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How to mechanically grind and polish steel fiber reinforcement concrete (SFRC) without exposing fibers?

Jointless steel fiber concrete flooring is a great floor solution and becoming more and more popular worldwide. A major concern with SFRC is exposed fibers or loose fibers at the wearing surface. The only way you can grind and polish with ZERO fiber exposure is to apply dry shake hardeners in 2-4 layers and using minimum 5-6 kg/m2 (1-1,2lb/sqft) of dry shake hardener. Applying more layers than just one or applying thicker layer has always been a risk. This article will provide a solution to this problem.

Steel fiber concrete flooring can provide superior resistance to minimize cracks in hardened concrete, as well as maximum resistance to withstand heavy loads. SFRC can be made totally without joints. Jointless floors are floors that have no saw cut joints at all, providing spaces without joints as large as 40 or 50 meter wide span.

SFRC concrete with 3kg/m2 of dry shake hardener after polishing

Steel fibre reinforcement concrete (SFRC) completely eliminate steel fabric reinforcement, saving on both materials and labour

The elimination of conventional reinforcement, and in many cases the reduction of sectional thickness can contribute to some significant productivity improvements. Steel fibers can deliver significant cost savings, together with reduced material volume, more rapid construction and reduced labor cost.

A major concern with SFRC in industrial or commercial project is exposed fibers or loose fibers at the wear surface.

Plain concrete (SFRC)

SFRC floor can be made totally without any topping, but there is always high risk that some fibers will exist on top of the surface after final finishing. Premature troweling has been proven to exhibit more fiber at the surface since
the cement paste layer can be moved to expose the fibers. Correct timing with a power trowel will produce a smooth, even finish with minimal fiber exposure. SFRC floors still cannot be used for polished concrete project without topping as grinding will always expose fibers.

Problems with dry shake hardeners

The most common way is to use dry shake hardeners on the top to suppress steel fibers near the surface. In most cases when dry shake hardeners are used; some still fibers exist on top after finishing and problem goes even worse if you mechanically grind and polish the surface; as you will remove cement paste which hide fibers. Typically, just 3-4 kg/m2 (0,6-0,8 lb/sqft) of dry shake hardener is applied on top and that is not enough if surface going to be polished as part of dry shake will mix up with base concrete and you have just ~1mm layer on top. In many cases grinding and polishing dry shake which have only 3-4kg /m2 (0,6-0,8 lb/sqft), you will grind through the dry shake or you exposed fiber which are in dry shake layer.

The only way you can grind and polish with ZERO fiber exposure is to apply dry shake hardeners in 2-4 layers and using minimum 5-6 kg/m2 (1-1,2 lb/sqft) of dry shake hardener or even 10-12 kg/m2 (2-2,5 lb/sqft) with lighter colors. Applying more layers than just one or applying thicker layer has always been a risk as dry shake hardener needs water from base concrete to hydrate and for bonding. Thicker or more layers will have amuch higher water demand; many contractors avoid applying dry shakes because of big risk of delamination.

Solution

Patent pending Concria Optimal Slab™ process enables contractors to apply enough dry shake hardener, 6-12kg (1,2-2,4 lb/sqft per m2 of Dry Shake hardeners in 2-4 layers can be easily bonded together with Concria™ Trowel Hard (Nano silica liquid) product.

Concria™ Trowel Hard is sprayed between the dry shake hardener layers. It delivers virtually pure silica in nanoparticles small enough to penetrate dry shake pore structure and glue all the layers together. In the pores, it reacts and creates new calcium silicate hydrate (CSH) that bonds to the existing CSH. It also bonds directly to other silica, including itself. When applied to dry shake hardened surface, it reacts, bonds and then uses bonded silica as a platform for additional bonding. It has shown in independent laboratory tests that even using 12 kg/m2 of dry shake in 4 layers, the dry shake hydration rate is almost 90 % where without Nano silica hydration rate is only 68 %. 

SFRC with dry shake hardener can be polished faster and more easily with Concria™ Fast power trowel polishing systems

Concria™ Fast power trowel polishing system has been used successfully in tens of millions sqft of polished dry shakes hardeners floors in more than 40 countries.
Power trowel polishing has an average labor reduction of 80 % compared to traditional planetary grinding. Contractors with power trowel capabilities can attract bigger jobs than ever before as well as satisfy customers who want great-looking floors.

Jointless SFRC with Light Gray SIKA dry shake hardener polished with Concria™ Fast at 80 000 m2 car manufacturing plant

Concria™ Fast is the fastest and best solution for grinding and polishing new dry-shake hardened floors in commercial or industrial facilities, where a long-lasting, high-quality finish is required.

Mika Ahonen
CTO / Founder of Concria
mika@concria.com