A METHOD AND APPARATUS FOR IMPROVING A BASE LAYER FOR ROAD COVERING

Abstract: For improving existing support layers in road systems the road covering (5) and at least a part of the support layer (6) is excavated by means of a cutter drum (4), and a binding medium (9) is added to the excavated mass (M) and the latter laid down into the excavation (8) in the road. A mixing drum (11) following the cutter drum lifts the mass up from the excavation and further mixes it before the mass is again laid back in the excavation and rolled in convential manner. The cutter drum (4) and mixing drum (11) is supported in a self driven-road machine (1), preferably of the scraper type.

Description: A METHOD ANDAPPARATUS FOR IMPROVING A BASE LAYER FOR ROAD COVERING Many roadways have simple coverings or surfacings such as oil gravel and the like, frequently situated on a weak gravel support or base layer subject to frost heave. Also roads with a usual asphalt surface may have an unsatisfac¬ tory support layer. In the spring breakup period such sup¬ port layers will be badly soaked resulting in serious damage of the coating. Maintainence of such roads may be very expensive when using traditional methods such as replacing or building up of material masses, requiring road broadening and thus ground acquirement. In an attempt to provide a simpler and cheaper method of enhancing weak support layers it has been proposed to re¬ move the road covering and underlying gravel layer by means of a rotary cutter to a depth of 10 to 20 cm (depending on the thickness of the base layer) while adding to the mass removed a bonding agent in the form of an emulsion, based on bitumene, and relaying the mass into the recess cut in the road. The cutting may be performed for example in sub¬ stantially the same manner as that used when cutting an as¬ phalt covering, while using a modified rotary cutter allowing a larger cutting depth. Practice has shown, however, that the proposed method does not provide a high-grade result owing to the impossi¬ bility of obtaining a satisfactory intermixing of the cut materials in the relaid mass, with the result that the sup¬ porting capability of the _new supporting layer still being inferior. According to the present invention this problem is now solved by disposing, rearwardly of the rotary cutter, a rotary mixer acting to lift the mass replaced in the recess and further mixing the components thereof before the mass is again deposited in the recess cut in the roadway and rolled in the manner usual when laying a road covering. The previously suggested method will then be practically feasible since a very good mixing is obtained of the compo¬ nents of the imrpovement mass, and consequently a supporting capability of the resulting supporting layer at least corresponding to that obtained by conventional improving of the old supporting layer. The method involves several advantages. Materials already present in the road are utilized and these materials are upgraded into high quality masses which no longer may cause frost heave and providing a far better support. Road expansion and new materials are not required, with other words a method very amiable to the environments. The invention will be explained in further detail with reference to the drawing in which figures 1 and 2 are partly sectional elevational andplanviews respectively with some parts removed, illustrating an apparatus for carrying out the method according to the invention, figures 3 and 4 are elevational and plan views to a larger scale, illustrating a preferred embodiment of a mixing element, and fig. 5 is a diagrammatic view of a preferred arrangement of the mixing elements. The apparatus can be incorporated in a preferably self- driven road machine of any convenient type suitable foruse in connection with the present invention, such as a scraper, e.g. of the type Caterpillar 613 Scraper, which has been found particularly useful. Thus, the machine per se is no part of the invention, and in the drawing it is merely indi¬ cated as a body or frame structure 1 (indicated with point- dash lines in the plan view of fig. 2 to more clearly illu¬ strate the underlying parts) carried by * front and rear pair of wheels 2 and 2* respectively, as seen in the direction of motion of the machine 1 as indicated with an arrow. In a per se known manner, on the underside of the machine body 1, between the front and rear wheel pairs 2, 2' there is mounted a rotary cutter 4 which can be lifted and lowered by a power cylinder 3 and adapted to be pressed down against the existing road paving 5, such as asfalt, for cutting the latter and at least an upper portion, for example to a depth of 15 cm, of the underlying support layer 6 which is to be improved, and which normally will consist of gravel. Spaced above the rotary cutter 4 is a semicircular back-up plate 7 against which the mass M cut by the rotary cutter 4 is hurled and guided around until it falls down on the opposite side of the cutter 4 into the excavation 8 in the road made by the rotary cutter, the cutter 4 rotating in the direction as indicated with arrow. Before the mass drops down into the excavation 8 an adhesive, preferably a bitumenous emulsion, is added which, also in a per se known manner, is sprayedradially inwardly toward the cutter 4, for example by means of a number of conveniently spaced nozzles as indicated with the arrow 9 in fig. 2. The rotary cutter 4 has inclined cutting teeth 10 which, in a per se known manner, are disposed on either side of a lateral plane through the center of the cutter cylinder in a pattern of oppositely directed helical lines acting during the cutting operation to press the cut mass M inwardly to¬ ward the center of the cylinder, involving a certain mixing effect between the fragments of the cut mass in addition to the mixing effect when the mass M is hurled against and guided around the back-up plate 7. Owing to this compres¬ sion caused by the helical pattern of the cutting teeth converging toward the center of the cutter the mass M will leave the cutter cylinder 4 at a width b, substantially narrower than the length of the cylinder 4, as indicated in fig. 2. The cutting elements 10 may have a configuration sub¬ stantially similar to those used on prior rotary cutter cylinders for cutting asphalt pavements, although they should be larger and heavier to cope with a cutting depth of 10 - 20 cm. Between the rear pair of wheels 2* and the cutter cylinder 4, according to the invention there is mounted a second liftable and lowerable cylinder or drum, namely a mixing drum 11 which is adapted to be lowered into the excavation 8 behind the cutter cylinder 4. Preferably the diameter and length of the mixing drum 11 are less than those of the cutter cylinder 4, the length however, being somewhat longer than " the width b, of the mass M in the excavation behind the cutter cylinder. Secured to the peripheral surfaceof the mixing drum 11 are a plurality of mixing elements 12 generally arranged, in a manner similar to that of the teeth 10 of the cutter 4, in a helical pattern converging toward the center of the drum. The rotary mixing drum 11 rotates in the same direc¬ tion as the cutter cylinder 4 as indicated with an arrow, and its mixing elements 12 will then relift the mass M from excavation 8 causing a further intermixing of mass particles and binding medium while the mass, owing to the coverging helical pattern of the mixing elements, is compressed into a narrower width b_ upon leaving the mixing drum. Similar to the back-up plate 7 of the cutter a back-up plate 13 placed above the mixing drum 11 assists in guiding the up- hurled mass further along the circumference of the drum. The back-up plate 13 may be semicircular like the cutter back-up plate 7 to guide the thus further mixed mass down into the open excavation 8 behind the mixing drum. However, in a perferred embodiment, the exit portion of the mixing drum back-up plate is substantially horizontally rectilinear or straight, an upwardly inclined belt conveyor 14 being disposed in a per se known manner immediately behind the mixing drum 11, receiving the mass from the mixing drum 11 and carrying the well mixed mass further onto a conventional asphalting machine as indicated at 15. From the asphalting machine 15 the well mixed mass M' is laid into the excava¬ tion 8 and treated in a conventional manner. Conveniently the drum 11 could be supported in a cradle 17 vertically movable in guides 16 to allow height adjustments thereof, the cradle on either side being provided with a runner or ski 18 resting at the bottom of the exca¬ vation 8 in the lowered or working position of the mixing drum. By this means the mixing drum is kept with the mixing elements thereof at a constant predetermined clearing above the bottom of the excavation. Thus, the cradle 17 with the mixing drum 11 is liftably and lowerably suspended in the machine frame 2, for example via a power cylinder 24, and the lower end of the conveyor 14 is hinged to the cradle and follows the movements of the latter, the conveyor being longitudinally displacable in a conventional manner by means of a pivotable slide means (not shown) . Fig. 3 and 4 show a convenient embodiment of the mixing elements 12. Here the mixing elements 12 have the form of "segments" each consisting of a rectangular, longitudinally curved base plate 19 to be secured to the preripheral sur¬ face of the mixing drum 11 through bolt holes 20. Welded edgewise along their longer dimension to the outside of base plate 19, i.e. the convex side thereof and substantially parallel to the longitudinal edges thereof are three substan¬ tially rectangular support plates 21. The support plates 21 are arranged end to end on the base plate 19, but lateral¬ ly offset to contact each other substantially at their cor¬ ners as best shown in fig. 4. Each of the support plates 21 carries a "mixing lug" 22 in the form of a rectangular plate or flat iron element welded in a spaced relationship edgewise along one shorter dimension on top of its support plate 21 obliquely in the diagonal direction through co- insiding corners of the support plates. Each mixing lug 22 may be provided with bolt holes 23 for possible securing thereto of a protective plate of a wear resistant material (not shown) . Fig. 5 diagramatically illustrates the location of the mixing elements or segments 12 on the circumference of the mixing drum 11, the latter depicted as unfolded in the plane of the drawing. As appearing from the figure the segments 12 are mounted with their longitudinal axis generally normal to the longitudinal direction of the mixing drum, and rela¬ tively offset in the drum longitudinal direction in a manner such that the support plates 21 with mixing lugs 22 form a converging helical pattern toward the center of the drum. With such arrangement of the mixing segments 12 the excavated mass in the excavation 8 will screw inwardly toward the drum center while mixing taking place as previ¬ ously explained. However, according to a preferred embodiment of the invention every other mixing lug, at least at a center portion of the mixing drum, can be disposed obliquely in the opposite diagonal direction as indicated by dash-point line 12' in figs. 4 and 5. This results in an enhanced mixing effect by the mass being pushed to and fro between the mixing lugs12, 12' during its motion along the mixing web circumference. The rotation of the mixing drum and cutter drum may be realized in any convenient conventional manner, e.g. by transmission from the drive machinery of the machine 1, possibly through a reduction gear, or by a separate internal combustion engin, hydraulic motor or other motor. Any detailed explanation of the mounting of the drums 4 and 11 in the road machine 1 is not considered necessary since this is assumed to belong to the routine of skill of an ordinary machine designer. Adequate rotational speed of the cutter 4 and mixing drum 11 will i.a. depend on the nature of the road pavement, however, as a mean value a rotational speed of 70 revs/min. and 140 revs/min. for the cutter drum and mixing drum res¬ pectively will generally give the best result. A container (not shown) for binding medium to be added to the mass at 9 may conveniently be disposed on the machine 1 together with a separate binding medium pump and counter. In addition the cutter 4 may have a speedometer associated therewith to permit control of added quantity of emulsion (quantity related to depth and advance) .

Claims: PATENT CLAIMS: 1. A method for improving support layers for road coverings by which a rotary cutter drum (4) during advancing along the road penetrates into the road covering (5) and at least part¬ ly into the underlying support layer (6) whereby the thus excavated mass (M) is mixed and a binding medium added there¬ to whereupon it is replaced in the excavation (8) in the road behind the cutter, c h a r a c t e r i z e d by the re¬ placed mass (M) in the excavation (8) being further mixed by means of a mixing drum (11) following the cutter drum (4) . 2. Apparatus for improving support layers for road cover¬ ings, comprising a rotatary cutter drum (4) adapted to pene¬ trate into the road while advancing along the latter, through the existing road covering (5) and at least partly into the support layer (6) , means (9) for spraying a binding medium into the excavated mass (M) , and a back-up plate means (7) above the cutter drum (4) acting to guide the excavated mass mixed with binding medium back into the excavation (8) in the road, c h a r a c t e r i z e d by including a mixing drum (11) behind the cutter drum (4) adapted to take up the replaced mass in the excavation (8) and to' further intermix the components thereof before the mass is again replaced in the excavation in the road. 3. Apparatus according to claim 2, c h a r a c t e r i z e d by said mixing drum (11) being height-adjustably supported in a cradle (17) provided with skis (18) adapted to slide against the bottom of the exca¬ vation (8) . 4. Apparatus according to one of the preceding claims, c h a r a c t e r i z e d by said mixing drum (11) carrying a plurality of mixing segments (12J on its circuference, said mixing segments (12) comprising substantially rectangu¬ lar plate elements (22) which are generally oriented in a helical pattern converging toward the drum center in the • direction of rotation of the drum. 5. Apparatus according to claim 4, c h a r a c t e r i z e d by every other plate element (22) being inclined in a diverging direction relative to the adjacent plate elements (22) .

Inventors: WENTZEL JARLE, WENTZEL, JARLE
Applicants: NODEST VEI AS, NODEST VEI A/S
Application year: 1985
Main classification: E01C23
IPC codes: E01C23