More info
Description / Abstract:
Introduction
This document describes the aggregate suspension mixture
proportioning method. The method is suitable for normalweight
concrete with workability ranging from zero-slump to
self-consolidating. This method may not be suitable for mass
concrete mixture proportioning. It is adapted from a method
originally published by Koehler and Fowler (2007).
The aggregate suspension mixture proportioning method is based
on the representation of concrete as a suspension of aggregates in
paste and air, as depicted schematically in Fig. 1. All solid
material finer than the No. 200 (75 μm) sieve is considered to be
part of the powder and, subsequently, the paste. To proportion a
concrete mixture, the optimal combination of aggregates for the
application is selected based on grading, size, shape, angularity,
and texture. Next, the total volume of paste and air required for
the selected aggregates is determined. Then, the composition of
paste and air—namely the relative amounts of water, each powder
material, and air—is optimized to achieve the desired concrete
rheology and hardened properties. Lastly, trial batches are used to
make adjustments. Although this document discusses concrete
rheology, measurements of rheology are not required to perform this
method. Guidance on measuring rheology is available in ACI
238.1R.
Key features of the method include:
a) The aggregates are selected on a combined basis, rather than
individually.
b) The volumes of aggregates and of paste and air are selected
based on the properties of the combined aggregates. Aggregates with
desired grading, shape, angularity, and texture for the application
will typically result in less volume of paste needed.
c) All material finer than the No. 200 (75 μm) sieve is
considered part of the powder content and, thus, part of the paste.
This material includes fines from the aggregate and separately
added fines, such as ground limestone filler.
d) The water-powder ratio (w/p) is considered when adjusting
workability and the water-cementitious materials ratio (w/cm) is
considered when aiming to achieve desired hardened properties. The
difference between w/p and w/cm is attributable to noncementitious
fines such as ground limestone filler and other mineral
fillers.
Calculations should be performed in a computer application. Use
of this method results in proportions based on aggregates in
saturated surface-dry (SSD) condition. The user should make
corrections for aggregate moisture content when making trial or
production batches.
Use of this proportioning method may result in otherwise
acceptable but different proportions than those determined in ACI
211.1.