Institute for Transportation

About the research

Typical concrete crack repair uses chemical sealants or surface treatment agents, which are often expensive and harmful to environment. The goal of this study was to develop an eco-friendly, cost-effective biogrout for concrete crack repair.

A biocement was developed using microbiologically induced calcium carbonate precipitation (MICP) technology. A biomass of urease-producing bacteria (UPB) (e.g., bacillus sphaericus), urea, and a soluble calcium solution were used for the MICP process. The study included two major parts. The first part was to develop a new soluble calcium solution for MICP by dissolving a limestone powder, a by-product from a limestone quarry, into an acetic acid-rich stage fraction 5 (SF5) solution derived from biomass pyrolysis and a fractionation system. The second part was to study mortar crack repair using MICP technology.

The results indicated that the properties of the new soluble calcium solution for MICP could be optimized from the study of different limestone powder-to-SF5 ratios, potential of hydrogen (pH) values of the obtained solutions, and procedures for applying the UPB and media (urea/calcium solutions) for calcium carbonate (CaCO₃) precipitation (i.e., MICP treatment). Using such a soluble calcium solution as a replacement for calcium chloride (CaCl₂) in the MICP process produced desirable CaCO₃ precipitation. The properties of the sand samples cemented using the limestone-SF5 calcium solution were comparable to those of the sand samples reported in previous studies, where CaCl₂ was commonly used as a soluble calcium solution. Cracks in mortar samples repaired using the MICP technology gradually healed with an increasing number of MICP treatment cycles. The samples treated with MICP had a significant reduction in water permeability. While water-treated samples were too weak to test, the MICP-treated samples had splitting tensile strength (TS) ranging from 32 to 386 kPa after 21 treatment cycles. For the samples having an initial average crack width of >0.52 mm, the TS clearly increased with the CaCO₃ content resulting from the MICP treatment. A scanning electron microscope (SEM) study suggested that there were two different forms of CaCO₃ on the crack surface of cracked mortar samples: one was vaterite and the other calcite. The CaCO₃ crystals had a size ranging from 5 to 20 μm, and they formed a porous matrix that filled in the mortar cracks.

Funding Sources:
Iowa Department of Transportation
Iowa Highway Research Board ($299,993.00)
Midwest Transportation Center
USDOT/OST-R ($44,916.00)
Total: $344,909.00

Contract Number: DTRT13-G-UTC37