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TECHNICAL PAPER

A STUDY ON PERFORMANCE

OF CLAY BASED

GEOPOLYMERS AT SWATHY MANOHAR*

ELEVATED TEMPERATURES K. MOHAMMED HANEEFA
SUNDAR RATHNARAJAN
MANU SANTHANAM

Abstract from environmental and durability causes, Portland cement
systems also face scarcity of raw materials for satisfying the huge
This study investigates performance of clay based geopolymers consumption needs . Hence, the industrial waste materials like
[8]
at elevated temperatures and compares with the conventional fly ash, and clay with reactive alumina and silica, shall be used
geopolymer systems. Class F fly ash, calcined clay, metakaolin, as an alternative to make cementitious system durable and
and combination of fly ash-calcined clay are used as binders sustainable.
in various geopolymer mixes. The geopolymer specimens are
exposed at 300, 600, and 900°C to evaluate the changes in Geopolymers are the inorganic cementitious materials
physical, mechanical and microstructural characteristics which developed from polymerization by the reaction of
can be corroborated to their performance. Visual observations aluminosilicates with activators in form of a highly concentrated
[9]
and mass loss variations showed that metakaolin specimens alkaline solution . They have similar desirable properties as
possessed the most intensive and branched cracking, even that of Portland cement systems with an 80 % reduction in CO 2
at 300°C exposure. Results of compressive strength test and emissions. As a material, the application of geopolymers have
thermogravimetric analysis (TGA) showed that fly ash and extended now from thermal resistant material to construction
fly ash-calcined clay (FACC) mixes perform better than the materials. However, their behavior with many of the exposure
other two mixes in long temperature range, especially when conditions are not yet fully understood for the combination of
temperatures cross 120°C. Also, broader humps in the X-ray new precursors and alkalis. Some of the typical aluminosilicate
diffractograms of the FACC samples indicates a high degree of precursors being used for the geopolymers are blast furnace
geopolymerisation. Thus, the paper supports the usage of the slag, fly ash, ceramic waste, metakaolin, kaolin, incinerator
largely available clays in India after calcination and advocates bottom ash etc., mostly based on their local availability.
the suitability of calcined clay for producing geopolymers to be Unlike most of the other construction materials such as organic
used at elevated temperatures.
polymers, cement, glass or ceramic, geopolymers are known
Keywords: Geopolymer, Elevated temperature, Calcined clay, for their high fire resistance properties [10] . This property has
Metakaolin, and Fly ash. defined most of the applications of geopolymers for past 30
years . However, this behavioral trend evolves with different
[8]
1. INTRODUCTION pozzolanas used in the geopolymer system, which is important
to define the range of its applicability. Kong and Sanjayan
Geopolymer system is being established as a promising suggested that Si/Al ratio of the geopolymer as the governing
alternative for the environmental and durability issues related parameter controlling the strength reductions on exposure
to Portland cement systems. The large carbon dioxide emission to high temperatures with the addition of different types of
during decomposition of limestone during the manufacture of pozzolans [11-12] . Nevertheless, such suggestions were arrived
Portland cement accounts for 5-8 % of the global annual human- based on studies on slag and fly ash based geopolymers alone,
made CO 2 emissions [1-3] . Alternatives to the carbon-intensive which needs to be reinvestigated and reinstated to deploy the
conventional Portland cement in construction industry in form use of other common pozzolans in geopolymers. Low-grade
of geopolymers would support the current carbon reduction clays after calcination could have an improved pozzolanic activity
strategies of the global nations by signing up to significant cut when partially substituted with cement clinker and hence,
in CO 2 emissions . Durability issues in concretes with ordinary calcined clay shall be used to produce geopolymer systems [13] .
[4]
portland cement (OPC) are in rise and lead to the deterioration Hence, the purpose of this investigation is to study the suitability
of structures well before their service life due to the higher and performance of clay-based geopolymers with calcined clay
permeability that such cementitious system possess [5-7] . Apart and its blend with fly ash at elevated temperatures.

THE INDIAN CONCRETE JOURNAL | MAY 2022 17
*Corresponding author : Swathy Manohar, E-mail: swathym@iitb.ac.in