Concrete solutions: fast-setting mixes gaining popularity
By PATRICK CALLANSkills Development
Quick-setting mixes settle into construction industry
When it comes to repairing large sections of concrete roads—especially on busy highways, bridges or urban areas—quick turnaround times are of the essence. Shutting down individual lanes or entire roadways for extended periods to allow workers to come in and do repairs not only leads to lengthy delays for drivers, it is also costly and time consuming for the construction teams doing the work.
These are just some of the many reasons why the North American construction industry is increasingly turning to fast-setting, quick strength-gaining concrete products, which are designed to have traffic back on the road safely and at full capacity within hours of the concrete being poured.
Quikrete unveiled one of the latest fast setting concretes, FastSet Latex Modified DOT (Department of Transportation) Overlay, in January at the World of Concrete trade show in Las Vegas. FastSet is a fiber reinforced, very low permeability, rapid-setting overlay material, specifically designed to speed up concrete bridge deck repair and to extend the service life of concrete bridge decks. Each 3,000-pound bulk bag (which should be mixed to a slump of eight to 10 inches) covers about 700 square feet when applied at a 0.5-inch depth; 350 square feet when applied at 1-inch depth; and 250 square feet when applied at a 1.5-inch depth.
FastSet is designed with a 90-minute working time and it reaches 3,000 psi in three hours, allowing traffic to resume promptly. It also possesses a unique ability to be applied from a half inch to full depth repairs (up to eight inches thick) in a single pass, rather than the multi-step process of restoring the bridge decks by making individual patches and then applying new wear surface. When the project is complete, FastSet provides a new 20-year wear surface.
“There are other latex modified overlays out there, but our DOT overlay is a single component, factory blended. The only thing you have to be concerned about is the amount of water you put into the mix,” states Frank Owens, vice-president of marketing for The Quikrete Companies Inc.
Owens explains other systems use mobile mixers that might have sand in one compartment, gravel in another, and several other moving parts before the liquid component is added. The process of blending multiple components on a jobsite can lead to significant variations in consistency, strength, product quality and set times.
“FastSet DOT overlay is already pre-blended, you just add water. The latex components and polymer components in the mix are all pre-designed and they’re already in there in a dry form,” he says.
When it comes to bridge deck repairs, most overlays require 1.5 inches of thickness to be applied, he says. At 145 pounds per cubic foot, concrete adds significant weight to a bridge deck that could be up to 40-years-old, which can stress the bridge and its structural components. But since FastSet is designed to be applied at 0.5 inches, “it cuts the weight by two thirds yet still provides the wear surface.”
The first major repair job done with FastSet took place in Butler, N.J. this past September. A bridge deck along Route 23 in northern New Jersey had suffered from years of harsh weather and withstood heavy loads on a daily basis, thanks to traffic from a nearby quarry. Using FastSet, the construction team placed and finished the overlay with 54 feet long by 15 feet wide passes in 20 minutes. The work was completed overnight and the bridge reopened to traffic the next morning. The restored bridge deck is expected to last 20 years.
“When we applied this product they didn’t even shutdown the bridge. We were applying to two lanes while one was open,” boasts Owens. “One of the great advantages of this product is we’ve been able to build in working time so that it can be placed and finished properly and still be able to open to traffic within a few hours.”
SETTING THE PACE
Not to be outdone is CTS Cement’s Rapid Set fast-setting hydraulic cement, which has a track record dating back to 1982. It is used for concrete applications requiring high durability and fast strength gain. Rapid Set cement is mixed with water and aggregates to produce high-performance, one-hour strength concrete, mortar and grout mixtures.
It gains strength much faster than traditional Portland cement— up to 15 to 20 MPa (2,250 to 3,000 psi) in 1.5 hours—and in most cases it can achieve the same strength in one day as the same amount of Portland cement mix would achieve in one month. Rapid Set concrete is primarily used on highway pavements, bridges, airport runways, tunnels, harbours, floors and precast sidewalks. It can extend the life of a bridge deck by 25 years.
More than 400,000 cubic metres (520,000 cubic yards) of Rapid Set concrete pavement has been placed in major airports and highways across Canada and the U.S. Jacques Bertrand, owner and founder of Béton Mobile du Quebec Inc., which specializes in providing custom-mix and specialty concrete, first used Rapid Set in 2002 for an expansion joint replacement on Pie IX Bridge across Rivière des Prairies in Montreal. His company has used it ever since.
“We use it regularly to repair bridge slabs, bridge decks, joint repairs, parking structures and numerous other repairs, mostly in the province of Quebec,” he says, adding the main advantage of using Rapid Set is to accelerate the work schedule. “The initial set would be about 15 to 20 minutes versus three hours for normal Portland cement. The final set for Rapid Set is about 45 minutes versus about five hours for Portland cement.”
Rapid Set is also used regularly to maintain Canada’s busiest bridge: Montreal’s Champlain Bridge, which crosses the St.Lawrence River to connect Montreal Island with the south shore.
Bertrand explains Rapid Set saves facility owners valuable time and money with quick turnaround. For example; when his company did repair work on Toronto’s Gardiner Expressway in 2011 and 2013.
Using Rapid Set concrete, the repair contractor completed a major bridge deck repair over a weekend (when there’s less traffic) with significantly lowered overhead costs. Most importantly, it greatly reduced the inconvenience of multiple and lenghty lane closures for the public. Although weekend labour is more expensive, it still far outweighs working during the week when productivity is low because of traffic congestion. Traffic control management can be as much as 20 per cent of the cost of the total job, he adds. “The higher material cost is offset by lower cost of traffic control and traffic management.”
ON SOLID GROUND
The old adage time is money could prove to be a driving force behind the continued popularity of fast-setting products like Rapid Set and FastSet in the coming years—especially in and around Canada’s busy metropolitan areas.
Owens says now that FastSet has met Quikrete’s expectations in the U.S. following a successful product launch, the plan is to bring it to Canada and begin distributing it through their local partners across the country.
Bertrand adds Rapid Set has been used for more than 12 winters on Quebec bridges and is now standard with Transport Quebec. And the City of Toronto is looking at doing more work with the pro
duct now that they have experienced three successful winters with it on the Gardiner Expressway.
Patrick Callan is On-Site’s assistant editor, send comments to email@example.com