106 



AMERICAN FORESTRY 



One of the most important details is the treatment of 

 the blocks. Douglas fir is unlike most woods from the 

 standpoint of impregnation, and it has been necessary to 

 develop treating methods especially for this wood in order 

 to get the results desired. Paving blocks of any wood 

 should be treated in such a way as not to cause any ap- 

 preciable loss in strength. The steaming process is not 

 suitable for treating Douglas fir blocks since the fiber 

 of this wood is injured by this treatment. The follow- 

 ing method has been developed for treating blocks and 

 has proven thoroughly satisfactory : 



The blocks shall be placed in the treating retort, direct 

 from the saw, and the preservative introduced and heated 

 to approximately 215 degrees F. for from one to four 

 hours. The preservative shall then be drained off and a 

 vacuum of 23 to 2G inches drawn to take out the surplus 

 vapors, etc., from the wood cells. The vacuum shall then 

 be broken by the introduction again of the preservative, 

 which is then pressed into the wood at a temperature of 

 180 degrees F. until the blocks have received from Id 

 to 18 pounds per cubic foot. After receiving the required 

 amount of oil, the pressure shall be released, and the tem- 

 perature of the oil gradually raised to 220 to 230 degrees 

 F., and held for one hour. This final heating expands 

 the oil and vapors within the wood, and causes a certain 

 amount of the preservative to be expelled, due to this 

 expansion, and also effects further seasoning of the wood. 

 A final vacuum of 23 to 2() inches shall then be drawn, 

 which dries the blocks of the surplus surface oil, leaving 

 a thoroughly impregnated block which will never "bleed" 

 after being placed in the street, since it is forced to do its 

 "bleeding" during its treatment. 



The above treatment produces an ideal block, which 

 retains its original strength and is amply fitted tii resist 

 swelling and decay. 



CONSTRUCTION DETAILS 



In general, the following details of construction should 

 give the best results in building a wood block pavement : 



Blocks should be cut from sound, strong, close-grained 

 lumber and accurately dressed. \'ariations in thickness 

 and depth should not exceed 1/16 inch. They should be 

 creosoted in accordance with the method above referred 

 to, and 10 to 12 pounds of oil per cubic foot left in the 

 wood. The blocks should lie placed uijon a smoothly 

 finished concrete base, painted with pitch or asphalt im- 

 mediately before blocks are laid. The painting should be 

 tliorougli, and a bond secured between the paint coat and 

 the concrete. 



Blocks should be laid in courses at an angle of 00 to 67 

 degrees with the curb and with as close joints as possible. 

 The lozver portion of the joints should then be filled 

 with very hot asphalt or pitch sufficiently fluxed to en- 

 able it to flow into the joints. The upper portion of the 

 joints should be filled with hot, dry sand, and the entire 

 surface rolled with a 10 to 14 ton roller to thoroughly 

 seat the blocks and to finish completely filling the joints 

 with sand. Liberal expansion joints should be provided 

 along each curb. The lower half should be filled with 

 bituminous filler and the upper half with clay. Fine 

 gravel, one-quarter to half an inch in diameter, should 

 .then be scattered over the surface and rolled into the 



blocks until a surface satisfactory to the engineer is 

 secured. A coat of fine sand should be spread over the 

 surface of the pavement and left for thirty days after 

 street is opened to traftic. Additional fine gravel coatings 

 may, if desirable, be spread on the surface from time to 

 time. 



Douglas fir has thoroughl_\- demonstrated its ability 

 to withstand the wear found on business streets. Almost 

 seven years ago a portion of Fourth Avenue, Seattle, was 

 ]javed with creosiited Douglas fir blocks. This street is 

 today in excellent condition, as shown by the accom- 

 panying photograph, and the city has had no maintenance 



TWO WOOD PAVING BLOCKS 



These blocks, one Douglas fir and tlie other Longleaf pine, are from 



Sections 7 and S of the Minneapolis Test Pavement and both have 



been under the same street conditions of heavy traffic for four years. 

 Tlie wear is practically the same on both woods. 



to pay. The wear on the blocks has been approximately 

 1/16 inch, and more than 3,300 vehicles daily pass over 

 this pavement. 



Eleven years ago Douglas fir blocks were laid on 

 Salmon Street, in Portland, Oregon. The city records 

 indicate that the maintenance has been less than one- 

 quarter cent per square yard per year. The wear on the 

 blocks is practically nothing. The blocks were not prop- 

 erly treated. 



There has been a great deal said regarding the value 

 of Douglas fir as a paving wood. E.xamples, as shown 

 above, indicate the abilitv of this wood to resist mechani- 

 cal wear. 



Four years ago Sections 7 and 8 of the Alinneapolis 

 test pavement on Nicollet Avenue were laid with Douglas 

 fir and Longleaf pine blocks. This pavement is sub- 

 jected to very heavy traffic and both sections are at the 

 present time in first-class condition. There is no indica- 

 tion from the condition of the pavement that two woods 

 were used. 



C. S. JUDD HONORED 



Forester C. S. Judd has recently been appointed by 

 Governor Pinkham, of Hawaii, as chairman of the Con- 

 servation Commission of Hawaii. 



