US2104411A

US2104411A - Method of producing a hot mix, cold laid paving mixture

Info

Publication number: US2104411A
Application number: US742148A
Authority: US
Inventors: Charles M Baskin
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1934-08-30
Filing date: 1934-08-30
Publication date: 1938-01-04
Anticipated expiration: 1955-01-04

Description

Patented Jan. 4, 1938 UNITED STATES PATENT QFFECE METHOD OF PRODUCING A HOT MIX, COILD LAID PAVING MIXTURE No Drawing. Application August 30, 1934, Serial No. 742,148

2 Claims.

This invention relates to the manufacture of bituminous pavements, particularly to a method in which high softening point and low susceptibility to temperature change asphalts are introduced in dense paving mixtures.

The general method used in preparing hot mix pavements is by preheating mineral aggregate to approximately 375 F. and coating this aggregate with asphalt ranging in softening point from 110 F. up to 140 F. This asphalt is also preheated to approximately 325 F. so that it will effectively spread over the mineral particle surfaces. The practical dimculties encountered with this general method are:

(1) The requirement of high mixing temperatures and large equipment such as kilns 24 feet long by feet in diameter, steam boilers to liquefy the paving asphalt which is usually shipped in tank cars, etc.

(2) lhe necessity of spreading out such mixtures on the road surface with the least time interval between the mixing and laying and immediately compacting same while hot.

(3) The inability to produce paving mixtures by the standard hot mix methods that will have a high stability to distortion under loads in hot weather and will not be inordinately brittle at low temperatures.

It is possible to produce high melting point paving asphalts (170 to 200 F. softening point) which would have approximately the same penetration or hardness at 77 F. as standard paving asphalts and yet have considerably higher penetration or be perceptibly softer at 0 F. The use of such high melting point low susceptibility to temperature change asphalt is restricted by virtue of the fact that it would require preheating the mineral aggregate to at least 425 F. and the asphalt to about 400 F. in order to obtain a homogeneous mixture. Furthermore, paving mixtures of such high temperatures would chill too rapidly and would not allow for sufficient transportation interval from mixers to road surfaces without having to constantly move the plant every mile or two. This difl'iculty is largely due to the fact that the lower the susceptibility of asphalt to temperature change, the higher its viscosity at elevated temperatures as compared to similar melting point asphalts that are high in susceptibility to temperature change.

An object of this invention is to manufacture bituminous pavements in which the asphalt used has a high softening point.

Another object of this invention is the manufacture of bituminous pavements in which the asphalt used has a low susceptibility to temperature change and thereby high stability to distortion under loads at summer temperatures.

According to this invention, the mineral aggregate is preheated to 150 to 350 F. This may be done in a drum 12 feet long, 4 feet in diameter, and mounted on a truck trailer so that it may be easily transported. The slightly preheated aggregate is then mixed with a priming oil or soft bitumen ranging in consistency from 300 seconds viscosity furol at 122 F. to 70 F. softening point, with or without preheating. At the same time powdered asphalt, having a softening point above 250 F., is introduced in the right proportion to obtain an asphalt having the desired melting point upon amalgamation with the priming oil or soft bitumen that is used. By this method a paving mixture is obtained in which the asphalt formed by amalgamation may be of any desired softening point according to the proportions of the priming oil or soft bitumen that is used with the powdered asphalt.

An advantage obtained in preparing a paving mixture of this type is that the priming oil or soft bitumen, together with the powdered asphalt, is only partially amalgamated when first mixed and may be laid hot or allowed to cool or partially cool before laying. Upon rolling and traffic the amalgamation of the priming oil or soft bitumen with the hard powdered asphalt is accomplished.

Inasmuch as the above description has been given merely for the sake of illustration and not for the purpose of limiting the invention thereto, it is intended to claim all inherent novelty in the invention as broadly as the prior art permits.

I claim:

1. A method of producing a paving mixture containing as a binder an asphaltic material having a softening point of 170 to 200 F. and adapted to be laid and compacted while cool by application of pressure, which comprises heating a mineral aggregate to a temperature of 150 to 350 F. and mixing therewith a preheated soft bitumen ranging in consistency from 300 seconds viscosity furol at 122 F. to 70 F. softening point and a powdered asphalt.

2. A method of producing a paving mixture containing as a binder an asphaltic material of 170 to 200 F. softening point, adapted to be laid and compacted while cool by application of pressure, which comprises heating a mineral aggregate to a temperature of 150 to 300 F. and mixing therewith a preheated soft bitumen ranging in consistency from 300 seconds viscosity furol at 122 F. to 70 F. softening point and a powdered asphalt having a softening point above 250 F.

CHARLES M. BASKIN.