This research presents the potential of combined carbon capture alongside compressive strength improvement in carbonated lime treated kaolin clay, and determines the suitability of the strength improvement for application to capping layer in road pavement. Using combined modification and carbonation treatment at controlled air voids, 4.7%-10% calcium carbonate was determined in kaolin treated with 4-8% calcium hydroxide contents in samples at 10% air voids. Strength increase was achieved in carbonated lime-treated kaolin from 170 kPa to 280 kPa compared with soaked non-carbonated lime treated kaolin, which shows significant increase of approximately 65%. This method of combined modification and carbonation in lime treated clay has the potential to capture carbon alongside improving the strength of the weak kaolin, and could be effectively used for combined carbon capture and road pavement functions.

A study was carried out on the cement stabilization of Makurdi shale treated with bamboo leaf ash (BLA), for use as flexible pavement construction material. Classification, Compaction, Consistency, California Bearing Ratio (CBR) and unconfined compressive strength (UCS) tests, were conducted on Makurdi shale specimen treated with Cement and BLA in combined incremental order of 2 % up to 14 % cement, and 4 % up to 20 % BLA of dry weight of soil sample respectively. Results of tests showed that Makurdi shale can be classified as an A-7-6, CH and high swell potential soil by the AASHTO, USCS and NBRRI classification systems respectively. The plasticity index (PI) reduced from 39.4 % for untreated Makurdi shale to 4.7 % at 14 % cement + 20 % BLA. Maximum dry density (MDD) of untreated shale increased from 1.49 Mg/m 3 to a peak value of 1.80 Mg/m 3 at 0 % BLA + 14 % cement. While, the optimum moisture content (OMC) of shale increased from 14.5 % to 33.1 % at 14 % Cement + 20 % BLA. Maximum soaked CBR and 7 day UCS values of 80 % and 1783.9 kN/m² was obtained at 14 % Cement + 20 % BLA. Based on the results of the different tests, the use of Makurdi shale treated with 14 % cement + 20 % BLA are recommended for use as sub-base materials in flexible pavement.

Laboratory tests were conducted on black cotton soil (BCS) treated with cattle bone powder (CBP) in incremental order of 2 % up to 10 % of dry weight of soil sample, to ascertain its suitability for use as flexible pavement material. Classification, free swell, compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS) tests, were conducted on BCS samples treated with CBP. Results of the tests showed that, BCS is an A -7 -6 and CL respectively using the American Association of State Highway and Transport Officials (AASHTO) and unified soil classification system (USCS) respectively. The plasticity index (PI) and free swell of BCS reduced from 29.3 % and 48 % to 17.8 % and 36 % respectively. The maximum dry density reduced from 1.