Study of the impact of kaolinite contained in lateritic nodules on the mechanical behaviour of concrete

For more than decades, research work has enabled the progressive mastery of the characteristics of lateritic concrete, although the performance of lateritic concrete is less satisfactory than that of ordinary concrete. The availability of lateritic gravel in Benin stimulated us to address the causes of this low resistance compared to common concrete. Specifically, our work concerned the impact of the presence of kaolinite naturally contained in lateritic nodules on the behavior of concretes. The mineralogical characterization of lateritic nodules and on the current aggregate showed that the kaolinite content in the nodules lateritic from Allada, Adjohoun, Houéyogbé and rolled gravel are respectively 13.00%; 21.00%; 7.00%; and 0.00%. The investigation is made on nodules which belong to the same granulometric zone and their hardness is equal to 46%. The rate of cleanliness, the absolute density of the nodules varies respectively from 96% to 97% and from 2.70 t/m3 to 2.76 t/m3. The compressive strength of lateritic concretes, for permanent preservation of test specimens in water, varies from 23.38 MPa to 24.42 MPa, 23.45 MPa to 24.40 MPa and 23.15 MPa to 24.15 MPa respectively at 28 days, 60 days and 360 days of ages while the strength of ordinary concrete is 27.57 MPa, 27.58 MPa and 27.58 MPa respectively at 28 days, 60 days and 360 days of ages. It appears from this analysis that kaolinite would adversely affect the mechanical performance of lateritic concrete after 60 days of storage in water. The negative effect of kaolinite on the mechanical behavior of lateritic concrete is not only related to the rate of kaolinite but also to other chemical elements contained in the nodules.