Packing More Value into the Mix

HEADNOTE

System optimizes concrete cost and performance

By facilitating collaborative, sophisticated approaches to business, information technology has transformed the global economy. It's now streamlining the concrete industry via the iCRETE(TM) system

for concrete producers. Using advanced algorithms that optimize the performance and cost of a mixture through improved particle packing and continuous process control, the iCRETE system provides improvements in production consistency, quality, and profits while reducing the environmental impact associated with concrete production. Producers also gain these benefits without completely redesigning their concrete plants or changing their existing raw materials.

Producers licensed to use the iCRETE system install sophisticated monitoring equipment and perform ongoing materials characterization tests. Through a direct Internet link integrated into the plant's batching software, the iCRETE computer program uses the information to adjust each batch to the current environmental and materials conditions. Compared with the producer's traditional mixtures, iCRETE mixtures have:

* Better workability;

* Reduced variability; and

* Up to 25% less portland cement.

Producers have found that iCRETE can help them satisfy performance specifications to provide normal and high-performance concretes that are also the most costeffective and environmentally-friendly products possible.

OPTIMIZED

The iCRETE system helps the producer select mixture proportions, and it ensures that the mixture is delivered as designed. Before production, the iCRETE software program uses inputs that include:

* Particle size and packing density for the cementitious materials and aggregates;

* Unit costs for all constituents; and

* Target values for strength and slump.

The iCRETE program then iteratively selects numerous mixture proportions and, using proprietary models, predicts the strength, slump, cohesion properties, and cost of each mixture. The software then compares these predictions against the target values to determine the optimal mixture.

The producer's plant may require some retooling to ensure that the accuracy of the batching and weighing equipment will be adequate to capture the advantages of the iCRETE system. Also, systems must be installed to continuously monitor the moisture content of the aggregates so the iCRETE system can, through a feedback mechanism, vary the amount of water added to each batch. The process leads to significantly less variability than is conventionally achieved, in turn leading to a lower average strength needed for a low probability of the concrete falling below the specified strength. The costs for retooling are therefore quickly recouped.

SPECIFICATION

Rather than attempting to instruct a producer in the finer points of making concrete, it's logical for designers to indicate what's needed in terms of strength, durability, and aesthetics. Designers, however, often lack confidence that the concrete will actually have the required performance; and contractors, concerned that they will be held responsible for any problems or that they'll get concrete that's difficult to place, refuse to relinquish control of the mixture ingredients. Performancebased concrete specifications can provide a solution, most notably by giving the responsibility for the mixture proportioning to those who have the most expertise-the ready mixed concrete producers. But how can designers and contractors have confidence in the performance and consistency of the delivered mixtures?

The iCRETE system assures project owners, architects, engineers, and contractors that the plant is efficiently configured, the production process is correctly controlled, the mixtures are properly batched, and the plant operators and truck drivers are trained and experienced. Peter Stamatopoulos, Quality Control Manager at Elmhurst Chicago Stone, a large ready mixed concrete producer in the Midwest U.S., may have initially been a skeptic, but he's since turned into a believer in iCRETE's ability to meet performance requirements. "The differences in cost savings, guaranteed strength, and durability were obvious," he said.

PERFORMANCE

Often, the specifications for tall building structures, super-flat floors, or high-durability bridge decks call for high-performance concrete with key characteristics such as high strength, very low shrinkage, or low permeability. The iCRETE system allows producers to consistently supply such mixtures, without running new trial batches for each new mixture. "Having visited a ready mixed plant to observe the new iCRETE system," reports Hamlin Jennings, a Materials Science Professor at Northwestern University, "I observed a system that imparts a higher degree of quality control than is presently employed by the industry. Although many of the technical components of the iCRETE system are not new, their combination into a system that optimizes concrete to reduce material cost while maintaining specified strength and slump is new. It is particularly new as a fieldtested system."

APPLICATIONS

Since iCRETE technology was developed in the mid-1990s, it's been used on such major infrastructure projects as the Great Belt Link in Denmark, the Channel Tunnel between the UK and France, and the Confederation Bridge between the Canadian provinces of New Brunswick and Prince Edward Island. It's now being used and evaluated in the U.S.

For example, Quadrozzi Concrete Corp., one of the largest ready mixed concrete suppliers in New York City, has adopted the iCRETE system. When Misha Tartarovsky, Quadrozzi's Quality Control Director, first learned about iCRETE from a concrete contractor, he was skeptical. "Most of what had been presented to me in the past was too complicated to be practical." When he viewed the process, however, Tartarovsky's reaction was, "This is so simple. Why didn't anybody think of this before?"

One beneficiary of Quadrozzi's adoption of iCRETE is Sorbara Construction, a contactor that builds high-rise buildings on a demanding two-day-per-floor schedule. On a project in Battery Park City, project manager Billy Kell tried iCRETEproportioned mixtures without telling the concrete installers or finishers. "I watched them working with it, and you could see this look in the guys' faces-that this was really different." The trial was a great success. In fact, when the trial ended and the conventional concrete was delivered to the site, the workers complained that there was something wrong with the concrete. Sorbara plans to use concrete batched using the iCRETE system on Frank Gehry's next big project in the city, the 76-story Beekman Place.

Another Quadrozzi job incorporating iCRETE mixtures is the new 1776 ft (540 m) tall Freedom Tower. For the first shearwall placement on October 22, 2007, the iCRETE system was used to produce 14,000 psi (96 MPa) concrete-the highest strength concrete ever placed in New York City. To control temperature rise in the massive walls, this concrete was produced with a portland cement content of only 527 lb/yd3 (313 kg/m3), supplemented with fly ash and slag cement to reach the required strength. Workability was so good that the 630 yd3 (480 m3) continuous pour was pumped over 400 ft (120 m) at 120 yd3/hour (90 m3/hour), and the concrete flowed readily around the dense assembly of reinforcing bars.

Catalina Pacific Concrete, a California ready mixed concrete producer, has also tested iCRETE mixtures. Using conventional and iCRETE mixtures with design strengths of 4600 and 10,000 psi (30 and 70 MPa), they recently placed flatwork samples at a building site in Century City (Fig. 1). The high strength iCRETE concrete was easily placed by pump (Fig. 2). Both normal and high strength iCRETE mixtures were also easily finished (Fig. 3). These examples show that iCRETE's sophisticated approach to concrete production can lead to high quality and efficiency-strong evidence that collaboration between concrete producers and iCRETE is going to be a major factor in the future of the industry.

Selected for reader interest by the editors.

-iCRETE, LLC

CIRCLE 52

AUTHOR_AFFILIATION

ACI member William D. Palmer Jr. is with Complete Construction Consultants, llC, which provides engineering, inspection, writing, and editing services to the construction industry. a licensed professional engineer in michigan and Colorado, he has served as engineering editor of Concrete International; Director of educational Programs at aCi; executive Director of The masonry Society; and editor-in-Chief of Masonry Construction, Public Works, and Concrete Construction. Palmer is Chair of aCi Committee e703, Concrete Construction Practices, as well as a member of aCi's Certification Programs Committee and aCi Committee 306, Cold Weather Concreting.