A severe drought in conjunction with poor underlying soil conditions resulted in the formation of large cracks on section 17 of the N1 (National Route 1) between Ventersburg and Kroonstad in the Free State.The situation required an urgent upgrade by SANRAL.
For a quick and cost effective solution that would prevent cracks penetrating the newly paved layer on section 17, a SMEC engineer had no hesitation in specifying SealGrid, a composite asphalt reinforcement interlayer manufactured by Kaytech.
SealGrid consists of high strength glass fibre roving, knitted to a paving fabric in a grid pattern.
Providing a high strength interlayer at very low strain, the glass fibre roving effectively stitches cracks together while the bitumen-impregnated paving
fabric provides a waterproofing barrier as well as a stress-absorbing underlayer. SealGrid leads to a dramatic reduction in reflective cracking under asphalt overlays and is unaffected by high temperatures and most chemicals.
It was recommended that SealGrid be installed between the 40mm AC-Medium layer and the milled surface. Prior to installation of SealGrid, Hillary Construction spray-applied a tack coat (CAT 65 latex modified emulsion) onto the area.
As soon as the emulsion had properly broken, SealGrid was installed and rolled with a pneumatic tyred roller (PTR) to ensure adequate adhesion. Paving of the asphalt layer can proceed immediately after successful rolling of SealGrid.
This project involved the successful installation of 10 000m2 of SealGridon select sections over a distance of 44.9km.
Providing excellent adhesion to existing surfaces, SealGrid ensures strong interlock between the existing surface and the new overlay and ensures a constant thickness bitumen SAMI interlayer. As SealGrid is flexible and conforms around shallow milled irregularities, no leveling layer is required; the paving fabric acts as padding between the milled surface and the glass fibre grid. SealGrid is highly versatile and may be applied under or between asphalt layers in many situations such as where high stresses may occur, on road widening schemes with differential settlement, or where stress cracking is possible over expansive clay sub-grades.
The mighty N1 national road, stretching from Cape Town to Beit Bridge on the Zimbabwean border, demands constant maintenance and upgrading by SANRAL. SealGrid can reduce traffic induced crack propagation by as much as a factor of greater than seven, equating to a much-increased life cycle of this section of the N1, and a great economic benefit to SANRAL.
For more information on Kaytech products and systems, visit www.kaytech.co.za
