Abstract
Cement-based material is one of the most versatile and largest amounts of building materials which can not only be used in load-bearing structure but also be used as decoration materials, like brick, wallboard, and tile. However, white calcium carbonate always be found on the surface of wallboard. This phenomenon is generally called efflorescence, which has no damage to wallboard, but has aesthetic impact. In this research, Bacillus mucilaginosus was pre-added to the cement matrix to reduce the efflorescence of wallboard. Image processing, thermogravimetric analysis and permeability test were used to characterize the efflorescence degree of wallboard. The results showed that the bacterium captured atmospheric CO2 by carbonic anhydrase and promoted the CO2to react with Ca(OH)2. This process not only reduced the content of Ca(OH)2 but also improved the compactness of wallboard. In addition, the maximal decrease of efflorescence area of wallboard was gotten when the content of microbial was up to 4% of the mass of cementitious material and the proportion of efflorescence area reduced from 32 ± 3 to 5 ± 1% of the whole area of surface layer. At the same time, the values of compressive and flexural strength were the highest and the surface layer of wallboard was the most compact. The observed reduction of efflorescence was indeed due to the effect of bio-mineralization. This promising method was noted to be cheap, convenient, environment friendly, and which has the potential in various practical applications.
Highlights
With the increasingly high demand for housing decoration, the diversity of the shape of wallboard was pursued, and the aesthetics of wallboard was noticed
The experimental results could be explained by the mechanism that B. mucilaginosus could capture atmospheric CO2 by carbonic anhydrase
Efflorescence degree would be increased when microbe content was more than 4% of the mass of cementitious material
Summary
With the increasingly high demand for housing decoration, the diversity of the shape of wallboard was pursued, and the aesthetics of wallboard was noticed. Most wallboard is made of cement based materials which can cause efflorescence. The materials of efflorescence are usually white and water-soluble compounds which deposit on the surface of masonry (ASTM C1400-11, 2011). Whitish deposits of water soluble salts are alkali sulfate or sodium chloride, which generally appear soon after erection of the facade. The appearance of white efflorescence depends on environmental circumstances, material parameters of bricks, mortar and concrete blocks, and may be influenced by treatments of the façade (Brocken and Nijland, 2004; Chwast et al, 2015). It was suggested that the appearance of efflorescence is due to the low compactibility of cement based materials
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