Civil Engineering July 2022 | Vol 30 No 6

Civil Engineering July 2022 27 soaked as in the standard method above. The soaked CBR need not be repeated if already done on a split from the same sample. Q Q Seal the second set in plastic bags for at least four days to dissipate pore pressures and determine the unsoaked CBR at OMC the next day (see note 1). Q Q Allow the third set to dry – preferably in the sun or in an oven at ≤ 50°C to about 0.5 OMC (weigh the moulds) – this might take a week. Report how long it takes. Seal in plastic bags and keep for at least four days in the labo- ratory to allow moisture equilibration before testing unsoaked. Weigh again to determine the moisture content (see note 2). Plot the CBR at the three efforts and three moisture contents against moisture content all on one suitable graph and read off the CBR at soaked, OMC and about 0.5 OMC at the usual percentage compactions. If there is insufficient material or funds to do all of this at the three efforts, just do it at the most appropriate effort for the layer from which the sample came or is intended, i.e. MAASHO for base, intermediate for subbase and Proctor for selected subgrade, giving preference to the unsoaked CBR at OMC. For example, if there is only enough material for one unsoaked CBR on a base course sample this should be at MAASHO OMC. If requested, also carry out the test after drying back to approximately one quarter (0.25) OMC, although this should ideally be done at the effort appropriate to the layer – those at 0.5 and 0.25 OMC are usually only done at MAASHO effort. CYCLED CBR The wet-dry cycled CBR and other tests for potential self-stabilisation are de- scribed in Frank Netterberg (2020).  NOTES 1. The unsoaked CBR was formerly done after overnight equilibration or even right away. However, experience has shown that this can result in lower unsoaked than soaked CBRs and at least four days is now recommended. 2. It is desirable to also determine the moisture content of the upper 25 mm of the specimen after the CBR test, preferably using the whole of the upper 25 mm. REFERENCES National Institute for Transport and Road Research. 1986a. Standard methods of testing road construction materials. TMH1:1986, Pretoria: CSIR, NITRR. Test methods A7 for MDD and OMC and A8 for CBR of untreated materials. South African Bureau of Standards. 2013. SANS 3001 Series: Test methods – GR40 for Determination of the California bearing ratio. SABS, Pretoria. South African Bureau of Standards. 2015. SANS 3001 Series: Test methods – GR 30 for Determination of the maximum dry density and optimum moisture content. SABS, Pretoria. Netterberg, F. 2020. Laboratory and field tests for identification of potentially self-stabilizing soils and for unsoaked CBRs. Unpublished note, Pretoria: Frank Netterberg, 8 pp. CELEBRATING OF BINDER EXCELLENCE Binding Roads, Linking People since 1971 Tel +27 11 323 2000 12 Commercial Road, Wadeville, Germiston PO Box 14159, Wadeville, 1422 www.tosas.co.za Binding roads, linking people.