Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/518784
by Bill Langer BARREʼS FUTURE Paving The feldspar found in Barre granite proved to provide the right combination of durability and traction needed to withstand steel wheels and horse hooves. 'The confusion…between hardness and toughness, has led to serious practical errors in the choice of materials for roads, inasmuch as the attention has been often directed exclusively to their hardness [resistance to wear], without any regard being had of their toughness [resistance to pounding and crushing].' Charles Penfold, 1840, A Practical Treatise on Best Mode of Repairing Roads, p. 11. The articles this year re-trace the history of the now world-famous Barre granite. By the late 1830s, Barre granite had begun to attract attention, largely from its use in the Vermont State House. Another boost to the fledgling in- dustry came in 1839, with a contract for 10 million paving blocks for the city of Troy, N.Y. As early as 1663, Boston had roads paved with round cobblestones used as ballast in ships from Europe. Ex- perience at the time demonstrated that the most enduring streets for heavy traffic in cities were not paved with cobblestones, but were paved with rectangular stone blocks 3- to 4-inches wide, 6- to 7-inches thick, and 8- to 12-inches long. Streets paved with cobblestones were difficult to keep in repair, hard on horses, and rougher on wagons than pavements made with rectan- gular blocks. Specifications for paving stones required rectangular faces and nearly straight edges. The corresponding dimensions of opposite faces could not vary more than one-half inch, and the surface had to be free from bunches or depressions exceeding one-half inch. Paving blocks had to be hard, which was the ability to resist the friction or grinding of steel rimmed wheels moving along them, as well as tough, which was the ability to with- stand the pounding or crushing action of horse hooves. But even if a rock was hard and tough, some rocks became smooth and glazed under traf- fic, affording a poor foothold for horses. The best paver blocks were, therefore, not only hard and tough, but wore roughly, thus affording horses good traction. The feldspars in Barre granite tended to fracture and create tiny depressions, while the stronger quartz crystals stood proud. This gave Barre granite the right degree of 'tooth' for use as paving blocks. Even though paving breakers did not need to possess the fine workmanship of the stone mason, they were highly skilled workers. A quickness in seeing and taking advantage of the natural splitting characteristics of the rock, as well as a deftness in handling the necessary tools, was requisite. A skilled paving breaker could turn out 100 blocks per day. Paving breakers usually were paid a certain sum for each thousand blocks they made. The price paid varied ac- cording to the size of block, kind of stone used, if tools were furnished, and whether or not the blocks were quar- ried by their employers. In Barre, blocks were almost always provided by the employer from a seemingly endless source of rock described by Alton Adams. 'Standing near the top of Millstone Hill…one may see great mounds of broken granite running up to more than 100 feet in height and covering perhaps an acre or more each, in many directions… On closer inspec- tion, each mound is found to be made up of irregular-shaped pieces of [waste] granite that vary from one to several feet in each dimension. Most of this now worthless stock may sometime be readily worked into pav- ing blocks.' Alton D. Adams, 1906, Wealth in Barre Granite, Mines and Minerals, p. 487 Road paver, circa 1895. Bill Langer is a consulting research geologist who spent 41 years with the U.S. Geological Survey before starting his own business. He can be reached at Bill_Langer@hotmail.com CARVED IN STONE • 204