Article
Effect of coarse aggregate size on strength and workability of concrete
Canadian Journal of Civil Engineering (Impact Factor: 0.56). 02/2011; 33(2):206213. DOI: 10.1139/l05090
ABSTRACT
The properties of concrete were studied when the proportions of 37.5 and 19.5 mm stone in the coarse aggregate were varied. With the cement content of 160 kg/m3 and the ratio of water/cement (w/c) greater than 0.9, the compressive strength is maximum at 25 percent by weight (w/o) of 37.5 mm stone. Conversely, for the cement content of 350 kg/m3 and w/c ratios of less than 0.50, maximum compressive strength is substantively reduced. For both 160 kg/m3 and 350 kg/m3 cement contents, workability improves slightly as the proportion of the 37.5 mm stone is increased. For 100 mm fixed slumps and cement content of less than 160 kg/m3, there was little change in compressive strength as the proportion of 37.5 mm stone increased. However, when cement content was increased from 190 to 350 kg/m3, maximum compressive strength was observed, which shifted downward from 50 w/o to 25 w/o of 37.5 mm stone. In general, to maintain a 100 mm slump, water demand decreased as the proportion of 37.5 mm stone in the coarse aggregate fraction increased.Key words: concrete, compressive strength, workability, slump, aggregate, size, cement.

 "This phenomenon can be explained by the physical entanglement of aggregates that contributes to compressive strength and fracture energy of concrete and that is more pronounced with larger aggregates [25] [26]. These results are coherent with those observed in the literature [21] [22] [23] [24] [25] [26] "
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ABSTRACT: a b s t r a c t When massive concrete structures (highrise buildings, tunnels, dams, nuclear power plants, bridges, protection structures, . . .) are subjected to extreme loadings (aircraft shocks, rock falls, nearfield detonations, ballistic impacts, . . .), the material undergoes triaxial compression loading at a high confinement. In order to reproduce high stress levels with wellcontrolled loading paths, static triaxial tests are carried out on concrete samples by mean of a very highcapacity triaxial press. It is a wellknown fact that the cement paste volume and the coarse aggregate size are two important parameters of concrete formulation. This article focuses on identifying the effect of coarse aggregate size and cement paste volume on concrete behavior under high triaxial compression. This article shows that at low confinement, the concrete strength slightly increases as the coarse aggregate size increases. At high confinement, the coarse aggregate size has a slight influence on concrete deviatoric behavior and a significant influence on concrete strain limitstate. The higher the coarse aggregate size, the lower is the mean stress level corresponding to concrete strain limitstate. Furthermore, this article highlights that at low confinement, the concrete strength significantly increases with an increase in cement paste volume. Increasing confinement tends to reduce cement paste volume effect on concrete strength. At high confinement, contrary to what has been observed in unconfined compression, the cement paste volume has little effects on concrete deviatoric behavior. Otherwise, decreasing cement paste volume increases concrete deformation capacity. At very high confinement levels and at very high deviatoric stress levels, the axial tangent stiffness of concrete increases as the coarse aggregate size or the cement paste volume is reduced.  [Show abstract] [Hide abstract]
ABSTRACT: To meet the requirement of nonlinear analysis and design for mass concrete structures, the mechanical characteristics of mass concrete specimens 25×25×40cm with threegraded aggregate 5–80mm under biaxial compressiontension and triaxial compressioncompressiontension was studied experimentally with the multiaxial concrete apparatus. In comparison with the corresponding wetscreened concrete specimens 15×15×30cm with twograded aggregate 5–40mm, it was found that the wetscreened effect and size effect under complex stress states were obvious, as under uniaxial stress state. By regression of the tests results, respective failure criteria for mass concrete in principal stress space and octahedronal stress space were proposed.  [Show abstract] [Hide abstract]
ABSTRACT: In this research, the relationship between the compressive strength, fc, and the dynamic shear modulus, Gd, of normal concrete at an early age was studied. To investigate the correlation between fc and Gd at an early age, different types of mixtures, including mortar and concrete, were prepared, and the corresponding fc and Gd values were measured every 12 h after initial mixing up to 72 h after casting. The influences of hydration age, watertocement (w=c) ratio, curing temperature, aggregate volume content, and maximum aggregate size on the Gd − fc relationship of concrete were studied. The Gd − fc relationship was then mathematically modeled by using multivariable power laws. The developed model is reasonably accurate to predict the early age compressive strength of concrete with variations in hydration age, aggregate content, and sizes. This type of model can be used directly in the field for the estimation of concrete strength when nondestructive testing (NDT) techniques are employed.
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