A large amount of heat can be liberated during cement hydration, causing very large temperature increases in mass concrete members. The non-uniform temperature field produced by the cement during curing can cause very high internal stresses that may crack the concrete. Concrete thermal cracking in very large structures is a well-known phenomenon and was studied extensively during the height of dam construction in the United States. In recent years concrete bridge member sizes have increased for structural and aesthetic reasons. Recent problems in San Antonio and Houston, Texas with thermal cracking and very high internal temperatures in mass concrete bridge members has renewed interest in studying early-age thermal cracking and its mechanisms. In order to predict the early-age thermal cracking risk of a concrete member, the temperature history, autogenous shrinkage, modulus development, tensile strength development, coefficient of thermal expansion development, creep behavior, and external restraint conditions must be known. A testing procedure has been developed to measure concrete heat of hydration, mechanical property development, and free shrinkage response at different curing temperatures. The concrete free shrinkage includes thermal and autogenous shrinkage components and is measured using a newly developed free shrinkage testing apparatus. The early age concrete creep is calculated from rigid cracking frame tests performed at different varying temperatures. Trends in early age creep behavior for different concrete mixtures common in mass concrete have been found and are used to develop a statistical model relating concrete mixture proportions and constituent material properties for use in mass concrete thermal stress modeling. The results from the test methods described are used in a new concrete early-age cracking risk and durability software package called ConcreteWorks. / text

SIFCON was first reported in 1984 and showed excellent potential as a structural material. Applications, however, have been slow to emerge. The aim of this investigation was to simplify the production of SIFCON and to identify practical applications. A direct infiltration test was developedt o assessth e effect of materials and admixtures on the infiltration properties of cement based slurries. A slurry was designed which could infiltrate fibre beds containing up to 16 percent by volume of fibres without the aid of vibration. To achieve this, novel use was made of viscosity modifying admixtures in conjunction with superplasticisers. The mechanical properties of the SIFCON produced using the new slurry were investigated in terms of compression and flexure. It was found that, while the outstanding parameters, in terms of strength and ductility, associated with SIFCON were apparent, the resulting material was strongly anisotropic. The compressive modulus of elasticity was found to be significantly lower than would be expected for conventional concrete of similar strength. Pull-out tests showed that the bond performance was ductile for ribbed reinforcing bars embedded in SIFCON, however, the dependenceo n fibre orientation was highlighted. SIFCON sections were successfully incorporated into reinforced concrete beams and the production of these beams demonstrated the benefits of the self compacting technique. The results of third point loading tests highlighted problems relating to the modulus of rupture of SIFCON, and the difficulties faced when introducing it into reinforced concrete structures. It was also found that the use of SIFCON in horizontally cast beams was inefficient in the compression zone. It is expected that the advances made in the development of the production process will lead to increased acceptance of SIFCON and that new applications will emerge.

Not available / text

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

No description available.

No description available.

No description available.

No description available.