The Studies on Partial Replacement of Cement by Eucalyptus Ash in Concrete

Abstract

Cement composites have become an inevitable part of the construction industry. Concrete is the most utilized material on earth next to the water. With the advent of urbanization and increase in infrastructure activities, consumption of cement concrete has escalated. The production process of one ton of cement emits about 0.7 tons of carbon-dioxide into the atmosphere. The emitted carbon dioxide will lead to the greenhouse effect causing global warming[1]. This in turn affects the rainfall pattern, melting of ice caps, and rise in sea levels. Hence there is a need to mitigate the use of cement and make the development sustainable.

Eucalyptus trees were grown across the Karnataka state in India as a part of afforestation in the recent past. However, it was recently proved that eucalyptus trees would suppress the groundwater table as it needs about 90 liters of water per day. Thus its cultivation was restricted by law and the same is being used for firewood and burning of bricks. Still, these are available in abundance and hence it has become an economical fuel source at the countryside. It acts as a source of bio-mass and curtails the use of non-renewable sources of energy[2]. The ash produced by the burning activity is either dumped in landfills which creates soil and air pollution in the neighborhood.  This ash contains cementitious property and it can be used along with cement[3]. Confining its movement in the concrete would reduce the usage of cement, air pollution, and exploitation of natural resources[4].

In this research, a concrete mix of M20 grade was designed according to IS: 10262-2000 for moderate exposure conditions. 53 grade ordinary Portland cement (OPC), river sand, and 20mm down size crushed stone coarse aggregates were used to prepare the concrete. 1:1.71:2.78 mix proportion was finalized for the workability of 75-100mm slump with 0.5 water-cement ratios.  To make the concrete eco-friendly, cement was partially replaced by eucalyptus ash at 20, 40, 60, and 80%. The fresh concrete property was determined by the slump cone test, which depicts that workability reduces with an increase in replacement levels of eucalyptus ash. Mechanical properties of concrete were determined by compression, split tensile, and flexural strength tests at 3, 7, 28, and 56 days. Mechanical properties proved that eucalyptus ash can be used as a supplement to cement up to 20%. At 20% replacement, concrete exhibited maximum compressive strength of 31.39 MPa on the 28^th day. After 20% replacement, the strength of concrete decreased gradually and it didn’t reach the target mean strength. Split tensile strength and flexural strength were almost proportional to compressive strength. It was noted that the density of concrete reduced with an increase in replacement levels due to the low specific gravity of eucalyptus ash. Water absorption increased with the increase in ash replacement levels. Microstructure analysis also proved that, by replacing eucalyptus ash up to 20%, concrete can be made sustainable when compared to conventional concrete. Thus, eucalyptus ash acts as a reliable source of supplement for OPC, and by the use of the same, OPC composites will be eco-friendly and boost sustainable development.