Precast Concrete Products
ABOVE: One of the major costs to precast concrete panel construction is shipping weight. Lightweight aggregates can help ease the load. BELOW: Lightweight cast stone and brick veneers are incredibly realistic, quick to install, and require no weight-bearing ledge.
Building (and racing) canoes made from concrete is a multi-disciplined engineering feat. Sponsored by the ASCA, the annual concrete canoe competition is designed to challenge and engage university and high-school-aged students. Hess supplies lightweight pumice aggregate and pozzolan to many of the teams. (U.S. Air Force Photo)
PRECAST CONCRETE products fill a wide range of infrastructure, structure and decorative needs, from bridge sections to tilt-up walls to fence panels to decorative cast-stone veneers and statuary. Modern mold material tech allows for an incredible mimicry of detail. Permanent dyes and skillful coloring techniques add to the real-thing feel. The level of quality control in precast manufacture is impressive, but there is nothing lightweight about sand-and-gravel concrete. In the precast industry, that weight can carry a significant penalty, especially when shipping expenses, the needed engineered support structure, and on-site handling costs are taken into consideration. Less weight also means opportunities for larger pieces, which translates into reduced mold costs, fewer joints, and faster assembly.
The challenge then becomes to choose the right lightweight aggregate and formulate a concrete mix design[01] that finds the sweet spot between light weight and functional strength.
The first place to look for weight reduction is in the aggregate, which accounts for 65 to 80 percent of cured weight. For that, the precast industry has two broad-option categories: Cost and energy-intensive manufactured options like synthetic particles; heat-expanded shales, clays, or slates; by-product aggregate like furnace slag and fly ash pellets (which require sintering—heating and compression—to acquire usable aggregate form), or naturally-occurring, ready-to-use materials like pumice, which needs only to be crushed and graded to size—as the calcining (super-heating process that creates the foamy, lightweight physical nature) has already been done by mother nature.
Pumice, the result of explosive volcanic events, has been used successfully, economically, and extensively as a lightweight concrete aggregate for two millennia, most famously by the Romans[02]. The use of man-made and function-enhanced lightweight aggregate is a modern development striving to provide the same mechanical and physical benefits of pumice—yet pumice remains the most widely used aggregate for lightweight concretes.
The use of lightweight aggregate of necessity means the batching and mixing procedures used for standard normal-weight concrete have to be tweaked to accommodate the physical and chemical make up of the lightweight aggregate.
Run the numbers, and it becomes evident that in most every case, the cost savings in transportation alone more than justify the effort to acquire lightweight aggregate.
01—For details on pumice concrete mix designs, download the PDF: Mix Designs for Pumice Concrete. Also see the PDFs: Properties of Hess Pumice Aggregates and Mixing and Placing Pumice Concrete.
02—For more on the topic, see Pumice and Roman Concrete.
Precast Decorative Concrete Products
Because decorative cast-stone veneer products are easy to install, long-lived, and realistically colored and detailed, they are an increasingly popular choice for an classic and appealing wall finish. Mold shapes and face-color detail can successfully mimic natural quarried stone in all its vast variety because various pumice aggregate grades can be blended to meet the detail demands of any mold. As for color, the pumice from the Hess deposit is the whitest pumice available commercially (GE brightness of 84).
These lightweight, fine-crafted stone veneers arrive on the job site ready to install without needing support ledges built into beefed-up foundations or skilled stone masons to dress each piece. Whether dry-stacked or mortar-jointed, these veneers give a wall a dynamic, fascinating beauty at a significant savings in both labor and weight.
Pumice powder (pozzolan) serves a significant role in lightweight mix formulations, providing additional strength and the density to withstand the ravages of the natural elements.
Whatever is being cast, Hess Pumice’s expertise in strong, lightweight pumice-concrete could be just what is needed to increase reach and competitively ship precast concrete products farther and more efficiently.
LINKED RESOURCES
—Download a Summary of the Pumice Pozzolan Research (including the effectiveness of pumice pozzolan to flatline ASR) from the University of Texas-Austin and the University of Utah.
—Download PDF: Instructions for Mixing and Placing Pumice Concrete.
—Download PDF: Pumice Concrete Mix Designs.
—Download PDF: Properties of Hess Pumice Aggregates.
—Visit the The Concrete Canoe website.
—Visit the Hess Pozz website.