The premature deterioration of RC structures is a major concern for infrastructure owners. Cracks accelerate the deterioration processes by providing preferential flow paths for water and aggressive agents. Therefore, to accurately estimate the degradation rate, methodologies to account for the effect of discrete and distributed cracks in service life prediction tools need to be developed. To account for the effect of cracks, their effect on moisture transport in concrete needs to be fully understood and quantified.
The research reported in this dissertation provides more insight to the effect of damage induced by freeze-thaw loading on moisture transport. This study includes an extensive experimental program on moisture transport in saturated and unsaturated damaged cement-based materials. Analytical study and numerical modeling are also used to determine the parameters that have significant effect on the mass transport. Furthermore, new nonlinear parameters are proposed to estimate the freeze-thaw damage in concrete using acoustic spectroscopy technique. Therefore, this study consists of four phases.
In the first phase, three objectives are studied: (i) how damage affects the saturated and unsaturated moisture transport as well as electrical resistivity of concrete. Conceptual models are developed based on the fundamentals of damage mechanics and fluid transport to analytically describe the effect of damage, (ii) whether one-dimensional analyses based on the Sharp Front Theory can explain the relationship between the saturated and unsaturated moisture transport in damaged concrete, and (iii) which transport property and therefore which measurement method is more sensitive to damage. The results show that damage differently affects each of the transport mechanisms, and saturated hydraulic conductivity is more sensitive to damage as compared to sorptivity and electrical resistivity. The 1D analysis, based on the sharp front theory, does not adequately describe the effect of damage on unsaturated transport.
In the second phase, damage was induced by freeze-thaw in mortar specimens. Mass transport properties were measured using electrical resistivity, rapid chloride permeability, sorptivity, drying, air permeability, water permeability, and desorption isotherm. The results indicate that the measured effect of damage depends on the mechanisms of transport used in the measurement technique and different techniques provide a different measure of the effect of damage. The water and air permeability are comparatively more sensitive to the presence of damage.
In the third phase, it is investigated whether classical isothermal unsaturated moisture transport can be used to simulate moisture ingress in damaged mortar and concrete. The results indicate that the unsaturated moisture transport model well simulates early stages of moisture ingress, where capillary suction is the prominent mechanism, for all damage levels. At later stages of moisture transport, where air diffusion and dissolution have significant contribution, simulation results diverge from the experimental results. In the fourth phase, it is investigated whether Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS) technique can be provided a method, using nonlinear parameter and nonlinear quality factor (Qfactor) parameter, to estimate the damage in the absence of prior knowledge of intact material?
The outcomes of this work can be used to develop methodologies to integrate the degree of damage measured on concrete structures using non-destructive testing into service life prediction models and therefore more accurately predict the service life of reinforced concrete structures. More accurate service life prediction models can help operators of infrastructure in scheduling the repair and maintenance activities. Service life prediction is a main deriver in life cycle costing and life cycle assessment analyses and therefore developing more accurate service life prediction models can help to more accurately quantify life cycle cost and environmental emissions and implications of concrete infrastructure.
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 77/10(E), Dissertation Abstracts International|
|Keywords:||Concrete, Freeze-thaw loading, Mass transport, Moisture damage|
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