Compositions – Exfoliated or intumesced
Patent
1990-08-24
1992-05-19
Bell, Mark L.
Compositions
Exfoliated or intumesced
106675, 106698, 106DIG2, C04B 1418, C04B 2006
Patent
active
051146177
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the addition of a novel, relatively smooth-surfaced, vesicular, expanded perlite to cement to make high-strength cementitious compositions for the manufacture of structural concrete, particularly precast, prestressed, strand-reinforced products such as planks for use in the construction industry. It also relates to the novel expanded perlite itself.
OBJECTS OF THE INVENTION
It is an object of this invention to provide a cementitious compound which, when added to aggregate and combined with water, provides strong, stiff, high-strength structural concrete.
It is another object of this invention to provide a cementitious composition for reinforced precast concrete products such as plank stock which improves the adhesion between the reinforcing strands and the concrete while retaining all of the above characteristics of the concrete.
Other objects and advantages will become apparent from the following description of the invention.
SUMMARY OF THE INVENTION
In accordance with our invention, we add a novel, relatively smooth-surfaced, vesicular, expanded perlite to the cementitious mixture. The expanded perlite is of relatively small particle size, 100 to 30 mesh, or smaller, and is generally spherical in shape. The expanded perlite is of relatively low density so that the resultant concrete may be lightweight and strong, and may have zero to low slump so that it can be cast into plank stock or the like. The bond between the concrete and the reinforcing strands is much improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a typical plank, such as is manufactured by members of the Spancrete Manufacturer's Association;
FIGS. 2A and 2B are photomicrographs at 17 times magnification and 100 times magnification, respectively, of the expanded perlite as manufactured and processed for use in accordance with the present invention;
FIGS. 3A and 3B are photomicrographs at 17 times magnification and 30 times magnification, respectively, of the prior art expanded perlite which is added to concrete to manufacture relatively low-density and low-strength insulating concrete for roofs of buildings; and
FIG. 4 is a graph of full-scale plant test data comparing the slippage of reinforcing strands in regular plank stock concrete and lightweight plank stock concrete made in accordance with this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a length of hollow core plank stock 1 with reinforcing strands 2 in the bottom portion thereof. Voids 3 are formed in the central portion of the plank stock in order to reduce weight.
It is now standard practice to cast a length of such hollow core plank stock 1 in a casting bed. One prevalent method is the use of a machine which moves at from 8 to 15 feet (2.4 to 4.5 m) per minute along the bed and deposits or casts the concrete over and around reinforcing steel strands which are prestressed and in tension. The concrete is formulated to have zero to low slump and high strength. The concrete is allowed to remain on the bed until it has set-up enough to have a compressive strength of at least 3000 psi (20.69 Millipascals - MPa) and has become adherent to the reinforcing strands. It is then sawed into predetermined lengths and moved to a storage yard for final curing. The plank stock 1 can be up to 500 feet (154 m) long. The lengths of the planks or spans cut from the plank stock can be 10 to 30 feet (3 to 9 m) long. The plank stock 1 can be from about 3 feet (1 m) up to 8 feet (2.4 m) wide and from 6 inches (15 cm) up to about 18 inches (46 cm) thick.
This is a continuous process in which the plank stock is cast in three layers, all in a single pass, with the middle mix being tamped in around oscillating cores in order to form hollows or voids 3 in the plank stock 1.
In order for the reinforcing strands 2 to be effective, the concrete must adhere to them. Other considerations in the formulation of the concrete for the planks are stiffness and light weight, both of which are des
REFERENCES:
patent: 2572483 (1951-10-01), Howle
patent: 2585366 (1952-02-01), Bollaert et al.
patent: 3100715 (1963-08-01), Leonard
patent: 4518431 (1985-05-01), Duvier, Jr.
patent: 4889747 (1989-12-01), Wilson
Smetana David A.
Williams R. Steve
Advanced Concrete Technology, Inc.
Bell Mark L.
Jones Deborah
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