HIGHWAY CONSTRUCTION 71 



Stone consolidated with improper binding material may present 

 a good appearance immediately after being rolled and be otherwise 

 an apparently good piece of work, still in damp weather a consider- 

 able amount of "licking up" by the wheels of the vehicles will take 

 place, which reduces the strength of the coating and causes the sur- 

 face to wear unequally. 



By the application of an immoderate quantity of binding of any 

 description the stone coating will become unsound or rotten in con- 

 dition, and if the binding be of an argillaceous nature, it will expand 

 during frost, owing to its absorbent properties, and cause the dis- 

 placement of the stones. The surface will become sticky, which 

 seriously affects the tractive power of horses, while the road itself 

 will suffer by the irregular deterioration of the surface. 



The use of such material as mentioned for binding enables 

 rolling to be accomplished in much less time than when proper bind- 

 ing is used, and the cost of consolidating the stone may be reduced 

 by 25 per cent; but, on the other hand, the stone coating which will 

 probably contain under these circumstances from 30 to 40 per" cent 

 of soft and soluble matter, and possibly present a smooth surface 

 immediately after being rolled, will quickly become "cupped" by 

 the wheel traffic, a bumpy surface^ being the result. This is caused 

 by the irregular wear, while the lasting qualities or "life" of the 

 coating will be shortened, giving unsatisfactory results to those 

 traveling over the road, and the work of renewing the surface of 

 the road in this manner may prove a failure on economical grounds. 

 There can be no doubt, and it is now being more generally recog- 

 nized, that sand as a material for binding in connection with rolling 

 operations, when applied in a limited but sufficient quantity, pro- 

 motes the durability of the stone coating, while the general results 

 are equally satisfactory; a firm, compact, and smooth surface is 

 obtained, and the subsequent maintenance of the road is minimized. 



A great amount of rolling is necessary when sand is employed 

 as a binding material, but economy is promoted, and the results are 

 more satisfactory when sand is used than by the use of the material 

 which gives to the stone an appearance only of having been properly 

 consolidated. If clean sand be used in combination with the screen- 

 ings from the crusher a very satisfactory surface will be obtained. 



