Immediately after mixing the concrete, the pores are highly connective and large, allowing for ample amounts of water and contaminates to pass through the body of the concrete. As the hydration reactions begin with the cement and water, the cement particles begin to stiffen and allow less water to travel through the pores. This continues until the hydrated cementitious structure is formed and the initial hardening of the concrete occurs. Finally, the cement gel forms as concrete hardening is initiated and the pores and capillary cavities are connected through the body of the concrete.
Concrete is a porous material, and the degree of porosity and permeability is directly related to its composition. According to the American Concrete Institute (ACI), porosity is a measure of the volume of voids in concrete. Permeability is the rate of flow of moisture through concrete under a pressure gradient. Therefore, concrete which is more porous tends to be more permeable. The more permeable the concrete surface is, the more moisture and pathogens can penetrate into the surface of the floor and continue to grow and thrive.
The degree of surface porosity is of great concern to the presence and growth of pathogens in the surface region of a concrete slab. A highly porous surface region of a concrete slab allows for the penetration of pathogens not often completely removed by routine maintenance cleanings. Once pathogens penetrate the surface, even extreme disinfection and abrasion methods are unlikely to fully eradicate their presence. As pathogens enter the concrete structure, excess moisture within the body of the concrete feeds the pathogen for continued growth. Water leaching in from the surrounding environment and permeation at the surface from spills gets trapped in the concrete composite through the pores within the body.
Polished concrete floors
To combat the issues associated with the permeation of concrete floors and excess moisture, current industry trends are seeing more installation of polished or sealed concrete floors. Industry statistics state 15 to 20 percent of floors installed are polished concrete.6 However, these alternatives are extremely susceptible to cracking and softening. Polishing concrete floors does create a luster to a shined finish, but also imparts cracks led from the concrete surface to the body of the concrete. Cleaning agents seep into the cracks and cause further degradation into the body of the concrete. Knicks, gouges, and scratches to concrete sealer causes a singularity effect. This means the bacteria on the surface of the sealer has the tendency to migrate toward the damaged spot and leach onto the concrete surface and into the concrete.
Concrete should be used as a substrate and not as a floor coating, as it absorbs bacteria within any cracks or through spills. Even with the use of disinfectants or cleaning agents, polished concrete floor is prone to further damage.
Pathogen growth
The harmful microbes reproduce rapidly at an exponential rate under favorable conditions. Factors such as oxygen, pH, temperature, and light influence microbial growth.7 Additional factors include osmotic pressure, atmospheric pressure, and moisture availability.8 In restaurants, schools, hospitals, and stores, contaminants are transmitted through touchpoints. Studies have found 40 percent of E. coli and similar bacteria strains are transferred from surfaces to fingertips when touched.9
The meat, dairy, and produce departments of stores are teaming with bacteria due to foodborne illnesses. These areas are specifically susceptible because of the large equipment which makes floor cleaning difficult. Extreme disinfection is required to kill pathogens, and this is not possible in all areas due to physical blockades.
