Assessing the chemical involvement of limestone powder in sodium carbonate activated slag
Materials and Structures (2017)50:136
DOI 10.1617/s11527-017-1003-0
ORIGINAL ARTICLE
Assessing the chemical involvement of limestone powder
in sodium carbonate activated slag
B. Yuan . Q. L. Yu . H. J. H. Brouwers
Received: 1 November 2016 / Accepted: 24 January 2017
Ó The Author(s) 2017. This article is published with open access at Springerlink.com
Abstract This study aims to investigate the effect of
limestone powder (LP) on the reaction of sodium
carbonate activated slag. The results show that the
incorporated LP up to 30% improves the strength
development, especially at advanced curing ages. A
slightly accelerated reaction is observed for samples
containing low amount of LP (B5%), while mixture
with 10% LP shows the optimized results with respect
to the heat release and strength development. Chemical effect of incorporating LP is observed at high
replacement levels (C15%), indicated by the formation of a new phase, natron (Na2CO310H2O). Besides,
relatively high contents of hydrotalcite-like phases are
generated when increasing the dosage of limestone
powder. The chemical changes, including the volume
changes of generating natron and the transformation of
natron to calcite, is potentially responsible for the
enhanced mechanical properties.
B. Yuan Q. L. Yu (&) H. J. H. Brouwers
Department of the Built Environment, Eindhoven
University of Technology, P.O. Box 513,
5600 MB Eindhoven, The Netherlands
e-mail:
B. Yuan H. J. H. Brouwers
State Key Laboratory of Silicate Materials for
Architectures, Wuhan University of Technology,
Wuhan 430070, People’s Republic of China
Keywords Limestone powder Sodium carbonate
activated slag Chemical effect Reaction kinetics
Reaction products Mechanical properties
1 Introduction
Alkali activated materials (AAM) have been attracting
worldwide attention during the last few decades
because of their good material properties and environmental benefits [1]. Nevertheless, depending on the
used raw materials and alkaline solutions, the performance of the resulted materials can be varied [2, 3]. At
present, most attentions are paid to the development of
mixtures with higher strength, or improved durability,
upgrading the-state-of-the-art of AAM [4–7]. However, the effects of supplementary materials on the
reaction of AAM are rarely studied, especially their
potential chemical involvement.
As a supplementary material, limestone powder
(LP) has been widely applied in Portland cement based
building materials because of its low price and good
performance [8–12]. The effect of LP on the hydration
of cement has been intensively investigated, ranging
from the filler effect to the chemical involvement in
cement hydration: (1) inert filler acting as nuclei sites;
(2) accelerating the hydration of C3S [13, 14] and (3)
reacting with C3A forming calcium carboaluminates
[14–16]. However, the function of LP on the reaction
of alkali activated materials has not been
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systematically studied yet. Up till now, only limited
efforts [17–19] have been devoted to this topic partly
because the system of alkali activated material (AAM)
is more complex than Portland cement system due to
the different activators and raw materials applied
[1, 20, 21].
It is reported that in the low-calcium containing
alkali activated metakaolin system, LP is dissolved in
the sodium hydroxide solution and its presence
enhances the release of Al and Si ions from
metakaolin, leading to the formation of layered
calcium carboaluminates [17]. While in high-calcium
containing alkali activated slag system, the function of
limestone is not well understood. LP is often regarded
as an inert filler in the slag based alkali activated
system [13–15]. Besides, intensive Ca2? ions will be
released from slag particles and thus the dissolution of
LP releasing Ca2? ions is actually detained compared
to its hydrolysis in the low-calcium containing alkali
activated system. As a result, LP is more likely to be
restricted to an inert filler, acting as nucleation sites.
Gao et al. [18] characterized waterglass activated slagfly ash-limestone blends, and reported that the incorporation of LP shows good filler effect by giving a
slightly higher strength than that of fly ash. However,
no trace of chemical involvement can be identified as
there are no monocarboaluminate or new phases found
on the XRD pattern. Most recently, Rakhimova et al.
[22] studied the influence of different LP on the
properties of slag activated by sodium carbonate based
waste and found that the 28 days strength was not
weakened up to 50% addition of LP (Blain fineness
C400 m2/kg). However, they stated that the benefits
on the strength development is mainly attributed to the
‘‘physical activity’’ of LP.
Compared to waterglass, sodium carbonate as an
activator shows enhanced contribution concerning
setting time and shrinkage [2, 23, 24]. Besides, the
production of Na2CO3 is more cost-effective and
environmentally friendly compared to other activators
[25]. It is noteworthy that LP could act differently in
sodium carbonate activated slag (SCAS) system due to
its particular reaction mechanism compared to slags
activated by waterglass or sodium hydroxide
[4, 26, 27]. As reported by Bernal et al. [4] and our
previous study [26], CO32- anions concentration in
the pore solution and the initially precipitated calcium
carbonate significantly control the sodium carbonate
activation process. According to the previous
Materials and Structures (2017)50:136
researches [4, 23, 28–30], the main reaction products
of sodium carbonate activated slag are C–(A)–S–H
gel, calcium carbonate (CaCO3), gaylussite (Na2Ca(CO3)210H2O), hydrotalcite (Mg6Al2CO3(OH)164H2O), etc. With respect to the carbonates groups in
the minerals, the presence of limestone could be
potentially involved in the reaction, e.g. Ca2? can be
potentially involved in the formation of C–(A)–S–H
gel. Furthermore, the incorporation of LP contributes
to the strength improvement and lowered cost. Moseson [19] developed concretes with strength up to
around 41 MPa at 3 days and 65 MPa at 28 days
while the CO2 emission and energy consumption is
reduced by 97% compared to Portland cement (PC)
based materials. However, that research was mainly
focused on the economic benefits and CO2 emission,
while the chemical function of LP on the reaction of
SCAS was not discussed.
The present research aims to study the effect of LP on
the reaction kinetics, reaction products and strength
development of sodium carbonate activated slag. The
heat evolution of mixtures with different LP incorporation levels was measured, up to 7 days. Furthermore,
the specimens was ground for microstructural analyses,
including X-ray diffraction (XRD), Thermogravimetry
and Derivative Thermogravimetry (TG-DTG) and
Fourier transform infrared spectroscopy (FTIR), etc.
The strength developments were characterized at
different curing ages. The fresh behaviour was evaluated. The chemical involvemen (...truncated)
