Concrete Admixtures - Carbon Admixtures
ASTM International, formerly known as American Society for Testing and Materials, has designated ASTM C494 Standard Specification for Chemical Admixtures, which covers the materials and test methods for the following types of admixtures:
- Type A: Water Reducing Admixtures
- Type B: Retarding Admixtures
- Type C: Accelerating Admixtures
- Type D: Water Reducing and Retarding Admixtures
- Type E: Water Reducing and Accelerating Admixtures
- Type F: Water Reducing, High Range Admixtures
- Type G: Water Reducing, High Range and Retarding Admixtures
- Type S: Specific Performance Admixtures
EdenCrete® has successfully demonstrated its Type S designation via AASHTO’s NTPEP program, according to ASTM C494 (AASHTO M194). Field work has confirmed EdenCrete® is compatible with all other types of admixtures covered under the ASTM specification.
Water reducers reduce the amount of water required to achieve the specified slump and flow characteristics of the concrete, and potentially lower the amount of cementitious material used in the concrete. Using less water also results in higher strength concrete. ASTM C494 defines types of water reducers based on their intended function.
Retarders extend the set time of concrete and are typically used in scenarios including long distance and/or time to job site, hot weather, or large mass concrete pours. Accelerators are used to decrease set times, often in colder weather to prevent the water in the concrete from freezing before the concrete can set, or when accelerated construction schedules require high early strength.
Specific performance admixtures have varying purposes not covered under the other admixture types. They include pigments, shrinkage reducers, viscosity modifiers, air detrainers, corrosion inhibitors, alkali aggregate expansion inhibitors, etc. EdenCrete® qualifies as a Specific Performance admixture due to the many benefits it provides to concrete, including but not limited to viscosity modification, enhanced durability, reduced permeability, and improved resistance to cracking.
ASTM covers air entraining admixtures under ASTM C260 Standard Specification for Air-Entraining Admixtures for Concrete. Air entrainers create micro air bubbles that are trapped in hardened concrete. The purpose is to improve durability (resistance to cracking) of concrete in freeze-thaw environments by providing space for water to expand when it does freeze. Air entrainment also improves workability of wet concrete.
There are several types of concrete admixtures. We will summarize each by purpose and include the effect of EdenCrete® liquid carbon nanotube concrete admixture related to each target property. The admixtures covered in this article are:
- Air Entrainment
- Water Reducing
- High Strength
- Corrosion Resistance
- Set Acceleration
- Set Retardation
- Flowability
State DOTs use concrete for highways, roads, bridges, curbs, sidewalks, drainage and retention systems, and stabilization. Each of these have engineering specifications unique to each project. The concrete must be able to resist harsh in-service conditions including heavy vehicle loads, deicing chemicals, and impact damage.
Commercial and residential projects use concrete in many different phases of construction. These applications include slab-on-grade, slab-on-deck, foundations, columns, footings, etc. The concrete must be able to withstand potentially high compressive loads, hydraulic pressure, high flexural loads, etc.
Concrete swimming pools typically use shotcrete, which is a pumped form of concrete that is sprayed and then carved into shape. Shotcrete should flow easily through pump equipment, hoses, and nozzles, as well as adhere well to reduce dust and waste from rebound. Shotcrete swimming pool shells are subject to alkaline chemicals, seasonal weather variation, and hydraulic pressure.