To make rings, heavy concrete of grade B15 (M200) is used.
For your information:
An additional increase in strength is provided by vibration compaction at low tide (they reduce the number of pores and possible destruction concentrators). The method of vibropressing allows you to get the exact geometric dimensions of the product and a smooth surface (with a roughness of up to 0.1 mm). This indicator reduces the tendency to siltation of the inner surface of the rings.
Recommended main dimensions, mm, GOST 8020-2016
Lxb or a
Manhole ring (cylindrical)
REINFORCED-CONCRETE NON-PRESSURE SPIGOT PIPES / TILE UNDER TS PIPE (PTS)