Fast Track Concrete: Work in the fast lane

Holcim Canada has developed a special concrete to meet the stipulation by the Ministry of Transport of Ontario that any necessary repair works to highway sections have to be performed overnight, within an eight-hour window. Full use of the highway is required by the end of the shift. A purpose-developed, high early strength concrete mix and the wholehearted commitment, night after night, of Holcim’s experienced staff guarantee continuing mobility.

 

 

In the Greater Toronto Area of Ontario, Canada, a series of high-traffic, multi-lane highways were built with a concrete base more than 30 years ago. When repairs are required, Ontario’s Ministry of Transport stipulates that the repair work must be done at night during an eight-hour window so that the affected portion of the highway could be reopened for the start of the morning rush hour. This challenging task required an innovative solution that achieves design strength (20 MPa) in less than four hours. High early strength was the primary target. Later strength development was not especially relevant given that 30 MPa is required after 28 days. A concrete mix design meeting these requirements was developed by Holcim Canada through its ready-mix division, Dufferin Concrete. The concrete mix design is called Fast Track and uses high performance cement, controlled temperature water and precise proportions of set accelerating admixtures.

 

Timing and know-how are key

Holcim Canada’s Dufferin Construction conducts the actual highway repair work, which requires pinpoint timing and coordination of concrete and construction crew activity in order to meet the customer’s demanding expectations. When a part of the highway has to be repaired, the highway typically closes at 22:00. The work flow has to be well organized and rapid in order for the highway to be reopened to regular traffic by 05:30. Dufferin Construction’s first step is to remove the asphalt surface and the concrete bed, which can range in size from 7 m2 to 35 m2. Once the “old” concrete is removed, the existing grade is leveled off and new dowels are drilled into the adjacent concrete pavement using a pneumatic gang drill.

 


Strict inspections at the plant

The raw materials constantly undergo meticulous inspections at the plant to ensure that all concrete deliveries comply with the required formulation. Tests are carried out to determine the air content, temperature, strength, slump, and flow properties of each concrete batch. Any necessary adjustments to the mix formulation, e.g. due to weather conditions, are made immediately to ensure delivery of a top-quality product to the site at all times. The truck mixer drums are also checked every day to ensure there is no concrete residue which may affect the mix.

 

Best-practice concrete placement

On delivery, it is critical that the concrete be at the prescribed temperature within a tolerance of just a few degrees to achieve the required high early strength. Each ready-mix truck is dispatched to arrive on site as soon as the area is ready for the new concrete. Once on site, accelerators are added to the mix by the dedicated concrete technician. Timing is now especially crucial because after the accelerator is added the workability of the concrete changes. In less than five minutes, the Fast Track concrete must be tested and poured at the prescribed slump. The concrete is quickly discharged into the repair area, tined and then covered with plastic sheets and thermal blankets for curing. In less than four hours,the concrete reaches 20 MPa in strength, and the highway is ready once again for traffic.



Dedicated crews bring expertise to the mix

A major part of the success of this innovative solution comes from having a dedicated crew from Dufferin Concrete which is assigned to all night-time Fast Track jobs for a year. The crew, consisting of a plant supervisor, a batcher, an on-site technician and a number of ready-mix drivers, have developed detailed knowledge of the product and how best to use it. This allows them to assess at all times whether the required concrete quality has been achieved or whether they need to intervene. It is thanks to their many years of experience and single-minded commitment that commuters in the Greater Toronto Area can expect less congested roads every morning on their journey to work.

 

“The challenge of managing the upkeep of major infrastructure in one of the world’s largest metropolitan areas and commercial hubs, while mitigating disruption to those it is designed to serve, is a delicate balance. Holcim Canada’s Fast Track solution makes use of innovative technology and expertise that helps achieve this and keep people and business moving.”

Eddy Marin, District Manager, Dufferin Construction Company