2.1 Materials
Ordinary Portland cement of 53 grade is used in the present work from KCP Cements, Guntur, Andhra Pradesh, confirmed with ASTM C 150-19 [23]. The snail shell powder is confirmed with ASTM C 618-08 [24]. The preliminary tests were done on the cement and snail shell powder of specific gravity, fineness, and specific surface area. The specific gravity for cement and snail shell powder was 3.16 and 2.41. Fineness for both the materials is 5%, and the specific surface area of cement and snail shell powder is 331 m2/kg, 19,000 m2/kg. The fine aggregates of size 2.36 mm are considered and confirmed with BIS, IS 383-2016 [25].
2.2 Snail Shell Powder Preparation
Snail shell powder is used in the present work, which is extracted by grinding the snail shells which were considered. The following points represents the process of snail shell production.
a.
Firstly, snail shells are collected from Bapatla Coastal Area, Guntur, Andhra Pradesh, free from organic matter.
b.
Wash them with clean water until the constituents like flesh in the shells were free and keep them under sunlight until dry.
c.
Grind the shells into powder, sieve the powder in 90µm and keep the powder in an air-tight container.
XRD analysis is presented in Fig. 1. The major constituent of snail shell powder is Aragonite (CaCO3) with a high dominion of 2θ = 26o and 33o. Quartz (SiO2) is the second principle constituent of snail shell, observed at various ranges of 2θ (46, 48, 53, and 58o). The significant peaks of cement observed in cement are Portlandite (180), Quartz (24, 28o), Alite (31, 33o), and Belite (35, 36o), other constituents observed at various ranges of 2θ presented in Fig. 1. The chemical composition of cement and snail shell powder is shown in Table 2.
Table 2 Chemical composition of Pozzolans
Chemical Constituent
|
SiO2
|
Al2O3
|
Fe2O3
|
CaO
|
MgO
|
K2O
|
Na2O
|
SO3
|
TiO2
|
P2O5
|
Mn2O3
|
LOI
|
Cement
|
64.12
|
4.95
|
3.18
|
65.89
|
1.8
|
1.02
|
0.61
|
1.95
|
-
|
-
|
-
|
0.35
|
Snail shell powder
|
33.52
|
4.78
|
3.17
|
54.89
|
1.10
|
0.98
|
0.25
|
0.03
|
0.12
|
0.21
|
0.02
|
1.42
|
2.3
Calculations of Mix
The mix proportion of cement composite mortar is 1:3:0.42, confirmed with I.S.: 2250-1981 [26]. Therefore, in that one portion Represents (OPC+SSP), three portions of Fine aggregates and 0.42 of Water/ Cement ratio is required. Table 3 represents the mix calculations needed in the present study.
Table 3. Required Mix Calculations
Sample Mix
|
Cement
|
Snail Shell Powder (SSP)
|
Fine Aggregates
|
Water Required
|
C0S
|
300
|
-
|
450
|
150
|
C5S
|
285
|
15
|
450
|
150
|
C10S
|
270
|
30
|
450
|
150
|
C15S
|
255
|
45
|
450
|
150
|
C20S
|
240
|
60
|
450
|
150
|
C25S
|
225
|
75
|
450
|
150
|
C30S
|
210
|
90
|
450
|
150
|
C35S
|
195
|
105
|
450
|
150
|
2.4
Compressive Strength Test
The compressibility test is performed on the mortar specimens of size 70.6 mm*70.6 mm*70.6 mm, confirmed with I.S.: 516-2013 [27]. Then, the samples were casted and kept in the water bath for 28 days for the hydration process as stated by I.S.: 9013-1978 [28]. Fig.2 shows the compressive strength test setup.
2.5
Water Absorption Test
A water absorption test was conducted on the specimens which were cured for 28 days in water. Then, taken out the samples and kept in the oven for 72 hrs at a temperature of 1000C, which is confirmed with I.S:1199 (1959) [29]. Discard the samples from the oven after 72 hrs and weigh them. Note the oven-dry weight of samples and note it as W1. Later keep the specimens in a water bath for 24 hrs to know the wet weight and report it as W2. By using equation 1, water absorption has been calculated and is represented in "%."
1
Where, W1=Weight of Oven Dried Sample, W2=Wet Weight of Mortar Sample
2.6
Sorptivity Test
A water penetration value is evaluated using Sorptivity in a prescribed time and confirmed with ASTM C 1585-20 [30]. The disc of 50mm thickness and 100mm of diameter is considered for the test. A non-absorbent coat like silica gel is applied on all disc surfaces except the surface exposed to the water surface. Figure 3 represents the setup of the Sorptivity test. First, the penetration of water from the exposure is determined concerning time. Then, the Sorptivity values are calculated by using equation 2.
2
Where S=Sorptivity (mm/min0.5),
∇W=Weight of samples concerning time, d=density of water, t=Elapsed time in minutes, and A=area of the disc.
2.7
Rapid Chloride Permeability Test
RCP Test was conducted to determine the electrical conductivity of the Cement + SSP composite mortar as per ASTM C1202-12 [31]. The discs are prepared with sizes of 50mm height and 100mm diameter. The specimens are placed between the reservoirs of RCP Test cells filled with 3% of NaCl and 0.3M NaOH, and these were used as negative and positive terminals. Fig 4 represents the setup of RCP Test samples. The flow of electricity between the two reservoirs can determine by Coulombs of equation 3.
2.8
Acid Durability Test
2.8.1
Mass Loss
The casted and water cured samples of size 70.6mm*70.6mm*70.6 mm are taken and kept in the oven for 72 hours at a temperature of 1000C to avoid moisture from specimens. Thereafter, taken out the samples from the oven and note the mass of samples as WO. Subsequently, prepare an acid solution of 5% concentrated H2SO4 with a pH of 0.3 which is maintained constant until the end of the test. Immersed samples in the acid solution for about 28 days. Finally, remove the samples from acid, keep them under the running water, and take mass as WA. The percentage loss of mass gives the durability under acid solution and is calculated using equation 4.
5
Where WO=Mass of oven samples, WA=Mass of Acid Samples
2.8.2
Dimension Loss
Dimension loss is also a factor in the durability analysis. Edges of specimens are marked as L1, L2, L3, and L4 and measured diagonals lengths as L1 L4 and L2 L3. Dimensions of samples were determined before placing them in an acid bath. Remove all samples from the acid bath after 28 days, keep them under the running water, and measure the diagonals. The loss of dimensions gives durability. Figure 5 represents the setup of dimension measurements.
2.9
Microstructural Studies
Scanning Electronic Microscopy (SEM) analysis is conducted to analyze the morphological behaviour of mortar samples. The samples are collected from the mortar of 10mm*10mm*5mm, which are smooth surfaces. Energy-dispersive spectroscopy (EDS) analysis is also conducted on the same samples to know the compositions of elements constituted in the samples. Moreover, the X-Ray diffraction (XRD) analysis was performed on the powder sample of 90µm and analyzed in X'Pert High Score software.