A study on self-healing concrete

Abstract

This research work is carried out to find the self-healing time and mechanical properties of concrete by using Bacillus Subtilis and Escherichia Coli. These bacterias has the capability of healing the cracks by itself. M20 concrete designed as per IS 10262–2009 is taken as reference sample. Different mixes were casted varying the percentage of bacteria. The above-mentioned bacteria were mixed in percentages of 2%, 3%, 4% and 6% by weight of cement separately and combination of both bacteria at 50% each to make total 2% and 3% of mixed bacteria by weight of cement. Calcium Lactate (a calcium-based nutrient for the bacteria) is mixed at a constant 5% for all mix variations. All the mixing, casting, curing and testing is done as per standard practice. Slump cone test gave an increased workability of 45% with bacteria Bacillus Subtilis. Standard size cubes of 150 mm were casted (nine for each mix), cured and tested at the age of 7, 14, 28 days. Some samples were tested in Compression testing machine till cracks were evident and measurable. The bacteria gets activated when water comes in contact with it, starts to feed on calcium lactate and grow resulting in self-healing of cracks in concrete. It is observed that the cracks were healed within 48 hrs for 2% Bacillus Subtilis, 32 hrs for 3% Bacillus Subtilis, and 72 hrs for 4% Bacillus Subtilis, even after 72 hrs no evident healing was observed for 6% Bacillus Subtilis all percentages of Escherichia Coli and mix bacteria. Hence the optimum dosage for self-healing of concrete is 3% Bacillus Subtilis. Both Compressive strength and Split Tensile strength, tests are done as per IS 516-2002 (reaffirmed 2018) and results gave an increase of 60%, strength for samples with 3% Escherichia Coli bacteria.