Optimization of lime-pozzolana mixes in stabilising gravels for the road base

Abstract

Global increase in traffic volumes coupled with high tyre pressures has led to high stresses on the pavement resulting into high strains. In order to withstand these stresses, increased pavement stiffness through stabilisation would be one of the remedies. Establishing economically optimal blends of lime pozzolana mix as an alternative binder to cement is very important in order to reduce; the cost of pavement stabilisation and carbon emission. This research involved determination of the chemical composition of lime and pozzolana in accordance to ASTM C25-99 and ASTM C 311/C311M: 2016. This was followed by titration mixture of lime-pozzolana in the distilled water with HCL, Phenolphthalein indicator and ethylenedinitrilo tetra acetic acid (EDTA) every after 24hrs to determine concentration of Ca2+. Sampling of laterite, lime and pozzolana using the quartering method, tests on laterite treated with lime-pozzolana mixes ranging from 0 to 8% was also done. The tests included; Plasticity Index (PI), California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) in accordance with BS 1377 Parts 2 and 4. Statistical analysis of the results was done using Analysis of Variance and Bonferroni’s Method. This research established that the reaction between hydrated lime and pozzolana follows a natural logarithmic trend and the rate of lime-pozzolana reaction follows a first order differential equation where the rate of reaction is inversely proportional to time. Addition of 4% lime and 4% pozzolana; improved California Bearing Ratio (CBR) from 45% to 79% (approximately 75% increment), USC from 1.30N/mm2 to 4.10N/mm2 (more than 3 times) after 28 days of curing and Plasticity Index (PI) decreased from 18.43% to 14.67% (approximately 20%). A reduction in the cost for stabilisation of road bases by approximately 30% if 4% lime and 4% pozzolana combination is used compared to the application of 8% lime alone was established. Utilisation of 1 tonne 100% lime compared to 1 tonne comprising of 50% lime and 50% pozzolana would result in reduction of energy consumption from 1.34GJ to 0.69GJ and emission of CO2 from 0.416 to 0.208 tonne respectively. The reaction between 4% lime and 4% pozzolana mix improved strength of laterite from 1.385N/mm2 to an average of 2.010N/m2 after 7 days of curing. The strength attained arising out stabilisation using the mix is higher than the recommended minimum of 1.5N/mm2 for road bases in the material specifications for roads and bridges for Uganda, 2005. Therefore lime pozzolana mix could be used as partial or full substitution for cement stabilisation.