Northern Michigan's Manthei Development Corp. has refined returned-concrete block fabrication and is now promoting its technology for ready-mix and precast producers. Given their massive size, versatile appearance and the considerable savings offered by using recycled concrete, concrete blocks produced with American Redi-Bloc custom forms and formliners are widely used for landscape walls and sea walls, in addition to numerous other applications, company officials note. Manthei has incorporated forming units at its Charlevoix and Petoskey ready-mix plants. The company has a third concrete plant in East Jordan, plus five aggregate operations and road building and underground contracting businesses across northern Michigan.

American Redi-Bloc forms are a proprietary precast concrete block form system. Each form can be modified to produce top blocks, middle blocks, bottom blocks and half blocks by the use of inserts. Heavy 31/48-in. steel construction assures years of service, and the hinged and cam-locked design allows for fast and easy stripping, set-up and pouring, Manthei officials note. At the company's plants, blocks are manufactured without requiring any additional workers; truck drivers can do the work between loads.

The natural surface appearance of American Redi-Blocs is created by a custom rubber formliner that is attached to the steel forms, resulting in a 1.5-ft. Yen 4-ft. face that simulates large quarried stone. In addition, top blocks are recessed to allow for planting to within 6 inches of the face, eliminating the need for any expensive capstones. The blocks can be colored with concrete stains and sealers to achieve various effects.

The blocks interlock using a key-way design and each successive row is slightly recessed to allow greater heights and retaining capacities without additional restraining systems. They can be set in place by two workers with a 3,000-lb. capacity forklift. Manthei reports the availability of an engineering service to provide low-cost design for many applications.

American Redi-Bloc forms are being promoted to concrete producers who, system developers note, can reap the benefits of using 100 percent recycled material. Manthei officials add that the units' massive size and volume make it easy to turn a profit on leftover concrete returned from the field. Manthei Development Corp., Charlevoix, Mich., 800/678-2235.