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TECHNICAL PAPER

Table 1: Chemical composition of flyash (%)

CaO K 2 O MgO Na 2 O
SiO 2 Al 2 O 3 Fe 2 O 3 TiO 2 P 2 O 5 SO 3
63.20 26.19 3.82 1.68 1.30 1.10 0.67 0.40 0.23 0.20

The surface area of fly ash as per IS: 3812 Part-1 (2013) by Blains 2.2 Mix details
2
air permeability was 342 m /kg . The chemical composition
[7]
of fly ash is specified in Table 1. For alkaline activator, sodium Four different mixes for different strength have been prepared
based silicates and hydroxides have been used. The percentage in GPCT. Same mix proportions have been used for GPCA.
rage of ingredients of liquid sodium silicates has been decided For doing comparison of strength, the cement concrete mixes
from the literature review. Also the molarity of sodium hydroxide having similar compressive strength to GPCT have been
was decided based on the strength of concrete by conducting prepared. The quantities of fly ash used for the production of
the preliminary trials with 8, 10, 12, 14, and 16 molar. The liquid four mixes of GPCT are 300, 380, 460, and 540 kg/cu.m. The
same quantities of fly ash have been used for the GPCA mixes,
form sodium silicates (SS) having Na 2 O-14.37 %, SiO 2 -33.10
only 4 % of the fly ash replaced by OPC. To enhance strength
% and Water 52.53 % has been used with 14 molar sodium
at ambient temperature, OPC is added to the GPCA mixes
hydroxide (SH) solution to prepare alkaline activator solution.
The total solid content in 14 molar NaOH solution was 40.73 %. as a curing agent. Based on the laboratory trials, the alkaline
solution to fly ash ratio and SS to SH ratio has been taken as 0.4
In fine aggregates, the combination of river sand (45 %) and
[10]
and 2 respectively . Also, based on the trials conducted in the
[8]
treated sea sand (55 %) has been used . The sea sand has been
laboratory, the total quantity of water for unit volume of concrete
washed by tap water to remove the salt, chlorides and other [8]
impurities present in the sea sand. After this treatment it named has been decided to take as 110 litres . The percentage of fine
aggregates in the mix was 35 % of the total aggregate content.
as treated sea sand. Various trials has been carried out to get
Considering the quantity of water available in the sodium
well graded fine aggregates. The combination of 45 % river
silicate and sodium hydroxide, the additional water has been
sand and 55 % treated sea sand becomes a well graded fine used to fulfil the total quantity of water required for one cubic
aggregates. For coarse aggregates, 20 and 10 mm black basalt
metre volume of concrete. For maintaining the workability of all
crushed angular aggregates has been used. Fine aggregates
mixes of GPC as similar to the mixes of cement concrete, the
and coarse aggregates have been conforming to IS: 383 (2016)
Plastiment 100 of Sika India has been used as a super-plasticizer.
[9] . The properties of aggregates are presented in Table 2 and Proceed with these parameters, the quantities of ingredients of
combine grading of all aggregates are shown in Figure 1.
geopolymer concrete and cement concrete for unit volume has
been calculated and shown in Table 3. The results of workability
Table 2: Properties of fine and coarse aggregates
by slump cone test are shown in Table 4.
COARSE
PHYSICAL AGGREGATE FINE AGGREGATE
PROPERTIES
20 mm 10 mm FA-I FA-II
River Treated 120
Type Crushed Crushed
sand sea sand
Maximum size 20 mm 10 mm 4.75 mm 4.75 mm 100
Particle shape Angular Angular Rounded Rounded 80
Fineness modulus 6.99 6.16 3.26 1.91 Cumulative percentage passing 60
Specific gravity 2.74 2.74 2.63 2.7 40
Bulk density (kg/cu.m) 1568 1624 1723 1562 20

Water absorption (%) 1.4 1.6 1.4 1.62
0
Silt content (%) 1.0 1.1 3.0 3.5 100 10 1 0.1
Sieve size (mm)
Moisture content Nil Nil Nil Nil
Lower limit Upper limit Test results
Zone of FA -- -- I IV
Figure 1: Combined grading curve of all aggregates

THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026 69