Kevin L. Rens

Optimization of Cementitious Material Content for Sustainable Concrete Mixtures

AbstractUtilization of fly ash in concrete reduces the use of virgin materials and offers benefits of reduced landfill materials and CO2 emissions avoidance—fly ash therefore contributes to industrial sustainability. This paper presents a method to optimize the cement and fly ash contents in concrete on the basis of the hardened concrete properties testing and environmental effects. Such fly ash concrete would develop an adequate 1-day and 28-day compressive strength and would be as durable as the ordinary portland cement concrete. Nine concrete mixtures with fly ash contents ranging from 15–60% and cementitious material contents from 338–391  kg/m3 (570-705  lbs/cu yd) were investigated. Environmental life cycle assessments (LCA) were completed by using a model developed for Denver, Colorado. The optimized fly ash concrete was selected to yield a similar 28-day compressive strength and durability to that of Colorado Department of Transportation (CDOT) Class D structural concrete. The durability aspects i...

Alternate Load Paths in Historic Truss Bridges: New Approaches for Preservation

Engineers who work on historic truss rehabilitation encounter projects for conversion of former vehicular bridges to pedestria n usage. The engineer finds today’s design vertical live loads to be on the same order as those used by the designer from a century ago. Material allowable stresses are also similar (or better). But design wind load is significantly higher. This paper examines non-traditional load paths as an alternative to conventional “skeleton” approach to analysis. The authors’ conclude that alternate load paths do exist and could be utilized by designers using commonly available computer software. Modern Wind Load Criteria One avenue for preservation is conversion of such bridges to pedestrian use. This kind of adaptive reuse permits ready access to historic structures and has the added advantage of providing incentives for continuing maintenance. But the prev ailing code, AASHTO Guide Specifications for the Design of Pedestrian Bridges (AASHTO, 1997) mandates higher design wind load than was used originally. Structural engineers attempting to convert historic bridges to pedestrian use often discover that the o ld structures don’t have the lateral capability to resist today’s AASHTO wind load criteria. This contributes to either a “heavy -handed” design approach, which is both expensive and detrimental to the historic character being preserved in the first place, or to condemnation of the bridge.

Development and analysis of high-performance green concrete in the urban infrastructure

Cement production accounts for approximately 5% of total global CO2 emissions from all human activities. In addition, the consumption of virgin aggregates for concrete infrastructure has created virgin material scarcity issues in many areas of the USA. High-performance green concrete (HPGC) with fly ash and recycled aggregates can help reduce the demand for material inputs and reduce pollution outputs associated with bulk material flow of urban concrete. Structural and durability tests showed that HPGC containing fly ash and 50% recycled aggregate (100% of the coarse aggregate fraction) performed equally or better than 100% ordinary Portland cement concrete with the same cementitious content. Durability improvements were more significant with Class F than Class C fly ash. For both Class F and Class C fly ash, greater per cent replacement of Portland cement with fly ash led to slower and lower strength gain, but still within acceptable strength criteria for Colorado Department of Transportation Class B concrete. This paper quantifies the sustainability of HPGC in urban infrastructure by addressing structural performance, environmental, economic and resource depletion impacts.

Rating City and County of Denver Urban Pavement Constructability Using a Profiler

The international roughness index (IRI) was developed in 1986 to generate a longitudinal roadway profile analysis tool for asphalt surfaces. The IRI is typically applied to freeway and rural highway facilities where uninterrupted spans of asphalt are expected. The city and county of Denver (CCD) in cooperation with the University of Colorado Denver have examined the application of the IRI to urban roadway facilities. Elements of urban roadways that influence IRI values include drainage infrastructure and cross-street access. This paper details the equipment and methodology used to address challenges in assessing urban constructed roadways with the IRI. Repeatability studies were completed using five different inspectors involved in the data collection activities. The results indicated that repeatability varied between different inspectors by approximately 2%. A before-repair and after-repair study was completed on newly resurfaced roadways around the CCD in an attempt to establish a set of baseline values for the application of the IRI to urban roadways. The IRI values for a sample of 23 test cases showed a weighted average postpaving improvement of approximately 36%. Recommended urban IRI values for good and acceptable surfaces are suggested at 150 in./mi (2,367.44 mm/km) and 220 in./mi (3,472.24 mm/km), respectively.

Bridge Health Index for the City and County of Denver, Colorado. II: Denver Bridge Health Index

Current bridge health index (BHI) in Pontis bridge management system applied to assess the bridge health conditions for 615 bridges in the city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. Both the calculation results and the computing methodology of the current BHI reveal that it is subjective to a municipality’s often imprecise cost data. This paper focuses on developing an alternate BHI. In order to understand the principle and procedure of the BHI calculation, the element weighting point was developed as a new concept in the analysis. The study concluded that the weighting point should reflect the effect of element damage on bridge health and function instead of a percentage of element value. Based on this conclusion, the current BHI was modified. The Denver BHI, a new diagnostic tool, was developed. It has already been adopted in the Pontis bridge management system of the CCD public works department.

Bridge Health Index for the City and County of Denver, Colorado. I: Current Methodology

Current Bridge Health Index (BHI) in Pontis Bridge Management System applied to assess the bridge health conditions for 615 bridges in city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. This paper explores both the calculation results and the computing methodology of the current BHI. The BHI was computed for the entire 615 CCD bridge network using the two current cost-based methodologies. Based on the analysis, it was concluded that the current BHI is subjective to a municipality’s often imprecise cost data. This coupled with the methodology of heavily correlating cost with a bridge’s condition reveals potential for modification to meet the needs of the CCD. The results of this study are used as a basis for developing an alternate BHI methodology.

Sustainable Concrete for the Urban Environment: A Proposal to Increase Fly Ash Use in Concrete

Sustainable concrete described as concrete incorporating by-products or waste materials is not a new topic. In fact, published research on the use of fly ash, as a replacement for cement in concrete dates back to the 1930s. Additionally, a considerable amount of research supports the use of sustainable concrete in pavements and/or structural components with beneficial results pertaining to reduction in CO2 emissions, reduction in cost, and achievements in strength and durability. Despite positive research, achieving a more permanent use of sustainable concrete in street and highway projects may require the advocacy for increased utilization of fly ash concrete. This paper argues that increased use of fly ash concrete can occur through continuing fly ash concrete research, motivating public policy efforts and, and furthering technology transfer. Additionally these strategies could contribute to a more committed application of sustainable concrete in street and highway projects.

Recent trends in nondestructive inspections in state highway agencies: can engineering education respond?

This paper presents how one university is addressing the problems of our deteriorating and failing infrastructure. Results of two recent questionnaires reveal that State Highway Agencies are beginning to shift their priorities to emphasize inspection and rating of infrastructure. While both public and private practices are responding, education as a whole tends to remain fixed to traditional analysis and design courses. While traditional courses are essential, new trends must be periodically injected into the curriculum. This paper will show the efforts of the Denver campus of the University of Colorado to educate both undergraduate and graduate engineers in these non-traditional aspects of Civil Engineering. The 3- credit course titled Condition Assessment and Failure Analysis of Civil/Mechanical Infrastructure included such topics as nondestructive evaluation (NDE), lock and dam inspections, bridge maintenance and inspection, structural failure analysis, vehicle accident reconstruction, engineering ethics, and the law. The design of new structures is being overshadowed by the need to maintain and rehabilitate existing structures. In addition, valuable educational material is found in our record of past engineering failures. It is hoped that by publishing information on this course other higher learning institutions will be encouraged to educate students as to the trends that are occurring in practice.

Durability of Sustainable Concrete Mixtures

Use of fly ash in concrete reduces the use of natural raw materials, offers benefits of landfill and CO2 emissions avoidance and therefore contributes to industrial sustainability. This paper presents the results of investigations to determine the various durability aspects of high volume fly ash concrete mixtures, made with ASTM Type I cement and Class C fly ash, yielding a similar 28-day compressive strength to that of Colorado Department of Transportation (CDOT) Class D structural concrete. The durability aspects investigated included the resistance to the chlorideion penetration (ASTM C 1202), the resistance to the repeated cycles of freezing and thawing (ASTM C 666 Procedure A), and the resistance to the sulfate attack (Mortar bars, ASTM C 1012). It is concluded that the high volume fly ash concrete mixtures are able to exhibit excellent durability characteristics with increased curing time. A concrete mixture with a cementitious material content lower than the CDOT specification and a fly ash content greater than the current CDOT limit, was able to meet Class D structural concrete requirements.

Ultrasonic Study at Cimarron Narrow-Gauge Railroad Bridge

Ultrasonic testing can be useful in evaluating components of historic metal bridges, although obtaining meaningful data can be hampered by field conditions. Results from ultrasonic testing on the pins of an historic wrought iron bridge near Cimarron, Colorado are presented. This paper discusses the checkered history of the bridge, the current structural assessment, field problems of obtaining meaningful ultrasonic data, and recommendations for their solution