US2174264A - Road covering - Google Patents

Description

Sept. 26, 1939. K. HALBACH 2,174,264

ROAD COVERING Filed July 24, 1935 Inventor: lfar/ //a [back '3 WZFZTM After may.

Patented Sept. 2 6, 1939 UNITED STATES ROAD COVERING Karl Halbach, Dusseldorf, Germany Application July 24, 1935, Serial No. 32,927 In Germany July 24,1934

3 Claims.

This invention relates to improvements in road-construction and to the making of roads, especially of macadamised roads.

In roads having a solid and rigid ground- 5 work or foundation covered by a mortar-bound macadamised layer, the latter is known to have a tendency to crack and fissure. In order to avoid or to diminish this disadvantage, joints or rabbets are provided at suitable intervals. Therefore, the use of slowesetting mortars, such as tress-lime mortar, trass-lime-cement mortar and the like has been favoured with a view of overcoming the difficulties. However, these slowsetting mortars are inferior to good Portlandcement mortars as regards their mechanical strength and they do not allow of obtaining dustfree, very hard, strong and resistant road coverings.

It is considered to be desirable in the art of road-construction to use the known cements or other hydraulic binders with similar quick-setting properties capable of giving quickly a high hardness and mechanical strength, instead of the slow setting and hardening mortars. However, if such mortars are used in the making of macadam-road coverings the rolling invariably causes the pebbles or broken stones to move to a certain extent during the setting of the cemerit-mortar which therefore does not adhere firmly to and does not combine intimately with all parts of the surfaces of the stones.

It is one of the objects of this invention to avoid these draw-backs and to allow of the construction of macadamised roads with the use of quick-setting cements or mortars.

According to this invention, a layer forming an elastic cushion is provided preferably temporarily during the making of the road, upon the macadam-layer.

This resilient layer is prepared from a water absorbing material substantially impervious to fresh mortar even under pressure, for the purpose set forth as the specification proceeds, and which I shall be referred to in this specification and in the claims as slag or comminuted slag for the reason that natural and artificial comminuted slags such as triturated artificial slag and natural lava slags (foam lava) show the properties set so forth and are well suited. A natural lava slag is the material known in Germany as lava sand or Lavakrotzensand. The slag is used in coarsely triturated form, the grains having a size up to 6 mm., preferably between 0.5 and 4 mm.

The macadam-layer is bound partially or wholly by mortar, preferably by a quick-setting mor tar of high hardness and mechanical strength.

The function of this layer is to prevent the pressure of the roller during the rolling being taken up only or mainly by the heads of the 6 pebbles or broken stones and to distribute pressure equally and also to the surface of the mortar or material between the individual stones.

If the mortar for the macadam-layer is prepared with, a relatively high amount of water, the ex- 10* cess of the water not consumed for the setting of the mortar is absorbed by this upper layer. The constituents of this layer should not penetrate into or mix with the mortar situated below, as otherwise the mortar would become meaequally distributing the pressure to the mortar between the stones and of taking up the excess of the mortar-water, is not performed by ordinary sand or gravel which, contrary to slag having the above mentioned properties, will be pressed into the mortar-layer thus meagering the mortar and diminishing the plasticity and strength of the surface mortar-layer the strength of which should be as high as possible,

- This upper layer which does not combine in any way with the surface mortar-layer may be 80 removed as soon as the mortar has hardened;

if not removed, for instance by a suitable brush, for re-use, this loose layer will be removed automatically by the trafiic.

It is advisable in connection with this invention to provide an elastic cushion-layer between the solid and rigid foundation and the macadam layer in known manner, for avoiding scattering of the stones, absorbing excess mortar-water, anchoring the stones and protecting a concrete 4o layer, often used as road foundation, against premature drying. In view of theabove mentioned properties of slag, this material is especially well suited also for this lower foundation layer and far superior to the usual sand or gravel, having a better water absorbing property and its particles having less tendency to rise into the upper mortar-layer during rolling.

The combined use of both layers simultaneously in making a macadamised road offers the further advantage that during the rolling and/or during the stresses in use, the pebbles or broken stones are protected against tottering or temporary displacement before the complete setting of the mortar or the like. The mortar cannot 5p give way or escape in any direction and is pressed by the two pressure-distributing elastic cushionlayers, situated below and above, firmly against the pebbles or broken stones thus causing an extraordinarily good connection and joining.

The invention permits the employment of the usual quick-setting cements in making mortar for the macadam-layer; for the reasons given above, the mortar can be made up with a relatively high and excessive amount of water in order to delay and prolong the setting.

The invention is illustrated by way of example in the accompanying drawing in which:

Figure 1 is a sectional view of a road covering according to the invention, and

Figure 2 is an enlarged sectional view of the surface-layers of a road covering according to the invention.

In Figure l, the solid and rigid foundation l which may consist, for instance, of concrete, is shown covered by a cushion-layer 2 which may consist, for example, of the aforesaid Lavakrotzensand. Above this cushion-layer 2 is situated the macadam-layer 3, the spaces or interstices between the pebbles or broken stones being filled out by mortar 4. This macadam-layer 3 is covered by an upper cushion-layer 5 which may consist of the same material as the lower cushion-layer 2.

The making of the road is carried out by first applying the cushion-layer 2 to the rigid foundation l. The layer 2 may have a depth of 1-2 cm. or more and may be rolled before further proceeding with the work, especially if this layer is made by using dry mortar. Then mortar is applied on the layer 2 and, contrary to the layer below, is not compressed but loose. If now pebbles or broken stones are spread over the mortar and rolling is effected, preferably with application of water, the loose mortar will rise between the stones into the spaces or interstices between them. The thickness of the layer of loose mortar predetermines the height to which the mortar will rise under the pressure of the roller and to which the gaps between the stones will be filled out.

On this compressed layer a further quantity of mortar is nowspread and worked in for closing the upper gaps and interstices by elutriating, which process may be assisted in known manner by simultaneous rolling.

After Well finishing this layer by elutriating, the upper cushion-layer 5 may be applied by sanding, preferably with lava-sand. The whole may be rolled again without danger of the lavasand being pressed into the mortar 4 of layer 3, preferably if this sand is of sufficient fineness and free of coarser particles which might cause too high a pressure on the mortar-plugs situated below; good results will be obtained by using a sand having a fineness up to 3 mm. in diameter.

Figure 2 illustrates more clearly this last rolling process. Between the heads such as 6 and 'l, of the pebbles or broken stones are the mortarplugs such as 8, 9, and ID. The arrow ll. indicates the outer diameter of the roller. It is evident that the cushion-layer 5 acts in such a way as to distribute the pressure of the roll equally, a relatively high pressure being applied also to the mortar- plugs 8, 9, and I0. Without this layer 5 the pressure would be taken up totally or mainly by the heads 6, 'l of the stones.

After the last rolling process is finished, the upper cushion-layer 5 may be removed. The uppermost edges of the stones may project a little out of the surface favouring the roughness of the surface of the finished road.

I claim:

1. A method of making a road pavement comprising the steps of preparing a mortar-bound layer, placing a temporary layer of granular particles consisting of a material selected from the group consisting of natural and artificial slags, upon said mortar-bound layer, and compressing said mortar-bound layer by transmitting pressure through the medium of said temporary layer to said mortar-bound layer, and then removing said intermediate layer.

2. A method of making a road pavement comprising the steps of preparing a macadam layer of broken stones and mortar, placing a temporary layer of granular particles consisting of a material selectedfrom the group consisting of natural and artificial slags, upon said macadam layer, and compressing said macadam layer by transmitting pressure through the medium of said temporary layer to said macadam layer.

3. A method as claimed in claim 1, in which comminuted foam-lava is used as temporary layer.

KARL HALBACH.

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