Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1994-05-10
1995-12-05
Bell, Mark L.
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106409, 106500, 106502, 106677, 106218, 106236, 106278, 428403, 428407, C04B 2010, C04B 1608
Patent
active
054724988
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to improved light weight aggregate for use in the production of building materials such as cementitious products, gypsum products, plaster boards and the like. The invention further relates to construction materials incorporating the aggregate, and to methods of manufacture of lightweight aggregate and of products incorporating the aggregate.
PRIOR ART
The preparation of low density concrete by incorporation of light weight aggregates such as vermiculite, cork, slag, asbestos, bagasse and the like in a hydraulic binder such as a cement/sand/water mixture is well known. Low density concrete having much improved characteristics may be prepared by incorporation of foam particles, for example polystyrene foam, as the light weight aggregate. However cementitious materials do not readily bond with these light weight aggregates which are hydrophobic. In use of polystyrene foam particles (which are by nature highly hydrophobic) it has been proposed to incorporate a binding agent in the cement, or to pre-coat the particles with a binding agent, the purpose of which is to promote adhesion between the foam particles on the one hand and cement on the other.
Various binding agents have been proposed including bituminous products, coal tars and mixtures of pitch with epoxy resins or phenolic resins. These binding agents are believed to act by softening the surface of the expanded polystyrene particles, thereby enhancing the bond strength between the particles and cured concrete.
The use of such materials has suffered from the disadvantages that bituminous and tar-like products when applied to polystyrene particles tend to result in a tacky surface causing the particles to coalesce into a mass which is difficult to disperse. Furthermore, the coatings have a strong bituminous odour which in the past has been detectable in the end product. More importantly the bonding strength between the polystrene foam particles and cured cement has been less than is desired.
Because the binder is tacky, it is usual to coat the polystyrene with binder in a mixer and then add cement and water to the same mixer to form concrete, so avoiding handling of the tacky aggregate. Alternatively the tacky aggregate has been detackified by subsequently dusting the bituminous coated polystyrene balls, in situ, with a finely granulated substance such as cement powder and then adding further cement and water for compression into moulds.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved light weight aggregate which avoids or at least ameliorates disadvantages of the prior art and which in preferred embodiments provides enhanced bonding between the aggregate and cementitious material. By enhanced bonding is meant a greater bond strength than obtainable with prior art light weight aggregates.
According to one aspect, the present invention consists in a light weight aggregate comprising light weight porous particles coated with a binding agent, said binding agent including at least 10% by weight thereof of one or more transition metal ions. The transition metal ion may be selected from the group commonly known as transition metals such as cobalt and chromium and this group also includes all known oxidation states of the transition metal. The transition metal ion may be in an ionic compound or complex.
In preferred embodiments of the light weight aggregate the porous particles are expanded polystyrene foam particles of from 0.5 to 15 mm average diameter and may be balls, beads, pellets or reclaimed particles. The preferred binding agent is a bitumen which is applied to the surface of the polystyrene particles from aqueous emulsion. The transition metal ion is desirably ferric ion present as iron oxide which is suspended in the aqueous phase of the bituminous emulsion by use of viscosity modifying agents prior to application of the emulsion to the polystyrene particles.
Desirably also the emulsion contains surfactants and dispersing agents which are bound to the polys
REFERENCES:
patent: 4332620 (1982-06-01), Quinn
patent: 4451529 (1984-05-01), Kerr, III et al.
Norton Gary P.
Stephenson Neville C.
Bell Mark L.
BST Holdings PTY. Limited
Marcheschi Michael
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