Significance Statement
Self-Consolidating Concrete (SCC) is one
of the best innovations in the concrete industry over the past 20
years. This research used fundamental rheology theory and aggregate
packing models to help understand and control dynamic segregation, a
common and tricky problem limiting the wide applications of
self-consolidating concrete.
Segregation is a common problem in
self-consolidating concrete, which is sensitive to mix proportions such
as superplasticizer dosage, as well as the size, volume, and gradation
of the aggregate. Dynamic segregation, when coarse aggregate lags behind
during the flowing process, is distinguishable from static segregation,
when coarse aggregate settles in concrete at rest. In the research
reported in this paper, a flow trough and a concrete rheometer were used
to study the effects of various aggregate properties and concrete
rheology on dynamic segregation of self-consolidating concrete. An
equation for the drag force was found useful to understand how various
mix proportions and concrete rheology affecting dynamic segregation.
Higher paste volume, lower superplasticizer percent by weight of cement,
lower slump flow, smaller coarse aggregate, and better gradation may
increase dynamic stability. Smaller aggregate size has more significant
effect than other aggregate properties. Mixtures with dynamic yield
stress less than 50 Pa exhibited severe segregation from both flow
trough and visual stability index (VSI) tests. Mixtures with static
yield stress of 250 Pa or higher had satisfactory dynamic stability,
while mixtures with static yield stress of 100 Pa or lower showed severe
dynamic segregation. No clear correlation was observed between concrete
plastic viscosity and dynamic segregation.
Abstract
Segregation is a common problem in
self-consolidating concrete (SCC), which is sensitive to mix proportions
such as superplasticizer dosage, as well as the size, volume, and
gradation of the aggregate. Dynamic segregation, when coarse aggregate
lags behind during the flowing process, is distinguishable from static
segregation, when coarse aggregate settles in concrete at rest. In the
research reported in this paper, a flow trough and a concrete rheometer
were used to study the effects of various aggregate properties and
concrete rheology on dynamic segregation of self-consolidating concrete.
An equation for the drag force was found useful to understand how
various mix proportions and concrete rheology affecting dynamic
segregation. Higher paste volume, lower superplasticizer percent by
weight of cement, lower slump flow, smaller coarse aggregate, and better
gradation may increase dynamic stability. Smaller aggregate size has
more significant effect than other aggregate properties. Mixtures with
dynamic yield stress less than 50 Pa exhibited severe segregation from
both flow trough and visual stability index (VSI) tests. Mixtures with
static yield stress of 250 Pa or higher had satisfactory dynamic
stability, while mixtures with static yield stress of 100 Pa or lower
showed severe dynamic segregation. No clear correlation was observed
between concrete plastic viscosity and dynamic segregation.
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