HK1050706A - Process and system for production of a warm foam mix asphalt composition - Google Patents

Description

Method and system for preparing warm-foam mixed asphalt composition

The present invention relates to a method and system for preparing a warm-foamed mixed asphalt composition.

Asphalt used in road construction or paving is typically composed of stone/gravel, sand, filler and binder components. In the present invention, this binder component is referred to as asphalt, but other binder components are equally suitable. The bitumen component may be a naturally occurring bitumen or derived from a mineral oil. Sand, stones/gravel and packing are referred to as aggregate material or granular aggregate material.

Bitumen is used as a binder for the mineral aggregate component. Bitumen is a small fraction of the total bituminous mixture, typically representing between 4 and 7% by mass (or between 10 and 15% by volume).

Bitumen compositions generally fall into two broad categories, namely "hot mix" bitumens and "cold mix" bitumens. As will be described in more detail below, another less common class of "warm mix" asphalts is also in use.

The hot mix asphalt has better comprehensive properties than the cold mix asphalt, and thus is used on roads with large traffic volumes. In the preparation of hot mix asphalt, the aggregate material is heated prior to adding the hot adhesive material to the aggregate for mixing.

Hot mix asphalt is typically prepared at temperatures between 150 ℃ and 190 ℃ and is often laid and compacted on roads at temperatures between 130 ℃ and 160 ℃. In some cases, even higher temperatures are used. Heating of bitumen and mineral aggregates is required for several reasons. The aggregate needs to be dry, the asphalt needs to have a low viscosity to be fully coated on the aggregate component, and the asphalt mixture needs to have a sufficiently low mix viscosity to be able to be laid, extended and compacted on the road. The type of bituminous mixture and the grade of bitumen determine to a large extent the preparation temperature. The hot mixed asphalt almost immediately achieves the final strength/stability. Thus, roads paved with hot mixed asphalt can be cut through almost quickly.

Fossil fuels are typically used to heat the bitumen components, which can generate environmentally harmful gases and dust, consume non-renewable resources and increase the overall cost of the bitumen. Furthermore, high temperature processing of bitumen constitutes a potential safety hazard.

Cold mix asphalt is cheaper, easier to use and more environmentally friendly than hot mix asphalt. In the process of making cold mix asphalt, the aggregate material is cold and moist when mixed with hot or cold binder material. To alleviate the mixing difficulty of cold-mix asphalt, the binder is typically foamed prior to mixing with the cold, moist aggregate material.

Various methods for preparing foamed bitumen are disclosed in norwegian patent application NO 854387 and international patent application WO 95/22661. However, the techniques involving cold mixing of asphalt produce blends with lower properties than conventional hot mix asphalt blends. This is due to a number of factors such as low coverage of aggregate with bitumen, the presence of water in the bituminous mixture, low ductility and compaction ability of the bituminous mixture. These factors make the bituminous mixture highly permeable to water and air, which makes the road surface formed in the end susceptible to wear, i.e. means that loose coarse aggregate is very easily lost from the road surface. The cohesion is also reduced, which will eventually lead to collapse of the material and lack of internal stability. This condition is common on road surfaces and is known to form ruts. Cold mixing of bitumen requires a certain curing time in order to increase the strength of the mixture. The curing time is usually from several days to several months. This in turn accelerates the deformation, cracking and surface wear of the asphalt pavement. For the reasons mentioned above, cold mix asphalt is commonly used on roads without large traffic volumes, for example, in countries in northern europe and australia.

In order to solve the above problem, patent application WO97/20890 proposes a process for preparing an asphalt composition at a lower temperature than the usual hot mixing process. By using bituminous binders, i.e. hard-component and soft-component binders, in different parts, the temperature used can be reduced. The hard and soft components together make up the asphalt to the standard final specifications. The soft component may be mixed with the mineral aggregate at a much lower temperature (60 ℃ C. -130 ℃ C., preferably 90 ℃ C. -110 ℃ C.). The hard asphalt component is then uniformly dispersed into the mixture in a powdered or milky form. Typically the "hard" bitumen component has a penetration of 50dmm or less. The temperature of this component is generally between 20 ℃ and 70 ℃. The asphalt mixture prepared by this method can be spread, spread and compacted at a temperature of 70 ℃ to 100 ℃. Laboratory and field experiments have shown the good performance of these bituminous mixtures. In the present invention, such an asphalt having a lower mixing temperature than the hot mixture is referred to as a warm mixture.

However, warm mix asphalt mixtures using emulsions have proven expensive and complicated to use during preparation, mixing, laying and compacting. Bitumen compositions prepared from bitumen emulsions require relatively high porosity in the bitumen/aggregate mixture to enable moisture removal during emulsification, compaction and maintenance. The emulsions used in the process typically contain from 30% to 50% moisture. Because of the emulsification site and additional storage tanks required in asphalt mixing plants, asphalt emulsions are expensive to produce, both in terms of product cost and equipment cost, for contractors. The cost-effectiveness of transporting emulsions is low due to the need to transport 30-50% water. The increase in the transport weight also increases the emission of environmentally harmful substances.

The preparation and handling of bitumen emulsions requires some additional measures due to the chemicals used in the preparation, the frost sensitivity of the final product and the requirement for separate storage tanks.

Thus, there is a need for a bituminous mixture that has the properties of hot mix bitumen, but also the environmentally favorable, low cost and easy to handle characteristics of cold mix bitumen. The growing awareness of health, safety and environment in public and industrial management has led to a great deal of effort aimed at reducing the use of non-renewable fossil fuels, conserving energy and consequently reducing emissions. In the asphalt industry, the reduction in the temperature at which hot asphalt mixtures are prepared helps to approach this goal.

The invention herein provides a process for preparing a bituminous composition which is capable of producing a bituminous composition having equal or better mechanical properties at a lower temperature than the production of a hot mix, with less energy input, at equal or lower cost. This object is achieved by a process for preparing a warm-mix asphalt composition comprising mixing a particulate aggregate material with a soft binder, and adding a foamed hard binder to the aforesaid particulate aggregate material and soft binder mixture.

FIG. 1 is a schematic diagram comparing a conventional hot asphalt mix production route with a warm-foamed asphalt mix production route of the present invention; fig. 2 shows an example of a hard adhesive foaming method.

After mixing the various components, the hard binder and soft binder will fuse into a binder component having the targeted properties. The stiff binder foam reduces viscosity, allowing the binder to completely coat and adhere to the aggregate component at lower temperatures.

The use of foamed hard binders has significant economic and environmental advantages over the use of powdered or emulsified asphalt, without causing damage to the nature of the resulting asphalt mixture and the paved road. Compared with the emulsion containing 30-50% of water, the water content is only 2-5%. This is of great importance for storage, performance, heating requirements and transport. In contrast to emulsion adhesives, foamed bitumen with low moisture content can cure rapidly with limited heating.

The dense asphalt mixture produced by the process of the present invention has a lower porosity than cold mix asphalt produced with a foamed binder component, as compared to cold mix foamed asphalt. The cold foam mix uses an adhesive having a soft penetration of between 180dmm and 700 dmm.

Furthermore, depending on the actual application, the foamed hard bitumen of the present invention has a maximum penetration value of less than 100dmm, as compared to a penetration value of the "hard" bitumen component used in the emulsion which is typically 50dmm or less.

Comparing the bituminous mixture of the present invention with cold mix bitumen using a binder foam, it should be emphasized that the mixture of the present invention can be used on heavily trafficked roads, but cold mix foamed bitumen can only be used on roads with a low traffic volume. This is because the bitumen used in conventional cold foam mixes has a high penetration, between 180 and 700 dmm. The final grade of bitumen in the process of the invention may be harder, typically having a penetration of between 60 and 250 dmm. Cold mix bitumen is usually prepared in situ, i.e. on the road, at ambient (cold) temperature, whereas bitumen prepared according to the present invention can usually be prepared at bitumen plants and/or on the road at temperatures between 60 and 100 ℃. This immediately affects the use and suitability of these bituminous mixtures.

In the present invention, either a creamy or non-creamy soft adhesive component can be used, but non-creamy soft adhesives are preferred. If a milky soft adhesive is used, the milky soft adhesive will contain a large amount of water. The water must be removed before the mixture reaches full coagulation and mixing intensity. The emulsion may be a cationic or anionic emulsion.

The hard binder component is added to the mixture as a foam. The soft binder may also be added as a foam, if advantages are present in certain cases.

The soft binder component may also be added to the aggregate at a relatively low temperature, i.e., at a temperature below 120 ℃.

The soft binder is typically added to the aggregate at a temperature of at least 70 c, preferably between 60 and 130 c, more preferably between 90 and 110 c.

In this application, a soft binder component is defined as a binder component having a penetration of at least 200 dmm.

Suitable soft binder components have a penetration of at least 500dmm, preferably at least 700dmm, more preferably at least 800dmm (measured at 25 ℃ according to ASTM D5). These soft adhesive components are generally characterized by their viscosity (measured at 100 ℃ according to ASTM D2171). The viscosity of the soft adhesive component should be less than 0.300pa.s, preferably less than 0.200 pa.s.

The bitumen produced in the present invention is primarily for use in roads, but other uses are also contemplated within the scope of the invention.

The dense graded asphalt produced in the process of the present invention preferably has a porosity of less than about 10%, more preferably a porosity of between 3 and 10%.

The bitumen produced in the process of the present invention may also be open graded bitumen having a porosity of between about 15 and 25%.

Embodiments of the present invention are described by the following examples.

Fig. 1 presents a comparative schematic of the process flow and fig. 2 shows a method of preparing an adhesive foam. Table II and table I are comparisons of performance and cost.

The asphalt production facility for preparing the asphalt mixture (fig. 1) using the method of the present invention comprises a drying drum, a mixer, a mixture storage bin, and an asphalt foam production facility. Stone/sand was added to the drying drum and heated to about 130 ℃. Warm stone/sand was then added to the mixer and mixed with the maltene at about 120 ℃. After the soft asphalt is thoroughly mixed with the stone/sand, hard asphalt is added to the mixture and mixing continues until finally the filler is added to the mixture at about 20 ℃. The product comprises 90% stone/sand, 2.5% soft asphalt, 2.5% hard asphalt and 5% filler by mass.

Controlled hot bitumen is flowed into the piping system through the first valve (a) to produce a foam (fig. 2). The first valve (a) allows a circulation flow back to the storage chamber, which ensures the stable temperature required by the system. Thermal oil or heater cables are wrapped around the pipe and insulated to control and maintain the temperature of the pipe system. The temperature selected depends on the properties of the bitumen, the hardness and the volume to be increased. Typically the temperature is between 130 ℃ and 180 ℃.

A controlled cold or warm water stream (5 ℃ to 80 ℃) is added to the bitumen through a second valve (B) in the order of contents from 2 to 7% and the bitumen begins to expand after the water has been injected into the bitumen stream. The bitumen is mixed homogeneously in a static mixer in the mixing chamber. The expanded bitumen, which has typically increased in volume by a factor of 10 to 20, is introduced through an outlet out of the mixing chamber and into the aggregate mixture through one or several nozzles.

Compared with the standard hot mixing method for preparing asphalt with the same performance, the method has the advantages that the carbon dioxide emission is reduced by 60-70%, the dust emission is reduced by 30-40%, and the fuel consumption is reduced by 40-60%.

Tables I and II below are comparisons of relative performance and relative cost, respectively, with hot mixes. In table 1, "means equal or equal, +", means equal or above average, and- "," means worse or below average, "? Which means uncertain, unknown or unmeasured.

Table I: comparison with the relative Performance of the Hot mixture

	Warm mix emulsions	Warm mix foam	Cold mix
				Performance of
Stability adhesion crack durability workability	＝＝＝＝＝	＝+＝++	----＝---
				Environmental impact
Fuel CO2/CO emission dust emissions	40-60% reduction, 40-70% reduction, 30% reduction	40-60% reduction, 40-70% reduction, 30% reduction	？？？
				Health aspects
Working in asphalt plants	Reduce 60-80 deg.C	Reduce 60-80 deg.C	Reduce the temperature by 100 ℃ and 160 DEG C
				Working at the laying point	Reduce 60-80 deg.C	Reduce 60-80 deg.C	Reduce 80-140 deg.C
VOC levels	Reduce	Reduce	0

Table II: relative cost comparison (hot mix ═ 1.0)

	Warm mix emulsions	Warm mix foam	Cold mix
				Cost of
Aggregate	1.0	1.0	1.0
				Fuel	0.5	0.5	0
				Binders (emulsion/dope, etc.)	1.5	1	1.5
				Total cost of	1.2	0.9	0.9

The above non-limiting example is only one embodiment of the present invention, and it is to be understood that other embodiments may be adopted within the spirit and scope of the present invention. The invention should be limited only by the attached claims.

Claims (17)

1. A process for preparing a warm mix asphalt composition, said process comprising mixing a particulate aggregate material with a soft binder, and adding a foamed hard binder to the mixture of particulate aggregate material and soft binder.

2. The process as claimed in claim 1, wherein a hard binder component having a penetration of less than 100dmm (measured at 25 ℃ according to ASTM D5) is used.

3. The process as claimed in claim 1, wherein a soft binder component having a penetration at 100 ℃ of less than 0.3Pa.s (measured at 100 ℃ in accordance with ASTM D2171) is used.

4. The method of claim 1, characterized in that the aggregate is heated to 60-120 ℃ before mixing with the soft and hard binders.

5. The method of claim 1, wherein the foamed rigid adhesive is prepared by a separate foaming process characterized by the steps of:

heating the unfoamed hard adhesive to a temperature between 130 ℃ and 180 ℃;

providing water at a temperature between 5 ℃ and 80 ℃; and

water in an amount of 2 to 7% by weight is injected into the heated unfoamed hard binder to expand it into a foam.

6. The process as claimed in claim 1, wherein foams having a water content of 5% or less are used.

7. A process according to claim 1, characterized in that the soft binder component is added to the aggregate at a temperature below 120 ℃.

8. The process as claimed in claim 1, wherein the temperature of the warm mixture after mixing is between 80 ℃ and 115 ℃.

9. The process as claimed in claim 1, wherein the dense-graded asphalt composition used is a warm mix asphalt composition.

10. The process according to claim 9, characterized in that the dense-graded asphalt composition having a porosity of between 2% and 10% is used as a warm-mix asphalt composition.

11. The process as claimed in claim 1, wherein the bitumen composition is a warm mix bitumen composition.

12. The process according to claim 11, characterized in that the composition of the bituminous open-graded composition having a porosity of between 14% and 26% is used as a warm mix bituminous composition.

13. The method of claim 1 wherein the soft binder is premixed with aggregate material in a warm-handling mixing apparatus into a semi-finished product for shipment to an asphalt paving site where the foamed stiff binder is added to the semi-finished product in a production paving apparatus.

14. A process according to any one of the preceding claims, characterized in that an asphalt component is used as the binder component.

15. Use of a bituminous composition prepared according to the process of any preceding claim in road paving.

16. A system for preparing a warm mix asphalt composition as claimed in claim 1, comprising a drying drum for heating and drying the aggregate components, a mixer for mixing the asphalt components and a mix storage silo, characterized in that said system further comprises foam production means for foaming the hard binder prior to introduction into the mixer.

17. The system according to claim 16, characterized in that the foam production device comprises a heating device for heating the hard binder component and a water or steam feed unit for subsequently introducing water into the hard binder for preparing the foam.