SPOTLIGHT: FIBRE-REINFORCED CONCRETE SLABS
Polished concrete floors are becoming an increasingly popular and fashionable trend for commercial, retail, and even residential construction projects. When the design was finalized for the impressive Torre Glorieta tower project, a plan for polished concrete floors on all 18 office levels was included. With the help of value-added concrete and on-site mixing, the crack-free floors were poured without a hitch.
The risk in polished concrete floors lies in the required absence of cracks and curled joints, a tall order for any job. However, for Constructora Cimet—the owners, designers, and managers of the Torre Glorieta project—this was not an issue. “I would consider the concrete on this construction site very high quality compared to the standard of others of this type done in Mexico City,” assesses Carlos Tapia, a consulting engineer on the project. So, how did they do it?
The Torre Glorieta’s pristine polished floors were accomplished in two ways. Firstly, no wire mesh was used. Instead, synthetic fibre was added to the cement powder to reduce the cracking that concrete suffers during the hardening process. Sholem Cimet, senior architect, explains:
“These type of slabs are normally made with electrowelded mesh. It gets stepped on, the concrete pipeline is on top of it, and all the people who are working to pour the concrete make the mesh sink and be too flexible. That actually does not work well. With this fibre, we don´t need to use electrowelded mesh. The fiber is mixed all over the slab and the final result is we have flat slabs with no type of cracking.”
The concrete crew used about three kilograms of fibre per square metre, pouring for about four hours at a time to cover half a slab. Macro synthetic fibre was used, which provides similar benefits to steel fibre, but without the potential for corrosion. As Tapia describes, the value of the fibre helped not only in the areas of durability and structural integrity, but the final appearance as well:
“In the continuous concrete castings that are made in each level, the use of fibre has allowed us to have a better finish in the casting joints, because the concrete, when it has fiber, has better properties of resistance and elasticity. This also allows a final product with a better appearance and can be used as a final finish.”
Constructora Cimet used a ProAll Reimer Mixer for all the building’s concrete, and using a volumetric mixer enhanced the crack resistance capabilities of the fibre. Fibre is optimally used when it uniformly distributed and randomly oriented within the concrete. This aspect was further enabled by the use of a volumetric mixer—adding the fibre as it was mixed meant even dispersal and exact amounts, as well as the ability to pour continuously.
The second reason for such quality concrete on the project also has to do with the use of a volumetric mixer: using a mobile mixer meant the concrete was mixed on site.
“In our city, due to the complex transit, the builders have to bring the concrete in mixing trucks that take more than one and a half or two hours of driving before it can be poured, which makes the concrete lose some of its main properties. With the opportunity to have a concrete manufacturing plant close to the structure, we have the advantage of using concrete with better properties than other construction sites,” explains Tapia.
Not only did the decision to use a volumetric mixer solve supply chain issues related to location and traffic, on-site production gave the concrete crew better quality control.
“You can see that it is concrete that even when it is inspected up close and in detail the cracks are minimal compared to any other construction that does not have the opportunity of having the concrete manufactured right there at the site,” says Tapia.