IE49695B1 - Construction materials,process for their manufacture and their application to road pavings - Google Patents

Abstract

1. Construction materials comprising from 94 to 97 % by weight of mineral aggregats and from 3 to 6 % by weight of polymer, characterized in that said polymer comprises at least 50 % by weight of an ethylene polymer having a molecular weight between 12,000 and 50,000, a density between 0.90 and 0.93 g/cm**3 and a viscosity in the molten state greater than or equal to 34 Pa.s, in admixture with another thermoplastic polymer when said ethylene polymer ist not used alone.

Description

The present invention relates to materials for use in construction and road pavings, to a process for making them and to their application to the manufacture of a road p.aving 'having improved mechanical properties.

Materials based on bitumen are well known and have long been used for the paving of roads, airport runways, ete.

These materials have been very successful commercially since they have mechanical strength and cracking resistance properties which are quite adequate for the majority of conditions under which they are used. However, certain sections of road are subject to particularly severe conditions Of use, and under such conditions the strength and resistance properties of materials based on bitumen are inadequate.

Additionally, storage and handling of bitumen materials are somewhat difficult under the climatic conditions prevailing in hot countries, and in such countries their use for road surfacing is somewhat difficult.

It has been proposed, for the above-mentioned reasons, to substitute bitumens by polymer-bonded aggregate-compositions. 49685 Thus U.S. Patent 3,112,681 describes paving compositions, manufactured by the hot plastic mixing technique, comprising to 99 wt. percent of aggregate bonded with 1 to 10 wt. percent of a linear polyethylene having a high, medium or low molecular weight and a melting point of between 43 and 135°C . British Patent 941,070 describes a composition of aggregates bonded with 1 to 10 wt percent of a low density polyethylene having a melt viscosity of between 0.1 and Pa.s; said polyethylene is used alone if its molecular weight is lower than 10,000 but should be mixed with a cracked petroleum resin if its molecular weight is higher than 10,000. Examples 1 to 3 of said patent teach that the mixing temperature of aggregates and polymer is higher as the molecular weight of said polymer is higher, and exceeds 204°C for a polyethylene having a molecular weight of ,000.

The compositions described by U.S. Patent 3,112,681 and British Patent 941,070 do suffer from various disadvantages.

Their properties are adequate when polyethylene is not used as a mixture with a further polymer component such as polyisobutylene or a cracked petroleum resin, which increases their cost price in an objectionable manner.

Moreover, the extremely high mixing temperature results in prohibitive energy costs for covering materials obtained in this way.

Various authors have recently thought it possible to overcome the disadvantages discussed above either by increasing the polymer content in the covering composition (see French Patent 2,158,254) or by adding a third mineral component to the composition which is capable of catalysing the oxidation of the polymer (see French Patents 2,306,953 and 2,338,306). These authors have however not contributed to solving the problem of Improving the resistance to fissuring of the compositions of aggregates which are bonded by the polymers.

The aim of the present invention is to put forward materials for construction and road covering which have improved properties, and can be manufactured at reduced energy cost.

The present invention is based on the idea that, contrary to the teachings of the prior art, said improvement should not be sought by varying the amount of polymer in the composition nor by adding a third mineral component to the composition, but rather by carefully selecting the polymer to be used in such a composition. The research on which the present invention is based caused us to deliberately depart from the teachings of the prior art and to propose the use of a polymer comprising at least 50% by weight of an ethylene polymer having a molecular weight 3 between 12,000 and 50,000, a density between 0.90 and 0.93 g/cm and a viscosity in the molten state greater than or equal to 34 Pa.s, in admixture with another thermoplastic polymer when said ethylene polymer is not used alone.

The materials for construction and road covering according to the invention comprise from 94 to 97% by weight of mineral aggregates and from 3 to 6% by weight of polymer. The term molecular weight is here taken to mean the average number molecular weight. The term viscosity in the molten state means the viscosity at 19O°C and at low shear (10 2S S measured, for example, using a rheometric balance of the KEPES type.

Said viscosity may reach, for a polymer according to the invention, up to about 200 Pa.s.

The ethylene polymers used according to the invention are either homopolymers obtained by polymerizing ethylene by means of a free-radical initiator - such as oxygen, peroxides or peresters - or copolymers of ethylene with at least one polar comonomer also obtained in the presence of a free-radical initiator, the polar comonomer being generally selected from the range comprising carbon monoxide, dicarboxylic acid anhydrides, carboxylic acid vinyl esters, acrylic acid esters, etc.

The polymer used in the composition of materials according to the invention is either an ethylene polymer or a mixture of several ethylene polymers selected as discussed above, or a mixture of an ethylene polymer, as discussed above, and a further thermoplastic polymer. Mineral aggregates used in the composition of materials according to the invention may be selected from a very wide range: basalts, limestone materials, silico-calcareous materials, sands, etc.

The ethylene polymer according to the invention differs from of U.S. Patent 3,112,681 by its density and from that of British Patent 941,070 by its viscosity, which explains the improved behaviour (particularly the resistance to fissuring) of the materials according to the invention when compared with materials employed in the prior art. On the other hand, however, the present invention does not substantially differ from the teachings of the prior art as far as the content of polymer in the material is concerned: it has only been possible to indicate that a content less that 3% by weight does not provide the materials with sufficiently high properties whilst a content greater than 6% by weight does not substantially improve the cracking resistance of the material and has an unfavourable influence on its cost price.

The process for manufacturing the materials according to the invention consists of mixing the mineral aggregates and the polymer at a temperature lying in the range of from 160 to 190°C. The mixing should be performed under efficient conditions and should be carried on for a sufficient period of time to provide a material which has a completely homogeneous constitution. Temperature regulation during the mixing operation is of particular importance because an uncontrolled elevation of the temperature always leads to the formation of regions of heterogeneity to the material, and the presence of these regions is responsible for a drop off in the properties of the material. It is usually perferable for the mixing temperature to be selected so as to lie in the range of 170° to 185°C. The manufacturing operation for producing materials according to the invention can be carried out in conventional mixing machinery.

Uses to which the materials according to the invention can be put vary over a wide field in the building industry and in public works. A first use consists in the production of pavings for highways, in particular certain portions of roads, airport runways, etc. which are subjected to particularly severe conditions of use. A further example of their use is for the manufacture of construction materials for tiled floors and prefabricated components; and when manufacturing the latter, the plant comprises a drying oven for the mineral aggregates, a mixer in which the mixture of dried mineral aggregates and polymer are homogenized, a transfer line on which the material according to the invention is compressed and cooled, followed by a device for cutting the cooled material to the desired 1q dimensions.

Concerning the first use referred to above, the invention also relates to an application of these materials to the manufacture of road paving having improved mechanical properties, wherein the said materials are spread out onto the surface to be paved, the length of time elapsing between manufacture of the material and the spreading out operation lying within the range of from 15 to 150 minutes. This characteristic of the process is necessary as a result of the fact that, in this application to highways, the materials 2o manufactured by mixing under the effect of heat are loaded in this state onto a lorry, the lorry is driven onto the site and its contents are then spread over the surface. However, during loading and transport, two factors are at play, one being that the temperature of the materials starts to drop and the other being that the materials are in contact with the surrounding air. It has been observed that, taking these two phenomena into account, the length of time elapsing between manufacture of the material and its spreading has a considerable effect on the quality of the mechanical properties of the road covering obtained. More precisely, these properties do start to worsen when this length of time exceeds 150 minutes, leaving the way open for the appearance of fissures.

At the other end of the scale, the properties of the covering have not reached their optimum value when this period of time is less than 15 minutes. Roads bearing a covering obtained by the process according to the invention possess, at ordinary temperatures, remarkable characteristics of resistance to 2 o compression, and values of the order of lOOkgf/cra at 20 C may be obtained without difficulty? this compression resistance is still at a high level at 60°C, so that it can be satisfactorily employed in hot countries. The mean granulometry of the mineral aggregates used in the paving composition will, as is usual, be comprised within the range of about 0.5 to 5mm and should be selected as function of what is available at quarries located close to the place of manufacture.

The following examples have been selected to illustrate the invention without in any way claiming to limit its scope. In particular, it should be understood that the polymer used in the composition of materials according to the invention may include negligible amounts of known anti-oxidants, particularly for slowing down alteration of the hot road surfacing material as a result of contact with air when the length of time during transport before it is spread is significant. It should also be borne in mind that the polymer used in the composition of materials according to the invention may be a mixture of a polymer of ethylene and another thermoplastic polymer such as polybutene-1, atactic polypropylene, rubber, an elastomer of the ethylene-propylenediene type, an ionomer, etc.

EXAMPLE 1 At a temperature of 170°C, a mixture of 97% of silicocalcareous aggregates (mean granulometry: 3mm) and 3% of 3 polyethylene A (density: O.918g/cm : average number molecular weight 12,000: viscosity in the molten state 175 Pa.s) were mixed together.

The contact time under heat conditions during this mixing operation was 7 minutes and made it possible to obtain complete homogeneity of the mixture. The homogenized mixture was then transported to a road construction site and spreading of it started 15 minutes after completion of mixing. Measurements of the resistance to compression of the paving obtained were . 49695 carried out, the outside temperature being 20 C: the yalue 2 was 100 kgf/cm . The appearance of the paving was then studied, and it showed no sign of fissuring.

EXAMPLE 2 At a temperature of 180°C, a mixture of 94 parts by weight of sand and 6 parts of weight of a polyethylene B (density 0.914 g/cm3, average number molecular weight 12,000, viscosity in the molten state 34 Pa.s) were mixed together. A contact time of 1 minute under heated conditions was sufficient in order to obtain complete homogeneity of the mixture. The homogenized mixture was then transported to a road construction site and spreading of it started 180 minutes after completion of mixing. The resistance to compression of the paving obtained was measured, the outside temperature being 20°C: a value of 105 kgf/cm2 was obtained. Over a period of several months, during which the covering was subjected to fairly high volume of traffic, there was no sign of fissuring.

EXAMPLES 3 to 8 The mechanical performance of materials obtained by mixing 96.5 parts by weight of basalts and 3.5 parts by weight of different polymers according to the invention was measured.

The mechanical performance was assessed by measuring the resistance to compression at 20°C and at 60°C, expressed in kgf/cm . The polymer used in Example 3 was the polyethylene A described in Example 1. The polymer used in Example 4 was a mixture of equal parts by weight of polyethylene A and an ethylene-vinyl acetate copolymer sold under reference number UE 633 by the National Distillers Company. The polymer used in Example 5 was a mixture of two parts by weight of polyethylene A to one part of zinc ethylene-anhydride maleic copolymer including 4% of anhydride units in the macromolecule. The polymer used in Example 6 was a mixture of three parts of polyethylene A to one part of zinc ionomer sold under the Trademark Surlyn by Du Pont de Nemours. The polymer used in Example 7 was a mixture of four parts of polyethylene A to one part by weight of powdered rubber obtained from recycling of tyres. The polymer used in Example 8 was a mixture of equal parts by weight of polyethylene A and polybutene-1 (density: 0.918 g/cm , melt index 0.5 dg/mn according to ASTM D-1238-73). In all these Examples, the polymer was mixed with the aggregate at a temperature of 190°C for a sufficient period of time to obtain a homogeneous mixture.

The results of the measurements assessed are summarized in the following table.

TABLE EXAMPLE N° RC (120°) RC (60°C) 3 158 71 4 149 67 5 192 116 6 125 48 15 7 140 84 8 171 90

Claims (8)

1. Construction materials comprising from 94 to 97% by weight of mineral aggregates and from 3 to 6 % by weight of polymer, wherein said polymer comprises at least 50% by weight of an ethylene polymer having a molecular weight between 12,000 and 50,000, a density between 0.90 and 0.93 g/cm 2 and a viscosity in the molten state greater than or equal to 34 Pa.s, in admixture with another thermoplastic polymer when said ethylene polymer is not used alone.

2. Construction materials according to claim 1, wherein said thermoplastic polymer is selected from polybutene-1, atactic polypropylene, ionomers and ethylene-propylene-diene elastomers.

3. Construction materials according to any of claims 1 and 2, wherein the ethylene polymer is a homopolymer.

4. Construction materials according to any of claims 1 and 2, wherein the ethylene polymer is a copolymer of ethylene and of a polar comonomer, said comonomer being selected from carbone oxyde, dicarboxylic acid anhydrides, carboxylic acid vinyl esters and acrylic acid esters.

5. A process for manufacturing materials according to any of claims 1 to 4, wherein the mineral aggregates and the polymer are mixed at a temperature between 160° and 190°C for a sufficient period of time to provide a homogeneous mixture.

6. A process according to claim 5, wherein the mixing temperature is between 170° and 185°C.

7. Application of the construction materials according to any of claims 1 to 4 to the manufacture of a road paving having improved mechanical properties by spreading out said materials on the surface to be paved, wherein the length of time elapsing between manufacture of the material and the spreading out operation lies between 15 and 150 minutes.

8. A process for the manufacture of construction materials substantially as described herein with reference to the Examples.