Cementitious mixtures

Description

FIELD OF INVENTION

THIS INVENTION relates to improved cementitious mixtures. The invention is primarily directed to cementitious mixtures which may be formed into building products. For example, the cementitious mixtures of the present invention may be moulded into blocks, formed into panels and such like. However, the invention is not limited to such use.

BACKGROUND ART

Cementitious mixtures are known for forming building products such as building blocks, wall panels and the like. Processes such as the “Besser” and “Columbia” processes for concrete or cinder blocks and such like have established widespread acceptance. Lightweight concrete formulations have also been formulated for wall panels and such like, but have at times resulted in building products having insufficient structural strength. Such products, including concrete blocks, often compromise on acoustic and thermal insulation properties as well as fire rating.

A composite panel developed by the applicant is disclosed in patent applications PCT/AU01/00945 and PCT/AU2004/000719. However, improvements in or alternatives to the formulations disclosed therein have been developed.

The present invention aims to provide improved cementitious mixtures which alleviate one or more of the disadvantages of the prior art. Other aims and advantages of the invention may become apparent from the following description.

DISCLOSURE OF THE INVENTION

With the foregoing in view, this invention resides broadly in a cementitious mixture including:

a light weight material, cement, resin, sand, fibrous material, and water;

the constituent components being selected to provide a settable liquid or mobile solid which, when set to form a solid, achieves a predetermined selection of parameters comprising two or more parameters selected from available parameters, said available parameters including density, compressive strength, sound insulation, thermal insulation and fire rating of the solid.

the constituent components being selected to provide a settable liquid or mobile solid which, when set, achieves a predetermined set of parameters including two or more of the density, compressive strength, sound insulation, thermal insulation and fire rating of the solid.

In another aspect, the present invention resides broadly in a cementitious mixture including:

a light weight material, cement, resin, sand, fibrous material, and water;

the relative concentrations of the constituent components being adjusted according to a predetermined formulation to provide a settable liquid or mobile solid such that, when set into a solid, the solid possesses a predetermined selection of parameters comprising two or more parameters selected from available parameters, said available parameters including density, compressive strength, sound insulation, thermal insulation and fire rating of the solid.

The light weight material is preferably selected from light weight polymeric or plastics materials, such as expanded polystyrene foam. More preferably, the light weight material includes recycled plastics and/or rubber products. The light weight material may also include wood chip, manufactured light weight formations or the like, the light weight material being selected for durability, cost, compatibility with the other constituent components of the mixture, and contribution to the aforesaid predetermined set of parameters.

The resin is selected from settable polymeric materials, preferably one-part settable polymers such as polyvinyl acetate, acrylic resins or such like. More preferably, the resin is or includes elastomeric materials, such as, for example, polybutadiene or derivatives thereof. One preferred elastomeric resin includes carboxylated butadiene styrene copolymer. Preferably, the resin and light weight material are selected to interact with one another to provide synergistically a composite material for inclusion in the cementitious mixture. The resin may be in liquid or powdered form.

Preferably, the fibrous material reinforces the solid, and may include, for example, synthetic or natural textile, wood fibre, glass fibre or such like preferably in the form of tow, staple or such like. The fibrous material may also include “extended” fibres, such as fibreglass, animal hair, plant fibre or such like.

BRIEF DESCRIPTION OF THE EXAMPLES

In order that the invention may be more readily understood and put into practical effect, reference will now be made to one or more examples of the invention wherein at least some of the aspects and embodiments of the invention are described from experimental work in the development of the invention. A cementitious mixture described in the examples embodies the best method of performing the invention known to the inventor to date for skinned panels for cold-room applications, such panels being clad, for example, with steel.

DETAILED DESCRIPTION OF THE EXAMPLES

Example 1

A lightweight concrete building material was formulated in accordance with the invention in order to test it for use in building and construction materials and components.

A slurry was prepared by mixing 6 kg cement, 1 kg sand, 3 litres water and 1 litre resin in a 20 litre bucket, stirring the mixture with a hand-held electric mixer to form a runny paste. 54 litres polystyrene beads and 50 ml fibre were combined in a 100 litre mixing vessel to ensure an even mix, and then the slurry was added thereto slowly whilst continuing to agitate the mixture. The mixture was mixed for a few minutes after all of the slurry had been added and checking visually that the lightweight material (polystyrene) had an even coating of slurry. The resin used for this test was carboxylated butadiene styrene latex, and the fibre used was 10 nm polypropylene fibre.

The mixture was then poured into a mould (rectangular prism) which had been pre-treated with vegetable oil mould release agent. The sides of the mould were tapped to settle the mixture, particularly into the corners of the mould. The mould was slightly overfilled, the excess material being removed to level off the moulded material with a straight edge. The mixture was not forced or compressed into the mould. The mixture was contained in the by a lid arranged to close the mould without compressing the mixture therein.

The mixture in the mould was allowed to set over a period of 24 hours to form a block, after which the block was removed from the mould. The block was allowed a further period of time to air dry, following which measurements were taken and tests performed on the block.

Immediately after demoulding, the block was found to be fragile. The moulded faces were hardened and did not release any unbound materials. The lid-face released a few crumbs of unbound ingredients. The block was moist and firm enough to handle with care without damaging or denting the faces. After drying, the block hardness increased significantly, and the following characteristics were recorded:

Dimensions (mm): 225×558×288

Volume (m³): 0.036158

Sample weight after 5 days ambient air drying: 6.5 kg

Density (kg/m³): 180

From the above, the inventor concluded that the formulation and method could be moulded to any desired shape including blocks, panels and profiles.

EXAMPLE 2

The block of Example 1 was tested for fire resistivity. A 50 mm thick sample was sliced from the block and positioned above a portable propane gas burner. The nozzle was carefully positioned 50 mm from the face of the slice. The burner was ignited and the flame directed to the centre of the face of the slice (the heated face). A timer was activated when the flame started. The test was continued and the time taken until particular benchmarks were attained. The benchmarks sought were firstly an indication that insulation failed by the opposing face being too hot to touch, that integrity of the slice failed by the flame being seen on the other side of the slice. The temperature of the opposing face was measured at five-minute intervals, with the result being as follows:

• • 5 min: The surface of the polystyrene beads on the heated face disintegrated within seconds of the application of the flame thereto. Surface charring was visible around the area of the flame. The flame did not spread beyond the radius of the flame source. A small amount of smoke was observed emanating from the opposing face.
  • 10 min: The heated face glowed red. The opposing face was a few degrees above ambient, and remained intact.
  • 15 min: The heated face glowed red. There was localised charring around the flame area. The opposing face was warm to the touch, and surface polystyrene exhibited a spongy feel when slight hand pressure was applied.
  • 20 min: The heated surface glowed red. Localised charring had not noticeably progressed beyond the 15-minute test. The opposing face remained warm and intact, but a circular scorch mark appeared on the surface.
  • 25 min: The heated surface glowed red. Localised charring had not noticeably progressed beyond the 20-minute test. The opposing surface felt hot (about 75° C.) and the polystyrene beads began to melt. The diameter of the scorch mark increased.
  • 30 min: The heated surface glowed red. Localised charring had progressed approximately 3 mm beyond the 25-minute test. The opposed face remained at about 75° C. The polystyrene beads melted away to about 50 mm diameter around the flame on the heated surface. The scorch mark increased to about 50 mm diameter.
  • 35 min: The heated surface glowed red. Localised charring had not noticeably progressed beyond the 30-minute test. Polystyrene beads melted away to about 75 mm diameter around the flame on the heated face. The scorch mark on the opposing face was about 75 min diameter.
  • 40 min: No noticeable change from the 35-minute test
  • 45 min: No noticeable change from the 40-minute test. Insulation remained intact.
  • 50 min: The heated surface glowed red. Localised charring bad progressed about 2 to 3 mm beyond the 45-minute test. Polystyrene beads melted away to about 90 mm diameter around the flame on the heated face. The scorch mark on the opposing face was about 90 mm diameter.
  • 55 min: No noticeable change from the 50-minute test.
  • 60 min: No noticeable change from the 55-minute test.
  • 65 min: Further minor erosion of localised charring around the flame area by about 2 mm. Otherwise there was no noticeable change from the 60-minute test.
  • 70 min: The opposing face temperature remained steady, but had minor erosion about 2 mm in the centre.

75 min: No noticeable change from the 70-minute test.

• • 80 min: Further minor erosion of localised charring around the flame area to a depth of about 10 mm. Otherwise there was no noticeable change from the 75-minute test.
  • 85 min: The opposing face temperature remained steady. Otherwise there was no noticeable change from the 80-minute test.
  • 90 min: No noticeable change from the 85-minute test.
  • 95 min: No noticeable change from the 90-minute test.
  • 155 min: Progressive erosion of localised charring around the flame area to approximately 20 mm depth. The temperature had increased, but was still not excessive to touch with a bare hand. Surface erosion on the opposing face had progressed to approximately 5 mm in depth.
  • 160 mm: Test terminated; gas bottle almost empty.

From the above test, it was determined that insulation and integrity failure did not occur in the test period. A small amount of smoke was observed in the early stages of the test, but was not considered excessive, and did not continue beyond the first stages of the test. Erosion of the heated face was very slow. As the opposing face warmed up, the surface polystyrene melted away and minor surface erosion was observed. The opposing surface did not increase to a temperature above which a bare hand could be held on the surface during the test period. As this test was an observation test only, no temperature measuring equipment was used.

The test sample slice exceeded all expected measures of fire resistivity. The result showed that the lightweight concrete example according to the invention could withstand a sustained temperature of 600° C. to 1900° C. (red glow is 1100° C. to 1300° C.) for in excess of 160 minutes. Such a result exceeds most building fire rating requirements, bearing in mind that a full scale fire rating test according to standardised procedures would be desirable for each building material and./or product formed from the improved cementitious mixtures of the present invention, as well as for its full range of application, fixing and finishing.

Although the invention has been described with reference to specific examples, it will be appreciated by persons skilled in the art that the invention may be embodied in other forms which are encompassed within the broad scope and ambit of the invention as defined by the following claims.