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Low-intensity mixers come in different shapes and sizes. There is no single definition of what is low-intensity mixing and what is high-intensity mixing. In this case, low-intensity mixers will be any mixer that mixes by lifting or folding the mix. A high-intensity mixer will be one that mixes by moving through the mixture with high shear forces to disperse cement. Central ready mixed and paving concrete plants in North America have historically favored large single-batch, low-intensity mixers. High-intensity mixers are becoming more common in central mixed concrete plants. High-intensity mixers have the advantage of higher achievable strengths given the same mix proportions, allowing for decreases in "over design" factors on given mix designs. Other advantages include short mixing times, reduced maintenance schedules, more compact design, and the ability to maintain output rates regardless of slump. Europeans and the Japanese have long used high-intensity mixers for all types of concrete production. Drum mixers are seldom used in plants larger than hand-fed, site-specific production sizes. In recent years, the idea of "blending the mixture at high velocity" has been tested at several locations in North America.