ADMIXTURES AND THEIR INTERACTIONS WITH HIGH RANGE CALCIUM ALUMINATE CEMENT
by Thomas A. BIER, Alain MATHIEU, Bruno ESPINOSA, Christophe MARCELON
presented at the UNITECR congress, Japan; 1995. 8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00 Abstract
Besides a careful choice of mineral raw materials, sophisticated applications of calciumaluminate cements (CAC's) cannot be achieved without the use of admixtures. Admixtures serve to control mostly the rheological behavior and setting (hardening)characteristics.
In this paper, different concepts of admixtures are presented in order to influence givenproperties such as flocculation, coulability and hardening.
The interactions of these admixtures with the CAC are shown by chemical as well asrheological measurements. The results are discussed with respect to practicalapplications. 8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00
An overview about possible admixtures withCAC's is given in /1/.
The major admixtures used in this study and
As with all hydraulic binders, the chemical and
mineral composition and the fineness of a CAC
determine the rheology and reactivity of the
system. This means that setting time and flow
behavior of a refractory concrete or mortardepend for a given water cement ratio only fromthe constituents other than the cement. These
other constituents influence the rheological andhardening properties of a concrete or mortarmore
Conductivity of stirred suspensions
considered as inert, a larger influence being
This technique, presented in recent publications
attributed to reactive fine fillers. And the largest
/2,3/, consists of measuring the electrical
influence is played nowadays by admixtures
conductivity of a stirred suspension of cement in
which are on purpose added to tailor the above
mentioned properties. The raw material togetherinfluence each other and constitute finally the
Conductivity is a very good picture of the ionic
performance of the concrete. These interactions
concentration in water. The conductivity of the
have in the past very often been represented by a
suspension gives information on the dissolution /
triangle of interactions as shown in Figure 1.
nucleation / precipitation steps of the hydrationreaction of cement in water. A schematic picture
of conductivity and related properties is shown inFigure 2, the above mentioned hydration steps
being represented as stages I, II and III.
Figure 1 - Components influencing the properties in arefractory concrete.
Amongst these components this paper deals with
according to ASTM C125-88 as"Materials other than water, aggregates, hydraulic
ingredients of concrete or mortar and added to
the batch immediately before or during itsmixing." and in the DBV - Manual :
Figure 2 - Sketch of a conductivity curve for a calcium
"Are chemical substances added to fresh
concrete or mortar in order to influence certainproperties of the fresh and/or hardened concrete. The quantities are so small that they don't haveto be taken into account for the calculation of themix design."
8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00 Self Flow Value
The self flow has been determined for pastes of
The paste is mixed and then filled into a cylinder
(diameter = 30 mm, height = 50 mm) which sits
on a glass plate. The cylinder is then withdrawn,
the paste starts to flow under its own weight and
a "cake" with a much larger diameter is obtained.
The size of this diameter, expressed in mm, is ameasure of how well the paste flows. As anindication : a flow of 80 mm represents a casting
Figure 3 - Conductivity curves of Ciment Fondu® withdifferent Li2CO3 concentrations. Strength after 6 hours
With increasing Li2CO3 content the massive
Setting time and strength after six hours
precipitation (hydration) starts earlier and hence
measured on 40 x 40 x 160 mm mortar prisms
the setting time starts earlier and the difference
between begin and end of set becomes smaller
accelerators or retarders. Tests are carried on
(steeper decrease in conductivity upon massive
This translates in earlier setting times and afaster hardening (smaller difference ? between
begin and end of set) as can be seen from thefollowing table I depicting mechanical propertiesfor accelerated Ciment Fondu® systems. Accelerators The most common, most effective accelerator for alumina cements is lithium carbonate. Lithium hydroxide acts more violent and is therefore Setting Time (min) Compressive Strength (MPa)
difficult to dose. However, for winter concreting it
Curves of the dissolution and precipitationbehavior of Ciment Fondu® and Li2CO3 mixes
have been presented and commented in the past
/2/. Figure 3 shows the influence of different
concentrations of lithium carbonate on the
precipitation behavior of Ciment Fondu®.
Table 1 - Comparison of macroscopic properties fordifferently accelerated Ciment Fondu® pastes. 8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00 Retarders The action of a retarder for the same system as
in the paragraph above is shown in Figure 4 for
Figure 5 - Conductivity curves for an accelerated
Ciment Fondu® system with different CT contents.
The Li2CO3 accelerates in this case thehardening (steep massive precipitation) but
Figure 4 - Influence of tri-sodium citrate on
shortens the setting time to much. The additional
conductivity curves of Ciment Fondu®.
use of CT adjusts the setting times withoutinterfering strongly with the hardening. As a
The contrary to Li2CO3 is observed : the time of
comparison the curve for the unique use of CT is
massive precipitation becomes longer the higher
the tri-sodium citrate content. Therefore thesetting times are prolonged. Plasticisers Cements pastes
But a second effect, not present with the
Different industrially available plasticisers have
acceleration, can be observed. The dissolution of
been tested. Figure 6 shows a comparison of CT,
Ca2+ and Al(OH)4- ions is much slower with
trisodiumpolyphosphate (TPP), Darvan 7 S and
increasing citrate content. The apparition of an
Melment F 10 in a Secar® 71 cement paste. The
'ear' (early precipitation of C2AH8) is even
action of the plasticisers is shown by the self flow
suppressed with high CT concentrations. This
entrains an improved workability as we will seelater. Retarders with accelerators The combination of retarders and accelerators is
possible and recommended, because the two
effects do not necessarily cancel each other out
but intervene at different stages of the hydration. Figure 5 gives an example for the use of Li2CO3with CT.
Figure 6 - Self flow values for a Secar® 71 cementpaste with different plasticiser additions. 8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00
Darvan 7S and Melment F 10 act in a similar
With all combinations of CT + plasticisers an
way : fairly high amounts are necessary (0,5
%) to obtain a plasticising effect. The self flow
added does not exist for the combinations (no
higher and less sensitive to dosage as for TPP
degradation of flow with over dosage).
With certain plasticisers even higher early self
flow values can be obtained as compared to
CT acts much faster (around 0,1 %) but has avery narrow range of dosage in order to obtain
optimum performance. This fluidifying effect is
a result of the slow down of ion dissolution as
Interactions of fine reactive fillers like silica fume
or reactive alumina with CAC and their influence
on hydration behavior have been shown earlier
plasticisers. It can be more easily dosed than
/4,5/. Plasticisers also react differently with such
CT and good flow properties are reached with
a system as compared to a pure paste. Figure 8
reasonable amounts of TPP addition (around
shows self flow values for the case of TPP and
CT for a Secar® 71/reactive alumina system.
For both CT and TPP an over dosage leads toa degradation of flow properties which has
been shown for the case of TPP in Secar® 71 /silica fume systems earlier /3,4/.
The positive effects of Melment F10 (high flowand little degradation) and CT (early flow) can be
combined by using both plasticisers. This is
Melment, Darvan and Mighty are all used with a
0,2 % CT addition. For comparison the pure CT
Figure 8 - Comparison of pure Secar® 71 cementpaste and cement /alumina paste for TPP and CTadditions.
Even without plasticiser addition the self flow is
enhanced for a cement/alumina systems. This is
in part due to an optimization of the particle size
distribution - an important parameter when
designing self or free flow castables /6/. Thisgood self flow can be enhanced, however, by the
addition of plasticisers like CT and TPP. An
sensibility to the amounts of plasticiser added.
Figure 7 - Self flow values for Secar® 71 cement
The above mentioned beneficial effect of fine
pastes with 0,2 % CT and plasticisers.
fillers on granulometric curves and therefore flowbehavior is not the only factor. There is alsochemical interactions which contribute to theplasticising effect : Figure 9 shows this for the
8 rue des Graviers – 92521 Neuilly sur Seine Cedex Tel : 33 (0) 1 46 37 90 00 Fax : 33 (0) 1 46 37 92 00
use of Darvan 7S with and without the addition of
plasticiser of the type TPP, Melment, Darvan,
It should be kept in mind that the control of
fluidity retards the systems which means that
a classical retarder like CT will play a double
role as well in the retarder/accelerator as in
The authors would like to thank all co-workers at
Figure 9 - Conductivity curves for Secar® 71 cement
Lafarge Fondu International and Lafarge Coppée
pastes with Darvan 7S and reactive alumina.
Recherche who contributed to the studies which
The addition of reactive alumina decreases the
led to this paper. Special thanks to Ms F. Kebli
dissolution of ions in the beginning which means
and Mrs D. Gauthier who carried out most of the
a better flow a fact demonstrated in Figure 8 for
work on self-flow and conductimetry.
/1/ J.D. Cox and J.H. Sharp ; "The use of
admixtures with calcium aluminate cements".
/2/ D. Sorrentino, J.P. Bayoux, R. Montgomery,
In order to optimize sophisticated refractory
A. Mathieu and A. Capmas ; "The effect of
admixtures have to be combined besides the
sodium gluconate and lithium carbonate on
careful choice of mineral raw materials.
the properties of calcium aluminate cements";
These different admixtures are employed to
/3/ Th. A. Bier, A. Mathieu, B. Espinosa and
J.P. Bayoux ; "The use of conductimetry to
It is important that the active binder system is
aluminate cements" ; UNITECR 1993.
plus fine reactive fillers and not only to the
Letourneux ; "Theory and practice of fume
silica - aluminous cement interactions" - PartII.
Setting time and hardening are controlled by
/5/ A. Mathieu, A. Capmas, J.P. Bayoux and
a retarder/accelerator couple. The use of
D. Richon ; "Calcium aluminate cement and
both, seemingly contradictory admixtures,
reactive alumina" ; UNITECR 1993.
/6/ A. Mathieu ; "Calcium aluminates in self
flowing castables" ; Bresilian Ceramic Asso-ciation Aguas de Lindoia, Brazil, June 1995.
The workability or flow - especially important
for SFC application - are best controlled by acouple of CT and a plasticiser or super-
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Management and security in IPv6-enabled and performance controlled Wireless Jorge Granjal ([email protected]), Vasco Pereira ([email protected]), Edmundo Monteiro ([email protected]), Jorge Sá Silva ([email protected]) The use of Wireless Sensor Networks (WSNs) in scenarios that demand controlled performance, such as industrial, military or healthcare, is yet a challenge to be met. These scena
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