Investigation of bagasse ash as a partial supplementary cementitious material

Abstract

Bagasse is a fibrous waste product of the sugarcane industry that remains after sugarcane or sorghum stalks are crushed to extract their juice. In Bangladesh, Sugarcane is produced in 2.05% land of the country and it contributes almost 5.52% to agricultural GDP. Bagasse is most often used as a biofuel for the generation of steam and power required to operate boiler in the sugar factory and in the manufacture of pulp in paper industry. As a result, these industries produce huge amounts of a solid waste material known as sugarcane bagasse ash (SCBA) in Bangladesh. The waste of bagasse ash is generally disposed in landfills or dumped nearby the industrial sites. Consequently, it is creating waste management problem, especially in the sugar milling sites. These wastes have an adverse effect on the environment, creating air pollution due to smell, dust and also affecting the fertility of soil.

The utilization of such waste materials as a supplement in cement manufacture provides two folds benefit; a) it makes cement production cleaner and b) it solves problems associated with waste management. From limited previous studies available, it is found that sugarcane bagasse ash could have pozzolanic properties and thereby, could be used as supplementary cementing materials. However, pozzolanic behavior of SCBA depends on burning process and temperature. The high carbon content is an obstacle to its use in cement/mortars. Therefore, it would be valuable if the unburnt carbon in SCBA could be removed through proper calcination.

This research work aims at exhibiting the idea of utilizing bagasse ash as supplementary cementitious material by elaborating upon their morphological, physical and chemical properties. Locally available bagasse and industrially leached bagasse were collected and burnt at various temperature ranges to obtain the most suitable burning process. The corresponding chemical composition of SCBA was investigated through XRF to investigate the suitability of bagasse ash to be used as supplementary cementitious material. The morphology and chemistry of bagasse ash was also studied by performing EDS analysis coupled with Scanning Electron Microscopy (SEM) technique. It was found that industrially leached bagasse burnt at 600-650 o C temperature shows satisfactory result to be used as pozzolan which have similar composition of class F fly ash. The burning of relatively fresh locally available bagasse did not yield suitable amount silica due to high alkali content like K2O, Na2O, CaO etc. Ash produced from industrially leached bagasse was then mixed with Portland cement at partial replacement level of 10%, 15% and 20% by weight to make mortar samples. Control samples with no bagasse ash were also made for comparison. It was observed that addition of bagasse ash increased the water demand and reduced drying shrinkage of cement mortar. Moreover, up to 10% replacement level, the compressive strength of mortar was found to be increased and then the strength showed a decreasing trend with 15% replacement level exhibited almost equal strength of the OPC mortar. It is therefore, evident that sugarcane bagasse ash has the potential to be used in cement production and thereby could resolve the waste management issues related to it.