Analysis on performance of eco-friendly engineered cementitious composite for construction and environmental sustainability

Engineered cementitious composite (ECC) is one of the versatile construction composites. The eco-friendly nature and performance depend on the materials and curing period. This analysis uses sisal fibres at suitable fly ash to cement dosage (f/c). It is responsible for a reduction in disposal (or) environmental problems. The impact of alkaline-treated sisal fibres with different combinations of polyvinyl alcohol (PVA) fibres on the characteristics of Indian Zone II fine aggregates (50% river sand + 50% Manufactured sand)-based ECC is analysed. Mix-1 prepared with 2% Sisal fibres, Mix-2 is 0.5% Sisal fibres + 1.5% PVA fibres. For this, a high f/c dosage (1.4) is considered. The compressive strength of composite is slightly improved from Mix-1 to Mix-2 at 28 days by the decreased content of sisal fibres. But the split tensile and flexural characteristics are moderately increased by 8.33%, and 5.45% from Mix-1 to Mix-2, respectively. These characteristics highly improved with the increased curing period (28 days to 120 days). The durability of the composite significantly influenced from 28 to 56 days, but slightly improved with the decreased content of sisal fibres. Scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) were used to evaluate these properties. Portlandite (P) and quartz (Q) content were highly reduced (formation of C-S–H gel) from 28 to 56 days due to hydration of unhydrated fly ash, fine aggregates, and other materials. The microstructure of both the mixes is densified with this gel. Mix-2 is moderately densified than Mix-1 due to the properties and arrangement of sisal fibres. These fibres are appropriately arranged in the partial replacement of PVA fibres compared to full dosage.


Introduction
Engineered cementitious composite (ECC) is a high crack resistive structural composite. The properties of materials influence the characteristics, such as self-consolidation, strength and durability. It improves the life span of structures and reduces construction costs. Demolishing of buildings, power plants (or) any other structures will reduce sustainability and cause environmental problems due to disposal, decreasing the availability of significant materials. In the preparation, coarse aggregates are eliminated for reducing the crack propagation and protect environment by existence (or) longevity of hills (Al-Gemeel et al., 2018;Braga et al., 2017;Gürbüz et al., 2020;Kewalramani et al., 2017;Ma et al., 2019;Tränkler et al., 1996). But it is responsible for mechanical strength in conventional concrete. To improve the strength of this composite, cement with suitable synthetic fibres especially polyvinyl alcohol (PVA) fibres can be used in preparation. A high dosage of cement causes early age cracks and global warming due to the emission of CO 2 into the atmosphere. So, a suitable dosage of cement with pozzolanic materials (fly ash, metakaolin, ground granulated blast furnace slag, etc.) is required to prepare composite. These pozzolanic materials also reduce the heat of hydration (Erdem et al., 2019;Kan et al., 2020;Kim et al., 2007;Muzenski et al., 2015;Şahmaran et al., 2009). The fibres in the composite will improve the ductility and strain hardening behaviour.
The properties and type of fibres are needed to be considered for the significant performance of ECC. Li et al., 2002 studied the influence of PVA fibres with proprietary oiling agents on the characteristics of the composite. This is applied at different concentrations (weight of oil to weight of fibre) on surface of the fibres. The ductility and mechanical characteristics were optimised at 1.2% oil content. Pakravan et al., 2015 analysed the impact of hybridization, shape and modulus of the fibres on the performance of composite. For this, PVA fibres and polypropylene (PP) fibres were considered. PP fibres with a combination of kidney-shaped PVA fibres improved the mechanical characteristics. Choi et al., 2012 studied the influence of polyethylene terephthalate (PET) fibres on the characteristics of the composite. The partial replacement of PVA fibres with PET fibres improved the mechanical characteristics of ECC. Ali et al., 2017 analysed the impact of different lengths of fibres on the performance of ECC. For this, a different combination of SMA fibres with PVA fibres is considered. Dispersion analysis revealed that the composite with 2% PVA fibres and 0.5% SMA fibres showed better characteristics. But the environmental and economic problems of these fibres demand the utilisation of natural fibres. The superplasticizers namely polycarboxylate ether can improve the flowability and selfconsolidation characteristics (Pan et al., 2015;Soe et al., 2013). Apart from this, the fine aggregates also will influence the performance of ECC.
Victor C. Li et al., 2008 studied the influence of silica sand on structural characteristics. The self-consolidation properties and flowability were improved with 250 μm grain size of silica sand at f/c-1.2. At this, the performance of structural elements is optimised. But the cost and availability of these fine aggregates demand alternatives. Sherir et al., 2018 analysed the utilisation of locally available mortar sand in place of silica sand. The flowability of this composite decreased by these fine aggregates compared to silica sand mixes. But the self-consolidation and mechanical characteristics were negligibly impacted. The durability of the composite is highly reduced by the mortar sand compared to silica sand-based mixes. Apart from this, morphological parameters of fine aggregates are needed to be considered in the preparation of ECC. Wu et al., 2019 considered the four natural grains of sand, namely Ottawa sand, Gabbro sand, MI Sand and 2NS Sand. Decreased roundness and sphericity improved the characteristics of ECC. So, morphological parameters and type of fine aggregates are needed to be considered in the preparation. The curing conditions and properties of specimens can influence the performance of the composite.
Felogolu et al., 2014 studied the influence of mixing techniques and curing conditions on the characteristics of High Tenacity Polypropylene-based HTPP-ECC at different dosages of higher water reducer (HRWR). The performance improved by combining a faster mixing speed with a longer mixing time. The water curing condition showed better results. Chung et al., 2017 analysed the impact of water-tobinder (w/b) ratio and characteristics of specimens on the composite. The mechanical characteristics increased with the reduced w/b ratio and specimen size. But these characteristics are highly reduced with the shape of specimens (cube to cylinder). These studies indicate the necessity of alternatives to fine aggregates, fibres and cement. In India, the availability of cost-effective and highly available crushed stone (or) manufactured sand, and river sand are available to replace traditional silica sand. The use of non-toxic, harmless natural fibres especially sisal fibres is helpful to encourage formers (or) the agricultural sector. Apart from this, the high content of fly ash from thermal power stations is helpful to reduce early age cracks and it responsible for significant performance.
Keeping in view all the above analysis, an environmentally friendly construction composite has been analysed and prepared in this experimental study to improve sustainability. The influence of material characteristics and curing period on the performance of Indian Zone II fine aggregates (50% river sand + 50% Manufactured sand)-based composite has been studied. For this, two mixes (Mix-1 is 2% sisal fibres, Mix-2 is 0.5% sisal fibres + 1.5% PVA fibres) are considered. Locally available crushed stone is used as manufactured sand to reduce the utilisation of river sand. The mechanical, durability and microstructural characteristics of these mixes are determined at w/b of 0.27 and f /c 1.4.

Methodology
The methodology is a workflow planned to study the impact of various factors on the performance of ECC. In this experimental study, the methodology mentioned in Fig. 1. implemented to determine the impact of sisal fibres fully (or) partially, and curing period on characteristics of the composite. The sustainability of the composite achieves with the considerations from Fig. 2.

Materials
To reduce the negative impacts of materials and enhance the environmental conditions, the materials mentioned in Fig. 3 were selected based on Fig. 4. In this experimental analysis, OPC-53 grade Ultratech cement with 2.5% TiO 2 from local suppliers is considered according to IS, 12269-1987. Class-F category fly ash from the local company-Vruksha composites is used based on ASTM120a. These materials are shown in Figs. 5 and 6. Indian Zone II river sand and Manufactured sand from Bhavyasri Traders were used as per IS383-, 2016. The chemical composition of these materials is mentioned in Table 1. Oil-treated (0.2%) PVA fibres with 12 mm length and 39 μm diameter are mentioned in Fig. 7. used. Sisal fibres with 12 mm length and 25 μm width from Vruksha composites are mentioned in Fig. 8. used. This is treated with alkaline treatment to reduce the absorption of water (Chowdary et al., 2020;Yusof et al., 2019;Naveen et al., 2019). For this, these fibres dipped under 6% concentrated sodium hydroxide (NaOH) solution for up to 30 min later, neutralised under 2% concentrated hydrochloric acid (HCL) before drying in an oven at 80 °C for 3 h. Polycarboxylate ether-based Turbopol CEA50 is used as per ASTM C494 (2013). Water from local sources is used that is free from impurities. The sieve analysis of fine aggregates is explained in Table 2 and shown in Fig. 9. Figure 2 represents the three considerations 1. Performance 2. Environmental 3.Economic benefits. The mechanical and durability characteristics of the composite are considered. For this, high-performance-based materials are selected. In this experimental study, less oiled (0.2%) PVA fibres are considered based on performance and economic conditions, shown in Fig. 7. The horseshoe cross-sectional sisal fibres from the sisal plant shown in Fig. 8. are considered. Proper utilisation of these materials for structures will improve urbanisation and sustain the natural geographical features.

Mix proportions
In this study, the mix proportions mentioned in Table 3 are considered to analyse the impact of dosage of sisal fibres (2%, and 0.5%) and curing period (28, 56, 90, and 120 days) on the performance of Indian Zone II fine aggregates (50% river sand + Manufactured sand)-based ECC. These mixes are considered to analyse the hydration of materials and the distribution of fibres.

Mixing process
The mixing process is implemented based on our experimental analysis and past researchers' studies (Ismail et al., 2019;Zhou et al., 2009Zhou et al., , 2012. Pan mixer of 120L capacity is used for significant mixing. Initially, cement, pozzolanic material (fly ash), and fine aggregates (river sand and Manufactured sand) are mixed for 3 min. Later, PVA fibres and sisal fibres are added and mixed for 2 min. To this mix, polycarboxylate ether-based Turbopol CEA50 and water are added and blended for 3 min to form a homogenous mix. This mixing process is represented in Fig. 10.

Curing of specimens
In this study, the curing condition-water curing under submersion of air considered. The cube 70.7 mm × 70.7 mm × 70.7 mm, cylindrical Ø150mm × 300 mm, prism 100 × 100 mm × 500 mm, and disc Ø100mm × 50 mm specimens were cast and demoulded after 48 h. These specimens were tested after 28, 56, 90, and 120 days of curing to determine the mechanical, durability, and microstructural characteristics.

Compressive strength test
The compressive strength of Indian Zone II fine aggregatesbased mixes (Mix-1 and Mix-2) was determined with the cube specimens of 70.7 mm × 70.7 mm × 70.7 mm in size. These specimens were placed under curing for 28, 56, 90, and 120 days of curing and subjected to the rate of loading 140 kg/cm 2 /min under a compression testing machine, according to IS516-, 2013.

Split tensile strength test
The split tensile strength of Indian Zone II fine aggregatesbased mixes at different combinations of sisal fibres was determined (2% Sisal fibres, 1.5% PVA fibres + 0.5% Sisal fibres) with the cylindrical specimens of Ø150mm × 300 mm in size. These specimens were subjected to the loading rate of 1.2 N/mm 2 /min under a split tensile testing machine as per IS5816-, 1999.

Uniaxial tensile tests
The uniaxial tensile tests were performed with the dog-bone specimens as per Japanese recommendations (JSCE 2005). The uniaxial tensile strength vs tensile strain curves were obtained at different contents (fine aggregates, f/c). The impact of the materials on these properties was analysed and determined the influence of curing period.

Flexural strength test
In this experimental analysis, the flexural strength of Indian Zone II fine aggregates-based (50% river sand + 50% Manufactured sand) mixes was determined with the prism specimens of 100 mm × 100 mm × 500 mm in size. These specimens were tested at different curing days (28, 56, 90, and 120 days) under a flexural testing machine according to IS516-, 1959.

Durability test
Rapid chloride penetration test (RCPT) was conducted to analyse the durability characteristics of the composite. The disc specimens of Ø100mm × 50 mm were used to determine the intensity of chloride ion penetration, according to ASTMC, 1202. NaOH and NaCl solutions were poured into the RCPT chambers and voltage of current was adjusted to 60 V to pass chloride ions. The impact of sisal fibres at different dosages (2% sisal fibres, 1.5% PVA fibres + 0.5% sisal fibres) on performance was determined.

Compressive strength
The compressive strength of the composite slightly increased from Mix-1 to Mix-2 with the reduced dosage of sisal fibres at all curing periods. As per analysis, the compressive strength increased by 3.46%, and 3.92% for Mix-1 and Mix-2 from 28 to 120 days of curing, respectively. These characteristics of mixes are mentioned in Fig. 11. It indicates that the compressive characteristics of composite highly improved by the increased curing period and reduced sisal fibre dosage.

Split tensile strength
The split tensile strength of the composite increased by 5.56% for Mix-1 from 28 to 56 days. These characteristics improved by 6.41% for Mix-2 with the increased curing period. Decreased content of sisal fibres increased by 8.33% from Mix-1 to Mix-2 mentioned in Fig. 12. It indicates the increased curing period and partial replacement of sisal fibres highly improved the strength of ECC.

Uniaxial tensile strength and strains
The tensile strength of both mixes improved from 28 to 120 days of curing as shown in Fig. 13. But tensile strains decreased with the increased curing period. It happened due to hydration of materials and the arrangement of fibres. However, Mix-1 showed better strain hardening behaviour compared to Mix-2. The maximum tensile strength of mixes is 4.5 to 5 N/mm 2 at increased curing duration.

Flexural strength
The flexural strength of Mix-2 increased by 5.45% from Mix-1 with the reduced dosage of sisal fibres. These characteristics improved by 10% for Mix-1 with the increased curing period from 28 to 120 days. For Mix-2, this increased by 9.48% from 28 to 120 days as shown in Fig. 14. It indicates the partial replacement of sisal fibres showed better results compared to full dosage at all considered curing days.

Durability characteristics
The durability of composite improved with increased curing period especially from 28 to 56 days compared to other durations (56 days to 90 days, 90 days to120days), shown in Fig. 15. This happened due to the formation of C-S-H gel (reduction in portlandite and quartz content). The pozzolanic action increased and unhydrated fly ash, fine aggregates reduced with the increased curing period. These characteristics improved from Mix-1 to Mix-2 with the reduced dosage of sisal fibres due to the properties and arrangement of fibres. A suitable combination of fibres and curing period will reduce environmental problems and enhance the characteristics of ECC.
The curing periods details are mentioned in Fig. 16, as ((1) -120 days, (2)-90 days, (3) -56 days, (4) -28 days) for Mix-1 and Mix-2. The difference between XRD curves at various curing periods was shown, and the impact of sisal fibres was analysed with the microstructure of Mix-1 and Mix-2. The portlandite and quartz content decreased with the increased curing period (formation of C-S-H gel) improved the microstructure of mixes. This phenomenon is considered based on past studies (Roychand et al., 2016). But the microstructure of Mix-1 is less densified compared to Mix-2 due to its properties and arrangement of fibres. This densification of mixes is shown in Figs. 17 and 18.
The microstructure of Mix-1 improved with the increased curing period from 28 to 56 days as shown in Fig. 17a, b. Later that, it improved slightly from 56 to 90 days (Fig. 17b, c) and 90 days to 120 days (Fig. 17c, d). It indicates that the increased curing period improved the microstructure. But the arrangement and properties of fibres also need to consider in preparation.
The microstructure of Mix-2 also improved with the increased curing period from 28 to 56 days as shown in Fig. 18a, b. Later that, it improved slightly from 56 to 90 days (Fig. 18b, c), but moderately from 90 to 120 days (Fig. 18c, d) of curing. The arrangement and properties of

Conclusion
According to experimental analysis of Indian Zone II fine aggregate-based composite, the following conclusions are mentioned: • The compressive strength of Mix-2 slightly increased from Mix-1 with a reduced dosage of sisal fibres. These characteristics of Mix-1 improved by 3.46% from 28 to 120 days. For Mix-2, this increased by 3.92% with the increased curing period. So, a partial replacement of sisal fibre in the composite will exhibit better results compared to the full dosage. • The split tensile strength moderately improved with the increased curing period. For Mix-1, this increased by 5.56% from 28 to 120 days. These characteristics of Mix-2 improved by 6.41%. A reduced dosage of the sisal fibres increased these characteristics by 8.33%. • The flexural strength of Mix-1 and Mix-2 improved by 10%, and 9.48% from 28 to 120 days respectively. These characteristics were increased by 5.45% with the decreased dosage of sisal fibres. • Durability of the composite increased from Mix-1 to Mix-2 by the decreased content of sisal fibres. These characteristics also improved with the increased curing period. It happened due to the formation of C-S-H gel (reduction in portlandite, quartz content) and the arrangement of sisal fibres. • The mechanical, durability and microstructural characteristics of mixes showed that the increased curing period, properties and arrangement of fibres (PVA and Sisal fibres) are needed to be considered in the preparation of composite. Based on the performance (Mechanical, durability, and microstructure characteristics) of mixes, Mix-2 is suitable for sustainable management and reduction in environmental problems. Its performance is optimised with the increased curing period. So, a suitable combination of the curing period and Mix-2 can be considered for appropriate constructions (structures, transportation facilities). Mix-2 indicates that the partial use of sisal fibres is responsible for significant performance compared to full use.