Application of Foam Concrete in Coal Mine

Due to its light weight, good thermal insulation and thermal insulation properties, seismic energy absorption and noise reduction, foam concrete materials are currently used in many fields such as domestic construction, floor heating and gardening. The application of foam concrete in China's coal mines has just started, but showed good momentum. In the near future, foam concrete used for coal mine will have a role to play in backfilling materials, supporting materials and water blocking materials in mines.

First, backfill.

1. Goaf backfill.

Our country is a big country for coal production and consumption. However, long-term coal mining has led to the formation of large-scale subsidence areas. According to incomplete statistics, the subsidence area in China reached 700,000 hectares by 2005. Mining subsidence led to the amount of da farmland abandoned, surface water damage, causing serious ecological disaster. The goaf backfill is the most direct and effective method to cure surface subsidence and mining damage. Backfilling of coal mined-out area is a worldwide problem. For a long time, the main technologies used at home and abroad include dry filling, water sand filling and cementation filling. Cementing and mining methods are mostly used in metal mines. General gravel, river sand or tailings as aggregate, and cement or lime cement materials to form a slurry or paste, and then sent by pipeline pump or gravitational gravity flow to the filling area mining methods. Compared with water sand filling, cemented and filled materials have great strength after cementation, which can be used for burial depth, large pressure and unstable rock mass with thick surrounding rock. Using cemented filling has become an inevitable trend of backfilling in coal mined-out area. In recent years, China successfully tested and popularized the application of new technologies such as high-concentration cement filling and high-water-setting and water-curing cementing and filling.

The cement used in conventional cement-bonded concrete filling materials is generally 42.5 ordinary portland cement, the dosage is 150-300kg / m3, the water-cement ratio is about 1.2-1.3, the compressive strength of concrete for 28 days is 5.0-10.0MPa, Accounting for 30 to 60%. General cost of coal increased by about 40 yuan / ton. Reduce the amount of cement and cost, is to find suitable for the new filling material in the mine an effective way. Foamed concrete has the advantages of convenient transportation, good fluidity and low price. It can maintain a certain strength by using tailings slag powder and cement with different gradation, and can be used as a new type of filling body in backfilling of coalmine goaf use.

2. Rush empty fill.

Roofing of mining face will form a certain range and height of empty roof, if not handled and filled in time, will cause the support body can’t play its supporting role, may cause a wider range of roof accidents and economic losses, may also result in gas build up.

The traditional method of dealing with these roof-top hollowing is to use hand-laid wooden stacks or chemically reinforced with polyurethane-based materials. Wood stack construction is slow, material consumption, wood stacks and roof contact surface is small, poor control, and the operation is very dangerous. There are high costs of chemical strengthening, easy to heat and other shortcomings. Filling foam roofs with foam concrete can overcome these drawbacks. By adjusting the foaming multiple and changing the water-cement ratio to adjust the compressive strength of foam concrete, the da can be increased to about 13MPa. When the material reaches the yield point under unidirectional compression, the material can still maintain a higher carrying capacity as the deformation increases. Because the material structure is closed-cell type, it has a good air tightness. This method of using foamed cement to fill up a hole can mechanize the work of handling the roof void, which is safe and fast in construction and can increase the support to the hollow wall to prevent the roof falling from continuing to expand and improve the interaction between the support and the surrounding rock, And to prevent the accumulation of harmful gases inside the hole to prevent ignition, is a new technology with many advantages.

Second, mine support.

Concrete has been the underground shaft engineering neutral shaft, well bottom, a variety of chambers and cast-in-wall not affected by mining. Rigid cast-in-place concrete only produces elastic deformation under the pressure of surrounding rock, and the failure phenomenon is more common when subjected to large rigid displacement.

Because of its certain flexibility, compressibility, and certain strength, foam concrete can be used as the following forms of support in the mine:

1. As a shrinkable support cushion.

Reduce and relieve the force of the stent, keep the stent uniformly loaded, and effectively release the initial elastic deformation energy of the surrounding rock.

2. Made of foam concrete block, used for roadway masonry and immediate support.

In recent years, the use of foam concrete block construction of ventilation airtight work has been in many mines in our country to promote the use of, due to the good retractability, the overall closure of superior performance, by field engineering and technical personnel The praise.

3. Canned pier.

One kind of foam concrete scaffold named Can has been used for more than 10 years in the United States, Australia and other countries. In recent years, the pier has been used in our country. In March 2009, Shanxi Coal Mine introduced a number of piers from Australia's Aria, produced by Hanson Burrel, Australia, with a maximum load of 200 tons. The pier has undergone scientific tests in the 402 dynamic pressure-controlled roadway under double test in Daning Mine, and the test has achieved satisfactory results. Compared with wood stack, the maximum load capacity of wood stack is 33.6 tons and the average bearing capacity For 28.48 tons; and the maximum bearing capacity of pier is 125.6 tons, the average carrying capacity of 75.75 tons, respectively 3.75 times and 2.66 times the wood stacks. From the road surface displacement, the use of woodpile support sections, the average top and bottom average approach is 221.6mm, the average amount of two closer to 154.5mm; and the use of pier support area, the top and bottom of the average The approaching amount is 85.37mm, and the average moving distance of the two groups is 34.2mm, which is 38.5% and 22.1% of the wood stack respectively. Pier supporting efficiency is 3-5 times the ordinary wood stacks.

Third, grouting plugging.

Grouting water blocking is an important technology in mine water control. At present, coal mine water injection grouting materials are mostly used cement slurry or cement - water glass slurry. Its main advantages are low cost, wide source of materials, but small cracks due to its easy to shrink after hardening. The cracks gradually expand under water scour and the water blocking effect is not satisfactory. The use of foam concrete as water-blocking material, as not affected by shrinkage deformation, closed-cell structure can effectively absorb the shrinkage deformation and increase the water flow path to achieve the purpose of sealing. Shengli Oilfield has achieved certain effects by using foam cement to block water, with an average effective period of 12.5 months.

Fourth, conclusion.