Concrete Repairs on National Road N1-19&20 Klein Rietspruit to Old Potch, South Africa

Abstract

The contract for concrete repairs on N1-19&20 between Klein Rietspruit and Grasmere, constructed under two separate contracts in the mid- to late 1980’s, commenced in July 2022. The project include slab replacement, full depth repairs, partial depth repairs as well as the replacement of joint seals.  Initial indications during design were that the subbase did not provide sufficient support, which caused longitudinal cracks in the middle of the slabs along the slow lane. Allowance was therefore made for the reconstruction of the subbase in these areas. The pavement was constructed using slipform pavers with a structure consisting of 235 mm jointed concrete pavement (JCP) on a 100 mm stabilised crushed stone base (C1). Some repairs were completed during 1987 & 1991, which also consisted of slab repairs; most of which are still in good condition. During construction it became obvious that the subbase was still intact and did not require replacement. Further longitudinal cracks that developed when adjacent slabs were removed indicated that a re-assessment of the failure mechanism was required. Another phenomenon was horizontal cracking that developed below sections where transverse cracks located close to transverse joints were found. It was also discovered that tiebars of different thicknesses were used along the longitudinal joints and that transverse joints were only cut to a depth of between 30 mm and 40 mm; considered shallow for the concrete thickness. The aim of this paper is to summarise the investigation into the failure mechanisms observed while repairing the pavement.