1. Introduction
The modern urban areas have become a concrete jungle, and concrete has become the second most consuming material after water on the planet. Cement is no doubt the major ingredient of concrete, and its production is responsible for huge carbon footprints, which makes the cement industry the third most CO
2 emitter in the world [
1]. The cement industry contributes a maximum of 8% of the global emission [
1]. There are two ways to reduce the CO
2 emission from cement manufacturing plants; the first is to optimize process technology by using alternative fuel or raw material, and the second is the use of Supplementary Cementitious Materials (SCM) as a replacement for cement [
2]. The supplementary cementitious materials are inorganic waste materials that possess hydraulic activity, pozzolanic activity, or sometimes dual nature [
3]. Among them, limestone is one of the most commonly used SCM, and it has been used up to 10% replacement without sacrificing the compressive strength [
4]. As a partial replacement for cement, limestone fillers can improve hydration in a low water-to-cement ratio [
5]. Therefore, it is recommended by the ASTM to use limestone effectively up to 5% [
6], whereas the BS recommends a 6% - 35% replacement level [
7]. Generally, limestone can be used both as a binder replacement and as an aggregate to improve the properties of concrete [
8,
9]. Overall, using limestone as a replacement for cement for up to 20% can enhance the strength, workability, and durability of concrete and mortars [
10,
11].
The use of Eggshells (ES) has been recommended through several research studies as a potential bio-filler in cementitious materials during the past decade. The eggshells fulfill the requirements of a standard limestone for calcium silicate products as per ASTM standard specifications for limestone [
12]. Incorporating eggshells as a partial replacement of cement improves the strength and other properties of cementitious materials, e.g., reduction in the setting time [
13,
14,
15], good radiation shielding properties [
16,
17], and can be used up to 20% replacement level under the elevated temperature condition [
18]. Several studies have been carried out on the optimal replacement of eggshells with cement considering strength as a deciding parameter, as shown in
Table 1. It can be seen that 9 out of 25 studies recommend 5% replacement, 7 studies recommend 10% replacement, and the rest recommend different other replacements. Most of the studies recommends 5% replacement because limestone has complete reactivity up to 5% replacement level [
2]. Likewise, eggshells have also been effectively blended in cement along with silica fume (SF) [
19,
20,
21], fly ash (FA) [
22,
23,
24], rice husk ash (RHA) [
25], rice straw ash (RSA) [
26], glass powder [
27], palm oil fuel ash (POFA) [
28,
29,
30,
31], and bagasse ash [
32]. In addition, eggshells have been used in special concrete as well, both in uncalcined and calcined forms like Foamed concrete [
33,
34], self-compacting concrete [
35,
36,
37,
38,
39], and geopolymer concrete [
40]. In general, using eggshells either in an uncalcined or calcined state has a positive impact on the hydration kinetics of cementitious materials [
41,
42,
43]. Apart from using eggshells in the cementitious matrix, they can also be used as fine aggregates up to 40% without affecting the compressive strength [
44].
Several SCMs and fillers have been proposed in the past few decades, while the search for new SCMs is still in progress. The chemical composition of SCMs may vary depending upon several factors like production processes and regions. For example, the composition of steel slag may vary depending on the type of furnace being used in the process of conversion from iron to steel [
67]. Similarly, the Australian Fly Ash (FA) contains more SiO
2 content than the Indonesian FA and accordingly imparts more strength due to its more pozzolanic activity [
68]. Therefore, it is essential to analyze the variation in the chemical compositions of different hydraulic and pozzolanic materials before proposing them for large-scale commercial application. Limestone is a less reactive hydraulic material [
69], and biological limestone like eggshells have similar properties containing an overwhelmingly high content of CaCO
3. A study reports 94% - 97% CaCO
3 as an average value depending on mineral nutrition, housing system for hens, age, and animal genotype [
70]. A study also reports higher content of 98.2% CaCO
3 [
71], whereas another study reports low as 86.75% in eggshells of white silky chicken [
72]. The quality of eggshells is defined as its resistance against breakage during handling of eggs [
73]. This resistance varies from case to case and depends upon the breed and age of eggs [
74], weight grade [
75], color [
76], and housing system [
77,
78]. However, this resistance majorly depends on the weight of an eggshell [
79,
80,
81,
82,
83]. Therefore, a good quality egg must have a heavier eggshell, while the weight of the eggshell also varies with its size, but an average value is about 10% of the total weight of the eggshell [
82]. Local weather is a significant factor affecting not only egg production but eggshell quality as well. For example, the high air temperature and the relative humidity cause heat stress, and that affects the egg's production and eggshell quality [
84,
85,
86]. Hens in hot and humid environments cannot consume sufficient calcium and produce softer eggshells [
86,
87]. Likewise, it is quite possible that eggs and eggshells from different countries could have different properties depending on their mineral contents. However, a diversity of weather conditions is possible across big countries like the USA. A brief review on the specific gravity as shown in
Table 2 depicts that specific gravity is different in different regions probably due to the local weather conditions and some other factors. Hence, it is important to analyze the eggshells from different countries before proposing them for large-scale industrial applications in cementitious materials.
Hong Kong is the biggest consumer of eggs in the world. Notably, the consumption per capita per year has been increasing drastically during the last decade. The domestic supply of eggs in Hong Kong was 196,000 tons in 2021. At the same time, the average consumption per capita was 26.09 kg/capita/year in 2020, as reported by the Food and Agriculture Organization (FAO) [
100]. According to the Observatory of Economic Complexity (OEC), eggs were the 175
th most imported product in Hong Kong in 2021, having a total import value of 284 million USD, which ranks Hong Kong fourth in the list of most egg-importing countries [
101]. Hong Kong’s market has diverse kinds of eggs from different countries of origin. Also, the import quantity of eggs was 200,000 tons, whereas the export quantity was only 4000 tons in the year 2021 [
100]. Therefore, Hong Kong is an ideal place to study the characteristics of eggshells from different countries of origin and for their sustainable utilization in cementitious materials. Not only this, but the public, and specifically the restaurants, have a positive attitude towards the recycling of waste eggshells for meaningful purposes [
102].
Many studies have been carried out on the viability of eggshells in cementitious materials as a cement replacement but the effect of different eggshells from different regions on the mechanical properties of cementitious material considering the quality has not been studied yet. The proposed study aims to assess the feasibility of using eggshells from different countries of origin as a cement replacement in cementitious material. For this purpose, the extent of variation in the basic properties (e.g., specific gravity and mineral content) of different eggshells and their effect on the end cementitious products were analyzed. This study will facilitate the stakeholders to develop environmentally friendly concrete containing eggshells as a cement replacement for commercial applications.
Figure 1.
Eggs available in Hong Kong markets (a) Number of egg brands by country of origin (b) Share of different countries in the import of eggs [
101].
Figure 1.
Eggs available in Hong Kong markets (a) Number of egg brands by country of origin (b) Share of different countries in the import of eggs [
101].
Figure 2.
Measured specific gravity of sample eggshells.
Figure 2.
Measured specific gravity of sample eggshells.
Figure 3.
Typical thermogram for eggshell (a) Weight loss (b), Differential Thermogravimetric Curve (DTG).
Figure 3.
Typical thermogram for eggshell (a) Weight loss (b), Differential Thermogravimetric Curve (DTG).
Figure 4.
Correlation between the stoichiometric analysis and thermogravimetric analysis of sample eggshells for mineral part.
Figure 4.
Correlation between the stoichiometric analysis and thermogravimetric analysis of sample eggshells for mineral part.
Figure 5.
Particle Size Distribution (PSD) cure of OPC, LS, ESs and CESs.
Figure 5.
Particle Size Distribution (PSD) cure of OPC, LS, ESs and CESs.
Figure 6.
XRD spectrum of CES indicates the existence of a blend of calcium carbonate, calcium hydroxide, and calcium oxide in comparison with LS and ES.
Figure 6.
XRD spectrum of CES indicates the existence of a blend of calcium carbonate, calcium hydroxide, and calcium oxide in comparison with LS and ES.
Figure 7.
(a) Compressive strength for 7th and 28th day, (b) Relative strength (RS) for 7tha and 28th day.
Figure 7.
(a) Compressive strength for 7th and 28th day, (b) Relative strength (RS) for 7tha and 28th day.
Figure 8.
Correlation between specific gravity and the CaCO3 in ES and LS.
Figure 8.
Correlation between specific gravity and the CaCO3 in ES and LS.
Figure 9.
Correlation between compressive strength and the CaCO3 content in mixes with uncalcined eggshells.
Figure 9.
Correlation between compressive strength and the CaCO3 content in mixes with uncalcined eggshells.
Table 1.
A review on the optimal replacement of ES with cement.
Table 1.
A review on the optimal replacement of ES with cement.
Ref. |
Type of ES |
Composite Type |
Optimal Replacement |
Cement Type |
w/b |
28th Day Strength |
[45] |
ES |
Ordinary concrete |
5% |
IS grade 43 |
0.39 – 0.50 |
Compressive, flexural |
[46] |
ES |
Ordinary concrete |
5% |
ASTM type I |
0.6 |
Compressive, split tensile |
[47] |
ES |
Ordinary concrete |
5% |
IS grade 53 |
0.5 |
Compressive |
[48] |
CES1 (500oC) |
Ordinary concrete |
10% |
OPC |
0.6 |
Compressive |
[49] |
ES |
Ordinary concrete |
10% (comp.),20% (flexural) |
CEM II/B-M |
0.4 |
Compressive, flexural |
[50] |
ES (Brown) |
Ordinary mortar |
5% |
CEM I 52.5 N |
0.5 |
Compressive, flexural |
[51] |
ES |
Ordinary mortar |
5% |
ASTM Type I |
0.4 |
Compressive, flexural |
[52] |
ES |
Ordinary concrete |
15% |
OPC |
0.45 |
Compressive |
[20] |
ES |
Ordinary concrete |
5% |
OPC |
0.5 |
Compressive |
[53] |
ES |
Ordinary concrete |
12% |
IS grade 43 |
0.4 |
Compressive, split tensile |
[54] |
ES |
Ordinary concrete |
20% |
ASTM Type I |
0.6 |
Compressive |
[55] |
Eggshell Ash (ESA) |
Ordinary concrete |
5% |
OPC |
0.55 |
Compressive |
[56] |
ES |
Ordinary concrete |
12% (comp.) 6% (tensile) |
IS grade 43 |
0.4 |
Compressive, split tensile |
[57] |
ES |
Concrete (waste as aggregates) |
10% |
IS grade 53 |
0.47 |
Compressive |
[58] |
ES |
Ordinary concrete |
15% |
OPC |
0.45 |
Compressive, flexural |
[59] |
ES |
Ordinary concrete |
7.5% |
OPC |
0.52 |
Compressive, split tensile, flexural |
[60] |
CES1 (750oC for one hour) |
Ordinary concrete |
15% |
Iraqi OPC |
0.5 |
Compressive |
[61] |
ES |
Ordinary concrete |
10% |
ASTM Type I |
0.5 |
Compressive |
[43] |
CES1 (900oC for 2 hours) |
Ordinary concrete |
10% |
ASTM Type II |
0.5 |
Compressive, flexural |
[62] |
CES1 (100oC for 12 hours) |
Seawater concrete |
5% |
OPC |
0.5 |
Compressive |
[63] |
ES |
High Strength Concrete (HSC) |
10% |
ASTM Type I |
0.32 |
Compressive |
[64] |
ES |
Fiber Reinforced Concrete (FRC) |
5% |
ASTM Type I |
0.5 |
Compressive, flexural |
[65] |
ES |
Ordinary mortar |
10% |
IS grade 53 |
0.5 |
Compressive |
[66] |
ES |
Ordinary concrete |
10% |
CEM I 52.5N |
0.5 |
Compressive, flexural |
[21] |
ES |
Ordinary concrete |
11% |
OPC |
0.5 |
Compressive, split tensile, flexural |
Table 2.
A review on specific gravity of eggshells from different regions.
Table 2.
A review on specific gravity of eggshells from different regions.
Reference |
Region |
Specific Gravity |
[88] |
Malaysia |
2.14 |
[89] |
India |
1.95 |
[40] |
India |
2.37 |
[50] |
France |
2.5 |
[90] |
India |
2.01 |
[91] |
India |
2.14 |
[92] |
NA |
2.13 |
[93] |
NA |
2.20 |
[94] |
Pakistan |
2.27 |
[95] |
USA |
2.09 - 2.18 |
[96] |
NA |
2.37 |
[46] |
India |
2.37 |
[97] |
Bangladesh |
2.66 |
[98] |
Ghana |
2.58 |
[99] |
India |
2.33 |
Average |
2.29 ± 0.21 |
Table 3.
Details of sample eggshells for experimentation.
Table 3.
Details of sample eggshells for experimentation.
Designation |
Country |
Color |
Source |
ES1 |
China |
Dark Brown |
Market |
ES2 |
China |
Light Brown |
ES3 |
Thailand |
Dark Brown |
ES4 |
Japan |
White |
ES5 |
Japan |
Dark Brown |
ES6 |
USA |
White |
ES7 |
USA |
Dark Brown |
ES8 |
Singapore |
Dark Brown |
ES9 |
Singapore |
White |
ES10 |
Malaysia |
Dark Brown |
ES11 |
New Zealand |
Dark Brown |
ES12 |
South Korea |
Dark Brown |
ES13 |
China |
Dark Brown |
Restaurant |
ES14 |
China |
Light Brown |
ES15 |
Japan |
Dark Brown |
ES16 |
Japan |
White |
Table 4.
Composition of OPC.
Table 4.
Composition of OPC.
Oxide Composition (%) |
Bogue’s Components (%) |
MgO |
Al2O3
|
SiO2
|
P2O5
|
SO3
|
K2O |
CaO |
Fe2O3
|
Others |
C3S |
C2S |
C3A |
C4AF |
1.12 |
5.45 |
19.10 |
0.13 |
4.51 |
0.67 |
65.50 |
3.00 |
0.43 |
67.66 |
3.74 |
9.37 |
9.13 |
Table 5.
Details of concrete mixes.
Table 5.
Details of concrete mixes.
Specimen |
OPC |
LS/ES/CES |
Fine Aggregates |
Coarse Aggregates |
w/b |
a/b |
Kg/m3
|
Kg/m3
|
Kg/m3
|
Kg/m3
|
Control |
600 |
- |
600 |
1200 |
0.5 |
3 |
Non-Control |
570 |
30 |
600 |
1200 |
0.5 |
3 |
Table 6.
Comparative composition of eggshells by thermogravimetric and stoichiometric analysis.
Table 6.
Comparative composition of eggshells by thermogravimetric and stoichiometric analysis.
Sample |
A1
|
B2
|
O3
|
V4
|
Thermogravimetric Analysis |
Stoichiometric Analysis |
CaCO3
|
CaO |
ΔW |
CO2
|
Ca |
CaO |
ΔW |
CO2
|
Ca |
% |
% |
% |
% |
% |
% |
% |
% |
% |
% |
% |
LS |
0.38 |
- |
55.79 |
44.21 |
43.82 |
39.87 |
55.78 |
44.22 |
43.84 |
39.92 |
99.62 |
ES1 |
1.14 |
1.63 |
54.83 |
45.17 |
42.40 |
39.18 |
54.44 |
45.56 |
42.79 |
38.96 |
97.23 |
ES2 |
0.94 |
3.35 |
53.61 |
46.39 |
42.10 |
38.31 |
53.59 |
46.41 |
42.12 |
38.36 |
95.72 |
ES3 |
1.24 |
2.89 |
51.76 |
48.24 |
44.11 |
36.99 |
53.68 |
46.32 |
42.19 |
38.42 |
95.87 |
ES4 |
0.91 |
2.00 |
54.23 |
45.77 |
42.86 |
38.76 |
54.36 |
45.64 |
42.73 |
38.91 |
97.09 |
ES5 |
1.09 |
2.08 |
55.29 |
44.71 |
41.54 |
39.51 |
54.22 |
45.78 |
42.61 |
38.80 |
96.83 |
ES6 |
1.15 |
2.46 |
53.70 |
46.30 |
42.69 |
38.37 |
53.97 |
46.03 |
42.42 |
38.63 |
96.39 |
ES7 |
1.30 |
1.99 |
53.61 |
46.39 |
43.10 |
38.31 |
54.15 |
45.85 |
42.56 |
38.76 |
96.71 |
ES8 |
1.22 |
2.37 |
55.92 |
44.08 |
40.50 |
39.96 |
53.98 |
46.02 |
42.43 |
38.64 |
96.41 |
ES9 |
1.05 |
2.23 |
53.95 |
46.06 |
42.77 |
38.55 |
54.15 |
45.85 |
42.56 |
38.76 |
96.71 |
ES10 |
1.22 |
2.10 |
55.93 |
44.08 |
40.76 |
39.97 |
54.14 |
45.86 |
42.55 |
38.75 |
96.69 |
ES11 |
1.34 |
2.58 |
52.98 |
47.02 |
43.10 |
37.86 |
53.80 |
46.20 |
42.28 |
38.50 |
96.08 |
ES12 |
1.51 |
2.11 |
55.27 |
44.73 |
41.11 |
39.49 |
53.97 |
46.03 |
42.42 |
38.62 |
96.38 |
ES13 |
1.23 |
3.42 |
54.18 |
45.82 |
41.17 |
38.72 |
53.39 |
46.61 |
41.96 |
38.21 |
95.35 |
ES14 |
1.01 |
2.28 |
53.73 |
46.27 |
42.98 |
38.40 |
54.15 |
45.85 |
42.56 |
38.76 |
96.72 |
ES15 |
1.09 |
2.47 |
55.28 |
44.72 |
41.15 |
39.51 |
54.00 |
46.00 |
42.44 |
38.65 |
96.44 |
ES16 |
1.34 |
4.01 |
53.51 |
46.49 |
41.15 |
38.24 |
53.00 |
47.00 |
41.66 |
37.93 |
94.65 |
Aver. |
1.17 |
2.50 |
54.24 |
45.76 |
42.09 |
38.76 |
53.94 |
46.06 |
42.39 |
38.61 |
96.33 |
Table 7.
Comparison of average composition of eggshells from different countries and extra pure limestone (LS).
Table 7.
Comparison of average composition of eggshells from different countries and extra pure limestone (LS).
Component |
Stochiometric Analysis |
Thermogravimetric Analysis |
Extra Pure Limestone |
Eggshells from different countries |
Difference |
% |
% |
% |
% |
% |
Ca |
40.08 |
40.03 |
40.24 |
0.21 |
C |
11.99 |
12.01 |
11.93 |
0.08 |
O |
47.93 |
47.97 |
47.83 |
0.13 |
CO2
|
43.92 |
43.99 |
43.70 |
0.30 |
CaO |
56.08 |
56.01 |
56.30 |
0.30 |
Table 8.
Details of D[4,3], D(50), and D(90) particles sizes of OPC, LS, ESs, and CES.
Table 8.
Details of D[4,3], D(50), and D(90) particles sizes of OPC, LS, ESs, and CES.
Material |
D [4,3] |
D (50) |
D (90) |
(μm) |
(μm) |
(μm) |
OPC |
17.53 |
11.56 |
42.86 |
LS |
20.27 |
17.74 |
38.90 |
ES-7 |
21.26 |
14.62 |
51.45 |
ES-13 |
16.76 |
10.14 |
42.67 |
ES-16 |
13.94 |
8.00 |
35.98 |
CES-7 |
30.21 |
24.98 |
63.83 |
CES-13 |
24.09 |
16.43 |
56.25 |
CES-16 |
31.27 |
24.87 |
66.68 |
Table 9.
Quantities of different phases after Rietveld analysis.
Table 9.
Quantities of different phases after Rietveld analysis.
S. No |
Calcined Eggshells |
CaCO3
|
Ca(OH)2
|
CaO |
% |
% |
% |
1 |
CES7 |
37.5 |
55.3 |
7.2 |
2 |
CES13 |
37.6 |
55.1 |
7.4 |
3 |
CES16 |
36.7 |
54.6 |
8.7 |
Table 10.
HM and LSF for the OPC and the OPC with 5% CES.
Table 10.
HM and LSF for the OPC and the OPC with 5% CES.
Mix |
CaO in CES |
CaO in OPC |
SiO2
|
Al2O3
|
Fe2O3
|
HM |
LSF |
% |
% |
% |
% |
% |
OPC |
- |
65.5 |
19.1 |
5.45 |
3 |
2.377 |
1.057 |
M-CES7 |
7.2 |
65.5 |
19.1 |
5.45 |
3 |
2.391 |
1.063 |
M-CES13 |
7.4 |
65.5 |
19.1 |
5.45 |
3 |
2.392 |
1.063 |
M-CES16 |
8.7 |
65.5 |
19.1 |
5.45 |
3 |
2.394 |
1.064 |