Comparison of different cement types for stabilization of the different road subgrades soils
It is paramount to determine the cement type that is most suitable and cost effective in stabilization of the different soil types prevalent in different parts of Kenya. In this study, seven Cement brands, 'Power Plus' 42.5 (CEM I), 'Power Max' 42.5 (CEM II1A-L) and 'Nguvu' 32.5 (CEM IIIB-P); Blue Triangle 42.5 (CEM I) and Blue Triangle 32.5 (CEM IV/A); Rhino 42.5 (CEM I) and Rhino 32.5 (CEM IVIB-P) were obtained from warehouses of the respective companies. Soil samples used were collected from ongoing projects in different regions of the country, namely Embakasi (Nairobi province), Kiambu (Central province), Machakos (Eastern province), Kilifi (Coast province), Kakamega (Western province) and Bomet (Southern part of Rift Valley province). The chemical compositions of the soil and cement samples were determined with respect to calcium, magnesium, aluminium, iron and silica. Strength of the soil, in terms of the California Bearing Ratio (CBR) of both the neat and treated soils were investigated. CBR is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mrnlmin to that required for the corresponding penetration of a standard material. Results showed that the CBR of soil treated with cement of strength 42.5 Nzmm' are higher than those treated with similar quantities of cement of strength 32.5 N/mm2. For treatment, a series of the various proportions (2, 4 and 6 as percentage) of the different cement types were added to the neat samples and the CBR of the resultant materials determined. The effects of the various proportions of these cements on the strength (CBR) of the soils were thus investigated with a view of determining which cement type could attain the design specifications of the different soil/gravels more cost effectively. The results showed that the CBR values attained on stabilization using the cements of strength of 42.5 N/mm2are higher than those attained using cements of strength of 32.5 N/mm2 at the same dosage. This shows that for all the soils tested, cements of strength 42.5 N/mm2 (Power Plus, Power Max, Blue Triangle 42.5 and Rhino 42.5) are better suited to be used at soil stabilizers than those of strength 32.5 N/mm2 ('Nguvu', Blue Triangle 32.5 and Rhino 32.5). Results show that cements of strength 32.5 N/mm2 can be used to achieve the same CBR as compared to the 42.5 N/mm2 cements. This can be attained by using larger quantities ofthe 32.5 N/mm2 cements as compared to the 42.5 N/mm2 cements, which would result higher costs (based on current market prices ofthe two types of cements). For faster economic growth on the limited resources, the use of cement of strength 42.5 Nzmrrr' should be encouraged while use of cement of strength 32.5 N/mm2 should be discouraged.