Materials
Ductile iron Ductile iron is the most common material used to manufacture manhole covers all over the world. It can stay for more than 50 years while attaining the same level of efficiency. Moreover, old ductile iron manhole covers can be recycled into new ones. Ductile iron has tensile strength of 500 Nmm2 which not only minimizes the risk of failure when installed, but also reduces the likelihood of breakages in transit and off loading. Composite
Composite manhole covers are made from fibreglass and polyester. On an account of it being a non-recyclable material, there is no risk of any theft cases. According to instarmac, manufacturing company in UK “The covers are made from an advanced composite structure, have no scrap value and cannot be melted down or reused, and are therefore an ideal solution to the prevailing problem.” Moreover, It comes in a variety of colours which makes it easily noticeable that it’s not cast iron, repelling thieves away. However, when asked about composite manhole covers, Mr. Su Ching said that it did not follow standards used in Malaysia, and that it doesn’t have the same strength as Ductile iron, limiting its use to sidewalks and green areas and not heavy traffic flow roads.
Gray iron Manufacturers avoid using Gray iron, explains Mr. Su Ching, due to its low tensile strength compared to ductile iron, being only 220 Nmm2. Moreover, when gray iron is mixed with magnesium to make it less subjected to corrosion, the material becomes brittle and loses its elasticity, making it more exposed to breakage. Concrete filling Concrete filled Manhole covers are made by filling galvanized iron rebars with reinforced high strength concrete. Concrete is an adequate replacement for cast iron; it’s a heavy strong cheaper material, with no recyclable value. However, it did not end theft cases, as thieves began to steal the rebar and sell it to scrap dealers at throwaway prices. Moreover, They can only be placed on high levels as for water hydrants, argued Mr. Su Ching. By time the concrete breaks down, leaving the rebar metal bare with no concrete making it unsafe for motorcyclists.