Construction World October 2015

ROADS AND BRIDGES

N1 REHABILITATION – Pienaarsrivier to Bela Bela

For the past 15 years, the N1 National Road north of Pretoria has been maintained by the Bakwena Concessionaire operating under license from the South African National Roads Agency Limited (SANRAL). Standard maintenance projects over the years had not prevented further cracking and rutting in certain sections.

In 2009 consultants Jeffares & Green were hired by Bakwena to design a more robust, permanent pavement solution, in which they specified Kaytech’s bidim A4 and Flo-Pipe drainage system to control the ingress of water into the layerworks. The project implemented in 2012 proved so successful along one section of the dual carriageway road, that Kaytech was again contracted to supply these top quality products for the next section between Pienaarsrivier and Bela Bela in Limpopo. Bidim is a continuous filament, nonwoven, needle-punched geotex- tile manufactured from 100% recycled polyester. The needle-punching process imparts several advantages including appreciable thickness, high porosity and a high drainage capacity both transverse and normal to the plane. Flo-Pipe is manufactured from the highest quality HDPE and is optimally slotted for maximum infiltration with minimal blockage. The twin-wall sandwich design provides strength and flexibility. This new section of road requiring rehabilitation presented with additional water problems. Since the road was so flat, large volumes of water were accumulated in the median and filtered through into the layer works causing major degradation. The solution was to install sub-soil drains in the median of the road. Concor Roads and Earthworks installed the drains which consisted of a trench (600 mm deep x 300 mm wide) lined with bidim. This was followed with a 110 mm Flo-Pipe encased in 19 mm concrete stone. Water collected by these drains was to be channeled into 110 mm Kayduct pipes connected to stormwater drains. The success of the project was proven soon afterwards when an inspection revealed large volumes of water flowing from the Kayduct pipes into the stormwater manholes. Besides the water problems in the median of the road, engineers identified severe cracking along the slow lane and shoulder of the road, in both directions. Since these parts of a road carry the largest volume of traffic as well as the heaviest vehicles, it was important to effectively reinforce the asphalt overlay. To solve the problem, design engineers specified Kaytech’s GlasGrid, a polymer-modified, bitumen-coated, woven fibreglass grid structure with a pressure sensitive adhesive. GlasGrid is designed to redirect crack stresses horizontally and to dissipate traffic-induced stresses. The exceptional engineering in the configuration of the fibreglass strands in GlasGrid provides a combi- nation of high tensile strength and high modulus of elasticity at low elongation. These properties make GlasGrid, pound for pound, stronger than steel. The reinforcement design involved milling out a m wide section of the slow lane to a depth of 110 mm. As a leveling course, a 40 mm bitumen treated base (BTB) layer was laid down, followed by adjacent rolls of 2,1 m wide GlasGrid 8511. To perfectly cover the 4m wide trench, these were laid down with a 100 mm overlap. A pneumatic Tyre Roller was used to ensure good adhesion of the GlasGrid onto the leveling course. After a SS60 tack course was sprayed onto the surface, a second BTB layer (70 mm thick), was installed over the GlasGrid. Once the fast lane subsoil drainage project was completed, a 40 mm asphalt-wearing course was laid down along the slow lanes. Independent laboratory tests prove that by reducing thermal and stress-related reflec- tive cracking, GlasGrid extends pavement life significantly. By completion of the project the contractor had installed 85 000 m 2 of bidim, 32 000 m of Flo-Pipe and 250 000 m 2 of GlasGrid 8511. The combination of skillful design and Kaytech’s superior products should considerably extend the lifespan expectancy of this major South African route. >

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FROM TOP TO BOTTOM: The existing surface was milled. A 40 mm BTB layer laid. Rolls of Glasgrid were laid with a 100 mm overlap.

CONSTRUCTION WORLD OCTOBER 2015