Concrete Pavement Construction Basics, June 2006

General principles • Everyone at the construction site, particularly foremen and supervisors, is responsible for recognizing and troubleshooting potential problems as they arise. • Batches of concrete should be consistent and uniformly mixed. • A major cause of pavement failure is unstable subgrade. The subgrade should consist of uniform material, and the subgrade system must drain well. • Dowel bars are important for load transfer at transverse joints on pavements with high truck volumes. Dowels must be carefully aligned, horizontally and vertically, to prevent pavement damage at the joints. • Stringlines control the slipform paver’s horizontal and vertical movement and ensure a smooth pavement profile. Once stringlines are set, they should be checked often and not disturbed. • Overfinishing the new pavement and/or adding water to the surface can lead to pavement surface problems. If the concrete isn’t sufficiently workable, crews should contact the project manager. Changes to the mixture or to paver equipment may reduce the problem. • Proper curing is critical to preventing pavement damage from rapid moisture loss at the pavement surface. • A well spaced and constructed system of joints is critical to prevent random cracking. • Joints are simply controlled cracks. They must be sawed during the brief time after the pavement has gained enough strength to prevent raveling but before it begins to crack randomly (the “sawing window”). • Seasonal and daily weather variations affect setting time and other variables in new concrete. Construction operations should be adjusted appropriately.

Does this child have a foreign body aspiration?

Context: Foreign body aspiration (FbA) is a serious problem in children. Accurate clinical and radiographic diagnosis is important because missed or delayed diagnosis can result in respiratory difficulties ranging from life-treatening airway obstruction to chronic wheezing or recurrent pneumonia. Bronchoscopy also has risks and accurate clinical and radiographc diagnosis can support the decision of bronchoscopy. Objective: To rewiev the diagnostic accuracy of clinical presentation (CP) and pulmonary radiograph (PR) for the diagnosis of FbA. There is no previous rewievMethods: A search of Medline is conducted for articles containing data regarding CP and PR signes of FbA. Calculation of likelihood ratios (LR) and pre and post test probability using Bayes theorem were performed for all signs of CP and PR. Inclusion criteria: Articles containing prospective data regarding CP and PR of FbA. Exclusion criteria: Retrospectives studies. Articles containing incomplete data for calculation of LR. Results: Five prospectives studies are included with a total of 585 patients. Prevalence of FbA is 63% in children suspected of FbA. If CP is normal, probability of FbA is 25% and if PR is normal, probability is 14%. If CP is pathologic, probability of FbA is 69-76% with presence of cough (LR = 1.32) or dyspnea (LR = 1.84) or localized crackles (LR = 1.5). Probability is 81-88% if cyanosis (LR = 4.8) or decreased breaths sounds (LR = 4.3) or asymetric auscultation (LR = 2.9) or localized wheezing (LR = 2.5) are present. When CP is anormal and PR show mediatinal shift (LR = 100), pneumomediatin (LR = 100), radio opaque foreign body (LR = 100), lobar distention (LR = 4), atelectasis (LR = 2.5), inspiratory/expiratory abnormal (LR = 7), the probability of FbA is 96-100%. If CP is normal and PR is abnormal the probability is 40-100%. If CP is abnormal and PR is normal the probability is 55-75%. Conclusions: This rewiev of prospective studies demonstrates the importance of CP and PR and an algorithm can be proposed. When CP is abnormal with or without PR pathologic, the probability of FbA is high and bronchoscopy is indicated. When CP and PR are normal the probability of FbA is low and bronchoscopy is not necessary immediatly, observation should be proposed. This approach should be validated with prospective study.

Pavement Surface on Macadam Base: Adair County Final Report, Iowa Highway Reserach Board Project HR-209

The quality and availability of aggregate for pc concrete stone varies across Iowa. Southwest Iowa is one area of the state that is short of quality aggregates. The concrete stone generally available in the area is limestone from the Argentine or Winterset ledges with an overburden of up to 150 feet. This concrete stone is classified as Class 1 durability and is susceptible to 'ID"-cracking. In addition, the general engineering soil classification rates the soils of southwest Iowa as having the poorest subgrade bearing characteristics in the state. 1 The combination of poor soils and low quality aggregate has contributed to premature deterioration of many miles of portland cement concrete pavement. Research project HR-209 was initiated in 1979 to explore alternative construction methods that may produce better pavements for southwest Iowa.

Restoration of Fricitonal Characteristics on Older Portland Cement Concrete Pavement:Final Report for Iowa Highway Research Board Project HR-224, June 1986

Safety i s a very important aspect o f the highway program. The Iowa DOT initiated an inventory o f the friction values of all paved primary roadways i n 1969. This inventory, with an ASTM E-274 test unit, has continued to the present time. The t e s t i n g frequency varies based upon traffic volume and the previous friction value. Historically , the state o f Iowa constructed a substantial amount o f pcc pavement during the 1928-30 period t o "get Iowa out o f the mud". Some of that pavement has never been resurfaced and has been subjected to more than 50 years o f wear. The textured surface has been worn away and has subsequently polished. Even though some pavements from 15 t o 50 years old continue t o function structurally , because of the loss of friction , they do not provide the desired level o f safety to the driver. As a temporary measure, "Sl ippery -When -Wet " signs have been posted on many older pcc roads due to friction numbers below t h e desirable level. These signs warn the motorist of the current conditions. An economical method of restoring the high quality frictional properties i s needed.

Evaluation of the RapidAir 457 Air Void Analyzer, March 2012

An adequate air void system is imperative to produce concrete with freeze-thaw durability in a wet freeze environment such as found in Iowa. Specifications rely on a percentage of air obtained in the plastic state by the pressure meter. Actual, in place air contents, of some concrete pavements in Iowa, have been found with reduced air content due to a number of factors such as excessive vibration and inadequate mixing. Determining hardened air void parameters is a time consuming process involving potential for human error. The RapidAir 457 air void analyzer is an automated device used to determine hardened air void parameters. The device is used in Europe and has been shown to quickly produce accurate and repeatable hardened air results. This research investigates how well the RapidAir 457 results correlate to plastic air content and the image analysis air technique. The repeatability and operator variation were also investigated, as well as, the impact of aggregate porosity and selection of threshold value on hardened air results.

Self-Consolidating Concrete—Applications for Slip-Form Paving: Phase II, May 2011

The goal of the project was to develop a new type of self-consolidating concrete (SCC) for slip-form paving to simplify construction an make smoother pavements. Developing the new SCC involved two phases: a feasibility study (Phase I sponsored by TPF-5[098] and concrete admixtures industry) and an in-depth mix proportioning and performance study and field applications (Phase II). The phase I study demonstrated that the new type of SCC needs to possess not only excellent self-consolidating ability before a pavement slab is extruded, but also sufficient “green” strength (the strength of the concrete in a plastic state) after the extrusion. To meet these performance criteria, the new type of SCC mixtures should not be as fluid as conventional SCC but just flowable enough to be self-consolidating. That is, this new type of SCC should be semi-flowable self-consolidating concrete (SFSCC). In the phase II study, effects of different materials and admixtures on rheology, especially the thixotropy, and green strength of fresh SFSCC have been further investigated. The results indicate that SFSCC can be designed to (1) be workable enough for machine placement, (2) be self-consolidating without segregation, (3) hold its shape after extrusion from a paver, and (4) have performance properties (strength and durability) comparable with current pavement concrete. Due to the combined flowability (for self-consolidation) and shape-holding ability (for slip-forming) requirements, SFSCC demands higher cementitious content than conventional pavement concrete. Generally, high cementitious content is associated with high drying shrinkage potential of the concrete. However, well-proportioned and well-constructed SFSCC in a bike path constructed at Ames, IA, has not shown any shrinkage cracks after approximately 3 years of field service. On the other hand, another SFSCC pavement with different mix proportions and construction conditions showed random cracking. The results from the field SFSCC performance monitoring implied that not only the mix proportioning method but also the construction practice is important for producing durable SFSCC pavements. A carbon footprint, energy consumption, and cost analysis conducted in this study have suggested that SFSCC is economically comparable to conventional pavement concrete in fixed-form paving construction, with the benefit of faster, quieter, and easier construction.

Integral Bridge Abutment-to-Approach Slab Connection Final Report, June 2008

The Iowa Department of Transportation has long recognized that approach slab pavements of integral abutment bridges are prone to settlement and cracking, which manifests as the “bump at the end of the bridge”. A commonly recommended solution is to integrally attach the approach slab to the bridge abutment. Two different approach slabs, one being precast concrete and the other being cast-inplace concrete, were integrally connected to side-by-side bridges and investigated. The primary objective of this investigation was to evaluate the approach slab performance and the impacts the approach slabs have on the bridge. To satisfy the research needs, the project scope involved a literature review, survey of Midwest Department of Transportation current practices, implementing a health monitoring system on the bridge and approach slab, interpreting the data obtained during the evaluation, and conducting periodic visual inspections. Based on the information obtained from the testing the following general conclusions were made: The integral connection between the approach slabs and the bridges appear to function well with no observed distress at this location and no relative longitudinal movement measured between the two components; Tying the approach slab to the bridge appears to impact the bridge; The two different approach slabs, the longer precast slab and the shorter cast-in-place slab, appear to impact the bridge differently; The measured strains in the approach slabs indicate a force exists at the expansion joint and should be taken into consideration when designing both the approach slab and the bridge; The observed responses generally followed an annual cyclic and/or short term cyclic pattern over time.

Testing Guide for Implementing Concrete Paving Quality Control Procedures, March 2008

Construction of portland cement concrete pavements is a complex process. A small fraction of the concrete pavements constructed in the United States over the last few decades have either failed prematurely or exhibited moderate to severe distress. In an effort to prevent future premature failures, 17 state transportation agencies pooled their resources, and a pooled fund research project, Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements, was undertaken in 2003. Its purpose was to evaluate existing quality control tests, and then select and advance the state-of-the-practice of those tests most useful for optimizing concrete pavements during mix design, mix verification, and construction. This testing guide is one product of that project. The guide provides three recommended testing schemes (Levels A, B, and C, depending on a pavement’s design life and traffic volumes, etc.) that balance the costs of testing with the risk of failure for various project types. The recommended tests are all part of a comprehensive suite of tests described in detail in this guide.

Evaluation of the MIT-Scan-T2 for Non-Destructive PCC Pavement Thickness Determination Final Report, July 2008

The MIT-Scan-T2 device is marketed as a non-destructive way to determine pavement thickness on both HMA and PCC pavements. PCC pavement thickness determination is an important incentivedisincentive measurement for the Iowa DOT and contractors. The thickness incentive can be as much as 3% of the concrete contact unit price and the disincentive can be as severe as remove and replace. This study evaluated the potential of the MIT device for PCC pavement thickness quality assurance. The limited testing indicates the unit is sufficiently repeatable and accurate enough to replace core drilling as the thickness measurement method. Further study is needed to statistically establish the single user and multi-user/device precision as well as establish an appropriate sampling protocol and PWL specification.

Cardiac and pericardial fistulae associated with esophageal or gastric neoplasms: a literature review

Pericardial and cardiac fistulae secondary to esophageal or gastric tumors are considered exceptional. They have never been the object of a literature review. We reviewed the medical literature between 1881 and 2001, searching for all published cases of pericardial or cardiac fistulae developed from esophageal and gastric tumors or favored by the applied therapy to these tumors. The cases of metastasization, tumor spread, and neoplasic pericardial effusion without fistula were excluded. Fifty patients were identified, with one original case. More than half the cases (56%) occurred in the last 25 years. Substernal pain is the main symptom. The majority of patients present at least one condition favoring fistula formation. The auscultation of a water-wheel murmur may suggest a pneumopericardium and therefore a pericardial fistula, as does a purulent pericarditis. Arrhythmias, signs of ischemia, and hematemesis point toward a ventricular fistula. Neurological and hemostasis disorders may be suspect of an atrial lesion. Diagnosis should be made by the association of a scanner and a transit. Prognosis is bad: 76% of the patients die in the first month. Pericardial or cardiac fistulae are part of the differential diagnosis of thoracic pain in patients with esophageal or gastric tumors and in patients who were treated for these pathologies. The diagnosis must be as quick as possible. An operation (patients with a good prognosis) or the placement of a stent (patients with a bad prognosis) is the only chance of survival

Improving the Accuracy and Usability of Iowa Falling Weight Deflectometer Data, May 2013

This study aims to improve the accuracy and usability of Iowa Falling Weight Deflectometer (FWD) data by incorporating significant enhancements into the fully-automated software system for rapid processing of the FWD data. These enhancements include: (1) refined prediction of backcalculated pavement layer modulus through deflection basin matching/optimization, (2) temperature correction of backcalculated Hot-Mix Asphalt (HMA) layer modulus, (3) computation of 1993 AASHTO design guide related effective SN (SNeff) and effective k-value (keff ), (4) computation of Iowa DOT asphalt concrete (AC) overlay design related Structural Rating (SR) and kvalue (k), and (5) enhancement of user-friendliness of input and output from the software tool. A high-quality, easy-to-use backcalculation software package, referred to as, I-BACK: the Iowa Pavement Backcalculation Software, was developed to achieve the project goals and requirements. This report presents theoretical background behind the incorporated enhancements as well as guidance on the use of I-BACK developed in this study. The developed tool, I-BACK, provides more fine-tuned ANN pavement backcalculation results by implementation of deflection basin matching optimizer for conventional flexible, full-depth, rigid, and composite pavements. Implementation of this tool within Iowa DOT will facilitate accurate pavement structural evaluation and rehabilitation designs for pavement/asset management purposes. This research has also set the framework for the development of a simplified FWD deflection based HMA overlay design procedure which is one of the recommended areas for future research.

Improving the Accuracy and Usability of Iowa Falling Weight Deflectometer Data: Tech Transfer Summary, May 2013

This study aims to improve the accuracy and usability of Iowa Falling Weight Deflectometer (FWD) data by incorporating significant enhancements into the fully-automated software system for rapid processing of the FWD data. These enhancements include: (1) refined prediction of backcalculated pavement layer modulus through deflection basin matching/optimization, (2) temperature correction of backcalculated Hot-Mix Asphalt (HMA) layer modulus, (3) computation of 1993 AASHTO design guide related effective SN (SNeff) and effective k-value (keff ), (4) computation of Iowa DOT asphalt concrete (AC) overlay design related Structural Rating (SR) and kvalue (k), and (5) enhancement of user-friendliness of input and output from the software tool. A high-quality, easy-to-use backcalculation software package, referred to as, I-BACK: the Iowa Pavement Backcalculation Software, was developed to achieve the project goals and requirements. This report presents theoretical background behind the incorporated enhancements as well as guidance on the use of I-BACK developed in this study. The developed tool, I-BACK, provides more fine-tuned ANN pavement backcalculation results by implementation of deflection basin matching optimizer for conventional flexible, full-depth, rigid, and composite pavements. Implementation of this tool within Iowa DOT will facilitate accurate pavement structural evaluation and rehabilitation designs for pavement/asset management purposes. This research has also set the framework for the development of a simplified FWD deflection based HMA overlay design procedure which is one of the recommended areas for future research.

Evaluating Roadway Subsurface Drainage Practices, 2013

The bearing capacity and service life of a pavement is affected adversely by the presence of undrained water in the pavement layers. In cold winter climates like in Iowa, this problem is magnified further by the risk of frost damage when water is present. Therefore, well-performing subsurface drainage systems form an important aspect of pavement design by the Iowa Department of Transportation (DOT). However, controversial findings are also reported in the literature regarding the benefits of subsurface drainage. The goal of this research was not to investigate whether subdrains are needed in Iowa pavements, but to conduct an extensive performance review of primary interstate pavement subdrains in Iowa, determine the cause of the problem if there are drains that are not functioning properly, and investigate the effect of poor subdrain performance due to improper design, construction, and maintenance on pavement surface distresses, if any. An extensive literature review was performed covering national-level and state-level research studies mainly focusing on the effects of subsurface drainage on performance of asphalt and concrete pavements. Several studies concerning the effects of a recycled portland cement concrete (RPCC) subbase on PCC pavement drainage systems were also reviewed. A detailed forensic test plan was developed in consultation with the project technical advisory committee (TAC) for inspecting and evaluating the Iowa pavement subdrains. Field investigations were conducted on 64 selected (jointed plain concrete pavement/JPCP and hot-mix asphalt/HMA) pavement sites during the fall season of 2012 and were mainly focused on the drainage outlet conditions. Statistical analysis was conducted on the compiled data from field investigations to further investigate the effect of drainage on pavement performance. Most Iowa subsurface drainage system outlet blockage is due to tufa, sediment, and soil. Although higher blockage rates reduce the flow rate of water inside outlet pipes, it does not always stop water flowing from inside the outlet pipe to outside the outlet pipe unless the outlet is completely blocked. Few pavement surface distresses were observed near blocked subsurface drainage outlet spots. More shoulder distresses (shoulder drop or cracking) were observed near blocked drainage outlet spots compared to open ones. Both field observations and limited performance analysis indicate that drainage outlet conditions do not have a significant effect on pavement performance. The use of RPCC subbase in PCC pavements results in tufa formation, a primary cause of drainage outlet blockage in JPCP. Several useful recommendations to potentially improve Iowa subdrain performance, which warrant detailed field investigations, were made

Evaluating Roadway Subsurface Drainage Practices: Tech Transfer Summary, 2013.

The bearing capacity and service life of a pavement is affected adversely by the presence of undrained water in the pavement layers. In cold winter climates like in Iowa, this problem is magnified further by the risk of frost damage when water is present. Therefore, well-performing subsurface drainage systems form an important aspect of pavement design by the Iowa Department of Transportation (DOT). However, controversial findings are also reported in the literature regarding the benefits of subsurface drainage. The goal of this research was not to investigate whether subdrains are needed in Iowa pavements, but to conduct an extensive performance review of primary interstate pavement subdrains in Iowa, determine the cause of the problem if there are drains that are not functioning properly, and investigate the effect of poor subdrain performance due to improper design, construction, and maintenance on pavement surface distresses, if any. An extensive literature review was performed covering national-level and state-level research studies mainly focusing on the effects of subsurface drainage on performance of asphalt and concrete pavements. Several studies concerning the effects of a recycled portland cement concrete (RPCC) subbase on PCC pavement drainage systems were also reviewed. A detailed forensic test plan was developed in consultation with the project technical advisory committee (TAC) for inspecting and evaluating the Iowa pavement subdrains. Field investigations were conducted on 64 selected (jointed plain concrete pavement/JPCP and hot-mix asphalt/HMA) pavement sites during the fall season of 2012 and were mainly focused on the drainage outlet conditions. Statistical analysis was conducted on the compiled data from field investigations to further investigate the effect of drainage on pavement performance. Most Iowa subsurface drainage system outlet blockage is due to tufa, sediment, and soil. Although higher blockage rates reduce the flow rate of water inside outlet pipes, it does not always stop water flowing from inside the outlet pipe to outside the outlet pipe unless the outlet is completely blocked. Few pavement surface distresses were observed near blocked subsurface drainage outlet spots. More shoulder distresses (shoulder drop or cracking) were observed near blocked drainage outlet spots compared to open ones. Both field observations and limited performance analysis indicate that drainage outlet conditions do not have a significant effect on pavement performance. The use of RPCC subbase in PCC pavements results in tufa formation, a primary cause of drainage outlet blockage in JPCP. Several useful recommendations to potentially improve Iowa subdrain performance, which warrant detailed field investigations, were made.

Quality Control/Quality Assurance Testing for Joint Density and Segregation of Asphalt Mixtures, TR-623, 2013

Longitudinal joint quality control/assurance is essential to the successful performance of asphalt pavements and it has received considerable amount of attention in recent years. The purpose of the study is to evaluate the level of compaction at the longitudinal joint and determine the effect of segregation on the longitudinal joint performance. Five paving projects with the use of traditional butt joint, infrared joint heater, edge restraint by milling and modified butt joint with the hot pinch longitudinal joint construction techniques were selected in this study. For each project, field density and permeability tests were made and cores from the pavement were obtained for in-lab permeability, air void and indirect tensile strength. Asphalt content and gradations were also obtained to determine the joint segregation. In general, this study finds that the minimum required joint density should be around 90.0% of the theoretical maximum density based on the AASHTO T166 method. The restrained-edge by milling and butt joint with the infrared heat treatment construction methods both create the joint density higher than this 90.0% limit. Traditional butt joint exhibits lower density and higher permeability than the criterion. In addition, all of the projects appear to have segregation at the longitudinal joint except for the edge-restraint by milling method.