Reinforced concrete construction

Critical chloride threshold, CT values for initiation of reinforced steel corrosion m
mortar typical of Florida coastal bridge substructures were determined in laboratory tests.
Previous research has reported CT values that vary by more than an order-of-magnitude,
making design life estimation for structures difficult. On this basis, experiments on
piling type specimens focused on [Cl-] contamination in the splash zone and coupling of
this steel to a large surface area submerged anode. The lower portion of simulated piling
was immersed and the region above the waterline periodically sprayed with NaCI
solution. Corrosion potential with respect to height above the waterline was monitored.
A temporary depolarization method for determining as to whether or not corrosion had
initiated is proposed. Chloride distribution at the reinforcement-concrete interface was
determined in piling using energy dispersive x-ray analysis and related to height with
respect to the waterline. Chloride threshold was related to corrosion potential.

This research tests the corrosion resistance of weathering steel against carbon
steel exposed to dry and humid cycles during laboratory experiments. Various
environments are tested and include the following parameters: chloride
concentration, pH and wetting time. Corrosion values from weight loss analysis are
given and studied for the same environments. X-ray diffraction characterized the
formation of different oxides as a function of the environment and gave a better
understanding on the formation of the protective patina on the weathering steel, and
validated that chamber experiments reproduce field conditions. The study is
supported by the design, test and validation of an easily deployable galvanic
atmospheric corrosion sensor that allowed the monitoring of the corrosion rate on
an hourly basis.

Weathering steel has been a primary construction material for bridges in the
United States. Notches caused by corrosion are observed on the flange of steel
I-beams. These notches reduce the cross section area of the structure and are
threats to bridge safety. A606-04 Type 4 cold rolled weathering steel samples
were studied in this thesis to understand the effect of notches that caused by
corrosion. Weathering steel samples were in the shape of plates, which simulated
flange of I-beams. The plate samples were notched across their surfaces by
applying electrical current through an electrochemical circuit composed of an
anode, a cathode and electrolyte. Sixteen samples were notched and cut into
appropriate shape for fatigue testing. S-N (Stress-Number of cycles to failure)
diagram established from fatigue data indicated that the fatigue strength
decreased below AASHTO category B. Weibull analysis was also performed to
understand the reliability distribution.

This research is aimed at investigating the corrosion durability of polyolefin fiber-reinforced
fly ash-based geopolymer structural concrete (hereafter referred to as GPC, in
contradistinction to unreinforced geopolymer concrete referred to as simply geopolymer
concrete), where cement is completely replaced by fly ash, that is activated by alkalis,
sodium hydroxide and sodium silicate. The durability in a marine environment is tested
through an electrochemical method for accelerated corrosion. The GPC achieved
compressive strengths in excess of 6,000 psi. Fiber reinforced beams contained
polyolefin fibers in the amounts of 0.1%, 0.3%, and 0.5% by volume. After being
subjected to corrosion damage, the GPC beams were analyzed through a method of crack
scoring, steel mass loss, and residual flexural strength testing. Fiber reinforced GPC
beams showed greater resistance to corrosion damage with higher residual flexural
strength. This makes GPC an attractive material for use in submerged marine structures.

One of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete bridge structures. Besides investigating durability of CFC cables and pretensioned concrete beams with CFC cables in adverse environments (alkali and seawater), flexure and shear tests were performed on single Double-Tee beams, together with service load behavior, fatigue strength and ultimate load capacity tests on a half scale model Double-Tee girder bridge system prestressed with CFC cables. Exposure to seawater and alkali environments has no adverse effect on the strength of the CFRP tendons as well as the pretensioned beams with CFRP. Based on the flexural strength tests on Double-Tee beams, the bond between CFRP tendons and concrete is satisfactory. The Double-Tee bridge system exhibited good fatigue resistance and adequate ductility under ultimate load conditions. The ultimate load capacity of the bridge is approximately three times the service load corresponding to two HS20-44 trucks and equals 2.4 times the first crack load. Finite element analyses were carried out to predict elastic deformations and collapse load of the Double-Tee bridge prestressed with CFC cables. Feasibility of using CFC cables in bridge structures is assessed based on the experimental and analytical parameters such as deflections, strains, crack distributions and crack widths.

Effects of (1) cement alkalinity (low, normal and high), (2) exposure conditions (RH and temperature), (3) rebar surface condition (as-received versus cleaned) and (4) density and distribution of air voids at the steel-concrete interface on the chloride threshold and time-to-corrosion for reinforcing steel in concrete have been studied. Also, experiments were performed to evaluate effects of RH and temperature on the diffusion of chloride in concrete and develop a method for ex-situ pH measurement of concrete pore water. Once specimens were fabricated and exposed to a corrosive chloride solution, various experimental techniques were employed to determine time-to-corrosion, chloride threshold, diffusion coefficient and void density along the rebar trace as well as pore water pH. Based upon the resultant data, several findings related to the above parameters have been obtained as summarized below. First, time for the corrosion initiation was longest for G109 concrete specimens with high alkalinity cement (HA). Also, chloride threshold increased with increasing time-to-corrosion and cement alkalinity. Consequently, the HA specimens exhibited the highest chloride threshold compared to low and normal alkalinity ones. Second, high temperature and temperature variations reduced time-to-corrosion of reinforcing steel in concrete since chloride diffusion was accelerated at higher temperature and possibly by temperature variations. The lowest chloride threshold values were found for outdoor exposed specimens suggesting that variation of RH or temperature (or both) facilitated rapid chloride diffusion. Third, an elevated time-to-corrosion and chloride threshold values were found for the wire brushed steel specimens compared to as-received ones. The higher ratio of [OH-]/[Fe n+] on the wire brushed steel surface compared to that of as-received case can be the possible cause because the higher ratio of this parameter enables the formation of a more protective passive film on the rebar. Fourth, voids at the steel-concrete interface facilitated passive film breakdown and onset of localized corrosion. This tendency for corrosion initiation increased in proportion to void size irrespective of specimen type. Also, [Cl -]th decreased with increasing void diameter. In addition, new ex-situ leaching method for determining concrete pore water alkalinity was developed.

This study presents and illustrates a methodology to calculate the capacity of an existing reinforced concrete bridge under a non-conventional blast load due to low and intermediate pressures. ATBlast program is used to calculate the blast loads for known values of charge weight and stand off distance. An excel spreadsheet is generated to calculate ultimate resistance, equivalent elastic stiffness, equivalent elastic deflection, natural period of the beam, the maximum deflection, and the maximum rotation in the support for a simple span solid slab and T-Beam bridges. The allowable rotation could be taken as to two degrees. Naval Facility Engineering Command (NAVFAC) approach was adopted, where the inputs were material properties, span length, and area of reinforcement. The use of the Fiber Reinforced Polymer for increasing the capacity of an existing bridge is also presented in this study. Parametric studies were carried out to evaluate the performance of the solid slab and T-Beam bridges under the assumed blast load.

A cyclic polarization procedure was designed to evaluate the pitting potentials of high performance stainless steels in synthetic concrete pore water at different chloride concentrations. Cyclic polarization scans were performed on high performance stainless steel reinforcements, S32201, S32305 and S32205. Pitting initiation was observed below the oxygen evolution potential for high chloride concentrations. S32201 and S32304 showed the presence of metastable pitting before reaching its pitting potential. Pitting resistance performance, based on cyclic polarization, was consistent with each material's respective Pitting Resistance Equivalent Number (PREN) value. For S32201 and S32304, pitting potential decreased as the chloride concentration increased, whereas S32205 did not pit at the chloride concentrations tested.

The construction industry is increasingly turning to the use of environmentally friendly materials in order to meet the sustainable aspect required by modern infrastructures. Consequently, for the last two decades, the expansion of this concept, and the increasing global warming have raised concerns on the extensive use of Portland cement due to the high amount of carbon dioxide gas associated with its production. The development of geopolymer concretes offers promising signs for a change in the way of producing concrete. However, to seriously consider geopolymer binders as an alternative to ordinary Portland cement, the durability of this new material should be evaluated in any comparative analysis. The main purpose of this study was to evaluate the durability characteristics of low calcium fly ash-based geopolymer concretes subjected to the marine environment, compared to ordinary Portland cement concrete with similar exposure. To achieve this goal, 8 molar geopolymer, 14 molar geopolymer and ordinary Portland cement concrete mixes were prepared and tested for exposure in seawater. Compressive strengths in the range of 2900 to 8700 psi (20-60 MPa) were obtained. The corrosion resistance performance of steel-reinforced concrete beams, made of these mixes, was also studied, using an accelerated electrochemical method, with submergence in salt water. The test results indicated that the geopolymer concrete showed excellent resistance to chloride attack, with longer time to corrosion cracking, compared to ordinary Portland cement concrete.

This manuscript predicts the behavior of a doubly reinforced concrete beam with a circular opening at its midspan by closely analyzing traditional beam theory and design. It then confirms these predictions with finite element modeling software while providing design suggestions. The analysis is limited to the tensile and compressive stresses and cracking behavior. The objectives are to determine the stress distribution around a circular opening that agrees with conventional beam theory. The beam behavior is examined from zero load to failure load. ANSYS is utilized in lieu of real world testing, and the appendix includes the finite element results for a beam including design recommendations. The results lay the foundation for a possible new design procedure of concrete beams with single or multiple circular openings. This research offers useful information that was unavailable previously. More research can be conducted to help designers to design lighter, more efficient concrete beams.