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Outline

The Yellow River is the second large one in CHINA. It originates from Qing-Tibet Plateau; pass over the Yellow Sand Plateau and the North-China Plain. The Yellow in Chinese means its water contain much sand and soil. In order to utilize the water in flood control, ice prevention, sediment reduction as well as water supply, irrigation and power generation, Xiaolangdi Multipurpose Dam Project (XMDP) was built in 2001.

 

XMDP is located at the last gorge of the middle stream of Yellow River near Luoyang, Henan Province. It controls 92.3% of the drainage area of Yellow River, almost 100% of the sand and 87% of the amount of water. The total dynamic investment of the Project is 34.7billion RMB and 200 thousand people need to be immigrated. The Project commenced in 1991 and completed at the end of 2001. XMDP consists of dam, flood discharge tunnels and underground power house. The elevation of the dam is 281m, and the highest part of the dam is 160m, the normal high water level is 275m.  The total reservoir capacity is 12.65 billion m³, of which 7.55 billion m³ is silt capacity and the long-term effective reservoir capacity is 1.05 billion m³. There are six powers and total generation capacity is 1.8 million KW.

 

In order to flush the silted sand and soil of the reservoir, there are three spillways to scour and flush the silted sand and soil at the bottom of the dam. Because of the high water fall and containing much more sand and soil, this yellow water run in high speed and cause heavy abrasion and cavitations erosion to the tunnels. See Fig. 1 and 2. No. 2 spillway is in the middle of these three ones and is the most serious damaged by high speed silt-laden flow.

 

        

      Figure 1   No. 2 Spillway              Figure 2 Spectacular Scouring and Flushing

Past Work Review

Hydropower outlet works, such as spillway, freshet, bottom outlet, spillway dam, stilling basin and so on, often easily suffered from the damage of abrasion and cavitations and has not been effectively solved so far. Every year the repairing and consolidating constructions consumed a great deal of financial and labor resources. With the great development of hydropower dams in China and the building of dams with high water head of fall and heavy flow in the future in the Southwest areas, the problem of hydropower outlet works easily suffering from damage of abrasion and cavitations is increasingly concerned by designers, researchers and managers in China. In solving that, besides the scientifically designing of hydraulic structures, advanced materials researching and applying is necessary and important to meet the need of hydropower projects.

In order to effectively control or slow down the surface damage of outlet works from abrasion and cavitations, special materials research and application have been continuously conducted, mainly focusing on two aspects: One is the High Performance Concrete (HPC) application technology with the applying mechanism “harder to harder”. We often use high grade cerement and high strength aggregate to produce the C60 HPC. But the result is not ideal. The other is the new organic polymer composite coatings with the applying mechanism “tougher to harder”, which is to prevent from the damage of abrasion and cavitations by the high tensile and tear strength and high toughness.

In the past, the technology of modification of epoxy resin was mainly researched to increase its toughness and reduce the brittleness to enhance the abrasion and cavitations resistant ability. However, due to many disadvantages, such as weakness aging and the susceptibility to oxidation by ultraviolet radiation of many C-O bonds in epoxy molecular, the bigger coefficient of linear thermal expansion which resulted in easily crack, tilt and delamination. During application, slow curing, sagging and the release of much VOC are inconvenient operation in situ. So epoxy resin has been simply applied in some repairing constructions and can not be applied in large hydropower projects.

Highlight of SPUA

Under the promotion of Prof. Huang, the concept of Spray Polyurea Elastomer (SPUA) has been gradually popularized in CHINA. SPUA is a kind of no solvents, no VOC, non-pollution and fast curing polymeric elastomer materials with excellent properties as the following:

(1)     Containing no catalysts, quickly setting, being sprayed on the curve, inclined and vertical surfaces with smooth appearance without any sagging, being able to sustain people to walk only after the coatings sprayed 1min and not be easily affected by the environmental temperature and humidity.

(2)     100% high solid content, no solvents and other volatile organic compound, non-pollution to environment, a real no VOC green product.

(3)     Excellent properties of good flexibility, high abrasion resistant, high adhesive strength to steel, concrete, asphalt and other substrates, high self tensile strength and elongation etc. and outstanding self-aging endurance.

(4)     Excellent endurance ability to high and low temperature from -25℃ to 150℃ in which can maintain good thermal stability to mechanical properties.

(5)     Being made into different color products by incorporated into different pigments and be able to be reinforced by adding some fillings such as short fibers.

(6)     Equipped with the special settings with high operating efficiency at the spraying speed about 10m²/min to spray 1mm thick coatings.

Lab Test

In order to test the properties of the damage of abrasion and cavitations by high speeding silt-laden flow, we design three C60 silicon fume HPC round samples whose dimensions is exterior diameter of 500mm, interior diameter of 300mm and length of 100mm. with different aggregates. Figure 3 is granite concrete with 2mm yellow SPUA lining and figure 4 is the same without lining. Figure 5 is limestone concrete. This apparatus can be conducted scouring experiments with three samples. Its main character and working functions include: high speed circular flow formed by the rotating wheel to scour the inside surface of concrete sample with the adjusting velocity from 20m/s to 50m/s, sand content of silt-laden flow of 0~10%, every scouring time of 30min and automatic displaying, inspecting and controlling the testing temperature which is required blow 40℃ during experiment. Table 1 shows abrasion results of C60 silicon fume concrete samples and SPUA sample scouring 1h at the flow of 40m/s with 10% sand contents.

      Fig. 3  SPUA Lining     Fig.4  Granite Concrete     Fig. 5  Limestone Concrete

Table 1  Abrasion results of SPUA and HPC samples scouring at high silt-laden flow

Abrasion resistant Materials Test items	SPUA lining	C60 HPC granite aggregate f28=65.6MPa	C60 HPC limestone aggregate f28=66.5MPa
Abrasive weight loss （g）	<2.5	98.0	414.0
Rate of abrasion （g/cm2. h）	<0.00266	0.104	0.440
Notes	No scouring traces and other changes in the lining surface, and even no traces on the orange peel surface due to spraying operation.	Lots of much obviously scouring traces and defects in the inside surface of samples and aggregates exposure obviously due to the surface mortar abraded

 

From table 1, it is obvious that the abrasion resistant property of SPUA is more excellent than HPC as C60 silicon fume concrete at high speeding silt-laden flow of 40m/s and its abrasion capability can reach above 15 times than HPC from the testing results.

Application in XMDP

In August 20～30 this year, Prof. Huang went to XMDP to apply SPUA on the surface of No. 2 spillway. There are three methods to investigate the application procedures in table 2.

Table 2  Three methods of the application procedures

Method Procedures	A	B	C
Water Jet	Yes	Yes	Yes
Bughole Filling	Yes	Yes	No
Moist Primer	Yes	Yes	Yes
Grey SPUA	2mm	2mm	2mm
Edge Ending	Foam Pipe	Foam Pipe + Epoxy Putty	Epoxy Putty

 

In over 10 years career to research and develop SPUA, Prof. Huang find that the Ф40～50mm polystyrene foam pipe (Foam Pipe) is an ideal material to end the polyurea edge as a smooth and slope. You can see this interesting phenomenon in Fig. 6 and 7.

Fig. 6 show the foam pipe is adhesive with double side tape on the concrete surface with moist primer. The left sample is applied as A method and the right is applied as B method. After 10 days scouring with high speeding silt-laden flow, the speed is more than 45m/s and sand content is more than 10%. Both of them are checked with excellent performance in Fig. 7. From the detail result in situ, we concluded that method A is the best way to apply polyurea lining in hydropower projects.

Actually, method A is under the instruction guide of SSPC Surface Preparation Course-Concrete. But the unique foam pipe technology to end the edge is a great discovery to contribute to polyurea industry both in China and all over the world. It is much more effective in edge ending than wire tape in large area projects, such as playground, water pound, sea wall , river wall and hydropower infrastructures.

 

        

Fig. 6 Edge ending with foam pipe before spray polyurea  Fig. 7 After scouring with high speeding silt-laden flow

Method C is simpler than A and B in Fig. 8. But after 10 days scouring with high speeding silt-laden flow, the lining was flushed away in Fig. 9.

        

          Fig. 8 Edge ending with epoxy putty            Fig. 9 After scouring with high speeding silt-laden flow

 

Furthermore we sprayed grey SPUA coating at Xin’anjiang reservoir spillway dam according to the above mentioned method A with 1200 square meters for a large scale test. See figure 10 and 11.

         

Figure 10  Substrate Preparation                                    Figure 11  Finished

Conclusion

With the excellent mechanical properties and the advanced applying application characters, SPUA is catching the eyes of engineers in many industrial fields and has been increasingly investigated and applied in recent years. The damage of abrasion and cavitations in hydropower outlet works is a severe problem and has been much concerned in the world for many years. Based on the needs of the abrasion resistant protection of outlet works, the excellent abrasion resistant SPUA materials and the suitable moist primer were developed and the scouring test at high speeding silt-laden flow was conducted by using self-developed apparatus. Furthermore, SPUA technology was firstly successfully applied in the hydropower constructions. However, the research works on the cavitations resistance and applications in other outlet works should continue to be carried out and we wish the continuing researching, developing and applying technology of SPUA will provide a new method for effectively slowing down or solving the hydropower outlet works suffered from the damage of abrasion and cavitations at high speeding flow or silt-laden flow.