It’s just another day at the office. Or in this case, the job site and the concrete specimens you’ve made have completed their initial curing phase. The specimens are now ready to be transported back to the lab to continue curing for another seven days, 28 days, or more. But how do you store them so that they will cure properly and continue to gain strength until they are tested? This can all be very challenging.
Accurate strength tests for concrete, grout and masonry specimens in the form of cylinders, beams, cubes and other shapes begin with proper curing as required by several ASTM and AASHTO standards, yet one of the most common errors found in CCRL (Cement and Concrete Reference Laboratory) audits is the inability to maintain specified curing temperatures and moisture levels. Improper curing conditions directly inhibit optimal strength development of concrete strength specimens.
Moisture Rooms or Concrete Curing Tanks are both acceptable methods for curing, and specific requirements for each are outlined in ASTM C511 and AASHTO M 201. Which method is right for you? An informal poll conducted by AMRL indicated the number of laboratories with Moisture Rooms versus Curing Tanks is evenly split, so both are equally popular and offer a viable solution. In this post, we'll educate you on the pros and cons to each and help you determine which procedure is right for your lab.
Moisture Rooms look like saunas or walk-in refrigerators full of fog. Ranging from the size of a small closet to a large room, they can be pre-fabricated modular units, or constructed in-place using masonry block or other moisture resistant materials. They are sealed and often have an exterior panel mounted with temperature and humidity monitoring equipment.
Diverse methods are employed for maintaining required temperature and moisture levels in the room, from simple fogging humidifiers to systems that blend hot and cold water supplies and distribute temperature-controlled water through a system of atomizing spray heads. Rooms using stand-alone foggers require a separate method of controlling temperature to the specified 23.0±2.0°C (73.4±3.5°F). Specimen storage is on racks or shelving, configured for maximum exposure of the specimen to moist air. Specifications require relative humidity levels to be maintained to at least 95%, such that the specimen surfaces both look and feel moist. Temperature and humidity levels must also be recorded.
- The best choice for greater quantities of larger specimens
- Easy to organize specimens by age and type
- Specimens are easier to access and handle with pallet jacks and carts, if needed
- Expensive to build or buy
- Complex installation sometimes requires integration of other equipment and systems
- Maintenance can be expensive and time consuming
We recommend the Gilson HM-630 Moisture Room Panel for a wide range of room sizes. This wall-mounted control panel features:
- A complete automated control solution, blending hot and cold water supplies for distribution through HMA-298 Atomizing Spray Heads. Requires installation of supply and distribution lines.
- Easy-to-read digital controller display for easy input of temperatures
- Manual bypass system for continuous maintenance of specified temperature and humidity levels if power interrupted
- Space for mounting of temperature chart recorder or data logger
We recommend the Aquafog Turbo XE Fogging Fans for humidifying rooms up to 1,150 sq. ft.
- Tap water from ordinary water supplies is forced past the high-speed fan blades
- Centrifugal force and high speed air flow atomize water droplets to produce uniform distribution
- Stainless steel, polyethylene and anodized aluminum construction means a long, corrosion-free service life
- Units with output from 1,760ft3 to 2,160ft3 per minute are available
Livestock watering tanks and other water storage units make ideal concrete curing tanks for limited numbers of specimens. This method is acceptable and can be a good alternative to moisture rooms, especially for temporary or field applications. Water by itself may leach out calcium hydroxide from concrete specimens and reduce their strength, so the water must be saturated with added calcium hydroxide (hydrated lime). Water temperature must be monitored, recorded and maintained at the same 23.0±2.0°C (73.4±3.5°F) level as moist rooms. Tanks can also be added and interconnected for greater sample capacity and heating/cooling efficiency. Accessories for heating and circulating the curing water make it easier to maintain specified temperature levels.
- Ideal for short-term and limited space applications
- Unsophisticated equipment sets up quickly and is inexpensive
- Sufficient moisture levels are never in question
- Minimal maintenance required (clean and refill tanks every 24 months)
- Tanks are not space-efficient for large numbers of samples
- Handling specimens requires waterproof gloves
- Occasional leakage or spillage can occur
- Large water surface can tend to humidify rooms
We recommend Gilson Steel or Plastic Curing Tanks. Each model has unique features and is available in a range of capacities and dimensions.
Steel Concrete Curing Tanks come in 103gal (390L), 142 gal (538L,) 252gal (954L), and 300gal (1,136L). Features of the steel units include:
- Pipe-reinforced top for extra-strong crush-proof rim
- Sturdy rolled seam with enclosed sealant to prevent leaks
- 22-gauge, zinc-coated galvanized steel with diagonal and horizontal corrugations for strength
- Drain plug for simple maintenance
Plastic Concrete Curing Tanks are available in 40gal (151L), 110gal (416L), and 180gal (681L) capacities with the following features:
- Heavy seamless construction from recycled materials
- Resists rust and impacts
- Flexible, with sloped sides to allow partial nesting in storage
Whichever method you choose, remember that proper curing is vital to allow the optimal development of strength for your concrete specimens.
Still need help choosing which concrete curing method to use? Contact our experts at 800.444.1508.