Al-Rafidain Engineering Journal (AREJ)

Abstract

Abstract
The investigation aims to study the effect of re-vibration time and amount of steel
fiber on the properties of concrete made with crushed cement-sand mortar as coarse
aggregate. Three mixes were prepared with 0.00, 50 and 100 percent replacement of
natural gravel by crushed cement-sand mortar aggregates. Mix proportions of concrete
were 1: 2: 3 by weight. The water cement ratio of 0.50 to 0.60 was used to obtain the
same workability for all mixes throughout the research. The specimens were cast to
investigate compressive and splitting tensile strength of concrete.
The results showed that concrete made of crushed cement-sand mortar as coarse
aggregate had lower workability than concrete made with natural gravel aggregate for
the same water cement ratio. This reduction in workability is reduced for the richer
mixes and the influence of coarse aggregate on the workability decreases with an
increase in the amount of cement in the mixture. Concrete compressive and splitting
tensile strength were improved due to re-vibration by about 19 percent at the peak value
(about one hour after initial vibration) with volume fraction of steel fiber of about 0.5
percent. The steel fibers improve the compressive strength of concrete by about 8-11
percent and the splitting tensile strength by about 10.3 percent for the same period of revibration.