a broad category of coarse particulate material used in construction, including sand, gravel, crus hed stone, slag, recycled concrete and geo- synthetic aggregates. used as a stable foundation or road/railbase with predictable, uniform properties, oras a low-cost extender that binds with moreexpensive cement or asphalt to formconcrete.
1. As compacted aggregates in bases, sub- bases and shoulders2. As ingredients in hot mix asphalt3. As ingredients in Portland cement concrete
composed of compacted aggregate and bitumen the aggregate transmits the load from the surface to the base and the bitumen (bituminous binder) holds the aggregate together for bituminous construction, aggregate is classified according to particle size
“The aggregate shall consist of hard,durable particles of fragments of stone orgravel and sand or other fine mineralparticles free from vegetable matter andlumps or balls of clay and of such nature itcan be compacted readily to form a firm,stable layers. It shall conform to thegrading requirements shown in table 3when tested by AASHTO T-11 and 27”.
SIEVE DESIGNATION MASS PERCENT PASSINGStandard Alternate US Grading A Grading B Grading C Grading D (mm) Std. 25 1" 100 100 100 100 10 3/8 50-85 60-100 5 No. 4 35-65 50-85 55-100 70-100 2 No. 10 25-50 40-70 40-100 55-100 0.5 No. 40 15-30 25-45 20-50 30-70 0.075 No. 200 5-20 5-20 6-20 8-25
The coarse aggregate material retained on the 2.00 mm (No.10) sieve shall have a mass per cent of wear by the Los Angeles Abrasion Test (AASHTO T-96) of not more than 45.
When crushed aggregate is specified, not less than 50 mass per cent of the particles retained on the 4.75 mm (No. 4) sieve shall not have at least one fractured face.
The fraction passing the 0.75mm (No. 200) sieve should not begreater than two thirds of thefraction passing the 0.425 mm (No.40) sieve.
The fraction passing 0.425 mm(No.40) sieve shall have a liquid limitof not greater than 35 and aplasticity index range of 4 to 9 whentested by AASHTO T-89 and T-90respectively.
AGGREGATES FOR PORTLAND CEMENT CONCRETE IMPORTANT PROPERTIES FORAGGREGATES THAT ARE USED IN CONCRETE PAVING MIXTURES:
Gradation The size distribution of theaggregate particles affects the relativeproportions, cementing materials andwater requirements, workability, pumpability, economy, porosity, shrinkage,and durability. The size distribution ofthe aggregate particles should be acombination of sizes that results in aminimum of void spaces.
Absorption The absorption and surfacemoisture condition of aggregates mustbe determined so that the net watercontent of the concrete can becontrolled.
Particle Shape and Surface Texture • Rough textured, angular, or elongated particles require more water to produce workable concrete. • Smooth, rounded, compact aggregates require more cementing materials to maintain the same water- cement ratio. Angular or poorly graded aggregates may result in the production of concrete that is more difficult to pump and also may be more difficult to finish. The hardened concrete strength will generally increase with increasing coarse aggregate angularity, and flat or elongated coarse aggregate particles should be avoided.
Abrasion Resistance The abrasion resistance of anaggregate is often used as a generalindex of its quality. Abrasion resistance applies only tocoarse aggregates. Aggregates vary intheir resistance to fracturing underimpact (toughness); and breaking downinto smaller pieces from abrasive action(hardness).
Durability Aggregates must be resistant tobreakdown and disintegration fromweathering (wetting/drying andfreezing/thawing) or they may breakapart and cause premature pavementdistress. Durability and soundness areterms typically given to an aggregate’sweathering resistance characteristic.
Soundness Test The soundness testrepeatedly submergesan aggregate sample in a sodiumsulfate or magnesium sulfatesolution. This process causes saltcrystals to form inthe aggregate’s water permeablepores. The formation of thesecrystals creates internal forcesthat apply pressureon aggregate pores and tend tobreak the aggregate.
Deleterious Materials Aggregates should be free ofpotentially deleterious materials such asclay lumps, shales, or other friableparticles, excess dust and vegetablematter are not desirable because theygenerally affect performance by quicklydegrading, which causes a loss ofstructural support and/or preventsbinder-aggregate bonding.
Particle Strength For normal concretepavements, aggregate strength is rarelytested. However, aggregatecharacteristics other than strength, suchas the size, shape, surfacetexture, grading and mineralogy areknown to affect concrete strength invarying degrees. Particle strength is animportant factor in high-strengthconcrete mixtures.
Purpose of mineral fillers in asphalt mixes: • The portion of the mineral filler that is finer than the thickness of the asphalt film and the asphalt cement binder form a mortar or mastic that contributes to improved stiffening of the mix. • The particles larger than the thickness of the asphalt film behave as mineral aggregate and hence contribute to the contact points between individual aggregate particles. The gradation, shape, and texture of the mineral filler significantly influence the performance of hot mix asphalt.
MINERAL FILLERS IMPORTANT PROPERTIES OFMINERAL FILLER USED IN ASPHALT CONCRETE APPLICATIONS
• Gradation – mineral fillers should have 100 percent of the particles passing 0.60 mm (No. 30 sieve), 95 to 100 percent passing 0.30 mm (No. 40 sieve), and 70 percent passing 0.075 mm (No. 200 sieve).• Plasticity – mineral fillers should be nonplastic so the particles do not bind together.• Deleterious Materials – the percentage of deleterious materials such as clay and shale in the mineral filler must be minimized to prevent particle breakdown.
Testing Methods: a. Penetration graded bitumen b. Viscosity graded bitumen c. Oxidised bitumen grades
Penetration Graded Bitumen Bitumen is classified by the depth to which a standard needle will penetrate under specified test conditions. This “pen” test classification is used to indicate the hardness of bitumen, lower penetration indicating a harder bitumen.
Viscosity graded bitumen Bitumen is also graded and specified by their viscosity at a standard temperature (typically 60°C). Specifications for viscosity graded bitumen normally give the nominal viscosity prefixed by a V, e.g. V1500.
Oxidised bitumen grades The degree of oxidation can range from very small, often referred to as air- rectification, or semi-blowing, which only slightly modifies the bitumen properties, through to “full” blowing, whereby the properties of the bitumen are significantly different to penetration grade bitumens.
Nomenclature and grading forthe oxidised bitumen products isbased on a combination of thetemperature at which the bitumenreaches a certain “softness” whenbeing heated up as expressed bythe ring and ball softening pointtest, and the penetration value.
Cut-back bitumen Cut-backs are bitumen preparations in which the viscosity of the binder has been reduced by the addition of a volatile solvent, normally derived from petroleum. Typically the solvents used are white spirit and kerosene. Cut- back products are typically used for spraying and some mixing applications.
Fluxed bitumen Fluxed bitumens are bitumen preparation where the viscosity of the binder has been reduced by the addition of relatively non-volatile oils. Typical fluxants include gas oil and vegetable based oils.
Modified bitumen Modified bitumens are bituminous binders whose performance properties, such as elasticity, adhesive or cohesive strength, have been modified by the use of one or more chemical agents. These agents may be polymers, crumb rubber, sulphur and polyphosphoric acid, among other materials. Modified bitumens are widely used in the production of roofing felt and in paving applications.
Bitumen emulsion Bitumen emulsions are products in which tiny droplets (the dispersed phase) of bitumen or bituminous binder are dispersed in an aqueous medium (the continuous phase). Bitumen emulsions are used largely in road surfacing applications, such as surface dressing, cold mixtures and slurry seals.
Asphalt Asphalt is a mixture of a bituminous binder with mineral aggregate (stone), sand and filler, typically containing approximately 4-7%m bitumen.
Bituminous concrete - is a type of construction material used for paving roads, driveways, and parking lots - made from a blend of stone and other forms of aggregate materials joined together by a binding agent. This binding agent is called “bitumen”
- has a thick, sticky texture like tarwhen heated, then forms a densesolid surface once it dries.- is also widely knownas asphalt in many parts of theworld.
Bituminous concrete isquite different thanstandard concrete, and containsno cement. Bituminous concrete isknown for its distinctive blackappearance.
Asphalt paving is also fullyrecyclable. Some manufacturers addrecycled tires or glassaggregate to recycled asphalt toincrease its strength andresilience.
Bituminous concrete is strongenough to handle years of vehicletraffic, and is relatively easy to repairor refinish. It also provides a smoother andquieter ride than cementsurfaces, which helps to reduce noisepollution around highways and otherbusy roads.
G. Asphalt Concrete Pavement -composite material used in the construction of roadways and parking lots - mixture of a petroleum byproduct, asphalt bitumen and aggregate materials
Methods of mixing asphalt1. Hot mix asphalt concrete, HMAC - produced by heating the asphalt binder to decrease its viscosity, and drying the aggregate to remove moisture from it prior to mixing ** Mixing is generally performed with the aggregate at about 300 °F (roughly 150 °C) for virgin asphalt and 330 °F (166 °C) for polymer modified asphalt, and the asphalt cement at 200 °F (95 °C)
2. Warm mix asphalt concrete, WMA - produced by adding either zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing **This allows significantly lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols and vapors
3. Cold mix asphalt concrete - produced by emulsifying the asphalt in water with (essentially) soap prior to mixing with the aggregate - commonly used as a patch for road surfaces
4. Cut-back asphalt concrete - same process as in cold mix, but instead of soap and water, kerosene or light petroleum products are employed to emulsify the asphalt binder
5. Mastic asphalt concrete - produced by heating hard grade blown bitumen (oxidation) in a green cooker (mixer) until it has become a viscous liquid after which the aggregate mix is then added, and then to be cooked again for another 6 to 8 hrs. - used for footpaths, roofing, flooring and other light-use paving projects
6. Natural asphalt concrete - occurs as the result of upwelling bitumen - exist below the Earth’s surface, but can seep its way up through porous sedimentary rocks and stones
• Caused by excessive loads.• Heavy loads creates deflection on the road surface, with insufficient underlying strength.• Repetitious underlying of the excessive load with roughen and crack the road pavement will ultimately result to complete failure of the roadway.
1. Bleeding or Flushing -this distress is caused by excess asphalt in the surface layer.
…cont’n Major bleeding can be corrected by cutting off excess asphalt with a motor grader or removing it with a “heater planer”.
…cont’nTo repair corrugations in an aggregate base overlain with a thin surfacetreatment, scarify the pavement, add aggregate as needed, mix well, re-compact, prime, and then resurface. Where the surface has 2 inches or more ofasphalt plant mix, corrugations can be removed with a “heater planer”. Afterremoval of corrugations, cover with a new surface treatment or new asphaltoverlay. To repair shoved areas, remove surface and base as necessary andreplace with a more stable material to prevent a recurrence. For out-of-seasoninclement weather repairs, smooth shoved areas with patching if the surfaceunevenness is hazardous to traffic.
3. Cracking, Alligator Interconnected cracks forming a series of small polygons resembling an alligator’s skin are called alligator cracks.
Types of Alligator Cracksa. Alligator Cracking without Surface Distortion
b. Alligator Cracking with Distortion of Intact Surfaces
6. Random Cracking The causes of random cracking are numerous and, in its early stages, difficult to determine. Consequences range from severe, such as deep foundation settlement, to slight, such as a construction error or mishap.
7. Polished Aggregate Although uncrushed gravels often have surfacesthat are initially smooth and potentiallyhazardous, crushed rock initially has a rough, skid-resistant texture. Under the action oftraffic, however, some aggregates - including manylimestones - become polished and slick, especiallywhen wet. The likelihood of aggregate becomepolished increases with the volume of traffic. Becausepolished aggregate results in a loss of skid resistance, itis potentially hazardous. The most economical repair isto apply a skid-resistant surface treatment.
8. Potholes Potholes are caused by water penetrating the surface and causing the base and/or subgrade to become wet and unstable. They also may be caused by a surface that is too thin or that lacks sufficient asphalt content, lacks sufficient base, or has too many or too few fines.
Potholes in Surface Treatments over Aggregate Base To repair potholes in surfacetreatments, take the following actions:• Clean out hole.• Remove any wet base.• Shape hole so that it has vertical sides.• Prime hole.• Fill hole with Asphalt Concrete.
Potholes in Asphalt Concrete To repair potholes in Asphalt Concrete,take the following actions:• Clean out hole.• Remove any wet base.• Square up pothole so that it has neat lines both perpendicular and parallel to the center line and have vertical sides.• Prime the pothole.• Fill the pothole with Asphalt Concrete.
9. RavelingRaveling is caused by a dry brittle surface; dirty,dusty, or soft aggregate; patching beyond basematerial; lack of compaction of surface duringconstruction; too little asphalt in mix; orexcessive heating during mixing.Note: If the raveling is not a part of the pavedsurface, no action should be taken. In otherwords, don’t patch beyond the edge of thepavement.
10. Channels or Rutting Channels are caused by heavyloads and high tirepressures, subgrade settlementcaused by saturation, poorconstruction methods, or asphaltmixtures of inadequate strength.
11. Intact Surface Where the depression is 1 inch or less and the surface is cracked but still largely intact, skin patch the area. Where the depression is more than 1 inch and the surface is cracked but still largely intact, repair with asphalt concrete.
12. Disintegrated Surface Where the surface is badly crackedand loose (regardless of amount ofdepression), remove the old surface. If thearea shows signs of mud being pumped tothe surface, remove all wet material,replace base material, compact, prime, andbuild up with Asphalt Concrete.
13. Upheaval or Frost Boil Upheaval is caused by expansion offreezing moisture in the lower courses ofthe pavement or subgrade or by theswelling effect of moisture in expansivesoils. When this distress occurs, repair byinstalling combination drains as necessaryand replacing base and surface.
I. Macadam Asphalt - pioneered by Scottish engineer John Loudon McAdam in around 1820 ** he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear
• The lower 200-millimetre (7.9 in) road thickness was restricted to stones no larger than 75 millimetres (3.0 in).• The upper 50-millimetre (2.0 in) layer of stones was limited to 20 millimetres (0.79 in) size and stones were checked by supervisors who carried scales
Tar-bound macadam or tarmac -The area of low air pressure created under fast-moving vehicles sucks dust from the road surface, creating dust clouds and a gradual unravelling of the road material. This problem was approached by spraying tar on the surface to create tar-bound macadam.
SURFACE TREATMENT•A surface treatment is an application ofasphalt materials to any type of road surfacewith or without acover of mineral aggregate.•This application produces an increase inthickness usually less than 1 inch.•Have a variety of uses
PURPOSES1. Waterproof the surface.2. Provide a wearing surface.3. Make the surface nonskid.4. Prevent hydroplaning.5. Rejuvenate an old road or runway.6. Make permanent improvements
TYPESSurface treatments may be applied to the basecourse of a new road or to the surface of an old roadas a method of repair. Surface treatments aregrouped into these categories:1. Sprayed Asphalt Surface Treatment2. Aggregate Surface Treatment
vSprayed Asphalt Surface TreatmentSprayed asphalt treatments contain no aggregates. They are simply applications of different types of asphaltic materials to a prepared surface.Three types of sprayed asphalt surface treatment:a. FOG SEALb. DUST LAYINGc. ROAD OILING
FOG SEAL• a fog seal is a light application of diluted slow-setting asphaltemulsion, used to renew old asphalt surfaces and seal smallcracks and surface voids. Fog seals are especially useful forpavements carrying a low volume of traffic.• Other uses: To seal surface voids in new asphalt plant mixes To prevent dust on sprayed asphalt with cover aggregate surface treatments To increase aggregate retention To provide a uniform dark color
FOG SEALThe asphalt emulsion is diluted with an equalamount of water, and the diluted material issprayed at the ROA of 0.1 to 0.2 gallon persquare yard, depending on the texture anddryness of the old pavement. In normalconditions, the separation and evaporation ofthe water is rapid, permitting traffic within 1 or 2hours.
DUST LAYING- consists of spraying an untreated surface with a low-viscosityliquid asphalt, such as SC-70, MC-30, MC-70, or a diluted slowsetting asphalt emulsion. The asphalt and dilutantpenetrate and coat the fine particles and temporarily relievethe nuisance of dust. The material is sprayed at a ROA of 0.1 to0.5 gallon per square yard.- When emulsion is used, it should be diluted with 5 or more partsof water by volume. Diluted emulsion dust-laying treatmentsusually require several applications. The dust stirred by trafficbetween applications eventually conglomerates and no longerrises.- This is an effective treatment in a very dusty environment whereone application of asphalt is insufficient.
ROAD OILING- differs from dust laying in that it is usually accomplished as part of aplanned build up of low-cost road surfaces over several years. Eachapplication may be mechanically mixed with the material being treated, orit may be allowed to penetrate. The light oils in the road oil penetrate intothe subgrade and tend to repel moisture absorption.- The objective in all roads oiling work is to form a dustless wearingsurface, combined with a strong water-repelling subgrade.Because soils vary widely, procedures for oiling area matter for local trialand error, rather than scientific analysis.- The amount of road oil, required in the first year of work will vary from0.75 to 1.0 gallon per square yard. The first application is applied at theROA of about one half of the total; succeeding applications are made inequal amounts. Road oiling treatments are placed several weeks apart,depending upon the character of the asphalt soil mat.
Aggregate Surface TreatmentThe sprayed asphalt with aggregate cover surfacetreatments are applications of liquid asphalt, followed byan application of aggregate. This can be done in one or morelayers of construction.• Two types of sprayed asphalt with covered aggregatesurface treatments : -SINGLE-SURFACE TREATMENT -MULTIPLE-SURFACE TREATMENT
SINGLE-SURFACE TREATMENTSingle-surface treatments are thin, bituminous-aggregatetoppings, applied to existing bases or surfaces, such asconcrete or asphalt. Construction involves applying abituminous prime or tack coat to the base or surface.This coating is followed by an application of bitumenand small-sized aggregate. Single-surface treatments aresometimes called seal coats, because they seal the surfaceof the road or runway.
Sequence of Operationsa.Applying prime coatb.Binder applicationc.Aggregate applicationd.Rolling
Applying Prime Coat•The first steps, such as sweeping, priming ortacking, and curing•The binder (bituminous material) is applied overthe prime coat with an asphalt distributor
Binder Applicationwhen you are applying the binder, it should be hot enough to spray properly andcover the surface uniformly. After the binder cools and cures, it should bind theaggregate tightly to prevent dislodgement by traffic. Individual aggregate stonesshould be pressed into the binder but must not be covered by the binder.Approximately one half of the individual aggregate stones should be exposed totraffic. The ROA for the binder material should be between 0.25and 0.30 gallon ofasphalt per square yard. For a single-surface treatment, the bitumen must beheated and applied to the surface while hot. The aggregate must be spread androlled before the bitumen cools. Under no circumstances is traffic permitted totravel upon uncovered fresh bitumen. The distributor should NOT apply bitumenuntil the aggregate is on hand and ready for application. When the distributormoves forward to spray the asphalt, the aggregate spreader should start rightbehind it. The bitumen should be covered within 1 minute if possible;otherwise, the increase in asphalt viscosity may preventgood binding of aggregate.
Aggregate ApplicationThe size and amount of aggregate, used for surface treatments, areimportant. You must use a size that matches the bitumen applicationrate. For a single-surface treatment, one-half inch to sieve number 4 isneeded. The amount of aggregate should be 25-30 pounds per squareyard. When aggregate is distributed properly, very little hand work isrequired. At longitudinal joints, the aggregate cover is stopped 8 inchesfrom the edge of the bitumen to ensure ample overlap of the bitumencoat. All bare spots should be covered by hand spreading, and anyirregularities of the distribution should be correctedwith hand brooms. Excess aggregate in limited areas should beremoved immediately with square-pointedshovels. When the aggregate spreader is properly setand operated, handwork is reduced to a minimum.
Rollingthe aggregate is usually rolled by pneumatic-tired rollers. Steel-wheeled rollers are not recommendedby themselves. If used, they should make only one pass(one trip in each direction). The rolling operation should thenbe completed with the pneumatic-tired rolls. Steel-wheeled rollers produce maximum compaction but must beused with care to prevent excessive crushingof the aggregate particles. Also, these rollers will bridge oversmaller size particles and small depressions in the surfaceand will fail to press the aggregate in these places in theasphalt.
Procedures for Rolling1. Rolling should be parallel to the center line of the roadway to reduce the number of times the roller must change direction.2. Succeeding passes should overlap one half of the wheel width of the roller. This action ensures that the aggregate becomes well embedded in the bitumen.3. Rolling should be completed before the bitumen hardens. This will ensure that the aggregate becomes well embedded in the bitumen.4. Succeeding passes should be made from the low side to the high side of the surface. This operation maintains the surface crown and prevents feathering at the edges.5. Rolling should be done at a slow speed.6. Rollers should be only wet enough to prevent bitumen from sticking to the wheels.7. . The power wheel of the roller should pass over the unrolled surface before the steering wheel(s) of the rollers. After rolling and curing, the surface is ready for traffic.
MULTIPLE-SURFACE TREATMENTA multiple-surface treatment is essentially the same as thesingle-surface treatment. However, the multiple-surfacetreatment consists of two or more successive layersof binder and aggregate. This type of treatment is done instages. Each stage is accomplished in the same manner asa single-surface treatment. The only difference isthat each additional layer of aggregate should be about onehalf of the size of the previous layer. This allows the smalleraggregate to interlock with the larger aggregate when rolled.