Utilization of Photoactive Kaolinite/TiO2
Composite in Cement-Based Building Materials
V. Matějka, P. Kovář, P. Bábková, J. Přikryl, K. Mamulová-Kutláková,
and P. Čapková1
Abstract. Titanium dioxide (TiO2) is the most studied photocatalyst with application potential in many branches of industry. Building industry represent the sector,
where the photoactive TiO2 have been already successfully utilized. Concretes,
plasters, paints are building materials where the photoactive TiO2 is widely tested.
However the amount of TiO2 in these materials is limited with respect to their final
properties. If the TiO2 replaces the certain amount of cement in concretes, the
resulting compressive strength decreases when this photocatalyst is added in
non-adequate content. The surface of kaolinite particles can serve as a matrix for
nanosized TiO2 growing what results in photoactive composite – kaolin/TiO2
formation. After the calcination of this composite the process of kaolinite dehydroxylation is responsible for metakaolinite formation and composite metakaolinite/TiO2 with latently hydraulic properties originates. If the metakoline/TiO2
is used for partial cement replacement the compressive strength of resulting samples is notably increased and its surface shows photodegradation ability against
rhodamine B.
1 Introduction
Self-cleaning and antibacterial properties, as well as photodegradation of
environmental pollutants are the added values which make the materials with
TiO2 perspective for applications in building industry. The increasing number of
V. Matějka, K. Mamulová-Kutláková, and P. Čapková
CNT, VŠB-Technical university of Ostrava, Ostrava, CR
e-mail: [email protected]
P. Kovář and J. Přikryl
ČTC AP a.s., Přerov, CR
e-mail: [email protected]
P. Bábková
CPIT, VŠB-Technical University of Ostrava, Ostrava, CR
e-mail: [email protected]
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V. Matějka et al.
experimental works dealing with photodegradation of NOx e.g. [1,2] or VOCs e.g.
[3,4] emphasized the importance of photocatalysis by TiO2 in control of environmental pollution. Limitation of massive utilization of photocatalytic technologies
arises mainly due to the higher price of building materials with photoactive TiO2.
Practically, TiO2 can be added to the bulk of building material or can be applied as
an ingredient of thin surface layer. The addition of TiO2 to the cement based building materials has to be reasonably considered mainly in respect to the final
strength.
Kaolin is a sub-group mineral and includes 4 different polymorphs: kaolinite,
dickite, nacrite and halloysite. If the kaolinite is heated, its dehydroxylation occurs
and metakaolinite is formed. Metakaolinite belongs to the group of material with
latent hydraulic properties. For metakaolinite hydraulicity activation, alkali activators as hydroxides of alkali metals and water glass are often used. In building
materials based on cement binder, hydraulic properties of metakaolinite are activated with Ca(OH)2 which originate during the process of cement hydratation.
With respect to this fact metakaolinite can partially replace cement binder without
loosing of strength of final product.
This work is focused on the kaolin/TiO2 (KATI) composite application in cement based building materials. As prepared composite KATI shows photodegradation activity against organic dyes which serves as model pollutants. After
the burning of KATI at the 600 °C the sample KATI600 is obtained. KATI600
combine latent hydraulic properties of metakaolinite and photoactivity of
nanosized TiO2. The increase in compressive strength of cement based testing
samples containing KATI600 is comparable with this increase obtained at the
samples containing commercially available metakaolin. Photodegradation activity
of testing samples with KATI600 is approved with discoloration of Rhodamine B
applied on the surface of samples.
2 Experimental
Composite KTiO2 preparation and characterization
Kaolin SAK47 – K (LB minerals) and titanyl sulphate – TiOSO4 (Precheza a.s.)
were used as received without any purification, for hydrolysis distilled water was
used. The process of KATI composite preparation is schematically described in
Fig. 1.
Fig. 1 Process of KATI composite preparation
Utilization of Photoactive Kaolinite/TiO2 Composite
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The amount of TiO2 in prepared composites was analyzed using X-ray fluorescence spectroscopy - XRFS (Spectro XEPOS), the phase composition was studied
using X-ray powder diffractometry - XRPD (Bruker D8 Advance). Photodegradation activity of prepared composites was evaluated on the basis of discoloration of
methylene blue – MB (Fluka) solution after the 1h irradiation with UV lamp (UVP
Ltd) emitted maximum light at 365nm.
Testing samples preparation
Compositions of testing samples expressed in weight fractions (wt. %) of all the
ingredients in prepared mixtures are shown in Tab. 1. In this table the letter M is
used for assignment of K, KATI or MEFISTO admixtures, respectively. Prepared
mixtures were schematically assigned as M(T)_w (where T shows the temperature
used for K or KATI calcination (400, 500 and 600 °C respectively), w represents
weight fraction (wt. %) of K, KATI or MEFISTO which replace the appropriate
amount of cement binder. Commercially available metakaolinite MEFISTO was
used as received without any thermal treatment. Ordinary portland cement (OPC)
CEM I 42.5R (Cement Hranice a.s.) was used as hydraulic binder. The weight
fraction of aggregates (three fractions of silica sands) and water was kept constant.
Testing samples were prepared according to ČSN EN 196-1 [5], ČSN EN 4501+A1 [6] respectively, their compressive strength after the 28-days hydration was
tested also according to ČSN EN 196-1 [5].
Table 1 Composition of prepared mixtures
W (aggregate)
Sample
w
w
w
(water)
(OPC)
(M)
0.1-0.6 mm 0.1-1.0 mm 0.3-1.6 mm
w(M)/
w(OPC)*100 w/(c+M)
wt. %
Ref
22.2
22.2
22.2
11.1
22.3
0
0
M(T)_5
22.2
22.2
22.2
11.2
21.2
1.1
5.2
0.5
0.5
M(T)_10 22.2
22.2
22.2
11.3
20.1
2.2
11.0
0.5
M(T)_15 22.2
22.2
22.2
11.4
19.3
3.0
15.5
0.5
M(T)_20 22.2
22.2
22.2
11.5
18.4
3.8
20.7
0.5
The photodegradation ability of surface of prepared samples was tested using
modified Italian standard UNI 11259:2007, utilizing photodegradation of rhodamine B [7].
3 Results and Discussion
Using XRFS the amount 22 wt. % of TiO2 was analyzed in composite KATI,
original kaolin contain 1 wt. % of TiO2. With respect to the TiO2 content the
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testing sample in which 20 wt. % of cement was replaced with KATI contain
0.5 wt. % of photoactive TiO2.
X-ray powder patterns of KATI before and after the calcination at selected temperatures are shown in Fig. 2. The sample KATI calcined up to 400 °C consist of
kaolinite and anatase, quartz represent typical admixture in raw kaolin. After the
calcination of KATI on temperatures higher than 500 °C the basal 001 diffraction
peak of kaolinite disappears what signalize transformation of kaolinite to metakaolinite, the anatase particles become better defined, what is apparent from the constriction of 101 diffraction peak of anatase.
Fig. 2 XRPD patterns of KATI, KATI(400), KATI(500), KATI(600)
Photodegradation ability of KATI freshly prepared and after the calcination at
400, 500 and 600 °C is shown on the Fig. 3. Calcination of composite up to
600 °C doesn’t decrease photodegradation activity of KATI and reach approx.
85 %, what means that approx. 85 % of amount of MB is removed after the 1h UV
irradiation.
Fig. 3 Photodegradation ability of KATI,
KATI(400), KATI(500), KATI(600)
against MB after 1h irradiation
Utilization of Photoactive Kaolinite/TiO2 Composite
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The influence of cement replacement with K and KATI on compressive
strength is shown in the Fig. 4. The compressive strength of the samples is related
to compressive strength of reference sample Ref (for Ref composition see table 1)
after the 28-days hydration, compressive strength of this sample reached
40.2 MPa. Addition of both calcined K and calcined KATI composite increased
compressive strength of prepared samples. The obtained values of compressive
strength at samples with KATI(600) are comparable with those obtained for samples containing MEFISTO. The values of compressive strength obtained for
K(600) are lower in comparison to samples with MEFISTO and KATI(600).
Fig. 4 Influence of calcined kaolin and calcined KATI composite on compressive strength
(after the 28 days curing) of cement-based testing samples
Photodegradation ability of the surface of testing samples against rhodamine B
is well documented on the Fig. 5.
Fig. 5 The pictures of the surfaces of testing samples painted
with rhodamine B
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Rhodamine B applied on the surface of testing sample KATI(600)_10 (the sample in which 10 wt.% of cement was replaced with KATI(600)) is in significantly
higher extent removed after the 26 h irradiation.
4 Conclusions
Partial replacing of portland cement with photoactive composite KATI(600) in
cement-based testing samples increases significantly their compressive strength
and the surface of prepared samples exhibits photodegradation ability against rhodamine B. Composite KATI calcined at 600 °C, at which synergistic effect of latent hydraulic properties of metakaolinite and photoactivity of nanosized TiO2 is
achieved, represents promising ingredient for cement-based building materials.
Further research will be employed to explain the effect of the presence of TiO2 at
composite KATI(600) on the compressive strength of cement mortars which is
significantly higher in comparison with compressive strength of cement mortars
with metakaolinite obtained after the 1h calcination of kaolin at 600 °C.
Acknowledgments. This research has been funded by the Czech Ministry of Industry and
Trade research project FT-TA4/025 and the Ministry of Education of the Czech Republic
project MSM 6198910016.
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