Does Grounding Rebar (Ufer) Weaken Concrete?
Does Grounding Rebar (Ufer) Weaken Concrete?
(OP)
Hello All,
Does anyone know where I can find information on this topic. Particularly helpful would be a study that provides ground fault current vs structural concrete strength and/or life expectancy.
Does anyone know where I can find information on this topic. Particularly helpful would be a study that provides ground fault current vs structural concrete strength and/or life expectancy.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
Our structural engineers are always worried about corrosion due to dissimilar metals (when you wire-tie the copper to the rebar) but IEEE Green Book (or Emerald Book?) says that won't happen when you're embedded in concrete.
You should be able to find lots of information on the Internet. In addition to Google, I'd check ecmmag.com and other trade journals, as well as erico.com and other grounding equipment vendor websites.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
The rebars need to be bonded, however, to earth mat nearby to avoid any undue sparking due to induced voltages or static voltage buildup.
I have come across some engineers counting te rebar metal in the earthing system design but I am not sure of the basis.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
I know about the NEC requirement but I'm being asked to verify that grounding the rebar does not weaken the concrete. Neither IEEE-80 nor 142 shed any light on the issue that I've been able to find. I think common sense should dictate this one. Not only would not grounding the rebar be in violation of the NEC but the damage to the foundation would be potentially far greater from a direct lightning strike or fault.
Simply quoting NEC scripture would likely invite more scrutiny and potentially a redesign of the system. One of our structural guys thinks that as long as the grounds are bonded to the top layer of the rebar (using a 2 row embedded cage) that any weakening that might occur would be minimal in the overall strength of the pad.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
But this dc resistance measurement of resistance to ground is not a good predictor of performance on lightning surges because of the high frequency nature of the event. Usually, shorter and straighter provides the best surge grounding.
As far as the OP question - the two main issues usually raised with Ufer grounds are corrosion of the rebar and damage from lighting.
When I worked for a large consulting firm, our corrosion engineers looked at the corrosion issue from time to time and always concluded that there should little if any galvanic current between copper and reinforced concrete.
As far as the surge current, anything is possible, but maybe the structurals don't realize that the steel columns are already tied to the concrete so a Ufer ground is not necessary to have concrete damage from lightning strikes.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
Maybe someone has a newer revision at hand and can check if this still reads the same.
The IEEE Green & Emerald books also both discuss concrete-encased electrodes -- but neither speak specifically to corrosion or galvanic action. All IEE color series books seem to be unanimous in stating that it's a good, cost-effective idea -- and I could find no stated disadvantages. One of them (green or emerald) warned that NOT connecting anchor bolts to rebars can cause concrete to dry out & weaken, and to suffer from both continuous low-level ground currents and high-magnitude fault currents.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
I routinely specify them and request structrual engineers to include the grounding detail of bonding ground conductors to rebars in footings and not single strucrual engineer has ever objected to it.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
RE: Does Grounding Rebar (Ufer) Weaken Concrete?
One of the other problems is rapid evaporation of concrete moisture. This also weakens the pad.
RE: Does Grounding Rebar (Ufer) Weaken Concrete?