Contractors sometimes add synthetic fibres to their concrete mix. These fibres of man-made polymers are specifically engineered to withstand the long-term alkaline environment within a concrete mix. They are used to minimise cracking, lower the permeability of the concrete and increase the strength of the structure.
They act as a secondary reinforcement element; the primary element being steel rebar. These synthetic fibres benefit both early-age and hardened concrete in a number of ways. In early-age concrete, volume changes can occur once the concrete is poured and begins to set. This can cause microcracks to form if the volume changes too much. The synthetic fibres block these cracks and act as an internal support system.
Synthetic fibres improve the strength of hardened concrete
In hardened concrete, synthetic fibres lower the permeability to water and moisture. This prolongs the durability of the structure and prevents moisture damage. The fibres also improve the impact and abrasion resistance of hardened concrete by holding the particles together, making the structure stronger. The fibres have great shock absorbing characteristics.
When normal concrete is compressed, it tends to shatter at the first crack that develops. However, by adding synthetic fibres, this tendency to shatter is eliminated. Cracks will still form under extreme compression, but the structure will still hold together somewhat due to the binding properties of the fibres and concrete particles.
Synthetic fibres as secondary reinforcement
Certain concrete structures may need additional reinforcement for extra load-bearing capacity. However, steel rebar may add to the weight and expense of the structure. In these cases, synthetic fibres can be used as a means to provide additional support without adding too much weight to the concrete.
Synthetic fibres which meet certain criteria can be used as non-structural secondary reinforcement. These fibres should have documentation that confirms their ability to hold concrete together after cracking. Synthetic fibres can also be used with other admixtures and cement chemistries for additional strength and durability benefits.
Guidelines for using synthetic fibres in concrete
Synthetic fibres should be used in concrete for:
- Reduction of concrete cracking as a result of shrinkage.
- Non-structural secondary reinforcement.
- Greater impact, abrasion and shatter resistance.
- Internal support and cohesiveness.
- Lower water and moisture permeability.
Synthetic fibres should not be used for:
- The control of cracking as a result of external forces.
- Replacement of steel rebar, where this is a necessity.
- Decreasing the thickness of a slab.
- The elimination of curling in thin slabs.
- Reducing the size of support columns.
- Thinning of bonded or unbonded overlay sections.
LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.
LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.
At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.