DE1295463B - Bituminous pavement compounds - Google Patents

Description

The invention relates to sulfur-containing, bituminous road paving compounds with improved physical properties.

The use of sulfur in bituminous mixtures has long been used known, although little use is made of it in practice. For example moldable mixtures are described in U.S. Pat. No. 403,548 which have high Contains sulfur concentrations in combination with pitch.

Furthermore, from the USA. Patent 1,063,899 moldings for Buildings or the like made of bitumen, sand or cement and very small amounts of sulfur known.

It is also used as an additive in bituminous mixtures for road pavements Sulfur known from the prior art. For example, in U.S. Patent 2182 837 describes a surface covering for roads, the 79 weight percent mineral aggregate and 21 weight percent of a mixture of elemental sulfur and bitumen in proportion 1: 1, although the sulfur has reacted chemically. For the same A sub-structure for roads is described in the literature, which consists of 90 percent by weight Mineral aggregate and up to 10 percent by weight of a sulfur-bitumen mixture in the The ratio is 1: 1.

According to the patent claims of this USA patent, the top layer consist of a reaction product of bitumen and sulfur. Furthermore, the U.S. Pat. No. 2,340,640, in which the use of small Amounts of sulfur in blown bitumen is recommended to prevent the breakdown of the bitumen to prevent under the influence of air. According to U.S. Patent 2,478,162 can add small amounts of sulfur and an amine to a road bitumen to increase the adhesion to the unit. In British patent specification 610 629 is also the chemical treatment of bitumen with sulfur at increased Temperatures described.

The use of sulfur in bituminous paving compounds was due to chemical changes in bitumen due to a reaction with sulfur or Sulfur compounds limited. Sulfur is also not yet in concentrations over 50 percent by weight, based on the bitumen mixture, in road paving compounds in elemental form has been used in such a way that sulfur does not react chemically with the bitumen, the mechanical strength of the bituminous road paving compounds has been improved.

Compared to the road pavement compounds known from the USA patent specification 2 182 837, in which the elemental sulfur is homogeneous with the bituminous binder Mixture forms, the road paving compounds according to the invention differ in that that the sulfur is present as a discontinuous phase in the binders. Through this there are special advantages with regard to the load-bearing capacity of the lining masses and the increase in Marshall stability, the latter especially when using a weak mineral aggregates. These improvements are made possible by the following in Test results reported to Table I are numerically documented.

It is particularly surprising in view of the state of the art that despite the formation of a separate sulfur phase in disperse form as a result Due to the high sulfur content used, there are no disadvantages when used as a paving compound rather, unexpected improvements result.

Bituminous road surfaces essentially consist of one or two layers of an asphalt bitumen (base and top layer), which on one or several layers of an aggregate (substructure) are applied, although in such Cases where the soil of the subgrade has a corresponding quality, the substructure can also be applied directly to the soil layer without an intermediate layer.

The structure of a particular road surface depends on a number on factors such as the volume and density of traffic to be expected, the load-bearing properties of the soil of the subgrade and the subgrade or Intermediate layer or substructure or top layer of available material as well as the climatic conditions and the influence of all these factors in economic Respect.

Bituminous road surfaces consist of a surface or Top layer of at least 2.5 cm thick and made of a bitumen-coated one and thereby adhering mineral aggregate.

This layer is applied to base layers, for example one bituminous substructure, crushed rock, slag, gravel or an already existing pavement, such as portland cement, concrete, bricks or paving stones. A typical bituminous road surface consists of a surface layer of asphalt bitumen, which is applied to a thicker layer of crushed minerals, both layers resting on an intermediate layer of compacted soil and be supported by it. In any case, the strength and with it the costs stand for the substructure, for a certain intermediate layer, a certain subgrade and a certain type of use directly related to the strength properties.

It has now been found that improved paving compositions therein exist that bitumen, elemental sulfur and mineral additives are present are, the weight ratio of sulfur to bitumen in the masses 1: 1 to 4: 1.

It is of course known that many types of bitumen have considerable Contain proportions of various sulfur compounds. It is also known To chemically implement sulfur with bitumen for a wide variety of purposes, e.g. B. after USA.-Patent 2 182 837. In view of this fact it must be emphasized again be that the lining compounds according to the invention only use elemental sulfur as an additive which did not react with the bitumen part of the masses.

The road paving compounds containing sulfur and bitumen according to Invention are particularly suitable for use in so-called »black road surfaces» too suitable where parts of the granulate thick substructure of the Ordinary road surfaces are replaced by thinner layers of black paving compound be, d. H. through a bitumen-bound substructure.

As a mineral aggregate, within the scope of the invention Pavement compounds can be used as a crushed inorganic material Sand, rock, crushed stone or slag, whereby the material is either acidic, such as granite, or basic, such as limestone.

Generally preferred for road construction and likewise for the bituminous pavement masses according to the invention by pyrogenic Used bitumen obtained from decomposition derived from petroleum residues, for example residual oils, blown petroleum bitumen, soft and hard residual bitumen. However, other pyrogenic residues such as tar or pitch can also be used alone as well as in Can be used in a mixture with each other and in a mixture with other types of bitumen.

Preference is given to bitumen with a penetration (ASTM method D 5) from 40 to 300. In addition, it is preferred that those within the scope of the invention bitumen used has a penetration index in the range from -1.5 to +0.5 and in particular from to 0. The penetration index gives a relationship between the penetration and the softening point according to the ring and ball method and is determined by the the following equation is defined: 800 20 - P.I.

50 log = () (S - 25), P 10 + P.I. in which P the penetration in dmm at 25 ° (ASTM D 5) means, S the softening point in "C after the ring and Ball method is (ASTM E28-58T) and P. 1. means the penetration index (see P. f e i f f e r and employees, "National Petroleum News", 40, pp. R-78/84, 1938).

In the context of the invention, elemental sulfur must be used, d. H. Sulfur in the free state and not chemically bound in a compound.

Any physical form of sulfur can be used with success, because the sulfur is generally mixed with the molten bitumen. the However, the mixing temperature should not exceed 177 "C because it is above this temperature a chemical reaction between the bitumen and the sulfur sets in, which leads to a Impairment of the physical properties of the road paving compounds according to the invention can lead. However, the mixing temperature of the sulfur must be at least as high as its melting point lie, namely at 112.8 "C. However, the mixing temperature is preferably between about 149 and 177 "C. Higher temperatures must therefore also be avoided, so that the amount of sulfur dioxide vapors that is usually heat from sulfur occur in the air, is kept as low as possible.

The proportions in which the three main components of the invention bituminous road paving compounds are of great importance. In particular should be the total volume of sulfur and bitumen, including where applicable existing filler, the void volume between the aggregate particles does not because otherwise the strength of the pavement layer will be reduced. Farther the amount of sulfur in relation to the amount of bitumen may have a weight ratio of about 4: 1. Namely, at higher weight ratios the sulfur is the continuous phase in the sulfur-bitumen mixture, with which a Reduction of the flexibility of the covering mass under load is connected. Farther but the weight ratio of sulfur to bitumen must be at least 1: 1, thus superior mechanical stability and high resistance compared to plastic deformation (low "flow" value) is achieved. That The example below explains how these important physical properties are can be achieved, and it also explains the importance of their presence relative proportions. Embodiment Six test sections of a compacted Asphalt concrete with dimensions of 1.5, 2.7 m were placed on the surface of a existing road surface with good load-bearing capacity (0.094 cm deformation under a wheel load of 4082kg).

The thickness of these compacted test coverings was 5.08 cm.

Mixtures were tested (see the table below) which contained both crushed rock and rounded sand. There were mixtures using these mineral aggregates with two different ones Quantities of sulfur to aggregate produced. The comparison mixtures did not contain sulfur and were only used for comparing behavior among the used for individual tests.

The properties of the compacted mixtures are shown in the table below: Table I Composition and stability properties of experimental mixtures in the road test Composition stability properties bitumen content sulfur content weight ratio Marshall stability 3) Marshall river 3) Load capacity 4) Weight percent Weight percent sulfur to bitumen (kg) (cm. 102) $ (kg / cm2) Crushed rock) 6.5 0 0 940 26.8 1.08 5.0 5.0 1.0 1730 26.8 1.86 4.0 9.0 2.2 2275 12.2 5.71 Rounded sand2) 7.25 0 0 450 25.4 0.54 5.5 5.5 1.0 1315 14.6 2.71 4.5 10.0 2.2 2700 19.5 3.15 t) Rock particles with a size of dust fineness up to 6.35 mm. 100% of the aggregate passed through a 9.5 mm sieve. 480/0 passed through a US Standard No. 8 sieve and 50/0 passed through a US Standard No. 200 sieve.

2) rounded sand; 100% passed through a U.S. Standard No. 4 sieve, 66% through a US standard No. 30 sieve and 10% through a US standard No. 200 sieve.

3) ASTM method A 1559.

4) (stability: flow). (120-river: 100).

The above test data show that a weight ratio of sulfur to bitumen of at least about 1.0 is required to both an adequate Achieve stability as well as low flow, d. H. a good resilience. Particularly when there is a solid aggregate, it is particularly preferable to a sulfur-bitumen ratio of at least 1.5: 1 and even better of 2: 1 to be used so that low flow values are obtained.

The meaning of the above data may become even clearer when one examines the effect that sulfur has on the layer thickness of an asphalt concrete required to produce a road surface with an axle load capacity of 8160 kg on a weak subgrade: Table II Weight Thickness Thickness Reducing required ratio of the Thickness of the Sulfur granular asphalt-bitumen layer to bitumen substructure concrete layer in% - 38.1 16.8 - 2.2 38.1 12.2 27 - 17.8 19.8 2.2 17.8 13.0 35 While sulfur is known to have good strength properties when solidified in a solid mass, it was not expected that increasing the addition of sulfur to bitumen would increase the strength of asphalt concrete, let alone as much as it does the example above shows. This increase in strength is also surprising insofar as the bitumen and not the sulfur forms the continuous phase which fills the voids between the individual particles of the aggregate. The aggregate is covered by the bitumen, and the sulfur crystals are merely physically suspended in the mixture and surrounded on all sides by the continuous bitumen mass.

In the production of the road paving compounds according to the invention it of course required the sulfur as intimately as possible with both the Bitumen as well as with the aggregate and any filler used to mix. The mixing must be done in such a way that the sulfur is finally whole is evenly distributed in the mixture of aggregate and bitumen.

Around the time during which the sulfur is at an elevated temperature is held to decrease as much as possible, it is best to add the sulfur to that already add the finished mixture of hot bitumen and the unit. With so-called "Hot mix systems", which are equipped accordingly, it is particularly easy to add powdered sulfur using the “filler screw”. The sulfur can but either in solid or in molten form one can be found. If you adding the sulfur in solid form (e.g. as a powder) is provided by the hot bitumen aggregate mixture the heat required to melt the sulfur.

To get the best results when using sulfur and bitumen To achieve in paving mixes, the sulfur and bitumen should as well optionally also used filler the voids between the aggregate particles practically completely fill out, which means that at least 60% the cavities are filled. The air becomes about 60% from the cavities of the aggregate by bitumen, sulfur and filler or any combination these three components are displaced. In most cases such a complete Filling of the cavities can only be achieved by applying the pavement mass in a known manner, z. B. compacted by tamping or rolling.

Claims (1)

Claim: road paving compounds, bitumen, elemental sulfur and contain mineral additives, characterized in that the weight ratio from sulfur to bitumen in the masses 1: 1 to 4: 1.