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New technology assures bitumen quality for SA roads

Bitumen Converter Technology at SprayPave on 12 July 2017.Lynne Mackie

The multistage bitumen converter uses pressure, heat and air to manipulate bitumen
on a molecular level

Spraypave has acquired technology new to the African continent that aims to resolve the shortage of high-grade bitumen for asphalt production.

SprayPave, a leading manufacturer and supplier of bitumen, modified binders and emulsions for road construction, has procured a multistage bitumen converter that changes bituminous products from one grade to another.

This enables SprayPave to enhance the penetration grades of bitumen required to produce asphalt.

The 20 tph multistage bitumen converter was acquired from Technix Industries in New Zealand, a company that has been in the bitumen business for over 100 years and is a global leader in bitumen technologies. The unit, located at SprayPave’s Cape Town plant, is the second to be commissioned worldwide after Fiji.

“We can now achieve predictable and repeatable conversion of penetration-grade bitumen available from South African refineries to grades that are both lower in penetration and higher in softening point than the feedstock bitumen,” says Eddie Jansen van Vuuren, general manager, SprayPave.

SABS certification

“Following several months of testing, we are delighted to have received SABS test results, which show that the 50/70 produced conforms to the SANS 4001-BT1 specification.”

Bitumen is an essential binding agent in asphalt. It is produced by refineries as a by-product of crude oil, but can only be supplied in broad grade ranges that seldom meet asphalt design specifications.

The multistage bitumen converter uses pressure, heat and air to precisely convert bituminous refinery feedstocks into superior-quality bitumen. The softness, penetration index and physical properties of the bitumen can be changed to meet exact design specifications.

Jansen van Vuuren points out that this technology addresses current and future issues around local bitumen supply, particularly in regions such as the Western Cape where refineries are unable to provide suitable penetration grades of bitumen for road binders. The converter can modify 70/100 penetration-grade bitumen to 50/70 or even 10/20, which is required for new high-modulus asphalt designs.

New specifications

Spray Pave Function on 1 August 2017

From left to right: SprayPave GM Eddie Jansen van Vuuren, Technix Industries owners Lynda and John Matthews, and Saied Solomons of Sabita

With certain chemical additives, the converter can also produce multigrade bitumen with specifications and performance characteristics spanning several penetration grades. “This is particularly significant as it will help manufacturers to comply with the new Performance Grade (PG) bitumen specifications in South Africa,” he says.

These specifications aim to improve the assessment of deformation resistance, fatigue properties, long-term performance and cracking potential of bitumen as an asphalt binder.

By enhancing bitumen penetration grades, the multistage bitumen converter can help asphalt producers to ensure they are using multigrade bitumen products that comply with the PG specifications.

The technology

To understand the technology, one needs to be aware of the complexity of bitumen as a substance:

  • There are more than 1 500 different crude oils in existence.
  • Bitumen yield ranges from 60% to practically 0%.
  • Each crude composition differs, as does the bitumen produced from it.

Bitumen is essentially a “wild mixture” of different substance groups: saturates, aromatics, resins and asphaltenes (SARA). You have good-quality bitumen if the SARA groups are present in the right balance to each other.

Asphaltenes are important, as they build the backbone of the bitumen. A well-balanced ratio of asphaltenes to resins yields high-quality bitumen. This can be achieved by engineering bitumen with the multistage converter.

Through the controlled processes in the converter, including the addition of pressure, heat and air, it is possible to rearrange chemical structures respectively to create asphaltenes. The gentle process and highly efficient addition of air and, therefore, oxygen (air rectification), preserves the highly polar aromatic/resin fraction and minimises coke build-up.

SprayPave owns one of the few IATROSCAN units in Southern Africa that can undertake SARA compositional analysis to ensure that quality bitumen is produced at its facilities in Alberton, Durban and Cape Town.

Spray Pave Function on 1 August 2017

Members of the SprayPave management team (from left): Danashia Padayachee, technical manager; Leslie Webb, branch manager: Cape Town; Victor Hannival, sales and marketing Western Cape; Eddie Jansen van Vuuren, general manager; Edwin Perumal, estimator; Willem Greeff, financial manager; Kalay Govender, branch manager: Durban; and Andre du Plessis, technical specialist

Multigrade bitumen

Multigrade bitumen is higher-performance “premium grade” bitumen with performance characteristics that span multiple grades of bitumen.

It is produced by chemically modifying conventional-grade bitumen to obtain improved properties over a wider road surface temperature range.

The bitumen feedstock is permanently modified in terms of its major physical properties, viscosity and penetration, using reagents and air rectification at briefly elevated temperatures in the multistage bitumen converter plant to achieve molecular rearrangements.

The process stabilises the composition of the bitumen while preserving precious resins. The modifications made to the feedstock bitumen by the converter are permanent and will not revert back to the lower-performance characteristics of conventional-grade bitumen.

Multigrade bitumen is characterised by being less temperature sensitive when compared with conventional-grade bitumen. It has the properties of hard-grade bitumen at high pavement temperatures coupled with the properties of soft-grade bitumen at low pavement temperatures.

Roads paved using asphalt with multigrade bitumen benefit from:

  • improved resistance to deformation, leading to reduced rutting and shoving of hot-mix asphalt pavements
  • reduced seal cracking at low pavement temperatures
  • reduced bleeding and chip stripping of chip-sealed roads
  • greatly enhanced pavement life and reduced maintenance costs.

Multigrade bitumen has better temperature stability, is more cost-effective compared to conventional-grade bitumen, can be used wherever conventional-grade bitumen is used for hot-mix asphalt and chip sealing, can be emulsified in the same way as conventional bitumen, can be transported and stored cold or hot, and can be handled and applied similarly to conventional bitumen.

TIMELINE

1981

SprayPave was established to offer binder spraying and hauling services, and was expanded to include the manufacture of bitumen binders in 2007, with its first bitumen emulsion produced in Alrode, Gauteng.

2010

SprayPave purchased an emulsion business in Durban, not only increasing its footprint, but also broadening its range of bitumen emulsions, cutbacks, precoating fluids and primes.

2012

SprayPave responded to the bitumen supply crisis in South Africa by exploring global technologies.

2014

SprayPave opened its Cape Town emulsion plant. The multistage bitumen converter was commissioned on this site in 2016. Testing commenced immediately to prepare for SABS accreditation of the converted bitumen products as per SANS BT1:2016.

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