Stephan Durham

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...

Performance of an Anti-Icing Epoxy Overlay on Asphalt Surfaces

AbstractThis paper summarizes the evaluation of a thin-bonded epoxy overlay placed on an asphalt-wearing surface in an effort to increase skid resistance, decrease wear of the bridge deck, reduce the development of bonded snow and ice during winter conditions, and provide a safe drivable surface. The uniqueness of this study is the installation of a polymer-based overlay with anti-icing/antiskid properties on an asphalt-wearing surface. This thin-bonded epoxy overlay was examined based on mean texture depth, surface friction, bond strength, ability to stop chloride intrusion, anti-icing properties, traffic safety, and cost. Mean texture depth and friction testing produced a durable wearing surface with good traction. Bond strength test results demonstrated that the asphalt layer will fail prior to the epoxy overlay. Chloride content of the concrete bridge deck decreased with the use of the thin-bonded overlay. The anti-icing property of the overlay is effective when precharged with deicing chemicals but s...

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.

Retrofitting Precast Bridge Beams with Carbon Fiber-Reinforced Polymer Strips for Shear Capacity

Advancements in fiber-reinforced polymers (FRPs) have made this an attractive material for rehabilitation and strengthening of bridge superstructures. FRP has primarily been used with the intention of increasing the bending strength of bridge members. However, this paper investigates the use of externally placed FRP strips to increase shear capacity of short-span, 5.7 m (19 ft), precast concrete channel beam bridges. A statewide survey revealed that as many as 389 bridges in the state of Arkansas are comprised of these members. Notably, beams within these bridges were designed under provisions that did not require shear reinforcement. In this research, four sections were retrofitted using carbon fiber-reinforced polymer (CFRP) strips and load tested to failure to measure the repair effectiveness. The performance of the retrofitted sections far exceeded that of unretrofitted sections. It was concluded that the addition of the CFRP repair increased the deflection ductility at least 123%. In addition, beams retrofitted with the CFRP strips experienced at least 26% more deflection after the initiation of a shear crack; therefore reducing the risk of a catastrophic failure.

FIBER-REINFORCED POLYMER SHEAR STRENGTHENING OF SHORT-SPAN, PRECAST CHANNEL BEAMS IN BRIDGE SUPERSTRUCTURES

A national study concluded that at least 14 states use precast channel beams for their bridge superstructures. Before the mid-1970s short-span (19-ft) precast channel beam bridges were designed by the Arkansas State Highway and Transportation Department for H15 loading without any provision for shear reinforcement. A recent statewide survey has identified 389 of these bridges that remain in service. About 3% are load posted. Approximately one-third of the 389 bridges are exhibiting deterioration that may be serious. During a recent investigation by the University of Arkansas, 33 precast channel beams were evaluated for structural strength. It was determined that many of these units have inadequate shear capacity. A shear crack frequency distribution curve was developed through examination of the 33 tested beams. A simple shear strengthening technique is presented consisting of fiber-reinforced polymer (FRP) strips as external stirrups. The technique has been developed so that it can be easily implemented in the field. The FRP strips are spaced to prevent the full formation of a diagonal crack between two adjacent strips and designed to ensure a flexural failure rather than a sudden shear failure. Four beams retrofitted with the proposed retrofit technique and two control beams were load tested to failure to evaluate the effectiveness of the technique. Results from the experiment show that the retrofitted beams exhibited at least a 290% increase in deflection ductility and a 418% increase in energy ductility.

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.

Structural Evaluation of Precast Concrete Channel Beams in Bridge Superstructures

During the period from the mid-1950s through the mid-1970s a large number of bridges were constructed throughout Arkansas using a 5.79-m (19-ft) long, precast, non-prestressed, concrete channel beam that was then standard. A survey of highway departments has identified 12 states that have used a similar bridge element in the past. It has been determined that nearly 400 of these bridges remain in use in Arkansas alone. Recently, the Arkansas State Highway and Transportation Department discovered that a number of these sections are exhibiting potentially serious deterioration. The deterioration appears to have been initiated by corrosion of the flexural reinforcement in the beam stems. An additional issue is that these beams were fabricated without any shear reinforcement. Moreover, some sections are showing signs of concrete degradation. The need to determine the in-place load capacity, serviceability, and durability of these sections has reached a critical level. To date, 20 beams have been removed from existing structures and tested for their flexural load capacity and the material properties of the concrete and longitudinal reinforcement. Results have varied depending on the extent of deterioration. However, in nearly every case shear failure has controlled the load capacity of a section. Based on this research, a draft field guide, intended for use by inspection crews, is being prepared. This guide will aid inspectors in prioritizing sections for repair, rehabilitation, and removal.

Live Load Distribution Factors in Two-Girder Bridge Systems Using Precast Trapezoidal U-Girders

The lever rule method is often used to determine live load distribution factors (LDFs) in two-girder bridge systems because of the ranges of applicability implicit in the simplified equations of the AASHTO LRFD bridge design specifications. This method is typically more conservative than the simplified equations, which take into account key parameters such as beam spacing, span length, longitudinal beam stiffness, and slab thickness. The lever rule method for yielding LDFs does not take into account these key parameters and only considers simple span distribution; therefore, a certain degree of conservatism is implied. This study demonstrates that the lever rule method in determining LDFs in two-girder bridge systems using precast trapezoidal U-girders is not overly conservative, as comparisons between LDFs from finite-element analysis (FEA) and the lever rule method of the AASHTO LRFD show that the lever rule method produces values for LDFs that are closely reflective of the actual response for shear and to a lesser degree for flexure. The effects of live load on parameters that include flexural response, slenderness, and span length are also considered.

Retrofitting Short-Span Precast Channel Beam Bridges Constructed without Shear Reinforcement

This paper investigates retrofitting precast, nonprestressed, channel beams (PCB) used in short-span bridges to improve beam shear strength and, consequently, beam ductility. Three retrofit approaches were investigated: applying carbon-fiber-reinforced polymer (CFRP) strips, applying an epoxy spray-on, and retrofitting by installing shear bars within the stems of the precast channel beam. Implanting shear bars into each precast channel beam stem was found to be the optimal retrofit based on improved beam strength, installation ease, and economics. The suitability of the shear bar retrofit was further explored by implementing the shear bar retrofit at a short-span precast channel beam bridge. Precast channel beam sections cast without shear reinforcement were used to construct Arkansas Bridge #02992 over the Flat Hollow Branch Creek. The bridge was constructed in 1955, but several of the beams used in the original construction have since been replaced with better-condition similar-style beams. The bridge i...

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.