With the increasing use of self-consolidating concrete (SCC), customers have higher expectations for the exposed finished surface. This means inspectors expect no bug holes—only the occasional aggregate-collection pocket—and of course, a smooth surface.
This higher expectation of surface quality challenges producers to closely monitor the surface condition of their casting beds. Many production managers are now spending some of that “saved” crew pouring time on care and maintenance of the bed's surface.
Fortunately for producers, some new anchorage methods can eliminate damage to this expensive surface. In the last 18 months, several innovative adhesive systems have been in beta testing in plants throughout the country. These tests have validated new approaches to securely affix edge forms, plywood overlay, blockouts, corners, and reveals to steel casting beds without welding or drilling.
Engineers at MILCO Concrete Concepts wanted to develop an approach for precast operations that used a special adhesive as the glue to an inexpensive forming system. Introducing the MILCO Spray Adhesive System accomplished this.
At the heart of the system is the MILCO adhesive-based form attachment. Working with engineers from 3M, developers created an adhesive that sturdily anchors forms for the tough demands of precast pours. The manufacturer reports that some producers have been able to use their set-ups for 50 pours.
Resists moisture, humidity
Producers have also discovered the adhesive is not materially affected by moisture or humidity, allowing for outdoor applications. It has been used successfully in climates where the casting bed temperature has ranged from below 32° F to 176° F.
Form removal and cleanup is easy, the manufacturer says. In most cases, a worker inserts a flat-bladed scraper under the edge of the form or block-out, causing the unit to release immediately as a whole. Any adhesive residue can be easily hand-scraped away following exposure to the sun's ultraviolet rays. The manufacturer also sells a citrus based adhesive remover that can aid in cleanup.
The adhesive is effective in securing all types of commonly used reveals, inserts, and blockouts. But once developers discovered just how secure the adhesive was, MILCO's engineers addressed another stage of the system. They've created an exclusive height-adjustable edging system that enables precasters to economically form new panels. They've designed their support to work with the TimberStrand LSL concrete panel form developed by Truss Joist, a Weyerhaeuser company.
The innovative casting system allows workers to insert standard 1 1/8-inch-thick panels into PVC track attached to the casting bed with their adhesive. This U-shaped channel form is about 3 ½ inches tall. They designed the channel with a deep well, so that workers can insert a height spacer on which panel forms can rest. There's enough room for up to 2 inches of rise, enabling producers to create form thicknesses from 6 to 10 inches using standard wood panel forms.
To cast panels with edge form installations, 8x8-inch blocks are installed on 24-inch centers along the channel's perimeter. After placing the vertical portion of an L-shaped bracket on the panel's surface, workers fasten the bracket with wood screws to the block. This provides sufficient lateral strength to the forms for the casting process.