The effect of various boron compounds on the antimicrobial activity of hardened mortars

Abstract

• Six different boron compounds (5% by mass to cement) were used to prepare cement mortars. • Dicalcium hexaborate pentahydrate (COL) and borax pentahydrate (BPH) were compatible with cement mortars. • COL and BPH addition decreased the flexural and compressive strength values within acceptable limits. • COL and BPH addition inhibited C. albicans and A. niger growth by at least 99%. This study has examined the effect of boron compounds on the mechanical and antimicrobial properties of hardened mortars. The antimicrobial activity of six different boron minerals and compounds was tested against six microorganisms, including Gram-positive and Gram-negative bacteria, yeast, and fungus. Cement mortars containing 5% (w/w) boron mineral addition by weight of cement were exposed to flexural and compression tests on the 7th, 28th and 90th days. At the end of the 90th day, the hardened mortar specimen prepared with 5% dicalcium hexaborate pentahydrate (COL) or 5% borax pentahydrate (BPH) decreased the compressive strength 7.41 % and 31.5 %, and flexural strength 13.5 % and 32 %, respectively. Although, there are decrements in both compressive and flexural strength, values remain within the acceptable limits specified in the material code. The antimicrobial activity of these specimens was evaluated with surface antimicrobial activity tests. The hardened mortar specimen containing boron compounds showed antimicrobial activity against C. albica ns and A. niger . It can be concluded that from these results, using 5 % COL and 5 % BPH as an additive or replacement to the mortar, is an alternative way to create antimicrobial surfaces within environments that have complained of mold problems and biodegradation, such as in reinforced concrete structures or in conventional buildings that need to be free of pathogenic microorganisms.