Hydro tunnel lining concrete crack control in the application of

Abstract: The crack is the concrete structure of the major diseases of aging, mainly by the shrinkage of their own quality of concrete, cement hydration heat, temperature, corrosion, ground deformation, load, alkali aggregate reaction, such as the original ground frost .. ....

Keywords:: tunnel lining concrete crack Dam
Concrete structures, cracks one of the major diseases of aging, mainly by the shrinkage of their own quality of concrete, cement hydration heat, temperature, corrosion, ground deformation, load, alkali aggregate reaction, ground frost and other causes.

Hydro tunnel lining concrete indicators of the general design C20P8F100. Construction conditions: pumping, mixing outside the cave, inside the cave, casting, inside temperature 17 ~ 180C. For the control of cracks, the construction of the following measures.

1. Control of shrinkage cracks
Concrete shrinkage cracks was mainly due to capillary pressures. Capillary pore water loss during the drying process step by step, resulting in a large capillary tension, the volume shrinkage of concrete, the concrete around the existing constraints, the internal tensile stress again, when the tensile stress tensile strength than concrete, they produced a shrinkage cracks.

Shrinkage crack control methods are:
1.1 Concrete units reduce water consumption: the increase in water so that the remaining water is bound to increase, therefore, to ensure the durability of concrete from the start, should lower the concrete unit of water consumption.

1.2 Influence of cement: Different cement, concrete shrinkage is different, according to the shrinkage order of: Slag Cement> Portland cement> fly ash cement.

1.3 reduce the concrete around the constraints: If the concrete around the constraint is too large, the internal tensile stress can not be released, leaving concrete dry tensile stress increases, therefore, should reduce the length of the concrete sub-positions, so that tensile stress inside the concrete to fully release.

1.4 Add expanders: appropriate amount of expansive concrete can be made after the volume expansion, the internal compressive stresses in the concrete, partially offset by the capillary porosity of the concrete tensile stress resulting from drying, and thus play a role in controlling shrinkage cracks.

The project area in the control concrete shrinkage cracks using the above methods 1 to 3. One unit of water consumption is 182kg, using ordinary 425 # cement mixed with fly ash pouring in, pouring section of about 10m in length.

2. Quality control due to their own lack of concrete cracks formed
High-strength concrete strength grade cement and cement consumption is relatively high, cracking phenomenon is relatively common, therefore, high strength concrete is not necessarily high-performance concrete, and high performance concrete with high volume because of stability, leaving less shrinkage cracking greatly improved performance, while high-strength concrete superplasticizer and superfine must be active admixture for a concrete part of the fifth and sixth, to increase the density of concrete and impermeability. because this project uses Pumping Technology, required slump and the larger volume of cement used, must be mixed with additives and the way to achieve both the reduction of water to make concrete slump loss without too much purpose, and add superfine active admixture to achieve lower water of heat, to improve and enhance the performance and saving cement concrete purpose.

Technology for fly ash in concrete water industry in the province is still at the exploratory stage, solid-substitution is not large, only 15%, but according to the data, the amount of cement in concrete for every unilateral change in 10kg, the corresponding heat of hydration down 1 ~ 1.20C, the result of this project, the concrete mixed with fly ash leaving the internal temperature decreased by about 5.5 ~ 6.50C, to some extent control the cracks.

3. Control of thermal cracking of hydration
After the release of a large number of cement hydration heat, the concrete form a larger temperature difference between inside and outside, resulting in the formation of temperature cracks under stress. In particular, the construction in the summer noon, the temperature is usually in Celsius 370C, open storage of the stone surface temperature of up to C 500C, concrete out of the boarding around 300C Celsius, higher internal temperature of concrete hydration. to control the hydration of concrete cracking, the following measures used in the construction
3.1 The cooling aggregate
The temperature control is mainly through the aggregate and built the arbor and sprinkler for cooling. And built the arbor to avoid direct sunlight and reduce the aggregate heat, 2 to 3 hours before pouring and then well water (about 170C for a full coarse aggregate sprinkler cooling. to take the above method after cooling, the internal temperature before pouring coarse aggregate of approximately 240C, fine aggregate internal temperature of about 260C, more obvious cooling effect.

Ice cooling 3.2
Acquired before the concrete pouring ice Zacheng small size of about 3cm, adding concrete raw meal, take out the full amount after mixing machine port temperature, according to a local port temperature to determine the ice volume. Practice, the machine control port temperature 180C, unilateral use of ice in the concrete around 60kg. for ice crushing workload of large particle size is difficult to control, add the ice needed to extend the post-mixing time and reduce the rate of concrete placement for overcome this problem, the actual work in the use of mixing water cooling method, that is a little crushed ice into the mixing pool to reduce water temperature. With this method, usually to the mixing water temperature drops to about C 3 ~ 70C .

3.3 pouring night
Daytime high temperatures, even using a variety of cooling measures is difficult to ensure the concrete placing temperature, and pouring the night - especially after the night of pouring, the temperature is relatively low, temperature control measures taken after the concrete easier to control the warehousing temperature. Therefore, the work processes more than the implementation arrangements for the other during the day, and the concrete placement arrangements at night.

Through the above temperature control, water control projects of concrete tunnel lining of the summer temperature in the mouth of the machine less than 180C, the 280C temperature control warehousing less effective in controlling the temperature cracks. Reposted elsewhere in the Research Papers Download http:/ / www.hi138.com 4. Concrete curing
As a result of ordinary Portland cement and Pumping Technology, the early heat of hydration of concrete larger. The measurement, usually in about 24h after pouring, the maximum internal temperature (about 330C, because of regulatory requirements at a time when steel formwork not yet removed, the surface can not directly spray water cooling, to reduce the concrete temperature, in addition to minimize the water-cement ratio, but in the pouring began after 18h of continuous steel formwork surface watering to cool the surface of concrete after form removal Maintenance around the clock to 14 days, this time inside the concrete tunnel lining after the temperature has dropped to 180C. whether by form removal before the cooling of steel template Observation of surface water spray, water spray to cool the surface of the steel template, and significantly higher than without the steel template surface temperature of the concrete cracks sprinkler much less, therefore, concrete curing temperature should start watering the template surface.

5. Cracks caused by steel corrosion control
Corroded Reinforcement 2 to 4 times volume expansion, the pressure generated on the surrounding concrete, smooth muscle may have cracks, or even fall off, thus affecting the use of the building. The steel corrosion mostly cavitation, causing ionization. Therefore, since the beginning of this project to note that the steel corrosion problem, and from the following aspects to be controlled on the steel corrosion.

5.1 The steel factory, the surface layer of dense oxide film, can play a protective role of reinforcement, but the film after contact with water or damp and slightly acidic due to water loss, so that corrosion of steel acid oxidation. Therefore, steel raw materials and semi-finished products after processing should be moisture-proof treatment. specific place and the practice is elevated above the waterproof poncho.

5.2 Cleaning the surface of reinforced before installation
Reinforced before installation, the surface must be clean, no dirt, rust on the site has to be polished with a clean wire brush and emery cloth to ensure the effective integration of steel and concrete, but also to prevent corrosion occurs due to ionization.

Reduce the concrete water-cement ratio and increased 5.3 concrete workability.

5.4 strengthen the vibration and improve the density of concrete, reducing the concrete carbonization speed, the bar long enough time is not exposed to air.

6. Control the deformation of rock around the tunnel
To prevent the cavern �� surrounding rock deformation zone of tunnel lining concrete cracks in the fallout of the tunnel excavation and support at an earlier stage �� surrounding area of ​​the bolting, anchor rod-shaped arrangement type as the plum, diameter 20mm, length 3m, between the row spacing 1.251 �� 1.25m, after the concrete lining of the consolidation grouting of the surrounding rock. To ensure the consolidation grouting anchor and quality, but also on the anchor lever pullout test, the pressure of consolidation grouting water and ultrasound tests.

By taking these measures, water control cracks in concrete tunnel lining will basically control the phenomenon, and achieved good results. Links http://www.hi138.com Research Papers Download