ABSTRACT
A B ST R A C T . For many applications, such as the repair of roads, bridges and runways, a quick hardening of repair materials is very important. With shorter repair times these construction projects may be opened again earlier for the traffic, and thus enormous costs may be saved. Thus, a quick development of strength is of economic interest. Burned oil shale is used for the preparation of portland oil shale cement having different classes of strength, whereby the portions of the portland cement clinker may be from 65 to 90 % and the portion of the burned oil shale may be from 10 to 35 %. For several applications the characteristics obtainable with the burned oil shale and its mixtures with portland cement are not acceptable. Based on several experiments it was found that the hardening of a blend of burned oil shale and portland cement could be accelerated in such a way that the usual compressive strength of portland cement concrete after 7 days has already been reached after 2 hours, and that the compressive strength after 28 days is reached in less than 24 hours. Although the development of strength is accelerated, the workability time could be controlled as desired. Depending on the application, the setting could occur within a few minutes or just after hours. As especially effective accelerators could be found: amorphous oxides and/or hydroxides of 3-and 4-valent cations as well as alkali earth metal aluminates. As a case study the high speed repair of runway 16/34 at Zurich Airport will be discussed.
