Page 3 - Open Access - Feb 2020

TECHNICAL PAPER

In the presence of fine limestone particles in the hydrating
cementing matrix, the ettringite precipitated initially is stabilised
as suggested in [32] , and the aluminates react with limestone to
produce carboaluminates as given in Equation 5 and Equation
6 with varying levels of carbonate ions (i.e., Hemi- or Mono) [24] .
Calcined kaolinitic clay catalyses this interaction further due to
the presence of reactive aluminate. Aluminates in calcined clay
could also increase the additional demand of gypsum to ensure
that calcite interaction proceeds after the consumption of
gypsum, which needs to be controlled to occur after the primary
silicate reaction [33] .
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Figure 2: Components of Limestone Calcined Clay Cement (LC ). - Limestone interaction with clinker phases
more details can be found in www.lc3.ch.
C 3 A + CaCO 3 + CH + H C 3 A.CaCO 3 .H 12 Equation 5
A widely adopted LC composition is 50:30:15:5 (clinker:
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calcined clay: limestone: gypsum) with limestone-calcined clay Limestone interaction with calcined clay/SCM
ratio of 1:2. It is important to note that the composition of the A SCM + xCaCO 3 + 3CH + H C 3 A.xCaCO 3 .H 12-11 Equation 6
ingredients can be optimised based on the requirement. All
four ingredients collectively contribute to multiple interactions. A major international collaborative project between leading
Additionally, there is ample opportunity to explore Limestone- universities such as EPFL (Switzerland), UCLV (Cuba), IITs Delhi,
Calcined Clay (LC ) mixture as a pozzolanic admixture for high Bombay and Madras (India) in partnership with an Indian non-
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performance concreting applications [29] . This attracts significant governmental organization called Development Alternatives
interest in the research community to understand, validate and has resulted in a systematic scientific study on Limestone
evolve such technology for large scale commercialization and Calcined Clay Cement (LC ), which has contributed vastly to the
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field adoption. development of such low clinker binders [34] . So far, two major
pilot-scale industrial productions have been made in the project
2.3 Chemistry of limestone calcined clay cement
in India; details of the same can be found in [35,36] . The current
The combination of finely ground limestone and calcined clay paper aims to throw light on the major outcomes of the research
has emerged as a global solution for large volume cement on ternary binder systems involving limestone and calcined
replacement, catering to the increasing demand for cementing clay. The studies on hydration, microstructure and concrete
materials and supplement clinker production. Studies of such performance with LC binder systems has led to significant
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ternary blended systems in paste and concrete reveal interesting insights into the structure-property relationships. This paper
physicochemical effects on the structure development, strength mainly relies on the results already published in [37], [38] and [39] , in
and durability performance. The chemical interactions in conjunction with some new studies carried out in the project.
LC binder include the clinker reaction, pozzolanic reaction, An overview of the research and development made in the
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limestone interaction with clinker hydration and hydration last six years is summarized in this paper with emphasis on the
products, and limestone-calcined clay interaction. Initially, the potential uptake of LC technology for standardization and field
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Bogues’ compounds react to produce C-S-H, CH and Ettringite applications.
as given in Equation 1-3. In the presence of excess aluminates in
clinker, ettringite converts to monosulphate (Ms). The addition 3. MATERIALS AND MIXTURES
of an aluminosilicate based pozzolanic admixture leads to the Ordinary Portland cement of 53 Grade conforming to IS 269 [40] ,
formation of pozzolanic C-A-S-H with variable levels of silica Type F fly ash from North Chennai, and Limestone Calcined Clay
and alumina in the pozzolanic C-A-S-H as given in Equation 4. Cement (LC ) from an industrial production (reported in [35,36] )
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This reaction leads to a significantly improved pore filling and were used as the binders in this study in Phase 1. The fly ash
produces major benefits on transport properties [30, 31] .
and cement were blended in the ratio of 30:70 to produce the
Clinker reactions: binder termed as FA30. The complete description of material
characteristics is provided in Dhandapani and Santhanam
C 3 S + 5.3H C 1.7 SH 4 +1.3CH Equation 1
(2017) . In an extension to Phase-1, some investigations are
37]
C 2 S + 4.3H C 1.7 SH 4 +0.3CH Equation 2 presented from the on-going studies at IIT Madras (i.e., Phase
C 3 A + 3CŜ + 32H C 3 A.3CŜ.H 32 Equation 3 2). Calcined clay from Bhuj, Gujarat (with around 60% kaolinite
content) and limestone from a cement plant in Ariyalur (with
Pozzolanic reaction: CaO content of 42%) were used to produce the ternary blended
A SCM + S SCM + CH+H C-A-S-H (varying stoichiometry) Equation 4 systems, with the formulations indicated in Table 2.

The IndIan ConCreTe Journal | FeBruarY 2020 33