Fresh concrete
Workability
In order to determine the workability of concrete, slump cone test was carried out. Freshly mixed concrete was tested for workability with different ratios of SCBA, and the results are given in Fig. 1. From results, it is shown that the more percentage of SCBA is used to replace cement in concrete, the more slump values are obtained; this can be attributed to the fact that the cement grains are finer than that obtained from the simple way used to grind the bagasse ash. As a result, the bagasse ash had a lower specific surface area than the replaced cement which in return requires less amount of water to cover the surface leading to more slump values.
In phase 3 where bagasse fibers were added to the mix with ratios 1 and 2% of the total weight of cement, the slump was less than 15 mm.
Hardened properties
Compressive strength
In phase 1, the mortar cubes were tested at ages 3 days, 7 days, and 28 days. For this phase, only compression tests were carried out. The results are given in Fig. 2.
The compressive strength test results are presented in Fig. 2. The maximum compressive strength is observed at 5% SCBA replacement, and after this ratio, the results decreased. This sample gives strength up to 1.68, 2.04, and 3.04 MPa at ages 3, 7, and 28 days respectively. These results increased by 3.7%, 18.6%, and 9.75% at ages 3, 7, and 28 days respectively when compared with the control mix. This increase is due to the pozzolanic reaction as the C–H formed from the hydration process of cement reacts with silica in SCBA and forms more C–S–H.
In phase 2, the concrete cubes were tested in compression. The specimens in this phase were tested at ages 7 days and 28 days. The results obtained from the compression test are shown in Fig. 3.
The results are presented in Fig. 3. The compressive strength of the concrete samples with 5% replacement showed an increase of 17%,and 20.4% at ages 7 and 28 days respectively when compared with the control mix, while for the 7.5% and 10% replacements, the 7-day compressive strength of the specimens was almost the same value as the control one, but at 28-day age, there was a reduction in the compressive strength at both percentages of replacement. And hence, 5% SCBA represents the optimum value to replace the cement in concrete. Similar results were obtained previously by other researchers [8, 17, 18], where 5% showed the highest results obtained for compressive strength at 28-day age. A recent study [19] showed that a 5% replacement resulted in a reduction in strength at 28-day age, while for the same ratio but at 120-day age, the results had the highest compressive strength values when compared to the control specimens.
For phase 3 where the bagasse fibers are added to the concrete mix, all the cube specimens showed a significant reduction in the compressive strength as shown in Fig. 4. These results can be referred to the improper treatment of fibers and mixing procedures, where the fibers should had special treatment to get rid of the glucose. As it is well known that the glucose affects the setting time of cement and can affect the properties of concrete, also during the mixing of concrete, the fibers were dry, so when they were added to the mixture, they absorbed a considerable amount of water which resulted in harsh concrete, and during the mixing process, it was clear that the mix needs more water. Previous research [20] showed that the treatment of the bagasse fibers significantly affects the behavior of the concrete.
Splitting tensile strength
In phase 2, cylinders of size 15 cm diameter and 30 cm height were tested for splitting tensile strength at age 28 days. The results at which the samples failed are shown in Fig. 5.
The results of split tension test are presented in Fig. 4. The splitting tensile strength is up to 2.97 MPa at age 28 days. The optimum splitting tensile strength is observed at 5% SCBA replacement. This result showed an increase by 33.2% when compared with control mix.
Flexure strength
Prism specimens of size 500 × 100 × 100 mm in phase 3, where sugarcane bagasse itself used, failed where all the results showed a significant reduction in flexural strength. Prism specimens were used only for bagasse fibers as it is thought to increase the flexural strength of the concrete. Since the obtained results were not satisfactory due to the aforementioned reasons (improper treatment of fibers), the results were disregarded.
Slab cracks
The bagasse fibers were added to concrete to check its effect on the crack formation in slabs, as the fibers can be used to bridge the cracks by resisting the tensile stresses obtained due to the shrinkage of concrete and to delay the formation of the cracks. Figures 6 and 7 show the cracks developed in the slab with fiber and in the control one. The cracks formed in the slab with fibers were scattered in large numbers and smaller in length and width, while the cracks formed in the control slab (without fibers) were fewer but having wider in width and taller in the length. Although the bagasse fibers were not properly treated, but still it can help to resist the tensile stresses created within the concrete slab and to reduce the width of the formed cracks.