2.i2 POPULAR SCIENCE MONTHLY. 



A MODEEN STEEET. 



By Dr. S. F. PECK HAM. 



NEW YORK CITY. 



A MODEEN" street is laid on a concrete foundation, the surface of 

 -^-J- which may consist of brick, asphalt block or sheet asphalt. 



It is of the greatest importance that the foundation should be 

 properly constructed. It is true that in cities where a large area of Bel- 

 gian block pavement has been already laid, sheet asphalt is often laid 

 upon these blocks; but while streets can be made in this way, they are, 

 when so constructed, more or less liable to criticism in several respects; 

 but chiefly from the fact that the Belgian block, as compared with con- 

 crete, is an unstable foundation, liable to yield under unusual or excess- 

 ive strain and always sure to carry the surface with it. While this 

 cause of the criticism is usually absent, especially upon residence streets, 

 there have been conspicuous examples of its presence in almost every 

 large city, where the custom of laying asphalt surfaces on Belgian block 

 prevails. We therefore consider the normal modern street as laid on a 

 concrete foundation. 



The French engineers determined the elements of this problem, 

 nearly half a century ago, by very costly experiments for which the city 

 of Paris was mainly responsible. As all the roadways of France are 

 more or less completely under governmental supervision, the results of 

 these experiments have been described in several masterly memoirs by 

 some very able French engineers, in the Annates des Ponts et Chaussees, 

 which is the official organ of the French governmental supervision of 

 bridges and roads. Space forbids mention here of more than a sum- 

 mary of these results. It was found that of all the materials that 

 were available, only a concrete made of Portland cement of good 

 quality mixed with clean sharp sand and broken stones was always to be 

 depended upon. If a concrete foundation could always be laid on well 

 drained earth properly rolled or rammed, that was never invaded by 

 frost and never disturbed by openings for all the multitudinous pur- 

 poses that disturb modern streets, concrete that will not stand such 

 rigid tests might be used instead of that made of Portland cement. But, 

 streets laid under such conditions and subjected to such use are an ex- 

 ception, indeed they are rare, and for that reason should not be made 

 the rule. The French engineers determined that under any circum- 

 stances, nine inches of concrete would hold any traffic; that six inchc? 



