Study On The Reason Of Urban Manhole Covers Damage And Research On Its Repair

Manholes play important role in the healthy development of a city, which contains manhole basic, wells room, wellbore, leveling layer, well circle and covers, but we can often see the phenomenon of the different manholes damage. This paper summarized two reasons of the manholes damage by the actual survey and reviewing the related literatures that the leveling layer would bear the shear force and pulling stress repeatedly when the cars run on the manholes, leading to the damage of the leveling layer, and the manholes would have different height with the road, then the manholes would bear the larger impact, the manholes would easily destroyed, on the other hand, well circle concrete would also bear shear force repeatedly, leading to the fatigue fracture, the vehicle load and the temperature stress would accelerate the well circle concrete damage. This paper combined the two reasons and the feature of the manholes structure, raised that the leveling layer and the well circle were used by fine stone steel fiber reinforced concrete and polypropylene fiber concrete respectively, and this paper researched and prepared the concrete materials of the new manholes leveling layer and well circle by experiment.This paper studied the material composition, mix proportion and concrete performance of leveling layer and well circle concrete, and analyzed the repair materials hydration mechanism by XRD and SEM. And then the effect of interface agent types and different repair materials on the adhesive property between new and concretes, adhesive property regular pattern was tested by micro-hardness of the vicinity of the interfaces. The results showed that:(1) In the new manhole leveling layer concrete, when steel fiber volume content was 1%, the flexural strength, the compressive strength and the splitting tensile strength was 13.73 MPa, 59.6MPa, 5.53 MPa at 28-day.(2) In the new manhole well circle concrete, when polypropylene fiber content was 0.10%, the flexural strength was 9.03 MPa, the compressive strength was 53.6MPa,the splitting tensile strength was 4.06 MPa at 28-day.(3) In the damaged manhole leveling layer repair materials, when the sulphoaluminate cement content is 15%, the 1-day mechanical strength of the repair materials was the highest, whose flexural, compressive strength would be up to 8.98 MPa, 38.8MPa. Then the incorporation of 5% of metakaolin, the mechanical strength would increase clearly at 28-day. Then when added the 1% steel fibers in the repair materials, the toughness of the repair materials was significantly increased, and the flexural, compressive strength would be up to 8.98 MPa, 38.8MPa, fully able to meet the standard of opening the traffic at 1-day.(4) Hydration products and microstructure of repair materials were analyzed by XRD and SEM, sulphoaluminate incorporation can promote early hydration, but the latter hydration was insufficient, metakaolin can promote the 28-day hydration, whose microstructure is more compact.(5) When added 5% metakaolin in the repair material, the adhesive strength would increase 17.2% at 28-day, and when added 1% steel fiber, the adhesive strength would be up to 2.35 MPa.(6) In the damaged manhole well circle repair materials, when added 0.1% polypropylene fiber in the system, compressive and flexural strength of repair materials would be up to 35.5MPa, 6.32 MPa, fully able to meet the standard of opening the traffic at 1-day. When the polypropylene fibers content was 0.1%, the adhesive strength of 1-day and 28-day would be up to 1.26 MPa and 2.02 MPa respectively.