3.1 Phase 1- WAC
Coarse aggregates cannot be just considered a filler material. Instead, it has been recognized as one of the constituent materials that greatly influences the mechanical properties of concrete mix. Herein, the effect on concrete’s compressive, tensile, flexural and combined (flexural and torsional) strength has been examined when WCA has replaced natural coarse aggregates with the same sizes (0.02m and 0.01m) having varying percentages in the mix.
3.1.1 Effect of AWC on the compressive strength (CS) of concrete
The results show that the CS decreases on increasing the Natural Coarse Aggregates (NCA) replacement percent by waste ceramic aggregates (AWC) as shown in chart 5. The CS was found to vary between 31.1MPa for PC (WAC-0AWC) to 21.55MPa for WAC-100AWC. The percentage reduction in CS of WAC-10%, WAC-20%, WAC-30%, WAC-50% and WAC-100% has been compared with that of PC (WAC-0%) as shown in chart 1. A decrease in CS of about 7.4% and 30.72% were observed in WAC-10AWC and WAC-100%, respectively, with respect to PC.
The curve mentioned previously in section two (Particle Size Distribution of Natural Coarse Aggregate & Ceramic Coarse Aggregate) concluded that both coarse ceramic aggregate and natural coarse aggregate fit within the confines of standard concrete aggregate, implying that coarse ceramic aggregate can be used in place of natural coarse aggregate in concrete.
The first observation is that ceramic coarse aggregate floor tiles have presented the lowest compressive strength from the results. This was expected because ceramic tiles are weaker and absorb more water than natural coarse aggregates.
The other possible explanation for the low compressive strength is that the coarse ceramic aggregate is poorer than the natural aggregate.
Another reason was the low crushing value of waste ceramic coarse aggregate (20.86%) in compression to natural coarse aggregate crushing value (34%). The crushing value of aggregate gives a relative measure of the resistance of an aggregate under a gradually applied compressive strength load.
More or less similar behaviour of ceramic aggregate replacement has been reported by Alves, A. V., et al. [9], Gonzalez-Corominas, A. et al. [14], Sekar, M. [17], Correia, J. R., et al. [18].
3.1.2 Effect of AWC on the tensile strength (TS) of concrete
Similar to the CS test, TS was also found to be decreasing on increasing the natural coarse aggregates replacement percent by AWC, as shown in chart 5. The TS was found to vary between 3.69MPa for PC (WAC-0%) to 2.95MPa for WAC-100%. The percentage reduction in TS of WAC- 10%, WAC-20%, WAC-30%, WAC-50% and WAC-100% has been compared with that of PC (WCA-0%) as shown in Chart 2. A decrease in TS of about 8.67% and 20.05% were observed in WAC-10% and WAC-100%, respectively, with respect to PC. The reduction in tensile strength was expected due to the intrinsic properties of the adhered mortar and its low adhesiveness to ceramic.
The results of this study have shown a similar performance to other studies conducted by different researchers such as Gonzalez-Corominas, A. et al. [14]; Gomes, M. et al. [15] and; D.J.M. Martins [16].
3.1.3 Effect of AWC on the flexural strength (FS) of concrete
The FS was found to decrease from 6.08MPa for PC (WAC-0%) to 4.67MPa for WAC-100%, as shown in chart 5. Furthermore, the percentage reduction in FS of WAC-10%, WAC-20%, WAC-30%, WAC-50% and WAC-100% has been compared with that of PC (WAC-0%) as shown in Chart 3, wherein a decrease in FS of about 8.67% and 20.05% were observed in WAC-10% and WAC-100% respectively with respect to PC.
As stated previously, the coarse ceramic aggregates reduced flexural strength. A higher replacement ratio of natural coarse aggregates with coarse ceramic aggregate resulted in a flexural strength loss of up to 5.6%.
The concrete (WAC- 20%) produced in the present study has shown the best mechanical performance compared to other mentioned studies such as Alves, A. V., et al. [9]; Nepomuceno, M. C., et al. [19]; Anderson, D. J., et al. [20].
3.1.4 Effect of AWC on the combined flexural and torsional strength (FTS) of concrete
The aggregate and cement paste interface is the weakest concrete zone, known as the interfacial transition zone. Therefore, different methodologies have been adapted to density the interfacial zone that can improve the mechanical strength of concrete.
The Ultimate Bending Stress (UBS) of WAC under torsion 243N.mm was found to vary from 3.25MPa to 2MPa; under torsion, 254N.mm was found to vary from 3MPa to 1.75 MPa and; under torsion 264N.mm was found to vary from 2.75MPa to 1.5MPa as shown in chart 5. However, the UBS of WAC-10% was 30.76%, 33.33%, and 36.36% greater than the PC/WAC-0% for torsion 243N.mm, 254N.mm and 265N.mm respectively, as shown in Chart 4. Further, the UBS of WAC-20% under torsion 243N.mm, 254N.mm and 265N.mm were found to be equal to that of PC.
The major reason for a higher value of UBS may be related to the high impact value of waste ceramic coarse aggregate (27%) in compression to natural coarse aggregate impact value (24%), where the aggregate impact value in determining a measure of resistance to sudden impact or shock which differ from its resistance to gradually applied compressive load.
A study by Anderson, D. J., et al. [20] examined the impact of ceramic aggregate surface texture, angular aggregate shape, and water absorption on concrete torsional strength. The ceramic tile used in this study is flat and smooth on one side compared to other crushed ceramic tile aggregates.
Finally, on the basis of Phase 1 results, 20% AWC was adopted as the optimal replacement percentage for NCA.
3.2 Phase 2- WCC
There is a tremendous saving of energy, cost (about 45%), and environmental pollution when replacing the cement with waste ceramic cement powder (CWC). Furthermore, authors and researchers such as Lavat A. et al. [21] and Puertas F et al. [22] have confirmed the pozzolanic nature of ceramic wastes. This section discusses the effect of using waste ceramic cement (CWC) as a replacement for ordinary Portland cement (OPC 43 grade) on the mechanical properties of concrete: CS, TS, FS and FTS.
3.2.1 Effect of CWC on the compressive strength (CS) of concrete keeping 20% AWC constant
The CS was found to vary between 31.11MPa for WCC-0% to 20MPa for WCC-30%, as shown in Chart 6. The percentage increase/decrease in CS of WCC-5%, WCC-10%, WCC-15%, WCC-20% and WCC-30% compared with that of WCC-0%, as shown in Chart 6.
An increase in CS of about 11.86% was observed in WCC-5%, whereas a decrease of about 10.70% was observed in WCC-15%, respectively, with respect to WCC-0%. For low CWC/OPC replacement volume ratios (5% to 10%), the likely Pozzolanic activity of CWC compensated the cement percentage reduction, where the mixture with WCC-10% was found to have the optimal value of CS (=32.89 MPa).
As mentioned in Table 2 (Chemical Analysis of CWC and OPC) that the chemical composition of the ceramic waste Powder mainly consisted of silica (SiO2) and alumina (Al2O3). Both oxides presented around 85% of the total material mass. These higher percentages of silicate and aluminate in the ceramic waste powder material could indicate some Pozzolanic reactivity.
The mass fractions of (SiO2 + Al2O3 + Fe2O3) in the ceramic waste powder conformed well to the requirement stated in IS 1489-1(1991) for natural pozzolana (i.e., >70%). On the other hand, the ceramic waste powder observed very small mass percentages of several oxides such as Fe2O3, CaO, MgO, and SO3. Also, the SO3 and the LOI conformed to IS 1489-1(1991) requirements. Therefore, ceramic waste powder qualified as a pozzolana material based on its mineral composition. WCC-30% had the lowest strength because it contained the maximum waste ceramic as a cement replacement.
Shamsaei M. et al. [23] studied the effect of ceramic powder on concrete compressive strength. By comparing previous studies to the current study, it was determined that the compressive strength in specimens containing Waste Ceramic Cement (CWC) only (10% replacement) was reduced by 6.77% [23]. In comparison, the compressive strength in specimens containing Waste Ceramic Cement (CWC) (10% replacement) with Waste Ceramic Aggregate (AWC) (20% replacement) was enhanced by 5.72% (WCC-10%). This leads to conclude that CS in specimens containing ceramic powder without ceramic aggregate was lower than in specimens containing both.
3.2.2 Effect of CWC on the tensile strength (TS) of concrete keeping 20% AWC constant
Concrete's TS can be reduced in part by replacing CWC in some places. Findings show that reduction ranges for TS are greater than those for Cs. Samples WCC-30% reduced splitting TS the most, while specimens WCC-5% reduced splitting TS the least. Chart 7 shows that the average splitting TS of WCC-5% was 12.19% lower than the reference model (WCC-0%).
Thus, the Pozzolanic effect of ceramic waste powder (WCC-5%, WCC-10%) on the mechanical properties of the mixture can be attributed to tensile strength [24].
The adverse effects of Pozzolanic material deficiency cannot be overcome for a higher CWC/OPC replacement ratio (30%). Heidari A. et al. [1] reported that “The sole Pozzolanic activity of the ceramic waste powder, as reasonably hypothesized on the basis of its mineralogical composition discussed in the literature, was not able to provide compensation probably due to the likely lower availability of the cement hydration products (portlandite) necessary for its activation”.
Shamsaei M. et al. [23] studied the effect of ceramic powder on concrete tensile strength. By comparing previous studies to the current study, it was determined that the TS in specimens containing 10% Waste Ceramic Cement (CWC) only was reduced by 19.65% [23] whereas, in specimens containing 10% Waste Ceramic Cement (CWC) and 20% Waste Ceramic Aggregate (AWC) was decreased by 19.78% (WCC-10%).
This concludes that the reduction in TS of specimens containing CWC without AWC was higher than in specimens containing both. The Pozzolanic behaviour of ceramic waste can be considered responsible for less reduction in tensile strength. Modarres et al. [24] referred that “the pozzolanic reaction produces a high percentage of calcium silicate hydrate, which improves the strength”.
3.2.3 Effect of CWC on the flexural strength (FS) of concrete keeping 20% AWC constant
From Chart 8 & Chart 10, Specimens WCC-5% showed an increment of 0.82% in FS with respect to the reference model (WCC-0%) whereas, in specimens, WCC-10%, WCC-15%, WCC-20% and WCC-30% the FS was found to show a decrement of 9.53%, 19.73%, 21.78% and 25.78% respectively compared to the reference model (WCC-0%).
The difference in the Flexural strength development of the samples WCC-0% and WCC-10% can be attributed to the Pozzolanic reaction.
Thus, the pozzolanic particles could be reasons that affect the FS. This finding has also been confirmed by Shamsaei M. et al. [23], who studied the effect of ceramic powder on concrete FS. By comparing previous studies to the current study, it was determined that the FS in specimens containing 10% Waste Ceramic Cement (CWC) only was reduced by 5.5% [23] whereas, in specimens containing 10% Waste Ceramic Cement (CWC) and 20% Waste Ceramic Aggregate (AWC) was reduced by 9.53% (WCC-10%).
This concludes that the reduction in TS of specimens containing CWC without AWC was higher than in specimens containing both. Besides, with increases in the percentage of ceramic waste, the FS decreases slightly.
3.2.4 Effect of CWC on the combined flexural and torsional strength (FTS) of concrete keeping 20% AWC constant
The Ultimate Bending Stress (UBS) of WCC under torsion 243N.mm was found to vary from 3.25MPa (WCC-0%) to 4.5MPa (WCC-30%); under torsion, 254N.mm was found to vary from 3MPa (WCC-0%) to 3.75 MPa (WCC-30%) and; under torsion 264N.mm was found to vary from 2.75MPa (WCC-0%) to 3.5MPa (WCC-30%) as shown in chart 10.
Heidari A. et al. [1] mentioned that ceramic powder and Ordinary Portland Cement (OPC) fit within the chemical properties of normal concreting cement, which implied that ceramic powder could replace OPC (43 Grade) in concrete.
The increased enhancement in UBS may be due to ceramic compounds containing Pozzolanic particles.
However, the UBS of WCC-10% was 69.23%, 67.67%, and 72.73% greater than the reference model for torsion 243N.mm, 254N.mm and 265N.mm respectively, as shown in Chart 9.
Finally, on the basis of Phase 2 results, 10% CWC and 20% AWC were adopted as the optimal replacement percentage for cement and NCA, respectively.
3.3 Phase 3- WSC
Using waste ceramic sand as a substitute for sand in concrete is a good step toward sustainability. This part discusses the effect of using the waste ceramic sand (SWC) as a partial replacement of river sand on the mechanical properties of concrete (CS, TS, FS and FTS)
3.3.1 Effect of SWC on the compressive strength (CS) of concrete, keeping 20% AWC and 10% CWC constant
Chart 15 shows that the CS decreases when the replacement ratio increases. At 28days of age, the maximum loss in strength, relative to the reference concrete, was found as 10.99%, 11.98%, 19.99%, 22.85%, and 27.12% in WSC-5%, WSC-10%, WSC-15%, WSC-20% and WSC-30% respectively as shown in Chart 11.
Leite, M. et al. [25], despite the Pozzolanic nature of aggregate, their low porosity does not allow Pozzolanic reactions to occur, as in the case of Waste Ceramic Sand (SWC). The experiment results show that the CS of waste ceramic concrete made by partial replacement of sand gives less compressive strength than the plain concrete.
This performance has been confirmed by Siddesha H. [26], who studied the effect of ceramic sand on concrete CS. By comparing previous studies to the current study, it was determined that the decrease in CS of specimens WSC-10% was 11.98% (present study), whereas; in a specimen with only ceramic sand (10%) as a replacement (no ceramic aggregate and cement) was 12.5% [26].
For WSC-20%, the CS decreased by 22.85%, whereas in concrete with ceramic sand only (without ceramic powder & ceramic aggregate) was decreases by 16 % [26].
3.3.2 Effect of SWC on the tensile strength (TS) of concrete, keeping 20% AWC and 10% CWC constant
The TS of various samples is shown in chart 15, indicating a reduction in the TS of WSC. The reduction may be the increase in porosity of the paste as the replacement ratio increases. For WSC mixes, a maximum reduction of 34.95% relative to the reference concrete has been found in WSC-30%, as shown in chart 12.
From the results above indicating a reduction in the TS of WSC. The reduction may be the increase in porosity of the paste as the replacement ratio increases.
Awoyera PO et al. [11] mentioned that both fine ceramic aggregate and river sand fit within the confines of conventional concreting sand, implying that ceramic sand can be used in place of river sand in concrete.
On the basis of the comparison between previous studies by Siddesha H. [26] and the present study, it was observed that the decrease in TS of specimens WSC-10% was 27.37% (present study), whereas; in the specimen with only ceramic sand (10%) as a replacement (no ceramic aggregate and cement) was 28.57% [26].
For WSC-20%, the TS was decreased by 32.52%, whereas the concrete with ceramic sand only (without ceramic powder & ceramic aggregate) was decreased by 33.33% [26].
This means that specimens containing SWC without AWC and CWC were found to have a higher reduction in TS than specimens containing all ceramic material in the same model.
3.3.3 Effect of SWC on the flexural strength (FS) of concrete, keeping 20% AWC and 10% CWC constant
From Chart 13, WSC-5% and WSC-10% showed an increment of 6.9% and 11%, respectively, in FS with respect to the reference model (WSC-0%) whereas, in specimens, WSC-15%, WSC-20% and WSC-30% the FS was found to show a decrement of 13.65%, 19.73%, and 25.98% respectively compared to the reference model (WSC-0%).
The obtained results of FS up to 10% replacement are consistently close to the findings of Reddy, M. V.et al. [27], who concluded the effect of ceramic sand on concrete flexural strength. On the basis of comparison between previous studies [27] and the present study, it was found that the specimens containing 10% SWC only was enhanced by 1.58% [27] whereas, in specimens containing 10% SWC along with 10% CWC and 20% AWC was increased by 11% (WSC-10%).
The obtained results of FS beyond 10% SWC replacement were found to be analogous to the findings of Siddesha H. [26], who studied the effect of ceramic sand on concrete flexural strength. By comparing previous studies to the current study, it was determined that the FS in specimens containing 20% SWC only was decreased by 25% [26] whereas, in specimens containing 10% SWC along with 10% CWC and 20%AWC was decreased by 19.73% (WSC-10%). On the other hand, another study conducted by Medina C. et al. [7] showed an increase in FS as the percentage of the fine aggregate replacement (ceramic sanitary) increased.
Ceramic fine aggregate concrete was able to achieve higher Flexural strength (up to 10% replacement) because of its higher early absorption capacity as well as the higher specific surface of the fine ceramic aggregate.
3.3.4 Effect of SWC on the combined flexural and torsional strength (FTS) of concrete, keeping 20% AWC and 10% CWC constant
The Ultimate Bending Stress (UBS) of WSC under torsion 243N.mm was found to vary from 7.25MPa (WSC-0%) to 4.5MPa (WSC-30%); under torsion, 254N.mm was found to vary from 6.75MPa (WSC-0%) to 4.25 MPa (WSC-30%) and; under torsion 264N.mm was found to vary from 6.25MPa (WSC-0%)to 4 MPa (WSC-30%) as shown in Chart 14.
The UBS of WSC-10% was 107%, 100%, and 100% greater than the reference model for torsion 243N.mm, 254N.mm and 265N.mm respectively. These ultimate bending strength increases can be described by the filling effect of the ceramic waste sand.
According to Nayana A. M. et al. [28], the microstructure investigation reveals that the mortar mixed with ceramic waste sand has fewer pores, improving flexural strength and durability.
Finally, on the basis of Phase 3 results, 10% Waste Ceramic Sand (SWC), 10% Waste Ceramic Cement (CWC) and 20% Waste Ceramic Aggregate (AWC) were adopted as the optimal replacement percentage for sand, cement, and natural coarse aggregate, respectively named Waste Ceramic Optimal Concrete (WOC).
2.4.3 Microstructure Analysis
The analyses of SEM and EDS intended to investigate the morphological properties of Plain concrete(pc) and waste ceramic optimal concrete (WOC) containing 10 % ceramic cement, 10 % ceramic sand and 20% ceramic aggregate, as shown in figs 8,9 and 10. The PC sample is selected as a reference model; the WOC sample is selected based on the optimal performance of each group of ceramic replacements. All the selected samples have taken from failed samples in a compressive strength test.
The SEM micrographs of PC have shown clear visibility of hexagonal plate-shaped crystals of CH and C-S-H gels. The SEM micrographs have also shown a presence of hydrous calcium-aluminate hydrate characterized by a needle-like structure. Several voids, pores, mixed distribution of C-S-H and C-H gel and needle-like ettringite crystal with visible micro-cracks inside the structure have been detected, as shown in Figure 6.
The result of the PC has shown a ceramic particle reacted with prism-shaped columns, which mainly consisted of Al and Si, which means that both components are the main chemical reaction that forms this binder, and this agrees with the conclusion of Siddique and Mehta [35].
The SEM micrographs of WOC have shown a little porous on the surface and a small scale of possible micro-cracks. It has been noticed an amount of C-S-H gel appears to have decomposed into finer particles, remains of calcium hydroxide crystals. The test has also shown an appearance of small round particles as unreacted cement and a sign of feldspar covering the surface area, which correlates in a positive way with the strength behaviour under compression [34], as shown in Figure 7.
It becomes difficult to fill the inter-granular space between the grains when the ceramic material is added to the mixture. Therefore, the addition of the spherical particles (ceramic waste) can work as a lubricant, reducing the inside friction among the grain. In addition, it was detected by Senff et al.[33] Due to orientation and settlement, the packing of particles formed from spherical grain is superior for isotropic structure.
The experiment results have shown an improvement in the internal microstructure of cement paste due to the addition of ceramic material, which acts as a promoter and filler amid hydration of pozzolanic and cement with free C-H. Moreover, the WOC samples have revealed a more uniform and filled structure in comparison to PC. It is noteworthy that C-S-H gel improved in the form of a ‘ stand-alone’ cluster, joined together with needle hydrates because of the deposition of Ca (OH)2 crystal, which extends in the OPC paste. Likewise, a dense and compacted structure was shown in the microstructure of cement pastes containing ceramic waste that fills fine pores. The Ca (OH)2 or C-H crystal has been reduced due to the ceramic cement pozzolanic action with free portlandite to produce new C-S-H.
Nanoparticles were observed in the concrete to perform as an activator and accelerate the cement hydration process. They also perform as an important part of cement paste during the formation of the size of Ca (OH) 2 crystal [45]. The SEM micrographs show some ceramic particles readily react with C-H to produce a new form of C-S-H, enhancing the concrete strength. The SEM micrographs have shown a black and white mass which is C-S-H gel spread on the aggregate and performed as a binder in concrete. All mixes have needle hydrates, but the degree of crystallisation varies from mix to mix.
Energy-dispersive spectroscopy (EDS) was used to investigate the microchemistry of the selected samples. It has been used to obtain a localized chemical analysis using an X-ray spectrum emitted through a solid sample bombarded with electrons focused beam.
When using the X-rays, distinct positions along the line are detected, while the SEM electron rays scan across the specimen along a predetermined line across the specimen. A detailed analysis of the X-ray energy spectrum is provided at each position.A plot of the relative elemental concentration along the line for each element versus is obtained. The elemental weight of the PC and WOC specimens is shown in Figure 8 & 9 . The detected main elements of PC concrete are C,O,F,Mg,Al,Si,Ca and Fe and C,O,F,Mg,Al,Si,S,K,Ca,Ti,Fe,Zr and Au for WOC concrete as sown in the Table 6 & 7.
Table 6 PC element
Standard
|
Element
|
Weight%
|
Atomic%
|
CaCO3
|
C
|
8.77
|
14.26
|
SiO2
|
O
|
52.67
|
64.29
|
MgF2
|
F
|
0.9
|
0.73
|
MgO
|
Mg
|
0.60
|
0.47
|
Al2O3
|
Al
|
2.05
|
1.48
|
SiO2
|
Si
|
9.56
|
6.64
|
Wollastonite
|
Ca
|
25.41
|
12.38
|
Fe
|
Fe
|
0.64
|
0.22
|
|
Totals
|
100.00
|
|
Table 7 WOC element
Standard
|
Element
|
Weight%
|
Atomic%
|
CaCO3
|
C
|
8.12
|
13.64
|
SiO2
|
O
|
51.72
|
65.27
|
MgF2
|
F
|
5.36
|
5.69
|
MgO
|
Mg
|
0.48
|
0.4
|
Al2O3
|
Al
|
1.43
|
1.07
|
SiO2
|
Si
|
3.97
|
2.85
|
FeS2
|
S
|
0.2
|
0.12
|
K
|
MAD-10 Feldspar
|
0.57
|
0.29
|
Ca
|
Wollastonite
|
25.41
|
12.38
|
Ti
|
Ti
|
0.03
|
0.01
|
Fe
|
Fe
|
0.56
|
0.2
|
Zr
|
Zr
|
0.4
|
0.09
|
Au
|
Au
|
8.33
|
0.85
|
|
Totals
|
100.00
|
|