MICHIGAN ROADS AND FORESTS 



11 



where the steel must be located to take care 

 of every liit of tension in the concrete. 



Because of the complications of stresses, it 

 is necessary, in designing reinforced bridges 

 and culverts, to have knowledge of those prin- 

 ciples, in order to make permanent and last- 

 ing structures. Too many culverts and small 

 bridges are being built without proper plans 

 in a cut and try manner, and are bringing the 

 f concrete and reinforced concrete into 

 disrepute. 



It is not my purpose to take up the design 

 of bridges so much as the fundamental prac- 

 tical principles, which must be observed in 

 order to produce a satisfactory and lasting 

 structure. 



Portland cement should be used in every 

 event in preference to natural, because it is 

 stronger and more reliable and hardens quick- 

 er. Use a cement which is of standard brand 

 and will pass standard specifications. 



Gravel and sand should be clean and sharp, 

 free from foreign matter and with no larger 

 than three per cent clay or loam. 



Water should be clean and free from acids 

 and alkali. 



Steel for reinforcement should be of high 

 tensile strength and of such shape, either 

 twisted or deformed, so as to give a firm bond 

 with the concrete. 



The mixture, for foundations, should be 1 of 



cement to 6 of gravel, and for reinforced arch 



and girders. 1 of cement to 3 of gravel. 



Mixing the concrete is the most vital thing 

 in the life of a structure, whether large or 

 small, and to get the mass as dense as pos- 

 sible. Mix well and mix wet will cure many 

 faults in working with concrete. 



Exposed surfaces of concrete may be made 

 sufficiently smooth by spading, so as to force 

 the stones back from the surface of the form 

 ard allowing the mortar to crowd to the face. 

 The forms should be sufficiently tight to pre- 

 vent the mortar running out. 



\\ ith these -precautions, surfaces can be ob- 

 tained that require very little patching or 

 plastering to make a neat job when the forms 

 are removed. 



The cost of reinforced concrete bridges for 

 spans varying from four feet up to forty feet 

 p.nd for other spans that can be broken up 

 into short spans in general will be slightly 

 in excess of that of steel constructed ones, 

 although in some localities it may be even 

 less. 



In order to get a proper idea of the relative 

 value of the different types of construction, it 

 is necessary to consider not only the first cost 

 but also in connection therewith the rate of 

 depreciation, maintenance charges, such as 

 painting, reflooring. etc. The total investment, 

 as represented by the first cost, plus the capi- 

 talized charges are the proper basis for com- 

 parison, and viewed in this light, the economy 

 of reinforced concrete construction is decided- 

 ly apparent. 



The advantages of reinforced concrete 

 bridge construction may be briefly stated as 

 follows: 



(1) Comparative low first cost. 



(2) Absolute permanence. 



Use of local material and labor. 

 With concrete bridges we have something 

 that improves with age and is permanent as 

 anything can be. All that is needed to make 

 them so is the use of the best materials, good 

 workmen and designs that have met the ap- 

 proval of engineers versed in such work. 



Andrew Emerson, the Ashland lumberman 

 who owns a sawmill in the vicinity of Iron- 

 wood, at a place called Dunham, and who has 

 carried on extensive operations at that point, 

 has made an assignment. The liabilities are 

 reported to be about $90.000. The secured 

 creditors have claims of $50.000. leaving about 

 $40,000 of unsecured claims. It is reported 

 that some of the unsecured creditors will make 

 an attempt to have set aside some of -Emer- 

 son's transfers to the secured creditors. The 

 assets consist of the Dunham store and saw- 

 mill and timber lands. 



CONCRETE PAVEMENTS. 



Ann Arbcr Has Solved Problem of Cheap and 



Satisfactory Paving. 



One of the most interesting papers read at 

 the annual convention of the League of Michi- 

 gan Municipalities wa? that of Mayor Wm. L. 

 Walr of Ann Arbor en "Ann Arbor's Xew 

 Pavement and Treatment of Old Pavement." 

 The city of Ann Arbor has be'en making his- 

 l> ry in the building of pavements the past 

 year, and Mayor YValz's paper caused the dele- 

 gates to sit up and take notice. He said: 



Ann Arbor has no municipal plant of any- 

 kind, and in selecting the subject. "Ann Arbor's 

 Xew Pavement." I did so because it was the 

 only city work that we were doing that I 

 thought might interest the delegates from 

 other cities. I had received a number of in- 

 quiries from other cities in reference to our 

 new pavement, so I believed that the question 

 cf good streets was a problem that other cities 

 were also trying to solve. I believe that our 

 new pavement has solved the paving problem 

 in our city, and maybe our experience will 

 prove of some benefit and assistance to other 

 cities that have the same problem to contend 

 with. 



I do not appear before you as an expert 

 or as one with technical knowledge on the 

 subject of street pavements, but in the ca- 

 pacity of an ordinary citizen who is willing to 

 give to his neighboring townsmen the experi- 

 ence of his own on this important que.-ti. .11. 

 and at the same time receive from them all the 

 ir.furmation they may give. 



Under cur existing paving laws in Ann Ar- 

 bor, the common council has no power to 

 order a street paved unless the council shall 

 be applied to in writing by the parties holding 

 a majority of the foot frontage of the real 

 estate on the line of such street or part thereof 

 proposed to be paved. Thus you see the first 

 step to inaugurate street paving must be made 

 by the property holders themselves. This con- 

 dition of affairs has prevented us from having 

 ir,..re paved streets tnan we now have. Main 

 citizens oppose pavement of streets in resi- 

 dence districts fcr several reasons. A few 

 because they prefer the dirt and muddy streets 

 to a pavement. si>nie on account of the dissatis- 

 faction with old pavements, and many on ac- 

 count of the expense, notwithstanding the fact_ 

 that the city pays for all street intersections 

 and 20 per cent of the balance. Our old pave- 

 ments in the residence sections cost from $2.03 

 per sq. yd. to $2.19 per sq. yd., but our new 

 pavement has been put down on one street 1 

 - cents per sq. yd., so the objection to 

 expense has been overcome. 



Up to two years ago, we used asphalt block 

 for paving streets in our residence districts, 

 and the work was awarded to the contractor 

 who put in the lowest bid. The paving put 

 down with this material is unsatisfactory, and 

 also there was more or less dissatisfaction 

 with the work of the contractor. To get bet- 

 ter pavements and to satisfy the people it was 

 deemed best to have the paving done by the 

 city under the direction of the city engineer 

 and the street commissioner. This seemed to 

 be a step in the right direction as the property 

 holders felt that they would get better pave- 

 ments and at a less cost than it was possible 

 for them to get under the work of any private 

 contractor. 



The kind of pavement we are now putting 

 down may be called "Concrete Paving" and it 

 seems to give the best of satisfaction and is 

 the cheapest good pavement we have been 

 able to put down.. To be move specific, I will 

 now give ycu a brief statement of how this 

 concrete pavement is put down. 



The street commissioner is required to ex- 

 cavate to such depth and width as may be 

 necessary to get the proper foundation and 

 level so that when the pavement is finished 

 the street will be at proper grade. After the 

 excavation has been made the street commis- 

 sioner is required to roll the subgrade with 

 a roller weighing not less than ten tons, anil 

 leave the subgrade at a uniform distance below 



the grade of the finished surface of the street. 

 Curbing. 



We put in the curbing which is built on both 

 sides of the street. The curbing is 14 inches 

 deep, 6 inches wide on top and 8 inches wide 

 at the bottom and is finished 6 inches on the 

 face. The core of the curb is composed of 

 concrete in proportion of one part of cement 

 to MX parts of gravel, and the facing is made 

 of cement mortar in proportion of one part 

 cement to two parts of sand. 



Body of the Pavement. 



The paving consists of a bottom layer of 

 concrete 5 inches thick composed of Portland 

 cement concrete, made in proportion of one 

 part of cement to eight parts of gravel and 

 sand, and the top layer of Portland cement 

 mortar 2 inches thick, made in proportion of 

 one part of cement to two parts of clean 

 sharp sand. The top layer is put on within 

 twenty minutes after the bottom layer and is 

 immediately struck with a template approved 

 by the city engineer, and as soon thereafter 

 as practicable troweled as directed. An ex- 

 pansion joint 1 inch wide is left at each curb 

 and every 20 feet transversely of the street. 

 Tar Coating. 



After the concrete has thoroughly set, there 

 is spread en the surface of the concrete a thin 

 coating of hot coal tar. and before this is dry 

 a coating of clean sharp sand is spread over 

 the entire tarred surface, care being taken to 

 fill the expansion joints flush with the surface 

 of the street with coal tar and sand. 



This, in brief, is the pavement we are now 

 laying in our city and from all appearances is 

 the best kind of pavement we have ever put 

 down, and we believe it will prove to be the 

 coming pavement. 



Cost and Advantages. 



This pavement is not costly. It costs con- 

 siderably less than one-half the cost of either 

 brick, asphalt block, or bitulithic pavement, 

 the kind of pavements we have used hereto- 

 fore. Two years ago we paved a street with 

 concrete and the total cost, including all ex- 

 penses, such as excavating, material, and labor 

 was $1.0254 per sq. yd. We have just finished 

 paving another street at a total cost of $1.06% 

 per sq. yd. This increase of cost over a year ' 

 ago is due to price of labor and cement being 

 higher now, and also to more excavating hav- 

 ing to be done on this street. The cost of 

 concrete pavement in Ann Arbor this year 

 may be itemized as follows: 

 Pavement proper. .$ .85 per sq. yd. 



Curb 6" x 14" 22 per lineal foot 



Tar and sand top. .. .01 per sq. yd. 



Cement 1.32 per bbl. 



Sand and gravel. . . 1.00 per load of 1% cu. yds 

 Labor 2.00 per day of 9 hrs. 



Five cents per sq. yd. added to cost for use 

 of tools and superintendence. 



Thus you see it is a cheap pavement to put 

 down and is without doubt one of the easiest 

 kinds of pavement to repair. 



Our present plan of having the city put down 

 concrete pavement has proven such a success, 

 and has so satisfied our citizens, that during 

 the present year the council has been peti- 

 tioned to pave with this kind of pavement, 

 nine streets. The demand for this kind of 

 pavement, I believe, shows that our citizens 

 have confidence in this pavement, and such 

 confidence speaks well for the future develop- 

 ment of our city. 



Xow in conclusion, I will say a word or 

 two as to the treatment of our old pavements. 

 Some of our old pavements, especially the 

 asphalt block, has proven so unsatisfactory, 

 that we had to do something to save it. In 

 many places the blocks were worn down to 

 only one-half inch in thickness. Our cit\ en- 

 gineer tried the experiment of spreading a 

 coat of hot tar and sand on the pavement, and 

 this, not onl3- filled up the depressions in the 

 pavement and made it smoother but it has 

 also prolonged the life of the pavement. This 

 same treatment has been applied to the brick 

 pavements with very satisfactory results, and 

 we have found the way of increasing the wear- 

 ing qualities of pavement. 



