Another theory holds that when rebar is too close to the surface and the concrete isn't properly vibrated, the concrete doesn't fully knit together over the bars. This causes the visible line. Like most discolorations that aren't stains, these marks are probably not erasable.
To be most effective for this purpose, the reinforcement needs to be near the top of the slab. For corrosion protection, however, most specifications require a minimum depth of concrete cover that usually ranges from 1 inch to 2 inches.
For example, if the distance between the outside surface of a reinforcing bar and the face of the concrete beam with a width of 6 inches is defined to be 2 inches, then the permitted tolerance is to be not less than 1 5/8 inches. In the case of longitudinal bars, tolerance is about ±3 inches.
Placing it directly in the ground is using it for a purpose it was not designed for, and it shows. Rebar is not corrosion resistant on its own, and the natural moisture of the soil will start to break it down soon after it comes into contact with it.
3 inches (75 mm) at the face of footings placed against rock or earth.
Steel reinforcement in concrete cast against the earth shall have a minimum cover of 3 inches (75 mm). Minimum cover for reinforcement in concrete cast in removable forms that will be exposed to the earth or weather shall be 1½ inches (38 mm) for No. 5 bars and smaller, and 2 inches (50 mm) for No. 6 bars and larger.
Reinforcing bar edge and end clearances are typically represented by the plan note “Minimum clear distance from face of concrete to near reinforcing bar is to be 50 mm (2 inches) unless otherwise noted or shown.” Reasonably acceptable clearances for bridge structures, other than bridge decks, shall be the clearance ...
You don't want to expose the rebar because it becomes more susceptible to corrosion. As the material deteriorates, it is more likely to cause concrete to fall apart.
The standard, 29 CFR 1926.701(b), states: "all protruding reinforcing steel, onto and into which employees could fall, shall be guarded to eliminate the hazard of impalement." The key words are "to eliminate the hazard of impalement." Exposure to impalement is always a consideration when employees are working above ...
Typically, if rebar is hit, the first and preferred solution is to move the fastening point. Only if this is not possible, the cutting of rebar should be considered.
There should be a clear distance at least equal to the bar diameter between parallel bars but never less than one inch. This assumes that the concrete will contain aggregate that is no more than three-fourths of these distances; otherwise the aggregate size or bar spacing must be changed.
There are numerous issues that arise as a result of using excessive reinforcement. The following are some of the most frequently encountered: Tie wire and other detritus on the outskirts. Without steel corrosion, there is cracking that mirrors the main rebars.
A 4"-thick concrete driveway for vehicles or ½-ton trucks does not need hot-rolled steel to last for decades. Thicker concrete, driveways with poor ground support, and driveways that often sustain heavy loads or vehicles should be strengthened. What is rebar?
Generally, a minimum of two #4 bars are required for residential footing. The rebar should be placed in a grid pattern with a spacing of no more than 18 inches apart. It is important to follow these minimum requirements to ensure that the footing can withstand the weight and pressure of the structure above.
The role of rebar in concrete footings
This results in a concrete footing that can better withstand the forces and loads it will experience over time. Reinforcements are typically positioned at the bottom of the footing's tension side, following a standard practice.
Rule of thumb is to have the minimum clear spacing between bars be 1.5x the maximum aggregate size. So if you have, say a 3/4" max. aggregate, you'd need 1.125" clear between bars. Rebar is about 15x stronger than concrete in compression, and way more than that in tension.
So if such bars will be exposed for more than, say, a couple of weeks, they should be covered. Mortar or grout droppings that are adhering firmly to bars need not be removed. If they will not come off easily, leave them. The effect of rust on the bond between reinforcement and concrete is debated endlessly on site.
As per ASTM standards, the minimum concrete cover for steel reinforcement in a footing should be 1.5 inches (38 millimeters).
Even though rebar can cause shrinkage cracking, there is a way to employ reinforcing steel that prevents this phenomenon.
Coat the rebar with a high-quality, corrosion-resistant coating and bonding compound. Coat the existing concrete with the same bonding compound. There are several epoxy formulations that work well for this application.
Rebar, or reinforcing bar, strengthens concrete to help it withstand tension and enhance its durability.
Rebar should almost never be showing from the concrete. If it is, the metal is exposed and able to be corroded by the weather which will compromise the reinforcement.
Reinforcing Bar Tolerances
Clearance from steel to earth, usually 3” for concrete or shotcrete cast directly against earth.
Critical edge distance (cac) is the distance from the concrete edge required to develop the concrete breakout strength of an anchor installation. For installations less than cac, reduction to the tension resistance is required in accordance with ACI-318 requirements as modified by ESR provisions.