Research Project Summary Information
Lightweight Concrete Wall Panel for Building Envelope(ST10625)
The design of building envelopes is complex because several functions must be simultaneously performed. Building envelopes protect against the elements, carry structural loads, dampen external noise, and provide a pleasing aesthetic appearance. “Sandwich construction panels” (panels composed of several layers that each perform a different function) are commonly used for envelopes of commercial buildings. These panels can be extremely expensive. Columbia University, the Contractor, has discovered a novel chemical additive for concrete that yields a lightweight material capable of carrying a wall panel’s loads. This chemical additive causes the material to have a closed-cell structure as opposed to the open-cell structure that occurs from conventional foaming agents. This difference in cell structure is the attribute believed to give the material its superior resilience. Columbia believes this new concrete material will satisfy all the requirements for building envelopes at a cost substantially less than for conventional sandwich panels.
The project called for the Columbia to refine the material’s chemical formulation, to ensure adequate strength properties are achieved, and to optimize the material’s sound absorption and thermal insulation properties. Columbia also aimed to evaluate the durability of the material with testing in its laboratory, and research and propose methods for producing architectural concrete faced material on a large-scale. The project further called for a prototype wall panel to be produced in a laboratory or at Oldcastle Precast’s South Bethlehem manufacturing facility and tested for thermal insulation and sound absorption properties.
The R-value of the proposed material could be more than three times greater than structural concrete of a typical density. The material will provide economic benefits in New York by reducing construction costs for buildings.
The developed material succeeded in many respects. The material achieved the compressive strength objective of being suitable for applications with minimal strength, and its thermal conductivity was comparable or superior to other lightweight concrete materials, due to the inclusion of perlite and recycled expanded polystyrene. The material’s sound absorption characteristic was excellent, as expected due to its low density. Unfortunately, the material failed to pass the freeze-thaw cycle test, which is an essential requirement in geographical areas with harsh climates. The addition of fibers to the concrete mix design could potentially increase the freeze-thaw cycle resistance of the lightweight concrete. A second difficulty discovered was that the mix design in its current form required simultaneous application of vibration and pressure, similar to those common in the production of concrete masonry units. This production approach is substantially different than that used by most manufacturers of full-scale concrete building envelope panels. A significant capital investment in new equipment would be need by a concrete panel manufacturer in order to produce panels using the new material.
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