CONCRETE PLASTIC FLOW

Evening Star, Issue 23375, 19 September 1939, Page 3

CONCRETE PLASTIC FLOW

Recent findings of investigations carried on at the University of California on plastic flow of concrete have just been published. In tests under longtime loading it was found that even after 10 years some plastic flow was discernible in plain concretes under sustained stresses of several hundred pounds per square inch,' although over 95 per cent, of the probable total flow toot place within five years. In a senes of reinforced concrete columns under load for more than five years it was found that in terms of stresses in the steel or concrete the movements due to drying, shrinkage, or to plastic flow are of practical importance principally during the first year. Tests to determine the effect or water-cement ratio and of aggregatecement ratio indicated that the denser the cement paste the less the flow { this being a ‘very important variable. Within the range of normal concretes tested it was observed that with pastes of the same quality the flow was practically proportional to the paste content of the concrete. Other tests showed that the flow under tensile stress was greater than that under compressive stress. Similar results were found in tests to determine the fibre strains in plain concrete beams under constant sustained bending movement, A low-heat type of Portland cement was found to exhibit markedly greater plastic properties, particularly at the early ages, than a normal Portland cement.