Use of Bioproducts Derived from Mixed Microbial Cultures Grown with Crude Glycerol to Protect Recycled Concrete Surfaces

Abstract

The large increase in the world population has resulted in a very large amount of construction waste, as well as a large amount of waste glycerol from transesterification reactions of acyl glycerides from oils and fats, in particular from the production of biodiesel. Only a limited percentage of these two residues are recycled, which generates a large management problem worldwide. For that reason, in this study, we used crude glycerol as a carbon source to cultivate polyhydroxyalkanoates (PHA)-producing mixed microbial cultures (MMC). Two bioproducts derived from these cultures were applied on the surface of concrete with recycled aggregate to create a protective layer. To evaluate the effect of the treatments, tests of water absorption by capillarity and under low pressure with Karsten tubes were performed. Furthermore, SEM-EDS analysis showed the physical barrier caused by biotreatments that produced a reduction on capillarity water absorption of up to 20% and improved the impermeability of recycled concrete against the penetration of water under pressure up to 2.7 times relative to the reference. Therefore, this bioproduct shown to be a promising treatment to protect against penetration of water to concrete surfaces increasing its durability and useful life.

Biotreatments Using Microbial Mixed Cultures with Crude Glycerol and Waste Pinewood as Carbon Sources: Influence of Application on the Durability of Recycled Concrete

“…The results showed that the amount of water absorbed increased with the time of contact with water, reaching a constant mass after 96 h. Both bioproducts decreased the amount of water absorbed, by more than 17% for SP and by almost 8% for SG compared to water-treated specimens. These results were very similar to those obtained when using a MMC–glycerol-based concrete treatment [ 29 ], with improvements of 20% with SG and 13% with NSG (non-sonicated glycerol) and less than the 40% reduction, as found by Chandra et al [ 72 ], using cactus extract impregnated in concrete. Moreover, the results obtained with the SP treatment were similar to the ones reported by Oliveira et al [ 41 ] when MMC cultivated with the same carbon substrate was applied in air lime mortars, obtaining a reduction of 17% in water absorption.…”

“…This may have been due to the fact that SP had a more homogeneous distribution than SG over the treated surfaces, as can be seen in SEM images ( Figure 9 ) [ 29 , 67 ] taken after the assays. The better distribution of the SP biotreatment may have been due to its lower viscosity.…”

“… Secondary electron image captured using SEM, caused by layers superimposed by the carbon distributions of SP ( a ) [ 67 ] and SG ( b ) [ 29 ]. …”

“…Due to these detrimental characteristics, numerous investigations have sought to improve the durability of the concretes produced from recycled aggregates, using different techniques such as the removal of the attached mortar [ 26 ], pre-soaking treatment in water [ 27 ] and autogenous cleaning processes [ 28 ], among others techniques. An alternative approach involves the use of bioproducts derived from polyhydroxyalkanoate (PHA) production processes as surface treatments, which reduce water absorption, improve the quality of the surface layer and protect the concrete structure, consequently increasing its durability [ 29 ].…”