand stabilized roadway and to correlate field performance with pavement design assumptions on a county road heavily trafficked by trucks hauling grain. The road was constructed during the summer of 1984. Three test sections comprised of different base thicknesses were incorporated in the roadway and were tested for compressive stength, structural rating, and rut depth. Annual crack surveys showed no appreciable difference in transverse cracking between the test sections and little to no rutting. The sandbase drainage characteristics beneath the roadway may have contributed to the satisfactory performance of the test sections. This project indicates that in spite of the inflated cost of construction due to the research nature of the work, a fly ash-sand base can be a viable alternative for roadway stabilization.

Crack Sealing Utilizing a Heat Lance, HR-2058, 1997

Four Iowa DOT asphalt concrete pavement crack sealing projects were selected to evaluate the benefits of heat lance crack preparation. Two, one-half mile sections, both with and without heat lance preparation, were constructed in Story, Monroe, Clinton and Wayne Counties in 1991 and 1992. They were visually evaluated annually from 1992 through 1996. The heat lance preparation did not yield improved seal performance or extended longevity. There was no perceivable difference between crack sealing with and without heat lance preparation.

Portland Cement Concrete Utilizing Recycled Pavement, MLR-77-3, 1977

Two objectives were involved in this recycling project: To determine if the asphalt concrete surfacing from an existing roadway could be removed, the existing portland cement concrete pavement broken, removed, crushed to 1-1/2 inch minus, proportioned through a conventional central mix proportioning plant with the addition of concrete sand, and placed with a conventional slipform paver; and to determine if a two course, composite pavement, each course of different mix proportions, could be placed monolithically with conventional slipform equipment after being proportioned and mixed in a conventional central mix plant. The project was completed with no major problem. The objectives were satisfactorily met. The project was a success to the degree that the Iowa D.O.T. is proceeding with at least two projects for the 1977 construction season that will utilize the old pavement as appregate for the new pavement.

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.

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.

Evaluation of Fly Ash in Portland Cement Concrete Pavement in Monona County, Iowa, Construction Report, HR-200, 1978

The primary objectives of this research project were: 1. Determine and recommend solutions for problems relating to shipping, storing and batching of fly ash. 2. Establish a procedure for batching, mixing and placing uniform concrete with specified air content and consistency. 3. Demonstrate that concrete of comparable quality can be produced.

Evaluation of Fly Ash in Portland Cement Concrete Paving in Woodbury County, Iowa, Final Report, HR-201, 1980

The earliest overall comprehensive work on the use of fly ash in concrete was reported by Davis and Associates of the University of California in 1937. Since that time, there have been numerous applications of the use and varying propertions of fly ash in portland cement concrete mixes. Fly ash is a pozzolanic powdery by-product of the coal combustion process which is recovered from flue gases and is, generally associated with electric power generating plants. Environmental regulations enacted in recent years have required that fly ash be removed from the flue gases to maintain clean air standards. This has resulted in an increased volume of high quality fly ash that is considered a waste product or a by-product that can be utilized in products such as portland cement concrete. There are several sources of the high quality fly ash located in Iowa currently producing a combined total of 281,000 tons of material annually.

Report on Fly Ash Variability, MLR-81-2, 1981

The physical-chemical testing of fly ashes indicates that, under normal operating conditions, a low variability of results can be expected from a particular generating plant unit. However, unannounced changes in coal source and/or plant operations do occur and they may result in an ash with undesirable properties. Since these properties can be detected by physical-chemical testing, it is recommended that this testing be performed on a lot-by-lot basis when a plant is supplying fly ash to a construction project.

Evaluation of Fly Ash in Bridge Deck Concrete, MLR-84-2, 1985

Fly ash was used in this evaluation study to replace 15% of the cement in Class D-57 structural concrete containing ASTM C494 Type B, retarding admixtures. Two Class "C" ashes and one Class "F" ash from Iowa approved sources were examined in each mix. When Class "C" ashes were used, they were substituted on the basis of 1.0 pound for each pound of cement removed. When Class "F" ash was used, it was substituted on the basis of 1.25 pounds of ash for each pound of cement removed. Compressive strengths of the retarded mixes, with and without fly ash, were determined at 7, 28 and 56 days of age. In most cases, with few exceptions, the mixes containing the fly ash exhibited higher strengths than the same concrete mix without the fly ash. The exceptions were the 7, 28, and 56 days of the mixes containing Class F ash. The freeze/thaw durability of the concrete studied was not affected by the presence of fly ash. The data obtained suggested that the present Class D-57 structural concrete mix with retarding admixtures can be modified to allow the substitution of 15% of the cement with an approved fly ash when Class III coarse aggregates are used. Setting times of the concretes were not materially changed due to the incorporation of fly ash.

Emerald Ash Borer, The Green Menace, April 2006

The emerald ash borer (EAB) is a very small but very destructive beetle. Metallic green in color, its slender body measures 1/2 inch in length and 1/8 inch wide. The average adult

Pest Alert: Emerald Ash Borer, September 2008

A beetle from Asia, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), was identified in July 2002 as the cause of widespread ash (Fraxinus spp.) tree decline and mortality in southeastern Michigan and Windsor, Ontario, Canada. Larval feeding in the tissue between the bark and sapwood disrupts transport of nutrients and water in a tree, eventually causing branches and the entire tree to die. Tens of millions of ash trees in forest, rural, and urban areas have already been killed or are heavily infested by this pest.

3D coronary vessel wall imaging utilizing a local inversion technique with spiral image acquisition.

Current 2D black blood coronary vessel wall imaging suffers from a relatively limited coverage of the coronary artery tree. Hence, a 3D approach facilitating more extensive coverage would be desirable. The straightforward combination of a 3D-acquisition technique together with a dual inversion prepulse can decrease the effectiveness of the black blood preparation. To minimize artifacts from insufficiently suppressed blood signal of the nearby blood pools, and to reduce residual respiratory motion artifacts from the chest wall, a novel local inversion technique was implemented. The combination of a nonselective inversion prepulse with a 2D selective local inversion prepulse allowed for suppression of unwanted signal outside a user-defined region of interest. Among 10 subjects evaluated using a 3D-spiral readout, the local inversion pulse effectively suppressed signal from ventricular blood, myocardium, and chest wall tissue in all cases. The coronary vessel wall could be visualized within the entire imaging volume.