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Flow velocity seldom causes abrasion problem for concrete pipes. Instead, the particles carried by effluent in high velocity may create abrasion problem of concrete. The abrasive effect is dependent on the size of particles and velocity. In most circumstances, the problem of abrasion shall be avoided for flow velocities less than 8m/s.
Concrete pipes are designed to crack in tensile zone so that steel reinforcement could take up the tensile stress. Flexural stresses are developed at the top and bottom inside surfaces and on the outside longitudinal cracks.
Stoplog consists of several sets of horizontal beams/logs stacked vertically. For narrow openings, the logs span between support slots at the ends of the openings. For wide openings, intermediate removable support posts may be required. They are prevalent in the past because of its low establishment cost, simple erection and easy operation.
The freeboard is defined as the vertical distance from water surface to the top of channel bank. The selection of freeboard is dependent on the consequence should overflow out of channel bank occurs. Other than that,consideration should also be given to prevent waves, superelevation and fluctuations in water surface from overflowing the channel banks.
A penstock is commonly used to control the flow and water level and for isolation of fluid. It mainly consists of a sliding door which is controlled by mechanical spindle moving through a hole in a frame built onto a structure. Penstock is the term used in UK while sluice gate is more commonly adopted outside UK. In the design of penstock, it is important to identify if it would take on-seating head or off-seating head.
During the construction of new pavement, vibratory roller and heavy equipment are needed to compact the filling material and bituminous material. These heavy equipment could generate very high impact load with short duration on the concrete pipes.
Concrete pipes are designed to be uniformly supported along the length to carry vertical loads on its top. They are normally not intended to serve as a beam to carry loads in longitudinal direction under poor ground supports (i.e. high and low spots in bedding).
For carbon dioxide attack, carbon dioxide dissolves in water to form a weak acid called carbonic acid. It would dissolve the cement matrix. However, the amount of carbon dioxide from the atmosphere is usually not sufficient to cause harm to concrete structures until additional source of carbon dioxide is available (e.g. decaying vegetable matter).
Flakiness Index is the percentage by weight of particles in it, whose least dimension (i.e. thickness) is less than three-fifths of its mean dimension. Elongation Index is the percentage by weight of particles in it, whose largest dimension (i.e. length) is greater than one and four-fifths times its mean dimension.
