89. Finishing the Surface.—Dry or pure cement must not be used for trimming up or smoothing off the surface of the walk. After the surface has been properly completed by straight-edge and trowel, see that the wire broom is used as directed to remove the glaze and to slightly roughen the surface.
See that the expansion joints are made as specified, and that they extend entirely through both courses of concrete.
90. See that the walk, after completion is properly protected from injury and from frost, and that the concrete is kept moist until it becomes well set.
[1]. In specifications to be used in any particular city the official name of the city government, as the City Council, the Commissioners of Public Works, etc., should be used instead of this general designation.
[2]. Such a proviso as this seems proper in justice to both the city engineer and the contractor; the former should not be held responsible for the acts of his assistants when they transcend the authority conferred upon them, and the latter should be put upon his guard with reference to requirements which he is not satisfied are sanctioned or approved by the city engineer.
[3]. It may be objected that this requirement is unusual and unnecessary, since such practices are recognized as wrong, and as presumptive of fraud and malpractice on the part both of the contractor and the inspector. It cannot, however, be denied that in many cities such means are employed by contractors to unduly influence the action of inspectors and that not infrequently the latter not only accept, but persistently demand, valuable considerations from the contractor. Silence of the specifications on this point cannot, of course, be construed into consent, but there is no good reason for the silence. There should be left no excuse for misconception of the position of the city or of the engineer upon this point.
[4]. This section is intended as much for the control and limitation of city officials as of contractors. The practice of carelessly or purposely allowing municipal contracts to be expanded greatly beyond the stated limits or the original intended volume and cost without formal authorization by the proper municipal body in which the power to make contracts is lodged, is dangerous and wrong and should be prohibited. In one instance coming to the notice of the author a contract originally intended to cover $50,000 worth of work was expanded by the department head without any authority from the city council until the final estimate reached the enormous sum of over $400,000.
[5]. As outlined in the introduction, these specifications are designed to secure the construction of the pavement in a proper manner, the city assuming responsibility for the character and utility of the work. The guarantee here proposed is therefore intended to cover only a proper compliance with the specifications, for which the contractor may properly be held responsible, and not the sufficiency or utility of the work, if constructed according to the specifications. The period of guaranty should therefore be short, not exceeding two years.
[6]. In the great majority of cases the most satisfactory and, in the end, the most economical foundation for a pavement is hydraulic cement concrete. Old paving-block foundation, if constructed as specified in Sect. 36, will give results equally as satisfactory, but if a fair market exists for the blocks taken up from the street, it will usually be found more economical to sell them and construct a concrete foundation for the new pavement. Broken stone or gravel foundations may serve the purpose fairly well upon a street of light travel, but it should never be used on streets of considerable or heavy travel. Its lower first cost is the only thing in its favor, but this will, in nearly every case, be more than offset by the better service and greater durability of the pavement, even on streets of light travel, if laid upon an adequate hydraulic concrete foundation. Proper repairs to pavement surfaces cut into for pipe work, etc., are difficult to make and hardly ever satisfactory over broken stone foundation for the reason that the lack of cohesion in the material allows it to loosen or crumble away from under the edge of the pavement surface, and it is difficult to restore it to its original solidity and strength. The first cost saved by its use is usually not great; for whenever its use would be permissible at all, a comparatively thin and lean concrete would give better results, at a very slight increase in cost. To illustrate: On a suburban street with light travel a concrete foundation four inches in thickness, the concrete made with Portland cement in the ratio of 1 cement, 4 sand, and 8 stone, would be stronger and in every way better than a foundation eight inches in depth of broken stone. At the usual prices of materials and labor, the former may cost about $0.46 per sq. yd., and the latter about $0.40 per sq. yd.; but for the latter there would be required ⅑ cu. yd. more sub-foundation excavation, worth about four cents, so that the equivalent cost would be $0.44 per sq. yd. The difference, two cents per sq. yd., is insignificant when compared with the greater value, better service, and greater durability of a pavement on the concrete foundation. It is sometimes held that the broken stone foundation provides necessary sub-drainage. But all the standard pavements are, or soon become, impermeable to water from the surface, and seepage from the sub-foundation can be better taken care of by the sub-drainage specified in Sect. 26, which should usually cost not more than five cents per square yard of the pavement; and if drainage be required, these sub-drains should be used even with the broken stone foundation.