The application of Trichoderma carbonate precipitation for bio-based concrete healing

Abstract

Reinforced concrete plays an indispensable role as a construction material in many fields worldwide and it contributes significantly to major projects. However, it has the drawback of developing cracks, which with time leads to further degradation of the concrete and its reinforcement. This causes a reduction in its service life, requires extensive repair and maintenance and increases the burden of planning and disposal of demolition waste. Thus it is considered as economically and environmentally unsustainable. An alternative and attractive approach is to put to use smart technologies that can help repair damage in concrete at the earliest possible stage, usually manifested as micro cracks. Such technology includes the use of selected microbial organisms which deposit calcium carbonate in the presence of appropriate nutrients, thereby repairing the inner damage. This research provides an overview of a new healing concept in bio-based concrete and involves species of fungus Trichoderma which can promote microbially-induced calcium carbonate precipitation. Different strains of Trichoderma harzianum, Trichoderma virens and Trichoderma citrinoviride which were isolated from Maltese soils as well as Trichoderma reesei were overlaid on cement paste casts with the use of different media in the presence or absence of calcium source (CaCl2). The growth of the hyphal mycelium was observed over a period of 7-15 days. Scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis were performed and confirmed the deposition of calcite on certain casts with particular fungal species. These indicated potential results that can eventually be implemented for further research in smart concrete for an ultimate scientific goal. Cement mortars were also produced from cement, sand (1:3) and water moisture. These were then cracked and filled with medium inoculated with the fungal strain that showed most potential in calcium carbonate precipitation. The study results have shown that two Trichoderma harzianum isolates (DM and FP) show optimal mycelium growth and calcium carbonate deposition on concrete as compared Trichoderma reesei which has been used as the control standard described in the literature.