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TECHNICAL PAPER

CAN WE FORMULATE

A GEOPOLYMER

OR AN ALKALI-

ACTIVED BINDER AS A

PORTLAND CEMENT? Martin CYr*

Abstract The formulation of geopolymers and other alkali-activated
binders is more complex for several reasons:
Geopolymers and more generally alkali-activated binders
represent possible alternatives to classical Portland cements. – There are many types of precursors which are very
Their formulation seems however more difficult to manage different from each other due to their chemical and
compared to cements, which might restrain their industrial mineralogical compositions: metakaolins, fly ash, blast
use. The complexity of their formulation is mainly linked to furnace slag, etc.
the wide variety of basic materials that compose them and – Precursors generally require more than water to react, so
the need to use activators. The purpose of this article is to other products (activators) must be considered to ensure
present a few indications for the formulation of geopolymers the desired performance.
and alkali-activated binders. It first defines the main precursors
and activators, emphasizing the couplings between the two. – The range of activators required for reactions is quite wide
Then it draws a parallel with Portland cements on the quantities and some, which work well with one precursor, may not
of binders and water, two important notions in formulation. work at all with another.
Finally, it describes some important details of the formulation
of geopolymers compared to Portland cements, in particular – The role of water is less easy to grasp than for Portland
the use of molar ratios of certain oxides. These ratios might cements, since it may or may not be incorporated into the
complicate the formulation of the material, but they allow reaction products.
the optimization of the composition to meet the targeted The purpose of this article is to present some indications for the
performance.
formulation of geopolymers and alkali-activated binders and to
Key words: alkali-activation, alkali-activated binders, Fly ash, show that it will probably be difficult to master their formulation
Formulation, Geopolymers, Ground Granulated blastfurnace as simply as for Portland cements.
slag, metakaolin.
2. MATERIALS
1. INTRODUCTION
Table 1 gives the chemical analysis of the metakaolins (mK)
It is relatively easy to control the formulation of a Portland and ground granulated blastfurnace slags (GGbs), and Table 2
cement paste / mortar / concrete since, in general, an increase reports the other characteristics of the metakaolins. The alkali-
in the quantity of cement in the mixture and a decrease in activated slag systems (section 3.1.1) were prepared with 7.87%
the water-binder ratio are sufficient to reach repeatable and (wt%) sodium metasilicate relative to the GGbs mass, i.e. a
reproducible performances. This is probably because most Na O of 4%. The water-solid ratio was 0.46. The geopolymers
eq
2
Portland cements are similar in composition and fineness from based on mK (section 4.3.1) were prepared with alkaline
one place to another in the world. In addition, these cements solutions made of pure amorphous silica (sigma aldrich, purity
require at least only water to react and achieve the desired 99%, particle size 350 - 600 µm), soda (purity 99%) and distilled
performance. water.

The IndIan ConCreTe Journal | JulY 2020 5
*Corresponding author : martin CYR, email : martin.cyr@insa-toulouse.fr