BITUMEN ROADS

Rotorua Morning Post, Volume 2, Issue 252, 16 June 1932, Page 6

BITUMEN ROADS

TRANS

VIAM.

Sir, — The letter in your issue of the 13th raises several points of more than passing interest to those interested in road construction. Your correspondent apparently has taken exception to a statement made by some resp'onsible person which was to the effect "that the hot sun of a summer day did not soften to any appreciable extent a bitumen road." Your correspondent then goes on to quote an extract from an item that appeared in your colums on January 15 regarding damage done to the bitumen roading in Haupapa Street by horses. However, the question of damage done on Haupapa Street is not in 'any way comparable with that done on the Te Ngae Road, for the simple reason that in Haupapa Street there was a surplus of surface bitumen made apparent by the surface bleeding which permitted marking by the shoes of horses though no permanent damage resulted as the bleeding was more or less superficial and quite easily dealt with by the -application of hard stone chips. I think, that your correspondent has quite missed the main point raised, for mere surface markings on a bleeding bitumen road surface are no indication tbat the body of the road itself is being damaged. Among highway engineers it is accepted as a first principle that a bitumen road derives its strength not from the bitumen which is inherently wealc,but from the hard stone that is incorporated with the bitumenous material in the road The bitumen in itself has no strength and acts merely as a binding agent. Consequent-ly, it can hardly be argued that the surface of bitumen that is in evidence on a hot summer day implies structural weakness in the body of the bitumen road itself, thereby spelling its destruction under traffic conditions. It is of interest to note that the bitumen work on the Te Ngae Road stood up to traffic of a density of 200 vehicles per hour on New Year's Eve (two hours after the road was completed) and of 1400 motor vehicles the following day, most of this being fast traffic. Roughometer readings (to determine the quality of running surface) taken six months after construction gave readings of 180 inches per mile over all but the first twenty chains. This is superior to readings given on the average of penetration bitumen surfaced roads and very definitely superior to the famous bitumen Hutt Road near Wellington, where roughometer readings average 275 inches per mile. "The first twenty chains of bitumen at Te Ngae gave 250 inches to the mile. For comparison purposes it is as well to state that good concrete roads give roughometer readings of 100 inches ner mile. — I am, etc.,

Rotorua, June 15, 1932.