Study on strength, durable and flexural behaviour of partial replacement of sugarcane bagasse ash over cement

Tonnes of cement are produced and used due to boom in infrastructure sector. During the process of production of cement, lot of CO2 has been emitted. It is estimated around 4%–8% of CO2 has been emitted from cement production. There is high need for address this issue. Because of its renewable nature and high silica content, Agriculture waste ash is gaining popularity as a viable alternative to traditional cementitious materials. It has been found by (Hernandez et al ) that Sugarcane bagasse ash shows good pozzolanic activity. Sugarcane bagasse ash (SCBA) is a waste-free renewable energy source made from sugarcane fibres. Many attempts have been made to study the SCBA as partial replacement for cement. The same has been checked in this study with extension for structural members have been done. The results of tests on concrete and concrete containing a partial replacement of cement made from sugarcane bagasse ash (SCBA) are the most important details in this text. The substitution of 10% SCBA resulted in the greatest increase in compressive strength, followed by a modest increase in split tensile strength maximum strength. The study findings allow for the conclusion that the Concrete that was built has high durability qualities. The flexural behaviour also showed very good performance. The use of Bagasse Ash shows improved performance due to is micro grain size and crystallographic nature. The replacement of 10% SCBA results in overall better performance.


Introduction
The boom in the infrastructure sector and other developmental activities in the construction field, the mandate of concrete are increasing with a very rapid speed. Worldwide, 4.1 billion metric tons of concrete is being produced in 2022, as per a report published by statista.com. Figure 1 shows the worldwide concrete production. Such volumes require massive amount of natural resources for aggregate.
Lifecycle of a material manufactured in this planet leaves some type of footprint that would have an impact on the environment. The risks associated this impact such as resource depletion, elevated carbon emissions, and waste accumulation must be managed. The possibility of such effects is imminent at every stage of production, from the extraction or harvesting of raw materials for manufacturing the required materials into common products till their disposal in their daily usage (Monteiro et al 2017). The CO 2 release in any cement-related production have gained its spotlight since they are significant adding up to around 71% of all yearly energy and industrial emissions (Fennell et al 2021). Polymer concretes use polymers as binders, and asphalt concrete uses bitumen as a binder. About 3.5 billion tonne of ordinary Portland cement (OPC) are produced annually on a worldwide scale (Fennell et al 2022). It is a key component of construction work and is utilized to create products like mortar and concrete. However, if the construction sector's growth and expansion are not designed properly, they might do significant harm to the environment. While there is need for sustainable concrete the construction sector is concerned about the need to implement more ecological methods and practices to lessen the negative impact that waste has on the environment (De Sande et al 2021).
Reducing CO 2 emissions and energy consumption for the cement production in a more sustainable form is a significant and ongoing problem. Attempts are being made to decrease energy consumption during the calcimine process by creating modified Portland cements. Agri waste ash, for fact, is gaining popularity as a viable alternative to traditional cementitious materials because of its renewable nature. This is partly attributable to the fact that these leftover ashes are readily available, relatively inexpensive, and exhibit excellent reactivity (Ataie and Riding, 2016). Because of their high silica content, the by-products of biomass combustion can be used as a sustainable energy source with potent pozzolanic qualities. Ash that has been finely ground can also be used as a filler ingredient to increase the packing density of concrete (Thomas et al 2021), (Balachandran et al 2021). India is the second largest producer sugarcane (32,000,000 tonnes per year in 2022-23 as per United States Department of Agriculture shown in figure 2. Sugarcane bagasse ash (SCBA) is used as a pozzolanic material in concrete. Sugarcane bagasse ash is rich in silica it has good pozzolanic properties (Rodier et al 2019). It has good blending in cement and partial replacement of sugarcane bagasse ash in cement it gives same strength in concrete (Murugesan et al 2020), (Khalil et al 2021). In order to effectively utilize sugarcane bagasse ash in concrete and prevent it from being thrown of as trash in large quantities, a thorough assessment of its pozzolanic activity is required (Chandra Paul et al 2019). Bagasse reduces waste because it is made from material that would otherwise be disposed. Looking for a renewable energy source from agriculture, sugarcane is at the top of the list (Manikanta et al 2020). Many experimental works carried out on similar studies has been reviewed before initiating the work (Adesina and Das 2020), (Cardell and Guerra 2016), (Castro et al. 2011), (Madduru et al 2020, (Sales, Lima (2010)). The blending of other particle also along with main particles which has been successful studies nowadays (Sathawane   (Senhadji et al 2014). Around 250 kg of bagasse is produced from 1000 kg of sugarcane (figure 3). This drives us to have interest over SCBA. This study attempts in partial replace of cement in the concrete with sugarcane bagasse ash (SCBA) and the effects on concrete. For new materials like sugarcane bagasse ash and manufactured sand studies on mechanical properties, durability is of paramount important for initializing confidence in engineers and builders. The work is extended to study the flexural behaviour of the concrete.

Materials and characterization
2.1. Materials Sugarcane bagasse was collected from several local sugar mills and the collected waste was washed with clean water to remove any unwanted contaminants. The cleaned bagasse was then equally spread and dried in sunlight to remove any moisture content. Following the grinding of the dry bagasse with a grinding machine, it was placed inside an electric furnace and heated at a temperature of 1200°C for four hours. The ash that was produced by the furnace was gathered, and then sieved to achieve a consistent size, and this ash was utilized for the entirety of the research. The production of Bagasse ash shown in figure 4.

Material characterization
Scanning Electron Microscope (SEM) analysis is performed on sugarcane. SEM produces a large magnified image of a small particle by using an electron gun. This helps us find the particles' size and structure in Nano sizes. The SEM image for Fly ash is shown in figure 1. The particle size is found by taking 30 random particles in  the picture and measuring them using ImageJ software. The maximum size of those 30 particles is 30.644 μm, and the minimum size is 8 μm. The mean size is 74.083 μm. This makes it evident that the size of the particles is not uniform, with a standard deviation of 15.972 μm. The particle size scattered distribution is also shown in figure 5. Water is available in the research laboratory of the college campus which is used to confirm the concentrating and curing of the water, it is tested as per IS: 456-2000. River sand is collected from the nearby river and it is sieved with the filter size of 1.18 mm for the mix. The general-purpose Portland cement is purchased from maa hardware's, Orissa, India. The coarse aggregate is crushed with 19 mm as per the Indian standard (IS: 383-1970). These materials purchased from various places as per the standard are used for entire research and study purposes.
X-ray diffraction analysis (XRD) is a non-destructive technique that provides detailed information about a material crystallographic structure, chemical composition, and physical properties. XRD works by irradiating a material with incident x-rays and then measuring the intensities and scattering angles of the x-rays that leave the material. Detailed information on the crystallographic structure for SCBA is shown in figure 6. It can be seen from figure 6 that the peaks are sharp indicating crystallographic structure of atomic arrangement.

Mix proportion
The mix proportion is developed based on a replacement of cement by sugarcane bagasse ash. The prepared proportion of different mortar mixes is shown in table 1. The replacement has been carried out as 2.5%, 5.0%, 7.5%. 10.0%. 12.5%, 15.0% and 20.0%. Mix ID has been developed accordingly.
The first mix is the control mortar mix containing 100% of ordinary Portland cement as a binder and is designated as C. Second mix consists of 2.5% cement replaced by equivalent weight by SCBA. Similarly the mix has been done up to 20% replacement and casted accordingly as seen in figure 7. The hardened concrete studies such as compressive strength, split tensile strength, modulus of rupture along with water absorption test, UPV test and acid attack test has been performed.

Compressive strength
Compression tests are conducted on the cube specimens. The strengths are seen during the curing period of 3 days, 7 days, and 28 days. Three specimens in each mix in each corresponding curing period have been tested under a compression testing machine. A total of 72 samples are tested. The Mean of the three results is shown in table 2. This mean value is similar within 10% variations, which is well below the standards.
The compressive strength of the SCBA blended cement composites shows good performance as seen from figure 8 bar chart. It has been observed that the strength increases consistently up to 10% replacement and starts decline after 10%. This is mainly due to its micro size and crystallographic nature. Figure 9 shows the rate of strength gain of each specimen. The rate of strength gain is high for 10% replacement specimen while it is too low in case of 20% replacement specimen. Almost all other specimen shows similar trend in strength gain trends. Table 3 shows the percentage increase in the compressive Strength of the concrete with respect to control specimen.. The highest percentage increase in compressive Strength was found to be 10.61% for 10% replacement concrete with respect to control specimen. The drop in strength also rapid and can been seen from following table.      Incorporating SCBA into cement accelerates hydration by promoting secondary hydration products. Due to sharp peak in XRD, the SCBA forms strong crystallographic nature. This causes more compact and dense microstructure resulting in enhanced compressive Strength upto certain limit. Figure 10 shows the scatter line plot for the percentage increases in compressive Strength. It is interesting to note that the rate of percentage increase in Strength decreases with aging.

Split tensile test
The split tensile strength of cylindrical specimens is evaluated at ages 7, and 28 days after curing in accordance with BIS: 5816-1999, figure 11 shows the results of split tensile strength. The dimension of the cylinder is 300x150mm as per the ASTM C496 standard for splitting tensile strength of the concrete. The split tensile strengths are found at the curing period 7 days and 28 days. Three specimens in each mix in each corresponding curing period have been tested under compression testing machine. Mean of the three results is shown in table 4. This mean value doesn't differ more than 10% which is well below the standards.
The Split tensile strength increases from 3.3 MPa to 3.9 MPa in case of 10% replacement. The bar chart showing the variation of split tensile strength of the specimens.

Modulus of rupture
In accordance with IS specifications, cubes and beam specimens are tested for modulus of rupture. Rectangular prism of size 15 cm×15 cm x 50 cm has been prepared for finding the modulus of rupture. The modulus of rupture is evaluated at ages 7 and 28 days. The modulus of rupture for the specimens is found at the curing period 7 days and 28 days. Three specimens in each mix in each corresponding curing period have been tested under compression testing machine. Mean of the three results is shown in table 5.
Modulus of Rupture ranges from 4.6 MPa to 5.4 MPa for SCBA 10% mix. The bar chart showing the variation of split tensile strength of the specimens in figure 12.

Water absorption test
A water absorption test has been conducted to predict the amount of water absorbed by the specimen. This test on the mortar specimens are carried out after 28 days of curing age. The water absorption test is carried out as per ASTM C 642 standard [23] . The cement mortar specimens are dried in a hot air oven at 110°C for 24 h, cooled to room temperature, and weighed as W d . After that, the specimens are allowed for curing for about 48 h and considered as W s . The percentage of water absorption is determined using the following expression. he quantity of water absorbed, determined with the help of water absorption test, provides the idea of the rate of porosity present in the Samples. Table 6 presents the water absorption of the specimens. The test is carreidout for one specimen for each case.
It can be observed from above table is that the water absorption is low in case of 7.5% replacement specimen. This is mainly due to the atomic structure nature and closure of voids due to it. Figure 13 shows the variation of water absorption by each specimen.  3.6. Ultrasonic pulse velocity test An ultrasonic pulse velocity test has been performed on the mortars to find the quality of the specimens. As per IS 13311 (Part 1) [22] , the UPV test is for concrete. Even though it is performed on concretes, many researchers performed the same on cement mortars. On that basis, we have decided to perform it on cement mortars. The ultrasonic pulse is generated through an electro-acoustical transducer transmitter on one surface of the mortar specimen and received by the transducer in contact with the surface at the other end. The velocity of the ultrasonic waves passed inside the specimen indicates the quality of the mortar specimens. The direct transmission method is used on all six sides of the specimen at 3 days, 7 days and 28 days. The mean value of the reading is reported in table 7. Table 2 of IS 13311-1 (Part-1) indicates the velocity criterion for quality grading. According to that, the velocity above 4.5 km s −1 is labelled as excellent, 3.5-4.5 km s −1 as good, 3.0-3.5 km s −1 as a medium, and below 3 km s −1 as doubtful. Table 8 shows that the velocity of the concrete mix for the curing period at 3 days, 7 days and 28 days ranges from medium to good quality. This property is due to fine particles, which improve the  pore-filling effect and makes the mortar mix as dense and compact. This proves well that the enhancement of quality and homogeneity. Figure 14 shows the bar chart indicating the UPV test results on mortars.

Evaluation of heat resistance
Heat resistance is a measure of the thermal endurance of plastic materials. This test has been performed on C and C+SCBA10.0 mix. Heat resistance property is evaluated by heating the control specimen and C+SCBA10.0 specimens in a muffle furnace at 250°C. Specimens are heated at a rate of 5°C min −1 using a hot air oven. After reaching 250°C, the specimens are held at this temperature for about 80 min to maintain thermal equilibrium. Then the specimens are taken out from the furnace and allowed to cool for 2 days (48 h) in open air. These specimens are then evaluated for compressive Strength. The same test is done with another specimen for higher temperature of about 500°C.
Concrete elements structures subjected to fire at elevated temperature breaks the binding property of the constituents Si, Ca, Al, H, O, etc, causing failure. Table 8 represents the residual compressive Strength of mortar specimens at different temperature. The residual compressive Strength of the control and C+SBCA10.0 specimens subjected to 250°C is 7.2 MPa and 9.6 MPa, respectively. Compared to the control specimen the residual compressive Strength of C+SCBA10.0 are 33% higher. Similarly, the residual compressive Strength of the control and C+SCBA10.0 samples subjected to 500°C is 3.85 MPa and 6.87 MPa, respectively.

Acid resistance test
Another important test conducted on the mortars is the acid resistance test. This test is used to evaluate the acid resistance property of the mortar specimens. Specimens C and C+SCBA10.0 are immersed separately in sulphuric acid (H 2 SO 4 ) and hydrochloric acid (HCl). 10 Litres of 5% HCl and 5% H 2 SO 4 are taken in containers separately, where the specimens are immersed for 28 days. After that, the specimens are taken out, washed out using distilled water, and dried for 48 h. Then compression tests are performed on this specimen to evaluate the residual Strength. The compression test results are presented in table 9.
The compressive strength of the specimen after the 5% Hydrochloric acid immersion of control mortar and C+SCBA10.0 specimens are found to be 6.85 MPa and 9.88 MPa, respectively. Similarly, the compressive Strength of the Specimen after the 5% sulphuric acid immersion of control mortar and C+SCBA10.0 specimens are 6.92 MPa, and 11.36 MPa, respectively. It is shown in figure 15.

Flexural analysis 4.1. Specimen preparation
The beams are casted by providing clear cover of 20 mm using wooden mould all around. The 31.75 mm thick plywood has been taken for preparation of the beam mould. The mould has been prepared for the size 150 mm × 200 mm and 2000 mm long inner dimension. To ensure realistic construction site conditions, all test units are built in the fully upright position. However, the castings of the specimens are slightly challenging because of the small cover to the reinforcement. Casting is done as a single unit in without any delay in concerting process. Two hooks using 12 mm diameter rods bound to the reinforcement cage for lifting the specimen. At first, the levelling of surface is done and is followed by oiling of mould. The cover blocks of size 20 mm are placed in bottom and sides of the mould. The reinforcement cage is prepared. 2 numbers of 16 mm diameter HYSD rods are taken for tension reinforcement and 2 numbers of 12 mm HYSD rods are taken as hanger rods. 8 mm diameter HYSD rods are taken for stirrups at 250 mm c/c. The formwork had been removed on the next day and left for curing for 28 days. The concreting is done after cage is kept into the mould. Specimen is prepared as shown in figure 16.

Test setup
The testing of beams is done using 50 ton capacity loading frame. Beam is simply supported and two point loading is given to study the flexural behaviour of the beam. The shear span is fixed about 450 mm and span of beam fixed about 1800 mm as shown in figure 17. The shear span to depth (a/d) ratio maintained as 2.5 for both beams.
25 ton capacity hydraulic jack is fixed and tightened sufficiently to avoid any movement of the jack. Three LVDT are fixed. One LVDT is at centre of the beam and others at the loading points. Two points loading is given with the help of a spreader steel beam under the jack. This is shown in figure 18. The loading has been applied with the rate of 0.2 kN s −1 and mid deflection value has been taken with the help of LVDT. The reading has been taken until the load drops after reaching the peak load.

Load-displacement response
The loads versus displacement response and crack pattern after testing under loading are noted. The vertical displacement is the net centre displacement recorded from LVDT during the experimentation. Specimen is prepared as per the standard geometry 710 × 150 × 150 mm and tested under three-point static load and the mode of failure is observed as bending and shear force failure respected to drop weight velocity. All the readings     are recorded using data acquisition system. The cracks and failure modes are observed and is differs for different mix as seen in figure 19. It can be seen that the first crack has been observed at the center of the beam as expected and travels vertically up. The load displacement plot has been plotted and shown in figure 20. Table 10 show the displacement comparison of the C and C+SCBA10 concrete mix.
It can be seen from load displacement response is that the addition of SCBA improves the strength of the beams. The peak strength has been observed to be 69 kN for conventional concrete. The peak strength for C +SCBA10.0 is found to be 86 kN.

EEEP Curve
The analysis is performed based on Equivalent Energy Elastic Plastic Curve (EEEP Curve) principle. This EEEP curve is a perfectly elastic-plastic representation of the actual response of the specimen. This bilinear EEEP curve is plotted such that it equals the area under the load-deflection curve until failure i.e. the energy dissipation capacity is equal. Figure 21 shows the various points of interest used to derive the EEEP curve.   The area (energy) under the backbone curve was then calculated up to the post-peak displacement that corresponds to the EEEP curve up to the lateral displacement Δ u . The slope of inclined portion of the EEEP curve corresponds to the Secant Stiffness at 40% of the maximum load in backbone curve. A horizontal line depicting the plastic portion of the EEEP curve was then positioned so that the area bounded by the EEEP curve and the back bone are equal. Thus the value of yield strength and yield displacement is calculated. The EEEP curves for our specimen are shown in figure 22.

Ductility Index
Ductility is defined by the degree to which a material can sustain plastic deformation. The ductility index is calculated from the ratio of ultimate displacement to the yield displacement. This is calculated based on the values from EEEP curve. C+SCBA10.0 specimens shows greater ductility index than Control specimen. Figure 23 shows the bar chart showing the ductility index of all beams. ∆ ∆ Ductility Index, u y ultimate deflection Yield deflection = 4.6. Stiffness and stiffness degradation Stiffness is the extent to which an object resists deformation in response to an applied load. The secant stiffness has been calculated corresponding to the ultimate load in the EEEP curve. The secant stiffness for control beam is about 8.85 kN/mm while for C+SCBA10.0 is found to be 15.714 kN mm −1 . The variation of the secant stiffness at each displacement as per the loading protocol is the stiffness degradation curve. It can be noticed that the stiffness decreases with increase in the subsequent loading. The reduction in the stiffness is due to the fact of  deterioration of strength and cracking of concrete beam. Figure 24 shows the stiffness degradation curve. It can be seen that performance of the stiffness degradation is better in case of C+SCBA10.0 beam.

Energy absorption
The energy absorption capacity has found using Equivalent Energy Elastic Plastic Curve (EEEP Curve). The energy absorption capacity for control beam is about 2207 kN-mm while for C+SCBA10.0 is found to be 2648 kN-mm.
The energy ductility index has been calculated for all specimens using EEEP curve. This energy ductility index indicated the capacity of the specimen to dissipate energy in its plastic zone. The energy ductility index for control beam is about 12.89 while for C+SCBA10.0 is found to be 17.89.

Result comparison
The detailed analysis has been performed and the results have been reported in table 11. Lot of interesting inference can be drawn by comparing the test results. The performance of concrete with C+SCBA10.0 dosages has improved in greater extent. This is achieved mainly due to the filling the micro pores of concrete.
The ultimate load has been improved by 24% than conventional concrete. The ductility of the beam also has been improved by 36%. The stiffness of C+SCBA10.0 has been improved in a considerable amount by 78%. The energy absorption has also improved by 20% which is also a significant contribution. The energy ductility factor denotes the plastic toughness of the beams has been improved by 39%. Figure 25 shows the result comparison.

Conclusion
A detailed experimental work has been carried out considering SCBA as replacing agent for cement. Some of the important conclusions made from the study have been listed here.
(a) The mean size of SCBA particle is 74.083 μm with standard deviation of 15.972. This shows it is well graded in micro (10 −6 ) range.
(b) The atoms are arranged in crystallographic structure which can be seen from XRD analysis.
(c) Compressive strength has been seen improved constantly up to 10% replacement.
(d) Split tensile and Modulus of rupture of concrete has been improved significantly with C+SCBA10.0 concrete.
(e) Lowest water absorption has been seen in case of C+SCBA7.5 concrete.
(f) UPV test shows almost all concrete is in good and excellent range.
(g) Heat resistant and Acid resistant tests also show improved strength for C+SCBA10.0 case.
(h) The ultimate flexural load has been improved by 24% for C+SCBA10.0 beam than conventional concrete beam.
(i) The ductility of the C+SCBA10.0 beam also has been improved by 36%. The stiffness of C+SCBA10.0 has been improved in a considerable amount by 78%.
(j) The energy absorption has also improved by 20% which is also a significant contribution. The energy ductility factor denotes the plastic toughness of the beams has been improved by 39%.
In nutshell, the use of Bagasse Ash shows improved performance due to is micro grain size and crystallographic nature. The replacement of 10% SCBA results in overall better performance. The tests can be extended to study structural behaviours such as Shear behaviour, Compression behavior using beams and columns.

Data availability statement
Raw data were generated at PSR Engineering College, Sivakasi. Derived data supporting the findings of this study are available from the corresponding author Arun Raja Lourdu on request.