What are embedments in concrete?
Embedments are any items for instance pipes, ducts, sleeves, and conduits placed in concrete elements for different purposes. Embedments are commonly manufactured from different materials. They are mostly used for services such as ventilation and passing cables.
Fig.2: Electrical Conduits Embedded in Concrete Floor Slab
When Embedments are Used in Reinforced Concrete Elements?
Commonly, embedments which are not detrimental to concrete are permitted to be installed in concrete. However, the task shall be carried out in such a way that does not impose risks on the concrete structure.
Under normal circumstances, all embedments manufactured from any materials that is not harmful to concrete and does impose dangers to structure are allowed provided that the following conditions, which are specified by ACI 318-11, are met.
Passing pipes, conduits, and sleeves through slabs, beams, and walls are prohibited unless concrete strength is not declined significantly.
The placement of conduits, pipes, and their fittings embedded within reinforced concrete columns are permitted provided that total embedment area is not greater than 4% of total concrete cross section used to calculate column strength.
Conduits, pipes, and sleeves shall be allowed to be assumed as replacing structurally in compression the displaced concrete if such embedments are met certain conditions.
For example, they are manufactured from iron or steel not thinner than standard schedule 40 steel pipe, not suffer deterioration, minimum spacing is three diameters, and maximum inside diameter is 50mm.
Pipes and conduits (in outside dimensions) shall not be greater than 1/3 of entire thickness of slabs, beam, or wall in which they embedded.
Spacing of pipes and conduits should be at least three diameters or width on center.
Pipes and fittings need to be designed to withstand the influence of materials, temperature, and pressure to which they are exposed.
Liquid and gas should not be placed into the pipe before concrete achieve its design strength. Water can be exempted from this condition provided that its temperature does not surpass 32oC.
Pipes shall be placed between bottom and top reinforcement in solid slabs apart from those used for snow melting and radiant heating as shown in Figure 3.
Fig.2: Radiant Heated Floor Placed in Reinforced Concrete Slab
Concrete cover for pipes, conduits, and fittings should be at least 40 for concrete subjected to earth or weather. If concrete is not exposed to weather or earth, minimum cover shall be 20mm.
The area of reinforcement provided normal to the piping should not be less than 0.002 times area of concrete section.
Pipes and conduits shall be fabricated and placed in such a way that does not affect cutting, bending of reinforcements and do not cause displacement of steel bars from their designated position.
The ACI code prevents the use of aluminum material in concrete except if it is properly coated or covered. This is because harmful reactions between concrete and aluminum, and steel and aluminum in the presence of chloride ions will take place. Consequently, concrete cracking and spalling will occur which are highly undesirable.
That is why the Code prevents the use of calcium chloride or any admixture contains chloride in concrete with aluminum embedments. Another un-favorite property of aluminum is its electrical conductivity because stray electrical currents will increase speed of harmful reactions.
318, A.C., 2011. Building Code Requirements for Structural Concrete (ACI 318M-11) and Commentary. Michigan: American Concrete Institute.