Utilizing binary ternary blended metakaolin and ground pond ash for reduced carbon footprint emissions and improved mechanical properties in concrete

ABSTRACT

In this empirical investigation, the effect of four concrete mixtures was examined, namely, control concrete (CC), binary blended metakaolin concrete (BBMC), binary blended pond ash concrete (BBPC), and ternary blended metakaolin and pond ash concrete (TBMPC). In this study, a total of 288 specimens were manufactured, including CC, BBMC, BBPC, and TBMPC, which were subjected to curing for 28 and 90 days. The mix compositions used were in a ratio of 1:1.75:2.22, with a water-binder ratio of 0.44. The study delved into an extensive examination of both the fresh and mechanical properties of these concrete mixtures. Additionally, the sustainability analysis for all mix proportions were computed. The results demonstrate significant enhancements in compressive strength (f_cs), split tensile strength (f_sts) and flexural strength (f_fs) with an increase of 17.82% and 19.81%, 12.32% and 13.50%, 13.34% and 14.39%. These improvements were observed specifically in the M₆P₆ mix, composed of 88% PC, 6% MK, and 6% PA. In the context of sustainability analysis, the PA₂₀ mix displayed the lowest carbon footprint emissions, measured at 351 kgCO₂/m³. On the other hand, the MK₆PA₆ mix demonstrated the highest CO₂ intensity, with values of 0.095 MPa/kgCO₂·m³ and 0.114 MPa/kgCO₂·m³.

Keywords
Metakaolin; Pond ash; Fresh properties; Mechanical properties; Carbon footprint emissions

1. INTRODUCTION

Globally, concrete plays a pivotal role and most extensively utilized construction material. It excels as the superior construction material when contrasted with alternatives like brick, wood, steel, and others [¹]. The widespread use of concrete has adverse effects on the ecosystem. This is primarily attributed to the presence of cement in concrete, leading to the release of substantial amounts of carbon emissions. In India, the cement sector is projected to generate approximately 390 MTPA by the end of 2023. Anticipated growth in Indian cement demand for 2024 suggests an increase of around 9%, bringing it to 425 MT [²]. According to NAQI and JANG [³], nearly half of the global cement production is dedicated to serving the concrete production industry, while the remaining portion finds application in various uses, including masonry mortar and filling cracks in concrete elements. A noteworthy observation that with the escalating demand and the anticipated growth in cement production in the years ahead, it becomes imperative to explore alternative materials that can effectively substitute cement. This strategic shift is a critical measure in the endeavor to mitigate CO₂ emissions [⁴, ⁵]. Conversely, there exists an immense global waste output, amounting to millions of tons, which holds the potential for recycling as a binder or aggregate element within concrete. This endeavor aims to curtail the carbon footprint of concrete production [⁶]. These waste materials encompass industrial byproducts [⁷,⁸,⁹,¹⁰,¹¹] and agricultural byproducts [¹²,¹³,¹⁴,¹⁵,¹⁶].

Metakaolin (MK) is a pozzolan obtained from kaolin, created through a process involving the heating clay rich in kaolinite to temperatures ranging from 500 °C to 800 °C [¹⁷]. MK is composed of varying proportions of alumina and silica, typically in the ranges of 40% to 45% for alumina and 50% to 55% for silica. Typically, it presents as a colorless powder with an average size of 2 μm diameter, making it significantly finer than particles in cement [¹⁸]. MK is widely recognized for its positive impact on enhancing the efficacy of concrete. This improvement is achieved through its reaction with existing portlandite to create secondary formation of calcium silicate hydrate gel and several other hydrates gel [¹⁹]. This observation has also been documented in [²⁰,²¹,²²,²³]. Consequently, utilizing metakaolin is a more cost-effective choice compared to using silica fume [²⁴]. Most studies that have investigated the use of MK as a pozzolan in concrete have shown significant improvements when used as a replacement [²⁵,²⁶,²⁷]. The incorporation of 15% MK leads to significant improvements in concrete [²⁸].

Moreover, the majority of research on the utilization of pond ash (PA) has primarily centered on its application as fine aggregates in concrete, mainly because of its coarser texture [^{29 30},³¹,³²]. Nevertheless, to achieve more substantial reductions in the carbon footprint of concrete, a greater emphasis should be placed on replacing cement, which stands out as the component with the highest carbon footprint in concrete production [³³]. Consequently, the process involves pulverizing PA through the use of a pulverizer machine to yield a finer product, known as finer PA, distinguished by its high silicate and aluminate content [³⁴, ³⁵]. As a result, the transformation of coarser PA into finer PA and its subsequent incorporation as a pozzolan is anticipated to lead to an overall reduction in the environmental impact of concrete [³⁶, ³⁷]. Based on the KURAMA and KAYA [³⁸] findings, it was deduced that incorporating PA as a replacement material for cement, up to a 10% dosage, can enhance the concrete attributes. Consequently, it holds potential for utilization in the concrete sector.

Ternary blended concrete (TBC), whether incorporating MK with fly ash [³⁹], MK with silica fume [⁴⁰], MK with rice husk ash [⁴¹], MK with GGBS [⁴²], MK with sugarcane bagasse ash [⁴³], MK with Alccofine [⁴⁴], MK with Nano silica [⁴⁵], MK with dolomite powder [⁴⁶], demonstrates enhanced mechanical properties and decreased porosity. Notably, the reduction in pore spaces in TBC becomes more pronounced with increasing dosages of pozzolans after 28 days.

In the existing body of research, the majority of scholars have directed their investigations towards the effects of binary blended metakaolin concrete (BBMC) and binary blended pond ash concrete (BBPC). Surprisingly, there has been a notable absence of investigation into the ternary blended metakaolin and pond ash concrete (TBMPC). As a result, the primary goal of this research endeavor is to investigate the impact and carbon footprint of BBMC, BBPC, and TBMPC mixtures.

2. MATERIALS AND EXPERIMENTAL PROGRAM

2.1. Materials

Pond ash (PA) was collected from Mettur, Tamil Nadu, India, was air-dried for 48 hours. It was then sifted through a 300-micron sieve to eliminate larger particles and finely ground with a pulverizer operating at 960 rpm. Meanwhile, metakaolin (MK) is a naturally occurring pozzolanic material sourced from Chennai, Tamil Nadu, India. Additionally, 53-grade Portland cement (PC) was purchased from a local supplier, meeting the BIS 12269–2013 [⁴⁷]. Figures 1 and 2 depict the scanning electron microscope (SEM) images of MK and PA, respectively.

Figure 1
SEM image of MK.

Figure 2
SEM image of PA.

In Figure 1, illustrates angular, and platy particle structure. In Figure 2, on the other hand, the spherical structure of PA has been disrupted and transformed into angular, fragmented particles. The PC served as the binding material for the entire experimental work. The physical properties and oxide composition of PC, MK, and PA is detailed in Table 1.

Table 1
Physical properties and oxide composition of PC, MK and PA.

ELEMENTS	OXIDES (%)
	PC	MK	PA
SiO2	21.9	50.11	51.4
Al2O3	5.63	43.08	29.2
Fe2O3	4.58	0.60	7.09
CaO	63.2	0.25	0.89
MgO	1.35	0.08	0.87
SO3	1.29	0.78	4.28
LOI	1.3	7.35	4.01
Specific gravity	3.14	2.60	2.17
Specific surface area (m2/kg)	302	2000	398

As per BIS: 3812–2013 [⁴⁸], the chemical constituents of MK and PA predominantly consist of SiO₂, Al₂O₃, and Fe₂O₃, with their sum exceeding 70.0%, categorizing them as pozzolanic materials. The LOI values for MK and PA were determined to be 7.35 and 4.01, respectively. Manufactured sand (M-sand) and coarse aggregate (CA) were sourced from a local supplier, with M-sand serving as the fine aggregates and the CA being used for the research work, possessing a size of 20 mm. The properties of M-sand and CA can be found in Table 2. In addition, potable water was employed for both the mixing and curing processes in this investigative study.

Table 2
Properties of the M-sand and coarse aggregate.

AGGREGATE	PROPERTIES
	FINENESS MODULUS	SPECIFIC GRAVITY	ABSORPTION (%)	BULK DENSITY (kg/m3)
M-sand	2.46	2.71	1	1850
Coarse aggregate	6.73	2.69	0.5	1695

2.2. Experimental program

This research work encompasses four types of concrete: control concrete (CC), binary blended metakaolin concrete (BBMC), binary blended pond ash concrete (BBPC), and ternary blended metakaolin and pond ash concrete (TBMPC). These concrete types were subjected to testing for slump and mechanical properties. In the case of CC, the mixture consisted solely of PC. BBMC mixtures were prepared with 4–20% of MK, BBPC mixes included 4–20% of PA, and TBMPC mixes integrated various proportions of both MK and PA. For this study, the concrete specimens were formulated using a mix composition of 1:1.75:2.22 at a water-cement ratio of 0.44. The specifics of the mix proportions are outlined in Table 3.

Table 3
Mix proportion of CC, BBMC, BBPC and TBMPC.

MIX DETAIL	BINDER CONTENT (%)			W/B RATIO	MATERIALS (kg/m3)
	OPC	MK	PA		OPC	MK	PA	FA	CA	W
CC	100	0	0	0.44	448	0	0	788	996	197
MK4	96	4	0		430.08	17.92	0
MK8	92	8	0		412.16	35.84	0
MK12	88	12	0		394.24	53.76	0
MK16	84	16	0		376.32	71.68	0
MK20	80	20	0		358.4	89.6	0
PA4	96	0	4		430.08	0	17.92
PA8	92	0	8		412.16	0	35.84
PA12	88	0	12		394.24	0	53.76
PA16	84	0	16		376.32	0	71.68
PA20	80	0	20		358.4	0	89.6
MK2PA2	94	2	2		430.08	8.96	8.96
MK4PA4	91	4	4		412.16	17.92	17.92
MK6PA6	88	6	6		394.24	26.88	26.88
MK8PA8	85	8	8		376.32	35.84	35.84
MK10PA10	82	10	10		358.4	44.8	44.8

The concrete samples were cast and demolded after 24 hours of ambient curing, then immersed in water for 28 and 90 days before undergoing testing at the concrete lab. The study necessitated the evaluation of mechanical properties using a total of 288 specimens, as outlined in Table 4.

Table 4
Details of the specimens.

MIX DETAIL	COMPRESSIVE STRENGTH (fcs)		SPLIT TENSILE STRENGTH (fsts)		FLEXURAL STRENGTH (ffs)		SUB TOTAL	TOTAL
	28 DAYS	90 DAYS	28 DAYS	90 DAYS	28 DAYS	90 DAYS
CC	3	3	3	3	3	3	18	288
MK4	3	3	3	3	3	3	18
MK8	3	3	3	3	3	3	18
MK12	3	3	3	3	3	3	18
MK16	3	3	3	3	3	3	18
MK20	3	3	3	3	3	3	18
PA4	3	3	3	3	3	3	18
PA8	3	3	3	3	3	3	18
PA12	3	3	3	3	3	3	18
PA16	3	3	3	3	3	3	18
PA20	3	3	3	3	3	3	18
MK2PA2	3	3	3	3	3	3	18
MK4PA4	3	3	3	3	3	3	18
MK6PA6	3	3	3	3	3	3	18
MK8PA8	3	3	3	3	3	3	18
MK10PA10	3	3	3	3	3	3	18

2.3. Test methods

2.3.1. Slump test

The fresh properties of the CC, BBMC, BBPC and TBMPC were assessed by means of a slump test. The test was performed immediately after the mixing process, as depicted in Figure 3a. The recorded slump value for all the mixtures were measured in millimeters (mm).

Figure 3
Experimental tests setup. (a) Slump test (b) f_cs test (c) f_sts test (d) f_fs test.

2.3.2. Mechanical properties

The mechanical properties of CC, BBMC, BBPC, and TBMPC were assessed in accordance with Indian regulations BIS 516–2004 [⁴⁹], as detailed in Table 5.

Table 5
The mechanical testing standards.

FRESH AND MECHANICAL PROPERTIES	DIMENSIONS	TESTING AGE	INDIAN STANDARDS CODE PROVISION
fcs test	150 × 150 × 150 mm	28 and 90 days	BIS: 516-2004 [49]
fsts test	150 × 300 mm (Ф × L)	28 and 90 days
Ffs test	500 × 100 × 100 mm (L × B × D)	28 and 90 days

f_cs test for CC, BBMC, BBPC, and TBMPC at 28 and 90 days was determined using a universal testing equipment with a 3000 kN capacity, as shown in Figure 3b. Likewise, f_sts test for these mixtures at 28 and 90 days was evaluated using the same 3000 kN capacity universal testing equipment, as shown in Figure 3c. Furthermore, the f_fs test for CC, BBMC, BBPC, and TBMPC were conducted at 28 and 90 days, employing a flexural testing equipment with a 100 kN capacity, as depicted in Figure 3d. The measured values for all mechanical properties of these mixtures were expressed in megapascals (MPa).

3. RESULT AND DISCUSSION

3.1. Slump test

Figure 4 illustrates the slump value of BBMC mixes with 4–20% MK substituting for PC. The optimal slump, which is a measure of the mixtures fluidity, was observed to be 87 mm for the CC mix. However, for BBMC mixes with 20% of PC replaced by MK, the slump was significantly reduced to 41 mm. This decrease in slump can be attributed to the high reactivity and larger surface area of MK than PC. This perspective was associated with DHINAKARAN et al. [⁵⁰], in which the workability of concrete declined as the percentage of PC replaced with MK increased. Similarly, TIWARI and BANDYOPADHYAY [⁵¹] observed that the finer texture of the pozzolan is crucial in maintaining the cohesiveness of the concrete mix and counteracting the decrease in workability as the MK content increases in the concrete. Similarly, the slump of BBPC mixes, with 4–20% of PC replaced with PA, is illustrated in Figure 4. The highest slump, measured at 87 mm, was seen in the CC mix, while the lowest slump was found to be 51 mm, occurring in the BBMPC with a combination of PA₂₀ mix. This variation can be ascribed to the increased fineness of PA particles. This observation was linked to KHAN and GANESH [⁵²], where the inclusion of PA and a gradual content increase of PA was associated with reduced concrete slump.

Figure 4
The slump value of CC, BBMC, BBPC and TBMPC mixes.

The alteration of the initial spherical particle shape due to grinding and the subsequent increase in fineness were the primary factors contributing to the decline in concrete workability [⁵³]. Moreover, the workability of TBMPC mixtures, incorporating various percentages of MK and PA, is depicted in Figure 4. The highest slump, measured at 87 mm, was noted in the CC mix, whereas the lowest slump, recorded at 31 mm, occurred in the TBMPC with a combination of MK₁₀PA₁₀ mix. The findings suggest that the slump value of TBMPC diminishes with a higher proportion of MK and PA substituting for PC. This slump reduction can be traced back to the porous qualities of MK and PA particles, which, unlike PC, absorb more water as the MK and PA content in the mix rises. Similarly demonstrated a notable slump decrease as PC was replaced with MK, SCBA, and MHA in the mixture [⁵⁴].

3.2. Compressive strength (f_cs)

Figure 5 shows BBMC mixtures with different MK percentages replacing PC, assessing their f_cs at 28 and 90 days. The highest f_cs, 35.25 MPa at 28 days and 42.93 MPa at 90 days, was achieved with 12% of PC replaced by MK. In contrast, the lowest f_cs, 29.43 MPa at 28 days and 36.73 MPa at 90 days, was observed with 20% of MK used as a PC replacement material in concrete. It is evident that the f_cs is enhanced when using MK up to 12%, but further increases in MK content lead to a reduction in f_cs. This perspective is supported by MOGHADDAM et al. [⁵⁵], where an increase in f_cs was noted with PC replacement by MK, up to 15%, at 28 days. Similarly, an enhancement in f_cs with a replacement of up to 10% of PC with MK in the mixture [⁵⁶]. Figure 5 illustrates BBPC mixtures with varying proportions of PA used as a substitute for PC to assess their f_cs at both 28 and 90 days. The highest f_cs, reaching 34.15 MPa at 28 days and 41.52 MPa at 90 days, was achieved with 12% of PC replaced by PA.

Figure 5
The f_cs of CC, BBMC, BBPC and TBMPC mixes.

Conversely, the lowest f_cs, measuring 28.82 MPa at 28 days and 35.47 MPa at 90 days, was observed in a mix with a 20% of PA. It’s evident that the f_cs is enhanced when incorporating PA up to 12%, but further increases in PA content lead to a reduction in f_cs. This conclusion is supported by ARGIZ et al. [⁵⁷], where an increase in f_cs was observed with the replacement of up to 10% of PC with PA, both at 28 and 90 days. Similarly, An enhancement in f_cs with the substitution of up to 10% of PC with PA in the mixture [⁵⁸]. Moreover, Figure 5 depicts TBMPC mixtures, incorporating varying proportions of MK and PA, in order to evaluate their f_cs at both 28 and 90 days. The highest f_cs, measuring 36.23 MPa at 28 days and 43.63 MPa at 90 days, was achieved in the MK₆PA₆ mix, while the lowest f_cs, at 30.17 MPa for 28 days and 37.02 MPa for 90 days, was recorded in the MK₁₀PA₁₀ mix. It is evident that f_cs improve with the use of PC replacement in the MK₆PA₆ mixture, but subsequently declines. The enhancement in strength observed at 28 and 90 days can be attributed to the large proportions of silica content found in both MK and PA. These materials undergo a reaction with the excess portlandite, resulting in the formation of secondary C-S-H gel. This substance is known for its contribution to the increased strength of concrete. However, as more MK and PA are introduced into the concrete mixture, the strength starts to diminish. This decline is mainly attributed to MK and PA diluting the PC, leading to a decrease in available portlandite for secondary product. A similar approach was tested by BHEEL et al. [⁵⁹], revealing an increase in f_cs when replacing PC with 10% of both MK and GGBS in the mixture at 28 days.

3.3. Splitting tensile strength (f_sts) and flexural strength (f_fs)

Figures 6 and 7 illustrate BBMC mixtures with different MK percentages replacing PC, with a focus on evaluating their f_sts and f_fs at 28 and 90 days. The highest f_sts and f_fs, reaching 3.97 MPa and 5.44 MPa for 28 days, and 4.26 MPa and 5.78 MPa for 90 days, respectively, was achieved with 12% of PC replaced by MK. Conversely, the lowest strength, measuring 3.52 MPa for f_sts strength and 4.78 MPa for f_fs at 28 days, and 3.77 MPa for f_sts and 5.13 MPa for f_fs at 90 days, was observed in the mix with 20% MK. It is evident that both f_sts and f_fs improve when utilizing MK up to 12% as a PC replacement in the mixture, but with further additions of MK in concrete, both strengths start to decline. This viewpoint aligns with the findings of KHATIB and CLAY [⁶⁰], where they observed an increase in f_sts and f_fs with PC replacement by MK, up to 10%, followed by a decrease after 28 days. The both f_sts and f_fs were enhanced when incorporating various dosages of MK as a pozzolan in concrete [⁶¹]. Similarly, Figures 6 and 7 depict BBPC mixtures with varying proportions of PA as a substitute for PC, focusing on evaluating their f_sts and f_fs at both 28 and 90 days. At 28 days, the highest f_sts and f_fs, reaching 3.94 MPa and 5.38 MPa, and at 90 days, 4.14 MPa and 5.72 MPa, were achieved with 12% of PA. In contrast, at 28 days, the lowest f_sts and f_fs was measured at 3.34 MPa and 4.83 MPa and at 90 days, the lowest f_sts and f_fs was assessed at 3.78 MPa and 5.06 Mpa with 20% of PA. It’s noteworthy that the use of PA enhances both f_sts and f_fs, particularly up to 12%. Similarly, ARGIZ et al. [⁶²] reported an improvement in both f_sts and f_fs with the substitution of up to 10% of PC with PA. Moreover, Figures 6 and 7 depicts TBMPC mixtures, incorporating varying proportions of MK and PA, in order to evaluate their f_sts and f_fs at both 28 and 90 days. MK₆PA₆ achieved the highest f_sts and f_fs at both 28 and 90 days, with values reaching 4.01 MPa and 5.52 MPa at 28 days, and 4.37 MPa and 5.88 MPa at 90 days. In contrast, MK₁₀PA₁₀ exhibited the lowest f_sts and f_fs values, measuring 3.48 MPa and 4.81 MPa at 28 days, and 3.76 MPa and 5.10 MPa at 90 days. It is evident that the f_sts and f_fs is enhanced with the use of PC replacement in the MK₆PA₆ mixture, but subsequently declines. The increase in strength observed at 28 and 90 days for BBMC, BBPC, and TBMPC can be attributed to the pozzolanic activity of MK and PA, which were quite similar, leading to the formation of an additional C-S-H gel. the reduction in strength can be attributed to the slower reaction of MK and PA than hydration of PC. This difference in reaction rates is due to the coarser particle sizes and higher levels of LOI in MK and PA than PC. This result aligns with TURKMEN and FINDIK [⁶³], where using slag and metakaolin as PC replacements, up to 10%, enhanced concrete both f_sts and f_fs.

Figure 6
The f_sts of CC, BBMC, BBPC and TBMPC mixes.

Figure 7
The f_fs of CC, BBMC, BBPC and TBMPC mixes.

3.4. f_cs and f_sts relationship

A regression equation has been established to relate f_cs to f_sts of BBMC, BBPC and TBMPC at 28 days. This equation, derived through a power regression, is represented by equations. (1), (2) and (3), is visualized in Figure 8.

Figure 8
Relationship between f_cs and f_sts of BBMC, BBPC and TBMPC.

For BBMC

(1) $${\text{f}}_{\text{sts}}=0.392{\left({\text{f}}_{\text{cs}}\right)}^{0.646}{\mathrm{R}}^{\text{2}}=0.943$$

For BBPC

(2) $${\text{f}}_{\text{sts}}=0.198{\left({\text{f}}_{\text{cs}}\right)}^{0.839}{\mathrm{R}}^{\text{2}}=0.923$$

For TBMPC

(3) $${\text{f}}_{\text{sts}}=0.299{\left({\text{f}}_{\text{cs}}\right)}^{0.720}{\mathrm{R}}^{\text{2}}=0.940$$

This association is consistent with the guidelines provided by ACI [⁶⁴], NEVILLE [⁶⁵], and CEB-FIP [⁶⁶], which are detailed in equations (4), (5) and (6), correspondingly.

(4) $${\text{f}}_{\text{sts}}=0.56{\left({\text{f}}_{\text{cs}}\right)}^{0.5}$$

(5) $${\text{f}}_{\text{sts}}=0.23{\left({\text{f}}_{\text{cs}}\right)}^{0.67}$$

(6) $${\text{f}}_{\text{sts}}=0.30{\left({\text{f}}_{\text{cs}}\right)}^{0.67}$$

Table 6 presents both the experimental and theoretical results of f_sts, derived from equations (4), (5) and (6).

Table 6
Comparison of experimental & theoretical f_sts.

MIX ID	EXPERIMENTAL fsts		THEORETICAL fsts, MPa			EXPERIMENT/THEORETICAL RATIO OF fsts
	FCS	FSTS	EQUATION (4)	EQUATION (5)	EQUATION (6)	EQUATION (4)	EQUATION (5)	EQUATION (6)
BBMC
CC	30.75	3.57	3.10	2.28	2.97	1.15	1.57	1.20
MK4	32.85	3.69	3.20	2.38	3.11	1.15	1.55	1.19
MK8	34.42	3.84	3.28	2.46	3.21	1.17	1.56	1.20
MK12	35.25	3.97	3.324	2.50	3.26	1.19	1.59	1.22
MK16	32.64	3.76	3.20	2.37	3.09	1.18	1.59	1.22
MK20	29.43	3.52	3.03	2.21	2.89	1.16	1.59	1.22
BBPC
CC	30.75	3.57	3.10	2.28	2.97	1.15	1.57	1.20
PA4	32.31	3.62	3.18	2.36	3.07	1.14	1.53	1.18
PA8	33.82	3.76	3.25	2.43	3.17	1.16	1.55	1.19
PA12	34.15	3.94	3.27	2.44	3.19	1.20	1.61	1.24
PA16	31.65	3.6	3.15	2.32	3.03	1.14	1.55	1.19
PA20	28.82	3.34	3.00	2.18	2.85	1.11	1.53	1.17
TBMPC
CC	30.75	3.57	3.10	2.28	2.97	1.15	1.57	1.20
MK2PA2	33.26	3.72	3.22	2.40	3.13	1.16	1.55	1.19
MK4PA4	35.01	3.89	3.31	2.49	3.24	1.18	1.56	1.20
MK6PA6	36.23	4.01	3.37	2.54	3.32	1.19	1.58	1.21
MK8PA8	33.45	3.66	3.23	2.41	3.15	1.13	1.52	1.16
MK10PA10	30.17	3.48	3.07	2.25	2.94	1.13	1.55	1.18

For BBMC, BBPC, and TBMPC, the ratio between experimental and predicted f_sts values is close to 1, except for [⁶⁵] equation (5). These findings are consistent with the earlier results [⁶⁶].

3.5. f_cs and f_fs relationship

A regression equation has been formulated to establish a connection between the f_cs and f_fs of BBMC, BBPC, and TBMPC at the 28 days. This equation, derived via power regression, is delineated as equations (7), (8) and (9), and graphically represented in Figure 9.

Figure 9
Relationship between f_cs and f_fs of BBMC, BBPC and TBMPC.

For BBMC:

(7) $${\text{f}}_{\text{fs}}=0.388{\left({\text{f}}_{\text{cs}}\right)}^{0.741}{\mathrm{R}}^{\text{2}}=0.971$$

For BBPC:

(8) $${\text{f}}_{\text{fs}}=0.562{\left({\text{f}}_{\text{cs}}\right)}^{0.636}{\mathrm{R}}^{\text{2}}=0.907$$

For TBMPC:

(9) $${\text{f}}_{\text{fs}}=0.366{\left({\text{f}}_{\text{cs}}\right)}^{0.757}{\mathrm{R}}^{\text{2}}=0.970$$

Equations (7), (8), and (9) outlines the connection between the f_cs and f_fs of BBMC, BBPC, and TBMPC. These equations are consistent with the standards set by JUKI et al. [⁶⁷], LEGERON and PAULTRE [⁶⁸], and BURG and OST [⁶⁹], represented by equations (10), (11) and (12), respectively.

(10) $${\text{f}}_{\text{fs}}=0.94{\left({\text{f}}_{\text{cs}}\right)}^{0.5}$$

(11) $${\text{f}}_{\text{fs}}=0.517{\left({\text{f}}_{\text{cs}}\right)}^{0.5}$$

(12) $${\text{f}}_{\text{fs}}=1.03{\left({\text{f}}_{\text{cs}}\right)}^{0.5}$$

Table 7 presents both the experimental and theoretical results of f_fs, derived from equations (10), (11) and (12).

Table 7
Comparison of experimental & theoretical f_fs.

MIX ID	EXPERIMENTAL ffs		THEORETICAL ffs, MPa			EXPERIMENT/THEORETICAL RATIO OF ffs
	fcs	ffs	EQUATION (10)	EQUATION (11)	EQUATION (12)	EQUATION (10)	EQUATION (11)	EQUATION (12)
BBMC
CC	30.75	4.87	5.21	2.87	5.71	0.93	1.70	0.85
MK4	32.85	5.24	5.38	2.96	5.90	0.97	1.77	0.89
MK8	34.42	5.32	5.51	3.03	6.04	0.97	1.76	0.88
MK12	35.25	5.44	5.58	3.07	6.12	0.97	1.77	0.89
MK16	32.64	5.17	5.37	2.95	5.88	0.96	1.75	0.88
MK20	29.43	4.78	5.10	2.80	5.59	0.94	1.71	0.86
BBPC
CC	30.75	4.87	5.21	2.87	5.71	0.93	1.70	0.85
PA4	32.31	5.16	5.34	2.94	5.85	0.97	1.76	0.88
PA8	33.82	5.25	5.46	3.01	5.99	0.96	1.74	0.88
PA12	34.15	5.38	5.49	3.02	6.02	0.98	1.78	0.89
PA16	31.65	5.1	5.28	2.91	5.79	0.97	1.75	0.88
PA20	28.82	4.83	5.04	2.78	5.53	0.96	1.74	0.87
TBMPC
CC	30.75	4.87	5.21	2.87	5.71	0.93	1.70	0.85
MK2PA2	33.26	5.29	5.42	2.98	5.94	0.98	1.78	0.89
MK4PA4	35.01	5.36	5.56	3.06	6.09	0.96	1.75	0.88
MK6PA6	36.23	5.52	5.65	3.11	6.20	0.98	1.77	0.89
MK8PA8	33.45	5.23	5.43	2.99	5.96	0.96	1.75	0.88
MK10PA10	30.17	4.81	5.16	2.84	5.66	0.93	1.69	0.85

In the case of BBMC, BBPC, and TBMPC, the ratio between experimental and predicted f_fs values is close to 1, with the exception of [⁶⁸] equation (11). The R² values for these relationships align with those documented [⁶⁹].

3.6. Sustainability analysis

In this research study, a sustainability analysis was conducted for sixteen mixtures to evaluate the carbon footprint of CC, BBMC, BBPC, and TBMPC, as detailed in Table 8. The data on carbon footprint emission for all concrete components were sourced from existing literature, with the exception of PA. Lack of data on PA carbon footprint in the literature has led to the reliance on a few assumptions in determining the carbon footprint. PA was obtained from a nearby thermal power plant in Mettur. It was transported to the testing laboratory, which was approximately 62 km away, using a 1000 kg-capacity diesel lorry truck. The emissions factor for this transportation was 0.192 kgCO₂/km. It is estimated that approximately 225 kWh of electricity will be needed to dry and sieve the 1000 kg of PA, as indicated by [⁷⁵]. The emissions factor utilized is 0.521 kgCO₂ per kilowatt- hour, according to [⁷⁶] one kg of PA is estimated to have a carbon footprint of 0.129 kg by using these emission factor values.

Table 8
Carbon footprint emissions for CC, BBMC, BBPC and TBMPC.

MIX DETAIL	PC	MK	PA	FA	CA	W	TOTAL CARBON FOOTPRINT EMISSIONS (kgCO2/m3)
	kgCO2/kg/REFERENCES
	0.82 [70]	0.33 [71]	0.129 CURRENT STUDY ESTIMATE	0.0066 [72]	0.0408 [73]	0 [74]
CC	367	0	0	5	41	0	413
MK4	353	6	0	5	41	0	405
MK8	338	12	0	5	41	0	396
MK12	323	18	0	5	41	0	387
MK16	308	24	0	5	41	0	378
MK20	294	29	0	5	41	0	369
PA4	353	0	2	5	41	0	401
PA8	338	0	5	5	41	0	389
PA12	323	0	7	5	41	0	376
PA16	308	0	9	5	41	0	363
PA20	294	0	11	5	41	0	351
MK2PA2	353	3	1	5	41	0	403
MK4PA4	338	6	2	5	41	0	392
MK6PA6	323	9	3	5	41	0	381
MK8PA8	308	12	5	5	41	0	371
MK10PA10	294	15	8	5	41	0	363

Figure 10 displays the carbon footprint of CC, BBMC, BBPC, and TBMPC. The carbon footprint of BBMC is as follows: 405 kgCO₂/m³, 396 kgCO₂/m³, 387 kgCO₂/m³, 378 kgCO₂/m³, and 369 kgCO₂/m³. These values are lower than that of the CC, which is 413 kgCO₂/m³. However, the carbon footprint of BBPC is as follows: 401 kgCO₂/m³, 389 kgCO₂/m³, 376 kgCO₂/m³, 363 kgCO₂/m³, and 351 kgCO₂/m³. These values are lower than that of the CC, which is 413 kgCO₂/m³. Furthermore, the carbon footprint of TBMPC is as follows: 403 kgCO₂/m³, 392 kgCO₂/m³, 381 kgCO₂/m³, 371 kgCO₂/m³, and 363 kgCO₂/m³. These values are also lower than that of the CC, which is 413 kgCO₂/m³. The observations indicate that the reduction in carbon footprint is more pronounced in BBMC, BBPC, and TBMPC than control concrete.

Figure 10
Carbon footprint of CC, BBMC, BBPC, and TBMPC.

The sustainability analysis can also be evaluated with CO₂ intensity, calculated as the average 28-day f_cs of concrete divided by the total carbon footprint. The CO₂ intensity of BBMC, BBPC, and TBMPC was calculated and is depicted in Figure 11. At 28 days, the best CO₂ intensity was observed at 0.091 MPa/kgCO₂·m³ for the 12% PC replaced with MK mix, 0.090 MPa/kg CO₂·m³ for the 12% PA mix, and 0.095 MPa/kgCO₂·m³ for the MK₆PA₆ mix. These values are higher than that of the CC mix (0.074 MPa/kgCO₂·m³). At 90 days, the optimal CO₂ intensity was noted at 0.111 MPa/kgCO₂·m³ for the 12% PC replaced with MK mix, 0.110 MPa/kgCO₂·m³ for the 12% PA mix, and 0.114 MPa/kgCO₂·m³ for the MK₆PA₆ mix. These values are also higher than that of the CC mix (0.088 MPa/kgCO₂·m³). In a similar vein, at 28 days, the lowest CO₂ intensity was determined to be 0.079 MPa/kgCO₂·m³ for the 20% MK mix, 0.082 MPa/kgCO₂·m³ for the 20% PA mix, and 0.083 MPa/kgCO₂·m³ for the MK₁₀PA₁₀ mix. Meanwhile, at 90 days, the lowest CO₂ intensity was calculated as 0.099 MPa/kgCO₂·m³ for the 20% MK mix, 0.101 MPa/kgCO₂·m³ for the 20% PA mix, and 0.102 MPa/kgCO₂·m³ for the MK₁₀PA₁₀ mix. The observation suggests that the CO₂ intensity of BBMC, BBPC, and TBMPC improves as PC is replaced with MK and PA in concrete, up to 12%. However, with further additions, it begins to decrease.

Figure 11
CO₂ intensity of CC, BBMC, BBPC, and TBMPC.

4. CONCLUSIONS

The primary goal of this research endeavor is to investigate the impact and carbon footprint of BBMC, BBPC, and TBMPC mixtures. The experimental study led to the following conclusions:

1. The highest slump, measuring 87 mm, was observed for CC, while the lowest slump for BBMC and BBPC were 41 mm and 51 mm, respectively, at the MK₂₀ and PA₂₀ mix. Furthermore, the maximum slump was recorded at 87 mm for CC, and the minimum slump for TBMPC was 31 mm at the MK₁₀PA₁₀ mix.

2. The compressive strength values for CC were recorded at 30.75 MPa at 28 days and 36.61 MPa at 90 days. In the case of BBMC, at 28 days and 90 days, the Peak and lowest f_cs values were noted at 35.25 MPa and 29.43 MPa, 42.93 MPa and 36.73 MPa, with 12% of MK, and 20% of MK. For BBPC, at 28 days and 90 days, the Peak and lowest f_cs values were achieved at 34.15 MPa and 28.82 MPa, 41.52 MPa and 35.47 MPa, with 12% of PA, and 20% of PA. As for TBMPC, at 28 days and 90 days, the Peak and lowest f_cs values were attained at 36.23 MPa and 30.17 MPa, 43.63 MPa and 37.02 MPa, with MK₆PA₆ and MK₁₀PA₁₀ mixes. The findings indicate that the f_cs of BBMC, BBPC, and TBMPC improves when using PC replacement up to MK₁₂, PA₁₂, and MK₆PA₆ mixes. However, additional incorporations of these materials into concrete result in a strength decrease.

3. The f_sts values for CC were recorded at 3.57 MPa at 28 days and 3.85 MPa at 90 days. In the case of BBMC, at 28 days and 90 days, the highest and lowest f_sts values were measured at 3.97 MPa and 3.52 MPa, 4.26 MPa and 3.77 MPa, with 12% of MK, and 20% of MK. For BBPC, at 28 days and 90 days, the Peak and lowest f_sts values were achieved at 3.94 MPa and 3.34 MPa, 4.14 MPa and 3.78 MPa, with 12% of PA, and 20% of PA. As for TBMPC, at 28 days and 90 days, the highest and lowest f_sts values were attained at 4.01 MPa and 3.48 MPa, 4.37 MPa and 3.76 MPa, with MK₆PA₆ and MK₁₀PA₁₀ mixes. The pattern suggests that f_sts of BBMC, BBPC, and TBMPC exhibits improvement when utilizing PC replacement up to 12% with MK, PA, and MK₆PA₆ mixes. However, incorporating these materials in higher proportions within the concrete results in a subsequent reduction in f_sts.

4. The f_fs values for CC were noted as 4.87 MPa at 28 days and 5.14 MPa at 90 days. Regarding BBMC, at 28 days and 90 days, the Peak and lowest f_fs values were measured at 5.44 MPa and 4.78 MPa, 5.78 MPa and 5.13 MPa, with 12% of MK, and 20% of MK. For BBPC, at 28 days and 90 days, the highest and lowest f_fs values were achieved at 5.38 MPa and 4.83 MPa, 5.72 MPa and 5.06 MPa, with 12% of PA, and 20% of PA. Similarly, for TBMPC, at 28 days and 90 days, the highest and lowest f_fs values were attained at 5.52 MPa and 4.81 MPa, 5.88 MPa and 5.10 MPa, with MK₆PA₆ and MK₁₀PA₁₀ mixes. The trend suggests that the f_fs of BBMC, BBPC, and TBMPC experiences improvement when utilizing PC replacement up to 12% with MK, PA, and MK₆PA₆ mixes. However, introducing these materials in higher proportions within the concrete subsequently leads to a reduction in f_fs.

5. The R² value suggests a strong correlation between f_cs and f_sts, as well as between f_cs and f_fs, in BBMC, BBPC, and TBMPC at 28 days.

6. The carbon footprint of BBMC, BBPA, and TBMPC decreased with increasing PC replacement by MK and PA, either separately or combined in concrete.

7. The experimental findings suggest that for BBMC, using 12% MK, for BBPC, using 12% PA, and for TBMPC, using MK₆PA₆ mix yields optimal results for construction purposes.

5. ACKNOWLEDGMENTS

The authors wish to acknowledge Department of Civil Engineering, K.S. Rangasamy College of Technology, Namakkal, Tamil Nadu for the facility and support extended for the research work.

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Publication Dates

• Publication in this collection
  22 Mar 2024
• Date of issue
  2024

History

• Received
  27 Nov 2023
• Accepted
  22 Jan 2024