Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1991-07-01
1992-11-03
Bell, Mark L.
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106605, 106646, C04B 2100, C04B 2204
Patent
active
051605406
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for producing concrete members having a uniform density over a range of densities, particularly within the range of 800-2000 kg/m.sup.3, where also the compression strength of the resultant concrete can be kept high, e.g. more than 12 MPa at a density of 1600 kg/m.sup.3.
It has proved to be that production of concrete mass preferably is made at stationary concrete stations and that the concrete mass is moulded in situ in moulds to transportable units or is transported to the building place in a liquid shape to be moulded and hardened in moulds. The advantages are several. Among others can be mentioned: and the finished product makes the concrete to be produced with a higher accuracy. stores of cement and ballast and so on.
Therefore most industrial countries on the whole have complete concrete stations for delivery of concrete mass to the working places.
The concrete with the greatest range of application today consists of a mixture of cement, ballast, which can be in the form of sand, gravel, or stone, and water and often some additives for changing the consistency of the mixture. While the density of the stabilized concrete is normally about 2300 km/m.sup.3, the strength requirements for the concrete can vary. The test method for the compression strength has been standardized and is carried out, in general by forming a cube of concrete with a side of 150 mm and with certain requirements of side-parallelism and angle-accuracy. After hardening of the cube at room temperature of 20.degree. C. a varying number of days, in most cases 8 and 28 days, the cube will be tested by pressing the cube between flat surfaces. The highest load applied to the cube is recorded before the cube starts cracking. A value of the compression strength around 60 MPa can be achieved under certain circumstances, but maximum values of about 40 MPa are most common.
For structures with lower strength requirements the expense of the concrete can be cheapened particularly by increasing the ratio of weight between the participating water and cement in the concrete mass, the so-called water-cement factor. This factor is indicated as vct.
The demand for relatively light-weight concrete structures has increased. However, the need for relatively high compression strength in these structures often cannot be comprimised and can be difficult to achieve. For example, known methods for forming concrete including the use of ballast can produce concrete having a density in the range of 2400 to 1600 Kg/m.sup.3, however, a compression strength of 12 MPa can be achieved over this range of densities only by the careful practice of manufacturing techniques. Also, even in applications not requiring 12 MPa of compression strength, densities in the range of 2000 to 800 Kg/m.sup.3 have been difficult to achieve.
Another known method for forming relatively low-density concrete includes the introduction of air into the liquid base concrete mixture. The blowing of air into the liquid base concrete mixture forms air porousities in the concrete reduces the density of the resultant concrete mass, and makes the concrete less affected by frost, among other factors, when used in bridges and in outdoor-balconies. However, the compression strength of the concrete mass will be dramatically lowered and the porousities can be so irregularly spread throughout the resultant mass that, at a density as low as 2000 kg/m.sup.3, reliability and usefulness of this method is debatable.
Also, another method of forming relatively light-weight concrete including the mixing of a lighter ballast into the base concrete mixture to lower the density has been tested. This method has not, however, rendered any better results. Rather, the practical limits for compression strength will be reached before densities below 2000 Kg/m.sup.3 are attained.
However, it has been proved that a concrete with closed porousities, so-called "porous concrete", with densities below 500 kg/m.sup.3, can be achieved by adding a foaming agent, available under known trademar
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"Parry's Chemical Eng. Handbook", McGraw Hill 6th Ed. .COPYRGT.1984 pp. 1-17.
Johansson Ingemar
Svedman Kjell
Bell Mark L.
Danes Verkstader AB
Wright Alan
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