Fiber materials are widely used in asphalt pavement and road engineering to improve stability, crack resistance, and durability. The Fiber Length and Diameter Test Method provides an accurate and reliable way to evaluate key fiber properties, helping laboratories and manufacturers ensure material quality and optimize engineering performance.

I. Experimental Instruments and Materials

1.1 Experimental Instruments

The experimental instruments and requirements are as follows:

a) Fiber Image Analyzer: See Appendix G.1.1;

b) Dropper: Approximately 100 mm long, with an inner diameter of 5 mm to 8 mm. One end is smooth but not closed, and the other end is fitted with a rubber bulb. The dropper is marked with 0.5 mL and 1.0 mL graduations.

c) Pipettes: several 5mL and 15mL tubes;

d) Microscope slides and coverslips;

e) Dispersant: a low-speed stirrer for dispersing samples;

f) Brown reagent bottles, small beakers, dissecting needles, tweezers, and filter paper;

g) Glass rod.

1.2 Test Materials

The test materials are as follows:

a) Distilled water or deionized water;

b) Immersion solution: a mixture of equal volumes of glycerol and distilled water.

II. Experimental Procedure

2.1 Fiber Sample Preparation

2.1.1 Preparation of Wood Fiber and Flocculent Mineral Fiber Samples

Prepare 5 fiber slides according to G.2.2. Staining is not required.

2.1.2 Polymer Fiber Sample Preparation

Take approximately 200 fiber samples from at least 5 different locations (note that only one fiber should be taken from the same bundle; multiple fibers should not be taken); then randomly select 50 fibers and divide them into three roughly equal portions; place one portion of the sample on a slide, dip a glass rod into an appropriate amount of soaking solution to immerse the sample, use a dissecting needle to evenly disperse the fibers, and cover with a coverslip. Prepare a total of 3 fiber slides.

2.1.3 Preparation of Bundle-shaped Mineral Fiber Samples

Approximately equal amounts of sample were taken from at least five different locations to form a fiber sample of about 5g. The sample was then ignited at 530℃~570℃ for 30min to remove the wetting agent. After cooling to room temperature, three fiber-supported glass slides were prepared according to 2.1.2.

2.2 Test Procedure

The test procedure is as follows:

a) Place the fiber microscope slide under the microscope. Adjust the focus until the image of a single fiber is clear. Slowly move the microscope slide using the stage, observe through the eyepiece to locate a representative fiber field of view, select an appropriate magnification, and capture static images;

b) For lignin fibers or flocculent mineral fibers, multiple non-overlapping fields of view may be selected on each microscope slide to capture corresponding static images, so that the total number of valid fibers is 40–50. The total number of valid fibers on 5 microscope slides shall be 200–250. Fine fibers or impurities with a length less than 0.2 mm, fiber fragments with severe longitudinal splitting, overlapped fibers, or unclear fibers shall be regarded as invalid fibers;

c) For bundled mineral fibers or polymer fibers, multiple static images shall be captured, including every fiber in the specimen while avoiding repeated measurement of the same fiber.

d) When measuring fiber length, select the fiber to be measured in a static image, and click on a single fiber on the display screen along the fiber direction to subdivide the fiber into multiple straight segments. The computer automatically draws the fiber skeleton structure and calculates the fiber length Li.

e) When measuring fiber diameter, select the fiber to be measured in a static image, click the two edge points in the fiber width direction on the display screen with the mouse, and the computer calculates the distance, which is the fiber diameter di;

f) When determining the maximum fiber length, reduce the magnification, slowly move the fiber slide using the stage, observe all the fibers on the slide through the eyepiece, find the three longest fibers, select an appropriate magnification, take a picture to form a still image, and then proceed to d) to determine the length of the selected fibers; measure all fiber slides in the same way, and take the arithmetic mean of all the measured values as the maximum fiber length Lmax.

III. Experimental Data Processing

3.1 The average fiber length L is calculated according to formula (H.1), accurate to 0.1 mm.

L = (∑_(i=1)^n L_i)/n （H.1）

Where: L—average fiber length (mm);

Li—length of the i-th fiber (mm);

n—total number of fibers measured.

3.2 The fiber length deviation rate is calculated according to formula (H.2) and is accurate to 0.1.

C_L = ((L_0 - L)/L_0) × 100% （H.2）

Where: CL—fiber length deviation rate (%);

L0—fiber specification length (mm).

3.3 The average fiber diameter d is calculated according to formula (H.3), accurate to 0.1 μm.

d = (∑_(i=1)^n d_i)/n （H.3）

Where d is the average fiber diameter (μm);

dt is the diameter of the i-th fiber (μm).

3.4 The fiber diameter deviation rate is calculated according to formula (H.4) and is accurate to 0.1.

C_d = ((d_0 - d)/d_0) × 100% （H.4）

Where: CA is the fiber diameter deviation rate (%);

d0—fiber specification diameter (μm)