Charles Korhonen

Hexagonal ice in hardened cement

Abstract Neutron diffraction from nearly saturated cement paste (made from D 2 O, water / cement ratio = 0.36 , hardened 3 months under lime-saturated D 2 O) has shown that the pore water transformed mainly to hexagonal ice (Ih) upon slow cooling below the (bulk) equilibrium freezing point of heavy water (276.8°K). The amount of ice increased continuously upon cooling to 227°K, and then decreased continuously upon heating. At every temperature below 276.8°K, the ice content was greater upon heating than upon cooling. The results were used to calculate the pore size distribution, which ranged mainly between a diameter of 3 and 30 nm.

Use of Accelerated Aging to Predict Behavior of Recycled Materials in Concrete Pavements: Physical and Environmental Comparison of Laboratory-Aged Samples with Field Pavements

Future behavior of recycled materials in highway applications is often difficult to predict. Accelerated aging is one means of exploring the long-term physical and environmental performance. Coal fly ash (CFA), routinely used as a cementitious replacement in portland cement concrete pavement, was selected as a model system in an accelerated aging approach. US-20 near Fort Dodge, Iowa, was used as a source of field-aged pavement slab material and concrete mixture proportions. This pavement, constructed in 1987, experienced early failure and distress. The role of CFA, if any, in the failure is not known. Three types of accelerated aging treatments were chosen and applied on laboratory prisms made with the US-20 mixture proportions: arrhenius aging (AA), cyclic loading, and freeze-thaw exposure. Physical and environmental response variables were used to examine the pavement slab and the aged laboratory prisms. The aging protocol affected both physical and chemical properties of the monoliths. It took about 9 months of elapsed time to age specimens to an equivalent age of about 4 years. The equivalent ages matched well with the time frame seen in the field for the onset of early distress. Most response variables for the aged laboratory prisms and the field samples were similar, suggesting that the aging method reasonably produced a pavement of similar age and distress. The AA treatment produced an unexpected loss of strength, suggesting that the accelerated aging promoted the onset of a deleterious reaction. Distinguishing the source of trace metals in leachates was difficult, for all components (CFA, aggregates, cement) had similar elemental compositions and leachability. The use of both physical and environmental response variables showed linkages between compressive strength, microcracking, fine pore structure, Cl diffusive leaching (efflux related to road salting that increases the concentration of Cl in the monolith), and Ca diffusive leaching (related to change in matrix structure and loss of Ca).

Reconstruction of Windsor Bridge Piers

The Windsor Bridge provides a two-lane highway crossing of the Susquehanna River in Broome County, New York. The structure comprises three 62.5-m (205-ft) simple-span through trusses supported by reinforced concrete abutments and solid-shaft piers. Having been built in 1935, it required rehabilitation in the early 1980s. The major effort included a deck replacement and complete structure repainting. What was expected to be relatively minor surface restoration of the foundation units became much more involved and complex. A coring program was initiated for predictions of the volume to be restored. The cores were petrographically examined and found to exhibit evidence of freeze-thaw damage and alkali-silica reactivity of the aggregate. The shafts, which were 2.13-m (7 ft) thick, were found to be delaminated from the freeze-thaw damage to depths of up to 610 mm (24 in.). An intensive evaluation of alternatives concluded that the most appropriate solution for this situation was to encapsulate the pier shaft w...

Locating Wet Cellular Plastic Insulation In Recently Constructed Roofs

Infrared scanners are quite successful in finding wet roof insulation, especially boards of rapidly absorbing insulations like perlite, wood fiber and fibrous glass. But wet areas develop more slowly and nonuniformly in the cellular plastic insulations, such as urethane, which are commonly used in new roofs. These differences can affect the outcome of an infrared survey of new roofs. To determine the feasibility of detecting incipient wet insulation, several recently constructed roofs were examined thermographically. It was usually more difficult to find moisture in new roofs containing cellular plastic insulations than in new roofs with more-absorbent insulations. This increased difficulty is due to the slower rate of wetting and to the nonuniform manner of wetting of some of the cellular plastics. Perlite, wood fiber and fibrous glass insulations tend to become uniformly wet throughout an entire board, whereas moisture initially concentrates at the perimeters of boards of some cellular plastic insulations. However, eight to ten months after construction, enough moisture can accumulate in most cellular plastic insulations to be visible to aninfrared scanner. Since this moisture is concentrated in a small portion of each insulation board, much of it would probably be overlooked by a nuclear or capacitance grid survey.

Maintaining buildings in the Arctic

Close interest in the work of CIB working commission W 40 on heat and moisture transfer has prompted the authors, who are scientists working with the US Army Cold Regions Research and Engineering Laboratory, to send us these two summaries of remedial work on houses in Alaska. The first indicates the scope for simple injection of urea formaldehyde foam to improve thermal insulation of old wood-frame buildings; the second shows how infra-red photography can cut the cost of repairs to leaking roofs.