Understanding Asphalt and Asphalt Mix Design
1.1 Origin of Asphalt
Bitumen, a blackish-brown substance with a consistency ranging from semi-solid to solid, is a byproduct of oil refining. It’s a mixture of hydrocarbons completely soluble in sulfide. Bitumen is processed to remove impurities, resulting in asphaltic bitumen, the base material for various asphalt types.
Bitumen Classification by Origin
- Natural: Natural oil seeps onto the surface, forming lakes. An example is Trinity Lake in Venezuela.
- Artificial: Derived from oil refining. Not all crude oils are suitable for bitumen production. Asphalt-based and mixed-base oils are adequate, while paraffinic-base oils are not typically used.
Asphalt Features
Asphalt is highly valued in road construction due to its waterproofing, adhesive, and cohesive properties. It performs well with aggregates and can withstand significant, instantaneous forces. However, it tends to flow under constant loads.
1.2 Types of Bitumen
According to road manuals, bitumen is subdivided into:
- Asphalt Cement (Hot) (CA): Bitumen in its original state.
- Liquid Asphalt or Cutback (CA + Fluidizer): Asphalt cement mixed with a fluidizer.
- Asphalt Emulsions (Fluidizer + CA + Emulsifier): Asphalt cement mixed with a fluidizer and an emulsifier.
A. Asphalt Cement
- CA 40-50: Sealing, Gasket
- CA 60-80: Used in Pavements
- CA 80-100: Used in Pavements
- CA 120-150: Surface Treatment
The two figures (referring to 
and 
presumably) show penetration ranges. Sometimes, AC is specified by viscosity.
Penetration Test: A disk-shaped sample (55mm diameter, 35mm depth, 70mm height) is heated in a water bath at 25°C. A 100g standard needle is placed on the sample surface in a penetrometer and released for 5 seconds. The penetration depth is then measured.
Other tests characterize CA, such as flash point, softening point, and ductility.
B. Cutback Asphalt
This type is mixed with aggregates at low temperatures. After placement, the fluidizer evaporates, leaving the asphalt to bind the aggregates.
1. Rapid Curing (RC) Cutback Asphalt
Consists of CA + fluidizer (benzene). The accompanying number indicates kinematic viscosity in Centistokes (CST).
- RC-70: 70 to 140 CST
- RC-250: 250 to 500 CST
- RC-800: 800 to 1600 CST
- RC-3000: 3000 to 6000 CST
Viscosity: A material’s resistance to flow.
2. Medium Curing (MC) Cutback Asphalt
Consists of CA + fluidizer (kerosene).
- MC-30: 30 to 60 CST
- MC-70: 70 to 140 CST
- MC-250: 250 to 500 CST
- MC-800: 800 to 1600 CST
- MC-3000: 3000 to 6000 CST
3. Slow Curing (SC) Cutback Asphalt
Currently in disuse.
- SC-70
- SC-250
C. Asphalt Emulsion
Consists of CA + fluidizer (water) + emulsifier (soap/alkaline solution). The emulsifier creates a stable suspension workable at room temperature. Asphalt globules repel each other due to the emulsifier’s polarity.
Classification by Electrical Charge:
- Anionic
- Cationic
Subdivision by Rupture Speed:
- Fast
- Medium
- Slow
A. Cationic Emulsion (C)
Used with negatively charged aggregates (silicon).
- CRS (Rapid Setting)
- CMS (Medium Setting)
- CSS (Slow Setting)
B. Anionic Emulsion (A)
Used with positively charged aggregates (limestone).
- ARS (Rapid Setting)
- AMS (Medium Setting)
- SS (Slow Setting)
Note: CRS-1, CRS-1h, CSS-1, and CSS-1h are commonly used. ‘h’ indicates a CA penetration between 40-90.
Saybolt-Furol Viscosity Test: The sample is heated, poured into a standard tube, and the time for 60ml to flow is measured in seconds at 25°C. Acceptable values are between 20-100 seconds.
Asphalt Mix Design
Asphalt mixtures typically use CA for better adhesion, combined with aggregates meeting specific requirements. Mineral filler (passing sieve No. 200) reduces asphalt consumption and adds rigidity.
Asphalt film thickness affects mix stability and durability. Thicker films slow oxidation, which degrades the asphalt-aggregate bond over time. Angular aggregates and thick materials enhance stability. Waterproofing is achieved by minimizing voids (ideally ≤ 5%) through a closed gradation and optimal asphalt content. Some voids (around 3%) are beneficial for absorbing consolidation under traffic.
Marshall Design Method
Effective for hot and cold mixes, this method involves preparing specimens with varying CA percentages (typically 3-6%) for a specific gradation. Density and voids are determined, followed by the Marshall test. The specimen is heated to 60°C, drained, and compressed in a testing machine. Load and deflection at rupture are recorded.
Data is plotted on graphs:
- Stability vs. Percent Asphalt
- Flow vs. Percent Asphalt
- Density vs. Percent Asphalt
- % Voids (Mix) vs. Percent Asphalt
- % Voids (Aggregate) vs. Percent Asphalt
Optimal asphalt content is based on:
- Maximum Stability (Pb1)
- Maximum Density (Pb2)
- 5% Voids in Mix (Pb3)
The average of these values determines the optimal percentage.
Tolerance:
- Surface Course: Pb_optimal ± 0.3%
- Intermediate/Base Course: Pb_optimal ± 0.5%
Requirements for Asphalt Mixtures
(Referencing 
for a table of requirements)
Minimum Percent Voids in Aggregate
(Referencing a table of aggregate void percentages)
Filler amounts are typically 1.2-1.3 times the bitumen amount for surface courses and 1.1-1.2 times for intermediate courses. Common gradations include dense, semi-dense, open, and fine.
Example: (Referencing an example of mix design calculations and
for data)
The 4.6% bitumen content falls outside the tolerance, so it might be rejected. However, scale accuracy should be verified. If the result is deemed unacceptable, the testing procedure or gradation should be reviewed.
Construction Process
Base and subbase construction with granular materials involves:
- Surface cleaning
- Material transport and unloading
- Compaction and thickness verification
- Density and CBR control
A. Irrigation of Coats
The base layer is cleaned to improve bonding with the prime coat, typically an emulsion (CSS-1), applied at 1-2 L/m² (
presumably shows this process). The prime coat binds loose particles and enhances the bond with the intermediate layer.
B. Asphalt Construction
The mix is manufactured on-site or by a contractor. The plant mixes and heats aggregates, dries them, adds filler and bitumen, and discharges the mix into a truck. The truck is coated to prevent sticking and covered for transport.
Asphalt Control
Samples are taken at the manufacturing site to control asphalt content, physical properties, and uniformity. Truck samples are also taken randomly (at least 3 per truck) and labeled with date, time, location, and truck ID. Temperature is checked upon arrival (135-160°C).
Spreading the Mixture
The truck empties into a paver, which spreads, levels, and pre-compacts the mix. Ambient temperature should be above 5°C, without fog or excessive wind.
Compaction
Appropriate rollers are used based on thickness. Compaction occurs at 110-140°C. Equipment includes tire rollers, tandem rollers, and manual compactors. The finished surface should be free of segregation, cracks, deformations, and exudation. Density is measured (target 97% of Marshall density), and core samples are taken. Macrotexture and friction coefficient are also monitored (minimum 0.6 after 4 months).
Longitudinal and Transverse Joints
Longitudinal joints form between lanes, while transverse joints form when paving stops. (
presumably illustrates this)
Bond Coat
Asphalt is applied between layers for adhesion. The surface must be clean, and conditions suitable. The material is similar to the prime coat but applied less intensively (0.4-1 L/m² for emulsion) (
likely shows this). Drying time varies with weather conditions (6-48 hours).
Failures in Flexible Pavements
1 Cracking: The longitudinal cracks are approximately parallel to the axis of way may be due to an unstable embankment collapsed, may also result in poor drainage that causes erosion.
The cracks at the edges due to a failure of support in many cases by poor compaction of SAP, coupled with poor drainage, heavy duty vehicles very close to the edge.
Cracks between tracks on a single carriageway is due to poor performance in longitudinal construction joints.
Transverse cracks appear due to a poorly executed construction joint or when the asphalt mixture is too stiff causing excessive contraction of the mixture.
Fatigue cracks (alligator) whether this phenomenon occurs early in life can have six cases.
· Traffic higher than expected
· Insufficient compaction
· Asphalt inappropriate for the climate
· Falla resistant soil base or subbase layer.
2 Deformations:
i. Ahuellamiento: deformations are formed along the strip through the movement of vehicles, may be due to a mix that has a low stability (percentage of asphalt inadequate), traffic flow greater than expected, problems compaction of the mixture due to abrupt reversals compaction roller or deficient.
ii. Ripples: On the pavement surface are presented alternating hills and valleys.
Its cause may be excess asphalt, location favors because they are steep slopes and areas of heavy traffic.
iii. Displacement: This is the lateral displacement of the mixture that accumulates on the inside very often in areas of closed curves where heavy traffic, is also produced by an excess of asphalt (low stability) and also due to excessive traffic and careers.
iv. subsidence and upheaval: s or is main cause of soil consolidation or swelling.
3 Disintegration:
i. Holes: they are holes of different sizes and irregularly shaped, are found on the surface.
One reason is insufficient asphalt content, also for failure of irrigation league.
The bumps originate due to detachment of the aggregate of the mixture into the folder of rolling (CR), this separation is also due to some asphalt or the presence of water in the mixture or dirty aggregates that do not allow a good bond, including pollution of Folder lie rolling with some solvent was placed.
ii. Decline at the edges: The evolution of edge cracks among other reasons because the road has insufficient width and insufficient pavement thickness.