Abstract:
The classical idea of particle packing is based on Apollonian concept, in which the
smaller sized particles fit into the voids left by larger particles. Well graded fine and
coarse aggregates having greater range of particle size will reduce the voids in
concrete and hence the paste required to fill those voids. Fine to coarse aggregate ratio
can be adjusted by trials to have maximum packing density of granular mix with
reduced voids between them. Crushed aggregate particles are very irregular in shape
and pack more poorly together than naturally formed gravel. Aggregate voids
increases the paste demand in the mix and this can be countered by use of very fine
sized Secondary Raw Materials (SRM) to partially replace cement without adversely
affecting the properties of concrete.
Present study focuses on determination of optimum fine to coarse aggregate ratio to
have a maximum packing density of granular phase of Self Consolidating Concrete
(SCC). SRMs including Fly Ash (FA) and Limestone Powder (LSP) were also utilized
to further improve the packing of mix. Flow, volume stability, heat of hydration and
mechanical characteristics of Self Consolidating Concrete made with and without
SRM were studied and compared to the mix formulation designed using EMMA based
on Modified Andreasen and Andersen (MAA) approach. The ratio of fine to coarse
aggregate was varied in 20-80% range, as a trial process, to see the effect in the degree
of packing of aggregates in the SCC. The packing density and compressive strengths
were found to be optimum when fine to coarse aggregate ratio was 50:50 in terms of
weights in trial mixes while that based on MAA approach this ratio was around 51:49
with distribution modulus “q” equal to 0.25.
Results showed that SCC prepared using SRMs (Modified Mixes) possesses higher
packing density than that of SCC mixes in comparison to Control Mixes (CM) having
no SRM. Modified Mixes (MM) show increased SP demand for target flow, higher
flow times, better strengths, reduced total linear shrinkages and reduced heat peaks in
calorimetry coupled with reduced air content. While MAA approach saves the time
and materials needed in SCC mix design in trial process.
