GB2117372A - Building materials - Google Patents

Abstract

In a mortar mixture aqueous siliconate is used in place of some or all of the water to provide a mortar that can be used as a damp-proof course. The aqueous siliconate also aerates the mortar and retards setting of the mortar.

Description

SPECIFICATION Improvements in or relating to building materials such as mortar, concrete and the like This invention relates to building materials such as mortar, concrete and the like.

In conventional building techniques, where a damp course is required, a bituminous layer (or a layer of polythene or such other preparatory material) is provided. Such a layer does, however, have serious failings; for example, the bituminous layer does not adhere to the structure above and below it and therefore an inherent weakness is built into the structure and if significant lateral forces are applied the structure may fail.

According to one aspect of the invention there is provided a mortar mixture characterised in that an aqueous siliconate is used in place of some or all of the water and the ratio by weight of silicone solids to water in the mortar mixture is in the range of 1 to 10 parts of silicone solids to 99 to 90 parts of water.

A mortar mixture as defined above can be used as a damp-proof course and has been found to be effective in such a use. The mortar adheres to the structure above and below, thereby providing strength to the structure and resistance to failure from lateral forces.

Furthermore, since the mortar relies on electrostatic repulsion rather than physical isolation, it provides an effective damp-proof course even if it becomes cracked.

The mortar can be used to provide a damp course or a damp-proof screed, for example, on a floor.

Other applications of the mortar are as a rendering or as a "plaster" on the inside of a damp house.

I have also found that very small air cells are introduced into the mortar as a result of the aqueous siliconate and that the existence of these air cells does not, surprisingly, seriously reduce the strength of the mortar. With very small air cells and even distribution of the cells, the crushing strength may even exceed that of conventional mortar.

Concentrations of silicone. solids in water of 6 percent by weight, 5 percent by weight and 3.5 percent by weight have all been tested and found to be satisfactory.

According to another aspect of the invention, a concrete is characterised in that it includes an aqueous siliconate resin.

The addition of aqueous siliconate is believed to result in aeration of the concrete; that is to say, that small air cells are generated within the concrete. The reduction in density of the concrete brought about by the introduction of the air cells into the concrete does not correlate with the crushing strength of the concrete.

The addition of aqueous siliconate results in less water than normal being required to bring the concrete to a working consistency. The use of less water strengthens the concrete. Thus there is scope, by the use of aqueous siliconate, to provide a concrete with a higher crushing strength to weight ratio than conventional concrete.

Preferably, the air cells are smaller than 2.0 mm and advantageously smaller than 1 mm in diameter.

According to another aspect of the invention a building material is characterized in that it includes low density beads distributed therethrough.

The building material may be concrete.

The low density beads preferably have overall dimensions ot less than 1 mm. The beads may for example be made of polystyrene. It will be appreciated that "low" density means a density that is several times lower than the mean density of the building material.

The technique can be applied to building materials other than concrete. In particular the technique may be employed in the baking of brick by the addition of carbon aerated compounds or other low density materials (not necessarily aerated) that can withstand high temperatures; this technique can also be applied to other building materials which have to be temperature cured or made by a similar process. The particles again preferably have overall dimensions of less than 1 mm.

The technique may also be applied to steel.

Certain examples of the invention will now be described with reference to the accompanying drawings, of which: Figure 1 shows a machine used for testing examples of the invention; Figure 2 shows a graph illustrating the results of the tests carried out by the machine of Figure 1; and Figure 3 shows a graph illustrating the results of some other tests.

A quantity of 4:1 sand/cement mixture (by volume) was thoroughly mixed in a mixer and the mixture was divided into two equal (measured on scale at 20 kg) quantities. To the first quantity was added clean tap water and the mortar mixed to a working consistency. The measured quantity of water used was recorded. The prepared mortar was transferred into steel cube moulds, worked in and firmly trowelled over to form the standard 100 mmxl 00 mmxl 00 mm, i.e. 100 mm3. The cubes were marked as conventional mortar and set aside to set.

Working consistency was chosen because any method involving complex dilutions, measurements or titrations on site, is to be avoided. The average bricklayer will function at best when a technique he is used to is presented in a new situation. Thus if the liquid aqueous siliconate is presented in a concentration which the bricklayer can pour into a sand and cement mixture instead of water to obtain a mortar whose working consistency "feels right", then the technology is likely to be applied correctly in practice.

The second measured sand/cement mixture was then put into the mixer once it had been washed and dried and the mixing procedure was repeated. In this case aqueous siliconate having about 3.5 percent by weight of silicone solids was added in measured amounts until the same "working consistency" was achieved. It was noted that to achieve an equivalent working consistency less aqueous siliconate was required than clean tap water.

The prepared mortar was transferred into cubes as previously and the 100 mm3 cubes were prepared and set aside.

For practical reasons 5, 1 00 mm3 cubes were prepared with siliconate mortar and 5 with conventional mortar as control. These cubes were left to set for two days and were then removed from the mould and left to dry. Five days later the cubes were tested on an Avery-Denison machine shown schematically in Fig. 1 where reference numeral 1 designates the cube being compressed. The results of the test were recorded and the results were tabulated in Table I below.

Table I Summary of compression tests Breaking Cube Sampling Dimension Weight Age in Breaking stress Density ref. date mm KG days load KN N/mm2 KGIM3 O/1 11.11.81 1003 2.10 7 155 15.5 2100 0/2 11.11.81 1003 2.25 7 150 15.0 2250 0/3 11.11.81 1003 2.25 7 155 15.5 2250 0/4 11.11.81 1003 2.25 7 150 15.0 2250 0/5 11.11.81 1003 2.25 7 150 15.0 2250 S/i 11.11.81 1003 2.25 7 155 15.5 2250 *S/2 11.11.81 1003 2.15 7 125 12.5* 2150 S/3 11.11.81 1003 2.15 7 160 16.0 2150 S/4 11.11.81 1003 2.10 7 175 17.5 2100 3/5 11.11.81 1003 2.05 7 170 17.0 2050 Key: 0/1 etc. sand/cement/water S/1 etc. sand/cement/Aqueous Siliconate *Excluded from experiment (a piece of organic material found in the cube).

Having concluded the breaking stress readings on the first batch of cubes, a further 4:1 sand/cement mixture (by volume using the same measuring apparatus) was thoroughly mixed as before, and two sets of 5, 1 00 mm3 cubes were prepared. The cubes as before were made by an experienced technician and allowed to set. As in the previous experiment the cubes were tested seven days later. The results obtained were recorded and are reproduced in Table II below.

Subsequently this procedure was adopted with a further twenty four cubes made over a period of 28 days (for practical reasons) and the cubes were left to dry in a constant temperature and humidity room for 28 days i.e. 4 weeks. The results of these tests reflected the results in Tables I and II.

Table II Summary of compression tests Breaking Cube Sampling Dimension Weight Age in Breaking stress Density ref. date mm KG days load KN N/mm2 KG/M3 0/6 18.11.81 1003 2.20 7 165 16.5 2200 0/7 18.11.81 1003 2.20 7 170 17.0 2200 0/8 18.11.81 1003 2.20 7 160 16.0 2200 0/9 18.11.81 1003 2.20 7 175 17.5 2200 O/10 18.11.81 1003 2.20 7 170 17.0 2200 S/6 18.11.81 1003 1.95 7 165 16.5 1950 S/7 18.11.81 1003 1.95 7 150 15.0 1950 S/8 18.11.81 1003 2.00 7 165 16.5 2000 3/9 18.11.81 1003 2.00 7 155 15.5 2000 3/10 18.11.81 1003 1.95 7 155 15.5 1950 Key: 0/6 etc. sand/cement/water S/6 etc. sand/cement/Aqueous Siliconate.

Figure 2 is a graph showing the results tabulated in Tables I and II. Breaking stress in N/mm2 is plotted on the y axis and the cube sample number shown on the x axis. The crosses on the graph show the results of the tests on the siliconate mortar and the circled dots show the results of the tests on the conventional mortar. A mean value for the breaking stress of the conventional mortar is shown by the chain dotted line L1 and a mean value for the breaking stress of the siliconate mortar is shown by the solid line L2. As can be seen, the two mean values vary by one N/mm2 in 16.0. This variation is insignificant which means that for most practical purposes both mortars can be considered to have equal bonding properties.In practice this means that architects can design structures using mortar of the invention to achieve the required damp proof course without building in a structural weakness.

The deviation from the mean in these experiments is almost certainly due to the differential drying rate and, of course, to the impossibility of achieving a perfect sand and cement mix. Some cubes will therefore have more cement than others, and the breaking stress will of course reflect this. For this reason the mean breaking stress value is the only meaningful value to use.

The above results are considered approximate and in order to obtain a more exact indication of the effect of the siliconate on breaking stress many more tests would have to be performed.

Nonetheless, the results do indicate that a comparable breaking stress can be obtained with the mortar of the invention.

The aqueous siliconate also acts as a retarder and even after two days the centres of the 100 mm3 cubes remained soft to the touch, provided water is prevented from evaporating from the cubes.

Examination of the samples tested also shows that the aqueous siliconate acts as an aerating compound and creates extremely small air cells in the mortar. When these are evenly distributed and of extremely small size, the crushing strength of the mortar can even be increased over that of conventional mortar.

The principle of aerating either mortar or concrete with extremely small diameter holes, for example, of not more than one mm., filled with air or some other gas could add a new dimension to concrete technology. The crushing strength to weight ratio of the mortar concrete could be significantly improved by this means.

Apart from the use of aqueous siliconate and other such compounds, other techniques may be advantageously employed to reduce the density of concrete. In particular small beads of low density, for example polystyrene spheres of diameter of the order of 1.0 mm or less, may be employed as an additive in the concrete. Such beads may contain air or they may merely be low density materials. The advantage of such beads over a pure aerating technique is that whereas air cells can combine and thus grow to an undesirable size, for example as the concrete is mixed, the beads cannot.

In order to test the damp-proofing characteristics of the aqueous siliconate, the following tests were carried out: A quantity of 4:1 sand/cement mixture (by volume) was thoroughly mixed and the mixture divided into two parts. To one part was added water to make conventional mortar and this mortar used in Tests 1 and 4 below. To the other part aqueous siliconate having 5 percent by weight of silicone solids was added instead of water and this mortar was used in Tests 2 and 3 below.

In all the tests the bricks used were flettons.

In Test 1 with conventional mortar, a conventional bituminous damp-proof course was embedded in the mortar, while in Test 2 the mortar with aqueous siliconate was used and no bituminous dampproof course employed. Test 3 was like Test 2 except that both bricks were saturated before the test was started. In Test 4 conventional mortar without a bituminous damp-proof course was used.

The results of the tests are shown in Figure 3 where days are plotted on the x axis and % water content is plotted on the y axis. The results of tests 1,2,3 and 4 are represented by lines T1,T2, T3 and T4 respectively.

In all the tests one brick was fixed on top of another by the mortar being tested. The first meter readings were taken about one hour after the bricks were set in mortar and these readings are shown on the y axis of the-graph in Figure 3. At the end of that day more readings were taken to give the reading for day 1. All four sets of bricks were then placed in buckets so that the lower brick of the set was in about an inch of water.

A third reading was taken 24 hours later and the percentage of water content of the bricks above the mortar layer was recorded. These values are illustrated on the graph for day 2. The procedure was repeated for days 3 and 4.

All the readings on the graph are for the percentage water content of the bricks above the mortar layer.

From the results of the tests it is clear that the mortar of tests 2 and 3 is as effective as a conventional bituminous layer in preventing rising damp. The difference in the levels of the lines T1 and T2 merely reflects a difference in the initial moisture content of the bricks.

An aqueous siliconate suitable for use in the invention is an aqueous solution of potassium methyl siliconate, for example that sold by ICI as R333 Silicone Masonry Water Repellent. Such compounds have been used previously in the construction industry to add to brickwork, concrete, natural stone or other such materials once they have been fully formed as part of a structure; this is in contrast with embodiments of the present invention where the aqueous siliconate is mixed with the construction material in the course of its preparation.

In the example of the invention described above, aqueous siliconate is added to the mortar. Other chemical compounds may be used in place of aqueous siliconate although the latter is preferable because of its known stability and acceptance by the construction industry. Other liquid chemicals employing water as a solvent and that may be used to provide a damp proof course are known and these may be used instead of aqueous siliconate.

Claims (18)

Claims

1. A mortar mixture characterized in that an aqueous siliconate is used in place of some or all of the water and the ratio by weight of silicone solids to water in the mortar mixture is in the range of 1 to 10 parts of silicone solids to 99 to 90 parts of water.

2. A mixture as claimed in Claim 1 in which the concentration of silicone solids in water is 6 percent by weight.

3. A mixture as claimed in Claim 1 in which the concentration of silicone solids in water is 5 percent by weight.

4. A mixture as claimed in Claim 1 in which the concentration of silicone solids in water is 3.5 percent by weight.

5. A mixture as claimed in any of Claims 2 to 4 in which the concentration of silicone solids is in the range of 3.5 to 6 percent by weight.

6. A mortar mixture as claimed in any of Claims 1 to 5 in which other chemical compounds suitable for use as a damp proof course are employed in place of aqueous siliconate.

7. A method of making a mortar mixture in which silicone solids are added during mixing and the ratio by weight of silicone solids to water in the final mortar mixture is in the range of 1 to 10 parts of silicone solids to 99 to 90 parts of water.

8. A method of retarding the setting of a mortar mixture, the method including the addition of silicone solids to the mixture.

9. A concrete characterized in that it includes an aqueous siliconate resin.

10. A method of aerating concrete in which air cells are added to the concrete, the diameter of the air cells being less than 2 mm.

11. A method as claimed in Claim 9 in which the diameter of the air cells is less than 1 mm.

1 2. A building material characterized in that it includes low density beads distributed therethrough.

13. A material as claimed in Claim 11 in which the beads have overall dimensions of less than 1 mm.

14. A mortar substantially as herein described.

1 5. A concrete substantially as herein described.

1 6. A method of making a mortar mixture substantially as herein described.

1 7. A method of retarding the setting of a mortar mixture substantially as herein described.

18. A method of aerating concrete substantially as herein described.