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TECHNICAL PAPER

Table 1: Chemical composition of the metakaolins and ground granulated blastfurnace slags

SiO Al O CaO MgO Fe O TiO Na O K O SO LOI
2 2 3 2 3 2 2 2 3
GGbs1 37.7 10.2 43.8 6.4 0.60 0.70 0.21 0.28 0.10 -

GGbs2 36.5 10.4 42.4 8.1 0.70 0.50 0.20 0.50 0.10 -
GGbs3 34.1 12.6 39.1 8.1 0.55 - 0.19 0.52 0.06 0.41
mK1 67.6 22.7 1.2 0.14 3.7 1.2 0.10 0.38 0.06 2.8
mK2 70.8 25.4 0.12 - 0.89 0.44 0.01 1.4 0.05 0.83
mK3 57.2 35.7 0.08 - 1.3 1.4 0.06 1.0 0.03 3.0

mK4 54.2 41.9 0.07 - 0.37 1.5 0.26 0.13 0.03 1.3

Table 2: Characteristics of metakaolins precursor. Note that this definition here excludes phosphate-
based activators (acid medium) and systems activated only by
ChARACTERISTICS MK1 MK2 MK3 MK4 lime (pozzolan-lime binders).
Specific gravity (kg/m ) 2500 2298 2400 2600
3
The pragmatism of the building materials industry can lead not
Specific surface area (BET) (m /g) 16 6 17 23 to eliminate from the formulation of an alkali-activated binder
2
mass % of impurities 50.4% 44.6% 22.2% 8.8% products allowing to solve certain industrial problems (slow
(Rietveld quantification) setting for example). Thus, it is not excluded to use Portland
cement or clinker, in addition to the activators mentioned,
mass % of reactive siO 26.8% 30.0% 42.1% 49.3%
2
on the condition of remaining outside the existing cement
mass % of reactive al O 22.7% 25.4% 35.7% 41.9%
2 3 standards: less than 5% so as not to enter into the composition
of a CEm III/C (minimum 5% clinker, the rest being blast furnace
3. ALKALI-ACTIVATED BINDERS AND slag) according to EN 197-1. This is the approach taken by the
GEOPOLYMERS United Kingdom in its document Pas 8820: 2016 - Construction
materials - alkali-activated cementitious material and concrete -
There are still some debates on the designations to use for Specification .
[2]1
alkali-activated binders and geopolymers. Without trying to
go into details, it was decided here to adopt certain principles 3.1 Focus on the main precursors - what
as reported by TC RILEm 224-aam . Thus, it is considered characteristics of the precursors do we need
[1]
that the terms alkali-activated binders relates to a broad class to know to formulate a geopolymer (GP) or an
of precursors formed of a silicate powder (with more or less alkali-activated binder (AAB)?
calcium) reacting thanks to an activator composed of a source of
alkalis used in solid or liquid form. alkali-activated binders have There are many types of precursors which are very different
less calcium than traditional Portland cements or aluminate and from each other due to their chemical and mineralogical
sulfoaluminate binders. Geopolymers represent a sub-category compositions, the main ones being metakaolins (mK), silico-
of alkali-activated binders, for which the precursor is essentially aluminous fly ash from thermal power stations (FA) and ground
an aluminosilicate containing very little calcium.
blast furnace slag (GGbs). These precursors differ not only from
The precursors can have varied natures, with more or less one another (for example, no calcium for mK, whereas it is an
calcium in their composition: blast furnace slag contains essential element in GGbs), but also within the same category
Ca abundantly (around 40%, which is still less than Portland (one can hardly speak of “metakaolin” as an unique material, as
cement), while aluminosilicates as metakaolins and silico- metakaolins can be quite different depending on the source of
aluminous fly ash (class F) have only a few percent. The activators kaolin and the way of calcining it). In addition to their differences
mainly include hydroxides, silicates, carbonates or alkali sulfates in chemical compositions, they are distinguished from Portland
which can provide cations called "alkali metals" (first column of cement by their atomic structure, the precursors being glasses
the periodic table: Li, Na, K, Rb, Cs, Fr), and thus increase the (molten and then rapidly cooled materials: Fa, GGbs) or
pH of the solution and accelerate the dissolution of the solid amorphous materials (no passage through a molten stage:

1 A Publicly Available Specification or PAS is a standardization document that closely resembles a formal standard in structure and format but which has
a different development model. The objective of a Publicly Available Specification is to speed up standardization. PASs are often produced in response
to an urgent market need.” source : Wikipedia

6 The IndIan ConCreTe Journal | JulY 2020