The Asphalt Mixture Intelligent Linear Shrinkage Coefficient Testing Machine is a high-precision laboratory instrument used to measure the linear shrinkage characteristics of asphalt mixtures under controlled conditions. It features intelligent control and stable performance, and is widely applied in asphalt pavement material testing, quality control, and research to evaluate deformation behavior during temperature variation.

Asphalt Mixture Linear Shrinkage Coefficient Tester

Model:TD720-2

I.Product Introduction

The TD720-2 Asphalt Mixture Linear Shrinkage Coefficient Tester is developed by our company in accordance with the Chinese standard JTG 3410-2025 Standard Test Methods of Asphalt and Asphalt Mixtures for Highway Engineering (T0720-1993), which incorporates design concepts from AASHTO and EN standards for evaluating the low-temperature performance and shrinkage behavior of asphalt mixtures. It is specifically designed for determining the linear shrinkage coefficient of asphalt mixtures, ensuring reliable and accurate test results.

II. Technical Specifications

Temperature control range (controller): -50 to 99.9°C

Power supply: 220 V

Temperature control accuracy: ±0.1°C

Water bath dimensions: 300 × 200 × 150 mm

Heating power: 1000 W

Refrigeration power: 280 W

Equipment temperature range: -50 to 60°C

Specimen length for shrinkage measurement: 200 ± 20 mm

Dial gauge measuring range: 0–12.5 mm

III. Test Procedure

1. Preparation

1.1 Specimen Preparation

Prepare slab specimens with dimensions of 300 mm × 300 mm × 50 mm using the wheel compaction method in accordance with T0703 of this specification. Then, cut the slabs sequentially into prismatic specimens of 20 mm × 20 mm × 200 mm using a stone cutting machine. Each group shall consist of no fewer than three specimens.

1.2 Specimen Measurement

Measure the dimensions of the specimens using a caliper. The length shall be the average of two measurements taken on opposite sides (L). The height and width shall be the average of measurements taken at both ends and at the middle section in different directions, accurate to 0.1 mm.

The deviation between the cut specimen dimensions and the standard dimensions shall not exceed ±2 mm in length and ±1 mm in height and width.

1.3 Physical Properties Determination

Determine the density, air voids, and other relevant physical properties of the asphalt mixture in accordance with this specification.

2. Test Procedure

2.1 Installation of Measuring Heads

Bond metal measuring heads to the center of both ends of the specimen. The end in contact with the dial gauge shall be fitted with a flat-head measuring tip, while the opposite end shall use a hemispherical measuring tip. Use 502 adhesive to bond the tips, applying slight manual pressure until firmly fixed.

Note: The measuring heads shall be accurately aligned along the central axis of the specimen, and the contact surface shall be perpendicular to the axis. After bonding, place the specimen on a glass plate.

2.2 Preparation of Temperature-Controlled Bath

Fill the constant-temperature bath with a methanol aqueous solution as the cooling medium. The liquid level shall be at least 20 mm above the top of the specimens. Adjust and maintain the bath temperature at the initial test temperature of +10°C.

2.3 Conditioning of Specimens

Place the glass plate and the specimens (a group of three) into the constant-temperature bath. The glass plate shall be elevated at least 30 mm above the bottom of the bath, and the spacing between specimens shall not be less than 10 mm.

During the entire test process, the orientation of the specimens shall not be reversed. Maintain the specimens at the initial test temperature for 30 minutes before starting the test.

2.4 Determination of Initial Reading (L₀)

After temperature conditioning, quickly remove the specimen from the bath. With one hand, pull out the measuring rod of the dial gauge (or displacement sensor), and with the other hand, place the specimen on the left end of the specimen holder, ensuring it is firmly positioned against the measuring rod and the inner positioning stop. Then gently release the measuring rod so that it contacts the measuring head.

Under a no-load condition, record the dial gauge (or displacement sensor) reading (L₀) as the initial shrinkage reference value, accurate to 0.001 mm. Immediately return the specimen to the methanol aqueous solution.

The time from removing the specimen from the bath to recording the reading shall not exceed 5 seconds. Otherwise, the specimen shall be returned to the bath and conditioned for approximately 10 minutes before re-measurement.

2.5 Cooling and Final Reading (Lₑ)

Place the specimen back in its original position in the bath. After all three specimens have been measured, start cooling the bath at a rate of 5°C/h (or other specified cooling rate) until the target final temperature of −30°C is reached. Stop cooling and maintain this temperature for 30 minutes.

Repeat the procedure described in 2.4 to obtain the final reading (Lₑ), accurate to 0.001 mm.

2.6 Measurement at Intermediate Temperatures

To determine the shrinkage coefficient over different temperature intervals, measurements may be conducted at every 10°C decrease. After each temperature drop, maintain the temperature for 30 minutes and determine the specimen length according to the method described in 2.4, then continue cooling.