DURA® is the trade-name for our own formulation of Ultra High Performance ‘ductile’ Concrete (UHPdC). UPHdC is an advanced cementitious based material, which is also known as the reactive powder concrete (RPC). DURA® is an ultra-high performance steel fibre reinforced concrete that combines the superior properties of both concrete and steel.
Question 2: What is UHPdC?
UHPdC is an advanced cementitious
based material that was developed on the principle that a material with a
minimum of defects such as micro-cracks and pore spaces will be able to achieve
a greater proportion of the potential ultimate load carrying capacity as defined
by its constituent materials. Unlike conventional concrete, UHPdC does not
contain coarse aggregate but instead uses very fine particles ranging from a
maximum size of 1000 m to less than 1 m. The fineness of the aggregates
results in an extremely dense UPHdC matrix by eliminating most of the pore
spaces inside the concrete.
Question 3: What is meant by ductility?
Ductility is the ability of a material to sustain significant of load under large deformation. For UHPdC, this is measured by beam under the provision of ASTM-C1018 (1997). The value measured is post-crack resistance, expressed as equivalent flexural strength (MPa) or fracture energy (N/mm).
Question 4: Why DURA® has superior ductility?
DURA® has superior ductility because the concrete paste is heavily reinforced by large amounts of discrete high-strength steel fibres. For example, 1 m3 of DURA® would have been reinforced by approximately 24 millions pieces of steel fibres or a total fibre length of 487 km. In other words, the concrete matrix is locally reinforced up to the microscopic scale, resulting in significantly improved tension strength and ductility.
Question 5: What strength grade is DURA®?
DURA® is equivalent to a Grade150 concrete or higher. Cube compression strengths of 70 ~ 90 MPa are typical after 24 hours; whereas after 28 days, DURA® achieves cube compression strengths of 140 ~ 170 MPa. In terms of flexural strength, under ASTM-C1018 (1997) test methods DURA® achieves flexural strengths of 15 ~ 35 MPa depending on the fibre volume.
Question 6: Can DURA® be used as a cast-in situ concrete?
DURA® is a very sensitivity material, therefore it is generally best to handle the material in a controlled environment, such as in the manufacture of precast products. Nevertheless, DURA® can be applied on site as cast in-situ concrete especially for jointing of precast elements or area where the amount of DURA® needed is not more than 300 kg/pour. Further research is being carried out in the area of in-situ applications of DURA®.
Question 7: How is DURA® different from conventional steel fiber reinforced concrete (SFRC)?
In terms of overall mechanical properties, DURA® is superior to conventional SFRC. The steel fibres used in the conventional SFRC have tensile strengths typically up to 1000 MPa and the fiber fracture may occur during cracking; whereas the steel fibres used in DURA® have tensile strengths above 2300 MPa, thus fracturing of the fibres will never take place, thus ensuring that the DURA® matrix retains high ductility during cracking. Due to its superior fracture mechanical properties, DURA® exhibits “Strain-Hardening” and “Displacement Hardening” behaviours during tension stress, whereas such behaviour is not demonstrated in conventional SFRC.
Question 8: How to assure the fiber uniformity in the concrete paste?
Fibre uniformity in the concrete paste is assured through application of special Quality Control procedures developed by Dura Technology Sdn Bhd.
Question 9: Will steel fibres “ball” during mixing?
No. Special mixing methods developed by Dura Technology Sdn Bhd prevent fibres from “balling” during mixing.
Question 10: What contributes to the superior durability of DURA®?
The concrete paste in DURA® is engineered in accordance with the principle of minimal voids and minimal void size. Thus mineral fines are used to improve its granular packing and density. Unlike conventional concrete that has relatively larger voids and capillaries that are continuous throughout the concrete matrix, DURA® has smaller and discontinuous or independent air voids in the matrix. Thus durability is enhanced by cutting-off the ingress path of harmful or corrosive substances.
Question 11: Does the steel fibre in DURA® rust?
Some rust staining may appear on the surface or skin of the structure due to rusting of steel fibres that lie right at the surface or skin of the concrete. The structural consequences of corrosion of fibres at the surface or skin of the concrete are not structurally significant.
Tests have shown that even in an aggressive and corrosive environment, the steel fibres will not rust beyond a depth of 2 mm from the surface or skin of the concrete. Therefore, under most service conditions, the likelihood of rusting of the internal steel fibres is negligible.
Question 12: Why rusting of steel fibres do not go beyond 2 mm below the surface of DURA®?
The matrix of DURA® is at least 20 times more impermeable compared to conventional concrete. The steel fibers that appear at the skin or surface will rust and expand 30% of its original volume. This extra volume will not generate sufficient internal expansive stress to spall the adjacent ultra high strength concrete due to the small size of the steel fibres. Rust (i.e. iron oxide) is water insoluble and does not conduct electricity; therefore rusting of steel fibres will stop beyond the depth of the surface rust zone and will not progress further because oxygen, moisture and chloride ions are not able to permeate deeper into the concrete.