PAVEMENT MATERIALS PAVEMENT MATERIALS ENGINEERINGENGINEERING

(CE-862) (CE-862) Lec-09

Fall Semester 2016 

Dr. Arshad Hussainarshad_nit@yahoo.com , Office Room#111, Tel:

05190854163, Cell: 03419756251

National Institute of Transportation (NIT)

School of Civil & Environmental Engineering (SCEE)

National University of Science and Technology (NUST)

NUST Campus, Sector H-12, Islamabad

ROAD AGGREGATESROAD AGGREGATES

Desirable properties of aggregates.

1) Resistance to crushing .2) Resistance to abrasion.3) Resistance to impact.4) Resistance to weathering.5) Water absorption.6) Porosity.7) Good adhesion.8) Good shape.9) Surface texture.10) Surface chemistry.

SUBBASESUBBASE A subbase is layer of material between

base and subgrade. Sometimes a granular material under a rigid pavement is called a subbase.

Subbase may consist of select materials, such as natural gravels, that are stable but that have characteristics which make them not completely suitable as base course. They may also be of stabilized soil or merely select borrow.

SUBBASESUBBASEThe purpose of a subbase is to

permit the building of relatively thick pavements at low cost. Thus , the quality of subbase can vary within wide limits , as long as the thickness design criteria are fulfilled.

BASEBASEA base course is defined as a layer

of granular material which lies immediately below the wearing surface of a pavement .

PURPOSE OF BASE COURSESPURPOSE OF BASE COURSES

Base and subbase courses under flexible pavements are primarily to increase the load supporting capacity by distributing the load through a finite thickness of pavement this will reduce shear and consolidation deformation in the subgrade.

PURPOSE OF BASE COURSESPURPOSE OF BASE COURSESBase courses are used under rigid

pavements for 1) Prevention of pumping.2) Protection against frost action.3) Prevention of volume change of

subgrade4) Drainage.5) Increased structural capacity.6) Expedition of construction.

PURPOSE OF BASE COURSESPURPOSE OF BASE COURSESTo prevent pumping a base course

must be relatively well graded, must be free from excessive fines and should be compacted to a relatively high density.

To provide drainage the base may or may not be a well graded material but it should contain little or no fines.

PURPOSE OF BASE COURSESPURPOSE OF BASE COURSESBase course designed for frost

action should be non frost susceptible and free draining.

Base course need not to be free draining to provide adequate structural capacity.

Base course should be well graded and should resist deformation due to loading.

PROPERTIES OF SOIL AGGREGATE MIXPROPERTIES OF SOIL AGGREGATE MIX

Density and stability: depends upon particle size distribution, particle shape, relative density, internal friction and cohesion.

An aggregate which contains little or no fines and is well graded gains its stability from grain to grain contact but usually has relatively low density but is pervious and non frost susceptible. This material is very difficult to handle during construction because of its noncohesive nature.

PROPERTIES OF SOIL AGGREGATE PROPERTIES OF SOIL AGGREGATE MIXMIX

An aggregate which contains sufficient fines to fill all the voids will still gain its strength from grain contact but with increased resistance against deformation. Its density is high, its permeability is low, and it may be frost susceptible. This material is moderately difficult to compact but is ideal from stability point, it will have relatively high shearing resistance.

An aggregate which contains great amount of fines has no grain to grain contact ,and the aggregate merely floats in the soil. Its density is low; it is practically impervious, and it is frost susceptible. In addition the stability of this type of mixture is greatly affected by adverse water conditions. The material is at times is quite easy to handle during construction and compacts quite readily.

PROPERTIES OF SOIL AGGREGATE MIX

PROPERTIES OF SOIL AGGREGATE MIX

Maximum CBR resulted when the quantity of fines was somewhat less than that indicated for maximum density.

CBR of mixtures made up of angular particles are usually somewhat greater than those containing mostly rounded particles .

PROPERTIES OF SOIL AGGREGATE MIX

Density as well as CBR increases as size of aggregate increased but optimum soil content decreased.

PROPERTIES OF SOIL AGGREGATE MIX

Permeability: The permeability characteristics of soil aggregate mixtures are dependent upon :

1) Grain size distribution.2) Type of coarse aggregate.3) Type of binder.4) Density.

Effect of plasticity: The liquid limit for base courses is 25 % and the plasticity index is 6 %.

Soundness: Soundness is defined as the ability of aggregate to withstand abrasion/ crushing. This is important from the standpoint of generation of fines under the action of rollers and traffic. Soft aggregate should not be used.

PROPERTIES OF SOIL AGGREGATE MIX

Aggregate which breakdown excessively under freezing and thawing should not be used.

Behavior under load : Laboratory test, as well as field performance, have indicated that the behavior of base course - subgrade combinations under load is reflected by the stability of base course itself.

PROPERTIES OF SOIL AGGREGATE MIX

Laboratory and field data indicate that a base course which contains quantity of fines slightly less than that required for maximum density will be stable.

If a granular base course is used for drainage purpose or for protection against frost action, it is essential that it remain open graded throughout the pavement life. This can be done by placing a thin blanket of sand or other fine granular material between the subgrade and base course.

PROPERTIES OF SOIL AGGREGATE MIX

GRADING REQUIREMENTSGRADING REQUIREMENTSThe purpose of gradation specifications

for base courses and sub bases is to assure adequate stability under repeated loads.

Proportioning materials of different specific gravities: Any gradation specification is valid only so long as the fine fractions and the coarse aggregates have approximately the same specific gravity.

GRADING REQUIREMENTSGRADING REQUIREMENTSAlthough the physical characteristics

of the soil aggregate mixture are dependent upon relative volumes of the course to fine aggregate. However it is not practical to attempt proportioning of materials on the basis of volume; therefore, specifications are always set up on the per cent by weight basis.

GRADING REQUIREMENTSGRADING REQUIREMENTS

If the coarse aggregate has a specific gravity considerably higher than that of the fine fraction, gradation will result in mixtures which are too rich. Conversely , if the specific gravity of the fine fraction is higher than that of the coarse aggregate, the quantity of fines will be low.

CONSTRUCTIONCONSTRUCTIONSoil aggregate mixtures: To ensure

adequate stability, base and subbase materials must be compacted to a high density . Moisture control is extremely important.

CONSTRUCTIONCONSTRUCTIONGranular base course materials

may be compacted in lifts ranging upto 6”, depending upon the type of compaction equipment. If smooth wheeled compactors are used , the lift should be controlled to about 4”.However if vibratory compactors are used , lifts upto 8 or 10” are permitted.

CONSTRUCTIONCONSTRUCTION

Field experience has indicated that compaction of base course materials to densities in excess of the modified AASHO values is quite common when vibrating compactors are used.

CONSTRUCTIONCONSTRUCTION

Care should be exercised to insure uniform distribution of the base course materials over the subgrade to prevent segregation.

Make certain that the clay binder and aggregate are thoroughly mixed.

AGGREGATE PRODUCTIONAGGREGATE PRODUCTIONAggregate production in the US is large

—some annual production figures include:Natural aggregates Sand and gravel: 1.13 billion metric tons

Crushed stone: 1.49 billion metric tons

Recycled aggregates: 200 million metric tons produced from demolition wastes (includes roads and buildings).

AGGREGATE PRODUCTIONAGGREGATE PRODUCTION Sand and gravel (estimated for 2003)

1.13 billion metric tons of sand and gravel produced in the US in 2003.

Value $5.8 billion Produced by 4,000 companies from 6,400

operations in all 50 states. Leading production states are: California, Texas, Michigan, Arizona, Ohio, Minnesota, Washington, Wisconsin, Nevada, and Colorado.

How were these aggregates used? 53% unspecified 20% concrete aggregates 11% road bases and road stabilization 7% construction fill 6% HMA and other bituminous mixtures 3% other applications

AGGREGATE PRODUCTIONAGGREGATE PRODUCTION Crushed stone (estimated for 2003)

◦ 1.49 billion metric tons of crushed stone produced in the US in 2003.

◦ Value $8.6 billion ◦ Produced by 1,260 companies from 3,300

operations in 49 states. Leading production states are: Texas, Florida, Pennsylvania, Missouri, Illinois, Georgia, Ohio, North Carolina, Virginia, and California.

◦ How were these aggregates used? 35% was for unspecified uses followed by construction aggregates mostly for highway and road construction and maintenance, chemical and metallurgical uses (including cement and lime production), agricultural uses, etc.

Recycled aggregates (1999)200 million metric tons of recycled

aggregates produced (or generated) in the US in 2000.

100 million metric tons of recycled asphalt paving materials recovered annually. 80% of this material is recycled with the other 20% going to landfills. Of the 80% that is recycled—2/3 used as aggregates for road base and 1/3 reused as aggregate for new HMA.

AGGREGATE PRODUCTIONAGGREGATE PRODUCTION

Recycled aggregates (1999)—cont.100 million metric tons of recycled

concrete is recovered annually. 68% of recycled concrete reused as road

base. 9% aggregate for HMA mixes 6% aggregate for new PCC mixes

AGGREGATE PRODUCTIONAGGREGATE PRODUCTION

Uniformly graded- Few points of contact- Poor interlock (shape dependent)

- High permeability Well graded

- Good interlock- Low permeability

Gap graded- Only limited sizes- Good interlock- Low permeability

TYPES OF GRADATIONS

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