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Scott Jones, David Hughes, Orville Werner
Abstract: As part of the 15 m raise of Hinze Dam, the existing 33 m high mass concrete spillway structure will be raised an additional 12.5 m. This will be achieved using conventional mass concrete placed on the top and downstream side of the existing spillway to form a new monolithic structure. Heat generated by the hydration of the cement and fly-ash will raise the peak temperature in the body of the new concrete relative to the stable and relatively uniform temperature within the existing concrete. The early, comparatively rapid volume expansion (and subsequent slow contraction) of the new concrete is externally restained along the interface and there is a potential for tensile stains to develop along the interface that are large enough to cause cracking through the body of the composite dam and potentially compromise the interface bond. The temperatures and thermal gradients induced are a function of the mix design, particularly the amount and thermal properties of cement used, and the sequencing of construction.
Two-dimensional transient coupled thermal-structural finite element (FEM) analyses were used to predict thermal deformations and stresses within the body of the spillway in the weeks and months after placement. Laboratory measured mechanical and thermal properties of the concrete and local boundary climatic data were input to the analyses. The measured adiabatic calorimeter curve showed that the fine grind and chemical composition of the local South East Queensland cement produced a rapid generation of heat which magnified potential thermal expansion issues with the early-age concrete.
Creep, shrinkage, viscous-elastic behaviour, and the increase in modulus of elasticity with age influence the degree to which expansion and contraction of the concrete are converted into stress. These variables, were either accounted for directly in the elastic FEM model, or were taken into account in the interpretation of the results.
This paper presents the assumptions, methods, and criteria used in the FEM analyses; the results of the material testing program; and the results and conclusions drawn from the analyses. A discussion on the concrete mix design trials recently completed on site is also included.
Keywords: Adiabatic Temperature, Creep, Mass Concrete, Placement Temperature, Pre-cool
Ted Montoya, David Hughes, Orville Werner
The existing Hinze Dam was raised beginning in 2007 to increase water storage capacity, improve its ability to regulate floods, and raise the level of structural safety as compared to the current dam. As part of the 15 m raise of Hinze Dam, the existing 33 m high spillway structure was raised using mass concrete. This new composite structure was constructed as a downstream raise, placing mass concrete on the downstream and top of the existing spillway. The designers of the composite spillway structure developed a finite-element model to consider the early expansion and subsequent slow contraction of the new concrete against the existing concrete. The temperature rise of the new section of mass concrete had to be monitored and controlled to reduce the tensile strains along its interface with the existing spillway, and differential temperatures had to be limited to avoid cracking of the new mass section. Low-heat cement for a conventional mass concrete mix was not readily available so a mix was developed using local materials.Learn more
Typical mass concrete dams are monolithic structures constructed with lowheat cement. The Hinze Dam spillway design was predicated on the use of materials readily available. The paper presents the assumptions, methods, and criteria that were used in developing the mass concrete mix. It also presents the means and methods for tracking temperature gain during construction of the raised spillway, and how temperature was influenced by placement temperature, construction sequencing, and seasonal conditions. Lastly, the paper will compare the actual performance of the mix with the design analysis, laboratory testing, and finite element studies that were performed during the design.