Elimination of global warming gas emissions by utilizing high reactive metakaolin in high strength concrete for eco-friendly protection

The manufacturing process of cement emits one metric ton of carbon dioxide greenhouse gas. Considering the situation reducing the gas emission without affecting cement production, industrial wastes like metakaolin (MK) can be partially replaced with cement due to high pozzolanic reactivity to arrive the high-strength concrete. This present examination attentions on the obtaining optimum percentage of metakaolin to be substituted for cement proportion and aims to determine the concrete sample’s mechanical characteristics, equivalent CO2 emissions, and energy factor for environmental advantages through comparison with metakaolin varied from 0% to 20% at 5% incremental rate was determined and compared with the conventional control mix. Concrete samples are tested at the periodical interval of 7, 14, and 28 days in addition results, 5% of metakaolin is the optimum percentage to be replaced for cement in concrete. The negative sign implies that replacing binder with MK gradually decreases energy requirements (−2.16% to −7.74%) as well as carbon dioxide emissions (−4.17% to −15.41%). The use of mineral admixture like high reactive metakaolin additional cementitious elements has a considerable effect and may have an impact on the creation of environmentally friendly, sustainable concrete. In conclusion, effective utilization of high reactive metakaolin in high-strength concrete leads to substantial cost, and reducing global gas emissions eventually reduces energy consumption and a notable decrease in environmental pollution.


Introduction
Advancement in solid waste management leads to the usage of alternate construction resources as an auxiliary to conventional resources like aggregates, cement, bricks, fine aggregate, coarse aggregate, ceramics, and timber. For protection, the ecological effects are being made for reprocessing dissimilar mineral wastes and effective utilization to produce resources that satisfy the basic requirement without affecting the environment.
The disposal of industrial waste has become a global challenge as a result of urbanization and technological advancements. In India, the country generates 160038.9 tons of solid waste trash per day (TPD), of which is handled. Totally, 29427.2 (18.4%) TPD is dumped in landfills, and 50655.4 (31.7%) TPD remains unaccounted. Consequently, the identification of cement substitutes had a significant impact on the construction industry working on sustainable construction practices and an approach to production to address environmental issues (Alonso and Themelis (2011), Kaza et al 2018, Rajesh (2019, Shahab and Anjum (2022)).
To achieve this high strength the water/cement ratio must be as low as possible without comprising the workability of concrete but lowering the water/cement ratio will consequence in less workable concrete. Adding superplasticizers can also be camouflaged to increase the workability for anticipated water content or decrease the proportioning of water for the required flowability of concrete in a fresh state. Mineral admixtures are utilized in high-grade concrete to increase mechanical strength. Dimension of structural components like beams Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. and columns are compacted subsequently reduced units are sufficient to transfer high loads. Since the dimension of members is compacted the charge for formworks is less as well as reduced cost of maintenance and repair. In bridge construction application of high-strength concrete develops unavoidable since longer simply supported spans with the least supports can be constructed and the construction of slabs and floors with compact sections is made likely conceivable (Annadurai et al 2014, Caldarone et al 2009.
In this context, cement manufacturers and researchers have considered using natural pozzolan or pozzolanic industrial waste and byproducts as cement replacement materials, such as fly ash, silica fume, powdered slag, rice husk, and metakaolin, as a significant method in sustainable and green concrete production technology to reduce the carbon footprint of Portland cement. Metakaolin is an amorphous, structured alumina-silicate with significant pozzolanic characteristics that is produced by calcining pure kaolinite clay at temperatures between 500°C and 800°C. According to the published literature, using metakaolin as a cement substitute in concrete at the right dosage enhances the material's mechanical properties, lowers its permeability and capillary water absorption value, and increases its durability (Kayali et al 2008, Wang et al 2016, Sakir et al 2020. Metakaolin is a clay-based mineral that is greater in appearance that is obligatory for treating amorphous alumino-silicate that makes it responsive to concrete (Rajesh Kumar et al (2016), Naik and Moriconi 2005). Additional binder through various percentages of fly-ash and metakaolin in the mix proportion by experimentation leads to low-cost concrete production and global gas discharges extermination (Anantha Lakshmi et al 2016, Surendra andRajendra 2016, Malagavelli et al 2018).
Experimental investigations remained accomplished through numerous proportions of metakaolin substituted with a binder in various mix grades and it was experiential that the mechanical properties of concrete were optimal at 15% additional by weight of cement. As the outcomes originate reassuring the consumption of metakaolin it can be pragmatic in bulky gage construction to reimburse the ecological and cost-effective improvements in the cement production and cement utilization (Nova 2013, Rao and. The workability was abridged while the inclusion of metakaolin was remedied with the usage of a superplasticizer (Narmatha and Felixkala (2016), Jagtap et al 2017, Hemanth et al 2017.
The addition of metakaolin by various percentages by weight of cement in mix designed as per IS 10262:2009 found that the basic characteristics of the concrete are determined at 15%, which provides an obligatory guarantee to use the metakaolin as a notable binder material having high pozzolanic properties replacement for cement in high-grade concrete. Thus, this alternative cementitious binder material will afford resolution for the ecological problems raised by the conservative cement utilization and manufacture (Sood et al 2014, Nivin et al 2015.
The impartial of the study is to determine the optimal replacement proportion of MK in the case of binder in mix proportion and determine the load-bearing characteristics of concrete mixed with MK by its various mechanical properties, equivalent CO 2 emission, energy factor and economic feasibility for environmental benefits were investigated experimentally.

Binder
In the present experimental investigation, the binder utilized in the mix is 53-grade OPC (IS 12269:1987). Initial examinations are done with the binder used for this experimental investigation and the characteristic tabulated in table 1.

Water
Potable tap water with a PH level of 6.5 to 7.5 is utilized for the concrete sample mix and curing of concrete sample.

Admixture
Superplasticizer-modified polycarboxylate ether was utilized for this present investigation.

Metakaolin
It is a clay-based mineral that is superior in physical and chemical characteristics that are mandatory for giving amorphous alumino-silicate that brands receptive to concrete. The metakaolin will react with the calcium hydroxide of the concrete component along the progression of hydration like the other conformist substitutes for pozzolanic materials. Figure 1 shows the sample of metakaolin mineral admixture. Based on life cycle analysis compared to conventional concrete when metakaolin used in concrete emits 445.9 kg of CO 2 eq. Reduction in CO 2 emission reduces energy consumption. Metakaolin (MK), Al 2 Si 2 O 7 is a highly amorphous dehydration product of kaolinite, Al 2 (OH)4Si 2 O 5 , which exhibits strong pozzolanic activity are given in equation (1)  Metakaolin (MK) is so fine, using it limits the concrete's workability, making the use of water reducers or airentraining admixtures necessary to obtain the appropriate workability. In order to keep the desired qualities, quality control must be increased. High-quality control must be constant to be effective (   3. Investigational methodology 3.1. Mix design As per the code of practice IS 10262 mix proportion for M50 concrete grade is prepared. Preparation of trail mix is done to appropriate the optimum percentage of modified polycarboxylate quantity to be added in concrete cubes to determine the compressive strength of concrete. The percentage of chemical admixture varies as 0.25%, 0.5%, 0.75%, and 1% by weight of cementitious materials. From the results, it was observed that without modified polycarboxylate the compressive strength was obtained at 52 N mm −2 . Similarly, 0.25% of modified polycarboxylate was increased by 12% and the other 0.5%, 0.75%, and 1% of modified polycarboxylate was decreased by 10%, 19%, and 24%. The maximum compressive strength is obtained from 0.25% of modified polycarboxylate when compare with other percentage variations of chemical admixtures. Hence the optimum percentage of 0.25% of modified polycarboxylate by weight of cementitious materials was added during the mixing of high-strength concrete specimens. Figure 2 shows the execution for the present research program.

Preparation of concrete Mix
Materials such as cement, Fine aggregate, and Coarse aggregate are batched by their weight and utilized in the concrete. Individual volume of materials to be mixed is as per concrete mix design. The chosen material is subjected to dry state mix meticulously for 30 seconds. After completion of the dry mix phase, water, and super plasticizer were added to obtain the concrete with appropriate workability as per mix design. Mix proportion of the binary blended system of MK given in table 5 Abiraami et al 2021.

Process of concrete
The process of concrete sample includes the selection of materials as per Indian standard specifications and the casting and curing of concrete samples for testing.

Sample casting and curing
The casting of 135 concrete samples was carried out as per IS code provision. Concrete cubes (   4. Outcomes and its inference 4.1. Workability Workability is the vital proper of concrete which is defined as the ability of concrete to flow that delivers privileged circumstances of concrete flow in the fresh state before its initial setting time. Table 5 gives the slump value of concrete cubes and the mix ratio of concrete highly influences the workability property of concrete. Concrete having the true slump-type workability stimulus concrete stability due to its ideal consistency (Gupta et al 2023).

Compressive load bearing characteristics
Compressive strength outcomes of the concrete cubical are exposed in table 6. In concrete mix with replacement of metakaolin for cement, at 28 days 5%, 10%, and 15% of metakaolin replacement (MK 5) contribute compressive strength 19.8% greater than the control mix (MK 0) correspondingly. But 10%,15%, and 20% additional metakaolin mix (MK 10, MK 15, MK 20) gave 12.3%,20.9%, and 31.5% reduced compressive strength than the conventional proportion of concrete (MK 0). Tables 6-8 shows the regular mechanical properties of concrete samples that are tested subsequently curative for 7, 14, and 28 days of time interval existences Gupta et al 2022aGupta et al , 2022bGupta et al , 2022cGupta et al , 2022d. The compression load-bearing characteristics outcomes of concrete trials given in table 6 illustrate that all the concrete samples prepared in these experiments are high strength 50Mpa. In that case, even the 7th compressive strength varied between a minimum of 25.65 N mm −2 and maximum compression strength of 45.94 N mm −2 for a 5% replacement of metakaolin. The 20% additional MK mix had revealed lower strength competitively than other MK replacement percentages. This states the addition of 5% MK was the optimal inclusion considering the progressive compressive strength concrete sample. The decrease in the compressive strength for other additional proportions of MK is due to the dilution effect of the clinker. The outcome of substituting a portion of the binder with the corresponding quantity of metakaolin. In metakaolin concrete due to filler impact, the pozzolanic response of metakaolin with Ca (OH)2 and combination effect react opposite of dilution effect. For that purpose, the optimum percentage of MK replacements in Metakaolin concrete mix proportions. The due effect is due to all cementitious pozzolanic reactions being at the closing stage or stopped. Due to inverse proportionality between the time interval and binder-MK reaction (Abdul Razak and Wong 2005).

Split tensile load carrying properties
The split tensile load-carrying properties of concrete mix samples are shown in table 7. At 28 days binary blended cementitious system, under split tensile testing load bearing characteristics of sample cubes with 5%, 10%, and 15% of metakaolin additional (MK 5) furnished compressive strength 2% greater than the conventional mix (MK 0) correspondingly. But 10%,15%, and 20% replacement of metakaolin mix (MK 10, MK 15, MK 20) displays 1.20%,2.10%, and 3.15% smaller compressive strength than the conventional mix (MK 0). The tensile load-bearing characteristics outcomes of the MK sample with a variable quantity of MK are displayed in table 7. The concrete sample is prepared as a binary blended cementitious structure. The average value of the 28th days split tensile load-bearing characteristics for the concrete made was about 4.95Mpa. Mechanical strength test results imply that the higher strength was achieved at MK 5 mixture. Analysis of results between the compression strength value with the split tensile value it is detected that the compression strength and splitting tensile strength of all mixture has direct proportionality with respect to strength bearing capacity. Thermal contraction and shrinkage cause early age cracking. Specimen failure when tensile stress in concrete is greater than the tensile load applied.

Flexural load carrying properties
Flexural load-carrying properties test results of concrete mix are displayed in table 8. At 28 days cementitious system replacement with metakaolin varied between 5%,10%,15%, and 20%. Considering all the mix metakaolin 5% addition in concrete mix (MK5) displays compressive strength 1.99% greater than the conventional mix (MK 0) respectively. But 10%,15%, and 20% additional of metakaolin mix (MK 10, MK 15, MK 20) furnished 1.20%,2.10%, and 3.15% slightly lesser compressive strength than the conventional mix (MK 0). Table 8 shows the stimulus of variable additional MK % with esteem to the flexural strength of concrete. The observation from the test results implies that the rate of strength amplified with curing periods at all MK substitutes. In the first 7th days of curing the extreme strength improvement is 5.5 N mm −2 for MK 5 concrete mix. It imitates at 28 days with extreme strength improvement of 6.65 N mm −2 with the same mix proportion of 5% additional. From the test results, it is experiential that there is an effect of curing days on flexural load bearing characteristics of concrete. These explanations recommend that the proportion of strength improvement was at 5% metakaolin additional. Growth of strength at initial and future curing periods of MK substitutions. The outcomes propose MK replacement with a 5% optimum percentage is beneficial for a long-term rate of strength increase. This can be accredited to the accessibility of MK for the pozzolanic bustle of MK with calcium hydroxide of ordinary Portland cement throughout protracted curing ages

Relationships between mechanical properties of concrete
Metakaolin is additional for binary blended cementitious systems compressive, split tensile, and flexural strengths were determined empirically, as illustrated in figures 4 and 5. From the above figures 4 and 5, the relationship between compressive versus tensile load-bearing parameters of binary and ternary blended cementitious systems with MK (Hemavathi (2020) Where, f t represents split tensile load-bearing characteristics in N/mm 2 and f ck represents compressive load bearing characteristics in N/mm 2 This equation is comparable with ACI Committee 363, 1993 which state that, f t = 0.59 fck 0.55 for concrete with compressive strength ranging from 21 to 83 N mm −2 . The relationship as f t = 0.462 fck 0.55 for concrete compressive strength less than 84 N mm −2 . From the above equations, it can be stated that the research results of this study coincide with the previous researches (Reddy Suda 2022).
The relationship between compressive versus flexural strength of binary blended cementitious system with Mk was obtained as   The equations obtained from MK mixes in this study are found to be within the range of previous researchers.
4.6. Equivalent CO 2 gas emission and energy factor Associated to cement manufacture, MK manufacture emits less CO 2 into the environment. The CO 2 releases from the manufacturing of MK (175 kg of Carbon dioxide for each ton of MK manufactured) are caused by the abstraction of unprocessed ingredients and the kiln, not by a chemical response (de-hydroxylation). However, the decarboxylation of calcium carbonate throughout cement production results in the emission of CO 2 (1 ton of binder production emits 520 kgs of CO 2 ), and the process of 1 ton of binder production emits 478.5 kg of CO 2 ; Additionally, MK demands a lesser amount of thermal energy throughout production than the cement (1 ton of MK production needs 2.95 GJ, intended from an environmental impact evaluation, and 1 ton of cement produced = 4.69 GJ) (Kelechi et al 2022. Without considering the transference of raw materials, carbon dioxide (CO 2 ) release is intended founded on chemical responses and energy consumption to manufacture 1 ton of cement and MK, which was premeditated as stated by (Cassagnabere et al 2010, Prakash chandar andRaganathan 2022).
On the one hand, MK manufacture emits less CO 2 into the atmosphere than cement manufacturing does. The global kaolin dehydroxylation reaction does not produce CO 2 .
The value of energy consumption and CO 2 emission are measured as per the guidelines of the CIPEC, Canadian Industry Program for Energy Conservation, Energy Consumption benchmark guide: cement clinker production. natural resource.
Emission of CO 2 and Energy saved stayed intended as follows in the equations (5) and (6) here, C o = CO 2 Emission by control mix (MK0) C i = CO 2 Emission by binary cementitious systems. The release of CO 2 and Energy saved was determined for all binary cementitious systems and control mix using equations (5) and (6). Figure 6 grants the values of energy ingestion and Carbon dioxide release into the atmosphere (Madlool et al 2011). The Eco-friendly equilibrium for the binders (cement + MK) based on the Carbon dioxide emission and energy condition is also presented in table 9.
The negative sign implies that replacing binders with metakaolin decreases energy utilization (−2.16% to −7.74%) and carbon dioxide emissions (−4.17% to −15.41%). The outcome shows that the determined replacement of MK provides an optimistic eco-friendly effect and saves raw materials consumption. Tables 10 and 11 shows the cost comparison between conventional concrete and metakaolin partially replaced concrete at its optimum percentage. The difference in the cost of conventional concrete and partially replaced metakaolin concrete is Rs.66. Hence, using partially replaced metakaolin concrete was found to be economically beneficial.

Conclusion
To conclude this present study, obtained the following test results: • Mechanical characteristics such as compression, split tensile, and flexural load bearing characteristics imply that mix proportion which includes 5% metakaolin replacement by weight of cementitious materials holds good test results compared to another concrete mix with varied percentages of replacement varies between 10% to 20%.   • Development of early age strength with esteem to compression, split tensile, and flexural load-bearing characters of concrete with metakaolin replacement is due to the collective consequence of alkali-aggregate and augment pozzolanic response.
• A decline in strength on an accumulation of metakaolin yonder above 10% is due to the presence of excessive lime quantity throughout the progression of hydration which consequences to decline in the strength of hardened cubical samples.
• Metakaolin has a good specific surface area with initial strength acquisition distinguishing constituents combined to progress the workability, strength, and augmented chemical attack.
• The result demonstrates that maximum replacement of MK provides a positive environmental effect and saves raw materials consumption.
• Regression analysis was used to build two correlation models between split tensile and compressive strength as well as for flexural and compressive strength. These models were tested by the predicted errors, which showed an acceptable range of prediction.
• As experimental outcomes found valid reasons for utilizing metakaolin it can be practical in awkward measure construction to recompense the development of eco-friendly and cost-effective material levied by the conformist binder manufacturer and convention.
• To conclude, the binary blended scheme gives rise to a substantial lessening of the price of concrete and complete eradication of carbon dioxide emissions.
The following recommendations can be considered for future studies: • Superplasticizers and water reducers can be added to concrete mix designs to increase workability and maintain a constant w/b ratio throughout all mixtures.
• This will improve the results obtained and make it possible to compare the results for the different samples more precisely.