South Amboy, N.J., concrete contractors Daryl and Glen Munk have developed all sorts of tricks to keep fresh concrete warm during the winter. The owners of Accurate Concrete have added a self-contained heating system to their mixer trucks so that they can bring their hot water along with them to jobsites.

The system was designed and built by Infern-O-Therm, a New Jersey-based manufacturer of both aggregate heating and cooling systems. The mobile unit consists of a Gallagher-style exchange unit powered by a UL-approved oil-fired burner, an electric generator, and a water circulation pump. The burner draws from the truck's fuel tank, using No. 2 diesel for fuel. The Munks also added plumbing and controls.

The mobile heating system enables producers to warm both aggregates and mixing water. By heating both, the system can help maintain the temperature of ingredients for up to 11 cubic yards according to ACI concrete temperature guidelines. Accurate trucks are equipped with 500-gallon water tanks that provide enough water for both batching and cleanout.

To heat the mixer water, the system uses a water tank constructed with a seamless fire tube, a secondary return flue, and an exhaust stack. The operator dials in the required temperature, and the unit warms the water. The fire tube rests on the tank's bottom along with the return flue. A water inlet coupling is located on the top of the tank. After the driver starts to fill the tank, the burner switches on to begin heating the water. Once the tank is full, a thermostat monitors temperature loss and automatically switches the burner back on to maintain temperature. Should the water level go below a preset level, the burner—interlocked with a low water safety valve—shuts down.

Another feature is hydronic heating of the aggregates. The Munks installed several 2-inch-diameter water lines just above the load-out conveyor in both the sand and coarse aggregate hoppers. While in transit, the driver opens a flow valve that turns on the circulating pump. Hot water recirculates throughout the aggregates and raises the material temperature.