EN_TCVN8820-2011

3.16 Maximum Specific Gravity Specific gravity of asphalt concrete mixture not having air void air void: 0, symbolized as Gmm.3.17 Bulk Specific Gravity The ratio of a compacted HMA weig

VIETNAMESE STANDARD TCVN 8820 : 2011

Standard Practice for Asphalt Concrete Mix Design Using Marshall Method

TABLE OF CONTENT

1 Application scope 5

2 Reference 5

3 Terms and Definition 6

4 Classification of asphalt concrete 8

5 Principle of asphalt concrete mix design using Marshall method 9

6 Bases for asphalt concrete mix design using Marshall method 9

7 Stages and content of asphalt concrete mix design 10

8 Procedure of asphalt concrete mix design using Marshall method 13

9 General requirements for Site Laboratory 25

Appendix A (for reference) Guideline for mixing design 27

Appendix B (for reference) Volumetric characteristics of asphalt concrete mixture Report on AC mix design with Marshall method……….34

Foreword

TCVN 8820: 2011 is compiled by Institute of Transport Science and Technology, proposed by MOT, authenticated by Directorate for Standards, Metrology and Quality, declared by Ministry of Science and Technology

STANDARD PRACTICE FOR ASPHALT CONCRETE MIX DESIGN USING MARSHALL METHOD

1 Application scope

1.1 This standard sets out guidelines of asphalt concrete mix design using Marshall method

1.2 This standard applies to the type of dense asphalt concrete mixture using binder as asphalt or polymer asphalt

1.3 For types of Gap-graded HMA, Open-graded HMA, and stone matrix asphalt, in addition to the application of this standard for mixture design, it also applies additional related standard specified in correspondent specification for construction of asphalt concrete pavement and acceptance

1.4 Technical requirements as bases for the acceptance of AC mix design are regulated in

specification for construction of asphalt concrete pavement and acceptance

2 Reference

Following reference documents are necessary for the application of this Standard For reference documents with issuance year specified, the version of that year will be applied For reference

document excluding the issuance year, the most updated version, including modifications, will be applied

TCVN 7572-2: 2006 Aggregates for concrete and mortar – Test methods - Part 2: Determination of particle size distribution

TCVN 7501:2005 - Bitumen − Test method for determination of density (Pycnometer method) TCVN 8860-1: 2011 Asphalt Concrete – Test methods – Part 1: Determination of Marshall Stability and Plastic Flow

TCVN 8860-4: 2011 Asphalt Concrete – Test methods – Part 4: Determination of Maximum Specific Gravity and Density of loose Bituminous Paving Mixtures

TCVN 8860-5: 2011 Asphalt Concrete – Test methods – Part 5: Determination of Bulk Specific Gravity and Unit Weight of Compacted Bituminous Mixtures

TCVN 8860-9: 2011 Asphalt Concrete – Test methods – Part 9: Determination of Air Voids.

TCVN 8860-10: 2011 Asphalt Concrete – Test methods – Part 10: Determination of Voids in Mineral Aggregate

TCVN 8860-11: 2011 Asphalt Concrete – Test methods – Part 11: Determination of Voids filled with asphalt

TCVN 8860-12: 2011 Asphalt Concrete – Test methods – Part 12: Determination of Remaining Stability

TCVN 8819 : 2011 Specification for construction of asphalt concrete pavement and acceptance

TCVN 4195:1995 Soil - Method of laboratory determination of specific weight AASHTO T 84-2000

Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate

AASHTO T 85-2000 Standard Method of Test for Specific Gravity and Absorption of Coarse

Aggregate

3 Terms and definition

3.1 Hot mix asphalt-HMA

The mixture includes aggregates (macadam, sand, mineral powder) with a defined mixing ratio, dried and mixed evenly and mixed with asphalt in accordance with designed ratio

3.2 Dense-graded HMA

An AC mixture type includes coarse aggregate, medium-sized aggregate and fine aggregate who volumes are relatively equal, so that these aggregates are well-compacted at compaction Dense-graded HMA has small air void content, usually 3-6%

3.3 Gap-graded HMA

An AC mixture type includes a great amount of coarse aggregate fine aggregate, and a very small amount of medium aggregate Grading curve of this type tends to be nearly horizontal at medium aggregate zone With this type, coarse aggregates are well-associated to each other, but tend to be segregated during spreading Gap-graded HMA usually have air void content greater than Dense-graded HMA

Porous asphalt for the construction of base course, in which mineral powder is not used commonly, has air void from 7% to 12%

3.5 Asphalt concrete with high roughness - higher slip resistance capacity

It is used for surface coating, which helps to prevent water splashed caused by vehicle running at high speed, increase slip resistance and significantly reduce road noise from running vehicles

Porous asphalt is usually used with air void content of 15-22% (Open graded friction course – OGFC

or Porous friction course - PFC) or Gap-graded HMA with air void content of 10-15% (Very thin friction course - VTO) The modified asphalt should be used to produce this kind of AC

3.6 Stone matrix asphalt or Stone mastic asphalt -SMA

Is a type of gap-graded HMA mixture This asphalt concrete mixture includes asphalt, aggregate and fiber SMA usually contains mineral powder and asphalt volume higher than Dense-graded HMA.SMA has a wide range of air void content, from 2% to 8%, depending on the use of SMA for surface coarse or base course

3.7 Maximum size of aggregate

The maximum aggregate size is defined as the smallest sieve size that requires 100% passing

In this Standard, square-eye sieve is used for aggregate content test.

3.8 Nominal maximum size of aggregate

Nominal maximum aggregate size is the largest sieve that retains 10% or more of the total aggregate mixture

3.9 Coarse aggregate

Coarse aggregate includes the particles that retain on 4.75 mm sieve They are mineral products from crushed rock or natural gravel, also called as macadam

3.10 Fine aggregate

Fine aggregate includes the particles that all passes through 4.75 mm sieve and retain on 0.075

mm sieve They are natural mineral products (natural sand) or products from crushed rock, also called

by mass of aggregates (coarse aggregate, fine aggregate, mineral filler)

Percent by mass of AC mixture, symbolized as Pb, is applied widely in the world and in this Standard.3.13 Optimum asphalt content

Asphalt content is determined when designing AC, corresponding to a designated aggregate mixing rate, meeting all technical requirements specified for the aggregate and AC regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance

3.14 Absorbed Asphalt Content

Amount of asphalt adsorbed by aggregate through voids on surface, expressed as the percent by mass of aggregate; symbolized as Pba

3.15 Effective Asphalt Content

Effective asphalt content is the total asphalt content minus the asphalt absorbed by the aggregate, on

a volume basis, symbolized as Pbe, expressed by percent by mass of AC mixture Effective asphalt content makes up the outer cover of aggregates and determines physical-mechanical properties of AC mixture

3.16 Maximum Specific Gravity

Specific gravity of asphalt concrete mixture not having air void (air void: 0), symbolized as Gmm.3.17 Bulk Specific Gravity

The ratio of a compacted HMA weight to the weight of an equal volume of water at a same

3.20 Voids in the Mineral Aggregate

Voids in mineral aggregate, VMA, are the air-void spaces that exist between the aggregate particles in

a compacted HMA, including air voids and effective asphalt content VMA is represented by the percentage in the compacted HMA mass

3.21 Voids Filled with Asphalt

The voids filled with asphalt (VFA) is the percentage of voids in the mineral aggregate (VMA) filled

with effective asphalt content

4 Classification of asphalt concrete

Some major classifications as follows:

4.1 Classification by the biggest nominal size of the aggregate particle

According to this classification, asphalt concrete is usually classified into types with the biggest

nominal particle size as: 37.5 mm; 25.0 mm; 19.0 mm; 12.5 mm; 9.5 mm and 4.75 mm (corresponding

to the classification according to the biggest particle size of 50 mm, 37.5 mm, 25.0 mm, 19.0 mm, 12.5

mm and 9.5 mm)

4.2 Classification by property of graded mix

According to property of graded mix, asphalt concrete is classified into:

a) Dense graded mix;

b) Gap graded mix;

c) Open graded mix

4.3 Classification by air void

According to air void, asphalt concrete is classified into:

- Dense asphalt concrete with air void of 3% - 6%

- Void asphalt concrete with air void is greater than 6 %

4.4 Classification by function in pavement structure

According to function in pavement structure, asphalt concrete is classified into:

- Asphalt concrete with high roughness, increased slip resistance: used for high-level motorways, highways, dangerous road sections This layer is coated on the surface of asphalt concrete, shortly after construction of underneath asphalt concrete layers or coated when upgrading the pavement

- Surface course mixture, including:

+ Wearing course mixture: usually apply dense asphalt concrete

+ Binder course mixture: usually apply dense asphalt concrete

- Both dense asphalt concrete and void asphalt concrete can be used Void asphalt concrete is

cheaper because of not using mineral powder and having lower asphalt content comparing to dense asphalt concrete

- Used for surface course at area having vehicle load not so great, at sidewalks, and at lane for bicycle and non-motored vehicles It can be used as a thin compensation layer before spreading asphalt concrete Aggregate of Sand-asphalt mixture is crushed sand, natural sand or a mixture of both

5 Principle of asphalt concrete mix design using Marshall method

Asphalt Concrete Mix Design Using Marshall Method aims to find the optimum asphalt content

corresponding to the selected aggregate mixture The mix design must comply with the following requirements:

- All the materials used (crushed stone, sand, mineral powder, asphalt) must satisfy

physical-mechanical criteria prescribed in Specification for construction of asphalt concrete pavement and acceptance

- Grading curve of the aggregate mixture after mixing must be within the limits of the grading envelope prescribed in Specification for construction of asphalt concrete pavement and acceptance

- The optimum asphalt content selected should satisfy criteria related to volume properties (air void, voids in the mineral aggregate, etc.), testing criteria according to Marshall method (stability, flow, etc.),

and additional criteria (if any) in accordance with Specification for construction of asphalt concrete pavement and acceptance.

6 Bases for asphalt concrete mix design using Marshall method

6.1 In Specification for construction of asphalt concrete pavement and acceptance, bases for asphalt concrete mix design and selection of optimum asphalt content are prescribed as follows:

- Technical requirements of physical-mechanical properties of coarse aggregate (macadam); fine aggregate (sand); mineral powder (asphalt concrete type using mineral powder)

- Limits of grading envelope of aggregate mixture: sieve size, sieve passing limits (upper, lower bounds) for each sieve size

- The appropriate asphalt type and technical requirements of physical-mechanical properties of asphalt; The reference asphalt level (as percentage in total volume of asphalt concrete mixture)

- Temperature for mixing asphalt concrete and temperature of casting sample of asphalt mixture by Marshall Method

- Sample compaction by Marshall method (conventional Marshall method, upgraded Marshall

method), number of compaction blow per face

- Technical requirements of volumetric criteria of asphalt concrete sample compacted by Marshall method: Air voids (Va); Voids in the Mineral Aggregate (VMA), voids filled with asphalt (VFA)

- Technical requirements of criteria of asphalt concrete sample by Marshall method: Stability, Flow, retained Marshall stability

- Technical requirements of other criteria related to the quality of materials, quality of asphalt concrete (if prescribed in Specification for construction of asphalt concrete pavement and acceptance)

6.2 The mix design of asphalt concrete by Marshall method must satisfy the above mentioned criteria

7 Stages and content of asphalt concrete mix design

Mix design of asphalt concrete is related closely to the construction progress of the construction work Mix design of asphalt concrete includes 4 stages:

- Stage 1: Preliminary design or cold bin mix design;

- Stage: Hot bin mix design;

- Stage 3: Job-mix formula verification;

- Stage 4: Control routine construction

Each stage in the design has its own role All stages are important, and it cannot skip any stage The content of asphalt concrete mix design at each stage is summarized in Figure 1

7.1 Preliminary design (Stage 1)

7.1.1 The main purpose of the preliminary design is to determine quality of aggregates available at construction site; compare with technical requirements to determine the suitability or not; and to justify

if the aggregate materials can be used to produce asphalt concrete which satisfy requirements of grain composition and criteria prescribed for asphalt concrete or not

7.1.2 In case where there are multiple sources of construction material, it should conduct multiple designs with different sources of material in order to determine an aggregate mixture with lowest price and the satisfaction of all technical requirements set out

7.1.3 At this stage, material samples for the design are taken from supply source or cold bin of mixing plant Grain composition of aggregate mixture are typically selected within the restricted domain of the grain composition chart prescribed in Specification for construction of asphalt concrete pavement and acceptance

7.1.4 The order of asphalt concrete mix design: 7 steps (Figure 1), see Section 8 for details

7.1.5 Meaning of preliminary design:

- To confirm the suitability of aggregates and the asphalt concrete mixture using these aggregates regarding to technical requirements of the project This stage is particularly meaningful if there are no data about the aggregate sources available at the construction site;

- As a basis for calculating construction cost;

- As a basis to carry out hot bin mix design

7.2 Hot bin mix design (Stage 2)

7.2.1 The purpose of this stage is to find the actual grading composition of the aggregate mixture and optimal asphalt content when producing asphalt concrete mixture at batching plant Grain composition

of aggregates in this stage shall be the same as at preliminary design stage

7.2.2 This stage shall be carried out after having results from preliminary design

7.2.3 The order of asphalt concrete mix design: 7 steps (Figure 1), similar as preliminary design stage; the difference: aggregates are taken from hot bin of batching plants for test and design

Figure 1: Stages and design order of asphalt concrete mixture

7.2.4 Right before implementing hot bin mix design, it should carry out calibration for cold bins of the batching plant and set up the chart representing the relationship between cold aggregate provision speed and conveyor speed The implementation as follows:

- Adjust the size of bin so that is will be equal or 3 times as the size of the biggest particle of the aggregate

- Operate the sand/aggregate conveyor of the batching plant with speed of 20%, 50% and 70% of the maximum speed Establish the curve representing the relationship between the aggregate provision speed (ton/hour) and conveyor speed (m/minute) for macadam and sand

- Based on the relationship curve of aggregate provision speed and conveyor speed, conveying speed for macadam and sand shall be calculated to achieve the ratio of macadam and sand under mix results in Step 2 of the preliminary design stage (Figure 1)

- Bring the entire batch plant into operation with conveyor speed for macadam and sand (similar to case of mass production, but not including the mix of aggregate with asphalt and mineral powder)

- When the batching plant in state of steady operation, aggregate sample from reserve hot bins (aggregate from each hot bin is regarded as one type of aggregate), mineral powder sample is taken

to analyze grain composition Mixing ratio of aggregates shall be calculated as Step 2 of the

preliminary design Conveyor speed shall be adjusted so that the grading curves will be similar to that

of Step 2 of the preliminary design

7.2.5 Meaning of Hot bin mix design:

- Prove the capability of producing asphalt concrete mixture at batching plant;

- The produced asphalt concrete mixture complies with technical requirements for the construction work;

- Bases for trial production and trial construction

7.2.6 If laboratory test data indicates that the asphalt concrete mixture satisfies technical requirements set forth, trial production of asphalt concrete mixture at batching plant and trial construction at site will

be carried out

7.3 Job-mix formula verification (Stage 3)

7.3.1 This stage includes five steps as follows (Figure 1):

- Step 1: Trial production - Based on results from of hot bin mix design, produce from 60 to 100 tons of asphalt concrete mixture at batching plant

- Step 2: Trial construction – Take asphalt concrete mixture from trial production to perform trial construction on a section of 200 - 300 m

- Step 3: Inspection on the trial mixed asphalt concrete (laboratory test for asphalt concrete produced

at batching plant)

- Step 4: Inspection on the asphalt concrete mixture after trial construction at site

- Step 5: Approval for the production formula of asphalt concrete

7.3.2 If test results at laboratory and site indicate that the trial produced asphalt concrete mixture complies with technical requirements regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance and is highly practical which can be constructed by available equipment, ensuring requirements of density, roughness and geometrical dimensions, etc., the Contractor could submit the production formula to the Consultant and the Employer for approval Production formula of asphalt concrete includes the following contents:

- Aggregate and asphalt sources for asphalt concrete mixture;

- Results of experiments on physical-mechanical properties of asphalt, macadam aggregate, sand, mineral powder comply with regulation in Specification for Construction of Asphalt Concrete Pavement and Acceptance;

- Grading composition of aggregate mixture;

- Ratio of aggregates: macadam, sand, mineral filler at cold bin and hot bin;

- Design results of asphalt concrete mixture and optimum asphalt content;

- The specified temperature values at: mixing, discharging the mixture from the mixer, transporting to the site, spreading, rolling;

- The construction plan at site such as: the thickness of the unrolled asphalt concrete layer, rolling diagram, rolling number per point, the surface roughness, etc

7.3.3 The approved production formula is the basis for all proceeding works: Production, construction, acceptance and final settlement between the Contractor and the Employers

7.4 Control routine construction (Stage 4)

Control routine construction includes two steps as follows (Figure 1):

- Step 1: Quality control during production, the quality control at this step is similar to Step 3 of mix formula verification

Job Step 2: Quality control after construction Job similar to Step 4 of JobJob mix formula verification;

7.4.1 Quality control during production

7.4.1.1 The purpose of this step is to control the quality stability of the asphalt concrete, ensuring that the tolerance of aggregate gradation and the asphalt content in comparison to production formula of asphalt concrete is within the specified limits regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance

7.4.1.2 This work is carried out under a defined plan with a certain sampling frequency Samples of hot aggregate and asphalt concrete mixture are taken from batching plant The purpose of this work is

to check the asphalt concrete produced daily then compare with the approved production formula to detect abnormal changes and have proper adjustments

7.4.1.3 When excessive changes are detected (quality of input materials, major variations in material quality, etc.), beyond the control capability of the batching plant, it should redesign the asphalt

concrete mixture and reconstruct the production formula of asphalt concrete

7.4.1.4 Frequency of sampling for inspection and inspection criteria for this stage is regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance

7.4.2 Quality control after construction

7.4.2.1 This work includes many different items, in which sample drilling to determine the density is directly related to the design of asphalt concrete mixture

7.4.2.2 This work is the basis for the acceptance and takeover of the construction work

7.4.2.3 Inspection criteria and inspection frequency in this stage is regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance

8 Procedure of asphalt concrete mix design using Marshall method.

Procedure of asphalt concrete mix design using Marshall method includes 7 steps as follows

8.1 Experiment to determine physical-mechanical properties of aggregate and asphalt

Carry out experiment to determine physical-mechanical properties of macadam, sand, mineral powder and asphalt Compare with the requirements in Specification for Construction of Asphalt Concrete Pavement and Acceptance to evaluate the quality If any material is not qualified enough, it should take alternative measure

8.2 Aggregate mixing

8.2.1 The purpose of aggregate mixing is to find the proportion of existing aggregates (macadam, sand, mineral powder), so that the aggregate mixture after mixing will have grain composition within the boundary limit of grain envelope regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance

8.2.2 Types of aggregates: macadam, sand, and mineral powder are produced separately For

macadam, two or three groups of grain size should be used for the design, depending on the

maximum nominal particle size of the asphalt concrete mixture Therefore, it is necessary to carry out the aggregate mixing to find the suitable aggregate mixture

8.2.3 Carry out analysis of particle size of aggregate groups: macadam, sand, and mineral powder with sieve sizes regulated in Specification for Construction of Asphalt Concrete Pavement and

Acceptance

8.2.4 Calculate to find the mixing ratio of aggregate groups (by percentage in total aggregate mass), providing that the gradation of the designed aggregate mixture is within the boundary limit of grain envelope regulated in Specification for Construction of Asphalt Concrete Pavement and Acceptance The aggregate gradation curve of the designed aggregate mixture must be even, in which the lower limit of one sieve size shall not change into the upper limit of the next sieve size or vice versa

8.2.5 Principle of mixing computation is detailed in Appendix A Mixing computation can be conducted

by applying a mathematical formula, using a Microsoft Excel spreadsheet or a specialized software (see Appendix A)

8.3 Prepare sample of aggregate mixture for casting Marshall sample

8.3.1 Number of aggregate sample required:

- To cast Marshall sample, determine bulk specific gravity of asphalt concrete, and implement

Marshall experiment: 15 samples (5 sample groups, 3 samples per group);

- To determine maximum weight of asphalt concrete mixture: 5 samples in case of applying he first way (see 8.5.5.1) or 2 samples in case of apply the second way (see 8.5.5.2)

- To check physical-mechanical properties of the asphalt concrete sample after having the optimum asphalt content: 3 samples

- To determine the remaining Marshall stability of the asphalt concrete sample after having the

optimum asphalt content: 2 samples

- To check the additional parameters of asphalt concrete after having the optimum asphalt content: the number of sample will follow Specification for Construction of Asphalt Concrete Pavement and Acceptance

8.3.2 Preparation of aggregates: Based on the number of samples required, prepare sufficient

aggregate volume, dry, and sieve to separate granular sizes, then mix the granular sizes to form separate aggregate mixture samples:

- In case of experiment by conventional Marshall method: the amount of aggregate mixture per sample is about 1,200 g;

- In case of experiment by improved Marshall method: the amount of aggregate mixture per sample is about 4,000 g

8.4 Mix aggregate with asphalt, compact Marshall sample

8.4.1 Predict the optimum asphalt content

8.4.1.1 For the design of asphalt concrete mixture, 05 sample groups of asphalt concrete shall be made, in which 05 asphalt content values of each are 0.5% different from each other respectively The selected value of asphalt content among 5 asphalt content values is necessary, so that it can

calculate the remaining 4 asphalt content values The selected value of asphalt content should satisfy the condition that the determined optimum asphalt content is within the middle range of the 5 values of the asphalt content of the asphalt concrete specimen The selected asphalt content is called the predicted optimum asphalt content

8.4.1.2 In case the reference asphalt content is given in Specification for Construction of Asphalt Concrete Pavement and Acceptance, the predicted optimum asphalt content will be selected within the range of such reference asphalt content

8.4.1.3 In case the reference asphalt content is not given in Specification for Construction of Asphalt Concrete Pavement and Acceptance, it is necessary to determine the predicted optimum asphalt content The predicted optimum asphalt content can be determined by the following formula:

P = 0.035a + 0.045b + Kc + FWhereas:

- P is the predicted optimum asphalt content (percentage in total mass of asphalt concrete);

- a is the percentage of aggregate on the sieve 2.36mm, in the form of an integer (e.g 22.3% is 22);

- b is the percent of aggregate material that can pass sieve 2.36mm and cannot pass sieve 0.075mm; this figure is used in the formula in the form of integer;

- c is the percent of aggregate material that can pass sieve 0.075mm; this figure is used in the formula

in the form of decimal number (for example, 6.25% is written as 6.25);

- K is 0,15 if the percent of material passing sieve 0.075m is from 11 to 15%; K is 0,18 if the percent of material passing sieve 0.075m is from 6 to 10%; K is 0,20 if the percent of material passing sieve 0.075m is from 0 to 5%;

- F is from 0.2 to 0.6 depending on coarse aggregate’s asphalt absorption If the aggregate material has low asphalt absorption (or low water absorption), choose low value and vice versa

8.4.2 Mix aggregate material with bitumen

8.4.2.1 Determine required number of asphalt concrete samples (according to 8.3) before preparation

of bitumen samples and trial mix of asphalt concrete, including:

- Prepare Marshall sample, identify bulk density of Asphalt concrete and Marshall test: Mix 5 groups of aggregate samples (each group include 3 samples) with 5 different bitumen contents (difference of 0.5% around the estimated optimal bitumen content)

- Identify the highest bulk density of Asphalt concrete: Mix 5 samples of aggregate material with 5 different bitumen contents if the first method was chosen (accordance with 8.5.5.1) or 2 samples with optimal bitumen content if the second method was chosen (accordance with 8.5.5.2)

- Check the mechanical and physical properties of asphalt concrete sample with reference to relative optimal bitumen content: Mix 3 samples of aggregate material with known optimal bitumen content (on the basis of design of asphalt concrete mix)

- Identify remaining Marshall stability of asphalt concrete sample with reference to optimal bitumen content: Mix 2 samples of aggregate material with know optimal bitumen content

- Check additional asphalt concrete properties with reference to optimal bitumen content: number of asphalt concrete samples in conformity with regulations of standards of asphalt concrete construction and acceptance,

8.4.2.2 Mixing procedure of aggregate material with bitumen is as below:

- Weigh to identify the weight of bitumen samples with reference to chosen bitumen content (content

is calculated with consideration of weight percent in asphalt concrete mixture)

- Put bitumen sample into dryer and increase the temperature to mixing temperature as regulated in standards of asphalt concrete construction and acceptance,

- Put aggregate sample into another dryer and heat it to a temperature which is 15 C higher than mixing temperature.

- Mix aggregate material with bitumen

8.4.3 Compact Marshall sample

8.4.3.1 Equipment for compacting Marshall sample, testing tools and compaction procedure are regulated by TCVN 8860-1:2011

8.4.3.2 5 sample groups of asphalt concrete mixture (each group of 3 samples) are put into moulds for compaction one by one Height of asphalt concrete samples after compaction in moulds must be in regulated range (63,5 mm ±1,3 mm with normal Marshall compaction of and 95,2 mm ± 1,8 mm with modified Marshall compaction)

Normally, aggregate mixtures with the weight of about 1200 g (with normal Marshall compaction method) or about 4000 g (with modified Marshall compaction method) shall result in compacted samples with proper height

8.4.3.3 In case that the height of compacted sample is not within regulated range, adjust the amount

of required aggregate material for sample compaction as below:

In which:

- A is 63, 5 mm when normal Marshall compaction method is applied

- A is 95, 2 mm when modified Marshall compaction method is applied

8.4.3.4 Compaction temperature for Marshall sample is regulated by standards of asphalt concrete construction and acceptance, depending on type of bitumen used

8.5 Tests and calculation of volume properties of asphalt concrete mixture

Tests and calculation of indexes required for volume properties for Asphalt concrete design shall follow below procedure:

1) Test to determine bitumen density in accordance with TCVN 7501:2005 It is possible to determine beforehand (refer to Article 8.1)

2) Test to determine coarse aggregate material density (in accordance with AASHTO T 85-2000; fine aggregate material density (in accordance with AASHTO T 84-2000; mineral powder density (in accordance with TCVN 4195:1995, test at 250C, which equivalent to water density of 1 g/cm3) It is possible to determine beforehand by following instructions in Article 8.1

3) Calculate bulk density, apparent density of aggregate mixture

4) Calculate effective density of aggregate mixture

5) Test to determine the maximum density of asphalt concrete mixture before compaction

6) Test to determine the bulk density and volumetric mass of compacted asphalt concrete sample.7) Calculate absorbed asphalt content

8) Calculate effective asphalt content

9) Calculate Voids in mineral aggregate of compacted asphalt concrete mixture

10) Calculate residual voids in compacted asphalt concrete mixture

11) Calculate voids filled with Asphalt in compacted asphalt concrete mixture

8.5.1 Test to determine asphalt density

Asphalt density is denoted as Gb

8.5.2 Test to determine aggregate density

8.5.2.1 Test to determine the density of coarse aggregate (crushed stone), fine aggregate (sand), mineral powder, which will provide results with reference to 3 types of density and water absorption:

- Bulk Density;

- Bulk Density-saturated surface-dry;

- Apparent Density;

- Water Absorption

8.5.2.2 Aforementioned test results are used for the following purposes:

- Bulk Density of aggregate material (crushed stone, sand) is used to calculate Bulk Density of

aggregate mixture

- Apparent Density of aggregate material (crushed stone, mineral powder) is used to calculate

apparent density of aggregate mixture

- As for mineral powder, because it is hard to accurately determine Bulk Density, Apparent Density is used instead of Bulk Density, this replacement shall not considerably affect calculation result

- Water absorption of aggregate material is the basis to estimate asphalt absorption (many documents recommend that asphalt absorption is about 0.5 water absorption)

8.5.3 Calculate Bulk Density and Apparent Density of aggregate mixture

8.5.3.1 Bulk Density of aggregate mixture

Bulk Density of aggregate mixture is calculated as below:

In which:

- Gsb is Bulk Density of aggregate mixture

- P1, P2, , Pn is the content of each material, as % of total mass of aggregate mixture

- G1, G2, , Gn is Bulk Density of each material in aggregate mixture

8.5.3.2 Apparent Density of aggregate mixture

Apparent Density of aggregate mixture is calculated as below:

In which:

- Gsa is Apparent Density of aggregate mixture

- P1, P2, , Pn is the content of each material, as % of total mass of aggregate mixture

- G1’, G2’, , Gn’ is Apparent Density of each material in aggregate mixture

8.5.4 Calculate effective Density of aggregate mixture

Effective Density of aggregate mixture is calculated as below:

In which:

- Gse is Effective Density of aggregate mixture;

- Gmm is the maximum Density of Asphalt concrete mixture (determined in accordance with Section 8.5.5);

- Pmm is the percent of mass of uncompacted mixture (Pmm= 100);

- Pb is bitumen content, as % of total mass of asphalt concrete mixture;

There are 2 methods to determine maximum density of asphalt concrete mixtures using different bitumen content

- Calculate effective density of aggregate mixture (Gse) by following formula 2 (Section 8.5.4) with known value of maximum density of asphalt concrete mixture (Gmm)

- Effective density of this aggregate mixture (Gse) is considered as unchanged for all bitumen contents (because absorbed bitumen amounts at different bitumen contents are almost equal) Calculate maximum asphalt concrete mixture at different bitumen contents following below formula

In which:

- Gmm is maximum density of asphalt concrete mixture;

- Pmm is the percent of mass of uncompacted asphalt concrete mixture ( Pmm= 100);

- Ps is ratio of aggregate material, calculated with consideration of the % in total mass of asphalt concrete mixture;

- Pb is bitumen content, calculated with consideration of the % in total mass of asphalt concrete mixture;

- Gse is effective density of aggregate mixture;

- Gb is density of bitumen

8.5.6 Test to determine Bulk density and volumetric mass of compacted asphalt concrete sampleBulk density of compacted asphalt concrete sample, denoted as Gmb, is determined in accordance with TCVN 8860-5: 2011

Volumetric mass of asphalt concrete sample is calculated by multiplying bulk density of asphalt concrete sample with volumetric mass of water When testing at room temperature 25oC, volumetric mass of water is considered as 1g/cm3

8.5.7 Calculate absorbed bitumen content

Absorbed bitumen content is calculated as below:

In which:

- Pba is absorbed bitumen content, % mass of aggregate mixture;

- Gse is effective density of aggregate mixture;

- Gsb is bulk density of aggregate mixture;

- Gb is density of bitumen

8.5.8 Calculate effective bitumen content

Effective bitumen content is calculated as below:

In which:

- Pbe is effective bitumen content, % mass of asphalt concrete mixture;

- Pb is bitumen content, % mass of asphalt concrete mixture;

- Pba is absorbed bitumen amount, % mass of aggregate material;

- Ps is ratio of aggregate material, % mass of asphalt concrete mixture

8.5.9 Calculate voids in compacted asphalt concrete mixture

Voids in mineral aggregate is calculated as below:

In which:

- VMA is Voids in mineral aggregate, calculated with consideration of % total volume of asphalt concrete mixture;

- Gsb is bulk density of aggregate mixture;

- Gmb is bulk density of compacted asphalt concrete sample;

- Ps is ratio of aggregate material, calculated with consideration of % mass of asphalt concrete mixture

8.5.10 Calculate residual voids of compacted asphalt concrete mixture

Residual voids is calculated as below:

In which:

- Va is residual voids of compact asphalt concrete mixture, calculated with consideration of % of volume of asphalt concrete sample;

- Gmm is maximum density of asphalt concrete mixture;

- Gmb is bulk density of compacted asphalt concrete mixture

8.5.11 Calculate voids filled with asphalt of compacted asphalt concrete mixture

Voids filled with asphalt is determined as below:

In which:

- VFA is voids filled with asphalt of compacted asphalt concrete mixture, calculated with consideration

of % of Voids in mineral aggregate (VMA);

- VMA is residual Voids in mineral aggregate, calculated with consideration of % volume of asphalt concrete sample;

- Va is residual voids, calculated with consideration of % volume of asphalt concrete sample

Appendix B shows a calculation example of volumetric properties of asphalt concrete mixture

8.6 Test to determine stability and plasticity of Marshall samples

8.6.1 This test is carried out after completion of tests on determination of Bulk density (and calculation

of volumetric mass) of Marshall compacted asphalt concrete samples

8.6.2 Requirements on equipment, testing equipment and testing procedure shall be in conformity with instructions in TCVN 8860-1: 2011

8.6.3 Cary out tests to determine stability and plasticity for 5 sample groups of asphalt concrete in relation to different used bitumen content, each group consists of 3 samples

8.6.4 Adjust stability testing results of samples with height different from standard sample (63,5 mm for normal Marshall method or 95,2 mm for modified Marshall method) by applying adjustment index (TCVN 8860-1: 2011)

8.6.5 Calculate average plasticity of 5 sample groups in relation to each bitumen content and average stability of 5 sample groups after adjustment

Appendix B shows an example of testing results of Marshall stability and plasticity

8.7 Choose optimal bitumen content

8.7.1 Make a relation graph between bitumen content and relevant criteria

8.7.1.1 Draw relation graphs between bitumen content and relevant criteria: stability, plasticity,

residual voids, Voids in mineral aggregate, voids filled with asphalt, volumetric mass of asphalt

concrete sample, in which horizontal axis represents bitumen content; vertical axis represents relative values:

- Stability – Bitumen content

- Plasticity – Bitumen content

- Residual voids – Bitumen content

- Voids in mineral aggregate– Bitumen content

- Voids filled with asphalt – Bitumen content

- Volumetric mass of asphalt concrete sample – Bitumen content.

8.7.1.2 Stability, Plasticity, Residual voids, Voids in mineral aggregate, voids filled with asphalt, volumetric mass of asphalt concrete sample are average values of 3 relative values of 3 testing samples

8.7.1.3 Figure 2 shows an example of relation graph between asphalt content and relevant criteria:Stability, Plasticity, Residual voids, Voids in mineral aggregate, voids filled with asphalt, volumetric mass of asphalt concrete sample base on data in Table B5, Appendix B

8.7.2 Determine optimal bitumen content

- Compare values: Plasticity, Voids in mineral aggregate, voids filled with asphalt that have just been determined with technical requirements in Standards of Construction and Acceptance of asphalt concrete pavement If such criteria are satisfied, identified bitumen content is the optimal bitumen content

- If they are not satisfied, can choose another bitumen content in relation to chosen residual voids (in range of 3.5% to 4.5%) and repeat above procedure If requirements are still not met, it is necessary

to adjust design of asphalt concrete mixture

8.7.2.2 Second method

Suitable for all types of Asphalt concrete

- Base on technical requirements in Standards of Construction and Acceptance of asphalt concrete pavement and base on formed relation graphs, determine the range of bitumen content that satisfies each relative criterion: Stability, Plasticity, Residual voids, Voids in mineral aggregate, Voids filled with Asphalt

- Determine the range of bitumen content that satisfies all criteria This is the range of optimal bitumen content (accepted range of bitumen content)

- Choose 1 value within this range of optimal bitumen content If it does not satisfy requirements, it is necessary to adjust design of asphalt concrete mixture

Figure 3 shows an example of graphs used to determine optimal bitumen content On the basis of bitumen content ranges that satisfy each relative criterion: Stability, Plasticity, Residual voids, Voids in mineral aggregate, Voids filled with asphalt (based on data in Figure 2) and range of optimal bitumen content in consideration of design requirements for asphalt concrete (with reference to TCVN 8819 :

2011, Table 3), determine the range of bitumen content that satisfies all criteria Optimal bitumen content chosen for design shall be within range of optimal bitumen content, normally it will be chosen

as the average value of that range

NOTE 2:

a) In case determined optimal bitumen content does not match with any bitumen content of tested samples, determination of asphalt concrete parameters (stability, plasticity, residual voids, Voids in mineral aggregate, volumetric mass) in relation of optimal bitumen content shall be interpreted from relative graphs

b) If necessary, form 3 samples of asphalt concrete with that optimal content and carry out tests to determine asphalt concrete parameters

Compare such testing results with relative required criteria stipulated in Standards of Construction and Acceptance of asphalt concrete pavement to check its suitability