Microfibers for concrete encompass a broad range of different material types that are predominately used as an additive to traditional cement mixtures as a way to prevent plastic shrinkage during the early-stage curing process. While microfibers for concrete are used to enhance specific qualities of cement, they are not technically a supplementary cementitious material and are instead a unique product offered by R-E-D Industrial Products. This article will take a closer look at what exactly is plastic shrinkage cracking, the three different types of microfibers for concrete applications, acrylic, polypropylene, and natural, and why R-E-D Industrial Products AC-50 and AC-60 acrylic microfibers outperform the competition.
Preventing Plastic Shrinkage Cracking with Microfibers for Concrete
Plastic shrinkage cracking in concrete is a type of cracking that occurs during the early stages of the concrete's curing process, typically within the first few hours to days after placement, and is the most notable issue that can be addressed by the addition of microfibers for concrete. Plastic shrinkage is caused by the rapid evaporation of water from the surface of freshly poured and still-plastic (not fully hardened) concrete. This evaporation of water can lead to the weakening of concrete. There are three specific stressors to consider:
Surface Drying: As the concrete is exposed to air and environmental conditions, especially in hot or windy weather, the surface layer of the concrete begins to lose moisture rapidly.
Differential Drying: The outer layer of the concrete dries more quickly than the inner portion, creating a moisture gradient within the concrete. This means that the surface layer contracts due to drying while the inner layer is still relatively moist and hasn't yet undergone significant shrinkage.
Tensile Stresses: The differential drying leads to the development of tensile stresses at the surface of the concrete. Since concrete is relatively weak in tension, these tensile stresses can result in cracks forming on the surface.
These cracks are referred to as "plastic shrinkage cracks" because they occur while the concrete is still in its plastic or unset state before it has fully hardened. These cracks are typically shallow and can be quite fine, resembling hairline cracks. They often radiate from a central point or appear in a random pattern on the surface. Preventing plastic shrinkage cracking is important because these cracks can compromise the appearance and durability of the concrete surface. To mitigate the risk of plastic shrinkage cracking, concrete workers often employ various strategies including microfibers for concrete as well as the following:
Use of Windbreaks and Sunshades: Protecting the concrete surface from direct sunlight and wind can help reduce the rate of surface moisture loss.
Fogging or Wet Curing: Spraying water mist or covering the surface with wet burlap or curing blankets can slow down moisture evaporation and reduce cracking.
Use of Retarding Admixtures: These chemical additives can delay the setting time of the concrete, giving more time for finishing and reducing the risk of cracking.
Proper Timing for Finishing: Timing the finishing operations (troweling) to coincide with the initial setting of the concrete can help close surface pores and minimize the potential for cracking.
Concrete Fibers: Create a spider web-like matrix to keep concrete interconnected while simultaneously protecting against surface-level abrasion and erosion
It's important to know that plastic shrinkage cracks are typically surface-level and do not compromise the structural integrity of the concrete. However, they can detract from the appearance of the finished surface and may serve as potential pathways for the impediment of moisture and contaminants if not properly repaired or addressed.
Which Concrete Microfiber is Best?
When it comes down to it, two main differentiating factors separate the different types of microfibers for concrete. The first is how well each microfiber addresses and prevents the possibility of plastic shrinkage during the curing process. The second factor separating the three different types discussed below is cost.
Acrylic Concrete Fibers
Acrylic microfibers for concrete are widely regarded throughout the industry as the premier additive material to prevent plastic shrinkage cracking. Products like the AC-50 and AC-60 acrylic fibers offered by R-E-D Industrial Products are made from the precursor material for the incredibly tough material carbon fiber and offer a 90% or higher percentage reduction in plastic shrinkage during the early-stage curing process.
Unlike the prevailing thought that microfibers help speed the water evaporation process, these innovative fibers form an ionic bond (unlike their alternatives) with the cement mixture and work to prevent the water from rising to the surface and increasing the possibility of shrinkage cracking. Originally developed by the Army Corp of Engineers to replace wire mesh, acrylic microfibers for concrete are an incredible additive for numerous applications including residential concrete slabs, architectural designs, sidewalks, 3D printing projects, and other non-structural usages.
Polypropylene Concrete Fibers
Polypropylene microfibers for concrete are the most widely used product available on the market today. Rather than forming the more cohesive ionic bond seen in acrylic fibers, polypropylene fibers only create a mechanical bond and do not change the chemical structure of concrete. This additive works similarly to other concrete fibers by slowing the rise of water to the surface and reducing the possibility of plastic shrinkage cracking. Polypropylene microfibers are available in several different sizes depending on the end application.
Natural Concrete Fibers
Natural microfibers, or buckeye fibers, for concrete applications, are derived from cellulose fibers found in tree pulp. These stringy materials are the lowest-cost additive and subsequently offer the lowest percent reduction (60%) of plastic shrinkage cracking in concrete. Natural concrete fibers are not an adequate substitute for wire mesh, unlike acrylic or polypropylene fibers, and do not provide any tangible increase to flexural strength in the concrete. Natural fibers are not recommended for high-volume commercial applications but are a valid additive for use in small-scale residential projects or for DIYers looking to reduce plastic shrinkage cracking in at-home usages.
R-E-D Industrial Products Microfibers for Concrete
With over forty years of combined experience working with customers to improve their concrete applications and address problems such as plastic shrinkage cracking, R-E-D Industrial Products is a wealth of knowledge on the subject. R-E-D offers high-quality acrylic microfibers designed to minimize plastic shrinkage cracking during the curing process. Our acrylic microfibers are a cost-effective solution for reducing surface cracking by up to 90% in fresh concrete, ensuring a smoother finish and improved longevity in challenging environments. When you choose to work with R-E-D Industrial Products, you can expect prompt delivery and reliable customer support. If you'd like to learn more about how our AC-50 and AC-60 acrylic microfibers can help, reach out to our team to discuss your project requirements and receive personalized recommendations.