Coating processes – With post-treatment of coating or coating material
Patent
1992-03-06
1994-08-16
Green, Anthony
Coating processes
With post-treatment of coating or coating material
4273722, 427359, 4273977, 427428, 106683, 106688, 106691, 106692, 106713, 106737, 106738, 106788, 106816, 106817, B05D 100, C04B 1402
Patent
active
053385730
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for producing a concrete type hard material from a cementitious mixture, to a cementitious mixture for creating said hard material, and to a hard material produced by the process.
In this specification concrete type hard material means a hard material having compressive and flexural strengths comparable to that of conventional concrete and thereby enabling the material to be used as a load bearing self supporting hard material.
Known hard materials produced from cementitious mixtures generally fall into two categories, viz mortar or concrete. Mixtures for producing mortars and concretes include a cement, usually either a hydraulic or non-hydraulic cement, and a filler. Additional components may be present in concretes or mortars, for example pozzolanic materials, accelerators, colouring agents, fibres etc. The fillers are generally referred to as aggregates and are divided into fine and coarse categories. The division between fine and coarse aggregates is generally regarded in the United Kingdom as occurring at a sieve size of 5 mm; ie aggregates above a sieve size of 5 mm are coarse aggregates and aggregates below a sieve size of 5 mm are fine aggregates and are often referred to as sand.
Concrete contains coarse aggregate usually in excess of 50% by weight and up to 20 mm in size whereas mortars do not contain coarse aggregate but fine aggregate and the maximum particle size of the fine aggregate or sand is generally less than 1.2 mm.
In use, mortars are distinct from concretes in that mortars do not have the requisite compressive and flexural strengths or dimensional stability to be load bearing and self supporting.
Conventionally, the constituents for producing concretes and mortars are normally mixed together with water before placing. Generally, the water addition is greatly in excess of that required for the hydration of cement, the surplus water being required to provide sufficient fluidity to the wet mixture to enable it to be laid and enable adequate compaction to take place.
The excess water required for compaction and ease of placing is otherwise detrimental to all the qualities of the final product including strength and durability and, frequently, leads directly to failure and loss of integrity due to self induced cracking arising from drying shrinkage.
Long reign durability or dimensional stability is important for concrete in order to maintain its load bearing capabilities. Accordingly, it is common to incorporate coarse aggregate into the mixture in order to reduce surface area within the mixture and thereby enable the mixture to be relatively fluid with the introduction of less water.
Accordingly for concrete, there is a need for larger aggregate sizes to be used to reduce the surface area and water demand so as to control shrinkage. However, the use of coarse aggregate sizes necessitate far thicker sections of material being placed than would otherwise be required. In addition with a wet mixed concrete, use of thin sections is also undesirable since this encourages rapid drying which induces cracking. Accordingly, laying wet mixed concrete in relatively thick sections is desirable to prevent cracking due to drying.
The problems of excess water addition are made worse when proper equipment for thorough mechanical mixing of the materials and for subsequent compaction are not available, as is frequently the case.
The work and cost involved in handling, mixing and placing the materials is greatly increased by the need for separate on-site mixing and for adequate compaction.
The need for formwork to contain the fluid concrete and resist the vibration or tamping which is necessary to achieve compaction further increases the difficulties in use.
It is a general aim of the present invention to provide an improved cementitious mixture and process for forming a concrete type hard material (of similar or better performance characteristics than concrete) which obviates the need to mix the constituents with water prior to laying and which produces a hard, st
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McGraw-Hill Dictionary of Scientific and Technical Terms, (3rd Edition) p. 37 (1984).
Askeland, Donald R., "The Science and Engineering of Materials" p. 543 (1984).
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Davies Derek
Hughes Kenneth
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