Investigation of concrete workability through characterization of aggregate gradation in hardened concrete using X-ray computed tomography

Concrete mixtures with different aggregate gradations and workability were prepared and X-ray computed tomography (XCT) is used to study the aggregate packing in hardened concrete. The workability of the mixtures was measured and then the aggregate spacing and distribution in the hardened concrete were investigated with an XCT scan of 40 gm resolution. The workability measurements showed segregation or poor workability in the mixtures with more than 20% of the coarse aggregates retained on a single sieve. In addition, in these mixtures, it was observed that approximate to 75% of the aggregates have a spacing < 600 gm and regions where no aggregate is present in the regions investigated. This close spacing of the aggregates means a high amount of a single sieve size leads to congestion in certain regions within the mixtures from poor aggregate packing. These mixtures were also observed to have poor workability. This suggests that segregation of the coarse aggregate plays an important role in the workability of fresh concrete. These observations provide important insights into how aggregate packing and distribution impacts the workability of flowable concrete.