LafargeHolcim teams with cladding, rainscreen veteran to spread UHPC
By Don Marsh
A few decades ago, load-bearing applications validated high strength (10,000 psi) concrete engineering properties and quality control methods. They set a standard for high performance concrete (HPC), recognized for compressive strength and low permeability characteristics. Post-1990 admixture technology and self-consolidating mix designs, coupled with value engineering and entrepreneurial spirit, have since guided practitioners to ultra-high performance concrete (UHPC) and innovative architectural applications—where lofty compressive (> 25,000 psi) and flexural strengths (> 5,500 psi) contribute to unprecedented durability, ductility and aesthetic characteristics.
The producer behind the first branded UHPC for the global construction market continues to look beyond compressive strength criteria. Teaming with South Bend, Ind.-based Shaffner Heaney Associates, LafargeHolcim has extended its Ductal product—with 18,000 psi design and 25,000 psi ultimate strengths—to the thin cladding and rainscreen market. Long the domain of metal panels and, more recently, fiber cement, rainscreen cladding systems typically comprise galvanized bracket- or channel-mounted 0.5- to 1-in. thick panels, insulation and water barrier. The systems are specified as alternatives to masonry veneer, architectural precast, glass fiber reinforced concrete and curtain wall glazing in low- to mid-rise commercial buildings. Architects opt for rainscreens to meet energy codes, eliminate failure-prone caulking conditions, and create long-term, low (or zero) maintenance enclosures that allow moisture to drain.
LafargeHolcim and SHApe Architectural, Shaffner Heaney’s newly designated design, fabrication and installation division, are bringing UHPC to the North American rainscreen and thin cladding market under the “Envel” façade banner. Both partners have deep experience in their respective fields. The world’s largest cement producer, LafargeHolcim launched Ductal this side of the Atlantic in 2001, two years after its debut in Europe. The proprietary product was developed at the LafargeHolcim Research Center in Lyon, France, one of the top cement, aggregate and concrete testing facilities the world over. Mid-1990s research and development in the lab yielded a cement-rich, fine aggregate, self-consolidating mix bearing specialty admixtures and polyvinyl alcohol fibers or steel microfibers. In North America, Ductal has been used in exterior and interior architectural applications, primarily as thin, lightweight cross section components.
SHApe Architectural’s curtain wall and rainscreen production, installation and marketing expertise dovetails LafargeHolcim’s cement and concrete competencies. Shaffner Heaney began building its business in 1972 as an architectural product representative/distributor and installer, and became a charter fabricator of Alucobond, one of the 1980s’ leading commercial building enclosure products. Ductal cladding and Envel rainscreen panels join an extensive metal panel system program Shaffner Heaney has developed over three decades.
“We want to offer the rainscreen and façade market a number of different products,” says Envel President Craig Heaney. “We started looking at thinner profile precast in 2011, and approached LafargeHolcim on rainscreen system opportunities. The architectural precast concrete market is mostly larger panels of conventional thickness. Many producers are unable or unwilling to scale from a 6-in. panel to a rainscreen or thin cladding product 1-in. thick or less. LafargeHolcim had demonstrated Ductal production in the plant and field for thin section architectural and structural work, and looked to a partnership to leverage our commercial building enclosure market presence.”
Envel runs 800 to 1,200 lb. Ductal batches. A 1/8-yd. placing bucket has a digital scale, alerting the operator of discharged material weights, thereby minimizing waste of a costly mix.
LafargeHolcim has produced the self-consolidating Ductal mixes in pan mixers and other vertical shaft mixers, but recommended a paddle style model for the Envel line. Along with a Model 21 Praschack Paddle Mixer, which imparts minimal air in the UHPC mixtures, Mixer Systems Inc. tailored a batch plant with E-150 control package; supersack hopper; and, 225-bbl. stubby sand silo. A weigh batcher is fed via the hopper and silo screw conveyors. Liquid pigment from a Solomon Colors ColorFlo system is conveyed to an overhead vessel. The batch plant is set up for two Ductal material packaging methods: pre-mixed, with binder, sand and dry additives in supersacks; or, partial premixed, with binder and dry additives delivered in conventional bags or supersacks, and sand sourced via bulk loader into a separate silo.
THREE DIMENSIONAL FINESSE
Custom SHApe Architectural Ductal offerings include three-dimensional “eyebrow” sections, detailed for slab/floor conditions. The U-shaped members are 0.5- to 0.75-in. thick and vary in height and length. SHApe staff fabricated the flat cladding and U-shaped eyebrow formwork, the latter requiring unusually robust bracing and seals to contain the pressure-prone SCC mixes. Rolling racks and frames are used to transfer the cured product to finishing, shipping preparation and crating areas.
TAILOR MADE MATERIAL
With minimal or no primary reinforcement, Ductal offers thin cladding or rainscreen specifiers a combination of performance characteristics such as superior strength, limited mass, low modulus and dimensional stability. LafargeHolcim ties the UHPC’s unique strength, ductility and durability to an “opportunity to create with broad limits and build with total confidence.”
Ductal Architecture Business Development Manager Kelly Henry notes that self-consolidating UHPC mixes open “a world of complex forms that design professionals previously considered impossible,” and deliver finished products or structures exhibiting benefits and performance features such as impact and abrasion resistance plus low permeability to curtail carbonation, chloride ion penetration and freeze-thaw damage. “A compact matrix means Ductal has extremely low porosity, contributing to its superior performance,” she adds. “It has up to 10 times the compressive strength and five times the flexural strength as conventional concrete.”
With a goal to prove these remarkable Ductal traits in early contracts, Henry observes, the Envel team has crafted formliners with intricate details, textures and impressions essentially foreign to conventional architectural concrete. One early rainscreen client sought scored geometric shapes during the casting process to present different color schemes that change from dawn to dusk, and appear to transition even when viewed from points a few feet apart.
Trial production on Envel panels started in October 2015 at a Shaffner Heaney cladding and rainscreen fabrication shop near the South Bend headquarters. Existing welding equipment and staff dedicated to an Alcoa Reynobond aluminum panel program enabled SHApe Architectural to build formwork for basic flat cladding plus three-dimensional components. Although surfaces, textures and colors are typically customized, the producer has standardized cladding around 4- x 8-ft. panels, 0.5 in. thick, and 5- x 12-ft. panels, 0.75- to 1-in. thick—all cut to dimension.
SHApe Architectural handles Envel engineering, sales, project management and, whenever possible, cladding or rainscreen installation. Support services are concentrated in South Bend, but also available through Shaffner Heaney project management offices in Indianapolis; Louisville, Ky.; and, Livonia, Mich. Indiana is strategic to most Midwest population centers, especially for a concrete load that can economically travel farther than typical precast products, yet Envel’s first major project is in New York City: A 26,500-sq.-ft. rainscreen for a NYU Langone Medical Center facility.
The LafargeHolcim–SHApe Architectural partnership is the first North American entity positioned for continuous or mass Ductal panel production. Prior to Envel, LafargeHolcim had established limited Ductal architectural product licenses with Florida’s Gate Precast Co., Denver’s Rocky Mountain Pre-Stress, and California’s Clark Pacific. The venture’s 10-plus charter employees joined 15 existing Indiana plant staff. LafargeHolcim’s North American Ductal team (currently 13) serves architectural and engineering customers from Calgary, Toronto, or Chicago offices. A Paris team of equal size supports markets across Europe and Asia.