The objective of this research was to quantify the effects of selected parameters on the accuracy of concrete cover measurements on bridge decks. This research involved three full-factorial laboratory experiments each designed to investigate one of three primary variables. These primary variables included distance to a parallel adjacent bar, distance to a reinforcement intersection, and incorrect bar size input for the cover meter. Each experiment also involved four secondary variables known to affect cover readings. These secondary variables included actual cover depth, meter brand, antenna type, and bar size. Statistical analyses were performed to determine the significance of each factor. A margin of error of 0.125 in., corresponding to the increase in diameter between successive U.S. standard rebar sizes, was established as the threshold for practical importance in the data analysis. Three primary findings resulted from the three experiments performed in this research. For the meters and antennas tested, the results of the field-of-view experiment indicated that, if the spacing is greater than approximately 4.0 in., the returned readings are within the threshold for practical importance established for this research. The results of the proximity-to-an-intersection experiment indicated that, regardless of where the measurement is taking place in relation to an intersection, the operator can be confident that the errors will be less than 0.125 in. as long as the bar in question is above the intersecting bar. The results of the wrong-bar-size experiment indicated that, if the operator of the cover meter does not know the actual rebar size in question, the measured cover will be within 0.125 in. of the actual cover depth as long as the meter input is within one bar size of the correct value. Obtaining accurate cover measurements on bridge decks is important for quality assurance, service life prediction, and rehabilitation programming.

Experiments were conducted to investigate the potential of using a quench and self-tempering heat treatment process with AISI 1117 steel to satisfy the mechanical properties of ASTM A 706 rebar. A series of quenching tests were performed and the resulting microstructure and mechanical properties studied using optical microscopy, microhardness measurement, and tensile tests. The presence of martensite throughout the samples contributed to the enhanced strength and strain-hardening ratio (tensile to yield strength) of the material. The experimental results showed that AISI 1117 is capable of meeting the ASTM standard. In addition to the experiments, a computer model using the finite difference method and incorporating heat transfer and microstructure evolution was developed to assist in future optimization of the heat treatment process.

Experiments were conducted to investigate the potential of using a quench and self-tempering heat treatment process with AISI 1117 steel to satisfy the mechanical properties of ASTM A 706 rebar. A series of quenching tests were performed and the resulting microstructure and mechanical properties studied using optical microscopy, microhardness measurement, and tensile tests. The presence of martensite throughout the samples contributed to the enhanced strength and strain-hardening ratio (tensile to yield strength) of the material. The experimental results showed that AISI 1117 is capable of meeting the ASTM standard. In addition to the experiments, a computer model using the finite difference method and incorporating heat transfer and microstructure evolution was developed to assist in future optimization of the heat treatment process.

About half of the total building stock in Turkey is masonry type building. Masonry buildings in Turkey, especially in rural areas, are constructed without any engineering knowledge mostly by their own residents. They generally have heavy roofs. Masonry type buildings also have thick and heavy wall materials. Heavy roof and wall material generate large inertial forces in the case of an earthquake. Brittle failure of walls leads to total failure of whole system followed by sudden collapse of heavy roof. The aim of this thesis is to understand failure mechanisms of brick masonry walls, prevent their brittle failure and allow the walls to dissipate energy during an earthquake. Furthermore, ultimate capacity increase was also targeted by using low cost and easy to obtain material. In order to find an economical and effective way in strengthening of brick masonry walls in their in-plane direction, steel rebars were used as post-tensioning materials in brick masonry walls and house tests. Springy connections were utilized in the reinforcing and post-tensioning bars in order to prevent early loss of post-tension due to wall cracking or rebar yielding. Separate tests were conducted with and without rebars and springs in order to compare their results. v The test results indicated that the ultimate lateral load capacity of 6m long brick masonry house increased up to about 6 times with respect to its nominal value. Energy dissipation also increased up to about 10 times of the original house. Lateral load capacity increase in 2m long rebar post-tensioned brick masonry walls were measured as about 17 times when compared with the original wall. The energy dissipation capacity was also increased about 30 times the nominal value. A general procedure was developed to assess the vulnerability of single storey masonry houses, which calculates the earthquake demand acting on each wall segment. Comparison of capacity versus demand enables evaluation of wall segments and leads strengthening calculations if necessary. Derived formulas were used to calculate post-tensioning force and design vertical and diagonal rebars. The procedure was demonstrated using properties of an existing house and strengthening cost was found to be about 10% of the building cost. The results of the conducted tests have shown that rebar post-tensioning of brick masonry walls is an effective and cost-efficient way of strengthening the walls in their in-plane direction and can be used as an economical and simple technique for seismically vulnerable masonry houses. Spring based connection detail has improved the post cracking performance of the walls at large deformations by keeping the wall reaction higher after ultimate strength has reached as well as increased the energy dissipation capacity of the walls.

Numerous cases of premature concrete deterioration due to alkali-silica reaction and/or delayed ettringite formation have developed within highway infrastructure in the state of Texas over the past two decades. Although experimental research and in-situ load testing on an international scale has indicated that moderate levels of deterioration are unlikely to pose a threat to structural safety, the discovery of reinforcing bar fracture in Japan due to ASR-related expansion has called into question the integrity of heavily damaged structures. A two-part experimental program was conducted at The University of Texas at Austin relating to ASR/DEF-induced reinforcing bar fracture. Work conducted under TxDOT Project 0-6491 included the fabrication and monitoring of four concrete specimens. Methods were employed to simulate a fracture of the transverse reinforcement within the time frame of the study and the applicability of various NDT monitoring techniques to detect bar fracture was evaluated. Furthermore, a number of reinforcing bar samples were tested and analyzed to investigate (1) the development of reinforcing bar cracking due to the bending operation and (2) the progression of cracks after application of an expansive opening force on bars with 90° bends. Research findings and conclusions form a preliminary assessment on the potential for reinforcing bar fracture within affected infrastructure in Texas. / text

Rebar carpet is an innovation that favors the working environment of the rebar workers and saves time. Reinforcement workers today are a vulnerable group. Heavy lifts and backbreaking postures are a part of their everyday work. It is already established that work with rebar carpets is both time-saving, economically beneficial and from a working environment point of view better than traditional reinforcement work. Despite all benefits it is used in rather few projects today. The purpose of this study is to identify how the construction industry embraces new innovations related to in situ concrete with post-tensioned reinforcement. The goals are to find out how designers, contractors and manufacturers are working to adopt rebar carpets in the construction process and to shed light on, factors affecting the adoption. The study is based on semi-structured interviews with designers, contractors and a representative of a rebar manufacturing company. Designers and contractors have not, generally speaking, been actively working to adopt rebar carpet. The governing factors for the use of rebar carpets is the designers and contractors knowledge and previous experience of rebar carpet. The contractors who have previous experience of rebar carpet can imagine using rebar carpet again and contractors with no previous experience believe that they need more knowledge of rebar carpet before they dare to try. Design engineers who have designed for rebar carpet before has it in mind when they design other projects. Designers who have no previous experience of rebar carpet demand more knowledge about how they can facilitate the use of rebar carpet.

This investigation determined that severe corrosion of steel can occur in the submerged portions of reinforced concrete structures in marine environments. Field studies of decommissioned pilings from actual bridges revealed multiple instances of strong corrosion localization, showing appreciable local loss of steel cross-section. Quantitative understanding of the phenomenon and its causes was developed and articulated in the form of a predictive model. The predictive model output was consistent with both the corrosion rate estimates and the extent of corrosion localization observed in the field observations. The most likely explanation for the observed phenomena that emerged from the understanding and modeling is that cathodic reaction rates under oxygen diffusional limitation that are negligible in cases of uniform corrosion can nevertheless support substantial corrosion rates if the corrosion becomes localized. A dynamic evolution form of the model was created based on the proposition that much of the steel in the submerged concrete zone remained in the passive condition given cathodic prevention that resulted from favorable macrocell coupling with regions of the steel that had experienced corrosion first. The model output also matched observations from the field, supporting the plausibility of the proposed scenario. The modeling also projected that corrosion in the submerged zone could be virtually eliminated via the use of sacrificial anode cathodic protection; the rate of corrosion damage progression in the low elevation zone above water could also be significantly reduced. Continuation work should be conducted to define an alternative to the prevalent limit-state i.e., visible external cracks and spalls, for submerged reinforced concrete structures. Work should also be conducted to determine the possible structural consequences of this form of corrosion and to assess the technical feasibility and cost/benefit aspects of incorporating protective anodes in new pile construction.

This research presents the results on an experimental investigation to identify the effects of rebar temperature, fly ash and water to cement ratio on concrete porosity in continuously reinforced concrete pavements (CRCP). Samples were cast and analyzed using pullout tests. Water to cement ratio (w/c) and rebar temperature had a significant influence on the rebar-concrete bond strength. The 28-day shear strength measurements showed an increase in rebar-concrete bond strength as the water to cement ratio (w/c) was reduced from 0.50 to 0.40 for both fly ash containing and non fly ash control samples. There was a reduction in the peak pullout load as the rebar surface temperature increased from 77o F to 150o F for the cast samples. A heated rebar experiment was performed simulating a rebar exposed to hot summer days and the rebar cooling curves were plotted for the rebar temperatures of 180o F - 120o F. Fourier transform infrared spectroscopy was performed to show the moisture content of cement samples at the rebar-concrete interface. Mercury intrusion porosimetry test results on one batch of samples were used for pore size distribution analysis. An in-depth analysis of the morphological characteristics of the rebar-concrete interface and the observation of pores using the scanning electron microscope (SEM) was done.

The objective of this research was to investigate the effects of twisted steel micro rebar (TSMR) fibers on 1) the mechanical properties of concrete used in bridge deck construction and 2) the early cracking behavior of concrete bridge decks. This research involved the evaluation of four newly constructed bridge decks through a series of laboratory and field tests. At each location, one deck was constructed using a conventional concrete mixture without TSMR, and one was constructed using the same conventional concrete mixture with an addition of 40 lb of TSMR per cubic yard of concrete. Regarding laboratory testing, the conventional and TSMR beam specimens exhibited similar average changes in height after 4 months of shrinkage testing. The electrical impedance measurements did not indicate a notable difference between specimens comprising concrete with TSMR and those comprising conventional concrete. Although no notable difference in behavior between conventional and TSMR specimens was apparent before initial cracking, the toughness of the TSMR specimens was substantially greater than that of the conventional concrete specimens. Regarding field testing, sensors installed in the bridge decks indicated that the addition of TSMR does not affect internal concrete temperature, moisture content, or electrical conductivity. The average Schmidt rebound number varied little between the TSMR decks and conventional decks; therefore, the stiffness of the TSMR concrete was very similar to that of conventional concrete. Distress surveys showed that the conventional decks exhibited notably more cracking than the TSMR decks. The TSMR fibers exhibited the ability to limit both crack density and crack width. For all of the decks, chloride concentrations increased every year as a result of the use of deicing salts on the bridge decks during winter. However, the chloride concentrations for samples collected over cracked concrete increased more rapidly than those for samples collected over non-cracked concrete. Although TSMR fibers themselves do not directly affect the rate at which chloride ions penetrated cracked or non-cracked concrete, the fibers do prevent cracking, which, in turn, limits the penetration of chloride ions into the decks. Therefore, the use of TSMR would be expected to decrease the area of a bridge deck affected by cracking and subsequent chloride-induced corrosion damage and thereby increase the service life of the bridge deck.

No description available.