Department of Civil Engineering, Earth and Foundation Structures, Faculty of Business and Built Environment, Tampere University of Technology, Tampere, Finland.
Inj Prev. 2018 Jun;24(3):224-231. doi: 10.1136/injuryprev-2017-042335. Epub 2017 Jul 28.
To assess the influence of grain size distribution and moisture condition on aggregates'Setting and methodsImpact attenuation of sands and gravels was tested using a guided headform with a uniaxial accelerometer inside. The result for impact attenuation was the acceleration value of the headform measured from four different drop heights and the Head Injury Criterion (HIC) calculated from it. The acceptable HIC value of a shock-absorbing layer is <1000, that is, less than the critical fall height. Tests were conducted with both dry and wet materials.
The impact attenuation of a shock-absorbing layer made of loose aggregate is determined mainly by the following material factors: maximum grain size, median grain size, uniformity coefficient, fines content, grain shape and moisture content. In addition, the moisture content of aggregate, especially sands, has a major impact on its impact attenuation capacity. Of the studied sands, coarse and gravelly ones had the best impact attenuation properties. Most of the examined sands were uniformly graded. None of the grain properties of gravels proved more significant than the others. Yet, open-graded gravel (dominant grain size 4-8 mm) containing a small amount (about10%) of sand fraction 0.06-0.6 mm, but with hardly any coarse sand (0.6-2 mm), was found to have good impact attenuation.
This study shows that the aggregates for shock-absorbing layer should always be tested wet in laboratory conditions corresponding the most critical situation. Standards should include a procedure for wet testing of aggregates.
评估粒度分布和水分条件对集料的影响
方法：使用内部带有单轴加速度计的导向头对头模进行测试，以测试砂石的冲击衰减。冲击衰减的结果是从四个不同的下落高度测量的头模的加速度值，并由此计算出头部损伤准则（HIC）值。减震层可接受的 HIC 值<1000，即小于临界下落高度。对干燥和湿润材料进行了测试。
结果：松散集料制成的减震层的冲击衰减主要取决于以下材料因素：最大粒径、中值粒径、均匀系数、细颗粒含量、颗粒形状和含水量。此外，集料的含水量，特别是砂的含水量，对其冲击衰减能力有重大影响。在所研究的砂中，粗砂和砾石砂具有最佳的冲击衰减性能。大多数研究的砂都是均匀级配的。没有一种砾石的颗粒特性比其他特性更重要。然而，发现含有少量（约 10%）0.06-0.6mm 砂级分但几乎不含粗砂（0.6-2mm）的开级配砾石（主导粒径 4-8mm）具有良好的冲击衰减性能。
结论：本研究表明，用于减震层的集料在最关键的情况下，应始终在实验室条件下进行湿测试。标准应包括集料湿测试程序。
