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Al Stemler of Lafarge Construction Materials was faced with an hourly throughput problem at Lafarge's Bow River Plant in Calgary, Alberta in spring 1991. Faced with increasing demand for curb, gutter and monolithic sidewalk construction, the plant's equipment couldn't handle the demand. Curb and gutter work requires a high cement content, low slump, and consistent mix. The plant's hourly production slowed from 130 yards per hour to just over 60 yards per hour with the low slump mix. Finally, the company decided to replace its low-intensity mixer with a high-intensity mixer, and mixed 1500 yards the first day the new mixer was in operation. "The high-intensity mixer is the most significant investment we made in equipment in more than 30 years," says Stemler. "Our mixes appeared richer and we received favorable comments from the field on the first day of operation with the twin-shaft, high-intensity mixer." The high-intensity mixer provides Lafarge uninterrupted production of many mix designs at consistent outputs. There are tradeoffs, however, to this gain in production. Not all existing batch plant weigh systems, controls, or plant infrastructures lend themselves to an economic retrofit. Modifications must be made, in many cases, that can be costly and time-consuming.