December 1991 Table of Contents

Features Post-Tensioned Reservoir Roof Replaced

After only 10 years of service, the roof of a 15-million-gallon reservoir in Greeley, Colorado was near collapse. The reservoir was originally designed and built as a partially buried tank with an exposed post-tensioned concrete roof. The concrete had been exposed to Colorado's extreme temperature cycles and subjected to repeated volume changes and freeze-thaw cycles. The 6-inch-thick post-tensioned roof slab had deteriorated significantly and was in imminent danger of collapsing. The Denver engineering firm of Richard Weingardt Consultants Inc. (RWC) was called in to evaluate the situation and recommend a solution. After reviewing a number of plans for repairing and strengthening the roof, the consultants decided the only viable solution was to replace the old roof entirely. Read more

Features Planning a Tilt-Up Project

Planning and coordinating a tilt-up project should be a team effort involving the architect, engineer, and the contractor. Preconstruction meetings are a good way for all parties involved in a tilt-up project the iron out details before work begins. Read more

Features Low permeability is critical

Understanding how seawater deteriorates concrete and carefully selecting a mix design can help ensure the maximum service life of the concrete surface. Concrete exposed to seawater may deteriorate from the combined effects of chemical and physical processes. Attack is slowed by reducing concrete permeability. Low permeability helps keep aggressive chemicals out of the concrete, slows leaching of soluble materials such as lime, and limits the depth of carbonation, thus better protecting reinforcing steel from corrosion. Read more

Features Welded Wire Sandwich Panels Shotcreted

Welded wire sandwich panels were the framework and structural reinforcement for an adaptable concrete construction system selected by the Habitat for Humanity volunteer group's traveling work camp series in the summer of 1991. Working on 14 previously prepared foundation floor slabs, the volunteers installed 4x8-foot wall panels made of expanded modified polystyrene sandwiched into a lightweight three-dimensional steel truss and faced with welded wire fabric reinforcement. After the exterior panels were erected, door and window frames were set in place, and dry-mix shotcrete was applied to both inside and outside panel surfaces. Habitat used the same welded wire sandwich panel system to build homes in Tijuana, Mexico, in 1990. Read more

Problem Clinic Effect of Crazing on Long-Term Floor Durability

We just finished an industrial floor job that meets flatness and levelness requirements and has no random shrinkage cracks. However, there is some craze cracking. The owner wants proof that these cracks won't get progressively worse with time and affect f Read more

Problem Clinic Waterproofing Concrete Storm Shelters

We build concrete shelters for farmers who want protection from tornados. The shelters have a 10x10-foot footprint and walls are 7 feet high. We cast the floor slab first, leaving a keyway at the edges, then cast the walls and roof in one pour. The shelte Read more

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