1. Notes on crushing strength of some Western Nigeria concretionary gravels and their selection for use as building material;Ackroyd;Minist. Transp., Ibadan, W. Nigeria, Tech. Pap.,1960
2. The correlation between engineering and pedological classification system in Western Nigeria and its implications;Ackroyd;Proc. Reg. Conf. Afr. Soil Mech. Found. Eng., 3rd., Salisbury,1963
3. Formation and properties of concretionary and non-concretionary soils in Western Nigeria;Ackroyd;Proc. Reg. Conf. Afr. Soil Mech. Found. Eng., 4th, Cape Town,1967
4. Genesis and hardening of laterite in soils;Alexander;U.S. Dept. Agric. Tech. Bull.,1962
5. Anonymous 1949 Determination of soundness of an aggregate by weathering the aggregate in sodium sulphate Afr. Roads Transp. 1 9257–258.