Dry spray jet concrete construction technology
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2. Spray concrete construction process measures All work processes must first carefully follow the design documents and construction specifications. Combined with past construction experience, the key points of each process are as follows:
1 On-site testing combined with past construction experience, through the indoor test can optimize the choice of both the construction needs, but also meet the design requirements of the shotcrete production process parameters and mix ratio. The method steps are as follows:
a. Select 2 to 3 sets of mix ratios through indoor tests, and prepare test syllabus for approval for production test;
b. Select the site (or designation by the supervisor), and select 6 to 9 representative sites for production tests according to the type and location of the surrounding rock.
c. According to the requirements of the design and test program, spray operations shall be carried out with the selected mix ratio. The injection range shall be tentatively set to 10m (or a unit volume), and sufficient wood molds or bottomless steel molds shall be installed on the rock face according to the specifications. Testing compressive strength, tensile strength, impermeability, bond strength with rock surface, etc.) At the same time, according to the test specifications, samples shall be taken as standard test blocks and cured under the same conditions;
d. Compare the physical properties of the test specimens that meet the design requirements (including the impact degree of blasting);
e. Arrange analysis and test records, select appropriate mix ratios and construction process parameters, such as comprehensive rebound volume, strength assurance rate, and construction efficiencies, and submit them to the design supervising agency for approval.
2 Prepare a well-prepared spray thickness control sign. There should be adequate ventilation lighting in the work area. Check all mechanical equipment and pipelines before spraying to ensure normal construction. Do a good job on the seepage surface, prepare the processing materials, and contact the warehouse for sample preparation.
3 Mixing and transportation Mixing ingredients are precisely prepared according to the experimentally determined mixing ratio. The stirring time should be sufficient. The mixing materials should be transported and stored in a rain-proof and anti-pollution manner. They must be screened strictly before entering the machine. Their transportation and storage time should be consistent with Technical indicators. Steel fiber concrete ingredients and stirring should be uniform. Transportation is carried by concrete mixer trucks.
The cement used for mixing is selected from the ordinary portland cement that meets the national standard, and its number is not lower than P.O32.5.
Aggregate: The fine aggregate used for mixing should be hard and durable, coarse and medium sand, the fineness modulus should be greater than 2.5, the moisture content should be controlled at 5 to 7%, and the coarse aggregate should be made of hard and durable pebbles or gravel. Over 15mm; Aggregate containing reactive silica should not be used.
Water: Mixing water should meet the requirements of the bidding documents.
Admixtures: The quality of accelerators shall comply with relevant DL/T5100 requirements and construction drawings and a quality certificate from the manufacturer. The initial settling time shall not be greater than 5 min and the final settling time shall not be greater than 10 min. The use of admixtures shall be supervised by the supervisor. Approved.
Mixing should follow the following rules:
When mixing with a forced mixer with a capacity of less than 400L, the mixing time shall not be less than 1min; when using a self-dropping mixer, the mixing time shall not be less than 2min; when the mixture contains additives, the mixing time shall be appropriately extended; The shotcrete is made of steel fiber feeders to add steel fibers to the mix. The mixing time is not less than 3 minutes.
4 Clean the rock surface to remove pumice from the excavated face, gravel and deposits on the foot of the wall, handle a smooth excavation surface, install a working platform, and flush the spray surface with a high-pressure water jet gun to use for the muddy rock formations that are easily deliquescent in contact with water. Pressurized wind to clean the rock surface; embedded signs to control the thickness of the sprayed concrete; buried in the drainage area of ​​the nozzle by the drainage of the catheter, poor water conductivity of the aquifer can be set up blind ditch drainage, drainage can be set at the drainage ring drainage. After acceptance of the warehouse surface, the rock surface with micro-osmotic water should be blown and dried before spraying.
In addition to removing the loose rock and scum from slopes and slopes, soil slopes should be leveled and compacted on the slopes, and then the soil slopes should be sprayed from the bottom to the top in segments. It is strictly forbidden to spray concrete on loose soil.
5 Reinforced mesh slope protection: Spray C20 concrete, steel mesh, anchor rods, drainage holes.
The reinforcement mesh is made of smooth steel (I-grade rebar) with a yield strength of 240 MPa. First spray 3cm~5cm thick concrete, and then as close as possible to the rock surface hanging steel mesh, for a larger part of the depression, can be added to expand the tension screw Wire Mesh, and then lay the reinforcement mesh, and the anchor rod and additional reinforcement (Or expansion bolts) firmly connected, and finally sprayed in 2 to 4 times to reach the designed thickness.
6 Injection points The shotcrete operation shall be performed in segments and segments in sequence. The injection sequence shall be from bottom to top to avoid that the rebound material covers the unsprayed surface. During stratified injection, the latter layer is carried out after the final layer of concrete is finally set. If the line is to be sprayed after the final setting of 1h, the sprayed layer shall be washed with high-pressure fengshui first. The spraying operation follows the excavation face, and the time for the final condensation of the concrete to the next cycle is not less than 3 h.
The jet operation strictly implements the operating rules of the jet machine: it shall feed the jetting machine continuously; keep the working jet pressure of the jetting machine stable; when completing or interrupting the jetting operation for any reason, the accumulated material in the jetting machine and the feeding pipe shall be cleaned to prevent Blocked pipe.
In order to reduce the amount of rebound and improve the quality of the spray, the sprinkler should maintain a good working condition. Adjust the wind pressure, keep the nozzle perpendicular to the sprayed surface, and control the spray distance in the range of 0.6m to 1.2m. Use the correct spiral trajectory spray construction process. The part that has just been sprayed is subjected to spray thickness inspection (detected by a buried point, needle probe, and a high-precision cross-section meter), and the double spray treatment is performed in time if the thickness requirement is not satisfied. Hanging nets must be sprayed until there are no obvious nets.