FATIGUE IN CONCRETE

Hokitika Guardian, 24 August 1926, Page 4

FATIGUE IN CONCRETE

Like the people who ride over hem, concrete roads get “tired” and require periods of rest that they may •ecuperate, Professor S. S- Steinlnirg, of the University cf Maryland, and assistant director of tho Highway Research Board of tho National Research Council at Washington, has discovered.Thfci is one of the subjects being studied at the University oi Maryland and oilier institutions engaged in highway research. “Considerable attention is being given to determining tlio causes of cracking in concrete roads,” said Professor Steinburg “The extent of cracks in a slab is dependent upon the underlying soil, tin- quality of the concrete, and the loads the pavement must bear. When a vehicle passes over a concrete pavement the slab is deflected. .1 he result is that under traffic) the road is suejected to a wave action, tho slab vising and falling with each passage of a wheel. On roads under heavy traffic at high speeds this motion may ho repeated many hundred times an hour. • “Experiments have been conducted in tho laboratory stimulating these field conditions, with tho discovery that concrete is subject to fatigue, which, in many respects, is analogous to muscular fatigue in human beings.

I After continued rapid application ol j load, the normal elastic properties of | concrete nro overcome, and the fatigue I limit is reached. The result is a break in the concrete and tlio appear- ! !V ,i<:o of a crack in the road. The , analogy to muscular fatigue is further ! evidenced by tbe fact that if befoio i failure the concrete is permitted to have long periods of rest, it recovers ' its ability to resist the applied forces. : and tho fatigue limit, or life of Hie slab, is extended. i “The stresses produced in. roads by , traffic, as well as the deflections and changes of length they cause, are measured by specially .constructed instruments installed in the road. An ' analysis, of these measurements serves to determine the. proper thickness of tho road slab in its different parts to support tlio traffic tlio road must carry.” A recent improvement described by Professor Steinburg is a new kind of cenici.it, which, when used in. conciote, has the- property of developing greater strength in 24 hours than is developed by Hm ordinary Portland cement in 28 days. This opens up remarkable possibilities in road construction. “Whereas by use of the ordinary - cement a road must ‘cure,’ or acquire 1 strength, for 1 I days after being laid, during which time it. is not permitted to carry traffic,it may now ho pos--1 si,bio to build a portion of a. concrete road on one day and open if to traffic ' tlio next. Studies are under way to determine more fully tlio physical properties and characteristics of this cement,” lie stated.