Inditherm Develops Innovative Low Voltage System for Accelerated Concrete Curing

Inditherm has developed a revolutionary new concept for accelerating in-situ concrete curing using blankets heated with its low voltage carbon polymer technology (CPT). The system provides protection to early age concrete, preventing damage from freezing and ensuring development of adequate strength.

The use of the blankets enables concreting practices to be undertaken in cold ambient conditions, allowing strength development and durability to satisfy service requirements. This should help construction companies achieve better control over their concreting operations, as well as helping to avoid costly penalties for late project completion

Currently, when a day is deemed a “cold weather day”, concreting operations usually have to be ceased or adequate procedures to protect the concrete have to be put in place. Implications of concreting during cold periods result in the following complications

• The degree of saturation of the concrete falls below critical level.
• The concrete freezes before a minimum strength of 3.5MPa has been achieved.
• The hydration reaction of the concrete stops and the concrete does not gain strength

If frost protection measures are not put in place, drastic measures, such as the removal and replacing the cast concrete, may be required.

Inditherm concrete curing blankets can overcome this by maintaining the temperature of the cast concrete at early ages or by raising the core temperature of the newly-cast element to accelerate the rate of strength development of the concrete.

Existing methods are extremely antiquated and generally consume vast quantities of fuel. Traditionally, rather than providing heat directly to the concrete, the ambient temperature in which the concreting is to take place is increased using hot air and open flame blowers within a purpose-built temporary enclosure.

Inditherm concrete curing blankets are re-usable, provide even temperature over their entire area and operating at low voltages, provide extremely energy efficient heating suitable for on-site application.

System Specification

Inditherm Concrete Curing Systems provide optimum performance by combining the following elements:

• The Inditherm heating material is based upon the patented CPT and is configured to provide the heating performance required. It may simply be required to stop the early age concrete from freezing or to raise the core temperature of the concrete, dramatically accelerating the hydration reaction of the cement, thereby increasing the rate of strength development of the concrete.
• Outer protection to the blankets is provided by HF welded, heavy duty, impermeable PVC cover available in various colour options. All seams are RF welded and cable input is through IP 67 Cable glands. The PVC material is easily repaired with a patch sealed using a hand held warm air heat gun.

Typical Inditherm concrete curing blanket (17m x 2m)

• Insulationis bonded onto the CPT and is a closed-cell, PU mounted foam that prevents absorption of water in the unlikely event that the curing blankets are accidentally pierced or damaged.
• Control units are manufactured to the required standard for on-site electrical distribution and are typically powered from 415/230/115 Volts mains in-put, stepped down to 50 Volts. The control unit enclosures are at minimum IP55 rated, with a lockable internal door with a display & operation interface, and an external door, for protection during on-site use. The panels have power-on LED indication and a mains isolator switch.

Typical Electrical Control Panel

• The operation of each blanket can be monitored by individual blanket operation LEDs. All power outlets to blankets are protected by DIN-rail mounted circuit breakers, appropriate for the size of each blanket. The size of the panel varies, depending on the size of the curing blankets and the number of outputs required.
• The control units are rated to SELV (Safety Extra-Low Voltage), not normally exceeding 50V, and use an electrically separated earth enabling the system to be used for both internal & external applications. The control units are mounted on a frame fitted with lifting eyes for easy transportation around site.
• Cables and Connectors. The Inditherm blankets sections are powered through multi-core screened (S-Y) cables. The size and number of cable cores are determined by the blanket size and the distance between the blankets to the control units. Extension lead connectors are multi-pin 32A, specified to the appropriate standard for the operating voltage of the blankets and the appropriate IP rating.

Installation and Storage

Inditherm Concrete Curing Blankets can be laid on concrete after a minimum of two hours from casting. This initial delay reduces the risk of damaging the finish to the concrete and inducing internal stresses within the crystalline structure of the hydrating concrete. The blankets are designed to operate up to a maximum temperature of 50 °C, gradually increasing and then maintaining the core temperature of the element throughout.

The blankets are stored in rolls and can be rolled out when required. Once the curing period or required concrete strength has been achieved, they can easily be rolled back up for storing or transfer to an adjacent pour site.

Blankets in use for curing a major car park construction

Blankets in use for curing a major car park construction

The strength of the cured concrete element can be determined by the testing of cubes heated to the same heating profile, by predetermined tables specific to the concrete mix tested at the curing temperature or by using the Maturity Method.

Performance

The effectiveness of the Inditherm technology has been proven by using it to heat in-situ concrete elements, such as rail electrification stanchion foundations, car park decks and wall panels. The Inditherm technology has been proven to heat mass foundations throughout to temperatures of 50 °C during freezing ambient conditions, thus eliminating consequential stoppages and resulting in a concrete of predictable quality and strength, with the added benefit of reduced project timescales.

Additional Uses

Inditherm heated concrete curing blankets have a number of alternative uses:

• Ground Heating. Because concrete should not be poured on frozen ground, the blankets can be used to heat the ground prior to casting.
• Preheating Formwork and Falsework. Heated blankets can be used to preheat concrete formwork and falsework to prevent temperature shock.
• De-icing of Aggregates. Although the use of frozen aggregates for concrete batching is acceptable, there must be no lumps of ice. Inditherm Curing Blankets are an ideal way of ensuring aggregates are ice-free prior to use.
• Pre-cast Concrete. Inditherm heating can be used to accelerate the manufacture of concrete elements in pre-cast units, replacing existing, antiquated steam practices. By using Inditherm, concrete cures far more rapidly and trials have shown that 28 day strength can be reached in as little as 4 days. This has tremendous implications for reducing lead times in manufacturing, cutting energy costs and improving health & safety.

Summary of Advantages of Inditherm Concrete Curing Blankets

• Allows concreting operations in low ambient temperature conditions.
• Allows earlier release of pre-stress.
• Reduced time to impose loading.
• Reduced stripping time of formwork and falsework.
• Allows more precise project scheduling, as concrete pours are more likely to take place.
• Reduced project stoppages and overall completion time.
• Simple operation.
• Low energy consumption.
• Safe low voltage.
• Simple storage; re-usable.
• Elimination of temporary enclosures.
• Improved health and safety on site, through elimination of naked flame burners.
• No risk of carbonation to concrete - a consequence of using open flame burners.

For further information contact David Catley, Business Manager, Inditherm Construction on +44 1709 761000 or atdcatley@indithermplc.com