## 1 Introduction  
As detailed in ACI 210R-93 [1], most of the abrasion erosion harm is attributed to the action of water-borne silt, sand, stone, rock, ice, and other scraps on the surface of concrete during the hydraulic structure operation. In Taiwan, all rivers originate from the peaks of mountain ridges. Due to high altitude mountain and steep valley, all rivers are short and steep, causing rapid flow during storms, especially in the typhoon season. The average annual rainfall in Taiwan is about 2.6 times the world average. Therefore, rainfall is concentrated in the months from May to October, which is about 78% of the average annual rainfall. In addition, due to the frequent earthquakes in Taiwan, the fast-flowing river carries large quantities of sand and gravel, causing the river sediment yield and the percentage of sand in the river to exceed 10 times the global average [2]. Therefore, the main abrasion-erosion harms are caused by friction and the impact of waterborne sand on the surface of hydraulic concrete [3]. Hydroraulic concrete structures often sustain surface damage after being subjected to the rapid flow of waterborne sand and gravel over a long period. The masses and flow speeds of these waterborne particles constitute a transient striking momentum, slowly chipping off the concrete surface. This disintegrating behavior is known as abrasive erosion and eventually shortens the service life of hydraulic concrete structures. During field observations ([PERSON] 2005), waterborne sand was one of the main causes of abrasion-erosion damage in hydraulic structures other than large stone impacts. Figure 1 illustrates the abrasion process of a concrete surface subjected to a high speed impingement jet of waterborne sand. First, the part of the concrete that belongs to the surface of the mortar gradually wears away., subsequently exposing the coarse aggregate. Next, due to the impact of waterborne particles, the broken coarse aggregate results in the formation of tiny voids in the interface between the paste and aggregate. After repeated impacts, voids are formed, which further derive into the concrete. The formation of voids is profoundly affected by the size of the coarse aggregate, the type of sand used, and the momentum of the rotating water jet. The abrasion rate depends on the hardness, shape, size, and quantity of the waterborne particle; the speed of the water jet; and concrete quality. Although good-quality concrete can withstand the impact of high flow velocity of jet and has almost no damage, the concrete cannot withstand the abrasion effect of scraps grinding or repeated impact on the surface for a long time. The fact that water-cement ratio, cement amount in concrete, slump, air content, type of coarse aggregate, type of finish, fly ash, silica tune, fibers, and curing affect the characteristics of a concrete surface layer has long been recognized. Because these factors also influence the compressive strength of concrete, a tendency to accept concrete strength as a criterion for abrasion resistance evaluation is evident in references [4; 5; 6; 7]. Such as [PERSON] et al. [8] discussed the influence of gravels on the abrasion of high strength concrete. Test results shows the high strength concrete with gravels shows a lower abrasion resistance than the high strength concrete with no gravels. [PERSON] et al. show that the abrasion resistance is influenced by the interface between the aggregate and the paste. Since many types of abrasion become concrete damage problem, there are many abrasion test methods. Some researchers [9; 10; 11; 12; 13] use current commonly used test methods to determine frictional attrition under specific conditions, including the case of limiting amount of tiny grains on a small surface area of concrete. In general, the abrasion resistance is determined by the interface properties between the paste and aggregate. A water jet containing an appropriate amount of sand can be used to compare the actual abrasion and erosion of concrete to improve the existing abrasion method.