Hot-mix asphalt paving mixture
A hot-mix asphalt paving mixture includes the use of a hard, angular, non-carbonate ½″ minus igneous crushed rock, washed rounded No. 100 sieve silica sand particles, ½″ minus recycled asphalt pavement particles, and a performance-graded bituminous liquid asphalt binder, thereby to produce an environmentally-friendly hot asphalt mixture that is laid with minimal compaction effort, and without the use of conventional compaction-aiding additives that chemically alter the viscosity of the liquid asphalt binder. During compaction, the rounded silica sand particles react with the igneous rock particles as a mechanical compaction aid, thereby allowing the angular particles to achieve proper aggregate interlock with minimal compactive effort. The aggregate composition comprises about 75% igneous crushed rock, about 5% processed round silica sand particles, about 20% recycled asphalt pavement, and about 5% binder. The resultant pavement is skid-resistant, resists rutting, and has a permanent dark color.
1. A hot-mix asphalt paving mixture for producing a given resultant pavement, comprising:
(a) an aggregate composition including, by weight:
(1) 70% to 80% hard angular non-carbonate crushed igneous rock having a size of about ½″ minus, said igneous crushed rock being selected from the group consisting of rhyolite, porphyry, granite, diabase, and basalt;
(2) 3% to 10% washed processed rounded silica sand, wherein about 85% to 100% of said silica sand, by weight, has a size distribution in the passing range of a Size No. 50 U.S. Standard Sieve; and
(3) 20% to 25% recycled asphalt pavement (RAP) having a size distribution less than ½″ minus; and
(b) a performance-graded virgin asphalt bituminous binder having an initial temperature of about 314° F. to 335° F., thereby to produce a hot-mix asphalt paving mixture, the quantity of said performance-graded virgin asphalt bituminous binder being from 3.5% to 5.5%, by weight, of said hot-mix asphalt paving mixture, whereby said given resultant pavement is skid-resistant, rut-resistant, and has a permanent black appearance.
2. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said silica sand is dust-free and has a chemical composition consisting of at a minimum of 99 percent silica by weight, and conforms to the size distribution of 20% to 50%, by weight, silica sand passing through a Size No. 100 U.S. Standard Sieve.
3. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said aggregate composition has the size dimensions:
U.S. Standard Sieve Size
Percent Passing by Weight
¾ Inch
100%
½ Inch
85%-100%
No. 4
50%-70%
No. 8
30%-55%
No. 30
10%-30%
No. 200
5%-12%.
4. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said recycled asphalt pavement includes an asphalt pavement binder, the sum of said asphalt pavement binder and said performance-graded virgin asphalt bituminous binder being between 4% and 7% by weight of said hot-mix asphalt mixture.
5. A hot-mix asphalt paving mixture as defined in claim 4 , wherein said performance-graded asphalt bituminous binder is selected from the group consisting of PG64-22, PG64-22H, PG64-22V, PG70-22, and PG76-22 performance-graded asphalt binder, whereby the given resultant pavement including said binder corresponds with the climate and expected traffic conditions.
6. A hot-mix asphalt paving mixture as defined in claim 5 , wherein the mixture characteristics of a laboratory-tested specimen of the combined hot-mix asphalt paving mixture, at a design level of 30 gyrations, are such that, by volume:
(a) the laboratory air voids value is between 3.5% and 4.5%;
(b) the voids in the mineral aggregate value (VMA) is at least 14.0%; and
(c) the voids filled with asphalt value (VFA) is between 60% and 80%.
7. A hot-mix asphalt paving mixture as defined in claim 6 , wherein said hot-mix asphalt paving mixture, when tested for moisture susceptibility, has a minimum tensile strength ratio of about 80%.
8. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said crushed igneous rock consists of recycled material produced as a by-product during quarry and mining operations.
9. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said silica sand is produced as one of the group consisting of a by-product of mining operations, a by-product of silica sand processing used for industries such as frac sand operations, and raw material for the production of glass.
10. A hot-mix asphalt paving mixture as defined in claim 1 , wherein said hot-mix asphalt paving mixture is compacted by a total of 3 to 5 passes by a 10-ton to 20-ton wheel vibratory roller at a temperature of between 275° F. to 330° F., thereby to produce desired field density of 91.5 of the theoretical maximum specific gravity of the hot-mix asphalt paving mixture, whereby owing to the improved workability and compactability produced by the interaction between the rounded silica sand particles and the hard angular non-carbonate crushed igneous rock in the hot-mix asphalt pavement mixture, said given resultant pavement has improved skid- and rut-resistance.
11. A method for making asphalt paved roads, which comprises:
(a) mixing together to form an aggregate composition, by weight:
(1) 70% to 80% hard angular non-carbonate crushed igneous rock having a size of about ½″ minus, said igneous rock being selected from the group consisting of rhyolite, porphyry, granite, diabase, and basalt;
(2) 3% to 10% washed processed rounded silica sand, wherein about 85% to 100% of said silica sand, by weight, has a size distribution in the passing range of a Size No. 50 U.S. Standard Sieve; and
(3) 20% to 25% recycled asphalt pavement having a size distribution of about ½″ minus; and
(b) mixing with said aggregate composition a performance-graded virgin bituminous asphalt binder having an initial temperature of about 314° F. to 335° F., thereby to produce a hot-mix asphalt paving mixture,
the quantity of said performance-graded virgin asphalt bituminous binder being from 3.5% to 5.5%, by weight, of said hot-mix asphalt paving mixture, whereby the mixture is easily compacted, and the resultant pavement is skid-resistant, rut-resistant, and has a permanent black appearance;
(c) placing said asphalt mixture within a conventional bituminous hot-mix paver;
(d) depositing said asphalt mixture in a homogeneous manner to a desired lane width and thickness; and
(e) initially compacting said mixture at a temperature of from 275° F. to 325° F. and at a pressure of about 600 kPa by between 3 to 5 passes with a 10-ton to 20-ton steel drum vibratory roller, thereby to achieve at least 91.5% of a desired theoretical maximum specific gravity.
12. A method for making asphalt paved roads as defined in claim 11 , and further including the step of:
(f) subsequently compacting said asphalt mixture by means of a 2-ton to 10-ton steel drum finishing roller, thereby to remove any surface irregularities produced by the initial compacting step.