CHAPTER III. STONE PAVEMENTS. 133. Stone Pavements.-Stone in a variety of forms has been employed as a paving material for more than 2500 years. The Romans used it in the form of large, irregularly-shaped blocks laid on a massive foundation of concrete. In this form it is unsurpassed in regard to solidity and durability, but it is objectionable for modern traffic. The surface of the large blocks wears smooth, and hence affords but an uncertain foothold for horses. These large blocks were superseded by round pebbles or cobblestones, obtained from the beach and gravel-pits. This class of pavement has been used extensively in the United States. It is recorded that Boston, Mass., in 1663 had many streets paved with pebbles. In 1718 cobblestone pavements were introduced into Philadelphia, and this city is the only one to retain them on a large scale at the present day. 134. Cobblestone Pavement.-Cobblestones bedded in sand possess the merit of cheapness and afford an excellent foothold. for horses, but the roughness of such pavements requires the expenditure of a large amount of tractive energy to move a load over them. Aside from this, cobblestones are entirely wanting in the essential requisites of a good pavement. The stones being of irregular size, it is almost impossible to form a bond or hold them in place. Under the action of the traffic and frost the roadway soon becomes a mass of loose stones. Moreover, cobblestone pavements are difficult to keep clean, and very unpleasant to travel over. 135. Specifications for Cobblestone Pavement.-The following is the common form of specification for this class of pavement: Stone. The stones are to be the best selected water or bank paving-stones, of a durable and uniform quality. Size of Stone.-No stone shall be less than four (4) inches nor more than eight (8) inches in any direction on the surface. No triangular or split stone will be allowed. All stones shall be set perpendicular and on their small ends, the large stones to be placed on the sides of the street, and the small ones in the center. Foundation and Laying.-The pavement shall be laid on a bed of good sharp sand or fine gravel, at least ten (10) inches in depth, except where clay or a similar substance is met with, when the sand must be eighteen (18) inches deep. The bed of sand or gravel shall be laid ready for the pavement at least thirty (30) feet in advance of the pavement. The stones after being set in position must be rammed with a heavy rammer until they are firmly settled in their beds. After the pavement is rammed a layer of sand or gravel two (2) inches thick is spread over it and left to work its way in between the stones. In consequence of the many defects of this class of paving its construction has been practically abandoned, but large areas still remain, which are being gradually removed. 136. Belgian Block Pavement.-Cobblestones were displaced by pavements formed of small cubical blocks of stone. This type of pavement was first laid in Brussels, thence imported to Paris, and from there to the United States, where it has been widely known as the "Belgian block" pavement. It has been largely used in New York City, Brooklyn, and neighboring towns, the material being trap-rock obtained from the Palisades on the Hudson River. 137. The stones being of regular shape remain in place better than the cobblestones, but the cubical form (usually five inches) is a mistake. The foothold is bad, the stones wear round, and the number of joints is so great that ruts and hollows are quickly formed. This pavement offers less resistance to traction than cobblestones, but it is rough and noisy. 138. Specification for Belgian Block Pavement.-The following is the common form of specifications for the Belgian block: Stone. The stones are to be obtained from the trap or other durable rocks. Size of Stones.-Each block shall measure not less than five (5) inches nor more than seven (7) inches in length; nor less than five (5) inches nor more than six (6) inches in width; in depth not less than six (6) inches nor more than seven (7) inches; nor shall |