Development of bio-based admixtures for cement-based materials

Recent developments in concrete technology enabled us to design highly flowable self-levelling mortar mixes. Generally, high flowability is obtained by incorporation of strong superplasticizers, which could also increase the amount of segregation and bleeding in the mixes. To eliminate this possible thread, viscosity modifying admixtures (VMA) should be added to the cement-based mixes. Advances in construction technology and rise in the importance of sustainability initiatives also reinforce the use of biological admixtures. Through the literature, nopal mucilage, brown algae, and bacterial cell walls were proposed as alternatives to conventional VMAs. However, these alternatives require extra processing which results with a higher unit cost compared to admixtures that could be directly obtained from nature, like the direct addition of cells. In this study, it is considered that incorporation of 4 vegetative Peanibacillus polymyxa, Sporosarcina pasteurii, Bacillus megaterium, and Bacillus subtilis cells may modify the viscosity of cement-based mixes and could serve as VMAs. Yet, it is also important to assess the influence of these cells on the hardened performance of the mix. This study aims to evaluate the influence of abovementioned bacterial cells on, initial setting time, rheology, capillary water absorption, compressive and flexural strength of cement paste and mortar samples. The vegetative cells were added to mixing water by 0.1% of binder weight at a w/b of 0.45. Based on our study, incorporation of cells caused modifications in both fresh and hardened state properties of cementitious mixtures. In conclusion, rheology of cement-based mixes could be improved by direct inoculation of live bacteria cells without sacrificing from the hardened state performance of the cementitious materials.