Correction of the determination for asphalt pavement surface texture depth by sand patch method

To enhance the accuracy of the sand patch method, this study proposes an improved sand patch method based on the original one through pre-test. The research has demonstrated that the mean texture depth (MTD) by the original sand patch method has a large fluctuation and low accuracy, measured supported by extensive on-site testing with a relative error ranging from 3.4 % to 55.0 %. In order to improve its precision, this study adopted a stepwise sand volume to determine the sand spreading diameter and proposed the steady-state range for both. The results showed that the steady-state range of sand volume and diameter varies under different texture depths. The recommended sand spreading volume for lower texture depth (MTD < 0.5 mm) is 25 ml, and for medium texture depth (0.5 mm < MTD < 1 mm) is 50 ml, and for higher texture depth (1 mm < MTD < 1.25 mm) is 75 ml. To facilitate on-site testing, a sand spreading diameter of 25 cm can be used as the criterion. Starting with a sand volume of 25 ml, the sand is spread incrementally bu step of 25 ml until the diameter reaches 25 cm, then the test data obtained is considered valid. The improved sand patch method has a relative error ranging from 3.3 % to 4.6 %, significantly enhancing the stability and accuracy of pavement texture depth test, successfully overcoming the limitations of the original sand patch method.