Concrete construction

With the growing environmental concerns related to the ever increasing
waste disposal problem in the US, the utilizing of recycled materials in Civil
Engineering construction has become an attractive option, which not only
supports the concept of green buildings, but can also bring about economic
savings by conserving natural resources and landfill spaces. However, the
questionable long-term performance of recycled materials often hinders the
widespread use in structural applications. The primary focus of this study was to
develop accelerated aging/testing protocols for predicting the durability of
recycled aggregate concrete (RAC), Type I Portland Cement, and up to 50% fly
ash replacement. Accelerated aging was accomplished by curing the specimens
at elevated temperatures regimes for specific durations. Stiffness-time master
curves were constructed using Time-Temperature Superposition (TTS) and
Stepped Isothermal Method (SIM) based on the Arrhenius Equation. All the
methods demonstrated that the stiffness decreased with time regardless of the
amount of fly ash. The Arrhenius method allowed stiffness prediction up to an
equivalent age of 14,000 hours developed from short-term tests lasting up to 144
hours. It was also found that SIM and TTS provide equitable results, potentially
reducing the number of specimens and testing time for durability prediction.

The corrosion propagation stage of D-CRP (types F and C) was tested under
immersion in water, high humidity, and covered with wet sand. The half-cell potential,
linear polarization test, and electrochemical impedance spectroscopy measurements were
performed. Selected specimens were terminated after 300 days of exposure and visually
inspected. Based on corrosion potential measurements obtained during the corrosion
propagation observation, and calculated corrosion rate based on LPR measurements: all
specimens were actively corroding. Additionally, EIS-Rc values were calculated for FS,
CS and CH specimens. The Rc_EIS were generally greater than Rc_LPR values. EIS
spectra for CI and FI specimens usually included mass transport limitations, as these
specimens were immersed. Both type of specimens immersed in water (FI and CI), appeared to have higher corrosion rate based on LPR-Rc. However, upon autopsy
it was revealed that a more modest amount of corrosion occurred on the reinforcing steel
of FI and CI terminated specimens.

Western Palm Beach County, FL is characterized by thick deposits organic soils at shallow depths. Because of their high void ratio and compressibility, these soils undergo large primary consolidation followed by extended periods of secondary compression causing excessive premature structural distress. Although soil stabilization has been largely used with remarkable results in soft, expansive and non-organic soils, limited research and practice exist in the implementation with highly organic soils. The main motivation of this research was to investigate the effects of cement stabilization on the compressibility behavior of organic rich soils, and develop mix design criteria for optimum cement contents necessary to induce the desired engineering behavior. This optimized mix design may provide guidelines for Deep Mixing Methods in organic soils.

Two duplex stainless steels rebars: UNS32304SS and UNS32101SS, were selected to investigate the corrosion initiation and propagation in reinforced concrete specimens. The investigation is divided in two phases with two different methods to accelerate the transport of chlorides through the concrete and initiate corrosion in a short period of time. After corrosion had initiated and propagated for some time; selected specimens were terminated for visual examination. On specimens selected for autopsy, the rebars in the top row showed corrosion to various degrees. Corrosion had propagated to such extent on the terminated specimens that the specimen showed cracks. Stray current might have caused accelerated corrosion on rebars where corrosion had initiated. Based on chloride concentrations measured at the rebar trace, corrosion initiated: on S32101 rebars on average at 7.9 kg/m3, and S32101 rebars on average at 6.0 kg/m3. The findings suggest that S32304 rebars corroded at a slower than S32101.

This study investigates corrosion initiation and propagation in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. Potential, LPR and EIS measurements were carried out. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values, which suggest mass transfer limitations. So far these specimens show no visual signs of corrosion such as cracks or corrosion products with one exception; where corrosion products have reached the surface. Moreover, the apparent corrosion rate values obtained suggest high corrosion rate. No crack appearance so far, could be explained by the high porosity of the specimens; the corrosion products are filling these pores. It is speculated that although, there might be mass transfer limitations present, the current demanded by the anode is being balanced by a larger cathode area due to macrocell effects, since the high moisture conditions likely reduced the concrete resistivity and increased the throwing power.