Study on the effect of Thiobacillus intermedius bacteria on the physico-mechanical properties of mortars of ordinary portland cement

Abstract

Most of concrete structural failures are attributed to poor workmanship and poor engineering designs. Some microorganisms present in sewer systems can degrade the concrete and/or mortar. Concrete failures due to microbial attack has not attracted much attention especially in developing countries such as Kenya. This study investigated the effect of Thiobacillus intermedius bacteria on the performance of Ordinary Portland Cement (OPC). Preparation of test mortar prisms was done using the bacterial solution as either mix water, curing water or both. The control mortar prisms were prepared and cured in distilled water. Compressive strength test was done after 7 th , 28 th , 56 th and 90 th days of curing respectively. Results showed significant drop in compressive strength for the mortar prisms prepared and cured in bacterial solution as compared to the control mortar samples. Soundness and normal consistency increased significantly for the bacterial treated cement paste as compared to the control sample. Scanning Electron Microscopy (SEM) analysis showed severe damage on the bacterial treated cement mortar. This was characterized by formation of deleterious expansive products like ettringite and gypsum. Control mortar sample exhibited even formation of hydration products within the pore system.

Chloride Ingress in Cement Mortars Exposed to Acidithiobacillus thiooxidans Bacteria

“…e formed AFt is expansive and deleterious. Comparable observations have been made by other authors [15,28,[32][33][34].…”

“…D app was determined using [26,27] Advances in Materials Science and Engineering where R is the gas constant, F is the Faraday constant, T is the temperature of the electrolyte in K, Zi is the valency of the ion I, Δ∅ is the effective applied voltage in V, and t is the duration of the test/exposure in seconds. ) as the key hydration products [15]. is was as expected because, under normal conditions, hydration process would result in even distribution of hydration products within the pore system.…”

“…Gypsum (CaSO 4 2H 2 O) and ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 26H 2 O) are the core products of corrosion when concrete is exposed to sulphuric acid reaction [14]. Ettringite is an expansive crystalline substance that may cause cracking of the attacked concrete surface [15]. Presence of microcracks in the concrete surface allows penetration of chlorides and moisture into the concrete/steel interface and hence simulates corrosion of the rebar [16].…”

Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars

“…e formed biogenic sulphuric acid attacks CH and C-S-H as the key hydration products of OPC leading to formation of secondary expansive materials such as gypsum and ettringite [34,35]. Similar observations were made by Munyao et al, 2020 [17], and Buvignier et al, 2019 [10]. e SEM image for OPC SK (SK) as presented in Figure 7 was dominated by excessive formation of ettringite and microcracks with elaborate erosion of CH plates.…”

“…(2) All the test samples were subjected to SEM analysis after 28 days of curing. In all the scenarios, there was a significant comparison of the SEM micrographs with other researchers' works already published [17,30,31].…”