Bituminous Mixtures PDF

Bituminous Mixtures What is Bituminous Mixture ? Hot-Mix Asphalt : Combination of aggregate and bitumen, heated and uniformly mixed together to obtain aggregate coated with bitumen 2 Contents Production of Bitu...

Bituminous Mixtures What is Bituminous Mixture ? Hot-Mix Asphalt : Combination of aggregate and bitumen, heated and uniformly mixed together to obtain aggregate coated with bitumen 2 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 3 Production in Laboratory Procedure for preparing specimens Heat and mix the aggregate and bitumen Place the material into a heated mold Apply compaction force Allow the specimen to cool and extrude from the mold Marshall hammer Impact force Compaction process Superpave gyratory compactor Shearing action 4 Production in Field – Hot Mix Plant 5 Production in Field – Hot Mix Plant Purpose Blend different sizes of aggregates Dry and heat aggregates  Moisture content < 0.5%  Mixing temperature Feed bitumen and filler Homogeneous mix of aggregates, bitumen and filler Safe, environmentally friendly Accurate and consistent 6 Classification of Hot Mix Plant Hot mix plant IRC 90 (2010) Hot mix Direction of flow Capacity of Hot Mobility of hot preparation of aggregates and Mix Plant mix plant methodology hot gases Output at 6% Continuous type Counter flow type Stationary type moisture content Output at 2% Batch type Parallel flow type Mobile type moisture content 7 Classification of Hot Mix Plant Capacity of Hot Mix Plant Output at 6% moisture content in aggregates Output at 2% moisture content in aggregates Example Hot mix plant capacity = 40/60 ton/hr  Output at 6% moisture content = 40 ton/hr  Output at 2% moisture content = 60 ton/hr 8 Classification of Hot Mix Plant Hot mix preparation methodology Continuous type Aggregates, fines and bitumen are continuously inducted into pugmill/drum mix in desired proportion and hot mix discharged without interruption Batch type Hot bitumen is added with the batch of hot aggregates and filler (if necessary) at desired temperature in desired proportion in mixing unit. The mix prepared in batch is transferred either into silo for its storage or directly fed into tipper for transportation 9 Classification of Hot Mix Plant Direction of Flow of Aggregates and Hot Gases 10 Classification of Hot Mix Plant Direction of Flow of Aggregates and Hot Gases Counter flow type Virgin aggregates entry => Exhaust gases discharge point Aggregates and hot gases flow => Opposite direction inside dryer drum  Higher heat transfer process efficiency  Lower exit gas temperature  Reduce plant emission and fuel consumption 11 Classification of Hot Mix Plant Direction of Flow of Aggregates and Hot Gases Parallel flow type Aggregates and hot gases flow ⇒ Same direction inside dryer drum  Lower thermal efficiency Low heat transfer near drum mixer ⇒ High fuel consumption  High stack temperature Aggregate drying ⇒ Near burner zone  Environmental hazard High blast of air from burner carries the dust from dry aggregates through the exhaust 12 Classification of Hot Mix Plant Mobility of Hot Mix Plant Stationary type Mobility type Portable type Major units fitted with Rigid and can’t be moved Integrated foundation pneumatic tyres More quantum of work Small quantum of work Higher frequency Frequent shifting 13 Batch Mix Plant & Drum Mix Plant 14 Components of Batch Type Hot Mix Plant 15 Components of Batch Type Hot Mix Plant Cold bin feeder Min. 4 bins with separators Bin gates with graded scale First bin – Fines Conveyor fitted under each bin Single deck vibratory screen at discharge  Remove oversize aggregates Cold elevator or cold feed conveyor Conveyor to dryer drum Position of Bin Vibrator in 1st Bin 16 Components of Batch Type Hot Mix Plant Dryer drum Revolving inclined cylindrical drum Burner and blower fan Longitudinal trough or channels: Flights  Lift the aggregates and drop it in veils through the burner flame and hot gases Aggregate moisture content  4 to 6% ⇒ Maximum efficiency  Higher moisture ⇒ Hourly production capacity reduces 17 Components of Batch Type Hot Mix Plant Dryer drum Dwell time: Retention time for aggregates in dryer drum. o Dependent on  Slope of the dryer drum  Revolutions per minute  Diameter and length  Number and arrangement of flights  Efficiency of burner Aggregate temperature (Pyrometers or thermocouple)  Higher temperature ⇒ Binder hardening  Lower temperature ⇒ Improper coating 18 Components of Batch Type Hot Mix Plant Primary pollution control device Primary dust collection system  Remove undesirable amount of dust coming from the exhaust  Cyclonic separators o Principle: Centrifugal separation o Location: Rear of dryer drum Exhaust stack Eliminates exhaust gases 19 Components of Batch Type Hot Mix Plant Hot elevator Carry aggregates to gradation units after heating and drying Stone box  Location: Edge of hot elevator discharge chute  Lowers and smoothens the flow speed of aggregates falling on screen sieves. 20 Components of Batch Type Hot Mix Plant Screening unit Gradation of aggregates  Primary – Cold bin feeder system  Secondary (hot condition) – Screening unit 21 Components of Batch Type Hot Mix Plant Screening unit Multi-deck vibratory screening  Series of vibrating screen  Hot elevator ⇒ Vibrating screen ⇒ Hot bins  Order: Coarse ⇒ Intermediate ⇒ Fines Rotary screening  Rotating screening drum – Screening + heating  Cold aggregates ⇒ Screening drum ⇒ Hot bins  Order: Fines ⇒ Intermediate ⇒ Coarse 22 Components of Batch Type Hot Mix Plant Hot bins Temporarily store heated and screened aggregates Individual compartments with min. 4 partitions Equipment  Overflow pipe Segregation of  Discharge gates Aggregates in  Levelling indicator each Hot Bin  Aggregate temperature measurement device 23 Components of Batch Type Hot Mix Plant Weigh hopper Aggregates – Hot bins to weigh hopper Sequence of aggregates collection Coarse ⇒ Intermediate ⇒ Fines (top) Aggregates – Transferred to pugmill 24 Components of Batch Type Hot Mix Plant Bitumen unit Equipment  Bitumen tank  Heating system  Bitumen pump  Delivery pipe Bitumen weigh bucket  Weigh and pump bitumen into pugmill through spray bar System to Measure and Deliver desired Quantity of Bitumen in Pugmill 25 Components of Batch Type Hot Mix Plant Mixing unit (pugmill) Chamber for mixing aggregates and bitumen Feed material quantity 26 Components of Batch Type Hot Mix Plant Mixing unit (pugmill) Batch mixing time  Time between opening of weigh hopper gate and closing of pugmill discharge gate  Mixing cycle o Begin at 30 seconds o Optimum: Dependent on  Material characteristics  Equipment properties  Operator's efficiency 27 Components of Batch Type Hot Mix Plant Mineral filler/dust control system Store mineral filler (rock dust, hydrated lime or cement) to protect from dampness and choking/ hardening from moistures Equipment  1st Screw feeder: Carries filler from filler tank  2nd Screw feeder: Carry dust collected from bag filter  Filler stock bin: Common chute for both 28 Components of Batch Type Hot Mix Plant Control panel Control operation of complete plant Information displayed  Plant load (% of plant capacity)  Composition of different materials  Running weight of materials  Total quantity of materials flow during specific period  Temperature 29 Components of Batch Type Hot Mix Plant Secondary pollution control device (bag house filter) 2 chambers  Dirty gas chamber  Clean gas chamber Operation  Dust laden flue gas enters dirty gas chamber  Moved to filter bags through open mouth  Suction pressure by vacuum pump ⇒ Gas sucks out Gas filtered and dust left on inner walls of filter bags  Shaker arrangement ⇒ Dust from bags to hopper 30 Components of Batch Type Hot Mix Plant Hot mix surge silo Temporary storage Hot oil circulation + thermo/ ceramic wool  Maintain hot mix temperature for 16 hrs approx. 31 Batch Mix Plant Advantages Limitations Well graded aggregates High cost  Secondary gradation control unit More plant space for commissioning Homogenous mix Smaller capacity plants (< 90 ton/hr)  Measurement of aggregates and uneconomical bitumen in desired quantity and mixing in pugmill 32  Components of Drum Mix Plant Advantages: Portable; Higher efficiency; Economy in basic cost; Lower fuel consumption; Reduction in man power and maintenance cost; Trouble free operation; Ability to produce large quantity of mix at relatively low temperature and environmental friendly. 33 Components of Drum Mix Plant Dryer cum mixing drum Rotary shell Function  Remove moisture from aggregates  Blend aggregates and bitumen 34 Components of Drum Mix Plant Dryer cum mixing drum Drum: 2 zones  Combustion zone Heating and drying of aggregates  Mixing zone Mixing of aggregates, filler and bitumen Rate of drying of aggregates o Dependent on moisture content o Dwell time: Factors  Length to diameter ratio = 4 to 6  Capacity of drum mixer 35 Components of Drum Mix Plant Dryer cum mixing drum Burner o Fuel = Light diesel oil/ furnace oil o Forced and induced draft principle  Exhaust fan = 55% air  Air blower = 45% Bitumen line  Liquid bitumen discharges by gravity into drum Bitumen fines receiver  Dust from mineral filler system to mixing zone 36 Drum Mix Plant Advantages Limitations Less cost No secondary gradation control unit Less space requirement No system to measure aggregate temperature Easy to transport Aggregate temp = Exhaust gas temp – 12°C Availability: Different capacity Quantity of hot mix prepared => Not as homogeneous as batch mix plant  40/60 to 400 ton/hr Less operation and maintenance cost 37  Factors Affecting Hot Mix Plant Presence of moisture in aggregates Altitude Aggregate heating not uniform & adequate 300 m elevation ⇒ 3.5% output reduction Dust content in mix Insulation of drum More surface area to be coated by bitumen Better insulation ⇒ More output; less fuel Moisture v/s Output Dust content v/s Output Altitude v/s Output Output (% of output at 2% moisture) 120% 110 1.2 300 Parallel Flow 100% 1.0 250 Counter Flow 100 Production rate 80% 0.8 200 Output, % Factor 60% 90 0.6 150 40% 80 0.4 Factor 100 20% 0.2 Production rate 50 70 0% 30% 50% 70% 90% 0.0 0 0% 2% 4% 6% 8% 10% Dust content 0 2500 5000 7500 10000 Moisture content (%) Elevation, m 38 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 39 Bitumen Behavior Temperature susceptibility High temperatures Intermediate Low temperatures Viscoelasticity (> 200°F) temperatures (below freezing) Aging characteristics Viscous fluid Viscoelastic Elastic solid Shorter loading time Stiffer bitumen Lower temperature Source: Notani et al.40(2021) Mineral Aggregate Behavior Types of aggregates Natural (bank-run or pit-run materials) Processed (Mined, quarried, crushed) Synthetic (Man-made material – Slag) 41 Mineral Aggregate Behavior Permanent deformation Aggregates – Provides shear strength Overloading of mix  Shear plane develops  Aggregate particles slide past each other  Shear stress > Shear strength Shear strength  Dependent on resistance to movement, or inter-particle friction Angular aggregates Round aggregates  Angular, rough-textured aggregates preferred over rounded, smooth- textured aggregates 42 Bituminous Mixture Behavior Primary stresses transmitted from wheel to HMA Vertical compressive stress Shear stress within the asphalt layer Horizontal tensile stress at the bottom of asphalt layer Tensile strain at the edge of high pressure radial tires Top down cracking 43 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 44 Desired Properties Resistance to permanent deformation – Stability Fatigue resistance Resistance to Low-temperature Cracking Moisture resistance – Impermeability Durability Skid resistance Workability 45 Desired Properties Resistance to permanent deformation – Stability Accumulation of small amounts of Primary causes unrecoverable strain (small deformations)  Inadequate mix stability from repeated loads applied to the pavement  Subgrade failure 46 Desired Properties Resistance to permanent deformation – Stability Methods to improve rutting resistance Internal friction (aggregates)  Angular and rough aggregates  Aggregate gradation – Develop particle-to-particle contact Cohesion (bitumen) – Lesser extent  Stiffer/ Modified binder 47 Desired Properties Fatigue resistance Pavement’s resistance to repeated bending under wheel loads (traffic) Primary causes  Insufficient pavement thickness  Air voids  Asphalt binder properties 48 Desired Properties Fatigue resistance Methods to overcome fatigue cracking  Adequate traffic load and composition during design  Use thicker pavements  Provide adequate subgrade drainage  Use moisture resistant pavement materials  Use modified binder  Use HMA resilient to withstand normal deflections 49 Desired Properties Low-temperature Cracking Occurrence of transverse cracks when the temperature at the surface of the pavement drops sufficiently to produce thermally induced stress in the HMA layer that exceeds the tensile strength of the asphalt mixture Primary causes  Magnitude, rate of cooling  Frequency of low-temperature occurrences  Stiffness of asphalt 50 Desired Properties Low-temperature Cracking Methods to overcome low-temperature cracking  Proper choice of bitumen  Avoid highly absorptive aggregates, or aggregates with high dust content 51 Desired Properties Moisture resistance – Impermeability Moisture damage – Result of water in combination with Stripping – Water or water repeated traffic loadings, causing a scouring effect as the vapor gets between the bitumen water is pushed into and pulled out of the voids in pavement film and the aggregates, breaks the adhesive bond between the aggregate and the asphalt binder film resulting in the asphalt to “strip” from the aggregate 52 Desired Properties Moisture resistance – Impermeability Methods to improve moisture resistance  Provide sufficient binder in mix  Provide sufficient compaction – Impermeable mat  Use of anti-stripping agents  Controlling dust and clay content 53 Desired Properties Durability Ability of mix to resist factors such as aging of the asphalt, disintegration of the aggregate and stripping of the asphalt film from the aggregate Primary causes  Traffic  Weather Methods to improve durability  Dense gradation ; sound, tough, moisture-resistant aggregate  Maximizing the asphalt film thickness on the aggregate  Compacting the mixture to be impervious 54 Desired Properties Skid resistance Ability of an asphalt surface to minimize skidding or slipping of vehicle tires Good skid resistance  Tire tread maintains contact with aggregate  Rough pavement surface Methods to overcome skid resistance  Aggregates – Rough textured and resist polishing  Minimize hydroplaning 55 Desired Properties Workability Ease with which a paving mixture can be placed and compacted Tender Mix – Internally unstable mix that tends to displace laterally and shove rather than compact under roller loads 56 Desired Properties  Shortage or excess of mineral filler Aggregate issues  Excessive medium-size sand or too much dust  Smooth, rounded aggregate particles  Contamination Causes of  Stiffness tender mix Bitumen issues  Too much/too little  Slow setting asphalt  Too much diesel oil in the bottom of trucks  Excessive moisture in a dense hot mix. Construction issues  Excessive mix temperature  Rolling equipment and techniques  Inadequate Bond to Underlying Layer 57 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 58 Volumetric in Mix Design Aggregates Specific gravity = Bulk, Effective, Apparent Mix Bulk Specific Gravity of Mix, 𝐺𝑚𝑏 Theoretical Maximum Specific Gravity of Mix, 𝐺𝑚𝑚 Air Voids Voids in Mineral Aggregates (VMA) Voids Filled with Bitumen (VFB) Binder absorption, 𝑃𝑏𝑎 and Effective Binder Content, 𝑃𝑏𝑒 Dust to Binder Ratio 59  Bulk Specific Gravity of Mix, Gmb SSD Method Automatic Vacuum Sealing Paraffin coating A = Dry mass of specimen in air Water absorption by vol > 2% Samples dipped in hot paraffin B = SSD mass of specimen in air (Recommended) A = Dry mass of specimen in air C = Mass of specimen in water Pressing and sealing with Parafilm B = Sealed specimen mass in air Applicable for water absorption C = Mass of sealed specimen in water A = Dry mass of the specimen in air by volume < 2% E = Initial mass of specimen in air D = Mass of dry specimen plus F = Specific gravity of bag paraffin coating in air % 𝒘𝒂𝒕𝒆𝒓 𝒂𝒃𝒔𝒐𝒓𝒃𝒆𝒅 𝒃𝒚 𝒗𝒐𝒍𝒖𝒎𝒆 E = Mass of dry specimen plus 𝑩−𝑨 𝑨 = 𝟏𝟎𝟎 × 𝑮𝒎𝒃 = paraffin coating in water 𝑩−𝑪 𝑩−𝑬 𝑩−𝑪 − F = Specific gravity of paraffin at 25°C 𝑭 𝑨 𝑮𝒎𝒃 = 𝑨 𝑩−𝑪 𝑮𝒎𝒃 = 𝑫−𝑨 𝑫−𝑬 − 𝑭 60 Theoretical Maximum Specific Gravity, Gmm Steps Separate loose mix  Warm Put in pycnometer Cover with water at 25°C Fit lid Apply vacuum  Gradual – 4 kPa  Start agitator  Hold vacuum for 15 min Release vacuum Fill with water and weigh 61 Effect of Binder Content on Gmb and Gmm Gmb 2.55 Gₘₘb Increase in binder content Gₘₘ 2.50  Gmb increases initially Specific gravity o More lubricity => Volume reduces 2.45 o Binder fills voids => More mass 2.40  After maximum value, Gmb reduces 2.35 o Voids filled with binder => More binder 2.30 => Volume increases 4.5 5.0 5.5 6.0 6.5 Gmm Binder content, % Increase in binder content Segregated mix  Gmm reduces Coarse => Low Pb => High Gmm o % aggregates reduces Fine => High Pb => Low Gmm o Volume of binder increases 62 Volumetric Properties Specific Gravity Ratio of density of material to density of water 𝑚Τ 𝑣 𝐺= 𝜌 Representation of Microscopic View of Aggregate, Bitumen, and Air Mixture 63 Volumetric Properties Beginning capital letter: G – specific gravity M – mass V – volume P – percent First lowercase subscripts: a – air b – binder s – stone (aggregate) m – mix Second lowercase subscripts: a – absorbed (binder only) a – apparent (aggregate only) b – bulk e – effective m – maximum Phase Diagram 64 Bulk Specific Gravity of Aggregates 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑣𝑒𝑛 𝑑𝑟𝑦 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒 𝐺𝑠𝑏 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒 + 𝑊𝑎𝑡𝑒𝑟 𝑝𝑒𝑟𝑚𝑒𝑎𝑏𝑙𝑒 𝑣𝑜𝑖𝑑𝑠 × 𝜌 𝐺𝑠𝑏 for aggregate blend 𝑃1 + 𝑃2 + ⋯ + 𝑃𝑛 𝐺𝑠𝑏 = 𝑃1 𝑃2 𝑃𝑛 + + ⋯ + 𝐺1 𝐺2 𝐺𝑛 65 Bulk Specific Gravity of Aggregates Example: Calculate 𝐺𝑠𝑏 for aggregate blend Material Proportion 𝑮𝒔𝒃 Coarse (Retained on 4.75 mm) 50.0 2.750 Fine (4.75 mm to 75 μm) 43.0 2.710 Filler (Passing 75 μm) 5.0 2.690 Mineral filler (Cement, OPC-43) 2.0 3.100 50 + 43 + 5 + 2 𝐺𝑠𝑏 = ⇒ 𝐺𝑠𝑏 = 2.736 50 43 5 2 + + + 2.750 2.710 2.690 3.100 66 Bulk Specific Gravity of Aggregates Example: Calculate 𝐺𝑠𝑏 for aggregate blend Material Type Coarse Fine Filler A (40% proportion) 100% (Gsb = 2.65) 0% 0% B (40% proportion) 60% (Gsb = 2.60) 40% (Gsb = 2.70) 0% C (20% proportion) 0% 20% (Gsb = 2.63) 80% (Gsb = 2.75) 67 Apparent Specific Gravity of Aggregates 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑣𝑒𝑛 𝑑𝑟𝑦 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒 𝐺𝑠𝑎 = 𝐵𝑢𝑙𝑘 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒 − 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 𝑝𝑒𝑟𝑚𝑒𝑎𝑏𝑙𝑒 𝑣𝑜𝑖𝑑𝑠 × 𝜌 𝐺𝑠𝑎 for aggregate blend 𝑃1 + 𝑃2 + ⋯ + 𝑃𝑛 𝐺𝑠𝑎 = 𝑃1 𝑃2 𝑃𝑛 + + ⋯ + 𝐺1 𝐺2 𝐺𝑛 Water absorption for aggregate blend 𝑃1 × 𝑊𝐴1 + 𝑃2 × 𝑊𝐴2 + ⋯ + 𝑃𝑛 × 𝑊𝐴𝑛 𝑊𝐴 = 𝑃1 + 𝑃2 + ⋯ + 𝑃𝑛 68 Calculating Gmm at Trial Binder Contents Step 1 : Determine Gmm at one trial binder content Step 2 : Determine Gse (Effective specific gravity of aggregates) 𝑃𝑠 𝐺𝑠𝑒 = 100 𝑃𝑏 − 𝐺𝑚𝑚 𝐺𝑏 Check : Gsa ≥ Gse ≥ Gsb Step 3 : Determine Gmm at other trial binder content 100 𝐺𝑚𝑚 = 𝑃𝑠 𝑃 + 𝑏 𝐺𝑠𝑒 𝐺𝑏 69 Calculating Gmm at Trial Binder Contents Example: Gmm at 5.5% binder content by weight of total mix = 2.520 Specific gravity of binder = 1.020 Gsb = 2.736; Gsa = 2.812 𝑷𝒔 𝟏𝟎𝟎 𝑮𝒔𝒆 = 𝑮𝒎𝒎 = 𝟏𝟎𝟎 𝑷𝒃 𝑷𝒔 𝑷𝒃 Calculate Gmm at 4.5%, 5.0%, 6.0% and 6.5% 𝑮𝒎𝒎 − 𝑮𝒃 𝑮𝒔𝒆 + 𝑮𝒃 Step 1: Determine Gse (Effective specific gravity of aggregates) 94.5 𝐺𝑠𝑒 = = 2.756 100 5.5 − 2.520 1.020 Binder content 𝑮𝒔𝒆 𝑮𝐦𝐦 4.5% 2.560 Check: Gsa ≥ Gse ≥ Gsb => OK 5.0% 2.540 Step 2: Determine Gmm at 4.5% 5.5% 2.756 2.520 100 6.0% 2.501 𝐺𝑚𝑚 = = 2.560 95.5 4.5 6.5% 2.481 + 2.756 1.020 70 % Air Voids in Compacted Mixture Volume of air voids in a compacted mixture, expressed as % of the total mix volume 𝑉𝑎 𝑃𝑎 = 100 × 𝑉𝑚𝑏 In terms of specific gravity, 𝑉𝑚𝑏 − 𝑉𝑠𝑏 + 𝑉𝑏𝑒 𝑃𝑎 = 100 × 𝑉𝑚𝑏 𝑀𝑠𝑏 + 𝑀𝑏𝑒 ൗ𝐺 𝑃𝑎 = 100 × 1 − 𝑚𝑚 𝑮𝒎𝒃 𝑀𝑚𝑏 ൗ𝐺 𝑷𝒂 = 𝟏𝟎𝟎 × 𝟏 − 𝑚𝑏 𝑮𝒎𝒎 71 % VMA in Compacted Mixture Voids in the mineral aggregate, VMA, are defined as the intergranular void space between the aggregate particles in a compacted paving mixture that includes the air voids and the effective asphalt content, expressed as % of the total volume 𝑉𝑎 + 𝑉𝑏𝑒 𝑉𝑀𝐴 = 100 × 𝑉𝑚𝑏 In terms of specific gravity 𝑮𝒎𝒃 𝑷𝒔 𝑀𝑠 ൗ𝐺 𝑽𝑴𝑨 = 𝟏𝟎𝟎 − 𝑉𝑚𝑏 − 𝑉𝑠𝑏 𝑠𝑏 𝑮𝒔𝒃 𝑉𝑀𝐴 = 100 × ⇒ 𝑉𝑀𝐴 = 100 − 100 × 𝑉𝑚𝑏 𝑀𝑚𝑏 ൗ𝐺 𝑚𝑏 72 % VFB in Compacted Mixture Voids filled with bitumen (VFB) is the percentage by volume of the VMA that is filled with the effective binder 𝑷𝒂 𝑽𝑭𝑩 = 𝟏𝟎𝟎 − 𝟏𝟎𝟎 × 𝑽𝑴𝑨 73 Binder Absorption Percentage by mass of binder that is absorbed into the aggregates 𝑀𝑏𝑎 𝑃𝑏𝑎 = 100 × 𝑀𝑠 In terms of specific gravity, 𝑉𝑏𝑎 × 𝐺𝑏 𝑉𝑠𝑏 − 𝑉𝑠𝑒 𝑃𝑏𝑎 = 100 × = 100 × × 𝐺𝑏 𝑉𝑠𝑏 × 𝐺𝑠𝑏 𝑉𝑠𝑏 × 𝐺𝑠𝑏 1 𝑉𝑠𝑒 𝑃𝑏𝑎 = 100 × − × 𝐺𝑏 𝐺𝑠𝑏 𝑉𝑠𝑏 × 𝐺𝑠𝑏 𝑮𝒔𝒆 − 𝑮𝒔𝒃 𝑷𝒃𝒂 = 𝟏𝟎𝟎 × × 𝑮𝒃 𝑀𝑠 𝑮𝒔𝒆 × 𝑮𝒔𝒃 1 ൗ𝐺 𝑠𝑒 𝑃𝑏𝑎 = 100 × − × 𝐺𝑏 𝐺𝑠𝑏 𝑀𝑠ൗ 𝐺𝑠𝑏 × 𝐺𝑠𝑏 74 Effective Binder Content Percentage by mass of binder that stays on the outside of aggregate particles and is not absorbed 𝑀𝑏𝑒 𝑃𝑏𝑒 = 100 × 𝑀𝑚𝑏 In terms of specific gravity, 𝑀𝑏 − 𝑀𝑏𝑎 𝑃𝑏𝑒 = 100 × 𝑀𝑚𝑏 𝑀𝑏𝑎 𝑀𝑠 𝑷𝒃𝒂 𝑃𝑏𝑒 = 𝑃𝑏 − 100 × × 𝑀𝑠 𝑀𝑚𝑏 𝑷𝒃𝒆 = 𝑷𝒃 − × 𝑷𝒔 𝟏𝟎𝟎 75 Dust to Binder Ratio Ratio of the percentage of aggregate passing the 0.075 mm sieve to the effective binder (Pbe) 𝑃0.075 𝐷𝑃 = 𝑃𝑏𝑒 Typical range = 0.6-1.2 Exceptions For 4.75-mm mixes, the allowable range is 0.9–2.0 For coarse-graded mixes whose gradation plots below the Primary Control Sieve (PCS) on a 0.45 power chart, the allowable range may be increased to 0.8–1.6. Consequences Dust-to-binder ratio: Too high or too low – Tender mix 76 Exercise Determine Pa, VMA, VFB, Pa and Pbe for the following conditions Bitumen content = 5.5% Gmm = 2.533 𝐺𝑚𝑏 𝐺𝑚𝑏 𝑃𝑠 𝑃𝑎 = 100 × 1 − 𝑉𝑀𝐴 = 100 − 𝐺𝑚𝑚 𝐺𝑠𝑏 Gmb = 2.430 Gb = 1.020 𝑃𝑎 Gsb = 2.685 𝑉𝐹𝐵 = 100 − 100 × 𝑉𝑀𝐴 𝑃𝑏𝑎 𝐺𝑠𝑒 − 𝐺𝑠𝑏 𝑃𝑏𝑒 = 𝑃𝑏 − × 𝑃𝑠 𝑃𝑏𝑎 = 100 × × 𝐺𝑏 100 𝐺𝑠𝑒 × 𝐺𝑠𝑏 77 Discussion on Volumetric Properties Voids in Mineral Aggregates, VMA Example a Increase in bitumen content  VMA decrease Workable mix ⇒ Easily compact  VMA increase Aggregate displaced and pushed apart by bitumen 78 Discussion on Volumetric Properties Voids in Mineral Aggregates, VMA Example b Bottom of VMA => Below specification  Modify aggregate gradation  Dry side Prone to segregation, high air voids  Wet side Rutting 79 Discussion on Volumetric Properties Voids in Mineral Aggregates, VMA Example c VMA curve completely below specification  Redesign/ change in aggregate source Note: Avoid bitumen contents on the wet side of minimum !!  Bleeding and/or exhibit plastic flow  Susceptible to rutting 80 Discussion on Volumetric Properties Voids in Mineral Aggregates, VMA Factors Nominal Maximum Aggregate Size  NMAS decreases → Total surface area of aggregates increases → % binder requirement increases → Higher Vbe and same target Va → Higher VMA 81 Discussion on Volumetric Properties Voids in Mineral Aggregates, VMA Factors Type and amount of laboratory compactive effort  Higher compactive effort => Higher VMA Major Factors  VMA for Gyratory > Marshall Aggregate gradation Aggregate shape, strength and texture Bitumen type & quantity Minor Factors Sample temperature 82 Discussion on Volumetric Properties Compaction Level VMA – Increasing the number of blows Air voids – Increasing the number of blows Reduction in VMA Reduction in air voids Decrease in asphalt content at minimum VMA 83 Discussion on Volumetric Properties Air voids Dense graded mix  Desired after service life – 4%  Desirable after construction – 6 to 8% Final air void content < 2%  Rutting and shoving  Reason: Increase in asphalt content or aggregates passing 75 μm Final air void content > 5% or after construction > 8%  Brittleness, premature cracking, raveling and stripping 84 Discussion on Volumetric Properties Voids Filled with Binder, VFB Main effect of VFB criteria  Limit maximum levels of VMA and asphalt content  Restrict the allowable air void content for mixes that are near the min. VMA criteria Light traffic  VFB fails at relatively high air voids (5%)  Avoids less durable mix Heavy traffic  VFB fails at relatively low air voids (< 3.5%)  Avoids mixes susceptible to rutting 85 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 86 Evolution of Mix Design First use of asphalt in pavement Marshall mix design procedure Between 625 B.C. and 604 B.C. Bruce Marshall – 1930s City of Babylon, Procession Street near Mississippi Highway Department King Nabopolassar’s palace was paved Adopted by US Army Corps of Engineers Hveem mix design procedure Superpave Mix Design Francis Hveem – 1930s Early 1990s California Division of Highways Sponsor – FHWA Kneading compactor Administrator – TRB  Steel and pneumatic-tire rollers Gyratory compactor 87 Mix Design Aggregate Selection Binder Selection Methodology Material Selection & Batching Sample Preparation & Specific Gravity Testing Treat with Volumetric Analysis Fail additives Optimum Binder Selection Fail Moisture Sensitivity Performance Testing Fail Issue Job Mix Formula Field Verification testing 88 Objectives of Mix Design Determine the combination of bitumen and aggregate that will give long-lasting performance as part of the pavement structure Procedures in mix design Determining an appropriate blend of aggregate sources to produce proper gradation Selecting the type and amount of bitumen 89 Objectives of Mix Design Pavement Performance Parameters Impermeability Durability Strength Flexibility Final goal of mix design Selection of a unique design binder content that will Stability achieve a balance among all of the desired properties Stiffness Workability Fatigue resistance 90 Objectives of Mix Design Overall Objective Sufficient bitumen ⇒ Ensure durability Sufficient mix stability ⇒ Meet traffic demands Sufficient air voids  Additional compaction under traffic loading  Thermal binder expansion Limit maximum void content ⇒ Restrict permeability of air and moisture Sufficient workability ⇒ Placement of mix without segregation Aggregate texture and hardness ⇒ Skid resistance 91 Marshall Method of Mix Design Bruce Marshall – Mississippi State Highway Department Modified and improved by U. S. Corps of Engineer Major features of Marshall method  Density-void analysis  Stability-flow test Optimum bitumen content  4% air voids  Check for stability, flow, VMA, VFB, dust-to-binder ratio 92  Marshall Method of Mix Design 1. Physical properties assessment 4. Density-Void Analysis 5. Stability-Flow Testing Dimensions, 60°C Gmm, Gmb, Va, Max. load VMA & VFB Total deformation 2. Aggregate blend combinations 3. Marshall Specimen Preparation 6. Job Mix Formula Gradation requirements 100 Cumulavtive % passing 80 60 40 20 0 Dia = 4" 0.01 0.1 1 10 100 Sieve size, mm Height = 2.5" Satisfying all design criteria 93 Preparation of Test Specimens Expected design asphalt content Experience 𝑷 = Approximate asphalt content of mix, % by weight of mix 𝒂 = % of aggregate retained on 2.36-mm sieve Centrifuge kerosene equivalency test 𝒃 = % of aggregate passing 2.36-mm and retained on 75-μm sieve Computational formula 𝒄 = % of aggregate passing 75-μm sieve 𝑷 = 𝟎. 𝟎𝟑𝟓𝒂 + 𝟎. 𝟎𝟒𝟓𝒃 + 𝑲𝒄 + 𝑭 𝑲 = 0.15 for 11–15% passing 75-μm sieve = 0.18 for 6–10% passing 75-μm sieve Specimens = 0.20 for < 5% passing 75-μm sieve 𝑭 = 0 – 2.0% (0.7% suggested) Binder contents = 5  Expected design asphalt content  ±0.5%, ±1.0% Total = 15 specimens Weight = 1.2 kg 94 Preparation of Test Specimens 95 Preparation of Test Specimens Mixing and compaction temperature Viscosity range – Unmodified binder  Mixing = 170 ± 20 cSt  Compaction = 280 ± 30 cSt  Viscosity (log-log cSt) v/s temperature (log °R) °R = °F + 459.7 Modified binder – DSR Preparation of mold and hammer Heat mold assembly and face of compaction hammer  95°C to 150°C 96 Preparation of Test Specimens Preparation of mixtures Adjust batch weights 63.5 × 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒 𝑢𝑠𝑒𝑑 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑚𝑎𝑠𝑠 = 𝑆𝑝𝑒𝑐𝑖𝑚𝑒𝑛 ℎ𝑒𝑖𝑔ℎ𝑡 𝑚𝑚 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 Weigh aggregates and bitumen Mix at mixing temperature Condition for 2 hours at compaction temperature Packing the mold Pour mixture and spade  15 times around perimeter  10 times over interior 97 Preparation of Test Specimens Compaction of specimens Marshall Method Light Medium Heavy Apply blows Criteria traffic traffic traffic  Based on traffic category Compaction, number of blows each end of 35 50 75  Axis – Perpendicular to base plate specimen  Height of free fall = 457 mm Cool at room temperature and extrude 98 Test Procedure Volumetric data Dimensions – Height and diameter Gmb Conditioning Water bath – 60°C for 30-40 min Max. load = Stability Testing Corresponding vertical deformation = Flow Within 30 seconds Loading rate = 50 mm/min Plot load and deformation 99 Interpretation of Test Data Measure stability and flow values  Apply corrections to stability values  % air voids v/s binder content Prepare graphs  % VMA v/s binder content Fit second order polynomial  % VFB v/s binder content Optimum binder content  Unit weight of total mix v/s binder content  4% air void content  Stability v/s binder content  Satisfy all other performance  Flow v/s binder content requirements 100  Interpretation of Test Data 2.44 6 18 Bulk Specific Gravity 2.42 16 Air voids, % 4 VMA, % 2.40 14 2 2.38 12 2.36 0 10 4.5 5 5.5 6 6.5 7 7.5 4.5 5 5.5 6 6.5 7 7.5 4.5 5 5.5 6 6.5 7 7.5 Binder content, % Binder content, % Binder content, % 100 14 4 90 12 3 Stability, kN Flow, mm VFB, % 80 10 2 70 8 1 60 50 6 0 4.5 5 5.5 6 6.5 7 7.5 4.5 5.5 6.5 7.5 4.5 5 5.5 6 6.5 7 7.5 Binder content, % Binder content, % Binder content, % 101  Criteria for satisfactory paving mix Asphalt Institute 102 Criteria for Satisfactory Paving Mix MoRT&H (2013) IRC 111 (2009) 103 Superpave Method of Mix Design Superpave (SUperior PERforming asphalt PAVEments) system 1987 – 5-year FHWA study to improve the performance of HMA pavements Consists of two interrelated elements  Bitumen specification as per Asphalt Institute MS-26  Mix design system that specified aggregate criteria and volumetric properties 104 Superpave Mix Design Procedure Material selection – Bitumen and aggregate Aggregate blending Mixing and short-term aging the selected bitumen and aggregate blend Compaction – Superpave gyratory compactor according to expected traffic levels Volumetric analysis Selection of best aggregate and asphalt blend Performance testing – Moisture sensitivity 105 Material Selection – Aggregates Consensus aggregate properties 106 Material Selection - Aggregates Source aggregate properties Properties of source aggregates – Can’t be modified by consensus Requirements specific to local areas 107 Material Selection - Aggregates Aggregate gradation Control points  Define type of mix Field production testing 108 Mixture Requirements Measure of the compactibility of the mix Field density – Behind screed before compaction Desired compaction – 89 to 91.5% of Gmm 𝟎.𝟒𝟓 Nini 𝑵𝒊𝒏𝒊 = 𝑵𝒅𝒆𝒔 Compact too quickly – Tender mix Less compaction – High permeability Number of gyrations to reach target density Ndes Field density – Middle of service life Desired compaction – 96% of Gmm Field density – End of service life Desired compaction – < 98% of Gmm 𝟏.𝟏𝟎 Nmax 𝑵𝒎𝒂𝒙 = 𝑵𝒅𝒆𝒔 Low air voids – Plastic mix – Rutting 109 Compaction Effort 110 Mixture Requirements – Volumetric 111 Test Equipment Higher angle of gyration – More compaction 112 Specimen Preparation and Compaction Preparation of aggregate and binder  Sample requirements  Aggregate batch weights  Binder contents Mixing and compaction temperature Preparation of mixtures  Preheating of aggregate and binder  Mix production and conditioning Compaction  Specified number of gyrations  Specified height 113 Specimen Preparation and Compaction Sample requirements 8 – Compacted to Ndes φ = 150 mm 2 – Gmm 6 – Moisture sensitivity 115 mm 2 – Nmax verification Performance testing Binder content Sample weight = 4,700 gm Anticipated binder content -0.5%, +0.5%, +1.0% 114 Mixing and Compaction Temperatures Unmodified binders Equiviscous temperature ranges  Normalize the effect of bitumen stiffness on mixture volumetric properties Viscosity range  Mixing = 0.17 ± 0.02 Pa-s  Compaction = 0.28 ± 0.03 Pa-s 115 Mixing and Compaction Temperatures Field recommendations Mixing temperature < 177°C  Aggregate sufficiently dried and uniformly coated Compaction temperature = 135-155°C  Adequate in-place density 116 Preparation of Mixtures Preheat aggregates Mixing temperature + 15°C (> 2-4 hrs) Preheat binder Mixing temperature AVOID – Elevated temperature for long duration Mix preparation Tare mixing bowl, add aggregates and mix Place on weighing scale, tare and add asphalt Mix aggregate and asphalt – Thoroughly coated  30-90 sec 117 Preparation of Mixtures Mix conditioning Both Gmb and Gmm samples Place in shallow pan (25-50 mm thickness) Conditioning time and temperature o Volumetric mix design  Allow binder absorption during mix design  Compaction temperature ± 3°C for 2 hours o Short-term conditioning  Mixture mechanical property testing  Simulate plant mixing and construction effects  135°C ± 3°C for 4 hours 118 Compaction of Mixtures Specified number of gyrations Specified height At Ndes gyration level Similar procedure except specified  Specimen height = 115 ± 5 mm height instead of no. of gyrations Preheat molds Specimen weight determination  Compaction temperature for 45-60 min Pour conditioned specimen in 1 lift Level mix and place paper disk on top Apply load = 600 kPa, 1.16° angle Release load and extract specimen 3840 − 3800 𝑥= × 7.5 − 7.0 + 3800 = 3810 gm (7.5 − 5.5) 119  Pa VMA Superpave Data Analysis Volumetric analysis VFA DP Air void content, Pa Voids in mineral aggregate, VMA Voids filled with asphalt, VFA Dust proportion, DP %Gmm @ Nini %Gmm @ Ndes 120  Pa VMA Superpave Data Analysis Density at Nini, Ndes determination VFA DP Obtain height of specimen at Nini and Ndes ℎ𝑁𝑑𝑒𝑠 Correction factor, 𝐶 = ൗℎ𝑁 𝑖𝑛𝑖 Calculate Gmb, estimated @ Nini 𝐺𝑚𝑏,𝑒𝑠𝑡 @𝑁𝑖𝑛𝑖 = 𝐶 × 𝐺𝑚𝑏 @𝑁𝑑𝑒𝑠 %Gmm @ Nini %Gmm @ Ndes Calculate % Gmm values 𝐺𝑚𝑏 @ (𝑁𝑖𝑛𝑖 𝑜𝑟 𝑁𝑑𝑒𝑠 ) % 𝐺𝑚𝑚 = × 100 𝐺𝑚𝑚 (𝑎𝑡 𝑡𝑟𝑖𝑎𝑙 𝑃𝑏 ) 121 Design Asphalt Binder Content Design asphalt binder content Air void content = 4%  96% of Gmm @ Ndes Verify values  % Gmm @ Nini  VMA  VFA  Dust proportion, DP Density at Nmax determination % Gmm @ Nmax < 98% 122 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 123 Performance Testing Rutting Repeated load creep tests Static creep tests Fatigue cracking Non-load associated cracking 124 Rutting High temperature + loading Laboratory tests Asphalt pavement Analyzer Hamburg wheel tracking 125 Repeated Load Creep Tests Asphalt Mixture Performance Tester Rutting : Flow Number 126 Repeated Load Creep Tests Repeated shear test at constant height High temperature testing 7-day maximum pavement temperature at 20 mm depth Shear loading = 5000 cycles 0.1 sec load, 0.6 sec rest period Measurement = Permanent shear strain 127 Static Creep Tests Testing at high temperature Suggested AMPT Flow Time Criteria AMPT – Flow time test Uniaxial loading – Single static load Load applied until Total axial strain = 2% Tertiary flow SST – Simple shear test Shear loading – Single static load 128 Cracking Flexural beam fatigue test Fatigue characteristics Four-point flexural loading 10 Hz Low temperature (usually 20°C) Fatigue endurance limit Strain level below which the fatigue life of the asphalt mixture is infinite and the pavement will not experience bottom-up fatigue cracking. Long life asphalt pavements 129 Non-Load-Associated Cracking Thermal cracking Lower pavement temperatures Tensile stress > Tensile strength Dependent on asphalt binder properties Tests Indirect Tensile Creep tests Indirect Tensile Strength test Critical cracking temperature Intersection of thermal stress curve and the mixture tensile strength curve 130 Testing Recommendations Conventional mixes Aggregates Natural, quarried and common synthetic (e.g., blast furnace or steel slag) Gradation Dense graded Bitumen Performance grade RAP Bitumen replacement ≤ 25% 131 Testing Recommendations Unconventional mixes Unconventional additives, modifiers, aggregates and/or recycled materials High levels of RAP and/or RAS or less commonly used recycled materials Non-standard mixtures or mixtures where the standard volumetric requirements have not been met 132 Contents Production of Bituminous Mixtures Behavior of Bituminous Mixtures Desirable Properties of Bituminous Mixtures Volumetric Properties Mix Design Performance Testing Field Verification of Bituminous Mixtures 133 Laboratory Design v/s Field Production Laboratory mixing bowl v/s 500 ton/hr HMA plant Causes of variability  Different physical handling of the aggregate  Particulate control  Differing environment for absorption Reconciliation of differences  Identify adjustments o Aggregate proportions  o Asphalt content  o Aggregate source properties × 134 Quality Control Tests and Calculations Bitumen content Aggregate gradation Maximum specific gravity of mix Bulk specific gravity of mix  Recommendation – Laboratory compaction without reheating Air voids Stability and Flow 135 Job Mix Formula Verification Compare field-produced mixture properties with JMF  Bitumen content  Gradation  Void analysis  Other specified tests Adjustments to JMF – May be required  Significant changes – New mix design  Adjusted JMF  Average results of plant-produced mix 136 Daily Mix Verification Random sampling Control charts o Data dispersion  Random about target value  Between the control limits Indications of problems  Values consistently higher or lower than the target value  Gradual or erratic shifts in data  Systematic cycling of data UCL = Upper control limit LCL = Lower control limit 137 Volumetric Adjustments Most common problem  Inadequate VMA and air voids Reason  Difference in curing time and temperature  Breakdown of aggregates 138 Volumetric Adjustments Suggestions to restore VMA Standardization of curing parameters Sampling and testing procedures Gradation change Increase fracture content of aggregate Reduce natural sand components and increase usage of manufactured sand Introduce highly fractured, durable, intermediate-sized “chips” into the aggregate structure Reduce dust  Increasing fine aggregates with less material passing the 75 μm sieve  Not return all material from dust collection system  Wash aggregates 139 Density Specifications Method specification Control strip specified density No reference density Control strip – Minimum length Comparison  Average density – Reference density  Number, type and size of rollers  Compare – 𝐺𝑚𝑚 of field produced HMA  Number of passes each roller  Field density > 102% of reference  Use of temperature measurements density => New control strip Applicability Least effective in assuring pavement performance  Smaller projects, light traffic  High variability 140 Density Specifications Bulk specified density 𝐼𝑛 − 𝑝𝑙𝑎𝑐𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 × 100 % 𝑜𝑓 𝑏𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝐿𝑎𝑏𝑜𝑟𝑎𝑡𝑜𝑟𝑦 𝐵𝑢𝑙𝑘 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 Typical range = 96-100% of laboratory compacted bulk density Theoretical maximum specified density % 𝑜𝑓 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝐼𝑛 − 𝑝𝑙𝑎𝑐𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 × 100 = 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑀𝑎𝑥. 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 Typical range = 92-96% of theoretical maximum density 141 Density Specifications Change in materials Poor quality aggregate that degrades during compaction, often associated with thin lifts % 𝑜𝑓 𝑏𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 > 100% Problems with plant or laboratory equipment or Poor sampling or testing techniques. % 𝑜𝑓 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 > 97% Excessive moisture in the plant-produced mix Improper baghouse operations Variable absorption rates of aggregate materials 142 Density Specifications Design air voids = 4% (96% of Gmm) In-place density = 96% of lab density = 92% of Gmm = 8% air voids 143