Flexure and Fatigue Behavior of RC Beam under the Combined Effect of Freeze-thaw Cycles and Seawater

Abstract

Concrete infrastructures constructed in the Arctic regions are susceptible to numerous environmental damages, including freeze-thaw cycles, seawater, and external loads. Previous studies showed that freeze-thaw cycles and seawater will exacerbate the deterioration, however, most of the studies considered the damages independently due to the limited testing conditions. The current design codes specify minimum requirement of concrete properties in accordance with exposure categories and classes in order to ensure the performance under the aggressive environment. To ensure the performance of concrete structures during their service life and the designs reliability, investigations based on experimental and analytical studies are imperative. The objective of this study was to investigate the effect of concrete strength on the flexure and fatigue behavior of RC beams. Subsequently, the flexure and fatigue behavior of RC beams exposed to combined effect of freeze-thaw cycles and seawater was investigated. The following procedures were performed to conduct the experimental studies. At first, a comparative analysis was conducted on previous studies related to the freeze-thaw cycles, seawater, and external loads with the background of cold region construction. Next, the current design codes were summarized which include exposure categories based on damage factors and the corresponding minimum requirement of concrete property. The minimum compressive strength of concrete specified in design codes was applied to investigate the effect of concrete strength. In the light of the limitations of previous studies, experimental schemes at the structural level were developed. Flexure and fatigue test were conducted according to the design code requirements and the limitations from previous studies. Total 12 RC beams were fabricated to experimentally investigate the effect of concrete strength, freeze-thaw cycles, and seawater. Measurement schemes considering temperature effect were established prior to the structural test since electronic measuring sensors have a specific allowable operation temperature range. The structural behavior including ultimate load, fatigue life, deflection, strain of rebar, and cracking behavior were measured under various temperature conditions. The experimental results demonstrated that normal strength concrete had greater deterioration under freeze-thaw cycles and seawater exposure. Freeze-thaw cycles and seawater decreased the material properties of concrete and structural behavior of RC beams, and the combined effect of freeze-thaw cycles and seawater accelerated the deterioration of RC beams. Conversely, the specimen with high concrete strength (60 MPa) exhibited superior performance compared to the specimen with normal concrete strength. Analytical studies incorporating finite element analysis, section analysis, and regression analysis were conducted for the behavior that were difficult to obtain from experiments. Freeze-thaw resistance increased as concrete strength increased, however, concrete strength at higher than 60 MPa is not recommended in cold region construction. To better evaluate the capacity of concrete structures under the effect of freeze-thaw cycles and seawater exposure, both static and fatigue tests were recommended to be conducted. To account for actual environmental conditions, the effect of freeze-thaw cycles and seawater should be simultaneously considered in experimental studies. Lastly, the definition of low temperature in design codes was recommended to be defined based on the target temperature of structures.