EFFECT OF COARSE AGGREGATE TYPE AND SPECIMEN GEOMETRY ON MECHANICAL PROPERTIES OF NSC AND HSC

Materials Engineering Dept., Faculty of Eng., Zagazig University, Zagazig, EGYPT

As a result of the argument occurred in the last two years in the Egyptian construction market

about the reliability of using dolomite as a coarse aggregate in normal strength concrete

(NSC), dolomites obtained from different locations were examined as a coarse aggregate. The

effects of washing dolomite before concrete mix and type of concrete curing were also

considered in first part of this paper. In the second part, the effects of aggregate types and

nominal maximum aggregate size (NMAS) on the compressive and indirect tensile strengths

for different specimen size and shape of high strength concrete (HSC) were studied.

The results show that the effect of dolomite washing on the compressive strength is varied

from marginal in the obtained dolomite from Alexandria to significant for concrete made of

Kilo 101 dolomite. The compressive strength of NSC with gravel aggregate is not affected by

the increase in NMAS, while, tensile strength decreased by increasing NMAS. For HSC, the

increasing in NMAS leads to the increase in the compressive strength of gravel concrete,

while NMAS has a marginal effect on the strength of basalt and dolomite concrete. The large

cylinder specimen size has higher compressive strength than the small one. The compressive

strength of dolomite concrete is higher than that of basalt and gravel concretes. Partial

replacement of gavel by dolomite or basalt (hybrid aggregate) is more effective in concrete

with NMAS =10 mm than that of NMAS =20 mm.