Gypsum Wallboard Core Structure and Effects on End Use Performance - FREE

Mark Flumiani, Bob Bruce and Tom Elliot
Completed for Canada Mortgage and Housing Corporation's (CMHC) External Research Program, May 2007


Commercial gypsum board panel products represent the most popular interior finishing surface in homes today. Gypsum is used for its ability to be easily set in a desired form, along with its ability to retain chemically bound water and therefore resist fire. Gypsum boards are made of a porous microcrystalline gypsum mineral “core” that contains cellular air voids sometimes up to 50% by volume. These cellular air voids are processed into the core during manufacture by adding aqueous pregenerated chemical foam bubbles to a flowable gypsum slurry resulting in a light weight convenient panel product. The characteristic core structures that are created using various chemical foam formulations and processes can differ significantly and likely contribute to the end use performance of the boards. Two important product performance features of gypsum boards are resistance to fire and fastening strength. It has been postulated that using a novel technique to describe and define lab produced examples of different core structures, one could correlate structure with observed fire resistance and fastening strength performance. Some other mechanical strength characteristics and end use performance features (eg. mold growth, moisture retention) are also likely effected by changes in board core structure but were not investigated in the scope of this report.

Scope and Objectives of Research

Representative laboratory board samples were created using various industry available chemical foams in specific formulation concentrations. The foam was generated using a lab scale continuous foam generation system comprised of a peristaltic pump to meter the foaming agent solution, an air compressor with a pressure regulator to control the air and a mixing impeller to blend the two phases into foam bubbles. A short initial comparison study of this continuous foam generation system versus batch generated foam was completed using set gypsum cubes evaluated for density and compressive strength. Based on formulations of promise from the cube study, board samples were created and imaged using X-ray computed tomography (CT). Subsequently, the board core structure was characterized by analyzing the 3D imagery from each sample. Duplicate boards were measured for both fire resistance properties and fastening strength performance. Fire resistance was determined through dimensional stability of samples after being subject to extreme temperatures in a laboratory kiln (1000oC for 2 hours; measured for shrinkage and degree of surface crack formation). Fastening strength was measured by a well known industry standard test (ASTM C473 / CSA A82.27), the Nail Pull Resistance test, using a mechanical force test apparatus.

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High Resolution CT scan image of 1/2" thick "z-profile" of a Foam D 10lb/ft3 board
High Resolution CT scan image of 1/2" thick "z-profile" of a Foam D 10lb/ft3 board
Bubble size distribution of CT scanned boards
Bubble size distribution of CT scanned boards

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