A METHOD OF PREPARING AND PRODUCING ASPHALT MATERIALS TO BE LAID OUT AS A COLD ROAD CONSTRUCTION OR PAVING MATERIAL

Abstract: It is well known that the traditional hot laying out of asphalt suffers from some disadvantages, and it has been endeavoured to replace it by a cold technique based on a mixture of stones and a bituminous binder emulsion adapted as to be actuated as a binder ("break") once the material has been laid out. Also this requires a high degree of planning in the asphalt plants as well as a high production capacity; besides, the cold techniques have been restricted with respect to a desirable high viscosity of the bituminous binder. The invention provides for a method, by which two separately prepared material fractions can be produced to stock and to depots and at any time be taken out and simply mixed preparatory to the laying out, such that the respective binder emulsions acting as breaking agents for each other. It is possible to use very high viscid bitumen in both emulsions. The invention also comprises the manufacture and distribution of the products in two parts as the factory aspect of the method.

Description: A method of preparing and producing asphalt materials to be laid out as a cold road construction or paving material. The present invention relates to a method of cold produc- tion of asphalt materials for a cold laying out as a road building or repair material. It is well known that the traditional preparation of as¬ phalt for laying out in smoking hot condition is highly en¬ ergy consuming and expensive in investment costs of the pro- duction equipment. It is undeniable that the associated heat¬ ing conditions results of high quality, inasfar as the ap¬ plied bituminous binder can be based on a bitumen having a high viscosity at normal road temperatures, but, when heated, adopts a substantially lower viscosity during the mixing and laying process, thus making the material shapeable and com¬ pressible. This 'hot' method, however, has noticeable limitations and drawbacks, not only with respect to the high heat con¬ sumption and the large investment costs, but also in that the method should be seen as a totality in connection with a given paving work. Since the material cannot be satisfacto¬ rily laid out and compressed if the transportation distance from the factory to the working site or the waiting time at the laying site is so long that the material is cooled sub- stantially, the method is sensitive to transportation dis¬ tance as well as to irregularities in the laying rhythm. Another drawback or limitation is that it is difficult or highly undesirable to prepare minor amounts of material, e.g. for small repair works. Finally, it should be mentioned that the "hot" method does not allow for a production of a high quality material to be stored for later use with small repair works. On this background it has been natural to speculate in a cold preparation of the material, and as known by skilled persons this is possible in bringing the bituminous binder to a cold stone material in a water emulsified and non-cohesive condition; by the formulation of the emulsion or by addition of different substances it is possible to determine when the emulsion should "break", i.e. render the bitumen particles adhering to each other and to the stone material under preci¬ pitation of the emulsion water. However, the method is very sensitive to variations in the laying rhythm, i.e. there will be severe risks that an already prepared material charge becomes unusable due to the breaking of the emulsion taking place too early or too late. An early breaking implies that the material conglutinates prior to the laying out, whereby it may be difficult or im- possible to lay the material in a satisfactory manner; by a late breaking, by which the material will be shapeable during the laying out, the laid out material, until the breaking oc¬ curs, will be unstable in response to mechanical influence, causing deformation of the material layer, and to rain water, which will act to wash out the unbroken emulsion, whereby the final binding will be inferior to the expected result. Al¬ ready during the transportation of the material to the site, traffic problems may be created owing to the fact that an initial breaking of the emulsion results in the still unbro- ken part of the emulsion being less viscid due to the water precipitated from the broken part of the emulsion, flowing from the vehicle transporting the material, this resulting in a surface mess of bitumen rich water which is very unpleasant for car drivers. On this background it has been endeavoured to adapt the breaking such that a complete breaking has taken place at the time the material leaves the mixer, but in these intermediate solutions it has been necessary to use material fractions with a content of a bitumen emulsion based on a low viscosity bitumen, such that the final product will be bound by a bitu¬ men that is less hard that achievable by the physically sim¬ pler cooling of a high viscid bitumen binder. With the present invention it has been recognised that these circumstances may be changed fundamentally such that an effective breaking of the cold emulsion may occur in the lay¬ ing phase, whether soon or long after the material was pre¬ pared. In connection with the invention, the "material" is to be understood as two or at least two material fractions, which are prepared with latent breaking agents that will, each, be activated by a mixing together with the other fraction, but otherwise leaving the material fraction with the binder emul¬ sion in a time non-determined, non-actuated condition. These terms may be relative, inasfar as materials specifically adapted for use within two months, could well be prepared such that their emulsions could breake more o less after three or eight months, should the material not be used as planned. According to the invention this may be easily realised in preparing, for later mixing together, two separate material fractions with binder emulsions of anionic and cationic type, respectively. These binder emulsions may each be adapted to be, over time, practically unlimited actuatable, also so as to not break by the mixing together with the associated stone fraction, and each of the two material fractions may thus be produced to stock, when only they are kept strictly separate. It is then possible at any time to collect from the stock re¬ spective portions of the two types, which, upon a mixing to¬ gether that need not be very intensive, may be brought to laying out whether in connection with larger construction or renovation works or with more isolated repair works. It is a known phenomenon that by a contact between re¬ spective anionic and cationic bituminous binder emulsions both emulsions will break, resulting in an actuated binder with the similar viscosity as the basic bitumen used in the emulsions, but this knowledge has not earlier been used with practical advantages should the idea have arised, a conclu¬ sion might have been that the reaction would be almost imme¬ diate, rendering the mixed material non-shapeable, but in practice no problems in this respect are observed. It may be a precaution, however, to seek to slow down the actual break- ing and hence the speed of coalescence in the laid out mate¬ rial, e.g. in using invert emulsions (water in oil). The advantages achievable by the very simple technique according to the invention are substantial. As a first sub- stantial advantage it is possible, in both types of material, to use emulsions based on bitumen with a very high viscosity, such that the resulting binder in the laid out product may be fully as strong or hard as in hot laid materials; the known cold laying techniques have had a weakness in just this re¬ spect, as it has been required to make at least partial use of emulsions based on relatively low viscid bitumen, which has restricted the applicability of these methods. As already indicated, the new technique will imply that the asphalt plants are free to run a production to stock, which can be done by an even production such that the produc¬ tion capacity can be adjusted to an average consumption and not to an acute maximum consumption during separate periods of time, this implying a much more economic production. In the same plants or in regional storing places for the two types of materials, of course, mixing facilities should be at disposal, operable with a capacity as required during periods with high consumption of the material to be laid out, but this equipment may be rather simple; it should be able to effect a mixing, but the mixing need not be particularly in¬ tensive or uniform, because in the laid out material a cer¬ tain migration of the anionic and cationic emulsions will oc¬ cur. Thus, it is not necessary to use real compulsive mixers, as a sufficient mixing is achievable already by a current merging of flows of the two types of materials. As mentioned, a more homogenous mixing could even have the adverse effect of accelerating the breaking of the emulsions to such an ex¬ tent that a sufficient shapeability was jeopardised. Something similar may apply to the production of the two material types themselves. The asphalt plant should not nec¬ essarily be equipped with a conventional compulsive mixing equipment, since for both types of material it will be suffi¬ cient to effect a spraying dosing of the emulsion e.g. on a falling flow of the stone material; when the material is thereafter stocked without any breaking of the emulsion, the emulsion may then, gradually, distribute itself over the sur¬ face portions of the stones that might be left uncoated by the spraying, such that the stones may nevertheless be fully coated when the time comes to mix the two types of material. This conditions a significant cost saving in processing equipment and labour in the asphalt plants. It should be noted, however, that the stone material will normally include a fine fraction such as sand, and when the material is processed as here described the fine fraction will tend to be preferentially coated. For this reason it may be preferred to effect a conventional homogenous mixing of the respective material types, unless the different fractions are processed individually. Also to be noted is that the emulsions are liable to un¬ dergo some degree of breaking as a result of their contacting the stone material. Such a partial breaking, which leaves the material fully shapeable, has the advantage of ensuring that the stones are durably coated with a cohesive and adhesive layer of binder. In periods with high consumption, the collection of the material from the stock or the storing places can be supple- mented by a delivery of the material directly from the pro¬ cessing equipment of the asphalt plant, inasfar as both of the material types may be equally usable after storing and immediately after being prepared. By the traditional "hot" method, as mentioned, a very good result is obtained, but it is to be noted that the asso¬ ciated strong heating is not only highly energy consuming, but also results in a ductility reducing hardening of the binder. With the invention this will be totally avoided, and it is an important result that a paving made in accordance with the invention may be still stronger than a conventional hot laid paving, and it may even be more resistant against weakening by the influence of rain water, inasfar as the ap¬ plied emulsions may contain active adhesion agents. With the invention it is a valuable result that the types of material may occur as packed in sacks, whereby they can be mixed to form very small total portions for execution of pro¬ nounced small jobs, this so for not having been a realistic possibility. Hereby the invention may provide for the option of the two types of material to be sold as sacked products in various building markets and yet still be applicable for ad¬ vanced laying out at a large scale. It is known to make use of two material fractions that are mixed together, but in the known art these stone frac¬ tions have been coarse and fine, respectively, treated with the same emulsion of a low viscid bitumen or with respective emulsions of high and low viscid bitumen. With the invention, a corresponding distinguishing will not be excluded, but it is clearly advantageous that it is possible to use the same stone material for both types of material. This also implies that the two material types are each "ready", both with re¬ spect to their stone contents and their content of bitumen, and consequently it will be a further possibility that e.g. for small repair works it will be possible to use but a sing¬ le sack of material, e.g. with a cationic emulsion, for the breaking of which the user may purchase a complementary breaking agent which is sprayed onto the material. For obtaining particularly good results it will be advan- tageous to use precoated stones, i.e. stones prepared with a coating of bitumen by a cold or hot process. Also various ad¬ ditives may be used, e.g. some polymers or fibre material that will stabilise the water against breaking of the emulsi¬ on. The use of solvents may be entirely avoided. With the method can be used almost maximum high viscid bitumen in both emulsions, e.g. with viscosities up to 200.000 mm /sec. at 60 C. A noticeable mixing of the emulsions or polymer modified bituminous emulsions will occur immediately by the bringing together of the two material types as well as by the compres¬ sion that is normally effected just after the laying out, and in most cases the road will be ready to receive both traffic and rain water as soon as the laying out and the mechanical aftertreatment is finished. The breaking and the binding oc- cur from the very beginning all over the material, from bot¬ tom to top, but the conditions can be controlled such that the material remains shapeable during the laying out. It should be mentioned that for just this reason it will be worth endeavouring that the preceding mixing operation should not be particularly efficient, whereby the mixing will be that much simpler to carry out. The invention will be well suited for treatment and utilisation of recycled asphalt, which will typically hold 4- 6% bituminous binder with good adhesion to the stones. The material is re-worked by an addition of a few percent of ad¬ ditional binder in emulsified form, whereafter the material or the respective material types will be ready for a cold laying out whenever required. The two types of material should not necessarily be mixed in the ratio 1:1, as in general terms they should only be mixed in a ratio such that the associated and desired pH-ad- justment for actuation of the emulsion breaking will be ob- tained. If one emulsion is more acid than the other is basic, then it is relevant to use a relatively smaller amount of the acid fraction. In principle the invention is extended to the use of con¬ tra-polar emulsions or agents which, breakingwise, will actu- ate each other when being mixed together, but otherwise being substantially non-breaking or at least non-breaking through a desired period of time, ranging from few hours to several years. This result is achievable by the use of the respective anionic and cationic emulsions, but probably it can be achieved also by means of other 'contra-polar systems' such as different, but mutually miscible liquids or solids in liq¬ uids or colloidal suspension or gells. The invention may be used with a wide variety of modifi¬ cations, e.g. as follows: - the bituminous binders in the respective emulsions are not of the same viscosity or rheology and may be hydro¬ carbon binders or bitumens modified by polymers or additives, or unmodified binders with or without additives such as sil¬ ica fume or filler or fibres or carbon black or adhesion agents; the bituminous emulsions are both cationic or both anionic or non-ionic or combinations such that the two sepa¬ rately coated material fractions when mixed together act as breaking agents for each other, either as PH modifiers or as buffers or as destabilising chemical reaction initiators; the bituminous or hydrocarbon binders in the res¬ pective emulsions react with each other after coalescence or cross-link upon contact such that a higher cohesion or vis¬ cosity results, with the benefit of enhanced properties of the mixture of two material fractions. the stone material may consist of pre-coated fines an uncoated coarse particles or pre-coated coarse particles and uncoated fines or blend of both or totally pre-coated ma¬ terial by methods including the use of bituminous and hydro¬ carbon emulsions, foamed bituminous or hydrocarbon of any po¬ larity, hot coating or any combination of these; the prepared material fractions may consist of more than two separate fractions and can be composed of fines or coarse fractions in any ratio such that when homogeneously mixed together the desired aggregate grating curve is formed; - the emulsion system may include a two component epoxy resin bitumen blend or polyurethane system as two sepa- rate emulsion systems made to break each other. - the bitumen in the emulsions may be of any viscosity, as suitable for respective applications; there is no upper limit, so viscosities of e.g. 200,000 og 500,000 *5 • ^ mm /sec. at 60 C may be applicable. Examples: Example l: Material for short term storage or to be laid the day it is produced. Aggregate: 40% 8/12 mm Rønnegranit 20% 5/8 mm Rønnegranit 40% 0/6 mm Sand Emulsions: A: 70% anionic emulsion based on B180 produced in accordance with ASTM class SS. B: 70% cationic emulsion based on B180 produced in accordance with ASTM class CSS. From the aggregate two mixtures are made with an identi¬ cal emulsion content of 7.4%, one based on type A emulsion and the other on type B emulsion and brought to separate storage bins. Preparatory to loading onto trucks for transportation to the site for the laying out the two mixtures are brought to¬ gether simultaneously in the ration 1:1 on a loading conveyor and consequently obtain a slight mixing falling onto the trucks. When laid the following compaction by rollers will cause the two emulsions to break each other and when fully com¬ pacted all the emulsion has broken whereafter the material obtains its final strength. Example 2: Aggregate: The same as in example 1, but now precoated with 1.5% B80. Emulsions: A: 70% anionic emulsion based on B80 produced in accordance with ASTM class MS. B: 70% cationic emulsion based on B80 produced in accordance with ASTM class CMS. Due to the precoating the emulsion content in the two mixtures is reduced to 5.3%. Storage, mixing, laying and compaction as in example 1. Materials that can be stored for a longer period of time. Example 3: Aggregate: The same as in example 2. Emulsions: A: 70% anionic emulsion based on B180 produced in accordance with ASTM class SS. B: 70% cationic emulsion based on B180 produced in accordance with ASTM class CSS. From the aggregate two mixtures are made with an identi¬ cal emulsion content of 5.3% and stored in two separate stockpiles. During storage the stockpiles should be covered to protect the material containing unbroken emulsion from rain. Prior to laying the two materials are brought together in a similar manner as in example 1. Example 4: Aggregate: 70% 6/16 mm recycled asphalt 30% 0/6 mm recycled asphalt Emulsions: A: 50% anionic emulsion based on B180 produced in accordance with ASTM class SS. B: 50% cationic emulsion based on B180 produced in accordance with ASTM class CSS. From the recycled asphalt two mixtures are made with an identical emulsion content of 4.4% and stored in two separate stockpiles. The material is hereafter treated as in example 3. Sacked materials for reinstatement purposes. Example 5: Aggregate: 70% 5/8 mm Rønnegranit 30% 0/6 mm Sand The aggregate is precoated with 1.5% B80. Emulsions: A: 70% anionic emulsion based on B180 produced in accordance with ASTM class SS. B: 70% cationic emulsion based on B180 produced in accordance with ASTM class CSS. From the aggregate two mixtures are made with an identi- cal emulsion content of 5.7%. The mixtures can be sacked in strong plastic sacks marked with an A for the anionic mixture and a C for the cationic mixture. When a reinstatement job, e.g. repairing a pot-hole is to be carried out material from sack A is mixed using a shovel with an equal proportion of material from sack C and com¬ pacted into the pot-hole resulting in a durable permanent re¬ pair.

Claims: C L A I M S : 1. A method of preparing asphalt materials for cold lay¬ ing out as a road construction or repair material, whereby a stone material is treated with a bituminous emulsion suited for breaking in connection with the laying out of the mate¬ rial, characterised in that two separate material fractions are prepared with mutually different emulsions, which are each, per se, long-term stable against breaking, but also ac- tive as a relatively quick-acting breaking agent for each other, preferably in consisting of an anionic and a cationic emulsion, respectively, said material fractions being mixed together preparatory to an approaching laying out, and the mixture then being laid out. 2. A method according to claim 1, characterised by the use of respective emulsions or polymer modified bituminous materials which are both based on a marked high viscid bitu¬ men, e.g. with a viscosity of up to 200,000 or 500,000 mm /sec. at 60°C. 3. A method according to claim 1, by which the two mate¬ rial fractions are each prepared by a non-compulsive mixing technique, e.g. by spraying the emulsion onto a falling flow of the stone material, whether pre-coated or not. 4. A method according to claim 1, by which the two ate- rial fractions are produced to stock and optionally brought out to local depots, in which, prior to a planned laying out of a desired total amount of material, they are mixed to¬ gether by a non-compulsive mixing technique, e.g. by a cur¬ rent merging of flows of the two fractions or rocked together in successive thin layers. 5. A method according to claim 1, whereby the two mate¬ rial fractions are packed and distributed in relatively very small amounts, e.g. packed in sacks of ordinary size. 6. A method according to claim 5, changed in that only one of the material fractions is distributed in small por¬ tions, while for the breaking actuation of its emulsion a relevant complementary spraying fluid such as an acid or a base is applied immediately prior to or even after the laying out. 7. A method according to claim 1, whereby for the stone material there is used precoated stones or re-cycled asphalt. 8. A system for producing asphalt materials according to claim 1, characterised in being equipped with means for a non-compulsive mixing of the stone material with the respec¬ tive two emulsions and with storage facilities for the res¬ pective, mutually separated material fractions. 9. A system according to claim 8 and further comprising an equipment for non-compulsive mixing of the two material fractions, for delivery of ordered amounts of material ready to be laid out. 10. A system according to claim 8 and further comprising satellite depots for the two mutually separated material fractions, such depots having equipment for a non-compulsive mixing of the two fractions for delivery of a material mix¬ ture ready to be laid out.

Inventors: HOVE LEO, HOVE, LEO
Applicants: HOVE LEO, VEJTEK INT AS, HOVE, LEO, VEJTEK INTERNATIONAL A/S
Application year: 1996
Main classification: E01C19
IPC codes: C08L95, E01C7, E01C19