APPARATUS FOR MEASURING THE WEAR OF CON¬ 
CRETE ROADS 
By A. T. Goldbeck, 
Engineer of Tests , Office of Public Roads and Rural Engineering 
Many miles of concrete roads have been built during the past few 
years, and the methods employed in their construction are rapidly becom¬ 
ing standardized. The concrete mixture is now made comparatively 
rich, and in general the aggregates are selected with as much care as 
present knowledge of these materials permits. Even yet, however, it 
is doubtful whether the right mixture is being used for the purpose: 
Whether it is too rich for economy or whether it should be made still 
richer. It is questionable what kinds of coarse aggregates give the most 
economical results: Whether they should be composed of hard, tough 
fragments of trap rock or of softer, more friable pieces of limestone of 
approximately the same degree of hardness as the mortar in which they 
are embedded; whether angular fragments of crushed stone should be 
used or whether round pieces of gravel are equally satisfactory. Definite 
knowledge on these points based on scientific information seems to be 
lacking. 
The ideal concrete road should wear uniformly and slowly. When 
due care is exercised in construction and the necessary precautions are 
taken in maintenance, uniformity of wear may to a large extent be 
controlled. But little is known about the rate of wear of concrete roads 
having various aggregates and carrying different kinds of traffic. General 
observation indicates that some roads with particular kinds of aggregates 
are wearing more slowly than others containing different coarse aggre¬ 
gates, even though the traffic conditions are nearly alike. We have, 
however, no definite idea of the amount of wear in these different roads. 
There must come a time in the life of every concrete road when, notwith¬ 
standing careful maintenance through crack protection and patching, 
its thickness will approach the minimum, making imperative the ex¬ 
penditure of a considerable amount of money for a new wearing surface 
to replace that gradually worn away by traffic. Every fractional part 
of an inch decrease in thickness therefore represents a very definite 
depreciation in the value of the pavement. Money can not be expended 
intelligently on various aggregates mixed with cement in different propor¬ 
tions for road construction without accurate knowledge of one of the 
most important factors governing the expenditure—namely, the probable 
rate of depreciation of the road as determined by actual wear. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
Vol. V, No. 20 
Feb. 14,1916 
