Welan gum is a recent type of microbial polysaccharide produced from fermentation by Alcaligenes [1–3], a very common and harmless bacterial species, which is inexhaustible and able to prevent mortar or concrete from bleeding and segregation, so it is potentially suitable for use as stabilizer or thickener in mortar and concrete [4–7]. The molecular structure of the saccharide unit [8,9] is shown in Fig. 1.
As welan gum is produced by bacterial fermentation, its quality is consistently high, and its quantity is hardly resource-limited. Welan gum is friendly to human health and the environment, and the manufacturing process is safe, cost-effective, and nonhazardous. Overall, the future looks bright for the wide application of welan gum.
By contrast, cellulose ether is normally extracted from cotton or wood in a chemical industrial process through a series of subsequent etherification steps [10,11]. It has good adhesive, thickening, and water retention properties, and is widely applied in construction as a concrete or mortar mix additive [12,13]. Currently, the most popular type is the non-ionic hydroxy-propyl-methyl cellulose– HPMC, with typical dosage of 0.1–0.6 wt% relative to cement, to achieve desired mortar or concrete mix properties. The molecular structure of HPMC unit is shown in Fig. 2.
However, production of high quality HPMC is strictly limited by the availability of high quality cotton, and quality varies between manufacturers as well as over time. Consequently, HPMC quality
is slightly variable and less consistent compared to welan gum quality, while its bulk manufacture is substantially less environmentally friendly.