mix design practice (bituminous mix) ce 463

85
O O BJECTIVE BJECTIVE O O F F B B ITUMINOUS ITUMINOUS M M IX IX D D ESIGN ESIGN . It is to determine a cost effective blend and gradation of aggregates and bitumen that yields a mix having: Sufficient bitumen to ensure a durable pavement Sufficient mix stability to satisfy the demands of traffic without distortion or displacement Sufficient voids in the total compacted mix to allow for a slight amount of bitumen expansion due to temperature increases without flushing, bleeding, and loss of stability

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Page 1: Mix design practice (bituminous mix) ce 463

OOBJECTIVEBJECTIVE O OFF B BITUMINOUSITUMINOUS M MIXIX D DESIGNESIGN

.

It is to determine a cost effective blend and gradation of aggregates and bitumen that yields a mix having:

Sufficient bitumen to ensure a durable pavement

Sufficient mix stability to satisfy the demands of traffic without distortion or displacement

Sufficient voids in the total compacted mix to allow for a slight amount of bitumen expansion due to temperature increases without flushing, bleeding, and loss of stability

Page 2: Mix design practice (bituminous mix) ce 463

Durability of bituminous mix is also refers to the ability of Durability of bituminous mix is also refers to the ability of of the mixture to resist abrasion of the surface due to of the mixture to resist abrasion of the surface due to scraping action of tires combined with waterscraping action of tires combined with water

The surface is more susceptible to abrasion if:The surface is more susceptible to abrasion if:

(i) (i) The void content is high allowing air and water to The void content is high allowing air and water to

prematurely harden the bitumenprematurely harden the bitumen

(ii) (ii) Incompatibility between aggregate and bitumen, Incompatibility between aggregate and bitumen,

making it easier to strip bitumen from the aggregatemaking it easier to strip bitumen from the aggregate

(iii) (iii) The asphalt film thickness is not sufficient to protect The asphalt film thickness is not sufficient to protect

the mix from the abrasive action of tires and water the mix from the abrasive action of tires and water

Page 3: Mix design practice (bituminous mix) ce 463

Maximum void content to limit the permeability of harmful air and moisture into the mix

Sufficient workability to permit efficient placement of the mix without segregation and without sacrificing stability and performance

For surface mixes, proper aggregate texture or hardness to provide sufficient skid resistance in unfavourable weather conditions

The final goal of mix design is to select a unique bitumen content that will achieve a balance among all the desired properties

Page 4: Mix design practice (bituminous mix) ce 463

DESIGN METHODS

MARSHALL METHOD

HVEEM METHOD

MODIFIED HUBBARD-FILD

METHOD

Page 5: Mix design practice (bituminous mix) ce 463

All mix design procedures involve preparing a set of trial mixture specimens using materials proposed for use on the project

All mix design procedures involve preparing a set of trial mixture specimens using materials proposed for use on the project

An estimation of the standard procedures will indicate that there are three key components of mix designAn estimation of the standard procedures will indicate that there are three key components of mix design

(i) Laboratory compaction of trial mix specimens

(ii) Stability (or strength) and volumetric testing, and

(iii) Analysis of results

(i) Laboratory compaction of trial mix specimens

(ii) Stability (or strength) and volumetric testing, and

(iii) Analysis of results

An additional step that is becoming more common s the evaluation of moisture susceptibility or the compatibility of the aggregate and the bitumen

An additional step that is becoming more common s the evaluation of moisture susceptibility or the compatibility of the aggregate and the bitumen

Page 6: Mix design practice (bituminous mix) ce 463

The laboratory compaction technique is intended to simulate the in-place density of bituminous mix after it has endured several years of traffic

Four compaction methods are currently in use:

Impact compaction, used in the Marshall mix design method

Kneading compaction, used in the Hveem mix design method

Several form of gyratory compaction

Compaction using vibratory impact hammers

Page 7: Mix design practice (bituminous mix) ce 463

There are several guidelines for adjusting the trial mix but it may not necessarily apply in all cases

Voids Low, Stability Low:- Voids may be increased in no. of ways

As a general approach to obtaining higher voids in the mineral aggregate the aggregate grading should be adjusted by adding more coarse ore more fine aggregate

It must be remembered, however, that lowering the bitumen content may decrease the durability of the pavement

Too much reducing in bitumen content may lead to brittleness, accelerated oxidation, and increased permeabilityIf the above adjustments do not produce a stable mix, the aggregate may have to be changeStability & void content of the mix may be increased by increasing the amount of crushed materials and / or decreasing the amount of material passing the 75µ

Page 8: Mix design practice (bituminous mix) ce 463

Voids Low, Stability Satisfactory:-

Low void content may eventually result in instability due to plastic flow or flushing after the pavement has been exposed to traffic for a period of time because of particle re-orientation and additional compaction

Insufficient void may also result because of inadequate bitumen content in finer mixes even though stability is initially satisfactory for specific traffic, however, durability will be affected

For these reasons, mixes low in voids should be adjusted by increasing or decreasing coarse & fine aggregates

Page 9: Mix design practice (bituminous mix) ce 463

Voids Satisfactory, Stability Low:-

Low stability when voids and aggregate grading are satisfactory may indicate some deficiencies in the aggregate

Consideration should be given to improving the coarse particle shape by crushing or increasing the %age of coarse aggregate in the mixture, or possibly increasing the maximum aggregate size

Aggregate particles with rougher texture and less rounded surfaces will exhibit more stability while maintaining or increasing the void content

Page 10: Mix design practice (bituminous mix) ce 463

Voids High, Stability Satisfactory:-

High voids contents are frequently associated with the mixes found to have high permeability

High permeability, by permitting circulation of air and water through the pavement may lead to premature hardening of the bitumen

Even though stabilities are satisfactory, adjustment should be made to reduce the voids

Small reduction may be accomplished by increasing the mineral dust content of the mix

It may be necessary to select or combine aggregates to a gradation which is closer to the maximum density grading curve

Page 11: Mix design practice (bituminous mix) ce 463

Voids High, Stability Low:-

Two steps may be necessary when the voids are high and stability is low

First voids are adjusted by the method discussed above

If this adjustment does not also improve the stability

The second step should be a consideration of aggregate quality as discussed in first & second cases

Page 12: Mix design practice (bituminous mix) ce 463

This method is applicable only to bituminous mixtures containing aggregates with max sizes of 25 mm or less

A modified Marshall method has been proposed for aggregates with maximum sizes up to 38 mm

MARSHALL METHOD OF MIX DESIGN

Steps preliminary to specimen preparation are:

(i) All materials proposed for use meet the physical requirements of the project specifications

(ii) Aggregate blend combinations meet the gradation requirements of the project specifications

(iii) For performing density and voids analyses, the bulk sp gr of all aggregates used in the blend and sp gr of the bitumen are determined

Page 13: Mix design practice (bituminous mix) ce 463

PREPARATO OF TEST SPECIMENS

At least 3 specimens for each combination of aggregates and bitumen content

Preparation of aggregates

Determination of mixing & compaction temperature

Preparation of mixtures

Packing the mold

Compaction of specimens

Page 14: Mix design practice (bituminous mix) ce 463

BULK SPECIFIC GRAVITY DETERMINATION

This test is performed according to ASTM D 1188 & ASTM D 2726

STABILITY & FLOW

DENSITY & VOID ANALYSIS

Page 15: Mix design practice (bituminous mix) ce 463

CORRECTION FACTORS FOR STABILITY VALUES

Page 16: Mix design practice (bituminous mix) ce 463

DETERMINATION OF PRELIMINARY DESIGN BITUMEN CONTENT

The design bitumen content of the bituminous mixture is selected by considering all of the design parameters

As an initial starting point, choosing the bitumen content at the median of the present air voids limits, which is four percent

All of the calculated and measured mix properties at this bitumen content should then be evaluated by comparing them to the mix design criteria as specified in MORT&H Cl. 500

If all of the design criteria are met, then this is the preliminary design bitumen content if not some adjustment is necessary or mix is redesign

Page 17: Mix design practice (bituminous mix) ce 463

SELECTION OF FINAL MIX DESIGN

The final selected mix design is usually the most economical one that will satisfactorily meet all of the established criteria

The design bitumen content should be a compromise selected to balance all of the properties. Normally, the mix design criteria will produce a narrow range of accept bitumen contents that pass all of the guidelines as shown by the example in Fig.5.6

Page 18: Mix design practice (bituminous mix) ce 463

Narrow range of acceptable bitumen contentsNarrow range of acceptable bitumen contents

Page 19: Mix design practice (bituminous mix) ce 463

EVALUATION OF VMA CURVE

In many cases, the most difficult mix design property to achieve is a minimum amount of voids in the mineral aggregate

The goal is to furnish enough space for the bitumen so it can provide adequate adhesion to bind the aggregate particles, but without bleeding when temperature rise and the bitumen expands

Normally, the curve exhibits a flattened U-shape, decreasing to a minimum value and then increasing with increasing bitumen content shown in Fig. 5.7 (a)

It is recommended that bitumen contents on the “wet” or right –hand increasing side of this VMA curve be avoided, even if the minimum air void and VMA criteria is met

Design bitumen content in this range have a tendency to bleed and or exhibit plastic flow when placed in the field

Page 20: Mix design practice (bituminous mix) ce 463

Relationship between VMA & Specification limitRelationship between VMA & Specification limit

Page 21: Mix design practice (bituminous mix) ce 463

Any amount of additional compaction from traffic leads to inadequate room for bitumen expansion, loss of aggregate –to-aggregate contact, and eventually, rutting and shoving in high traffic areas

Ideally, the design bitumen content should be selected slightly to the left of the low point of the VMA curve, provided none of the other mixture criteria are violated

When the bottom of the U-shaped curve falls below the minimum criteria level required for the nominal maximum aggregate size of the mix. This is an indication that changes to the job-mix-formula are necessary

Specifically, the aggregate grading should be modified to provide additional VMA

Page 22: Mix design practice (bituminous mix) ce 463

Minimum % voids in mineral aggregate (VMA)Minimum % voids in mineral aggregate (VMA)

Page 23: Mix design practice (bituminous mix) ce 463

IILUSTRATION OF VMAIILUSTRATION OF VMA

Page 24: Mix design practice (bituminous mix) ce 463

EFFECT OF AIR VOIDS

It should be emphasized that the design range of air voids (3 to 5%) is the level desired after several years of traffic

The air voids after the construction is about 8%

The bituminous mixtures that ultimately consolidate to less than 3% air voids can be expected to rut and shove, if placed in heavy traffic locations

Problem can occur if the final air content is above 5% or if the pavement is constructed with over 8% air voids initially. Brittleness, premature cracking, raveling, and stripping are all possible under these conditions (Fig. 5.8)

Page 25: Mix design practice (bituminous mix) ce 463

Effect of Marshall compactive effort on VMA and air voids

Page 26: Mix design practice (bituminous mix) ce 463

EFFECT OF VOIDS FILLED WITH BITUMEN

The main effect of the VFB criteria is to limit maximum levels of VMA and subsequently, maximum levels of bitumen content

VFB also restricts the allowable air void content for mixes that are near the minimum VMA criteria

Mix designed for lower traffic volumes will not pass the VFB criteria with a relatively high % air voids (5%) even though air void criteria range is met. The purpose is to avoid less durable mixes in light traffic situations.

Mix designed for heavy traffic will not pass the VFB criteria with relatively low % air voids (less than 3.5%) even though that amount of air voids is within the acceptable range

Because low air voids contents can be very critical in terms of permanent deformation

The VFB criteria helps to avoid those mixes that would be susceptible to rutting

Page 27: Mix design practice (bituminous mix) ce 463

The VFB criteria helps to avoid those mixes that would be susceptible to rutting in heavy traffic situations

The VFB criteria provide an additional factor of safety in the design and construction process in terms of performance

Page 28: Mix design practice (bituminous mix) ce 463

MODIFIED MARSHALL METHOD FOR LARGE AGGREGATE

This method has been developed by Kandhal of the National Centre for Bitumen Technology for mixes composed of aggregates with maximum size up to 38 mm

The procedure is basically the same as the original method except for these differences that are due to the larger specimen size that is used:

(a)The hammer weights 10.2 kg and has a 149.4.mm flat tamping face. Only mechanical operated device is used for the same 457 mm drop height

(b)The specimen has a 152.4 mm dia by 95.2 mm ht

(c)The batch weights are typically 4 kg

(d)The equipment for compacting and testing are proportionately larger to accommodate the larger specimens

Page 29: Mix design practice (bituminous mix) ce 463

(e) The number of blows needed for the larger specimen is 1.5 times (112 blows) that required of the smaller specimen (50 or 75 blows) to obtain equivalent compaction

(f) The minimu stability should be 2.25 times and the range of flow values should be 1.5 times the same criteria for the normal-sized specimens

(g) Similar to the normal procedure, these value should be used to convert the measure stability values to an equivalent value for a specimen with a 95.2 mm thickness, if the actual size varies, the following table should be used as C.F.

Page 30: Mix design practice (bituminous mix) ce 463

C.F. FOR MODIFIED MARSHALL METHOD FOR LARGE AGGREGATE

Page 31: Mix design practice (bituminous mix) ce 463

Design steps for a rational design of a bituminous mix

1.Selection of aggregate2.Selection of aggregate grading3.Determination of specific gravity4.Preparation of specimen5.Determination of specific gravity of compacted bituminous mix6.Stability test on compacted bituminous mix7.Selection of Optimum Bitumen Content

Page 32: Mix design practice (bituminous mix) ce 463

The optimum bitumen content for the mix design is found by taking the average value of the following three bitumen contents found from the graphs:

1.Bitumen content corresponding to maximum stability

2.Bitumen content corresponding to maximum unit weight

3.Bitumen content corresponding to the median of design of designed limits of % air voids in total mix

Page 33: Mix design practice (bituminous mix) ce 463

GRAPHS

Page 34: Mix design practice (bituminous mix) ce 463

MODIFIED HUBBARD-FIELD METHOD OF BITUMINOUS MIX DESIGN

This method was developed by P.Hubbard and F.C. Field

This method was in fact intended to design sheet bituminous mix

It was later modified for the design of bituminous mixes having coarse aggregate size up to 19 mm

Page 35: Mix design practice (bituminous mix) ce 463

TESTING EQUIPMENTS:

(I) Mold having dia. 152.4 mm is used

(II) Testing assembly consisting of internal ring dia of 146 mm through which the specimen

is extruded by applying load through the compression machine

(iii) Compacting equipment including tampers and compression machine of capacity of 5000 kg

Page 36: Mix design practice (bituminous mix) ce 463

TEST SET - UP

Page 37: Mix design practice (bituminous mix) ce 463

PROCEDURES:

Once the desired blend and gradation of the mineral aggregates is arrived

Batch weights are worked out for producing specimens of compacted size, 152 mm dia. & ht. 70 to 76 mm

These weighed aggregates and bitumen are heated to the temperature of approximately 1400C

Then, this mix is placed in the preheated mould and tamped in two layers by 30 blows each with the specified tampers

This specimen is tamped again on the reverse side by 30 blows by each of the two tampers

Page 38: Mix design practice (bituminous mix) ce 463

Then a static load of 4536 kg is applied on the specimen for two minutes

After this, the specimen is cooled in water to temperature less than 37.80C, maintaining the same compressive load

Finally, the specimen is removed, weighed and measured

This specimen is placed in the test mold assembly over the test ring of internal dia. of 146 mm and the plunger is loaded on the top of the specimen

The entire assembly is kept in a water bath maintained at 600C for atleast one hour in position under the compression machine

Page 39: Mix design practice (bituminous mix) ce 463

The compressive load is applied at a constant rate of deformationof 61 mm per minute and the maximum load in kg developed during the test is recorded as the stability value

The average stability value of all the specimens tested using a particular mix is found

A s in the case of Marshall method, the tests are repeated for other bitumen contents

The value of specific gravity, percent voids in total mix and % aggregate voids are calculated

Page 40: Mix design practice (bituminous mix) ce 463

For determining the OBC, first the bitumen content corresponding to 3 or 3.5 % voids in total mix is worked out from the graph

The corresponding stability is read from the stability curve

If this stability values are within the specified limits then the mix is considered satisfactory

If both stability and void requirements are not satisfied by a mix, the mix should be redesigned to correct the deficiency

The following graphs are plotted:

(i)Stability Vs Bitumen content(ii)Unit wt. Vs Bitumen content(iii)% voids in total mix Vs Bitumen content(iv)% aggregate voids Vs Bitumen content

Page 41: Mix design practice (bituminous mix) ce 463

GRAPHICAL PLOTS

Page 42: Mix design practice (bituminous mix) ce 463

Criteria specified by the Asphalt Institute for the Design of Bituminous Mix

Property Light to Medium Traffic

Heavy & very heavy traffic

Stability, kg 545-910 910

Voids, total mix, % 2-5 2- 6

The final selection of the mix design should be based on economics and suitability of the mix from the test requirements

Page 43: Mix design practice (bituminous mix) ce 463

HVEEM METHOD OF BITUMINOUS MIX DESIGN

(ASTM D 1560 & ASTM D 1561)

Page 44: Mix design practice (bituminous mix) ce 463

This method was developed by Francis N. Hveem who was materials & research engineer for the California Division of Highways

EQUIPMENT & MATERIALS REQUIRED FOR DETERINING THE APPROX. BITUMEN CONTENT

Kerosene – 4 litersBeakers – 1500 mlFilter papers – 55 mm diaTimerOil – SAE No. 10 lubricating 4 liters etc.Centrifuge- hand operated capable of producing 400 times gravity

Page 45: Mix design practice (bituminous mix) ce 463

The maximum size of aggregates used in the test mixes should not exceed 25 mm

In this method, specimen of 102 mm dia. & 64 mm

The principal features of the Hveem method of mix design are the surface capacity and Centrifuge Kerosene Equivalent (C.K.E.) test on the aggregates to estimate the bitumen requirements of the mix, followed by a stabilometer test, a cohesiometer test , swell test and a density voids analysis on test specimens of the compacted paving mixtures

Page 46: Mix design practice (bituminous mix) ce 463

The first step in the Hveem method of mix design is to determine the “approximate” bitumen content by the C.K.E.

The gradation of the aggregate or blend of aggregates employed in the mix is used to calculate the surface area of the total aggregate

Total %

passing

Max size

4.75 2.36 1.18 0.600 0.300 0.150 0.075

Surface area factor m2/kg

0.41 0.82 1.64 2.87 6.14 12.29 32.77

Page 47: Mix design practice (bituminous mix) ce 463

Demonstration of calculation of surface area

Sieve size % passing S.A. factor (m2/kg)

Surface area (m2/kg)

19.0mm 100 0.41 0.41

9.50mm 90 0.41 0.41

4.75mm 75 0.41 0.31

2.36mm 60 0.82 0.49

1.18mm 45 1.64 0.74

600mic 35 2.87 1.00

300mic 25 6.14 1.54

150mic 18 12.29 2.21

75mic 6 32.77 1.97

Surface area =

8.67 m2/kg

Page 48: Mix design practice (bituminous mix) ce 463

C.K.E. Procedure for Fine Aggregate

(a) Place exactly 100 g of dry aggregate [ representative of the

passing 4.75 mm material] in a tared centrifuge cup assembly fitted with a screen & a disk of filter paper

(b) Place bottom of centrifuge cup in kerosene until the aggregate becomes saturated

(c) Centrifuge the saturated sample for two minutes at a force of 400 times gravity [ turning by handle approx 45 revol.per minute

(d) Weigh after centrifuging and determine the amount of kerosene retained as a percent of the dry aggregate weight; this value is called the Centrifuge Kerosene Equivalent (C.K.E.)

(e) If the sp. Gravity of the aggregate sample is greater than 2.70 or less than 2.60 make a correction to the C.K.E.

Page 49: Mix design practice (bituminous mix) ce 463

Chart for determining surface constant for fine material, Kf from C.K.E.

Page 50: Mix design practice (bituminous mix) ce 463

SURFACE CAPACITY TEST FOR COARSE AGGREGATE

The capacity test for the larger aggregate involves these steps:

Place exactly 100 g of dry aggregate which passes the 9.5 mm andRetained on the 4.75 mm into a metal funnel (this fraction is considered to be representative of the coarse aggregate in the mix)

Immerse sample and funnel into a beaker containing SAE No. 10 lubricating oil at room temperature for 5 minute

Allow to drain for 2 minutes

Remove funnel and sample from oil and drain for 15 minutes at a temperature of 600C

Weigh the sample after draining and determining the amount of oil retained as a percent of the dry aggregate weight

Necessary correction has to be made if the sp gravity of aggregate is greater than 2.70 or less than 2.60

Page 51: Mix design practice (bituminous mix) ce 463

Chart for determining surface constant for coarse material, Kc, from coarse aggregate absorption

Fig. 6.3

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Chart for determining Kf and Kc to determine surface constant for combined aggregate, Km

Page 53: Mix design practice (bituminous mix) ce 463

Chart for computing oil ratio for dense-graded bituminous mixtures

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Chart for correcting bitumen requirement due to increasing viscosity of bitumen

Page 55: Mix design practice (bituminous mix) ce 463

ESTIMATED DESIGN BITUMEN CONTENT

Preliminary estimation of the design bitumen content

Using the C.K.E. value obtained and the chart in Fig. 6.2, determine the value Kf (surface constant for fine material)

Similarly, using the C.K.E. value and the chart in Fig. 6.3, determine the Kc (surface constant for coarse material)

Using the values obtained for Kf and Kc and the chart Fig. 6.4, determine the value Km (surface constant for fine & coarse material combined)

Km = Kf + correction to Kf

The correction of Kf obtained from Fig. 6.4 is positive if (Kc-Kf) is positive and is negative if (Kc-Kf) is negative

Page 56: Mix design practice (bituminous mix) ce 463

With values obtained for Km, surface area, and average specific gravity, use case 2 procedure of the chart in Fig. 6.5 to determine the oil ratio

Determine the bitumen content (bitumen ratio) for the mix using Fig. 6.6 corrected for the grade to be employed, using the surface area of the sample, the grade of the bitumen and the oil ratio from Fig 6.5

Page 57: Mix design practice (bituminous mix) ce 463

Specific gravity of coarse aggregate (bulk) = 2.45

Specific gravity of fine aggregate (apparent) = 2.64

Percent fine passing 4.75 mm sieve = 45

Then,

Avg. sp. gr. =

To demonstrate the use of the charts in Figs. 6.2 through 6.6

100

55

2.45+

45

2.64

Surface area of aggregate grading = 6.6 m2/kgC.K.E. = 5.6% oil retained, coarse = 1.9(corrected for sp gr this values is 1.7 %

Page 58: Mix design practice (bituminous mix) ce 463

From Fig. 6.2 determine Kf as 1.25From Fig. 6.3 determine Kc as 0.8From Fig. 6.4 determine Km as 1.15

From Fig. 6.5 determine the oil ratio for liquid bitumen as 5.2 %

From Fig. 6.6 determine design bitumen content (bitumen ratio) for AC-10 bitumen as 6.1% by weight of dry aggregate

Page 59: Mix design practice (bituminous mix) ce 463

PREPARATION OF TEST SPECIMENS

A series of stabilometer test specimens is prepared for a range of bitumen contents both above and below the approximate design bitumen content indicated by the CKE procedure

One specimen with the amount of bitumen as determined by the CKE

Two specimens above the CKE amount in 0.5 increments, and one 0.5 % below the CKE amount

For highly absorptive aggregates and non-critical mixes, increase the steps in bitumen content to 1.0% and use more specimens as necessary

Page 60: Mix design practice (bituminous mix) ce 463

PREPARATION OF BATCH WEIGHTS

About 1200 g of dry aggregates of desired gradation is taken and filled the mold having 101.6 mm dia. & 63.5 mm ht. When the aggregates and bitumen have reached the desired mixing temperature, transfer the batch mix into a suitable flat pan and cure for 2 to 3 hrs at a temperature of 146 ± 30 C in a oven equipped with forced draft air circulation

After curing is complete, place batch mix in heating oven and reheat mixture to 1100C

Then the batch mix ready for compaction

Page 61: Mix design practice (bituminous mix) ce 463

COMPACTION

The compaction of the test specimen is accomplished by means of the mechanical compactor that imparts a kneading action type of consolidation by a series of individual impressions made with a ram having a face shaped

With each push of the ram, a pressure of 3.45 Mpa (500psi) is applied, subjecting the specimen to a kneading compression over an area of approximately 2000 mm2

Each pressure is maintained for approximately 0.4 sec.

Place the compaction mold in the mold holder and insert a 100 mm dia paper disk to cover the base plate. So the base plate will act as a free-fitting plunger during the compaction operation

Page 62: Mix design practice (bituminous mix) ce 463

Spread the prepared mixture uniformly on the preheated feeder trough

Using a paddle that fits the shape of the trough, transfer approximately one-half of the mixture to the compaction mold

Rod the portion of the mix in the mold 20 times in the centre of the mass and 20 times around the edge with the round-nose steel rod

Transfer the remainder of the sample to the mold and repeat the rodding procedure

Place the mold assembly into position on the mechanical compactor and apply approximately 20 tamping blows at 1.7 MPa to achieve semi-compacted

Page 63: Mix design practice (bituminous mix) ce 463

Condition of the mix so that it will not be unduly disturbed when the full load is applied

The exact no. of blows to accomplish the semi-compaction shall be determined by observation

The actual no. of blows may vary between 10 & 50, depending upon the type of material and it may not ne possible to accomplish the compaction in the mechanical compactor because of undue movement of the mixture under the compactor foot

In such instances use 178 kN static load applied over the total specimen surface by the double plunger method, in which a free-fitting plunger is placed below & on top of the sample

Page 64: Mix design practice (bituminous mix) ce 463

Apply the load at the rate of 1.3 mm per minute and hold for 30 ± 5 seconds

After the semi-compaction, remove the steel shim and release mold tightening screw sufficiently to allow free up-and –down movement of mold and about 3 mm side movement of mold

To complete compaction in the mechanical compactor, increase compactor foot pressure to 3.45 Mpa and apply 150 tamping blows

Place the mold and specimen in an oven at 600C for 1 hour, after which a “leveling-off” load off 56 kN is applied by the “double-plunger” method and released immediately

Page 65: Mix design practice (bituminous mix) ce 463

SPECIMEN FOR SWELL TEST

Prepare the compation mold by placing a paraffin-impregnated strip of ordinary wrapping paper 19 mm wide, around the inside of the mold 13 mm from the bottom to prevent water from escapping from between the specimen and the mold during the water immersion period of the test

The paper strip is dipped in melted paraffin and applied while hot

Compaction molds are not preheated for swell test specimens

The remainder of the compaction procedure for swell test specimens is the same as for the stabilometer test specimens except for:

Page 66: Mix design practice (bituminous mix) ce 463

When compaction is completed in the mechanical compactor, remove mold and specimen from compactor, invert mold and push specimen to the opposite end of mold

Apply a 56 kN static load [head speed 6 mm/min] with the original top surface supported on the lower platen of the testing press

It is advisable to place a piece of heavy paper under the specimen to prevent damage to this lower platen

Page 67: Mix design practice (bituminous mix) ce 463

TESTS AND ANALYSES ARE NORMALLY PERFORMED IN THE ORDER LISTED

Stabilometer Test

Bulk Density Determination

Swell Test

Stabilometer Test

Place the compacted specimens for stabilometer tests in oven at 60 ± 3 0C for 3 to 4 hours

Adjust compression machine for a head speed of 1.3 mm/min with no load applied

Check displacement of stabilometer with a stailometer with a calibration cylinder and if necessary adjust to read 2.00 ± 0.05 turns

Page 68: Mix design practice (bituminous mix) ce 463

Stabilometer Test

Adjust the stabilometer base so that the distance from the bottom of the upper tapered ring to the top of the base is 89 mm

For specimens having overall ht. outside the range between 61 mm & 66 mm, stabilometer should be corrected as indicated in Fig. 6.14

Remove the mold with its specimen from the oven and place on top of stabilometer. Using the plunger, hand lever and fulcrum, force the specimen from the mold into the stabilometer

Place follower on top of specimen and position the entire assembly in compression machine for testing

Page 69: Mix design practice (bituminous mix) ce 463

Stabilometer Test

Using a displacement pump, raise the pressure in the stabilometer system until the gauge (horizotanl pressure) reads exactly 34.5 kPa (5psi)

Close displacement pump valve, taking care not to disturb the 34.5 kPa initial pressure (This step is omitted on stabilometers that are not provided with the displacement pump valve

Apply test loads with compression machine using a head speed of 1.3 mm/min

Record readings of stabilometer test gauge at vertical test loads of 13.4, 22.3, and 26.7 kN

Page 70: Mix design practice (bituminous mix) ce 463

Stabilometer Test

Immediately after recording the horizontal pressure reading under maximum vertical load 26.69 kN, reduce total load on specimen to 4.45 kN

Open the displacement pump angle valve and by means of the displacement pump, adjust test gauge to 34.5 kPa (This will result in a reduction in the applied press load which is normal and no compensation is necessary)

Adjust dial gauge on pump to zero by means of small thumbscrew

Page 71: Mix design practice (bituminous mix) ce 463

Stabilometer Test

Turn displacement pump handle smoothly and rapidly (two turns per second) and to the right (clockwise) until a pressure of 690kPa is recorded on the test gauge

During this operation the load registered on the testing press will increase and in some cases exceed the initial 4.45kN load. This change in load is normal and no adjustment is required

Record the exact number of turns required to increase the test gauge reading from 34.5 kPa to 690 kPa as the displacement on specimen [2.5 mm dial reading is equivalent to one turn displacement]

Page 72: Mix design practice (bituminous mix) ce 463

Stabilometer Test

After recording the displacement, first remove the test load and reduce pressure on the test gauge to zero by means of the displacement pump; then reverse the displacement pump and additional three turns and remove specimen from stabilometer chamber

BULK DENSITY DETERMINATION

After completion of the stabilometer tests, the specimens have cooled to room temperature

The procedure for this test is presented in ASTM D 1188, ASTM D 2726

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SWELL TEST

Allow compacted swell test specimen to stand at room temperature for at least one hour (This is done to permit rebound rebound after compaction)

Place the mold and specimen in 190 mm dia x 64 mm deep aluminum pan

Place the perforated bronze disk on specimen, position the tripod with dial gauge on mold and set the adjustable stem to give a reading of 2.54 mm on the dial gauge

Introduce 500 ml of water into the mold on top of the specimen and the measure distance from the top of the mold to the water surface with the graduated scale

Page 74: Mix design practice (bituminous mix) ce 463

SWELL TEST

After 24 hours, read the dial gauge to the nearest 0.025 mm and record the change as well

Also, measure the distance from the top of the mold to the water surface with the graduated scale and record the change as permeability or the amount of water in ml that percolates into and / or through the test specimen

Page 75: Mix design practice (bituminous mix) ce 463

…The stabilometer value is calculated as below:

S = Ph D

22.2

Pv-Ph + 0.222

S = stabilometer valueD = displacement on specimenPh = horizontal pressure equal to stabilometer pressure gauge reading taken at the instant Pv is 2.76 Mpa [22.24 kN] total loadPv = Vertical pressure [typically 2.76 Mpa = 22.24 kN total load

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Density & Voids Analysis

Using the specific gravity of the test specimens and the maximum specific gravity of the paving mixture determine using ASTM D 2041

Compute the % air voids as

Va = 100 x (Gmm-Gmb)/(Gmm)

Where, Gmm = maximum sp gr of paving mixture

= 100/ [(Ps/Gse or Gsb + Pb/Gb)

Ps = aggregate content, % by total wt of mixture

Gse = effective sp. gr of aggregate

= (Pmm-Pb)/ [(Pmm/Gmm)- (Pb/Gb)]

Page 77: Mix design practice (bituminous mix) ce 463

Three Graphical Plots are prepared

1. % age of bitumen content Vs Unit weight (g/cc)

2. %age of bitumen content Vs % air voids

3. %age of bitumen content Vs Hveem stability

Page 78: Mix design practice (bituminous mix) ce 463

C = L

W (0.2H+0.0176 H2)

Where,

C = Cohesiometer valueL = Weight of shots in gmW = Diameter or width of specimen in cmH = Height of specimen cm

Using the specific gravity of the test specimens and the apparent specific gravity of aggregate the percent voids in the total mix is calculated

Page 79: Mix design practice (bituminous mix) ce 463

DESIGN CRITERIA BY HVEEM METHOD

TEST VALUECRITERIA

LIGHT TRAFFIC

MEDIUM TRAFFIC

HEAVY TRAFFIC

Stabilometer value, R

> 30 > 35 > 37

Cohesiometer value, C

> 50 > 50 > 50

Swell, mm < 0.762 < 0.762 < 0.762

Air void, % > 4 > 4 > 4

Light traffic = Design EAL < 104

Medium traffic = Design EAL b/w 104 and 106

Heavy traffic = Design EAL > 106

Page 80: Mix design practice (bituminous mix) ce 463

STEPS FOR SELECTING BITUMEN CONTENT

(a) Using the Fig 6.17 insert in step (1) of the pyramid, the bitumen contents used for preparing the series of mix design specimens. Insert the bitumen contents in order of increasing amounts from left to right with the maximum bitumen content used in the square on the right

(b) Select from step (1) the three highest bitumen contents that do not exhibit moderate or heavy surface flushing & record on step (2). Surface flushing or bleeding is considered “slight” (acceptable) if the surface has only a slight sheen. It is considered “moderate” (unacceptable) if sufficient free bitumen is apparent to cause paper to stick to the surface but no distortion is noted

Page 81: Mix design practice (bituminous mix) ce 463

Surface flushing is considered “heavy” (unacceptable) if there is sufficient free bitumen to cause surface pudding or specimen distortion after compaction

(c) Select from step (2) the two highest bitumen contents that provide the specified minimum stabilometer value and enter them in step (3)

(d) Select from step (3) the highest bitumen content that has at least 4.0% air voids and enter in step (4)

(e) The bitumen content in step (4) is the design bitumen content. However, if the maximum bitumen content used in the design set step (1) is the bitumen content entered on step (4), additional specimens must be prpepared with increased bitumen content in 0.5% increments and a new design bitumen content determination should be made

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PYRAMID USED IN DESIGN OF BITUMEN CONTENT

Step 2 Specimens with no more than slight flushing

Step 1 Design series

Step 3 Specimens meeting minimum stability

Step 4 maximum bitumen content with 4 or more % air voids

Page 83: Mix design practice (bituminous mix) ce 463

FOR DETERMINING R-VALUE OF SOIL SUBGRADE WITH THE HELP OF STABILOMETER TEST

Page 84: Mix design practice (bituminous mix) ce 463

For evaluating the value of resistance value (R-value) of soil sugrade material, stabilometer is employed

The compaction is done using a kneading compactor with 24.6 kg/cm2 pressure, 100 times

After the compaction, a load is applied at a rate of 907 kg/minute to record the exudation pressure required to force water out of the specimen

Expansion pressure is also noted permitting the specimen to remain in water for 16 to 20 hours

The stabilometer resistance R-value is determined by placing the specimen in the stabilometer and applying the lateral and vertical pressures as specified

Page 85: Mix design practice (bituminous mix) ce 463

The R-value of soil is calculated from the formula:

R = 100 - 100

2.5

D2

Pv

Ph

1 1

Pv = vertical pressure applied (11.2 kg/cm2)Ph = horizontal pressure transmitted at Pv = 11.2 kg/cm2

D2 = displacement of stabilometer fluid necessary to increase the horizontal pressure from 0.35 to 7 kg/cm2

measured in number of revolutions of the calibrated pump handle