Cold Weather Ruined Your Concrete Slab? Never Mind!
This blog aims to tackle the condtruction of dam dilemma in freezing regions. We figured out the reasons and solutions for the technical difficulties. We believe that the technical requirements under cold conditions are similar. If you are also concerned about these issues, keep reading!
Skim these cases in alpine regions. You may find what you need. Let’s get some inspiration from these project solutions!
1. Brief introductions of five projects suffering freezing and thaw
Project 1: Lotus Dam
The crest of the dam is 71.8 meters high and 902 meters long. As the highest reservoir in Lotus Dam Water Piles, its total storage capacity is 4.2 billion cubic meters. The dam site is located in the mainstream of Mudanjiang River in Hailin County, Heilongjiang Province. Its climate is below freezing all year round. With an average temperature of 3.2 ℃ for many years, its greatest temperature is 37.2 ℃, andthe minimum is-45. 2 ℃.
Project 2: Xiaoshan rock-filled slab
The crest is 85.90 meters high 290meters long. The reservoir has a total storage capacity of 107 million cubic meters and an installed capacity of 160MW.
Project 3: Songshan concrete rock-filled slab
It measures 80.8 meters high. The length of its crest is 259 meters, with a total reservoir capacity of 133 million cubic meters.
Project 4: Shuanggou concrete rock-filled slab
The maximum height of the Shuanggou dam is 110.5 meters and the crest’s length is 294 meters. The total storage capacity of the reservoir is 38.8 billion and the installed capacity is 280MW
Project 5: Pushihe Pumped Storage Power Station
The crest height is 78.5 meters, and the length is 80.8 meters. The annual average temperature is 6.6 ℃, the maximum temperature is 35.0 ℃, and the minimum is-38. 5 ℃. Locating in alpine regions makes the construction of the selected rock dams even more difficult. Also, a series of technical problems caused by the changes in the external environment of the panel itself is a big headache to the crew.
Here is a list of the most common causes and solutions of concrete defects during the winter months.
♦ Water-proof structure with peripheral and in-between cracks
In winter, under the combined effect of the ice and the rising water, the displacement of the plate joints is severe. The water barrier structure of the concrete surface of the Lianhua Dam was severely damaged. The water-stop construction used by the panel is classic: a stamped rubber square plate, encased in a galvanized iron sheet.
At the joint of the panel, the bolt is pulled off. The angle steel is stretched and bent. The rubber plate is torn off, and the SR-3 packing in the joint between the plates is damaged.
The water-proof mode adopted by the panel layer of Lianhua Dam in the water level fluctuation area is as follows. We adopted a new buried structure with pp fiber added in the mix to improve the frost resistance and reduce the forces from ice pull-out, expansion, and thrust. We also adopted this new buried water-proof structure in Shuanggou and Pushihe face rock-filled dams.
♦ Frost heave resistance of cushion material
Permeability reaches from 10 to minus 3 cm of capacity per second or 10 to minus 4 cm of capacity per second. The guarantee technology still has the anti-seepage ability even when there exist cracks on the surface.
Yet, maintaining this specification in cold areas will lead to poor drainage. As soon as the temperature declines, the liquid will diverse into solid. As the volume expanded, cracks appear on the concrete slabs.
If the drainage of the buffer material is uneven, the moisture will change from a liquid to a solid when the temperature is below zero. The cushion material expands in volume and changes from moisture to solid. The volume expansion of layer materials leads to the failure of the concrete slab.
The cushion material of conventional power stations in high cold regions requires that the permeability coefficient should not be less than ten negative cubic centimeters per second. The climate of Pushihe Pumped Storage Power Station is even more severe. So the cushion material should be gravel drainage material instead of fine sand. The permeability coefficient should be no less than ten negative quadratic centimeters per second. Last but not the least, former used teel fiber is replaced by the macro fiber which is less likely to withstand corrosion.
♦Crack resistance of slab concrete
1. The panel itself is thin and exposed to air in a large area. It is very sensitive to the coldness
2. The external reason is the sudden drop of temperature
3. Shrinkage tension in the process of concrete drying.
All these factors working together lead to cracks in the slab, thus the anti-seepage index of the concrete slab decreases.
1. Additives: anti-cracking agent, high-efficiency water reducing agent, air-entraining agent and fly ash, etc.
2. Concrete shrinkage rate, ultimate expansion rate, and concrete water-ash mixture ratio are determined by experiments.
2. Bullet points of our renovated methods
1. Still building the slope rolling? No! Let’s combine!
The conventional method for building the slope rolling. A new form of slope consolidation is adapted to extrude the side walls.
Based on the present technology and the terrain, we combined placing cushion material with making slope-fixing mortar. The specific operation process is as follows: first, support the formwork on the upstream slope of the dam, and then fill the cushion material in it. In this way, a gap will appear between the template and the cushion material. Finally, pour mortar into the gap.
During vibration rolling, the module will provide reliable support for mortar and cushion materials. Finally, it will achieve the compactness of the upstream slope of cushion materials, and form a mortar protective layer. As the filing process goes, the cushion materials will finally form a framework.
The incoming Pushi dam will also adopt this technology.
2. Renovate the way of spaying process:
Adopt the principle of “twice oil, twice sand, and once mill”. When the dam is larger than the common slab, its liding speed of sliding mode is less than conventional ones.
To reduce friction, our spraying process is: “twice oils, twice sands and once mill”.
A flexible isolation layer with no more than 3 mm’s thick is formed in this way. The modified emulsified asphalt is tightly bonded with the surface of the slope-fixing mortar.
3. Confront different heights when sealing the dam body? Build erect slab bridges!
The quarry is located upstream of the dam, so all the materials on the dam need to cross the toe slab on the dam. There is no precedent in China.
To meet the different height requirements of filling dam bodies, five-span toe slab bridges need to be erected in Shuanggou Dam.
The bridge adopts Bailey steel bridge. The pier abutment is of a reinforced concrete structure. The middle abutment is combined with a toe slab and concrete structure. This renovation makes transporting building materials accessible.
Fiberego has rich experiences in the construction of face dams in alpine regions. Besides the cases above, the following construction experiences of face dams in alpine regions are also valuable:
1. Kokoya Dam.
According to the comprehensive situation in this area, after pouring and forming the concrete slab, tar plastic is evenly smeared on the slab. Coloring it into black helps to absorb sunlight.
2. Haba River Pass Dam.
Located on the Haba River in Xinjiang, the dam has a height of 40.5 m. It is located at 48 degrees north latitude, and the minimum temperature is -44.8 ℃. Completed in 1996.
3. Chalong Dam, Naqu River, Tibet.
It has a dam height of 39m, a crest elevation of 4388m, and an extreme minimum temperature of-41. 2 ℃. Built in 1996, it was the highest dam in the world.
√ Semi-permeable design
√ Low-temperature properties of panel caulking energy materials
√ Brush black paint on water level change area
4. Xiaoshan Dam locates in the Songjiang River in Fusong, Jilin Province.
It has a height of 86.3 meters and a minimum temperature of-40. 5 ℃. Built in 1997, the main problem was that part of the anchor bolt is broken and part of the waterproof filler in the expansion joint is damaged. Its water proof structure no longer has a sealing function, threatening the safety and stable operation of the dam.
How do we select bonding materials?
Seal the water stop mask at the top of the panel with adhesive. We have chosen JGN-II architectural structural adhesive from the Chinese Academy of Sciences.
To protect the water stop material, choose the surface covering film. The materials must be elastic and ductile. It must have the following features like low-temperature resistance, freeze resistance, water resistance, aging resistance, corrosion, and tear resistance.
For anti-aging, the water-stop fillers should be strong sealing and elastic. The best choice is polyurethane.
Last step, choose the proper forms of wind pressure
Angle steel sealing and expansion bolt anchoring.
The angle steel measures L40x90 is used to buckle the back first.
The M10 bolt with round head is used to implant the concrete slab in the next step.
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