Key Factors Affecting the Performance of Modified Asphalt Equipment: Additive Characteristics, Heating Method, and Mixing Time Correlation Analysis

Modified asphalt equipment (e.g., mixing tanks, shearing machines, dosing systems) is critical for producing high-performance modified asphalt—used in highway pavements, airport runways, and municipal roads—with properties like improved high-temperature stability and low-temperature crack resistance. The equipment’s performance directly determines the uniformity, stability, and quality consistency of the final modified asphalt. Among influencing factors, additive characteristics, heating method, and mixing time are the most critical, as their interactions account for over 70% of variations in modified asphalt quality. This article analyzes each factor’s impact and their correlations, providing guidance for optimizing equipment operation and product quality.

1. Additive Characteristics: The Fundamental Factor Shaping Equipment Adaptability

Additives (e.g., SBS, APP, rubber powder) are the core of modified asphalt, and their physical-chemical properties determine the equipment’s required mixing intensity, temperature range, and dosing precision. Mismatched additives and equipment often lead to poor dispersion (additive agglomeration) or material degradation.

1.1 Additive Type and Equipment Requirement Matching

SBS (Styrene-Butadiene-Styrene) Copolymer: The most widely used additive, with high elasticity but poor compatibility with base asphalt. It requires equipment with high-shear mixing capabilities (shear rate ≥ 5,000 s⁻¹) to break SBS particles into 1–5 μm micro-particles and disperse them evenly. For example, SBS-modified asphalt production must use a colloid mill or high-shear mixer; ordinary agitators (shear rate < 1,000 s⁻¹) result in SBS agglomeration, reducing asphalt’s high-temperature stability (dynamic stability drops by 30–50%).

APP (Atactic Polypropylene): A thermoplastic additive with good heat resistance but high viscosity. It requires equipment with strong agitation torque (≥ 50 N·m) to melt APP pellets (melting point 160–180°C) and mix them with asphalt. Equipment with insufficient torque causes APP to stick to the mixer wall, forming lumps that affect asphalt uniformity.

Rubber Powder (Waste Tire-Derived): A porous, low-density additive that absorbs asphalt oil components. It requires equipment with pre-mixing and soaking functions—first soaking rubber powder in hot asphalt (160–170°C) for 10–15 minutes to expand pores, then using a paddle mixer for secondary mixing. Without pre-soaking, rubber powder floats on the asphalt surface, leading to uneven distribution and reduced low-temperature crack resistance.

1.2 Additive Particle Size and Dosing Precision

Particle Size Impact: Fine additives (e.g., SBS powder < 1 mm) require lower shear intensity but higher dosing accuracy (error ≤ ±0.5%) to avoid local over-concentration. Coarse additives (e.g., rubber powder 2–5 mm) need higher mixing intensity but allow slightly larger dosing errors (±1%). For example, using SBS granules > 3 mm in a high-shear mixer increases shear time by 50% and wears the mixer blades faster.

Dosing System Adaptability: Powdered additives (e.g., APP powder) require a screw dosing system with anti-bridging design (to prevent powder compaction in the hopper); granular additives (e.g., SBS granules) use a vibratory dosing system to control feed rate. A mismatched dosing system (e.g., using a vibratory feeder for fine powder) causes feed fluctuations, leading to additive content deviations of ±2%—exceeding the industry standard (±0.5%).

2. Heating Method: A Critical Factor Controlling Temperature Uniformity and Energy Efficiency

Modified asphalt production requires precise temperature control (typically 160–190°C) to ensure additive melting, avoid asphalt aging, and maintain material fluidity. The heating method of the equipment directly affects temperature stability, energy consumption, and asphalt quality.

2.1 Common Heating Methods and Their Performance Comparison

Heating Method
Working Principle
Temperature Uniformity
Energy Consumption (kWh/ton)
Suitable Additives

Electric Heating
Heating tubes embedded in the mixer wall heat asphalt directly
±3°C
80–100
Small-batch production (SBS, APP)

Thermal Oil Heating
Circulating thermal oil (heated by a boiler) transfers heat to the mixer jacket
±2°C
60–80
Large-batch production (rubber powder, SBS)

Direct Fire Heating
Burners heat the mixer outer wall directly
±5°C
50–70
Low-sensitivity additives (rubber powder)

Temperature Uniformity Impact: Thermal oil heating uses a jacketed structure, ensuring even heat distribution (temperature difference < 2°C between the mixer center and wall). This avoids local overheating (which ages asphalt, increasing its brittleness) or underheating (which prevents additive melting). Electric heating is suitable for small batches but has higher local temperature fluctuations (±3°C), while direct fire heating is prone to hot spots (±5°C) and is only used for low-sensitivity additives.

Energy Efficiency and Safety: Direct fire heating has the lowest energy consumption but poses a fire risk (asphalt is flammable). Thermal oil heating balances efficiency and safety, making it the most widely used method for large-scale modified asphalt plants. Electric heating is safe but has high energy costs, limiting its use to small workshops.

2.2 Heating Control System Precision

Advanced equipment uses a PID (Proportional-Integral-Derivative) temperature control system with real-time temperature feedback (via PT100 sensors, accuracy ±0.5°C). The system adjusts heating power dynamically—e.g., reducing power when temperature approaches the set value (180°C) to avoid overshoot. A low-precision control system (e.g., on-off control) causes temperature oscillations (±10°C), leading to inconsistent additive dispersion and reduced asphalt performance.

3. Mixing Time: The Key Factor Balancing Uniformity and Production Efficiency

Mixing time directly affects additive dispersion uniformity and production efficiency. Too short a time leads to poor dispersion; too long increases energy consumption and asphalt aging. The optimal mixing time depends on additive characteristics and heating conditions, requiring a balance between quality and efficiency.