The construction of cement mortar fabric should usually be carried out after the spiral steel pipe is laid, the pressure test is qualified, and the soil is compacted according to the design requirements. Because the steel pipe has small rigidity and a thin wall, the pipeline must be in a stable state during the fabric construction process. If The fabric anti-corrosion layer is made first, and then the tube is lowered. During the construction, the anti-corrosion layer is damaged due to large deformation during lifting, transportation, and soil return.
Before fabric construction, the inner wall of the pipe must be cleaned to remove soft floating rust, soil, scale, grease, welding slag, and other attachments; the protrusion of the inner wall of the steel pipe shall not be greater than 1/3 of the planned thickness of the anti-corrosion layer; The lateral deformation shall not be greater than the planning rules, and shall not be greater than 2% of the inner diameter of the pipe.
The inner anti-corrosion layer of cement mortar can be constructed by mechanical spraying, manual plastering, dragging, or centrifugal prefabrication. If it is necessary to use the prefabrication method to make the inner anti-corrosion layer, protective measures should be taken for the anti-corrosion layer during transportation, installation, and backfilling.
During construction, cement mortar is mainly mixed, the mass ratio of cement and sand is 1: (1-2), the slump of cement mortar is 60-80 mm, and the compressive strength of cement mortar should not be lower than 30 MPa.
The inner anti-corrosion layer of cement mortar constructed by the mechanical spraying method is smooth, fine, and dense, with uniform thickness and good effect. Foreign countries began to adopt mechanical spraying construction in the 1930s, and China has used it in Shanghai, Qingdao, Dalian, and other cities since the 1960s. When the mechanical spraying method is used for construction, the elbows, tees, special pipe fittings, and pipe sections adjacent to the gate valve can be painted by hand, and the lubricated sudden change is connected with the mechanical spraying fabric.
In addition, the drag tube or centrifugal prefabrication method is also widely used, and will not be described in detail here. Regardless of the construction method adopted, the maintenance process is the key link to ensure that the anti-corrosion layer in the cement mortar does not have cracks and hollowing. Therefore, after the anti-corrosion layer in the cement mortar is formed, the pipeline must be blocked immediately to prevent air convection; after the final setting, carry out moist maintenance. Generally, the maintenance time of Portland cement should not be less than 7 days, and slag Portland cement should not be less than 14 days; before watering, it should be blocked continuously and kept moist.