Invention that reduce or eliminate force mixing in production of asphalt pavings and cement concrete

Abstract

 Interfacial Engineering:"Technology to model, synthesize, charactericze, and understand, and manipulate interfaces including those between surface and bio molecules. The production of materials free from agglomerations/aggregatation, perfectly dispersed and stable in synthesis and application". (Reg Davis. University of Florida. (1999).
The interaction between dust particles and the liquids of mixes in the production of asphalt and cement concrete, develops only when the dust particles are dispersed in the liquid. When force mixing a set mass of dust particles by the paddles of the mixer, an unknown portion of the particles are agglomerated and thus not interacting with the liquid.
The reason for the invention was the requirement of the dispersion of the dust material before the particles are in contact with the liquids. The knowledge, methods and proposed means contributes to the invention. Force mixing of dust material is destructive to all durable properties of the products of asphalt pavings and cement concrete. The result of the invention is shown by the regularity in the results from tests on mix by the "TOD, Test of dispersion method"
The requirement of the technique of the invention for improved dispersion of dust material in the poduction of said products was shown by irrigularities in the results of TOD test on mixes produced by the known methods of mixing.

Description

[0001] The interaction between dispersed dust particles and a liquid produces a volume of binder of mix with the properties of a suspension. The interaction of dispersed particles in a suspension induce to the liquid a number of properties i.e. expanding the liquid volume equally to the volume of dispersed particle, increasing the viscosity of the liquid through close packing in the liquid, and the facts that the glue phase of suspension is a continuous phase enclosed by the structure of coarse particles, the suspenion is hydrostatic solid in the resistance to preassure and ductile/cohesive i.e tough at strain.

[0002] The interaction between dust particles and the liquids of mixes develops only from dust particles dispersed in the liquid. When force mixing a set portion of dust particles by the paddles of the mixer, an unknown portion of the particles are agglomerated and thus not interacting with the liquid. The reason for the invention is the requirement of dispersion of the dust materials before contact with the liquids. The knowledge, methods and proposed means contributes to the invention. Force mixing of dust material is destructive to all durable properties of the products of asphalt pavings and cement concrete.

The knowledge of the invention

[0003] The aggregate material used in industrial production of asphalt pavings and cement concrete is selected for the resistance to wear.

[0004] The positive influence of dust particles in liquids is hidden by the difficulty to disperse. To disperse a controllable amount of the dust material in mix in the short time alowed for in the mixing process for production of said products, have proved to require an invention in particle technology. The whole mixing process, inlets of aggregate materials, dust materials and liquid from weigh hoppers to the mixer, mixing period and discharge of ready mix from the mixer is completed in 60 sec. In order to create a controlled interaction between liquid and .particles require the planing by advanced particle technology. The expression "dispersed" means by the invention that the dust material is spread in all parts of the liquid of the mix without the use of force mixing.

The history of particle technology

[0005] "Particle technology begin shortly after the second World War. Particle products were attractive because of the high surface to volume ratio avilable for interaction with the liquid. In 1945 it was predicted that the science and technology of fine particles would be of major importance in the development of future products.

Particle engineering:

[0006] The ability to seize selectively synthesized particles and assamble them in to building blocks at acceptable cost, quality and quantity.

Interfacial Engineering:

[0007] Technology to model, synthesize, characterize, understand, and manipulate interfaces including those between surface and bio molecules. The production of materials free from agglomerations/aggregatation, perfectly dispersed and stable in synthesis and application.

Charaterization:

[0008] "Measurement having superior visual reference and measurement at even finer sizes. Improved interparticle and particle force measurement". Reg Davis. University of Florida. (1999). The above points 5-8 introduce a number of statements of wanted results but no solution or means how to produce them in the production of asphalt and cement concrete.

The particle technology of the invention.

[0009] In the design of mix composition the quantity of different fractions of solids are determined by weight whereas for the mixng with the liquids in accordance with the invention, the fractions of solids are recognized by number of particles/unit weigth. In that respect the dust material advances from being the smalest by weigth in mix to the largest in number of particles in the mixing process.

[0010] As the interaction between liquid and dust particles is the provider of durability of the glue phases over time, this raises the requirement of the invention to describe example of method and means for finding dust material dispersed in the glue phases of asphalt pavings and hardened cement concrete. By force mixing, only an uncontrolled part of the dust particles are dispersed whereas the major part of particles is found clustered to the surface of larger aggregte.

[0011] The properties of the glue phase of suspension The Asphalt pavings and hardened cement concrete is produced by selected amounts of coarse fraction, the main part being > than 4 mm, fine aggregates, the main part being < than 4 mm and filler and cement particles < than 0.074 mm. Filler and cement are hereafter defined as "dust particles". The liquid of the asphalt mix production is the bituminous liquid wheras the liquid of cement concrete production is the water. Both hereafter with reference to the mixing process defined as "liquids". When the volumes of the glue phases are increased by the volume of dispersed dust particles, the glue phases of the products are sufficient to form a continuous phase through the skeleton of the coarse aggregate particles of the mix. The continuity and inclosure of the glue phases by the surfaces of the coarse fraction particles makes the glue phases of the products ductile/cohesive. In addition the enclosed glue phases makes the products hydrostatic solid. (Enclosed liquids are hydrostatic solid). The products deform to break by a flow. (Reference to rheology). Without the properties of interaction the products deforms by cracking before breaking. (Reference to mechanical properties). The products meets the requirements of the Particle engineering, Interfacial Engineering and Charaterization set out in Points 5-8 and 11 above.

The mixing (Twin-Shaft Through Mixer (Figure 1 refers)

[0012] The coarse fraction particles are first mixed with the liquids for example 8 sec. this to develop a surface area of liquid equal to the surface area of all coarse fraction particles, the dimensions of the area are a) the breadth given by the length of the shafts in the mixer b) the length of the area determined by the flow of surface area of liquid on the coarse fraction particles at a set period of time as an example 1 5 sec, and c) a device for discharging the dust particles in sufficient state of dispersion along the breadth of the area and d) discharge the fine fraction particles in the same area, mix as an example 10 sec and discharge the ready mix from the mixer. The material flow in the mixer is shown by figure 1.
The fine fraction of the mix is discharged by mass if directed to the donward flow in the mixer of the liquid suspension on surface of the coarse fraction paticles. The asphalt mixing temperature is in range of 125°-140°C.
When the discharge of the fine fraction is directed towards area outside of the down ward flow the mass off the fine fraction is dispersed by controlled rate of discharge over time. Then the discharge require high amount of liquid properties in mixed material.

Earlier patent applications

[0013] One of the mixers used for production of asphalt and cement concrete is the "through mixer". Figure 1 refers. From earlier patent and applications are lerned that the coarse fraction of the asphalt mix and cement concrete production, is coated in advance with the liquid before admixing the dust material. EP 1 586 706 A2 and EP 95 916 902.0-2303 respectively.
In both applications the example of means given for discharge of the dust materials on to the surface of the flowing coarse fraction, is a conveyor belt or a screw. The discharge is made at a controlled rate of flow. This disclose that the dust material is discharged in a narrow string of mass of particles on the breadth of the area declared open by the invention for recieving dispersed dust particles. It is understood that to spread the mass of dust material of the string through the bredth of mass of coated aggregates in the mixer require movements in the mix by the force of the mixer paddles. By this operation, unknown part of the material form agglomerations clustred to the surfaces of larger aggregates. Agglomerates are not contributing to the development of the properties of interaction in the glue phases of the products. The agglomerates are revealed by the measures of properties of interaction not being regulair.

[0014] An example of mix composition used by the invention, table a) and b) refers, a) shows an amount of dust material in a 4 ton mixer of 114 litre. With the discharge time set to 17 sec. Re: Patent application EP 1 586 706 A2, the rate of discharge is 114/17 = 7 litre/sec. This shows that the dust material is discharged in a string of particles of whitch large part is to be ditributed in mix by force mixing. It reveals that the inventor of the applications lacked the thought of the invention.

One material composition used by the invention

[0015] Example of material compositions a) asphalt paving mix and b)cement concrete mix:
a)Asphalt paving mix Aggregate material 0 - 16 mm. 4 ton mixer.

Coarse fraction	2407 kg	=908 lit.
Fine fraction	1052"	=397 "	(Density of aggregate 2.65gr/cm3)
filler (Dust particles)	301 "	= 114 "
bituminous liquid	240"	= 240 "

b)Cement concrete mix Aggergate material 0 - 16 mm 4 ton mixer

Coarse fraction	2407 kg	= 908 lit.	(Density of aggregate 2.65gr/cm3)
Fine fraction	1052 "	= 397 "
Cement (Dust particles)	392 "	= 126 "	(Density of cement 3.1 gr/cm3)
Water	264 "	= 264 "
Plasticizers	2 "

When the dust material is dispersed in the gluephase of the products the rheology, i.e. the flow of the mix and product is relative to the proportion of the fine fractions 0 -2 mm material to liquid content of mix. This means that the amount of the fraction in mix is to be reduced when the liquid volume in mix is reduced.

Dispersion of dust particles in production of cement concrete in the "Free Falls" mixer (Figure 2 refers)

[0016] The coarse fraction particles are first mixed with the liquids for example 20 sec. This to develop the surface area of liquid equal to the surface area of all coarse fraction aggregate particles of the mix, the surface area exposed by the rotaion of the cylindrical drum of the Free Falls mixer. Secondly the dust material is discharged in to the mixer over time period of, as an example, 25sec. The dust material is first lifted up by shelfs or a screw the blades of the screw fitted to the internal circulair wall of the drum. This makes free dust material fall down over the endless upward flow of the watered coarse fraction and the area in the mixer open to recieve dispersed dust particles for interaction with the liquid is a) provided by the rotation of the drum and b) the length of time of discharge of the dust material to the mixer. Last the fine fraction material is discharged as a mass to the mixer and dispered by a continuous free fall in the mixer during the mixing time of, for example, 30sec. Then mix is discharged from the mixer.

Dispersion of dust particles in production of cement concrete in the pan mixer (figure 3)

[0017] The function of the paddle system of the pan mixer breaks the flow of the course fraction when mixed with the liquid i.e there is no continuous flow of the course fraction in the mixer. In order to reduce the force mixing of the dust material, (The cement) is dispersed before interacting with the liquid by a slow rate of discharge to the mixer over the time of example 30s and then mixing for 20s before the fine fraction is added and mixed 1 5 sec before mix is discharged from the mixer.

The application of the invention

[0018] The known design of plants for production of asphalt- and cement concrete are not easily adaptable to the invention of dispersion of the dust material before the material is interacting with the liquid in the mixer. The knowledge in particles technology, rheology, interaction, mixing and the example of device for dispersion given will teach the owner of the respective plant how and when the invention of acceptable dispersion is obtained. The meaning of the invention is teached by the example of possision of the divice shown by figure 1.
Production plants, asphalt or cement concrete can be equipped with two weight hoppers, one for weighing the coarse fraction of the invention and one for weighing the fine fraction of the invention, this in order to operate the supply of the two fractions to the mixer independently.

Claims

1. Method to be used when producing asphalt and cement concrete mixes for reduction or eliminating of force mixing characterized by that the dustmaterial of the mix, in asphalt mixes consisting of particles of filler and in cement concrete of particles of cement and occasionally filler, is spread in the mix of the liquid and the coarse fraction where the particles through interaction between the surface of particles and the liquid develop a volume of rheologic binder phase that is viscous, ductile and cohesive, this state of mix obtained through first mixing the liquid with the particles of the coarse fraction in a mixer whereafter the dust particles are dispersed before being mixed with the liquid and coarse fraction, this by letting the flow of the mix in the mixer, pass under the inflow of the dust fraction material to the mixer whereby, the size of the by dust particles covered surface area in the mix of liquid and coarse fraction is controlled by the time period of discharge of the dust particles and the breadth of the flow of the same particles in to the mixer, whereafter the fine fraction of the mix is discharge and the particles dispersed in the by the dust particles and liquid developed suspension.

2. Method in accordance to claim 1 Characterized by that the force mixing of dust material, filler or cement, in production of asphalt respectively cement concrete mix by the mixing paddles of the twin-shaft through mixer, is reduced or eliminated by that the dustmaterial of the mix, in asphalt mixes consisting of particles of filler and in cement concrete of particles of cement and occasionally filler, is spread in the mix of the liquid and coarse fraction where the particles through interaction between the surface of particles and the liquid develop a volume of rheologic binder phase that is viscous, ductile and cohesive, this obtained through first mixing the liquid with the particles of the coarse fraction in the mixer whereafter the dust material is dispersed before being mixed with the liquid and coarse fraction, this by letting the flow of the mix in the mixer pass by under the inflow of the dust fraction material to the mixer, whereby the size of the by dust particles covered surface area in the mix of liquid and coarse fraction is controlled by the time period of discharge of the dust particles and the breadth of the flow of the same particles in to the mixer, whereafter the fine fraction of the mix is discharge and the particles dispersed in the by the dust particles and liquid developed suspension.

3. Method in accordance to claim 1 Characterized by that the force mixing of dust material, cement and ocasionally filler, in production of cement concrete by the shelfs in a "Free fall concrete mixer" is reduced or eliminated by that the dustmaterial of the mix is spread in the mix of the liquid and the coarse fraction where the particles through interaction between the surface of particles and the liquid develop a volume of rheologic binder phase that is viscous, ductile and cohesive, this state of mix is obtained through first mixing the liquid with the particles of the coarse fraction in the mixer whereopon the dust material is dispersed before being mixed with the liquid and coarse fraction this by letting the flow of the mix in the mixer pass under the inflow of the dust fraction material to the mixer whereby the size of the by dust particles covered surface area in the mix of liquid and coarse fraction is depending on the length of the time period of discharge of the dust particles and the surface area exposed to the dust particles by the rotation of the vatered coarse fraction in the mixer, whereafter the fine fraction of the mix is discharged and the particles dispersed in the by the dust particles and liquid developed suspension.

4. Method in accordance to claim 1 Characterized by that the force mixing of dust material, cement and ocasionally filler in production of cement concrete mix by the mixing paddles of the "pan-mixer", is reduced or eliminated by that the dustmaterial of the mix, is spread in the mix of the liquid and the coarse fraction where the particles through interaction between the surface of particles and the liquid develop a volume of rheologic binder phase that is viscous, ductile and cohesive, this state of mix obtained through first mixing the liquid with the particles of the coarse fraction in the mixer whereafter the dust material is dispersed before being mixed with the liquid and coarse fraction this, by dispersing the dust material over a time period on the top of the by high intensiyty broken and renuwed surface of liquid and coarse fraction in the mixer whereafter the fine fraction of the mix is discharge and the particles dispersed in the by the dust particles and liquid developed suspension.

5. Method in accordance to claim 1 Characterised by that in order to maintain the level of the properties of the rheologic binder volumen, viscous, ductile and cohesive, the weight of 0-2 mm fraction inclusive dust material to be reduced at reduction in the liquid content of the mix.

6. . Method in accordance with Claim 1 Characteristic by that att production of asphalt mixes in accordance with Claim 1 the production can be made at 125°-140°C mixing temperature.

7. Method in accordance with claim 1 Characrerized by that when the discharge of the fine fraction is made where the flow of the material in the mixer is directed downvards the forse mixing is reduced by the force of gravitation and the pressure equalizing in the material in the mixer.

8. Method in accordance with claim 1 Characrerized by that when the discharge of the fine fraction is made outside the area of down flow in the mixer the particles are to be dispersed before in contact with the flow of the suspension in the mixer.

9. Deivice for dispersion of dust material Divice for dispersion of dust materials in the production of asphalt and cement concrete characterized by a tube, in the one end open to recive the dust material from a weigh hopper, the discharge part of the tube positioned over the mixer, the material feeded through the tube by a screw, over the mixer the tube have a slott along its bottom, the opening of the sloth is adjustable to different rate of dispersion of the dust material before this interct with the material flowing in the mixer.

10. Device to be fitted on the inside of the "Free fall" mixer Charactericed by that the shelfs inside the drum for mixing the material the blades of the shelfs has a srewed form in order to make the material in mixing to flow att a continuous rate for developing and maintaning the material in a continuous flow in the mixer.

Drawing