Home Improvement--General/new concrete driveway
Todd G wrote at 2008-06-23 17:08:06
The problem you described sounds like lignite to me. I have heard it described to look like brown pits, tobacco spit stains, and rust.
For others looking at this for an answer to their own problems I would like to clarify some things for you. Ron's assessment indicates that he doesn't think it is very likely that lignite would be a problem associated with concrete. Unfortunately his answer is not correct for all parts of the country. Many power plants are located on the banks of rivers in the midwest. Power plants use coal mixed with some lignite and parts of it make it back into the rivers. (not quite sure how?) This is where sand companies mine sand for use in concrete. The sand plants know about it and attempt to sell delignited sand to concrete producers. They run it through water and the lignite being a lighter material tends to separate from the sand. It doesn't happen with any great regularity, but it does on occassion happen. The problem usually shows on concrete that is not sealed or cured immediately after finishing operations have concluded. You will find more often when it gets wet by rain or sprinkler within the first few days after it is down. It will continue to show more and more marks each time it gets wet. The brown spots will disolve and wash away. As long as you don't have more than one or two of these per foot it is best to let them fun their course for a few weeks and then seal the surface with a high solids sealer. You can buy these sealers from any home improvement store. If you exterior concrete is exposed to deicing salts and fertilizers you should seal them every year.
Dave wrote at 2008-07-18 19:48:44
I recently had a new patio poured with the same type of staining results you just mentioned. I have had it confirmed by 3 knowledgeable professionals that it was the result of lignite in the sand that was added at the concrete plant. Lignite is normally removed at reputable sand companies out of the Missouri and Kansas Rivers. We just got a bad batch. Now I'm trying to find out how to remove the brown lignite stains once the concrete cures for the re-quired 30 days. Call me, maybe we can share the solution. Dave daytime # 816-474-1100 ext # 5314.
Steve wrote at 2010-10-06 14:07:08
There easily could have been lignite in your concrete. Wasnt a bad batch where there was sand clumps.
Concrete Professor wrote at 2013-04-22 22:02:38
These particles are typically referred to as lignite and are akin to coal. Lignite is found in a lot of natural river sands used in the manufacture of concrete. A.S.T.M. C33 actually has a specification for the limitation of lignite in sand used to make concrete. These particles are very light in weight and will rise to the surface carried by the bleed water. When they are at or near the surface the particles will become saturated with water, swell and cause popouts, typically leaving behind a dark brown stain giving the concrete the appearance of rusting. Very, very common. Sealing the driveway with a good acrylic based sealer will usually keep this from occurring. Your concrete driveway should be sealed every 2 to 3 years, depending on your environment, to keep it protected from the elements.