The Birmingham age-herald., 1920-10-05

Neal. Mrs. $. l.. Ledbetter, Mrs. c. M. Simmons. E. C. Robinson, Ed Norman, Garrard Harris, W. H. Woodall, w. A. Currie,~ Henry Houze, M. 5. Grace and Hunter Armstrong.
 selection. that the responsibility for dett rmining the class of pavement to be used. began to be placed more ppon the city engineer. Such change in con- ditions has resulted in the engineers getting together more frequently and as far as possible the cause of failure in many instances, and also deciding upon the class of pave ment or pavements that were nost suitable under given traffic, climatical subsoil and other conditions u Nls known that an asphaltic cement Whlch isN soft enough to not cause the oaVe- ment to crack during cold weather in the far north, would, in all probability be too soft to be used in a warmer climate, where if used, the pavement " uld \becom soft and work towaros the gutters or into rolls, during the h ot summer weaG CT.
 It Is also determined, by chem
 fcaI and physical analysis, the as-
 phaltic cement which has the
 proper hardness and ductility for
 use III the pdNChSht
 existing cIimaticnI and traffic con-
 ditions, and also that it contained
 no foreign substance that would
 decrease its value for such use. The
 writer has no hesitnncy in saying
 that having determined the pros
 babIe traffic conditions that will
 exist on any street in Birmingham,
 1t is possible to prepare speciffca-
 tions for a bituminOus pavement.
 which if followed out to the letter,
 would insure beyond reasonable
 doubt n satisfactory pavement. Hut
 unfortunately, in the construction
 of bituminOus pavement, many
 persons have to be depended upon.
 There is testing laboratory, which occupies about the same relation to the paving engineer as the druggist who fills tEe physicians prescriptions oc- cupies to him. It has been a custom of the city to hand to the testing a set of specifications, ana it was the duty of the chemist to analyze the asphalt to be used, in order to ascertain whether or not it was necessary to add or eliminate anything from it, ill order that it would comply with the specifications.
 THE MIXTURE
 An OTQlndTy SneeI dSpHdiI pd"c-iiCiie contains mineral aggregate. consisting of coarse sand, graded down through finer sand all the way to mere mineral powder. The proportions to be such that practically all the voids in the larger material are filled by the next succeeding size, and that sufficient as rhaltic cement is added to paint all the surfaces of the various mineral par ticles, and that they are all thoroughly mixed, in the asphalt plant, at the proper temperature, to be dumped into the trucks for delivery on the street When this is done the duties of the testing laboratory cease, except tha small samples of the mixture ar' taken by the city inspector on thu street, when it is dumped for spread ing, and sent to the laboratory for an |alysis, in order to determine whethe Tor not the mixing was properly done Tt is the duty of the city inspector oi the street and the assistant enginee Ito see that the mixture is properl, sreaded and rolled, and that no ma terial is allowed to enter the pave ment which is hot enough to indicat potable scorching or cool enough t prevent proper spreading and rolling IA great deal, of course, depends upol lilc Shlll, NOHcSlJ cAii0 CACh 6y VI Si contractor. Although he is also de pendent for results largely upon tn faithfulness and competency of his efn ployees. In spite of all these precau tio1s, absolute results cannot be guar anteed for every yard of pavement. I tke chemist is careless in his analysis or his assistant at the asphalt plnat i Incompetent or inattentive, the char acter of the material or the result may be faulty. If the city engineer ol the street is careless ,or incompetent or the contractors help unsklilled, tn best results will not be obtained. Take for instance. the pavement on First avenue. from Thirty second street to Firty-first street. This pavement. theoretically. should be the same throughout. Yet after four years use. small areas are rolling into ridges under the traffic. which h probably due to carelessness on the part of the i'm
 spection lahorntory's mnn mt the plant. in not seeing that the mix ture was uniform and according to the specifications.
 EXCESSIVE CRACKING On other sterets where excessiv cracks have occurred locally the indi Sd eHS Woulu De tndt tHe dSpHtltl cement was harder than that used ol other portions of the street. rhel again, if the surface of the pavem mt when new, is rough and uneven, i would indicate carelessness or incom potency on the part of the city inspec tor. Of course the ideal plan woul,
 be fo:- the city to own and operat Its own laboratory. and this is done il many cities wfere sufficient work i being carried on to justify the resula employment of competent chemist directly under the control of the cit, engineer. In order to bring the mat lter more closely under the supervision