The present invention relates to a binder for binding inert materials such as gravel or sand.

The present invention provides a binder formed by mixing carbamide (urea) and methanal (formaldehyde). These compounds react i-rreversibly with one another to produce a compound that it very stable against many organic and inorganic solvents; in particular, the final compound is not soluble in water. The final compound can be used to form a matrix binding an inert material. The binder is non-toxic.

In a preferred embodiment an accelerator is combined with the methanal and carbamide, and in a particularly preferred embodiment the accelerator is a member of the hydroxy-tricarboxylic acid series (for example Ce He O), hereinafter referred to as HTA. While the binder can be obtained without using an accelerator, the reaction is very slow. The precise amount of accelerator to be added depends on the desired reaction time.

Preferably, the composition of the binder is as follows (% by weight):

Carbamide 10 to 70%

Methanal 10 to 70%

HTA 0.05% to 33%

The present invention also provides a building material comprising an inert material dispersed through a matrix, the matrix being formed from a binder as specified above.

The inert material can be any organic or inorganic material which does not react with the binder. Possible materials include the following: sand, soil, clay, silicas, wood, rubber, stones, pebbles, partly bound cementatious masses, wood chips, grass, slag or waste dump material, coal particles, or a combination of these or other materials or other inert materials. The particulate size of the inert material is not critical, although it must clearly be less than the size of the article to be produced. The particulate size need not be constant.

The building material can be shaped, moulded or plastered, until it sets. It can be used to make many items, for example as a road surface, building blocks, bricks, paving slabs, kerbstones, balustrades and many others.

It is found that a binder concentration of around 2% (by mass) gives good results, but other concentrations can be used.

The present invention also provides a method of manufacturing a building material, the method comprising mixing methanal, carbamide and an inert

material. The components can be mixed in any order - for example the three components could be mixed together in one operation. Alternatively, either the carbamide or the methanal could be mixed with the inert material, and the other of the carbamide or methanal could then be added.

In a preferred embodiment, the method comprises the steps of: (a) mixing methanal and carbamide to form a binder; and (b) mixing the inert material with the binder. This method is preferred when a road is being surfaced. The inert material is spread over the road, and the binder is then sprayed onto the inert material. The binder is then mixed into the inert material, for example by raking the inert material.

In a preferred embodiment an accelerator, for example an HTA, is added for the reasons outlined above.

The reaction between the methanal and the carbamide is relatively slow, taking around 4-5 hours at room temperature if HTA is present in the quantity described in the example below. The inert material must be added to the binder before the reaction is complete.

Preferably, the temperature of the mixture is kept below 30°C. If the temperature were significantly above this temperature the reaction, which is exothermic, would be too fast so that there would not be sufficient time to add the inert material to the binder.

In preferred embodiments one or more of the following can be added:

1) a plasticiser to vary the flexibility of the final product. Standard plasticisers such as phthalates, glycols, acetates or hydrocarbons can be used;

2) a preservative to prevent bacterial or fungal growth or insect infestations. This is particularly useful where wood chips or other organic materials are used;

3) a U.V. blocking or absorbing compound to absorb or block ultra-violet rays, to extend the life of the final product or totally stop U.V. degradation. This is useful if the product is to be used in the open air. Standard materials such as organic phenols, phosphates or inorganic oxides can be used;

4) an anti-rust or anti-corrosion compound to prevent corrosion of articles which come into contact with the final product - this is important, for example, if the final product is formed around steel re-inforcing rods;

5) a water proofing compound to prevent water or other liquids permeating into the inside of the product. Suitable water proofing compounds can be used, such as bitumen types or silicones, silanes and oils. Emulsions of these compounds can also be used;

6) a buffer to alter the pH of the product.

If one or more of these additives is used, itthey can be introduced at any convenient point. For example if a road is being constructed in the manner

defined above it would probably be simplest to combine the additive(s) with the binder before spraying the binder onto the inert material.

In one preferred embodiment the composition of the final product is as follows: inert materials 1% or greater; binder 1 - 50% plasticiser 0 - 20% preservative 1 - 30%

UV blocking agent 1 - 10% anti-rust agent 1 - 10% water proofing agent 0.05 - 60%

A preferred embodiment of the invention will now be described in detail, by way of example with reference to the accompanying Figures in which:

Figures 1 and 2 show the "Unconfined compressive strength" (UCS) of products according to the present invention and a conventional product; and.

Figure 3 shows the "California bearing ratio" (CBR) of products according to the present invention and a conventional product.

F.xamplp

The binder is made by mixing the following raw materials together.

a) 50% m/m solution of carbamide: 1 litre 28% m/v solution of methanal: 1 litre a Hydroxy-Tricarboxylic Acid: 50 gm

b) The raw materials in (a) are mixed fully until the solution is clear. The temperature is kept below 30°C during this step.

c) The following materials were mixed together;:-

material to be bound 96 kilograms plasticiser 500 grams

U.V. blocking material 500 grams anti-rust agent 100 grams water proofing agent 1500 grams

d) Once the materials listed in (c) have been mixed together, the binder solution formed in step (a) above is added. Water is then added, until the mixture has the consistency of thick paste. The water may be of any hardness, and sea water can also be used without a detrimental effect on the final product. This mixture can now be formed, moulded or plastered, and left to set.

Tests

Various laboratory tests have been carried out to determine the strengths and workability of the products of the invention. A binder according to the present invention was used to bind gravel in these tests.

When using various dosage rates and combined with different MOD .AASHTO (modified American association of state highways and traffic offices) strengths (compaction) the compressive crushing strengths were determined at 7 days and 14 days intervals. In each case the samples were previously submerged in water for 4 hours prior to crushing.

All these tests were compared to a conventional material in which the binder is 3% (by mass) cement.

TV P Samplp

The sample can best be described as a Ferricrete with a TRB classification as a A2-4 type material with grading modules of 2.2 and plasticity index of 6. The TRH 20 classification of the material is a class B which indicates a material which is likely to ravel and form corrugations as a gravel road wearing course.

This sample contained sand, silt and gravel, and probably a small amount of clay. (Gravel is defined as having a particle size greater than 4.75mm, sand as having a particle size between 4.75mm and 0.075mm, silt as having a particle size between 0.075mm and approximately 20 μm, and clay as having a particle size of around l-2μm.)

Unconfined Compressive Strength Tests

A binder of this invention (referred to as ECOTEC binder) was mixed into the sample in liquid form using four different dosages i.e. 0.5%; 1.0%; 1.5% and 2.0% w/w active chemical ingredients.

The various dosages were done at the standard compactive effects i.e. 90% and 100% of modified AASHTO density. Unconfined compressive strength (UCS) tests were carried out at the above mentioned compactive efforts.

The results were as follows:

ACTIVE \ COMPACTION 7 DAYS (MPa) 14 DAYS (MPa) (MOD AASHTO)

0.5% 100% 0.379 0,527

0.5% 90% 0,420 0,590

1.0. 100% 0,557 1,075

1.0% 90% 0,837 1,091

1.5% 100% 0,475 1,647

1.5% 90% 1,625 1,556

2.0% 100% 1,743 2,276

2.0% 90% 1,859 1,805

A parallel set of tests was done on the same material using 3% Ordinary Portland Cement (OPC) to act as a control standard.

In general the 2% ECOTEC binder tests came out stronger than the control sample. The results of the control samples are as follows:

CEMENT COMPACTION CRUSHING STRENGTH (UCS) (MOD AASHTO)

(7 days MPa)

3,0% 100% 1,057 3,0% 90% 1,029

These results are illustrated in Figures 1 and 2.

California Bearing Ratio Tests

A parallel set of untreated soil (of the same sample as used for the UCS tests) was used as control for the ECOTEC binder treated samples:

NATURE SOIL E ECCOOTEC BINDER STABILISED SOIL

CBR VALUES AACCTTIVE CHEMICAL CBR VALUE

23 0.5% 104

28 0.5% 131

29 1.0% 180

34 1.0% 216

52 1.5% 217

58 1.5% 237

MOD AASHTO AVERAGE 95%

These results are illustrated in Figure 3.

Comments

When crushed the sample using the ECOTEC binder failed consistently showing classic planes of failure as expected from well stabilised samples.

All tests carried out were strictly according to specifications i.e. 4 days soaked tests on CBR samples and 4 hours soaked tests on UCS samples. The samples using the ECOTEC binder were almost waterproof, and the water did not penetrate to the core of the samples. This is an important aspect in road building as water penetration into road layers reduces the life of roadworks.