Enhancement of Concrete Properties and Structural System for Telecommunication Manhole Covers

Abstract

One of the most common structural function of the “steel concrete open sandwich composite slabs” is the telecommunication (TE) manhole covers. Most of the (TE) manhole covers that are being currently used in Egypt and Middle East are manufactured using a normal strength concrete embedded in a steel frame. The main advantage of those manhole covers is the low cost in comparison to the cast iron covers. Moreover, a common problem associated with cast iron manhole covers is the theft of the cover and then selling it on the black market. The most common problem that is associated with the current concrete (TE) manhole concrete covers is the deterioration of concrete and collapsed covers that result in large holes all over the roads causing many potential safety hazards and jeopardizing peoples' lives. Consequently, most drivers try to avoid pass-over the covers to avoid accidents. This study aims to enhance the concrete properties and structural system of (TE) manhole covers in order to improve its durability, and serviceability. Through this study, different improvement materials were added to the concrete mixtures to enhance the mechanical properties such as compressive, flexure, and abrasion resistance, in addition, to achieving homogeneity of concrete with the asphalt color. Moreover, the effect of steel fibers on the flexural strength was studied by using two different shapes of steel fibers (corrugated segment and hooked-end). A Scanning Electron Microscope (SEM) images extracted from specimens to analyze the microstructural of the concrete. In order to enhance the structural system and increase the load carrying capacity of the (TE) covers, shear connectors and headed studs were used in different geometries to reinforce covers. All covers were tested according to European standards for gully tops and manhole tops for vehicular and pedestrian users (BS EN 124, 2015) till failure. The parameters investigated in the experimental program are the concrete strength, shape and distribution of shear connectors, top steel strips and depth of concrete section. The ultimate capacity, failure modes, and deflection, as well as strain development in the bottom steel plate are presented and discussed. Moreover, a theoretical program was implemented according to different codes and design guidelines and compared with the experimental results to check the formulas adaptation. Finally, the performance of the developed (TE) manhole cover was verified by installing the developed cover in a heavy traffic zone. It was found that, using the enhanced (TE) cover will save about 90% of the annual cost. Moreover, both bent bars and concrete strength significantly enhanced cover ultimate capacity and make it comply with BS EN 124 for the covers class C250. In addition, using head studs and high strength concrete make covers comply with class D400. Using iron strips with the drop panel bump shape, headed studs and high strength concrete doubled the cover ultimate capacity, and make the cover suitable for classes higher than D400. Furthermore, Narayanan et al. formula (Narayanan et al., 1994) satisfactory predicted the punching resistance contributed by the shear connectors for normal strength concrete. However, tensile resistance of the connector method yields more accurate results in case of high strength concrete. In addition, using either the BS-8110 or Eurocode 2 is recommended in case of headed stud shear connectors. On the other hand, using either the ECP 203 (2018) or ACI 318 (2019) is recommended in case of bent bars or stirrups as shear connectors. In addition, the effect of steel fibers on punching resistance can be neglected. The study concluded that, the proposed concrete mix along with the enhanced structural system can be used to produce economic-black-high performance (TE) covers.