Table 1. Chemical Composition of Sugarcane Bagasse Ash
Cement was partially replaced by sugarcane bagasse ash at 0%, 5%, 10%, 15%, & 20% and the properties of concrete in both wet and hardened states are investigated experimentally and the results are compared. M25 grade design mix concrete (1:1.9:3.55) with 0.5 water cement ratio was used for this experimental research. Workability, compressive strength, split tensile strength, flexural strength, bond strength, and sulphate resistance tests were conducted to investigate the feasibility of sugarcane bagasse ash as a cement replacement material in concrete. Based on the results of the present experimental investigation, it is suggested that sugarcane bagasse ash without treatment/heating can be used to replace up to 10% cement in concrete.
Concrete is the most preferred construction material all over the world. Approximately three tons of concrete is being used per person on the planet in each year. The constituents of concrete are cement, fine aggregate, coarse aggregate, and water. Concrete as well as cement are indispensable in the construction industry and directly linked with the global economy. Nowadays, researchers are searching for alternate materials to replace the ingredients of concrete because of unavailability of natural aggregates and also the high amount of carbon dioxide emission during cement manufacturing. Cement production requires a high amount of energy. Producing a ton of cement requires approximately 4.7 million British Thermal Unit (BTU) of energy that is equivalent to 400 pounds of coal (Emissions from the Cement Industry, 2012). The burning of fossil fuels to heat kiln also results in CO2 emission as shown below.
CaCO3 +heat —› CaO+CO2
India is the second largest country in consumption of cement after China. Cement consumption in India is about 270 million metric ton per year and in China is about 2.4 billion metric ton per year (Major countries in worldwide cement production, 2012-2017). Cement production is growing by 2.5% annually. During manufacturing of oneton cement, half a ton of carbon dioxide is released (Reddy et al., 2016), which in turn will cause environmental problems like global warming and ozone depletion. Research is going on to replace cement by industrial and agricultural waste, such as blast furnace slag, fly ash, silica fume, rice husk ash, wheat straw ash, sugarcane bagasse ash, etc. (Singh et al., 2016; Chusilp et al., 2009; El-Sayed et al., 2017).
Sugarcane bagasse ash is the by-product of sugar industries. Approximately 1500 million tons of sugarcane is being produced per year all over the world. India is the second largest producer of sugarcane bagasse in the world after Brazil. India is producing around 300 million tons of sugarcane per year. Sugarcane leaves produce around 30 percentage of bagasse after extraction of its juice for sugar manufacturing purpose. Most of the sugar industries are using this sugarcane bagasse for burning purpose as a fuel. After burning, bagasse leaves around eight percentage of sugarcane bagasse ash (Reddy et al., 2016).
Disposal of sugarcane bagasse ash is a serious concern. It is harmful to the environment as well as human beings. Countries like India and Thailand use this material for landfill and also as a fertiliser. But there is no scientific background for using sugarcane bagasse ash as fertiliser. So, using it as a fertiliser is not a right way to dispose of this material. Also dumping this waste in the soil will cause soil pollution and may also pollute ground water. The fine particles of bagasse ash may enter windpipe and cause a health hazard. Hence, proper disposal and utilisation of this materials is a must.
Sugarcane bagasse ash is being experimented as a cement replacement material in some parts of the world, including India. According to these studies, it shows an improvement in certain properties of concrete including compressive strength for a limited percentage of replacement. Sugarcane bagasse ash contains a higher amount of silica content compared to ordinary portland cement, which is suggested as the main reason for this improvement in the properties.
Literature review (Reddy et al., 2016; Payá et al., 2002, Ganesan et al., 2007; Shafiq et al., 2008; El-Sayed et al., 2017) have revealed that sugarcane bagasse ash has been heated at around 650 oC to 1000 oC before conducting the experiments, for reducing the carbon content and particle size. Heating of sugarcane bagasse ash releases CO2 and the process is also energy intensive. In this study, sugarcane bagasse ash was not heated.
This research focuses to evaluate sugarcane bagasse ash as a partial replacement material for cement in concrete, based on the experimental study of properties of concrete in wet and hardened states and to arrive at an optimum percentage replacement.
53 grade Ordinary Portland Cement (OPC) conforming to IS 12269:1987 was used for mixing concrete. River sand passing through 4.75 mm sieve and retained on 75 μm sieve with a specific gravity of 2.5 was used as fine aggregate and 20 mm down crushed natural stones with a specific gravity of 2.62 was used as coarse aggregate (IS: 2386 (Part 3) 1963).
Sugarcane bagasse ash with a specific gravity of 1.75 (IS: 4031 (Part11) 1988) used in this research was collected from NSL Sugars Ltd, Maddur, Karnataka. The chemical composition of sugarcane bagasse ash is shown in Table 1.
Table 1. Chemical Composition of Sugarcane Bagasse Ash
Mix design was carried out according to IS 10262:2009 and IS 456:2000 for M25 grade concrete and the proportion 1:1.91:3.55 was obtained.
Five different proportions of concrete mixes including control mix were prepared with 0.5 water-binder ratios for slump cone test, compressive strength test, split tensile strength test, flexural strength test, bond strength test, and durability test. Mix proportion used for preparing concrete for five types of concrete is shown in Table 2.
Table 2. Ratio of Materials for each Proportion
Normal consistency of cement-SCBA (Sugarcane Bagasse Ash) paste was determined as per IS: 4031-1988 (Part4). Initial and final setting time was determined by using this consistency according to 4031-1988 (Part5).
Workability test was conducted as per IS 1199:1959. The results obtained from workability tests of each proportion of concrete is shown in Table 3.
Table 3. Slump of Concrete
A decrease in slump with the increase in sugarcane bagasse ash content up to 10% replacement was observed. After which, an increase in slump was noted. The trails were conducted by the weigh batching method and the specific gravity of sugarcane bagasse ash is almost 60% of that of cement. This difference was not captured in mix design. In order to compare the different proportion, all parameters except percentage replacement of sugarcane bagasse ash were kept the same. This could be the reason for the irregularity of the slump values.
The compressive strength of concrete was determined as per IS 516:1959 for the 7, 14, and 28 days of curing. 75 cubes of 150 mm were cast in five different proportions.
The split tensile strength of concrete was determined as per IS 5816: 1999 for the 28 days of curing. Five cylinders with 150 mm diameter and 300 mm height were cast for each proportion of concrete.
Flexure strength of concrete was determined as per IS 516:1959 for the 28 days of curing. Three beams of 700 mm x 150 mm x 150 mm were cast for the each proportion of concrete.
Bond strength test of concrete with reinforcement was conducted according to IS 2770:1967- (Part 1), in UTM. Properties of the bar and concrete influences the bond strength of concrete. The 16 mm diameter 550-grade High Yielding Strength Deformed bars (HYSD) were used to cast the specimens for the bond strength test. Around 100 mm of 650 mm length bar was embedded inside the concrete cube with 150 mm dimensions while casting. Three specimens were tested for each proportion. Test set up is shown in Figure 1.
Figure 1. Bond Strength Test Set-up
The bond strength was determined by the formula: Bond strength = P/πdl
where P = Ultimate load in N, d = Diameter of reinforced bar, l = embedded length of reinforcement bar.
A durability test was conducted according to ASTM C 1012 for checking the effects of sulphate attack on concrete. Three cubes of 150 mm x 150 mm x 150 mm were cast for each mix proportion. The specimen was immersed in water for 28 days, and later, it was immersed in 10% concentrated MgSO4 solution for 28 days. The cubes were tested to find the compressive strength.
Scanning Electron Microscopy is one of the most versatile techniques to analyze the morphology and micro-structural characteristics of solid objects. Due to the high resolution of the microscope, SEM can be used for the study of composition and structure of concrete (Nemati, 1997).
SEM and EDX analysis were conducted at BMS College of Engineering, Bangalore, India. Small pieces were collected after compression testing, which was used for SEM and EDX analysis. A very thin coating of gold sputter was applied on the surface of samples to enable or improve the imaging.
Table 4 shows the results of consistency and setting time test for different mix. The result indicates that the water demand for making a fine paste of cement-SCBA mix is increasing with increasing percentage replacement. There is a reduction in both initial and final setting time, which indicates a faster setting of concrete.
Table 4. Consistency and Setting Time of Cement –SCBA Mix
Compressive strength increased up to 5% replacement of cement by sugarcane bagasse ash and then, there is a reduction of strength. The compressive strength of concrete after 7,14, and 28 days of curing is shown in Figure 2.
Figure 2. Compressive Strength of Concrete (After 7, 14, and 28 Days Curing)
Split tensile strength increased up to 5% replacement of cement by sugarcane bagasse ash and then, there is a reduction of strength. Test results of the split tensile test is shown in Figure 3.
Figure 3. Split Tensile Strength of Concrete
Flexural strength increased up to 5% replacement of cement by sugarcane bagasse ash and then, up to 15% replacement, the flexural strength was almost the same. Before 20% replacement, flexural strength started decreasing, but the percentage decrease is very less. Even up to 20%, the reduction in strength is only 4% that of reference mix as shown in Figure 4.
Figure 4. Flexure Strength of Concrete
Bond strength of concrete in each proportion was determined after 28 days of curing. Bond strength increased up to 10% replacement and then, there is a reduction of strength, but the strength difference between 0% replacement and 15% is very small around 0.5% as shown in Figure 5.
Figure 5. Bond Strength of Concrete
The compressive strength of cubes after sulphate attack was compared to that of reference mix (Merida & Kharchi, 2015). Figure 6 shows the compressive strength after 28 days of sulphate attack. The compressive strength after 28 days curing in normal water and 28 days in MgSO4 has decreased with increase in the percentage of sugarcane bagasse ash. Based on this test result, sugarcane bagasse ash cannot be recommended for cement replacement in areas prone to sulphate attack.
Figure 6. Compressive Strength of Concrete After Sulphate Attack
EDS spectrum of concrete with sugarcane bagasse ash of proportions 0%, 5%, 10%, 15%, and 20% is shown in Figures 7(a-e). SEM images of concrete with different proportions of SBA are shown in Figures 8(a-e). A small piece of specimen was collected after compression test for these tests.
Figure 7. EDS Spectrum of Concrete with (a) 0% SCBA (b) 5% SCBA (c) 10% SCBA (d) 15% SCBA (e) 20% SCBA
Figure 8. SEM Images of Concrete with a) 0% SCBA b) 5% SCBA c) 10% SCBA d) 15% SCBA e) 20% SCBA
SEM images of the samples show large amount of white blocky crystals and needle like crystals. EDS analysis identifies the presence of calcium, silicon, aluminium, iron, sulphur, and carbon. Based on SEM and EDS images, white blocky crystals can be interpreted as gypsum and needle like crystals as ettringite.
Based on the experimental work, the following conclusions are arrived.
The authors acknowledge the support provided for the research by Faculty of Engineering, CHRIST (Deemed to be University), Bangalore, India.