Fly ash--Recycling

Three vital factors, namely environmental protection, savings in costs, and
strength/durability benefits, make it advantageous to incorporate fly ash of controlled
quality and composition in all concrete made from construction demolition (C&D)
recycled aggregate. The specific objective of this research was to compare the
performance characteristics of High-Volume-Fly-Ash (HVFA) structural concrete
containing C&D aggregate with that of normal recycled aggregate concrete containing no
fly ash.
A coordinated experimental program was undertaken which comprised of ( 1)
Compressive and Split Tensile strength tests; (2) ASTM durability tests by measuring
resistance to chloride-ion penetration; and (3) Flexural strength tests on reinforced
concrete beam specimens. Three mix designs were used, all of which had the same
water/cement ratio of 0.45 and the same amount of recycled aggregate/yd^3. Mix 1
contained cement and no fly ash, Mix 2 contained 16% replacement of cement by weight, and Mix 3 contained 40% replacement of cement, called a HVF A mix. Results
indicate that fly ash increases compressive strength, improves both moment carrying
capacity and tension resistance, and increases resistance to chloride-ion attack.

This thesis addresses municipal ash-modified and fly ash-modified concrete utilization for the transportation infrastructure. The mix design included unmodified (control) concrete (Mix A), fly ash-modified concrete (Mix B), and municipal ash-modified concrete (Mix C). The laboratory investigation was carried out through compressive, tensile, testing of the cylinders and flexural testing of concrete slabs on grade comprised of varying proportions of coal fly ash and MSW bottom ash. The load-strain relationships for experimental pavements was obtained through slab testing, modeled as a two-way infinite slab on an elastic foundation. A finite element model using STAAD-III was used to predict the stresses and deflection of the slab. For comparison, a simplified analysis was also performed to obtain stresses and deflections variations of the slabs, following ACI Committee 436. Based on the results presented in this report, conclusions were drawn to evaluate the ideal mix design for municipal ash-modified and fly ash-modified concrete.