Influence of aggregate characteristics on workability of superworkable concrete

Abstract

Physical characteristics of aggregates have a significant influence on the performance of concrete. Compared to conventional concrete, the mix design of highly flowable concrete is more complex and should ensure that the mixture can develop adequate static and dynamic stability. The selection of aggregate plays a major role for the mix design and mixture optimization of flowable concrete. The study seeks to understand the influence of physical characteristics of coarse and fine aggregates, including packing density, texture or roughness, fine particle content, shape, and quantity of flat and elongated particles on the workability, rheological properties, and mechanical properties of superworkable concrete (SWC). Three types of sands with different fineness moduli of 2.5, 2.6, and 3.0 and different textures (smooth and rough) were used. Seven types of coarse aggregates with different texture characteristics, flat and elongated particle contents, and different shapes were investigated. Sand-to-total aggregate volume ratio was varied between 0.45 and 0.60. Test results indicated that the packing density, the quantity of fines passing 315 µm sieve, and the shape of coarse aggregate can have significant effect on rheology, stability, and compressive strength of SWC. For the crush aggregate with 5–14 mm particle sizes (CA14), a 13 % increase in aggregate packing density from 0.69 to 0.79 by the use of optimum sand-to-aggregate ratio and natural sand can lead to more than 50 % reduction in surface settlement, i.e. 50 % increase in static stability. For the CA14 coarse aggregate, a good relationship was established between surface settlement and quantity of fine particles with diameter smaller than 315 µm. Mixtures with rounded coarse aggregates had 22–42 % higher surface settlement compared to those made with crushed aggregates of the same maximum size aggregate.