Arizona republican., 1914-10-23

there was bitulithic laid in excess of seven million square yards in the United States and Canada alone, not counting the work done abroad. It | is conceded that from the standpoint 1 of it's resiliency, noiselessness, clean Illness Ca no mean item), appearance and initial cost, an asphaltic pave ment is more desirable than any of tie other standard pavements. I be- lleVc that there are but two ways in which it might be said that the others are superior, durability and tractiVe qualities. I will now show why bitulithic, while retaining the above-named advantages of an as phaltlc pavement, is also at least on g par as regards the other TWO items.
 The main point of difference be- tween bitulithic and sheet asphalt
 is the low percentage of voids and the inherent stability of the former Sheet asphalt is a combination of sand and asphalt. The sand will
 contain voids of from 33 per cent to 40 per cent of volume and to this will be added Il per cent or F per cent of asphalt, leaving voids in tie completed pavement from g to 2S per cent.
 Bltulithic is combination of crushed rock, graded from size the largest diameter of which is approximately one-half the tctal thickness of the proposed wear ing surface, say an inch and quar- ter for a two-inch pavement, down to the finest of dust, that passing a screen having forty thousand meshes to the square inch. so graded that
 each smaller size of rock and dust will fit into the vOids of the size inn
 mediately larger, thus truly giving a mineral aggregate with voids reduc . l ed to the minimum of ' per cent to II per cent To this is then added sufficient Bithulithic cement Ca spe- cialN treated bitumen or asphalD to thoroughly coat each particle (tha 1 amount to be definitely determined | by laboratory tesD usually from : per cent to 9 per cent, giving a
 completed pavement with voids prac- | tcally zero, a pavement whose spe- | c11ic gravity is more than 90 per cent
 of that of the rock which forms it's | principal part
 l The inherent stability of Bithuithic
 is by reason of the stability of the aggregate composing it, the smaller
 aggregates fitting as they do into
 the voids of the larger. As an illus
 tration of this stability in contrast | to the lack of same in sheet asphalt
 suppose we take the concrete base of
 a pavement ready for surfacing and l spread two inches of sand over same
 you will agree with me that vehicles
 passing over it would cut nearly ii
 not entirely through the sand. Then
 We see that it is the asphalt in a
 sheet asphalt pavement that gives that pavement it's stability. Tha l asphalt takes the wear. on the other hand, if we spread a couple of inches
 of perfectly graded rock together
 with a certain amount of sand ant i fine dust on this concrete base you
 will agree that vehicles will cut int
 same but slightly if at all. A 1 familiar example of this i3 the knowr stability and compactness of a wei 1 constructed macadam road whose only
 fault is the lack of binder to keep the 1 surface from tearing apart and disin- 1 tegrating under the suction of automo- | bile traffic and moisture. Hence the
 addition of the asphalt to the aggre-
 gate, for a Bithulithic pavement is not
 to give it stability. but merely for the purpose of a binder to hold the par
 ticles together, to keep out moisture