GB2518126A

GB2518126A - A device and method for improving the strength of cement or concrete

Info

Publication number: GB2518126A
Application number: GB1310788.3A
Authority: GB
Inventors: Adam Gabriel Wojcik; Gregorio Ossola
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-17
Filing date: 2013-06-17
Publication date: 2015-03-18
Also published as: GB201310788D0

Abstract

A method (fig.1) and device 8 is described for treating rubber particles with radiation. The method requires that the rubber be cleaned, and irradiated before being ready for incorporation with the remaining ingredients and cured to form the required composite. The device 8 is capable of rotating the rubber particles 10 whilst exposing them to radiation from a source 13, preferably electromagnetic radiation in the UV or UVC spectrum. The device ensures that the maximum amount of the surface area of the rubber particles is exposed to the radiation source as possible. Exposure of the rubber particles to the radiation source improves the bond strength between the rubber particle and the remaining ingredients that make up the matrix of the composite. Such composites may include cements and concretes.

Description

A Device and Method for Improving the Strength of Cement or Concrete.

This invention relates to a method of improving the strength of cement or concrete. More specifically but not exclusively it relates to a method of improving the strength of cement or concrete containing rubber particles by enhancing the bond strength between a cured cement matrix and the rubber particles incorporated therein, thereby improving the overall mechanical properties of the composite material created.

Conventionally an aggregate is used to bulk out a cement based composite material, thereby reducing its overall cost. The idea of utilizing rubber as an aggregate in cement and concrete is well attested in the literature, principally as a means of utilizing waste rubber from recycled tyres as a part replacement for stone or other inorganic based aggregates.

Waste rubber is commercially processed by means including washing, shredding, and grading, and normally finds use in playground safety mats and as a noise retardant in road surfaces. The uses of such waste rubber are limited as the vulcanization process used in the original processing of the rubber means that the waste rubber cannot easily or economically be recycled. However, it is generally reported that utilizing waste rubber in the form of small millimetre sized particles, (known as crumb) unfortunately leads to a substantial decrease in the mechanical properties of the resultant concrete composite.

Major properties which are degraded include flexural strength and compressive strength.

The resultant degradation in mechanical properties have prevented the use of rubber waste in commercial concrete construction and products. The reasons for the degradation in properties of the composites are complex and not well understood, but the bond strength between the rubber and the cement matrix, which acts as the binder and hence the major load transfer component, has been implicated. Studies to alter the bond strength have been undertaken and a variety of methods have been put forward in the literature, including surface chemical pre-treatments based on primers. It is a disadvantage of the use of primers that the property benefits vary, but their cost, and questions surrounding their impact on the environment, have not led to any known commercial application or exploitation of this technology.

According to the invention there is provided a method for improving the strength of composites containing rubber particles comprising the step of exposing the rubber particles to radiation prior to inclusion in the composite, such exposure enhancing the bond strength between the composite and the rubber particles incorporated therein, thereby improving the mechanical properties of the composite.

According to a further aspect of the invention there is provided a treatment unit for the exposure of rubber particles to radiation, the treatment unit comprising an array of tubes substantially transparent to the radiation, the tubes containing the particles to be irradiated, wherein the tubes are moveable thereby agitating the rubber particles to increase the amount of the surface of the rubber particles exposed to the radiation.

Advantageously, the pre-treatment described in one form of the invention is entirely chemical free.

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a block diagram of the processing stages used to create treated rubber crumb as required for one form of the invention; and Figure 2 shows one embodiment of an irradiation treatment unit which can be used to deliver the desired pre-treatment effect.

As shown in Figure 1, the method 1 commences with the waste rubber being cleaned 2 of any major contaminants, such as organics (for example oil and grease) and foreign solids (such a metal particles). The crumb is then exposed 4 to radiation for a predetermined time and is then ready for incorporation 7 into a cement matrix. The treated rubber can then be mixed with dry cement to form a premix for later use, or can be mixed with all the remaining ingredients, including inorganic aggregates, and cured by the addition of water, to form a rubber-cement-aggregate concrete.

The exposure of the rubber to radiation alters the nature of the surface of rubber particles, before they are subsequently incorporated into (and thereby bonded to) the cement matrix.

The process relies upon the effect, which has been reliably demonstrated experimentally to occur, to be maintained as the cement hydrates and cures.

Experiments conducted have shown that a type of radiation that is effective is electromagnetic in nature and is that that is commonly referred to as ultraviolet (UV) light and is preferably that within the UVC sub-band of the wavelengths in the electromagnetic spectrum. However, it will be appreciated that any other form of radiation may be used and may obtain similar results.

Polymers are known to be affected by such wavelengths of electromagnetic radiation, the radiation causing a number of electron transitions within molecules, which can both break and make bonds, depending on the molecule being irradiated. In the case of rubber, the precise nature of the chemical changes is not fully understood but the creation of surface dangling bonds and surface dipoles (also referred to as moieties) is expected and, given that most adhesion mechanisms rely upon interactions between such surface diploes to create secondary bonding, the presence of such dipoles is likely to improve overall bond strength.

Secondary bonding includes bonding types commonly known as Van der Waals, and Hydrogen bonding.

The main stage of the process described above requires that the rubber, which is usually acquired in the form of fine crumb, be exposed for a period of time to radiation using a suitable source. Discharge tubes can be used for the case of LJV radiation. This can occur within a treatment unit such as the one substantially shown in figure 2. Preferably the treatment unit 8 permits the exposure of a substantial part of the whole surface of the crumb rubber 10 by ensuring that each crumb particle is bombarded by UV radiation from all sides. Practically this can be achieved in a variety of ways and Figure 2 shows only one such embodiment comprising an array of rotating hollow cylinders 9 arranged in a single plane, containing the crumb rubber 10, together with a set of linear UV light sources 13 arranged above and below the plane of the cylinders, means of providing power to the light sources, means 11 of rotating each cylinder about its main axis, at a given speed, using a motive power unit 12, during UV exposure, and preferably means of timing the exposure to allow unattended operation and prevent under or over exposure to the UV radiation. For UV radiation, quartz glass would be a suitable material for the rotating cylinders 9 being substantial transparent to the wavelengths in this band.

A beneficial degree of exposure can be achieved by a variety of other means, such as by spreading out the crumb rubber in the form of a thin planar layer, on a horizontal supporting surface and exposing the crumb from above, or below, or both, to UV radiation.

If exposed from above, improved exposure can be achieved by making the supporting surface reflective to UV; if from below, then the surface must be transparent to UV, such as would be provided by using quartz glass sheet or other similar material which does not absorb strongly in the UV band of the electromagnetic spectrum. With such a planar exposure unit a further advantageous effect may be achieved by agitating the crumb rubber so as to encourage rotation of crumb particles and hence exposure of parts of a particle's surface that would otherwise be hidden or shielded from the full effect of the UV radiation.

Agitation can be achieved, advantageously on a continuous basis, by mechanical means, such as might be provided by a mechanical agitator, or by vibrational means such as might be achieved by a source of vibrational energy. Agitation can also be achieved on an intermittent basis by providing means for collecting, stirring and re-applying the crumb layer to the exposure surface, at regular time intervals, such that fresh crumb surface is exposed purely as a result of statistical randomness, provided that sufficient re-application stages have occurred.

Preferably the incorporation of the treated crumb rubber into the cement or concrete, and subsequent curing by the addition of water, should be done as soon as possible after the radiation treatment to ensure that the maximum benefit is achieved and that any contamination of the treated crumb rubber product, which might be expected to reduce the bond strength between the rubber and the matrix, does not occur. Alternatively the treated crumb can be bagged and stored until such time as it is required for mixing with the principal ingredients of cement and concrete and then cured by conventional means.

The radiation treatment claimed here is substantially designed to be used as a single treatment, and does not require use with other forms of pre-treatment such as those which have already been described in the literature as applicable to crumb rubber and cement composites, however, it will be appreciated that any non-radiation based treatment, such as the application of a chemical coupling agent, capable of enhancing the bond strength between a cement matrix and a further phase such as crumb rubber, may also benefit from radiation exposure to gain an advantageous effect. Such non radiation based pre-treatments might be applied before 3, after 6 or both before and after, the irradiation method described herein.

It will be appreciated that the waste rubber crumb may be obtained commercially. Such waste rubber crumb is manufactured mainly from discarded automobile tyres. The tyres have the internal components, such as steel and fibre reinforcement, stripped and the remaining rubber is shredded and graded to produce the rubber crumb. It will be appreciated that the manufacturer may clean and pre-process the rubber crumb in order to make it suitable for radiation treatment. However, if obtained un-cleaned, the rubber should preferably undergo a cleaning stage 2 and this may need to form a further part of the inventive process.

It will be appreciated that whilst the invention is described in relation to inorganic cements and concretes, the rubber particles may be incorporated in any other suitable matrix to form a composite.

Claims

Claims 1. A method for improving the strength of composites containing rubber particles comprising the step of exposing the rubber particles to radiation prior to inclusion in the composite, such exposure enhancing the bond strength between the composite the rubber particles incorporated therein, thereby improving the mechanical properties of the composite.
2. A method according to claim 1 in which the radiation is electromagnetic and lies within the Ultra Violet part of the electromagnetic spectrum.
3. A method according to claim 1 or 2 in which the electromagnetic radiation lies within the UVC part of the electromagnetic spectrum.
4. A method according to any preceding claim in which the matrix comprises a cement or concrete.
5. A method according to any preceding claim further comprising the step of exposing the rubber particles to radiation in a treatment unit.
6. A method according to claim S further comprising the step of agitating the rubber particles in a predetermined manner during irradiation to ensure as complete an exposure of the surface of the rubber particle to the radiation as possible.
7. A method according to claim 6 in which the agitating of the rubber particles includes rotating, or tumbling, or shaking.
8. A method according to any preceding claim in which the exposure of the rubber particles to the radiation is continuous or interrupted throughout the exposure process.
9. A treatment unit for the exposure of rubber particles to radiation, the treatment unit comprising an array of tubes substantially transparent to the radiation, the tubes containing the particles to be irradiated, wherein the tubes are moveable thereby agitating the rubber particles to increase the amount of the surface of the rubber particle exposed to the radiation.
10. A treatment unit according to claim 9 in which the tubes are rotatable around their long axis, the tubes being rotated by a suitable motor.
11. A treatment unit and a method of treating rubber particles as hereinbefore described with reference to the accompanying diagrammatic drawings.