• Open-Graded (or Uniformly- Graded) Friction Course (OGFC) – Primarily coarse aggregate with few fines • Stone Mastic (Matrix) Asphalt (SMA) – Mid-size aggregate missing or reduced Stone Matrix Asphalt Open Graded Friction Course Dense Mix Hot Mix Asphalt Mixture Design Objectives Specific Mix Design Objectives
The aggregate structure of open graded friction courses makes them particularly susceptible from raveling. To avoid accelerated raveling, their use should be avoided in areas where snow and ice occur.
– Wet Process – rubber is added to the liquid asphalt binder before being mixed at the hot mix asphalt plant (i.e., rubber is wet before mixing) – Dry Process – rubber is added at the same time the asphalt and aggregate are mixed (i.e., rubber is dry before mixing) Designing with Asphalt Rubber
What Defines Asphalt Rubber? ASTM D6114 • Asphalt rubber is a blend of asphalt cement, reclaimed tire rubber and certain additives, in which the rubber component is at least 15% by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles Swelling of Crumb Rubber
Open graded friction courses (OGFCs) are a type of pavement that have been built across the United States since the 1950's. These asphalt mixes contain only a small portion of fine aggregate, creating a pavement with a relatively large percentage of air voids.
Open Graded Asphalt is a porous asphalt mix formulated to provide large voids (in excess of 20 per cent) to allow surface water to drain away and hence increase safety for the motorist. The demand for low traffic noise surfacing has greatly increased in the last few years, especially in urban areas.
An open-graded HMA mixture is designed to be water permeable (dense-graded and SMA mixes usually are not permeable). Open-graded mixes use only crushed stone (or gravel) and a small percentage of manufactured sands. There are two types of open-graded mixes typically used in the U.S.: Open-graded friction course (OGFC).
ACFC is used as the final riding surface on high speed roadways where superior skid resistance is needed (such as rural highways and interstates). ACFC thickness is typically ½ to ¾ inch (12 to 19 millimeters). ACFC is never used as a leveling or base course since it should never be overlaid.
OGFC is more expensive per ton than dense-graded HMA, but the unit weight of the mix when in-place is lower, which partially offsets the higher per-ton cost. The open gradation creates pores in the mix, which are essential to the mix's proper function.
Open-graded aggregate means aggregate containing little or no mineral filler or in which the void spaces in the compacted aggregate are large.
Bituminous Concrete(BC)
What is the speciality of an open-graded bituminous mix? Explanation: Open-graded mix is the one in which fine aggregate and filler are missing. In a gap-graded mix, some coarse aggregates are missing. Binder is absent in case of an unbounded mix.
The gap graded asphalt mixtures are the mixtures in which the aggregate particles of certain sizes are partially missing. The gap graded asphalt mixtures will have higher air-voids when compared to dense graded asphalt mixtures.
The terms “asphalt concrete”, “bituminous asphalt concrete” and the abbreviation “AC” are typically used only in engineering and construction documents and technical literature where the definition of “concrete” is any composite material composed of mineral aggregate glued together with a binder, whether that binder is ...
The primary difference between the two is that asphalt is made by mixing aggregate with bitumen, a sticky black hydrocarbon which is extracted from natural deposits or crude oil. Concrete is made by mixing an aggregate material with a cement binder and then allowing the mixture to harden, forming a rock-like substance.
Open-graded friction course (OGFC) has been used since 1950 in different parts of the United States to improve the surface frictional resistance of asphalt pavements. OGFC improves wet weather driving conditions by allowing the water to drain through its porous structure away from the roadway.
Published: Dec 2004 Revised: January 2008 What is PG? PG stands for performance grade. The performance relates to climate and the binder’s performance and the binder’s distress resistance in that climate.
Traffic In the AASHTO flexible pavement design, traffic is considered in terms of ESAL for the terminal PSI (Table 20.13 for p t = 2.5.) We must assume the structural number of the pavement.
ii ABSTRACT Open-graded friction course (OGFC) has been used by several state departments of transportation (DOT) since 1950. While many DOTs report good performance, many other states
INTRODUCTION . An “open-graded friction course” is defined as a thin, permeable layer of asphalt that integrates a skeleton of uniform aggregate size with a minimum of fines. These mixes contain a small percentage of fine aggregate which produces a large number of air voids.
When it comes to asphalt, you have many choices as homeowners. There are three different grades available in asphalt. The grades available are I-2, also known as base; I-5, known as top ;and the I-4 or commercial top grades.
Mineral fibers have been added to mixes to increase the ability of asphalt to coat the aggregate. As with most paving jobs, deficiencies on any existing pavement structure should be corrected. The base layer used for placement should be dense graded to avoid structural failure.
Different states have reported average pavement longevities as short as 6 years, while others have reported more than 12 years of service life before needing any maintenance. This represents huge variability, and spans the gap between a viable paving option and one that isn’t practical.
In addition, particles on the roadway, particularly snow removal materials such as sand and salt, can clog up the pores in the pavement, limiting their drainage capability. Snowplows have also shown a tendency to deteriorate traffic markings on such pavements.
In addition, open graded friction courses are generally quieter than typical pavements. There has been a wide range of experience with OGFC’s in different regions. While a large majority of states have experimented with these pavements, there is a large split over whether they will continue to be built. Placing an open graded friction course.
An “open-graded friction course” is defined as a thin, permeable layer of asphalt that integrates a skeleton of uniform aggregate size with a minimum of fines. These mixes contain a small percentage of fine aggregate which produces a large number of air voids. The pavement consists primarily of single size coarse aggregate with a high asphalt content. The aggregate skeleton is responsible for the pavement's ability to resist trucks and carry the loads without undergoing permanent deformation. The load is carried by the stone while the asphalt keeps everything in place.
Maintenance issues that apply to open-graded friction courses include patching that must be done without disrupting surface permeability. Any surface treatment should depend on the size and severity of the failure.
Over the past five years, the Oregon Department of Transportation (ODOT) has placed more than 3,600 lane miles of open-graded surface mix.
This results in more air voids because there are not enough small particles to fill in the voids between the larger particles. The curve is near-horizontal and near-zero in the small-size range.
For over 60 years, open-graded friction courses (OGFC) have been used to improve the frictional resistance of asphalt surfaces throughout the United States. OGFC allows surface water to drain through and away from the roadway. Benefits include: reduced hydroplaning; improved wet pavement friction; less vehicle splash and spray; better surface reflectivity; and quieter roadways.
Open-graded mixes are very safe due to their rapid drainage surfaces and excellent skid resistance. Chances of hydroplaning after heavy rainfalls are greatly reduced by the OGFC’s void structure. The aggregate structure creates a higher degree of friction and permeability for the pavement surface. This permeability improves friction during inclement weather and reduces splash/spray or hydroplaning due to increased surface drainage. Water can quickly enter and drain through the structure due to its 15 to 25 percent void range.
The Arizona Department of Transportation (ADOT) began experimenting with open graded friction courses as early as 1954 . They wanted a roadway surface with good skid resistance, good rideability and appearance. Over the years the gradation has changed slightly with more emphasis placed on using a single size aggregate.
The OGFC-AR sections on the three projects were audibly quieter than the HMA control section for between four and twelve months with an average of nine months. The SBS sections were audibly quieter from zero to fourteen months with an average of five months.
The performance of the OGFC-AR section on the Bellevue project matched that of the Lynnwood project with wear and raveling exceeding the depth of the overlay in the wheel paths as shown in Figure 18.
It can be concluded that rubber modified open-graded friction course “quieter pavements” have not worked in the state of Washington as cost effective pavement choices. This conclusion is based on both the acoustical performance and the wear performance of the three test sections.
Mineral fibers have been added to mixes to increase the ability of asphalt to coat the aggregate. As with most paving jobs, deficiencies on any existing pavement structure should be corrected. The base layer used for placement should be dense graded to avoid structural failure.
Different states have reported average pavement longevities as short as 6 years, while others have reported more than 12 years of service life before needing any maintenance. This represents huge variability, and spans the gap between a viable paving option and one that isn’t practical.
In addition, particles on the roadway, particularly snow removal materials such as sand and salt, can clog up the pores in the pavement, limiting their drainage capability. Snowplows have also shown a tendency to deteriorate traffic markings on such pavements.
In addition, open graded friction courses are generally quieter than typical pavements. There has been a wide range of experience with OGFC’s in different regions. While a large majority of states have experimented with these pavements, there is a large split over whether they will continue to be built. Placing an open graded friction course.