What is hot cement? When does it occur? Does it affect our concrete?
The American Concrete Institute (ACI) defines hot cement as newly manufactured product that has not had an opportunity to cool after burning or grinding. Freshly produced, cement is discharged from the kiln at temperatures near 180° F. In most situations, manufacturers store cement for several days before shipment, and its temperature approaches that of ambient air. Sometimes strong customer-demand reduces this cooling period, and cement has a higher temperature when it reaches the end user. During the 1950s the Portland Cement Association conducted extensive laboratory and field tests on concrete produced with hot cements. On concrete pavement projects that used cement with temperatures as high as 167° F at the mixer, researchers found no significant effect on compressive or flexural strengths, volume change, checking or cracking when mixwater temperature was adjusted to compensate for the hot cement. The researchers concluded that the temperature of the freshly mixed concrete, and not the temperature of the separate ingredients, affects concrete properties (Ref.1). However, hot cement can contribute to slump loss, especially if the cement has false- setting tendencies. Hot cement can also increase water demand and increase rate of slump loss by raising concrete even though it comprises only 10 to 15 percent of concrete's weight. Elevated cement temperatures will increase concrete mix temperatures about 1° F for each 8° F increase in cement temperature. Producers are advised to establish a maximum limit of 170° F on cement temperature, as it enters the concrete (Ref. 2). To manage concrete temperatures, one concrete producer equipped drivers of his bulk- haulers with hand-held infrared heat meters. At the cement terminal drivers would first measure all the silos' temperatures, and then load material from the cooler ones. References 1. William Lerch, "Hot Cement and Hot Weather Concrete Tests," Portland Cement Association, 1954. 2. ACI 305R-91, Hot Weather Concreting, American Concrete Institute, Farmington Hills, Mich., 1994.