as reinforced structural fill under the approaches to a bridge over the CSXT Railroad, as well as to raise the grade of two connecting roads in Cuyahoga County, Ohio. Te sand, which was sup- plied by Kurtz Brothers, Independence, Ohio, came from a Ford casting facility and was a narrowly graded fine sand, with 98% passing the #30 mesh and 75% larger than the #70 mesh. Approximately 10% of the sand mixture was bentonite, while the seacoal content was 3%. In addition to meeting the regula-
A bulldozer spreads recycled casting sand for a bridge abutment.
ture-density relationship and constant head permeability. Te sand was classi- fied as a poorly graded sand (meaning the material consists mainly of particles of nearly the same size) with some gravel and silts. Te unit weight was lower than more well-graded sands, but a lighter unit weight is a benefit around heavy structures, such as bridge foundations. Te optimum water content was compa- rable to other sands, and the permeability coefficient was on the border between sands and fine sands/silts. Te permeabil- ity was sufficient for embankments and structural fills in the project where storm water controls limit infiltration. Te sand also underwent a water
leaching test and an organics test. No organic contaminants beyond regula- tory parameters were detected. Te casting sand was delivered in
dump trucks and spread with a bulldozer, like any other sand. According to the contractor, Hoffman Construction Co., Black River Falls, Wis., despite heavy rain, the sand was placed and compacted with no problems. Te contractor viewed casting sand preferable to conventional sand in this project because it did not freeze in the winter and arrived with a moderate moisture content, which pre- vented dust issues and reduced the water needed for compaction. Because the sand was already
approved for use before the bidding process, the contractor was able to bid a lower price.
Case Study 2: Retaining Wall Backfill
In 2007, Great Lakes Construc- tion used 11,500 tons of foundry sand
CONSIDERING THERMAL RECLAMATION
Before relegating its sand to landfills or beneficial reuse, metalcasting facilities may also consider thermally reclaiming the sand. According to Gerald Reier, president of GMD Envi- ronmental, thermal reclamation systems for resin-bonded sand typically reclaim 90% of true silica sand, which can be used as new sand throughout the metalcasting facility. “If you start with a high purity sand, it could be continu- ally processed for years,” Reier said. “Weaker or poorer sand grain will fracture and become a fine particle that is removed in the first pass. If the sand doesn’t break away from the sys- tem, it will be continually recycled.”
As the sand is thermally reclaimed, Reier said it becomes stabilized and cleaner than purchased new sand. While most
36 | MODERN CASTING April 2011
new sand comes in with a significant amount of fines that requires more binder, the fines are removed during reclamation. Most facilities using thermal reclamation are nobake casting facilities, but according to Reier, equipment exists that will efficiently thermally reclaim green sand, as well. “Almost every sand casting facility out there except for a very small company could justify buying a thermal reclamation system with savings on new sand and disposal costs,” he said. “In a feasibility study, it has been found that metalcasters will only need 10% new sand on an annual basis [with thermal reclamation].” While Reier notes that U.S. companies’ interest in thermal rec- lamation has stalled, growing numbers of facilities in China, Italy and Mexico are incorporating the sand recycling systems.
tory requirements of Ohio EPA DSW 0400.007, additional engineering and test data showed the sand met Ohio Department of Transportation (ODOT) requirements, specifically under Supplemental Specification 871 “Embankment Construction Using Recycled Materials.” ODOT require- ments examined the sand’s Atterberg limits, gradation, moisture-density relationship, pH, chloride and sulfate levels, and contaminant levels. A virgin material with uniform
grain size like the Ford casting sand would be difficult to compact in the field, but the presence of clay and seacoal helps with the compaction and provides additional shear strength. Uniform grain size also helps with drainage, which was important in the project because the sand was backfilled behind a wall and water needs to drain quickly to prevent lateral pressures building on the wall. Kurtz Brothers used this particular project as a demonstration of casting
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68