1. INTRODUCTION
⌅Production
of Portland cement clinker is one of the most energy extensive and
ecologically unfriendly production, and in order to meet the goals of
global sustainable development, requires new more solutions (1-31. Gartner, E. (2004) Industrially interesting approaches to “low-CO2” cements. Cem. Concr. Res. 34 [9], 1489-1498. https://doi.org/10.1016/j.cemconres.2004.01.021.
2.
Damtoft, J.S.; Lukasik, J.; Herfort, D.; Sorrentino, D.; Gartner, E.
(2008) Sustainable development and climate change initiatives. Cem. Concr. Res. 38 [2], 115-127. https://doi.org/10.1016/j.cemconres.2007.09.008.
3. Provis, J.L.; van Deventer, J.S.J. (2014) Alkali activated materials. State-of-the-art report. RILEM TC 224-AAM. Springer. https://doi.org/10.1007/978-94-007-7672-2.
).
This is also important with regard to production of white cement
clinker as a base for production of pigmented Portland cement.
Analysis
of contemporary trends showed, that annual production of white clinker
cements as a base of pigmented cement, is of about 35 million tonnes and
continues to increase further by 8-10% per year in order to meet the
growing demands of consumption market (44. Taylor, M.; Tarn, C; Gielen, D. (2006) Energy efficiency and CO2 emissions from the global cement industry. Energy Technology Policy Division. International Energy Agency. Retrieved from https://cyberleninka.org/article/n/259584.pdf (Accessed on: July 19, 2022).
, 55.
White cement market forecast by type (White portland cement, white
masonry cement, and others) and end use (Residential, commercial, and
industrial): Global opportunity analysis and industry forecast.
2018-2025. Retrieved from https://www.alliedmarketresearch.com/white-cement-market. (Accessed on: July 19, 2022).
).White
Portland cement clinker is produced by firing until sintering of a raw
mixture at the higher temperatures ? 1500-1600°С compared to those
required in the production of traditional Portland cement ? 1400-1450°С (66.
Krivenko, P.V.; Runova, R.F.; Sanickij, M.A.; Rudenko, I.I. (2015)
Shhelochnye cementy: monografija, Ltd “Osnova”, Kyiv (2015) (in
Russian).
).
White pure (high-quality) limestone sand and white kaolinite clays are necessary to use as raw materials for the manufacture of these cements. The following restrictions are applied to these raw materials: the content of contaminating not desirable oxides in raw limestones and clays are not allowed to exceed, for example, FeO < 0.15%, Fe2O3 < 1.5%, Mn2O3 <0.03%, Сr2О3 < 0.01%, MgO < 3.0%. Above all, special conditions are to be strictly followed in the production of these cements in order to escape the contamination of a raw mixture bimetallic iron in kilns with linings from magnesite bricks, and to use non-metallic grinding media in grinding operation.
In view of strict restrictions as to content
of iron oxides in raw materials (being fluorites, they promote the
formation of the melt), this circumstance makes the conditions for the
sintering of clinker worse. For this reason, in order to improve the
conditions for clinker formation, the fluxes-mineralizers such as
fluorspar/sulphates (CaF2 and CaSO4) and sodium silicofluoride (Na2SiF6) are added to the raw mixture (77. Blanco-Varela, M.T.; Puertas, F.; Vázquez, T; Palomo, A. (1996) Modelling of burnability of white cement made with CaF2 and CaSO4. Cem. Concr. Res. 26 [3], 457-464. https://doi.org/10.1016/S0008-8846(96)85033-2.
).
In
order to increase the degree of whiteness of the white cement clinker
even with low contents of iron, the cement clinker is subjected to a
special treatment?whitening (8-108. Chistjakov, G.I. (1976) Vlijanie uslovij otbelivanija klinkera na dekorativnye svojstva cementov; V kn.: Shestoj mezhdunarodnyj congress po himii cementa. Moscow, 3, I58-161. (in Russian).
9. Luchinskij, G.P. (1971) Himija titana, Himija, Moscow, (1971) (in Russian).
10. Simons, P.Y.; Dachille, F. (1976) The structure of TiO2 II, a high-pressure phase of TiO2. Acta Crystallographica. 23 [2], 334-336. https://doi.org/10.1107/S0365110X67002713.
), the essence of which is to reduce Fе2О3 to Fe3O4.
This helps to remove greenish colour and increases the degree of
whiteness of the final cement. The calcination of clinker takes place in
weakly reducing atmosphere and is followed by quick cooling and
additional whitening. Also, special manufacturing
apparatus-decolouriser, in which the cement clinker is subjected to
short-term renewable exposure of gaseous medium without access of oxygen
at 800-1000°С with a following quenching /cooling down to 200°С can be
used. In the production of white cement, the process of whitening can be
repeated many times.
All the above makes a manufacturing process quite complicated and results in a considerable increase in the cost of white cement production.
The alkali-activated cement can be
considered as a real alternative to Portland cement since their
manufacture is based on the chemical reaction of different wastes or
bu-products. From one part the use of wastes from the different process
as the metallurgical industry, production of phosphor, energy generating
industry (as granulated blast furnace slag, steel making, electro
thermo phosphorus, non ferrous slags, ashes of heat power stations,
etc.), and from the other some alkali-containing wastes that enable to
produce an alkaline solutions. These cements have compressive strength
reaching 40-120 MPа, high adhesion, durability, corrosion resistance and
other special properties (66.
Krivenko, P.V.; Runova, R.F.; Sanickij, M.A.; Rudenko, I.I. (2015)
Shhelochnye cementy: monografija, Ltd “Osnova”, Kyiv (2015) (in
Russian).
, 11-2411.
von Weizsacker, E.U.; Hargroves, C.; Smith, M.H.; Desha, C.;
Stasinopoulos, P. (2009) Factor five: transforming the global economy
through 80% improvements in resource productivity. Earthscan, London
(2009). ISBN 9780415848602.
12. McLellan, B.C.; Williams, R.P.; Lay,
J. van Riessen, A.; Corder, G.D. (2011) Costs and carbon emissions for
geopolymer pastes in comparison to ordinary Portland cement. J. Clean. Produc. 19 [9], 1080-1090. https://doi.org/10.1016/j.jclepro.2011.02.010.
13.
Gluhovskij, V.D. (1979) Shhelochnye i shhelochno-shhelochnozemel’nye
gidravlicheskie vjazhushhie i betony. Vishha shkola, Kyiv, (1979) (in
Russian).
14. Gluhovskij, V.D. (1981) Shlakoshhelochnye betony na
melkozernistyh zapolniteljah: Monografija. Vishha shkola, Kyiv, (1981).
(in Russian).
15. Gluhovskij, V.D. (1992) Izbrannye Trudy. Budіvel’nik, Kyiv, (1992). (in Russian).
16. Krivenko, P.V. (1992) Special’nye shlakoshhelochnye cementy: monografija. Budіvel’nik, Kyiv, (1992). (in Russian).
17.
Kryvenko, P.V.; Pushkar’ova K.K. (1993) Dovgovichnist’ shlako-luzhnogo
betonu: monografija. Budivel‘nyk, Kyiv, (1993). (in Ukrainian).
18. Krivenko, P.V. (1994) Alkaline cements. Alkaline Cements and Concretes: Materials First Intern. Conf. Kyiv, 11-19.
19.
Krivenko, P.V.; Petropavlovskij O.N.; Gelevera A.G.; Voznjuk G.V.;
Pushkar V.I. (2009) Promyshlennye shhelochnye cementy i ih effektivnost. Nauchno-tehnicheskij sbornik. Aktual‘nye problemy stroitel‘stva“. Rivne, 64-71. (in Russian).
20. Krivenko, P.V. (2017) Why alkaline activation - 60 years of the theory and practice of alkali-activated materials. J. Ceram. Sci. Technol. 8 [3], 323-334. https://doi.org/10.4416/JCST2017-00042.
21.
Shi, C.; Krivenko, P.; Della, Roy (2014) Alkaline activated cements and
concretes: Monograph Engineering & Technology, London, (2014). https://doi.org/10.1201/9781482266900.
22.
Fernández-Jiménez, A.; Garcia-Lodeiro, I.; Maltseva, O.; Palomo, A.
(2019) Hydration mechanisms of hybrid cements as a function of the way
of addition of chemicals. J. Am. Ceram. Soc. 102 [1], 427-436. https://doi.org/10.1111/jace.15939.
23.
Krivenko, P.; Petropavlovsky, O.; Kovalchuk, O.; Pasko, А.; Lapovska,
S. (2018) Designof the composition of alkali activated Portland cement
using mineral additives of technogenic origin. Eastern-Europ. J. Enterp. Technol. 4 [6 (94)], 6-15. https://doi.org/10.15587/1729-4061.2018.140324.
24. Krivenko, P.V.; Petropavlovsky, O.N.; Gots, V.I.; Rostovskaya, G.S. (2009) Alkali activation of composite cement. Ibausil. Internationale Baustofftagung (Weimar). 1, 445-456.
).
Numerous
research works have proved a possibility and feasibility of the
production of white alkali-activated cements for decorative purpose
using granulated blast furnace slags (1313.
Gluhovskij, V.D. (1979) Shhelochnye i shhelochno-shhelochnozemel’nye
gidravlicheskie vjazhushhie i betony. Vishha shkola, Kyiv, (1979) (in
Russian).
, 25-2825.
Chaouche, M.; Gao, Х.Х.; Cyr, М.; Cotte, М.; Frouin, L. (2017) On the
origin of the blue/green color of blast-furnace slag-based materials:
Sulfur K-edge XANES investigation. J. Am. Ceram. Soc. 100, 1707-16. https://doi.org/10.1111/jace.14670.
26.
Labrincha, J.; Puertas, F.; Schroeyers, W., Kovler, K.; Pontikes, Y.;
Nuccetelli, C. (2017) 7-From NORM by-products to building materials.
Naturally occurring radioactive materials in construction. Woodhead
Publishing, 183-252.
27. Sidochenko, I.M.; Krugljak, S.L.; Rumyna,
G.V.; Gluhovskij, V.D.; Skurchinskaja, Zh.V. (1974) A.s. № 446480
Vjazhushhee. Zajavl. 15.01.73. Bjul. izobret., 38. (in Russian).
28.
Gluhovskij, V.D.; Pis’mennaja, A.Ju.; Rumyna, G.V. (1981) Ispol’zovanie
krasnogo shlama dlja poluchenija shlakoshhelochnogo dekorativnogo
vjazhushhego. J. Stroitel’nye materialy, izdelija i sanitarnaja tehnik. 4, 35-36. (in Russian).
).
The pigmented cements reproduced by the addition to the composition of
the alkali-activated slag cement of pigment alone or in combination with
white kaolinite clay. The kaolinite clay acts as a structure-forming
element of the cement matrix and at the same time acts as a whitening
additive. However, a positive result as to the required degree of
whiteness of the resulted cement (>70%) could be achieved only with
the slags containing low contents of iron oxides (0.3- 0.4%).
Some attempts were taken to produce paints using the alkali-activated cements (2929. Krivenko, P.V.; Kovalchuk, A.Y. (2019) Management of the decorative properties of alkali cements. J. Build. Eng. 2 [95], 280-285.
).
A disadvantage of these paints is that after six months under exposure
of weather conditions they lose their decorative properties because of
the appearance on the surface of stains consisting of alkali metal
compounds. In the studies reported in (2222.
Fernández-Jiménez, A.; Garcia-Lodeiro, I.; Maltseva, O.; Palomo, A.
(2019) Hydration mechanisms of hybrid cements as a function of the way
of addition of chemicals. J. Am. Ceram. Soc. 102 [1], 427-436. https://doi.org/10.1111/jace.15939.
, 3030.
Bernal, S.A.; Provis, J.L.; Myers, R.J.; Racktl, S.N.; van Deventer,
J.S.J. (2015) Role of carbonates in the chemicalevolution of sodium
carbonate-activated slag binders. J. Mater. Struct. 48 [3], 517-529. https://doi.org/10.1617/s11527-014-0412-6.
),
the reasons of efflorescence were analyzed, however, they did not show
the ways on how to manage risk of efflorescence, which is a critical
point for decorative materials.
The research works reported in (2929. Krivenko, P.V.; Kovalchuk, A.Y. (2019) Management of the decorative properties of alkali cements. J. Build. Eng. 2 [95], 280-285.
, 3131.
Krivenko, P.V.; Kovalchuk, A.Y.; Ostrovskaja, L.M. (2011) Studying of
posibility of increase of slag-alkali cements whiteness degree. J.
Collection «Building materials, producters and technical equipment».
Kyiv, Research Institute of Building Materials and Products. 41, 10-14
)
studied a possibility to produce white alkali-activated slag cements
based on blast furnace slags and alkaline compounds using titanium
oxide, kaolin and calcium carbonate as whitening additives. However, the
ways on how to manage whiteness of these cements depend on the chemical
composition of the slag and it has not been studied until now. In the
studies reported in (3232. Krivenko, P.; Petropavlvskyy, O.; Puskar, V.; Ostrovska, L. (2011) Decorative alkaline cements. IV Intern. Symp: Non-Traditional Cement & Concrete. Brno, 257-265.
) only one slag with a modulus of basicity (CaO+MgO / Al2O3+SiO2) Мb = 0.91 of unknown chemical composition was used in the production of
the white alkali-activated slag cement. The influence of the contents of
iron oxide of the slag on whiteness was not studied at all.
A
decorative multicomponent cement based on Roman cement modified by
alkalis, whitening, air entraining and plasticizing additives and
admixtures is described in (3333.
Kryvenko, P.; Sanytsky, M.; Kropyvnytska, T.; Kotiv, R. (2014)
Decorative multi-component alkali activated cements for restoration and
finishing works. Adv. Mat. Res. 897, 45-48. https://doi.org/10.4028/www.scientific.net/AMR.897.45.
).
Despite the fact that content of iron oxide varied in the composition
of this cement within a range of 0.64-2.75%, their influence on
decorative properties was not studied. Moreover, the achieved strength
value sat an age of 28 days were too low (21.5-27.5 MPa), thus
restricting their use only to obtain decorative plaster mixtures, and
not for concretes.
Very few studies have been done for obtaining
white and non-ferrous cements based on alkali-activated slag. In some
industrial wastes were used as pigments, but only for clinker cements,
but not in alkali-activated slag cements (34-3734.
Fernandes de Magalhães, L.; França, S.; dos Santos Oliveira, M.;
Fiorotti Peixoto, R.A.; Araújo Lima Bessa, S.; da Silva Bezerra, A.C.
(2020) Iron ore tailings as a supplementary cementitious material in the
production of pigmented cements. J. Clean. Prod. 274,123260. https://doi.org/10.1016/j.jclepro.2020.123260.
35.
Barros Galvão, J.L.; Dias Andrade, H.; Brigolini, G.; Fiorotti Peixoto,
R.A.; Castro Mendes, J. (2018) Reuse of iron ore tailings from tailings
dams as pigment for sustainable paints. J. Clean. Prod. 200, 412-422. https://doi.org/10.1016/j.jclepro.2018.07.313.
36.
Fontes, W.; Gonçalves Fontes, G.; Pinto Costa, E.C.; Castro Mendes, J.;
Brigolini, G.; Fiorotti Peixoto, R.A. (2018) Iron ore tailings in the
production of cement tiles: a value analysis on building sustainability. J. Amb. Cons. 18 [4], 395-412. https://doi.org/10.1590/s1678-86212018000400312.
37.
Ghalehnovi, M.; Roshan, N.; Hakak, E.; Asadi Shamsabadi, E.; de Brito,
J. (2019) Effect of red mud (bauxite residue) as cement replacement on
the properties of self-compacting concrete incorporating various
fillers. J. Clean. Prod. 240, 118213. https://doi.org/10.1016/j.jclepro.2019.118213.
).
The additive of СаСО3 was also tried in some cement composition, including in the
alkali-activated slag cements, but not as a whitening additive, but as a
filler (38-4038.
Rashad, A.M.; Morsi, W.M.; Khafaga, S.A.; (2021) Effect of limestone
powder on mechanical strength, durability and drying shrinkage of
alkali-activated slag pastes. Innov. Infrastruct. Solut. 127. https://doi.org/10.1007/s41062-021-00496-y.
39.
Borziak, O.S.; Plugin, A.A.; Chepurna, S.M.; Zavalniy, O.V.; Dudin,
O.A. (2019) The effect of added finely dispersed calcite on the
corrosion resistance of cement compositions. IOP Conference Series:
Materials Science and Engineering. 708: 012080. https://doi.org/10.1088/1757-899X/708/1/012080.
40.
Chepurna, S.; Borziak, O.; Zubenko, S. (2019) Concretes, modified by
the addition of high-diffused chalk, for small architectural forms. J. MSF. 968, 82-88. https://doi.org/10.4028/www.scientific.net/msf.968.82.
). The additive of ТіО2 to the clinker cement-based concrete sand mortars was tried, as reported in (4141. Hohol, M.; Lubenets, V.l; Komarovska-Porokhnyavets, O.; Sanytsky, M. (2020) Effect of Nano-TiO2 and ETS antifungal agent addition on the mechanical and biocidal properties of cement mortars. Proceedings of EcoComfort 2020. 134-141. https://doi.org/10.1007/978-3-030-57340-9_17.
, 4242. Hohol, M.; Sanytsky, M.; Kropyvnytska, T.; Barylyak, A.; Bobitski, Y. (2020) The effect of sulfur- and carbon-codoped TiO2 nanocomposite on the photocatalytic and mechanical properties of cement mortars. Eastern-Europ. J. Enterp. Technol. 4 [6-106], 6-14. https://doi.org/10.15587/1729-4061.2020.210218.
),
but not as a whitening additive; it was used as an antifungal and
bactericidal additive to mortars or nano admixture to enhanced
photocatalytic, hydrophobic and mechanical properties with the effect of
self-cleaning of the surface and antimicrobial properties.
The use of the alkali-activated slag cement as a base in the production of pigmented cements was not considered by other researchers as alternative to white clinker cement.
The analysis held suggested to draw a conclusion the lack of information about the following problems associated with the production of white and pigmented alkali-activated cements:
-
the influence of the FeO-content on whiteness of the decorative alkali-activated slag cements;
-
behavior and influence of whitening additives (ТіО2, kaolin, СаСО3) on decorative, physico-mechanical and performance properties of the decorative alkali-activated slag cements in the conditions of highly alkaline environment;
-
adhesion of the white and pigmented alkali-activated slag cement mortars to a substrate;
-
shrinkage deformations;
-
risk of efflorescence and capillary suction;
-
water retaining characteristics;
-
freeze/thaw resistance and weather resistance;
-
stability of colour under exposure of ultraviolet radiation and in the conditions of steam curing.
Thus, it shows that this research line is relevant and is of scientific interest and novelty. A purpose of the present research was to make a comparative study on the influence of whitening additives on structure formation processes and evolution of physico-mechanical properties of the decorative alkali-activated slag cements depending upon the FeO-content of the composition of granulated blast furnace slag.
2. EXPERIMENTAL PART
⌅2.1. Materials
⌅Granulated blast furnace slags varying in the FeO-content were used as an aluminosilicate component of the alkali-activated slag cements. Chemical composition of the slags and other raw materials used in the study is given in Table 1. X-ray pattern of blast-furnace granulated slag D is shown in Figure 1.
| Material | Oxide content, % by mass | Total | Мb * | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SiO2 | Al2O3 | CaO | MgO | FeO | SO3 | MnO | TiO2 | Na2O | LOI. | |||
| Slag D | 37.9 | 6.85 | 45.35 | 5.21 | 0.31 | 2.6 | 0.11 | 0.35 | 1.13 | 1.34 | 101.15 | 1.13 |
| Slag М | 38.9 | 6.8 | 47.0 | 4.6 | 0.35 | 1.8 | 0.55 | - | - | 0.78 | 100.78 | 1.13 |
| Slag Т | 43.0 | 7.0 | 43.5 | 6.3 | 0.42 | - | 0.05 | 0.26 | - | 0.5 | 101.03 | 1.00 |
| Slag К | 38.2 | 4.6 | 48.5 | 4.6 | 1.65 | 1.1 | 0.81 | - | 0.79 | 0.60 | 100.85 | 1.24 |
| Kaolinite clay | 48.77 | 30.94 | 2.62 | 0.8 | - | - | - | 0.25 | - | 13.06 | 96.44 | - |
| Red mud | 9.8 | 17.7 | 9.6 | - | 54.2 | - | - | 4.5 | 4.0 | - | 99.80 | - |
*Mb= CaO+MgO / Al2O3+SiO2
The mineralogical composition of slag D is represented by gehlenite Ca2Al2SiO7 (d - 0.286; 0.241; 0.231; 0.176 нм), merwinite Ca3MgSiO8 (d - 0.264; 0.190; 0.186; 0.164 нм), rankinite Ca3Si2O7 (d - 0.385; 0.320; 0.302; 0.291; 0.273 нм), larnite (d - 0.28; 0.273; 0.260; 0.219 нм) and some quartz (d - 0.423; 0.333; 0.184; 0.155 нм).
All granular slags (except for slag T) belong to the main ones from Mb = 1.13-1.24 and are represented mainly by the vitreous phase, the content of which is 76-83%. Slag T with Mb = 1 refers to neutral slags.
A specific surface area of the slags varied from 4300-4414 cm2/g by Blaine. The slags were ground in a ceramic mill with alubit (high alumina) grinding media and lining. For comparison, a steel mill was used.
Sodium metasilicate pentahydrate (Na2O·SiO2·5H2O) in a form of a non-hydroscopic powder in a quantity of 10% by mass of the cement was used as an alkaline activartor.
Quartz river sand was used as fine aggregate. Partial residues on sieves with openings of 0.63, 0.315 and 0.14 mm were 5.1%, 16% and 65%, respectively.
Titanium dioxide TiO2 (rutile); kaolin (whiteness - 84%) and calcium carbonate СаСО3 (whiteness - 90%) were used as whitening additives. In order to add colour, various pigments of mineral origin as well as red mud were used. The quantity of pigment was 5% by mass of the cement. About pigments the some characteristics are: Titanium dioxide TiO2 (rutile) with a particle size between 0.4-2 µm and a whiteness ≥ 95%: a delaminated kaolin with a whiteness ≥ 84%, an specific surface area 12-20 m2/kg and a particle size 0.4-10 µm and plates of calcium carbonate CaCO3 with a whiteness - ≥ 90%), a particle size 9-20 µm. To give colour, various pigments of mineral origin were used, as well as red mud. The amount of pigment was 5% by weight of cement.
Sodium carboxymethyl cellulose was used as a water retaining additive and an additive to prevent efflorescence.
2.2. Preparation and characterization of cement pastes and mortars
⌅Technology-related
and physico-mechanical properties of the alkali-activated slag cement
pastes were determined in accordance with national standards and other
normative documents acting currently in the Ukraine. Preparation of the
cement pastes and mortars was done in accordance with the requirements
described in (4343.
DSTU B V.2.7-181:2009 (2009) Cementy luzhni. Tehnichni umovy.
Ministerstvo regional’nogo rozvytku ta budivnyctva Ukrai’ny, Kyiv. (in
Ukrainian).
). Optimization of the compositions of
decorative slag-alkali cements was carried out according to the plans of
full factorial experiments at three levels with three and two factors
of type 33 and 23 (4444.
DSTU EN 196-1:2019 (EN 196-1:2016, IDT) (2020) Metody vyprobuvannja
cementu. Chastyna 1. Vyznachennja micnosti. Minbud Ukrai’ny, Kyiv. (in
Ukrainian).
).
Strength characteristics were determined in accordance with (4545.
Voznesenskij, V.A.; Ljashenko, T.V.; Ogarkov, B.L. (1989) Chislennye
metody reshenija stroitel’no-tehnologicheskih zadach na JeVM. Vishha
shkola, Kyiv. (1989). Retrieved from http://mx.ogasa.org.ua/handle/123456789/331 (in Russian).
). Shrinkage and weather resistance was determined in accordance with procedures that are described in (4646.
Butt, Ju.M.; Timashev, V.V. (1973) Praktikum po himicheskoj tehnologi
vjazhushhih veshhestv. Vysshaja shkola, Moscow. (in Russian).
). Freeze/thaw resistance was determined in accordance with (4747.
DSTU B V.2.7-47-96 Betony. (1997) Metody opredelenija
morozoustojchivosti. Obshhie trebovanija. Gosudarstvennyj komitet po
delam gorodskogo stroitel’stva i arhitektury, Kyiv. (in Ukrainian).
).The second basic test method with freezing of the specimens at t = -20оС
in a 5%-solution of NaCl was applied. Stability of colour samples after
normal condition and steam curing was determined under exposure of
ultraviolet radiation - in accordance with Ukrainian national standard (4848. DSTU B V.2.7-268:2011 (2012) Portlandcement kol’orovyj. Tehnichni umovy. Minregion Ukrai’ny, Kyiv. (in Ukrainian).
). Risk of efflorescence was evaluated in accordance with (4949. DSTU B V.2.7-69-98 (1999) Dobavki dlja betonov. Metody opredelenija jeffektivnosti. Kyiv : Gosstroj Ukrainy. (in Ukrainian).
). Adhesion of the mortar to a substrate was determined in accordance with the procedure described in (5050.
EN 1542-1999 (1999) Products and systems for the protection and repair
of concrete structures.Test methods. Measurement of bond strength by
pull-off, European Committee for Standardization.
).
The heat release of hydrated cement compositions was determined by the
semi-diabatic (thermos) method in accordance with DSTU B V.2.7-289:2011
(EN 196-9:2010, MOD) using an installation, the schematic diagram of
which is shown in Figure 2.
Determination of whiteness of the specimens was done using a spectrophotometer NS810 with a range of wavelengths of 400-700 nm. A Ral 9016 sample with whiteness index L = 98.85 was used as reference sample. The specimens prepared from the alkali-activated slag cement paste of normal consistency after 28 days of hardening were studied in this test.
A
phase composition of the slag sand quantity of glassy phase was
determined using a X-ray device DRON-2 with a copper tube and nickel
filtrate U = 42 kW, I = 18 mA, within the range of angles 2θ = 20-62о.
Identification of the hydration products was done using data of
computer data base PC-PDF, Version 2.13a, Copyright JCPDS -
International Centre for Diffraction Data, the program “XPowder” and
data base AMSCD, as well as information provided in (5151.
Gorshkov, V.S.; Timashev, V.V.; Savel’ev, V.G. (1981) Metody
fiziko-himicheskogo analiza vjazhushhih veshhestv. Vysshaja shkola,
Moscow, (1981). (in Russian).
, 5252. Semenov, E.I. (1981) Mineralogicheskie tablicy : Spravochnik. Nedra, Moscow, (1981). (in Russian).
).
The images were taken using a scanning electron microscope (SEM) equipped with microprobe analyzer REMMA-102-02.
3. RESULTS AND DISCUSSION
⌅3.1. Optimization of the cement in degree of whiteness
⌅At the first stage of optimization, the influence of whitening additives on the degree of whiteness of the cement and its physico-mechanical properties was studied using a full factorial design of experiment 33. Factors/variables, levels of their variation and experimental design matrix with functions of responses are shown in Table 2 and Table 3.
| No | Factors/Variables | Units of measurement | Coded factors | Levels of variation | ||
|---|---|---|---|---|---|---|
| -1 | 0 | +1 | ||||
| 1 | TiO2 - content | % | Х1 | 0 | 4 | 8 |
| 2 | kaolin - content | % | Х2 | 0 | 7 | 14 |
| 3 | СаСО3 - content | % | Х3 | 0 | 12 | 24 |
| No | Matrix of design in coded form | Matrix of design in natural values | Compressive strength (Rcomp.), MPa, at days | Initial setting time, min. | Degree of whiteness (W) after 28 days of normal curing, % | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| steel mill | ceramic mill | |||||||||||
| Х1 | Х2 | Х3 | ТіО2 | kaolin | СаСО3 | 2 | 7 | 28 | ||||
| % | % | % | ||||||||||
| 1 | +1 | +1 | +1 | 8 | 14 | 24 | 25.2 | 30.4 | 38.6 | 33 | 88.4 | 94.4 |
| 2 | -1 | +1 | +1 | 0 | 14 | 24 | 31.5 | 38.8 | 46.2 | 36 | 74.8 | 79.8 |
| 3 | +1 | -1 | +1 | 8 | 0 | 24 | 29.7 | 40.2 | 46.4 | 38 | 83.5 | 89.1 |
| 4 | -1 | -1 | +1 | 0 | 0 | 24 | 35.4 | 46.8 | 56.0 | 37 | 66.0 | 70.5 |
| 5 | +1 | +1 | -1 | 8 | 14 | 0 | 32.5 | 41.0 | 52.2 | 57 | 83.0 | 88.6 |
| 6 | -1 | +1 | -1 | 0 | 14 | 0 | 36.1 | 43.9 | 49.9 | 46 | 63.2 | 68.5 |
| 7 | +1 | -1 | -1 | 8 | 0 | 0 | 35.9 | 46.2 | 57.0 | 69 | 83.7 | 89.4 |
| 8 | -1 | -1 | -1 | 0 | 0 | 0 | 39.0 | 47.4 | 56.7 | 54 | 60.3 | 64.3 |
| 9 | +1 | 0 | 0 | 8 | 7 | 12 | 31.4 | 39.5 | 48.5 | 42 | 82.2 | 87.9 |
| 10 | -1 | 0 | 0 | 0 | 7 | 12 | 36.1 | 44.2 | 52.1 | 36 | 63.7 | 68.1 |
| 11 | 0 | +1 | 0 | 4 | 14 | 12 | 31.8 | 39.2 | 45.0 | 40 | 81.4 | 87.1 |
| 12 | 0 | -1 | 0 | 4 | 0 | 12 | 35.5 | 45.8 | 52.3 | 47 | 77.5 | 82.8 |
| 13 | 0 | 0 | +1 | 4 | 7 | 24 | 30.1 | 39.4 | 47.5 | 34 | 81.2 | 86.9 |
| 14 | 0 | 0 | -1 | 4 | 7 | 0 | 35.5 | 45.0 | 54.7 | 54 | 75.5 | 80.8 |
| 15 | 0 | 0 | 0 | 4 | 7 | 12 | 33.5 | 42.4 | 49.8 | 40 | 77.7 | 83.2 |
Remark. Quantity of sodium metasilicate - 10% by mass of the cement.
The slag D that was ground in a traditional steel mill and because of this was contaminated with metal from the grinding media, and the same slag that was ground in a ceramic mill.
As a result of the processing of the data of Table 3 the regression equations were produced under three responses - strength at 28 days of curing (R28), initial setting time (τ) and degree of whiteness (W) for the case when the slag was ground in the ceramic mill:
Strength values of the cements at 28 days of curing were within a range: 38.6-57.0 MPa, initial setting time: 33-69 min, and degree of whiteness: 64.3-94.4%. Diagrams of strength, initial setting time and whiteness are given in Figures 3-5. For easier plotting, each of 3-factor equations was divided into three pseudo 2-factor equation at Х3 (СаСО3) - 0%, 12%, and 24%.
The decorative alkali-activated slag cement pastes showed good strength gain at the early ages and even at 2 days of curing (25.2-39.0 MPa).
Depending upon the degree of whiteness, white clinker cement is classified into three grades: 1 grade ≥ 80%, 2 grade ≥ 75%, 3 grade ≥ 70% (53). Coming from this classification, a majority of the white alkali-activated slag cements, even when the slag was ground in a steel and ceramic mill, can be considered as white cements since they had degree of whiteness ≥ 70% (see Table 3).
Analysis and processing of the obtained data (Table 3) showed, that in case of the slag D with the FeO-content of 0.31%, in order to achieve the degree of whiteness of the alkali-activated slag cement of at least 70% and class 42.5 R in compressive strength, the percentage (by mass) of each of the whitening additive should be: 5% for ТіО2, 15% for kaolin and 24% for СаСО3.
3.2. The influence of the FeO-content of the slag on the degree of whiteness of alkaline cement
⌅In order to study the influence of the FeO-content on the degree of whiteness of the alkaline cement, the slags М, Т, and К with the FeO-contents of 0.35%, 0.42% and 1.65% by mass, respectively, were used side by side with the slag D. Moreover, an additional composition based on the slag К and with the added FeO in order to bring its total content to 2.95% was formulated. The results of the study are given in Figure 6. The mathematical dependence of the degree of whiteness (W) on the content of FeO was expressed by the regression equation presented in the figure. As it follows, FeO contained in the slag affects negatively the whiteness of the resulted cement.
3.3. Optimization of the composition of the white alkali-activated slag cement depending upon the FeO-content of the slag
⌅In order to eliminate negative influence of FeO of the slag, the quantities of the whitening additives were chosen in such a way that to reach the degree of whiteness not less than 70%, not depending upon the chemical composition of the slags. Optimization of the cement composition was done with the help of plans a full factorial design of experiment type 23. Factors, levels of variation and the results of the study are shown in Table 4, Table 5 and Figure 7.
| Factors/variables | Units of measurement | Coded factors | Levels of variations | ||
|---|---|---|---|---|---|
| -1 | 0 | +1 | |||
| FeO - content | % | Х1 | 0.35 | 1.65 | 2.95 |
| ТіО2 - content | % | Х2 | 0 | 5 | 10 |
| kaolin - content | % | Х2 | 0 | 7.5 | 15 |
| СаСО3 - content | % | Х2 | 0 | 12 | 24 |
| No | Plan in coded form | Plan in natural values | Degree of whiteness (W), % | Plan in natural values | Degree of whiteness (W), % | Plan in natural values | Degree of whiteness (W), % | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Х1 | Х2 | FeO | ТіО2 | FeO | kaolin | FeO | СаСО3 | ||||
| 1 | +1 | +1 | 2.95 | 10 | 73.6 | 2.95 | 15 | 60.0 | 2.95 | 24 | 57.4 |
| 2 | +1 | -1 | 2.95 | 0 | 52.8 | 2.95 | 0 | 52.0 | 2.95 | 0 | 51.9 |
| 3 | -1 | +1 | 0.35 | 10 | 86.5 | 0.35 | 15 | 73.1 | 0.35 | 24 | 70.6 |
| 4 | -1 | -1 | 0.35 | 0 | 64.6 | 0.35 | 0 | 65.1 | 0.35 | 0 | 65.1 |
| 5 | +1 | 0 | 2.95 | 5 | 61.6 | 2.95 | 7.5 | 56.0 | 2.95 | 12 | 54.7 |
| 6 | -1 | 0 | 0.35 | 5 | 73.9 | 0.35 | 7.5 | 69.2 | 0.35 | 12 | 67.8 |
| 7 | 0 | +1 | 1.65 | 10 | 80.9 | 1.65 | 15 | 67.8 | 1.65 | 24 | 65.5 |
| 8 | 0 | -1 | 1.65 | 0 | 59.6 | 1.65 | 0 | 59.8 | 1.65 | 0 | 60.0 |
| 9 | 0 | 0 | 1.65 | 5 | 68.6 | 1.65 | 7.5 | 63.8 | 1.65 | 12 | 62.7 |
Approximation of the data allowedto produce the equations of regression which adequately reflectthe results of the experiment:
The isosurfaces produced using these equations (see Figure 7) show that just the additive of TiO2 is the best whitening additive and it allows to provide whiteness of the alkali-activated slag cement pastes reaching 87%.
As a result of the analysis of the obtained regression equations a factor of influence of each coefficient of the equation was assessed, that is the influence of each of the whitening additives on the degree of whiteness of the resulted cement. The results are given in Figure 8.
As it follows from Figure 8, a favorable influence of TiO2 on the whiteness is considerably higher than the unfavorable influence of iron oxide. However, in the case of the additives of kaolin and CaCO3, the favorable influence is lower than the unfavorable influence of iron oxide, thus reducing their efficiency as whitening additives compared to that of TiO2 and requiring more quantities to be added.
From
the other side, the additives added in the increased quantities can
deteriorate physico-mechanical and performance properties of the white
alkali-activated slag cements. According to some authors (5454.
Kovalchuk, O; Grabovchak, V; Govdun, Y. (2018) Alkali activated cements
mix design for concretes application in high corrosive conditions. Matec Web Conf. 230 [94], 03007. https://doi.org/10.1051/matecconf/201823003007.
),
the addition of between 10-15% of kaolin by mass results in a
mechanical strengths decline. This strength declines in the
alkali-activated slag cements can be somewhat compensated due to the
addition of 2-3% by mass of Portland cement or Portland cement clinker.
However, in any case, the addition of kaolin in quantities exceeding 20%
by mass and CaCO3 in quantities exceeding 45% by mass in the composition of the alkali-activated slag cement is not desirable (see Figure 9). In case of the slag with the high FeO-content (higher than 1.65%) the additive of TiO2 alone or in combination with other additives should be used for whitening.
3.4. Structure formation processes in the white alkali-activated slag cement
⌅3.4.1. Phase composition and morphology of hydration products
⌅According to the results of XRD analysis (Figure 10), a phase composition of the alkali-activated slag cements without whitening additives is presumably represented by C-S-H gel (d - 0.333; 0.307; 0.296; 0.281; 0.215; 0.187;0.281;0.182 nm), xonotlite (d - 0.3871; 0.3061; 0.2021; 0.193 nm) and calcite (d - 0.383; 0.302; 0.281; 0.227; 0.209; 0.191; 0.187 nm).
The prevailing phases of the white cement with the 5% additive of ТіО2 by mass are: calcite (d - 0.383; 0.303; 0.281; 0.21; 0.229; 0.209; 191; 0.187; 0.161; 0.152 nm), CaMg(CO3)2 (d -0.536; 0.4; 0.362; 0.287; 0.267; 0.218; 0.177 nm) and quartz (d - 0.425; 0.333; 0.182; 0.152 nm), TiO2 (d - 0.324; 0.248; 0.23; 0.169; 0.162 nm).
A phase composition of hydration products of the white cement with 15% kaolin by mass is presumably represented by C-S-H gel (d - 0.305; 0.28; 0.18 nm), C-(A)-S-H(B) (d - 0.304; 0.28; 0.180 nm), tobermorite (d - 0.333; 0.307; 0.297; 0.286; 0.214; 0.201; 0.182 nm), calcite (d - 0.385; 0.303; 0.249; 0.228; 0.209; 0.192 nm), weak diffractions of analcime (d - 3.43; 2.92; 0.286; 0.272; 2.52; 1.74 nm) and hydronepheline (d - 0.467; 0.435; 0.407; 0.385; 0.369; 0.343; 0.297; 0.283; 0.259 nm). The quantities of analcime and hydronepheline, according to (6) tend to increase constantly in the long-term. Non reacted phases of the slag are represented by ghelenite (d - 0.286; 0.242; 0.228 nm) and quartz (d - 0.424; 0.333; 0.183 nm). Diffractions lines (d - 0.435; 0.417; 0.385; 0.357; 0.309; 0.234 nm) are characteristic of kaolinite.
The cement composition with 24% СаСО3 by mass is represented by CSH(B) (d - 0.304; 0.28; 0.180nm), presumably tobermorite gel (d - 0.305; 0.279; 0.18 nm), tobermorite (d - 0.33; 0.307; 0.298; 0.285; 0.24; 0.214; 0.201; 0.183 nm), calcite (d - 0.383; 0.303; 0.248; 0.228; 0.209; 0.192; 0.191 nm),and quartz (d - 0.426; 0.334; 0.183; 0.152 nm).
The study of the morphology of the hydration products (see Figure 11) showed that the following types of particles were visualized: plate-like crystals with layered structure, thread (string)-like crystals, spherulites and hexagonal plates, grains and aggregations of irregular shape. Microprobe analysis of elemental composition and the results of XRD analysis showed that the plate-like and thread (string)-like crystals are characteristic of low-basic calcium silicate hydrates; spherulites and hexagonal plates - aluminosilicate hydrates of alkaline and alkaline-alkali-earth composition; aggregation of irregular shape - various gels. The obtained microstructure of the resulted cement stone is homogeneous and without defects.
3.4.2. The influence of additives on the migration of Na + -ion to the white alkali-activated slag cement pastes
⌅Acceleration of the binding of the Na+-ion in the alkali-activated slag cement pastes helps to prevent risk of efflorescences on its surface during service life. Homogeneity of distribution of the Na+-ion from the surface of the cement pastes to its center was evaluated with the help of a scanning electron microscope (SEM) equipped with microprobe analyzer.
Figure 12 shows the alkali-activated slag cement pastes prepared without additives at 28 of curing. The elemental (Na+-ion) distribution in the center (19.8% by mass) and on the surface (18.7% by mass) are very similar. This is evidence of the absence of critical mass transfer of Na+-ion and its binding in insoluble compounds.
The elemental composition of the alkali-activated slag cement pastes with TiO2 is shown in Figure 13. With account of the Na2O-content in the center (20.5% by mass) and on the surface (34.7% by mass). An assumption can be put forward that the whitening this additive (TiO2) does not prevent migration of free (non-bound) alkali to the surface.
The elemental composition of the alkali-activated slag cement pastes with kaolin is shown in Figure 14.
Analysis of the elemental distribution of this paste shows that in the
center and on the surface the kaolin affected positively the degree of
binding of free alkali with the formation of insoluble aluminosilicate
hydrates. Kaolin is known to possess weak acidic properties and for this
reason, considerably increases its cation-exchange capacity in an
alkaline medium (5555.
Karavajev, T.A. (2015) Vodno-dyspersijni farby: tovaroznavcha ocinka:
monograph. Kyi’vs’kyj nacional’nyj torgovo-ekonomichnyj universytet,
Kyiv. (2015). (in Ukrainian).
). A quantity of Na2O
in the center (22.02% by mass) and on the surface (14.2% by mass) is
evidence of the absence of mass transfer of free alkali from the center
to the surface. That was confirmed by XRD (see Figure 10) with the formation of aluminosilicate hydrates of analcime and hydronepheline: and also from the studies by SEM analysis (see Figure 11).
The elemental composition of the alkali-activated slag cement pastes with CaCO3 is shown in Figure 15. Quantities of Na2О in the center (17.56% by mass) and on the surface (16.64% by mass) in the cement paste composition with СаСО3 is an evidence of the absence of mass transfer of alkali and its
binding with the formation of aluminosilicate hydrate. This correlates
well with the data reported in (4040.
Chepurna, S.; Borziak, O.; Zubenko, S. (2019) Concretes, modified by
the addition of high-diffused chalk, for small architectural forms. J. MSF. 968, 82-88. https://doi.org/10.4028/www.scientific.net/msf.968.82.
) on the deeper hydration processes taking place in the slag-containing cements in the presence of СаСО3.
3.4.3. Heat release in the process of hydration of the pigmented alkali-activated slag cement
⌅Curves of heat release of the white alkali-activated slag cement, depending upon its constituent composition, are represented in Figure 16.
When the cement composition is mixed with water, the heat starts to release almost immediately and its nature is connected with hemosorption processes, dissolution of the slag glass and formation of colloidal and crystalline products. A conclusion can be made that the higher quantities of the whitening additives in the cement composition the lower is a cumulative heat release. Peak of heat released is shifted from 7 or 8 h (the reference cement composition without additive) to 9 or 11 h (the compositions with the additives). This can be attributed, first of all, to the lower contents of the slag in the cement composition. This is especially evident in the compositions with the additives of kaolin and CaCO3. Accumulative heat release of the composition with the additive of CaCO3 (55.1 J/g) is higher than that of the composition with the additive of kaolin (44.0 J/g), though a quantity of the additive of CaCO3 - 24% is much higher compared to that of the additive of kaolin - 15%. This can, evidently, be attributed to the binding or absorption of some portions of alkali by kaolin and, as a result, the lower reaction ability of the liquid medium relatively to the slag.
3.5. Evolution of physico-mechanical and performance properties of the alkali-activated slag cements and mortars
⌅3.5.1. Compressive strengths
⌅The influence of optimal quantities of the whitening additives strengthen standard-specified ages and in the long-term are given in Figure 17. As it see in this Figure 17, the white alkali-activated slag cements have the values of compressive strength in the range 49.0-56.8 MPa at 28 days and 66.8-67.5 MPa at 180 days. All these white cements have good strength gain, and, judging by their strength at 2 days (35.0-37.0 MPa), can be considered as quick-hardening cements (class 42.5R or 52.5R, according to EN 197).
Kaolin
possess weak acidic properties and for this reason in the conditions of
a highly alkaline medium increases considerably its cation-exchange
capacity (5555.
Karavajev, T.A. (2015) Vodno-dyspersijni farby: tovaroznavcha ocinka:
monograph. Kyi’vs’kyj nacional’nyj torgovo-ekonomichnyj universytet,
Kyiv. (2015). (in Ukrainian).
). For this reason, it
starts actively participate in structure formation processes with the
formation of alkaline and alkaline-alkali-earth zeolite-like
aluminosilicate hydrate (66.
Krivenko, P.V.; Runova, R.F.; Sanickij, M.A.; Rudenko, I.I. (2015)
Shhelochnye cementy: monografija, Ltd “Osnova”, Kyiv (2015) (in
Russian).
), which guarantee the high performance properties of the final hardened cement pastes.
On the contrary, to ТіО2 and СаСО3, kaolin acts not only as a whitening additive, but also as active mineral additive capable to affect considerably technology-related, physico-mechanical, and performance properties.
Since a part of alkali is bound by kaolin, strength values of the alkali-activated slag cement pastes at standard-specified ages are somewhat lower (by 10-11%) compared to those of the composition without additive. However, after 3 or 6 months, this difference disappears, and the high strength values are achieved due to the deepening of hydration processes, synthesis of low-basic calcium silicate hydrates, synthesis of analogs to zeolites and feldspars and absence of the processes of destruction.
On contrary to the additive of kaolin, TiO2 is almost inert with regard to components of the alkali-activated slag
cement. А small optimal quantity of this additive (approx. 5% wt.)
almost does not affect the compressive strengths (Figure 17). Of interest is the influence of the additive of СаСО3 on strength values. As it follows from Figure 17,
despite large quantities of this additive (approx. 24% wt.) the
strength of the alkali-activated slag cement pastes at 28 days was only
by 1.5% lower compared to that of the cement composition without
additive, and by the age of 180 days this difference practically not
exist. This can be attributed to the following: known-in-the-art is that
one of the methods of how to increase strength of concrete is to fill a
cement matrix with mineral additives - finely dispersed mineral
particles of various nature and fractional composition (5454.
Kovalchuk, O; Grabovchak, V; Govdun, Y. (2018) Alkali activated cements
mix design for concretes application in high corrosive conditions. Matec Web Conf. 230 [94], 03007. https://doi.org/10.1051/matecconf/201823003007.
, 5656.
Kropyvnytska, T.; Semeniv, R.; Kotiv, R.; Kaminskyy, A.; Hots, V.;
(2019) Studying the effect of nanoliquids on the operational properties
of brick building structures. Eastern-Europ. J. Enterp. Technol. 5/6 [95], 27-32. https://doi.org/10.15587/1729-4061.2018.145246.
, 5757.
Lutskin, Y.; Shynkevych, O.; Myronenko, I.; Zakabluk, S.; Surkov, O.
(2018) The influence of the content on structure and properties of
geopolymer composites on silicate matrix. Matec Web Conf. 230, 03011. https://doi.org/10.1051/matecconf/201823003011.
).
Finely dispersed carbonate rocks (5858.
Huang, W.; Kazemi-Kamyab, H.; Sun, W.; Scrivener, K. (2017) Effect of
cement substitution by lime stone on the hydration and microstructural
development of ultra-high performance concrete (UHPC). Cem. Concr. Compos. 77, 86-101. https://doi.org/10.1016/j.cemconcomp.2016.12.009.
, 5959.
Li Leo, G.; Kwan Albert, K.H. (2015) Adding lime stone fines as
cementitious paste replacement to improve tensile strength, stiffness
and durability of concrete. Cem. Concr. Compos. 60, 17-24. https://doi.org/10.1016/j.cemconcomp.2015.02.006.
)
have certain chemical similarity with the alkali-activated slag cement
and in size of particles, close to those of particles of the
alkali-activated slag cement. Despite some chemical inertness, this
circumstance, nevertheless, causes their interaction with hydration
products of the alkali-activated slag cement as centers of
crystallization or nucleation and enables to form crystal contacts. As a
result, a more perfect microstructure is formed (6060.
Smirnova, O.M.; Belentsov, Y.A.; Kharitonov, A.M. (2019) Influence of
polyolefin fibers on the strength and deformability properties of road
pavement concrete. J. Traffic Transp. Eng. 6 [4], 407-417. https://doi.org/10.1016/j.jtte.2017.12.004.
), thus ensuring the higher performance properties of the concretes and mortars.
3.5.2. Shrinkage deformations
⌅Shrinkage deformations were measured on the prismatic mortar specimens 4×4×16 cm (cement : sand = 1:3); at RH of 60% and a temperature of 20±2ºC. Side by side with taking measurements of shrinkage deformations, the values of moisture loss were measured.
The results obtained from measurements of shrinkage of the white alkali-activated slag cement mortars and moisture loss with optimal quantities of the whitening additives are given in Figure 18. A rather good correlation is observed between shrinkage and moisture loss, except for the mortar with the addition of СаСО3.The lowest values of shrinkage until stabilization were observed in the specimens with the additive of CaCO3 - 0.54 mm/m. The compositions without additive and with TiO2have somewhat higher value of shrinkage - 0.55-0.60 mm/m. The highest value of shrinkage (0.77 mm/m) were observed in the compositions with the additive of kaolin (see Figure 18 a). Due to its small quantity (5% by mass) and chemical inertness, the additive of TiO2 almost does not affect shrinkage. For this reason, the values of shrinkage deformation in the compositions without additive and with TiO2 are very close.
The
effect of kaolin on shrinkage is greater due to its higher content (15%
by mass). This can be attributed to the fact that the alkaline cations
of a liquid medium enter into interaction followed by peptization and
following swelling of kaolin (6161. Spravochnik himika 21. Himija i himicheskaja tehnologija. 98. Retrieved from https://www.chem21.info/info/72743/. (Accessed on: June 19, 2022). (in Russian).
).
Later, as soon as physical water leaves the specimen, a reverse process
takes place, resulting in the higher value of shrinkage. This
correlates well the values of moisture loss of the composition with the
additive of kaolin obtained in the study (see Figure 18 b).
As was mentioned earlier, the lowest value of shrinkage deformation are measured in the composition with the additive of CaCO3, despite its high content in the cement composition - 24% by mass (Figure 18 a) and despite the fact that the values of moisture loss of this composition are among the highest values (Figure 18 b). This can be due to the following: high values of moisture loss are joined with higher content of calcium carbonate (24% by mass) and its finer particles. However, on contrary to kaolin, calcium carbonate is practically inert in an alkaline environment and is not subjected to peptization and following swelling. Besides, as was mentioned earlier, the particles of finely dispersed calcium carbonate can act as centers of crystallization and to form quickly a rigid crystal framework, which restrict shrinkage, and to fill a pore space of the cement stone and to form a denser and more rigid structure. For this reason, in this case, high values of moisture loss do not mean the higher shrinkage deformations.
3.5.3. Freeze/thaw resistance and weather resistance
⌅The results of test of the white alkali-activated slag cement mortars for freeze/thaw resistance are given in Table 6. Mortar specimens 4×4×16 cm (cement : sand = 1:3) after hardening for 28 days curing were tested. The specimens contained 5% mineral pigment by mass. With the consideration of appropriateness, the testing was restricted by150 cycles of freezing/thawing.
| Nos | Additive | Strength after 28 days, MPa | Compressive strength change, %, after freezing/thawing, cycles | Grade in freeze/ thaw resistance | |||
|---|---|---|---|---|---|---|---|
| 45 | 75 | 100 | 150 | ||||
| F75 | F110 | F150 | F200 | ||||
| 1 | without additive | 56.7 | +1.21 | +0.83 | -0.52 | -1.73 | F200 |
| 2 | ТіО2 (5%) | 56.3 | +1.0 | +1.1 | -0.68 | -2.2 | F200 |
| 3 | kaolin (15%) | 51.8 | -0.42 | -1.66 | -2.42 | -3.48 | F200 |
| 4 | СаСО3 (24%) | 56.0 | -0.33 | -1.85 | -2.7 | -3.87 | F200 |
After 150 cycles of freezing/thawing (being equivalent to F200) the mass losses of the specimens were absent, the maximum compressive strength decline was 3.87%, scaling of the surface of the specimens was not observed. Thus, according to the results of the test represented in Table 6, all the mortars correspond in freeze/thaw resistance to brand F200.
The results of test of the pigmented alkali-activated slag cement mortar for resistance to wet/dry cycles are given in Table 7. Beam specimens 4×4×16 cm (cement : sand = 1:3) cured in normal conditions for 28 days were tested. The hardened specimens were exposed to alternate drying for 6 h at t = 105 ± 5оС and wetting (immersion into water) at 20±2оС during 6 h. The strength was determined after a certain number of cycles. The cements are considered weather resistant, if after 100 cycles of alternate wet/dry, the strength decline of the specimens is less than 25%. As it follows from Table 7, a conclusion can be mortar composition have passed successfully test for weather resistance.
| Nos | Additive | Compressive strength of the dried specimens, MPa | Strength decline, %, after freezing/thawing, cycles | |||
|---|---|---|---|---|---|---|
| 25 | 50 | 75 | 100 | |||
| 1 | without additive | 56.9 | -2.0 | -3.37 | -4.64 | -5.82 |
| 2 | ТіО2 (5%) | 56.5 | -2.51 | -3.85 | -5.2 | -6.46 |
| 3 | kaolin (15%) | 53.0 | -3.84 | -5.7 | -7.33 | -9.2 |
| 4 | СаСО3 (24%) | 56.3 | -3.04 | -4.45 | -5.9 | -7.25 |
3.5.4. Colour stability under exposure to ultraviolet radiation or steam curing
⌅Colour
stability was assessed in accordance with the testing procedure
prescribed in the National standard of Ukraine DSTU B V.2.7-268:2011
Portland cement, colored. Technical specification (4848. DSTU B V.2.7-268:2011 (2012) Portlandcement kol’orovyj. Tehnichni umovy. Minregion Ukrai’ny, Kyiv. (in Ukrainian).
) (see Figure 19).
Colour stability of the
pigmented alkali-activated slag cement was determined on disc-shaped
specimens prepared from a cement paste of normal consistency in
accordance with the Ukrainian national standard DSTU B V.2.7-181:2009 (4343.
DSTU B V.2.7-181:2009 (2009) Cementy luzhni. Tehnichni umovy.
Ministerstvo regional’nogo rozvytku ta budivnyctva Ukrai’ny, Kyiv. (in
Ukrainian).
). Two disc-shaped specimens prepared from
each composition were stored in the air as reference samples, two
disc-shaped specimens were subjected to steam curing, and two
disc-shaped specimens - to ultraviolet radiation. Mineral pigments in a
quantity of 5% by mass were used.
Irradiation of the disc-shaped specimens by ultraviolet rays is done with the help of a mercury-quartz lamp with a power of 240±20 W for 48 hrs. The disc-shaped specimens were place data distance of 0.5 m from a source of ultraviolet radiation and a luminous flux was directed on the munder the angle of 45±2°.
Colour stability of the pigmented alkali-activated slag cement pastes was evaluated visually by comparing the colors of the disc-shaped specimens subjected to ultraviolet radiation or steam curing with colors of the reference disc-shaped specimens. As it follows from Figure 19, after exposure to ultraviolet radiation or steam curing the color almost did not change.
3.5.5. Risk of efflorescence
⌅Risk of efflorescence in the pigmented alkali-activated slag cement mortars was assessed under procedure of DSTU B V.2.7-69-98 (4848. DSTU B V.2.7-268:2011 (2012) Portlandcement kol’orovyj. Tehnichni umovy. Minregion Ukrai’ny, Kyiv. (in Ukrainian).
)
on specimens 4×4×16 cm (cement: sand = 1:3). After 28 days of hardening
in normal conditions the mortar specimens were dipped a in container
filled with distilled water to a depth of 4-5 cm and blowed with air
with a temperature of about 25оС for a least of 3 h per day during 7 days.
A phenomenon of efflorescence on the open surface of the specimen was evaluated visually by the presence of salt deposits. As it follows from Figure 20, no salt deposits were observed.
In addition to standard test for the evaluation of the risk of efflorescence, other tests were also performed in the conditions of indoor and outdoor application. In order to model the exposure of various service conditions of indoor and outdoor application. Mortars (cement : quartz sand = 1:3; W/C = 0.46-0.53) were applied on a walls of the building from the outside to evaluate the exposure of appropriate weather factors in winter-spring-summer periods: (t = -15…+30оС, snow, rain, sun radiation, R.H. = 70-100%); and from the inside (t = 18-24оС, R.H. = 55-80%. The test period was 9 months. In order to prevent efflorescence, a water retaining additive (sodium carboxymethyl cellulose), in a quantity of 0.25% by mass, was added in the decorative alkali-activated slag cement mortars. Test results are shown in Table 8 and Table 9.
| Pigment color | White alkali-activated slag cement with whitening additives | White clinker cement | ||
|---|---|---|---|---|
| ТіО2 | kaolin | СаСО3 | ||
| Braun | ||||
| Yellow | - | |||
| Red mud (terracotta color) | - | |||
| Pigment color | White alkali-activated slag cement with whitening additives | White clinker cement | ||
|---|---|---|---|---|
| ТіО2 | kaolin | СаСО3 | ||
| Braun | ||||
| Yellow | - | |||
| Red mud (terracotta color) | - | |||
From Table 8 and Table 9 is deduced that no salt deposits were formed on the decorative mortars tested in indoor and outdoor applications.
The use of red mud as pigment resulted in nice uniform terracotta color. Above all, according to (2828.
Gluhovskij, V.D.; Pis’mennaja, A.Ju.; Rumyna, G.V. (1981) Ispol’zovanie
krasnogo shlama dlja poluchenija shlakoshhelochnogo dekorativnogo
vjazhushhego. J. Stroitel’nye materialy, izdelija i sanitarnaja tehnik. 4, 35-36. (in Russian).
, 6262.
Ocheretnyj, V.P.; Koval’skij, V.P.; Mashnickij, M.P. (2006)
Kompleksnaja aktivnaja mineral’naja dobavka na osnove othodov
promyshlennosti. Sbornik nauchnyh trudov po materialam IV
mezhdunarodnoj nauchno-prakticheskoj Internet-konferencii “Sostojanie
sovremennoj stroitel’noj nauki - 2006”. Poltavskij CNTJeI, Poltava, 116-121. (in Russian).
),
the use of red mud allows to solve ecological problems, to increase
strength of the alkali-activated slag cement due to the alkali contained
in it, as well as to improve decorative characteristics of the resulted
cement stone.
A final consideration from this study: the surface of the decorative mortars based on the white clinker cement usually have an inhomogeneous glossy surface, which is not acceptable from the point of use for decoration purposes, however, the hardened alkali-activated slag cement mortars have an uniform matte surface.
3.5.6. Adherence tests to a substrate
⌅Adherence tests were carried out in accordance with the methodology set out in EN 1542-1999 (5050.
EN 1542-1999 (1999) Products and systems for the protection and repair
of concrete structures.Test methods. Measurement of bond strength by
pull-off, European Committee for Standardization.
). A
cement-sand mortar with a composition of 1:3 was applied to a concrete
slab 30×30×10 cm. The concrete class of the slab was B20, and the water
absorption of the slab was 6.2%.
After the mortar hardened, the samples were made on a concrete base in the form of cylindrical cores with a diameter of 5 cm in the amount of 5 pieces and were stored under laboratory conditions at a temperature of 20±2°C and relative humidity of the air about 65% for 27 days. The test of samples for separation from the base was carried out on a tensile testing machine FM-250 (Germany). The destruction occurred in the zone of contact of the mortar with the slab or with a partial detachment of the slab of concrete. The test results are presented in Table 10.
| Pull-out strength, MPa | |||
|---|---|---|---|
| Reference (without additive) | ТіО2 (5% by mass) | kaolin (15% by mass) | СаСО3 (24% by mass) |
| 5.44 | 5.31 | 5.52 | 5.22 |
Remark. Further whitening additives, all compositions of the pigmented alkali-activated slag cement mortars contained 5% mineral pigment of red color by mass.
3.6. Feasibility study of the use of whitening additives
⌅Considering the amount of whitening additives used in this study and the requirements as whiteness of the alkali-activated slag cement (at level of 70-72%) and a class resistant 42.5R in compressive strengths, and having into in account the iron oxide in the blast furnace slag, the economic efficiency of the three whitening additives used in this study are presented in Table 11 and Figure 20.
| Whitening additive (cost in relative units) | Cost of the whitening additive, in relative units | ||
|---|---|---|---|
| FeO - 0.35% by mass | FeO - 1.65% by mass | FeO - 2.95% by mass | |
| ТіО2 (7.5) | 5% 37.5 relative units |
7% 52.5 relative units |
9% 67.5 relative units |
| Kaolin (3.1) | 15% 46.5 relative units |
20% 65 relative units |
- |
| СаСО3 (1) | 24% 24 relative units |
45% 45 relative units |
- |
Remark. The top number (nominator) - a required quantity of the whitening additive (in % by mass), the bottom number (denominator) - cost of the whitening additive (in relative units).
A comparative cost of the whitening additives at the content of iron oxide of 0.35% of the slag is given as an example in Figure 21.
According to these results, a conclusion can be made that the best choice in terms of cost is СаСО3, despite its high content. However, its use is restricted (≤ 45%) at the FeO-content of the slag ≤ 1.65% (Figure 9). Increasing the FeO content will require increasing of the СаСО3 content, which will lead to a decrease of strength.
The additive of kaolin was found to be the most expensive solution and is restricted (≤ 20% by mass) at the FeO-content of the slag ≤ 1.65% (Figure 9). However, an advantage of kaolin is not only its whitening properties, but its chemical activity due to binding of free alkalis and synthesis of zeolite-like hydrates due to this a low risk of efflorescence.
In terms of cost, the additive of ТіО2 takes a position between kaolin and СаСО3, however, its potential as a whitening additives much higher and it can be used for the full range of the FeO-content of the slag (from 0.35% and up to 2.95%).
4. CONCLUSIONS
⌅-
A comparative study of the influence of whitening additives, these are: TiO2, kaolin, and СаСО3, in order to produce white and pigmented alkali-activated slag cement and with the degree of whiteness of at least 70% and class 42,5R, in the compressive strength, on the structure formation properties and on the evolution of physico-mechanical and performance properties was performed.
-
A conclusion was made that the principles to be laid in the compositional build-up of the white alkali-activated cement should take into account not only the influence of the whitening additives on the processes of whitening, but the FeO-content of the granulated blast furnace slag.
-
By using examination techniques such as calorimetry, X-ray diffraction analysis, scanning electron microscopy, microprobe analysis, a conclusion was made that the whitening additives used in the study make the processes of structure formation much deeper, resulting in a more complete binding of the Na+-ions in insoluble compounds, thus providing high durability. The additives of kaolin and СаСО3are found to be the most actively taking part in these processes eliminating risk of efflorescence and increasing color stability of the pigmented alkali-activated slag cement.
-
A comparative feasibility study of the use of the whitening additives depending upon the FeO-content of the granulated blast furnace slag suggested to conclude that the use of СаСО3 is the most advantageous in terms of cost, however, its quantities are to be restricted by the FeO-content of the slag (≤ 1.65% by mass). The additive of TiO2 takes a position between CaСО3 and kaolin, but its advantage is that the granulated blast furnace slags with the FeO-content up to 2.95% by mass can be used.