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.

No abstract

Acceptance testing of ready-mixed concrete occurs after the product has been delivered to the consumer in the field. The testing process commences with the collection of a relatively small but representative sample of the fresh concrete. ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed Concrete, states that two or more portions of material should be collected at regularly spaced intervals during discharge of the middle portion of the batch. There is concern within the industry that field technicians are opting to obtain only one portion of concrete from the material initially discharged from a truck. A study undertaken at Valparaiso University investigated the first issue of collecting only one portion of concrete. The primary objective of this research was to determine if the measured properties for a single portion sample taken from the middle of a batch differ statistically from that for a two-portion sample also taken from the middle of the batch. Concrete was sampled 46 times across 11 different construction sites with fresh properties and 28-day compressive strength measured in each case. Construction projects were selected to provide a range of concrete mixture specifications, site conditions, and target property values. Findings indicate that it is not necessary to collect a sample of two or more portions from a revolving drum truck mixer. Rather, a single portion sample of concrete is sufficient for acceptance testing purposes.

No abstract

No abstract