Mix design practice (bituminous mix) ce 463

O BJECTIVE O F B ITUMINOUS M IX D 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

Durability of bituminous mix is also refers to the ability of of the mixture to resist abrasion of the surface due to scraping action of tires combined with water The surface is more susceptible to abrasion if: (i) The void content is high allowing air and water to prematurely harden the bitumen (ii) Incompatibility between aggregate and bitumen, making it easier to strip bitumen from the aggregate (iii) The asphalt film thickness is not sufficient to protect the mix from the abrasive action of tires and water

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

DESIGN METHODS MARSHALL METHOD HVEEM METHOD MODIFIED HUBBARD-FILD METHOD

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 design 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

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

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 permeability If the above adjustments do not produce a stable mix, the aggregate may have to be change Stability & 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

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

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

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

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

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: All materials proposed for use meet the physical requirements of the project specifications Aggregate blend combinations meet the gradation requirements of the project specifications 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

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

BULK SPECIFIC GRAVITY DETERMINATION This test is performed according to ASTM D 1188 & ASTM D 2726 STABILITY & FLOW DENSITY & VOID ANALYSIS

CORRECTION FACTORS FOR STABILITY VALUES

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

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

Narrow range of acceptable bitumen contents

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

Relationship between VMA & Specification limit

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

Minimum % voids in mineral aggregate (VMA)

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)

Effect of Marshall compactive effort on VMA and air voids

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

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

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: 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 The specimen has a 152.4 mm dia by 95.2 mm ht The batch weights are typically 4 kg The equipment for compacting and testing are proportionately larger to accommodate the larger specimens

(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.

C.F. FOR MODIFIED MARSHALL METHOD FOR LARGE AGGREGATE

Design steps for a rational design of a bituminous mix Selection of aggregate Selection of aggregate grading Determination of specific gravity Preparation of specimen Determination of specific gravity of compacted bituminous mix Stability test on compacted bituminous mix Selection of Optimum Bitumen Content

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: Bitumen content corresponding to maximum stability Bitumen content corresponding to maximum unit weight Bitumen content corresponding to the median of design of designed limits of % air voids in total mix

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

TESTING EQUIPMENTS: Mold having dia. 152.4 mm is used 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

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 140 0 C 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

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 37.8 0 C, 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 60 0 C for atleast one hour in position under the compression machine

The compressive load is applied at a constant rate of deformation of 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

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: Stability Vs Bitumen content Unit wt. Vs Bitumen content % voids in total mix Vs Bitumen content % aggregate voids Vs Bitumen content

Criteria specified by the Asphalt Institute for the Design of Bituminous Mix The final selection of the mix design should be based on economics and suitability of the mix from the test requirements Property Light to Medium Traffic Heavy & very heavy traffic Stability, kg 545-910 910 Voids, total mix, % 2-5 2- 6

HVEEM METHOD OF BITUMINOUS MIX DESIGN (ASTM D 1560 & ASTM D 1561)

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 liters Beakers – 1500 ml Filter papers – 55 mm dia Timer Oil – SAE No. 10 lubricating 4 liters etc. Centrifuge- hand operated capable of producing 400 times gravity

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

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 m 2 /kg 0.41 0.82 1.64 2.87 6.14 12.29 32.77

Demonstration of calculation of surface area Sieve size % passing S.A. factor (m 2 /kg) Surface area (m 2 /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 m 2 /kg

C.K.E. Procedure for Fine Aggregate 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.

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

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 and Retained 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 60 0 C 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

Chart for determining surface constant for coarse material, Kc, from coarse aggregate absorption Fig. 6.3

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

Chart for computing oil ratio for dense-graded bituminous mixtures

Chart for correcting bitumen requirement due to increasing viscosity of bitumen

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

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

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 m 2 /kg C.K.E. = 5.6 % oil retained, coarse = 1.9 (corrected for sp gr this values is 1.7 %

From Fig. 6.2 determine Kf as 1.25 From Fig. 6.3 determine Kc as 0.8 From 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

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

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 ± 3 0 C in a oven equipped with forced draft air circulation After curing is complete, place batch mix in heating oven and reheat mixture to 110 0 C Then the batch mix ready for compaction

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 mm 2 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

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

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

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 60 0 C for 1 hour, after which a “leveling-off” load off 56 kN is applied by the “double-plunger” method and released immediately

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:

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

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 0 C 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

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

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

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

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]

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

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

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

… The stabilometer value is calculated as below: S = Ph D 22.2 Pv-Ph + 0.222 S = stabilometer value D = displacement on specimen Ph = horizontal pressure equal to stabilometer pressure gauge reading taken at the instant Pv is 2.76 Mpa [22.24 kN] total load Pv = Vertical pressure [typically 2.76 Mpa = 22.24 kN total load

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)]

Three Graphical Plots are prepared % age of bitumen content Vs Unit weight (g/cc) %age of bitumen content Vs % air voids %age of bitumen content Vs Hveem stability

C = L W (0.2H+0.0176 H 2 ) Where, C = Cohesiometer value L = Weight of shots in gm W = Diameter or width of specimen in cm H = 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

DESIGN CRITERIA BY HVEEM METHOD Light traffic = Design EAL < 10 4 Medium traffic = Design EAL b/w 10 4 and 10 6 Heavy traffic = Design EAL > 10 6 TEST VALUE CRITERIA 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

STEPS FOR SELECTING BITUMEN CONTENT 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 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

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

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

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

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/cm 2 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

The R-value of soil is calculated from the formula: R = 100 - 100 2.5 D 2 Pv Ph 1 1 Pv = vertical pressure applied (11.2 kg/cm 2 ) Ph = horizontal pressure transmitted at Pv = 11.2 kg/cm 2 D 2 = displacement of stabilometer fluid necessary to increase the horizontal pressure from 0.35 to 7 kg/cm 2 measured in number of revolutions of the calibrated pump handle

Mix design practice (bituminous mix) ce 463

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Mix design practice (bituminous mix) ce 463