The prevalence of concrete and cement-based materials in the civil infrastructure plus the risk of failure makes structural health monitoring an important issue in the understanding of the complete life cycle of civil structures. Correspondingly, the field of nondestructive evaluation (NDE) has been maturing and now concentrates on the detection of flaws and defects, as well as material damage in early stages of degradation. This defect detection is typically usually done by looking at the impulse response of the medium in question such as a cement-based material. The impulse response of a solid can be used to image a complex medium. Classically, the waveform is obtained by an active setup: an ultrasonic signal is generated at one location and recorded at another location. The waveform obtained from imaging can be used to quantitatively characterize the medium, for example by calculating the material's diffusivity coefficient or dissipation rate. In recent years, a different monitoring technique has been developed in seismology to measure the velocity of different kinds of waves, the Coda Wave Interferometry (CWI). In this CWI technique, the main focus is given to the late part of the recorded waveform, the coda. CWI is now successfully used in seismology and acoustics. In the current research, CWI is applied on concrete in different damage states to develop basic knowledge of the behavior of the wave velocity, and how it can be used to characterize cement-based materials. By comparing two impulse responses, the relative velocity change between the two impulse responses is used to characterize damage. Because of the stress-dependency of the velocity change, the calculations can also be used to directly calculate the Murnaghan's and Lam´e's coefficients. The newer technique of CWI is applied - the Stretching Technique (ST) [27]. The first goal of this research is to establish the viability of using CWI in cement-based materials. Next, we use the ST in the application of stress as we compress concrete samples for the detection of thermal damage, ASR-damage and mechanical softening.

<p>This PhD thesis is divided into two parts. Part one dealswith the development of the material and the mechanicalproperties of Steel Fibrous Cement Based Composites (SFCBC) forimproving bridge design and construction. It familiarizes thehydration mechanisms of the high performance concrete with thehelp of Powers´ and Jensen´s models. Concretes withdifferent water-cement ratio were compared with each other withrespect to degree of hydration and hydration products. Thisanalysis showed that high performance concrete has higherstrengths not because it has more gel solid, but due to ithaving less porosity and higher filler content compared toordinary concrete.</p><p>A number of experiments were performed to achieve a mixdesign method for a SFCBC, which has good workability, highearly and long-term strength and good durabilitycharacteristics. A Self-compacting and self-leveling fibrouscomposite, which has ultra high strengths (Compressive strength<i>f</i><i>c</i>= 180 ~ 220MPa and flexural tensile strength<i>f</i><i>föi</i>= 14 ~ 32MPa depending on the volumefraction of fibers) was produced. This composite was alsotested under different curing conditions in order toinvestigate the effect of curing on hydration andself-desiccation shrinkage. These tests showed that SFCBCshould not be water-cured under a long period andself-desiccation influences the compressive strengthnegatively. Test of scaling at freezing showed that SFCBC hasvery good durability characteristics.</p><p>Part two deals with the behavior of SFCBC in the anchoragezones of prestressed bridges. The prismatic composite specimenswere tested for different volume fractions of fibers underdifferent concentrations ratios of strip loading. The resultsof these tests showed that the ultimate strength of the SFCBCspecimens was approximately twice that of ordinary concretewith the same size (<i>f</i><i>c</i>= 60MPa reinforced with stirrups). Therefore,SFCBC has good possibility to replace the traditional rebars inthe anchorage zones of prestressed bridges.</p><p>This composite has different behavior than the traditionalconcrete e.g. crack formation, failure criteria, effectivestrength and angle of friction. A vertical crack on thecenterline was occurred while wedge developed under the loadingplate. In contrast to ordinary concrete, the cracks could notreach to the bottom of the blocks.</p><p>The tests results gave the ideas of that this material actslike metals or plastics in the high fiber content. Thismaterial is neither very brittle as concrete nor very ductileas metals but it is somewhere between them.</p><p>Upper-bound plasticity solutions were utilized for modelingthe bearing capacity of SFCBC. Predictions of this method aregood enough to estimate the bearing capacity of SFCBC in theanchorage zones of prestressed bridges.</p><p><b>Keywords:</b>Process improvement of bridges, Prestressedconcrete, High performance concrete, Ultra high performanceconcrete, Hydration, Cement based composites, Fibers,Self-compacting concrete, Bearing capacity, Anchorage zones,Tests</p>

Thesis (M.S. in civil engineering)--Washington State University, August 2008. / Includes bibliographical references (p. 79-80).

Thesis (M.S. in civil engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Feb. 4, 2010). "Department of Civil Engineering." Includes bibliographical references (p. 134-135).

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 364-367).

Thesis (Ph. D.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 204 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 190-195).

Precast, prestressed concrete panels (PCPs) and cast-in-place (CIP) concrete slabs are commonly used in Texas and elsewhere. Because PCPs are placed between bridge girders, and CIP concrete slabs are cast over the PCPs, PCPs act as formwork, cost and time for construction can be reduced. However, current designs may be further optimized if it can be shown that the reinforcement in the CIP deck can be reduced. Another issue involves cracking of PCP during fabrication and transportation to the site. The goal of this dissertation is to recommend changes to the CIP-PCP bridge decks that will lead to more cost-effective bridges. The first phase of the research is to suggest an optimized reinforcement layout for cast-in-place (CIP) slabs. Because the capacity of these decks is much greater than the design loads, a decrease in top-mat reinforcement will have minimal effect on the margin of capacity over design loads. Two options were selected, reduced deformed-bar reinforcement; and reduced welded-wire reinforcement. These two options are evaluated through restrained-shrinkage tests and field applications. The second phase of this dissertation is to reduce cracks in precast, prestressed concrete panels (PCPs) which occur during fabrication, handling, and transportation. Most cracks in PCPs are collinear (occur along the strands). They can be reduced in two ways. The first is to reduce initial prestress. The second is to place additional transverse reinforcement at edges. / text

The goal of this study was to revise the development length equation of ACI 318- 05 and to better reflect test results for high-strength concrete. The revision of the equation was accomplished using test results tabulated in the Database 10-2001maintained by ACI committee 408. Equations for development length in ACI 318-05 and ACI 408.3 examined to understand the issues to be considered for revision on the variability of test data. The development length equation in ACI 318-05 was very conservative for [compressive strength of concrete][less than or equal to]14,000 psi based on the experimental data in Database 10-2001 of ACI Committee 408. On the contrary, the ACI 318-05 may be less conservative for high-strength concrete, [compressive strength of concrete] [greater than or equal to]14,000 psi . Thus, modified design equations were proposed to provide realistic values for normal strength concrete and conservatively for high-strength concrete. The ACI 318-05 equation was modified for 1) compressive strength of concrete and 2) confinement as expressed by the term [minimum side cover, cover over the bar or wire, or one-half the center-to-center spacing of the bars or wires] + [contribution of confining reinforcement across potential splitting planes] / [normal diameter of bar] in ACI 318-05. The basic assumption is that bar stress is a linear function of development length, and development length is the length required for bar stresses to reach the yield. / text