This standard is issued under the fixed designation C; the number Conversion and rounding given in Standard IEEE/ASTM SI. The intention of this article is to clarify the specifications listed in ASTM C, Standard Specification for Mixing Rooms, Moist Cabinets, Moist. ASTM C Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage. Tanks Used in the Testing of Hydraulic Cements and Concretes.

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Since there seems to be a lot of confusion and misunderstanding regarding curing facilities and their requirements, I decided to write an article about them.

This article is not an exhaustive account for x511 mix designs, regional specifications, or capabilities of each laboratory. Each laboratory will need to consider the unique requirements of their testing needs when designing and maintaining a curing facility. This article can be utilized as a general guideline for curing materials that include Portland cement concrete, masonry mortar, masonry cement, concrete beams, grout, and hydraulic cement see Table 1.

The requirements for this soaking period are temperature and the use of calcium hydroxide. No recording thermometer or thermostatic control is required. Tanks compliant with C will also meet wstm requirements of C Importance The importance of having a properly functioning curing facility cannot be overstated.

Trying to cut corners on curing can produce erroneous test results.

The ability of a lab to properly cure and store specimens is vitally important to achieving accurate results on compression tests. Dry conditions, low temperatures, and abundant fresh water leaching can all lead to low strength atm.

High temperatures can lead to falsely high strength. Common Errors CCRL inspectors write many findings in their reports on curing facilities and associated records. Curing facilities, be they tanks or rooms, require lots of documentation.

Depending on the type of material you are working with, you should refer to the applicable specification or standard to determine whether you need to maintain tanks or a curing room, or even a tank within a curing room. Curing rooms range in size, and it is recommended that labs install shelving in a configuration convenient to the size and shape of the room. Both curing tanks and moist rooms have their benefits and drawbacks.

ASTM C Standard

Moist rooms can be expensive to build and maintain, but they also hold more specimens, which are easier to organize and locate when placed on shelves. Curing tanks might be a more cost-effective solution, but temperature control can be difficult, and they take up a lot of floor space. Tanks also require additional documentation.

Whichever option you choose, you must be capable of heating or cooling the system, regardless of your geography, even if the laboratory is located in a region with a fairly consistent climate. Have you ever wondered which option your competitor is using? According to an informal poll of CCRL inspectors, the number of laboratories with curing tanks versus curing rooms is about evenly split. They both seem to be equally popular.

Requirements for Curing Tanks If your lab chooses to use curing tanks alone not inside a curing roomthe following information should help clarify some of the requirements. Essentially, your tanks need to be made of a non-corroding material like thick plastic or metal. Fill the tanks with water that has been saturated with lime calcium hydroxide, a. The temperature of the solution in the tanks must also be monitored. Tanks are available from typical laboratory suppliers, but also from farm supplies, as they can also be used as food and water troughs for animals.


If you have more than one tank, you have two options for configuration. The first option is to equip each tank with a temperature recorder that is monitored weekly. If you decide to go this route, you will need to have at least one calibrated chart recorder or digital recorder per tank see Figure 1.

Alternatively, you can connect your tanks with tubing, basically creating one large astn see Figure 2. If you choose this option, you must make sure that there is a means of evenly circulating the curing solution throughout all of the tanks.

Most labs that choose this method use a fish pond circulator.

The Cure for The Cure: A Guide to ASTM C and Your Curing Facilities

Take extra care to ensure that the flow between the tanks is even. Accidentally draining and overflowing a tank can occur if there is an equipment malfunction. Whether you have multiple tanks or just one tank, you must d511 routine maintenance.

For tank maintenance, you are required to thoroughly stir each tank at least monthly to replace depleted calcium ions. At least every 24 months, you must clean and refill each tank with calcium hydroxide to saturation. Requirements for Moist Rooms If your lab tests a lot of samples or tests a variety of materials, a curing room might be the best choice for you.

There is also the option of using a smaller moist cabinet for specialized projects rather than building an entire room. Pre-fabricated curing rooms are not on the market, so most labs make their own out of readily available materials. The size of your room will depend on how much space is available in your lab and how many samples you plan to store.

Moist rooms are made from walk-in refrigerators, insulated shipping containers, or scratch built rooms. In both moist cabinets and rooms, care must be taken to ensure air-tight seals on doors and walls. This will significantly help maintain the temperature and humidity requirements. In both cases, extreme care must be taken to prevent water from dripping onto the stored specimens, since lime can leach out and lower the strength. In order to maintain an extremely humid environment, you must have a good water supply and humidifying equipment, and the temperature must be maintained at After installing the main room and insulating it, labs need to c5111 misters onto water lines spaced throughout the room.

A common problem with misters is that they c5111 to clog. Without proper maintenance and upkeep, the misters will atm to drip water on the specimens before clogging entirely. The system used in most grocery store produce sections works very well for this purpose. It is highly recommended that laboratories institute a program in which the spray nozzles are switched out with a second set that has been soaking in a mild acid such as vinegar to slow the clogging process.

Maintaining two sets of working spray nozzles will be less time consuming than continuously repairing dripping nozzles, or suffering the consequences of improperly cured materials. There are two options to fulfill this requirement. You may use either a chart recorder or a digital recorder.

More labs currently use chart recorders. Some of the drawbacks include the pen drying out and having to be replaced often, and the temperature not reading correctly.

The benefit of a chart recorder is that the information is readily available and in full view at all times, and labs that use these tend not to get written up for not evaluating the weekly temperature data. It is important to choose temperature charts that are easily read and do not have a scale so small that the pen or marker line width exceeds the scale lines.


Digital temperature recorders or data loggers are gaining popularity. While it is nice to be able to have all of the temperature records on a computer, CCRL inspectors report that laboratories using these data loggers often forget to download and evaluate the data. Unless you are a new lab, thinking of rebuilding, or moving to a new building, you probably already have a curing facility set up. The best way to make sure that you have a well-circulated, temperature-controlled facility that meets all of the requirements is to take the time and money to get it right the first time.

First, heavily consider the placement of your moist room or tanks. It is best to have them inside and against an interior wall. If you have to install a moist room against an exterior wall, try to give at least 6 inches of dead air space. Tanks near drafty bay doors will also wreak havoc on any kind of temperature control you think you have. To help reduce exposed surface area, try covering the tanks with large pieces of Styrofoam insulation.

Take the time to install insulation, piping, replaceable misters, heating and cooling units, circulators, and temperature recording devices as applicable. Also consider all the man hours lost to constant maintenance and quick-fixes, not to mention having to spend time writing corrective action reports for your AASHTO re: In the end, remember that no matter how much precision is used to mix your ingredients, your curing methods will impact the strength of the material you are testing.

Special thanks to Jan Prowell and the other employees of CCRL who shared their experiences evaluating curing facilities and records.

It depends on the type of water and what is in the water. There is no set lbs of calcium hydroxide per gallon of water. The water should be saturated. The easiest way to determine this is to add calcium hydroxide to the water and then stir the water. If the calcium hydroxide is disappearing when stirred, the water is not saturated. Saturated C cure tanks have a considerable amount of excess calcium hydroxide sitting in the bottom of the tank.

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Login to be able to comment. Comment cannot be empty. You typed the code incorrectly. The gold standard for laboratory accreditation in the construction industry. The Cure for The Cure: Some of the most common errors include: Show oldest on top Show newest on top. How much calcium hydroxide do you use per gallon of water for a cure tank?

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Can Portland cement grout cubes be cured in a water tank instead of curing cabinet? From Table 1 it looks like it. Please type the code above. Subscribe to new comments.