Effect of the Microbiological Contamination of a Superplasticizer on the Mechanical Properties and Durability of High-Strength Concrete

The present study evaluated the effect of the microbiological contamination of a commercial superplasticizer on the mechanical and durability properties of high-strength concrete. Unlike previous studies focused on the chemical performance of admixtures, this work investigates the influence of microbiological contamination of a commercial superplasticizer on concrete behavior, an aspect that has received little attention in the literature. The microorganism present in the admixture was isolated and presumptively identified using conventional microbiological techniques, including culture-based methods, macroscopic and microscopic characterization, Gram staining, and lactophenol blue staining, and was presumptively identified as Candida albicans. Subsequently, the performance of concrete produced with a reference superplasticizer was compared with that of concrete prepared using the microbiologically contaminated superplasticizer. The evaluated properties included slump, compressive strength, density, water absorption, void index, capillary water absorption, and resistance to magnesium sulfate attack. The results demonstrated that microbiological contamination did not produce significant differences in workability, compressive strength, or the physical properties of the concrete. However, concrete produced with the contaminated admixture exhibited a greater loss of compressive strength after exposure to magnesium sulfate (12.61% compared with 4.68% for the reference mixture) and a 64% increase in the secondary capillary absorption coefficient, suggesting increased pore network connectivity that facilitated sulfate ingress and consequently increased deterioration under aggressive exposure. Therefore, although the microbiological contamination of the superplasticizer did not significantly affect the initial mechanical properties of high-strength concrete, it may compromise its durability under aggressive environmental conditions, highlighting the importance of proper storage practices and rigorous quality control of chemical admixtures.