| PRODUCTS |
FROM KERBS TO SURFACE,
IT’S ALL CONCRETE With gravel roads causing horrific accidents, Bryan Perrie, CEO of Cement & Concrete SA, says there is substantial scope for more low-volume concrete roads to increase road safety in the country. Joined in-situ (poured into place) concrete can be used to construct economical and durable rural low-traff ic volume roads which can be used as access roads or farmto-market pavements, designed to handle speeds of up to 90km/h in unpopulated areas and up to 65km/h speeds as low-volume city roads. Protections and maintenance “ I n joi nted low-volume roads, load transfer by aggregate interlock is generally adequate. When close-joint spacings are used, reinforcing steel isn’t needed, but reinforcing mesh should be used in oddshaped panels and for those with manholes and other openings,” says Perrie. Moreover, concrete roads have a relatively maintenance-free life of up to and (Above right): Cutting concrete requires machinery, skill and patience. (Above from top): Manhole covers are a safety feature which require highly skilled, mass-production capabilities and concrete. Kerbs are in high demand.
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PRECAST | ISSUE ONE | 2022
beyond 30 years, depending on the traffic load. Maintenance of concrete roads mostly involves re-sealing joints and carrying out minor repairs every 10-15 years. Joi nt s a r e pr ov ide d i n c onc r et e pavements to limit stresses and control cr ac k i ng resu lt i ng f rom rest r a i ned contraction and the effects of restrained warping and traff ic loads, to facilitate construction and level control and to accommodate movements. Joints must provide adequate load transfer to ensure adequate performance of the pavement. This can be achieved by the use of sawn construction joints at relatively close spacings and keyways at construction joints. Materials, materials, materials Perrie says the correct choice of materials is vital for the construction of durable lowvolume concrete roads. Cement should be CEM I, CEM Il A 42.5 or higher, complying with the requirements of SANS 50197. Where extenders (ground granulated blast furnace slag or fly ash) are used, these should comply with the requirements of SANS 50450 and SANS 55167. When extenders are used, allowances should be made in the concrete mix design,
“Concrete roads have a relatively maintenancefree life of up to and beyond, 30 years, depending on the traffic load.” particularly with regard to early strength under field conditions to ensure timeous cutting of joints. Curing methods and regimes may also have to be improved, especially in inclement weather. “Satisfactory aggregates for use in low-volume concrete roads and streets are those that comply generally with SANS 1083 Aggregates for Concrete. In addition, the fine aggregate should possess an acid insolubility of at least 40% for skidresistance. This requirement is satisfied when quartzose sand is used. Calcareous sands, such as dolomite, are acceptable if blended with at least 40% of a suitable quartzose sand,” explains Perrie. He adds that the mixing agent should be clean, potable water or other water free of substances that may impair the strength,
