Caseshow - Technical Advice
Standardization construction and management (three concentrations, two access systems)
1, Construction site standardization
Site construction procedures need to be tightly standardized. This requires standardizing the specifications for the facilities to be used. These facilities include the highway construction site concrete mixing station, the steel processing field and all prefabricated field facilities. This standardization should eliminate hidden dangers from quality defects; enhance the image of the highway construction project as a whole, as well as substantively improving the overall quality of the project.
There is also a need to take advantage of the benefits that come from centralized management so as to allow concentration on construction activities. This centralization of management should apply to the work at the concrete mixing station, the steel processing field and to prefabricated field construction. The ultimate end is concentrated concrete mixing, pre casting of components and reinforced processing i.e.” three concentrations”. Such centralization of management should effectively eliminate the occurrence of many quality defects at the root.
2, Standardization of mixing station
After signing the contract, the construction unit should construct the mixing station in accordance with precepts of "industrialization, intensification and professionalism". The concrete used in each contract must be mixed together in one go (“concentrated mixing”), with the amount automatically calculated. Small mixing machines are not to be used to produce concrete.
3, Aggregates warehouse construction and management:
Aggregates of different particle size and variety are stacked in different warehouses. It is suggested that the warehouses be roofed with canopies; after the raw aggregates have been transported into the warehouse, inspection marks should be suspended over these warehouses.
Concrete reinforcing bars processing plant standardized construction.
4, Standardization of Concrete reinforcing bar processing plant.
Construction of the concrete reinforcing bars processing plant should be done by the project department, under unified management. The production of the concrete reinforced bars for Pile foundation, pier, the slab beam, and T beam should be done in a standardized fashion and all materials collected and transported to the site for installation after having been subject to inspection. The standardized construction of the concrete reinforced bars should fully exploit the advantages of a centralized operation and more effectively ensure the correct specifications for design size, spacing, the thickness of the protective layer of the concrete reinforced bars and the pre-stressed concrete reinforced bars. It should also prevent the concrete reinforcement spacing and the protective layer from going beyond what is required, along with allaying several other common quality defects.
5, Standardization of construction techniques:
Standardize highway construction, improve management, improve construction efficiency and overall quality of the construction projects. It will better accord the way construction technologies are used. Generally speaking it will likely suit the actual site conditions of the construction process found in situ and emergent operation procedures.
We need to implement two access systems to ensure the template quality. During site acceptance inspections they should accord with provincial standard guides when as regards T beam moulds double lining machines and pier mould section size, stiffness, smoothness and seams. Those rejected as not passing inspection will ensure the construction quality of precast beam, the double lining of the tunnel, the bridge pier structure, and will optimize the appearance of the structure.
Acceptance inspection the section size set for the double lining machine, the stiffness, smoothness, seam indicators should all be subject to., should maintain strict control of the double lining machine positioning and maintenance, after uninstalling of the template, abrasive brush and repair and maintenance work should be conducted to ensure that after repeated use it still meets requirements of precision, smoothness and fineness. This should eliminate common quality defects such as obvious unexpected concrete cracks in the second lining, serious faulting of slab ends, and undesired levelness.
6, Suggestions on how to curb common quality defects on the prefabricated T beam, concrete surface and tunnels:
(1) Use steel framework installation shed and use “membranes method” installation to install steel bars. This will enable all-day installation work, and non-interrupted work.
(2) Install water spray pipes on the beam head and beam end to ensure adequate curing; in another word, no defective curing.
(3) Set up monitor station at the bridge precast yard; carefully inspect and test the appearance and size of the beam slab, strictly prohibiting disease-carrying beam slabs to be installed on the bridge.
(4) Cease using the traditional pre-tensioning construction technology and instead commence use of smart pre-tensioning equipment to minimize human error and impose accurate tension. This will also enable timely checks of the elongation indicator, synchronize double controls of tension and elongation and synchronous balancing between the tension and elongation. It will standardize the tensioning process, avoid loss of pre-tension, permit automatic generation of reports, eradicate data fraud and allow remote monitoring.
7, Reinforce the quality control of the reinforcement concrete cover and the spacing of the reinforcing steel bar. Follow below suggestions on how to improve the pass rate of the reinforcing bar protective cover.
Suggestions on the control of the thickness of the bar cover and the spacing of the bars.
(1) With regards to the manufacturing of the reinforcing bars, use numerical controlled bending machines and microcomputer programming. This will bring reliable precision to the processing and unified specifications to the products. Moreover, it reduces human error.
(2) With regards to the placing of the factory produced semi-finished reinforcing bars, make sure membrane is installed and tie wire is used to fix the bars. This will ensure that the design and specification for the placing of the reinforcing steel bars will be followed, thus clearing away any issues as regards the thickness of the protective cover on the structural reinforcing steel bars
(3) Use quincunx round cake shaped high strength resistant mortar blocks for cushion pads for the protective cover of the reinforcing steel bars. Make sure that the pads can resist enough compression and not break. Use double tie wires to fix the reinforcing steel bars. The vertical and horizontal spacing of the bars shall not be more than 0.8m, bottom beam position shall not be over 0.5m. Ensure there are no more than four cushion blocks per square meter.
(4) Increase the sampling frequency for inspecting the quality pass rate for the protective covers of the reinforcing bars, strictly prohibiting grouting bars with unqualified cover.