Effective Shoulder Design and Maintenance, 2007

Granular shoulders are an important element of the transportation system and are constantly subjected to performance problems due to wind- and water-induced erosion, rutting, edge drop-off, and slope irregularities. Such problems can directly affect drivers’ safety and often require regular maintenance. The present research study was undertaken to investigate the factors contributing to these performance problems and to propose new ideas to design and maintain granular shoulders while keeping ownership costs low. This report includes observations made during a field reconnaissance study, findings from an effort to stabilize the granular and subgrade layer at six shoulder test sections, and the results of a laboratory box study where a shoulder section overlying a soft foundation layer was simulated. Based on the research described in this report, the following changes are proposed to the construction and maintenance methods for granular shoulders: • A minimum CBR value for the granular and subgrade layer should be selected to alleviate edge drop-off and rutting formation. • For those constructing new shoulder sections, the design charts provided in this report can be used as a rapid guide based on an allowable rut depth. The charts can also be used to predict the behavior of existing shoulders. • In the case of existing shoulder sections overlying soft foundations, the use of geogrid or fly ash stabilization proved to be an effective technique for mitigating shoulder rutting.

High Performance Concret Bridge Deck Overlays for County Bridges, October 2007

The Iowa Method for bridge deck overlays has been very successful in Iowa since its adoption in the 1970s. This method involves removal of deteriorated portions of a bridge deck followed by placement of a layer of den (Type O) Portland Cement Concrete (PCC). The challenge encountered with this type of bridge deck overlay is that the PCC must be mixed on-site, brought to the placement area and placed with specialized equipment. This adds considerably to the cost and limits contractor selection. A previous study (TR-427) showed that a dense PCC with high-range water reducers could successfully be used for bridge deck overlays using conventional equipment and methods. This current study evaluated the use of high performance PCC in place of a dense PCC for work on county bridges. High performance PCC uses fly ash and slag to replace some of the cement in the mix. This results in a workable PCC mix that cures to form a very low permeability overlay.

Neotropical woodlice (isopoda) colonizing leaf-litter of pioneer plants in a coal residue disposal environment

The irregular disposal of coal combustion residues has adverse impacts on terrestrial ecosystems. Pioneer plants and soil invertebrates play an important role in the recovery of these areas. The goal of this study was to investigate the colonization patterns of terrestrial isopods (Oniscidea) in leaf litter of three spontaneous pioneer plants (grass - Poaceae, shrub - Euphorbiaceae, tree - Anarcadiaceae) at sites used for fly ash or boiler slag disposal. The experiment consisted of eight blocks (four per disposal site) of 12 litter bags each (four per plant species) that were randomly removed after 6, 35, 70 or 140 days of field exposure. Three isopod species were found in the litter bags: Atlantoscia floridana (van Name, 1940) (Philosciidae; n = 116), Benthana taeniata Araujo & Buckup, 1994 (Philosciidae; n = 817) and Balloniscus sellowii (Brandt, 1833) (Balloniscidae; n = 48). The isopods colonized the three leaf-litter species equally during the exposure period. However, the pattern of leaf-litter colonization by these species suggests a conflict of objectives between high quality food and shelter availability. The occurrence of A. floridana and the abundance and fecundity of B. taeniata were influenced by the residue type, indicating that the isopods have different degrees of tolerance to the characteristics of the studied sites. Considering that terrestrial isopods are abundant detritivores and stimulate the humus-forming processes, it is suggested that they could have an indirect influence on the soil restoration of this area.

Development of Performance Properties of Ternary Mixtures and Concrete Pavement Mixture Design and Analysis (MDA): Effect of Paste Quality on Fresh and Hardened Properties of Ternary Mixtures, TPF-5(117), 2012

The purpose of this study was to investigate the effect of cement paste quality on the concrete performance, particularly fresh properties, by changing the water-to-cementitious materials ratio (w/cm), type and dosage of supplementary cementitious materials (SCM), and airvoid system in binary and ternary mixtures. In this experimental program, a total matrix of 54 mixtures with w/cm of 0.40 and 0.45; target air content of 2%, 4%, and 8%; a fixed cementitious content of 600 pounds per cubic yard (pcy), and the incorporation of three types of SCMs at different dosages was prepared. The fine aggregate-to- total aggregate ratio was fixed at 0.42. Workability, rheology, air-void system, setting time, strength, Wenner Probe surface resistivity, and shrinkage were determined. The effects of paste variables on workability are more marked at the higher w/cm. The compressive strength is strongly influenced by the paste quality, dominated by w/cm and air content. Surface resistivity is improved by inclusion of Class F fly ash and slag cement, especially at later ages. Ternary mixtures performed in accordance with their ingredients. The data collected will be used to develop models that will be part of an innovative mix proportioning procedure.

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.

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.

Effects of Deicing Salt Trace Compounds on Deterioration of Portland Cement Concrete, HR-271, 1987

A study was made of the detrimental effects of trace amounts of calcium sulfate (occurring naturally in halite deposits used for deicing) on portland cement concrete pavements. It was found that sulfate introduced as gypsum with sodium chloride in deicing brines can have detrimental effects on portland cement mortar. Concentrations of sulfate as low as 0.5% of the solute rendered the brine destructive. Conditions of brine application were critical to specimen durability. The mechanisms of deterioration were found to be due to pore filling resulting from compound formation and deposition. A field evaluation of deteriorating joints suggests that the sulfate phenomena demonstrated in the laboratory also operates in the field. A preliminary evaluation was made of remedies: limits on sulfates, fly ash admixtures, treatment of existing pavement, and salt treatments. This report gives details of the research objectives, experimental design, field testing, and possible solutions. Recommendations for further study are presented.

Control of Concrete Deterioration Due to Trace Compounds in Deicers, HR-299 Phase I, 1988

This report presents the results of research on the influence of trace compounds from rock salt deicers on portland cement mortar and concrete. An evaluation of the deicers in stock throughout the state showed that about ninety-five percent contained enough sulfate to cause accelerated deterioration of concrete. Of the impurities found in rock salts, sulfate compounds of calcium and magnesium were found to be equally deleterious. Magnesium chloride was found to be innocuous. Introduction of fly ash eliminated the damage to portland cement mortar caused by sulfates. When used with frost resistant Alden aggregate in fly ash concrete and exposed to a variety of deicer brine compositions, the concrete did not deteriorate after exposure. With the exception of a high calcium brine, the behavior of the frost-prone Garrison aggregate was independent of deicer treatment; the high calcium brine reduced frost damage with this aggregate. Two approaches to reducing sulfate deterioration from deicers are suggested as (1) limiting the amount of sulfate to about 0.28 percent, and (2) making concrete sulfate-resistant by using fly ash. Techniques for making existing concrete deicer-sulfate-resistant are essential to a practical solution.

Control of Concrete Deterioration Due to Trace Compounds in Deicers, Phase II, HR-299, 1989

This report presents results of research on ways to reduce the detrimental effects of sulfate-tainted rock salt deicers on portland cement concrete used for highway pavements. Repetitious experiments on the influence of fly ash on the mortar phase of concrete showed significant improvement in resistance to deicing brines is possible. Fifteen to twenty percent by weight of fly ash replacement for portland cement was found to provide optimum improvement. Fly ashes from five sources were evaluated and all were found to be equally beneficial. Preliminary results indicate the type of coarse aggregate also plays an important role in terms of concrete resistance to freeze-thaw in deicing brines. This was particularly true for a porous ferroan dolomite thought to be capable of reaction with the brine. In this case fly ash improved the concrete, but not enough for satisfactory performance. An intermediate response was with a porous limestone where undesirable results were observed without fly ash and adequate performance was realized when 15% fly ash was added. The best combination for making deicer-resistant concrete was found to be with a non-porous limestone. Performance in brines was found to be adequate without fly ash, but better when fly ash was included. Consideration was given to treating existing hardened concrete made with poor aggregate and no fly ash to extend pavement life in the presence of deicers, particularly at joints. Sodium silicate was found to improve freeze-thaw resistance of mortar and is a good candidate for field usage because of its low cost and ease of handling.

Fast Track Portland Cement Concrete Pavement, HR-538, 1997

In 1987, 1.5 km (0.935 mi.) of Spruce Hill Drive in Bettendorf, Iowa was reconstructed. It is an arteriel street with commercial usage on both termini with single family residential dwellings along most of the project. A portland cement concrete (PCC) pavement design was selected, but a 14 day curing period would have been an undue hardship on the residents and commercial businesses. An Iowa DOT Class F fast track concrete was used so the roadway could be used in 7 to 10 days. The Class F concrete with fly ash was relatively sticky and exhibited early stiffening problems and substantial difficulty in obtaining the target entrained air content of 6.5%. These problems were never completely resolved on the project. Annual visual field reviews were conducted through 1996. In November 1991, severe premature distress was identified on the westbound two lanes of the full width replacement. The most deteriorated section in a sag vertical, 152 m (500 ft.) of the westbound roadway, was replaced in 1996. Premature distress has been identified on a dozen other conventional PCC Iowa pavements constructed between 1983 and 1989, so the deterioration may not be related to the fact that it was fast track pavement.

Pooled Fund Study of Premature Concrete Pavement Deterioration, HR-1063, Supplementary Study, 1997

Recently, a number of roads have begun to exhibit the onset of deterioration at relatively early ages. Since this deterioration appears to be the result of materials issues, data concerning raw materials, design, and paving conditions have been collected and analyzed for correlation between independent variables and deterioration. This analysis shows that there is a positive and statistically significant correlation between deterioration and the following variables: alkali and sulfate content of the cementitious materials, impermeable base course, paving temperature, and the presence of fly ash. This study also concludes that there is a significant need for improvement in data collection and maintenance by many organizations responsible for the production of concrete.

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.

Drying Shrinkage in P.C. Concrete, MLR-89-5, 1990

Crack formation has been a problem on some recently constructed bridges in Iowa. Drying shrinkage has been considered a contributing factor in that cracking. The study was undertaken to evaluate some of those material properties that contribute to the magnitude of drying shrinkage. Cement content, cement composition, fly ash and retarding admixture were the factors studied. Concrete prisms were cast for seven mixes and, after curing, were exposed to 100 deg F heat at ambient humidity for 280 days. The following were observed from the testing: (1) Higher C3A content cement concrete produced larger shrinkage; (2) Use of fly ash increased shrinkage; (3) Use of retarder increased shrinkage; and (4) Lowering the cement content reduced the shrinkage.

Evaluation of Rapid Determination of the Chloride Permeability of Portland Cement Concrete by AASHTO T277-83, MLR-86-11, 1987

An Iowa D.O.T. Laboratory built machine was constructed for the chloride permeability testing of concrete by measuring electric current through a specimen between a salt solution and a base solution. This study had two purposes. The first was to evaluate the machine's performance. To do this, three concrete mixes were made consisting of different cement factors and water/cement ratios. Each mix was tested for chloride ion content by the 90- day salt ponding method and for chloride permeability at a 28-day cure by the permeability machine. The results from each test were evaluated to see if there was correlation between chloride ion content and the chloride permeability. It was determined that there was a correlation and that the permeability machine was satisfactory for determining chloride permeability in concrete. The second purpose of this study was to examine the effects that pozzolans have on the chloride permeability of concrete. Four mixes were made: one without any pozzolans as a control, one with class C fly ash, one with class F fly ash, and one with silica fume. Specimens from each mix were evaluated for chloride ion content by the 90-day salt ponding test and by the laboratory built machine for chloride permeability after curing 28 days. Specimens from these mixes were also taken from the salt ponding slabs after completion of the ponding test to examine the effect chloride ion content has on the operation of the chloride permeability machine. Specimens containing pozzolans were also examined for chloride permeability after a cure of 180 days. It was determined that the addition of pozzolans to concrete lowers the chloride permeability as measured by the permeability machine. Class F fly ash and silica fume in the concrete had a major effect in lowering the chloride permeability in concrete as measured by the permeability machine.

Fine Sand for Use in PC Concrete, MLR-88-6, 1989

In several locations of Iowa, it is becoming more difficult to produce concrete sand consistently at a reasonable cost. Both ASTM and AASHTO have specifications for concrete sands that allow a finer, poorer graded sand than Iowa specifications. The objective of the study was to develop standard mix designs to permit the use of finer graded sand for PC concrete. Three hundred cylinders were made from five sands available in the state. Based on the results of the study, the following are recommended: (1) Create another class of concrete sand by: (a) lowering the current mortar strength ratio from 1.5 to 1.3, (b) raising the allowance for the percent passing one sieve and retained on the next from 40 to 45, and (c) including a provision that 25 to 60 percent passing the number 30 sieve is required for the sand; and (2) Modify the standard paving mixes with and without fly ash for use with the finer sand as follows: (a) 8% more cement and fly ash for B-2 to B-5 mixes, (b) 7% more cement and fly ash for A-2 to A-5 mixes, and (c) 5% more cement and fly ash for C-2 to C-5 mixes and water reduced mixes.