Concrete Products is the leading source for Concrete Plants, Concrete Mixers, Precast, and Ready Mix news.

A New Twist on Optimization

38 Sign 400

Building and infrastructure innovations honed at the Loveland, Colo., plant are in service coast to coast—and across the Pacific Ocean.

Many precast producers have devised engineering solutions netting orders for products or structures shipped beyond their typical service area. With deliveries to every state except Alaska, plus a recently fabricated product now bearing loads in China, few peers can match the geographic expanse Colorado Precast Co. (CPC) has reached from its Loveland plant, about 50 miles north of Denver.

CPC’s capacity for high-tonnage innovations that can economically travel far and wide is most recently evident in the reinforcement of septic and utility tanks up to 32- x 10-ft. or 15,500-gal. capacity. In lieu of much conventional bar and mesh, the producer has turned to Helix 5-25 Micro-Rebar, made from cold drawn, high tensile, zinc-coated steel wire. Each piece is .5-mm wide x 25-mm (1 inch) long, with equivalent 0.02-in. diameter in a rectangular cross section—twisted a minimum 360 degrees. Michigan-based Helix Steel cites an optimal dosage range of 10 to 45 lb./yd., and packages Micro-Rebar in 45-lb. boxes or 2,200-lb. supersacks.

39 Fibers 400

Colorado Precast is able to replace nearly all conventional reinforcement—shown here in the top of a 1,250-gal. tank, cast in two pieces—with Micro-Rebar. Initial users have kept dosing a manual process, although Colorado Precast is testing a magnet device developed in house to automate transfer. Helix Steel underscores the importance of separating Micro-Rebar, due to settling during packaging and delivery.
39 Rebar 400

Confronting the quality (bar tolerances) and schedule challenges of steel placement for tapered, thin-walled tanks, CPC staff sought rebar and mesh alternatives. Engineers had seen twisted steel fibers for temperature and shrinking cracking control, but not primary reinforcement. When a pallet-sized sample of Helix 5-25 arrived in Loveland, they initially tried full rebar substitution on a 1,250-gal. septic tank, dosing Micro-Rebar at 22 lb./yd. Vacuum test results on early specimens compelled staff to think bigger.

The larger the structure for which most, if not all, conventional reinforcing steel gave way to Helix 5-25, the more time CPC crews saved in routine bar bending, placing and tying. Engineers topped out testing with a 15,500-gal. tank of hybrid design, where instead of a compression and tension dynamic with conventional reinforcement only, the cross section becomes a composite. Micro-Rebar dosed at 45 lb./yd. replaced all but a few #5 bar at the edges and penetrations.

LOAD DISTRIBUTION

CPC’s legacy 15,500-gal. tank design required 90 hours of labor to prep, tie and install about 4,500 lb. The hybrid design replaces 3,200 lb. of conventional steel with 810 lb. of Micro-Rebar, and cuts labor involved in reinforcement by an estimated 65 man hours. Performance levels measured in testing per National Precast Concrete Association Certified Plant and Colorado state guidelines have positioned CPC to propose Micro-Rebar as the principal or sole reinforcing factor on tanks for private and public projects.

40 Pour 400

The Helix 5-25 product extends the efficiency Colorado Precast realizes with the use of self-consolidating mixes, based on Sika ViscoCrete polycarboxylates.
40 Tank 266

Augmenting acceptance, especially on the agency front, is Helix Steel’s Uniform Evaluation Report (UES 0279), stating: Micro-Rebar may be used to reduce shrinkage and temperature cracking of concrete, and as tension and shear reinforcement under certain ACI 318, International Building Code and International Residential Code conditions. High tensile strength attributable to the rectangular cross section, combined with the patented twist, gives Micro-Rebar what Helix engineers note is a unique ability to engage cracking at the micro level before a crack becomes visible. With uniform distribution throughout the concrete matrix, they add, the product activates in tension to disperse a load, regardless of where forces invite cracking. One pound of Micro-Rebar equates to about 11,500 pieces. At a modest dosage of 18 lb./yd., a matrix of properly mixed concrete will have four Micro-Rebar per cubic inch.

The reinforcement was developed in the late 1990s through U.S. Army Corps of Engineers-commissioned university research. Helix Steel President Luke Pinkerton licensed the technology for commercial use in 2003. Along with CPC, the company is working with other precast producers who have realized wide acceptance of utility or drainage structures where Micro-Rebar is bearing 70–100 percent of tension and shear loads. Demonstrations, promotion and testing are securing the reinforcing alternative in specifications up to state department of transportation levels. — Helix Steel, Ann Arbor, Mich., 734/322-2114; www.helixsteel.com