Page 4 - February-2022

TECHNICAL PAPER

POWDER PACKING OPTIMIZATION

FOR CLINKER REDUCTION IN

CONCRETE MARK ALEXANDER*

MATTHEW HOLMES

Abstract accounts for the bulk of its GHG emissions. This is the result
of the liberation of CO 2 during the calcining of limestone, as
Due to the vast quantities of concrete that are produced well as the burning of coal fuel and energy intensive milling
annually, the material represents substantial greenhouse gas processes. However, clinker provides the desired strength,
(GHG) emissions, with clinker contributing the most significant deformation and durability properties of concrete. Therefore,
portion. This paper presents an investigation aimed at reducing there has been extensive research surrounding the reduction
the clinker content required to achieve compressive strength of clinker content while ensuring the attainment of required
[2]
while not detrimentally affecting workability, using particle engineering properties . Typical outcomes have been the
packing modelling and limestone filler to replace clinker. The partial replacement of clinker with supplementary cementitious
compaction interaction packing model (CIPM) and the modified materials (SCMs) and the use of ‘alternative’ binders. However,
Andreasen and Andersen curve (MAAC) were applied and both have only enabled limited clinker reduction on a large
integrated, the former for powder packing and the latter for fine scale, primarily due to issues of availability, limited replacement
and coarse aggregate packing. The CIPM was calibrated based ratios and, in the case of alternative binders, highly sensitive
on compaction effort applied experimentally, and predicted reactant materials, likely better suited to niche markets.
powder packing densities were validated experimentally. This research investigated optimization of the packing density
The integrated model was then applied to obtain optimized of concrete materials to reduce the clinker content of concrete.
concrete mix designs with maximum packing density. Results Such optimization has been investigated by others [3,4] where it
showed that workability could be retained but compressive was confirmed that the largest potential for clinker reduction
strength decreased relative to a reference mix. The binder by this method was the optimization of the powder phases
efficiency index (kg binder/MPa/m concrete) showed very (<125 µm) of concrete. The optimization undertaken in this
3
acceptable performance relative to the international literature, research was the maximization of packing density without
confirming that packing optimization was able to effect detrimentally affecting workability. This was done with the aim
clinker reduction without detrimentally affecting compressive of minimizing the mass of reactive binder required to achieve
strength for strength classes < 50 MPa. There remains a need 1 MPa of compressive strength per cubic meter of concrete, an
to maximize filler content in concrete mixtures and to better indicator known as the binder efficiency index (bi).
understand the fundamental influences of powder packing,
to develop predictive processes that incorporate indicators 2. METHODS
of practical usability (such as water demand and expected
workability) while maximising packing density. 2.1 Particle packing modelling
To minimize excessive trials, analytical particle packing models
Keywords: Particle packing modelling, Clinker, Filler, Fly ash, were applied to guide the selection of material quantities for
Compressive strength
maximizing packing density. A review of existing particle packing
models identified the integration of two packing models [the
1. INTRODUCTION compaction interaction packing model (CIPM) and the modified
Andreasen and Andersen curve (MAAC)] as a feasible solution to
Concrete, the most widely used construction material known particle packing optimization. Both models were implemented
for its robust engineering properties, is actually a relatively in Microsoft Excel.
low greenhouse gas (GHG) emitter. However, due to the vast
quantities of concrete manufactured globally, equivalent to 2.1.1 CIPM
1 ton per person annually , significant GHGs are associated
[1]
[3]
with the use of this construction material. When considering the The CIPM is an extension of the compressible packing model
manufacture of concrete, clinker, the basis of Portland cement, (CPM) considering a poly-disperse system of particles to
[5]
THE INDIAN CONCRETE JOURNAL | FEBRUARY 2022 7
*Corresponding author : Mark Alexander, Email: mark.alexander@uct.ac.za