Improved Aggregate Gradation for Portland Cement Concrete Mixes, HR-563, 1996

Improving the aggregate gradation for a portland cement concrete mix may result in higher compressive strengths. With an improved gradation, the cement factor may be reduced to achieve a more economical concrete mix since cement is the most expensive component in a Portland cement concrete mix. This project located on I-80 westbound in Scott County, Iowa examined three different mixes. 1. Standard Class C mix with project aggregates. 2. Standard Class C mix with an improved aggregate gradation. 3. Standard Class C mix with an improved aggregate gradation and 10% cementitious reduction.

Early Entry Sawed Portland Cement Concrete Transverse Joint Ends, MLR-97-5, 2003

Experiments with early entry light sawing of Portland cement concrete (PCC) contraction joints began in Iowa in 1989. Since that time, changes in early sawing equipment have occurred as well as changes in specifications for sawing. The option to use early sawing for transverse contraction joints was specified in 1992. A problem happening occasionally with early sawing was the break out of some of the concrete around the end of the joint as the saw blade approached the edge of the slab. To prevent this, it was proposed that the sawing would terminate approximately 1/2" to 3/4" before the edge of the slab, creating a "short joint". This procedure would also leave a concrete "dam" to prevent the run-out and waste of the hot liquid joint sealant onto the shoulder. It would also eliminate the need for the labor and material for applying a duct tape dam at the open ends of each sawed joint to stop hot liquid sealant run-out Agreements were made with the contractor to apply the "short joint" technique for 1 day of paving. The evaluation and results are compared with an adjoining control section. The research found no negative aspects from sawing the "short joint". Three specific findings were noted. They are the following: 1) No joint end "blow-out" spalls of concrete occurred. 2) The need for the duct tape dam to stop liquid sealant overflow was eliminated. 3) Joint end corner spalls appear to be caused mainly by construction shouldering operations equipment. The "short joint" sawing technique can be routinely applied to early entry sawed transverse contraction joints with expectations of only positive results.

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.

Asphalt Cement Concrete Pavement Recycling Cass and Montgomery Counties, HR-1018, 1986

This demonstration project consisted of three adjacent highway resurfacing projects using asphalt cement concrete removed from an Interstate highway which had become severely rutted. The salvaged asphaltic concrete was later crushed and hauled to a plant site where it was combined with virgin materials to resurface the three projects. Only two of the projects were used for performance evaluation as the third project was in an interchange area including ramps and was otherwise too short. It was concluded that recycling was cost effective and a high quality surface can be constructed using recycled asphalt cement concrete.

Asphalt Cement Concrete Longitudinal Joint Adhesive Crafco PN 34524 (Iowa DOT New Product C-98-7), HR-2084, 2000

The joint between two lanes of asphalt pavement is often the first area of a roadway which shows signs of deterioration and requires maintenance. As the final lift of hot asphalt is being placed in a construction project, it is being forced p against the adjoining lane of cold asphalt, forming the longitudinal joint. The mating of the two lanes, to form a high quality seal, is often not fully successful and later results in premature stripping or raveling as water enters the unsealed joint. The application of a hot poured rubberized asphaltic joint sealant along the joint face in the final stage of construction should help to form a watertight joint seal. A new product, especially formulated for the longitudinal joint in asphalt pavements was proposed to improve joint sealing. The following describes the experimental application of the new product, Crafco, PN 34524.

Asphalt Rubber Cement Concrete Webster County, HR-555, Construction Report, 1993

Discarded tires have become a major disposal problem in the U.S. Different techniques of recycling these discarded tires have been tried. The state of Iowa is currently evaluating the use of discarded tires ground into crumb rubber and blending it with asphalt to make asphalt rubber cement (ARC}. This was the sixth project this process has been used in. This project is located on US 169 from the east junction of IA 175 west and north to US 20. Only the binder course was placed this year with the surface course to be let at a later date. There are four test sections, two sections with conventional mixtures and two with ARC mixtures.

Thin Bonded Portland Cement Concrete Overlay, HR-520, 1990

A four and one-half inch thick, bonded portland cement concrete (PCC) overlay and integral widening were used to rehabilitate a 4.5 mile section of Iowa route 141 from US 169 to Iowa 210 in Dallas County. There was a substantial amount of cracking in the old 20 feet wide PCC pavement. Most of the widening, which was tied to the original slab by dowel bars, was placed as a four feet wide section on one side. Coring has shown that the overlay is well bonded and testing with the Delamtect has shown less than 1% debonding. Midpanel transverse cracks in the old pavement have reflected through the overlay (as expected). Some new transverse cracking has occurred. This cracking has not caused any significant problems. In general, the overlay is performing quite well.

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.

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.

Bonded, Thin-Lift, Non-Reinforced Portland Cement Concrete Resurfacing, MLR-77-2, 1977

A research project involving 2, 3, 4, and 5 in. (5.1, 7.6, 10.2, and 12.7 cm) of bonded portland cement concrete (PCC) overlay on a 1.3 mile (2.1 km) PCC pavement was conducted in Clayton County, Iowa, during September 1977, centering on the following objectives: (1) Determine the mixing and proportioning procedures required in using a conventional, central mix proportioning plant to produce a dense PCC mixture using standard mixes with super water reducing admixtures; (2) Determine the economics, longevity and maintenance performance of a bonded, thin-lift, non-reinforced PCC resurfacing course using conventional procedures, equipment and concrete paving mixtures both with and without super water reducing admixtures; and (3) Determine if an adequate bond between the existing pavement and an overlay of thin-lift, dense, non-reinforced PCC can be obtained with only special surface cleaning and no surface removal or grinding. The conclusions are as follows: (1) Normal mixing equipment and proportioning procedures could be used using a conventional central-mix proportioning plant. This was successful when used with super water reducing admixtures. Only minor changes need be made in procedures and timing. (2) The time has been too short since the completion of the project to determine how the new pavement will perform, however, initially it appears that the method is economical and no reason is seen at this time why the life of the pavement should not be comparable to an all new pavement. (3) The initial test results show that bond strength, regardless of which method of cleaning is used, scarifying, sand blasting or water blasting, far exceed what is considered the minimum bond strength of 200 psi (1379 kPa) except where the paint stripes were intentionally left, thus showing that the paint must be removed. (4) It appears that either cement and water grout or sand, cement and water grout may be used and still obtain the required bond.

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.

Iowa D.O.T's Experience with Recycling Portland Cement Pavement and Asphalt Cement Pavement, MLR-77-4, 1977

This report provides details of IADOT's experience removing and crushing asphaltic concrete and portland cement concrete for recycling. The recycled material was used on interstate highways for the subbase and shoulders. The major problem IADOT encountered on this project was the removal of reinforcing steel from the broken concrete. The contractor used hydraulic powered shears to clip off all protruding steel during the removal and loading of the concrete on the grade. This project took place in 1977.

Evaluation of Type I Cement Fast Track Concrete, MLR-87-6, 1988

There are projects where opening the pavement to traffic in less than the 5 to 7 days is needed, but an 8 to 12 hour opening time is not necessary. The study examined fast track concrete with Type I cement and admixtures. The variables studied were: (1) cure temperature, (2) cement brand, (3) accelerators, and (4) water reducers. A standard water reducer and curing blankets appear to be effective at producing a 24 hour to 36 hour opening strength. An accelerator and/or high range water reducer may produce opening strength in 12 to 24 hours. Calcium chloride was most effective at achieving high-early strength.

Vibration Study for Consolidation of Portland Cement Concrete, MLR-95-4, 1999

The Iowa Department of Transportation has noticed an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements can be observed in several sections of PCC highways across the state of Iowa. Also, excessive vibration is believed to be a factor in the premature deterioration of several pavements in Iowa. To address the problem of excessive vibration, a research project was conducted to document the vibratory practices of PCC slipform paving in Iowa and determine the effect of vibration on the air content of pavement. The primary factors studied were paver speed, vibrator frequency, and air content relative to the location of the vibrator. The study concluded that the Iowa Department of Transportation specification of 5000 and 8000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds observed on the three test paving projects. Excessive vibration was clearly identified on one project where a vibrator frequency was found to be 12,000 vpm. When the paver speed was reduced to half the normal speed, hard air contents indicated that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8000 vpm. Analysis of variance testing indicated many variables and interactions to be significant at a 95% confidence level; however, the variables and interactions that were found to be significant varied from project to project. This affirms the complexity of the process for consolidating PCC.

Vibration Study for Consolidation of Portland Cement Concrete, Preprint, MLR-95-4, 1997

The Iowa Department of Transportation has discovered an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements has been observed in several projects across the state. Overconsolidation is also believed to be a factor in acceleration of premature deterioration of at least two pavement projects in Iowa. To address the problem, a research project in 1995 documented the vibratory practices of PCC slipform paving in Iowa in order to determine the effect of vibration on consolidation and air content of pavement. Paver speed, vibrator frequency, and air content relative to the location of the vibrator were studied. The study concluded that the Iowa Department of Transportation specification of 5,000 to 8,000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds on the three projects that were examined. Excessive vibration was clearly identified on one project where a vibrator frequency of 12,000 vpm was discovered. When the paver speed was reduced to half the normal speed, hard air contents indicate that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8,000 vpm. The study also indicates that the radius of influence of the vibrators is smaller than has been claimed.