The sustainable use of industrial wastes such as coal fly ash and carbide lime is an effective procedure to enhance the long-term performance of reclaimed asphalt pavement (RAP) under extreme freeze-thaw and wet-dry conditions. This study evaluates the impact of lime content (L) and dry unit weight (g d) on the durability and long-term performance of compacted RAP-fly ash-carbide lime mixes. For all mixtures tested, specimens were statically compacted inside a cylindrical mould to their target dry unit weights. Single-level variables used in the stabilisation process included: fly ash (FA) content of 25% (in relation to the RAP), optimum water content of 9% (modified compaction effort) and seven days of curing. Three target dry unit weights equal to 17, 18 and 19 kN/m 3 (the last one determined using the modified Proctor energy) as well as three different lime contents (3, 5 and 7%) were also used in the analysis. Both the accumulated loss of mass (ALM) after wetting-drying and freezing-thawing cycles and the splitting tensile strength (q t) of the specimens tested were evaluated as a function of the porosity/lime ratio index (h/L iv). Compacted RAP-fly ash-carbide lime mixtures performed better when subjected to wetting-drying cycles than to freezing-thawing cycles. The results indicate that the porosity/lime ratio index controls not only the mechanical response but also the long-term performance of compacted RAP-fly ash-carbide lime mixes, which substantially broadens the applicability of the index.
The use of industrial wastes such as coal fly ash (CFA) and carbide lime (CL) can enhance the long-term performance of recycled asphalt pavements under freeze–thaw conditions as well as reduce consumption of natural resources. Further improvement of the mechanical properties of such blends can be achieved by adding small quantities of sodium chloride (NaCl). Blends of recycled asphalt, CFA, CL and sodium chloride were therefore assessed in terms of their durability to freeze–thaw exposure. Additional splitting tensile tests were performed to evaluate strength improvements after adding sodium chloride. Specimens were moulded with three different dry unit weights and two different lime percentages, and cured for 7 d. The accumulated loss of mass was evaluated as a function of the porosity/lime index, which broadens the applicability of this index by demonstrating it, and influences not only strength but also long-term performance. The improvement in engineering properties provided by sodium chloride was found to be related to the formation of mineral phase thomsonite and to sodium chloride acting as a catalyser.
The use of industrial residues instead of virgin materials is a good alternative for a more sustainable approach to disposing of and managing waste. Soil improvement with coal fly ash (CFA) is particularly attractive for geotechnical earthworks. This study investigated the strength, stiffness and durability of Osorio sand-CFA-lime blends with a variety of improvements by assessing the impact of varying the lime content, fibres, sodium chloride (NaCl) and dry unit weight. Moreover, to contribute to a more rational dosing methodology, strength, stiffness and durability results were correlated to the porosity/binder index [η/(Biv)0.28]. Durability was assessed by comparing wet-dry (WD) and freeze-thaw (FT) cycles, and WD cycles were found to present better performance than FT cycles. Ranks were established for the different components of the blends according to the WD and FT results. The addition of NaCl alone was more effective in improving unconfined compression strength (qu) results than fibres alone. While fibres significantly decreased stiffness at very small-strain shear modulus (G0), NaCl increased G0. The application of η/(Biv)0.28 demonstrated that not only can it predict mechanical behaviour, but also the long-term performance of Osorio sand-CFA-lime blends with or without the addition of NaCl and fibres.
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