Fly ash

Supplementary cementitious materials (SCMs), are beneficial when used as partial replacement of cement in concrete mixtures for coastal concrete structures, blended with Portland cement (binary or ternary mixes), i.e., high-performance concrete provides improved properties when exposed to marine harsh environment. In order to characterize selected durability properties of different concrete mixtures, a testing program was established. The intent of this study consists of testing 10cm diameter x 20cm long concrete specimens prepared with a range of different mix designs. 1) to evaluate the rate of water absorption due to capillary suction, referred to as sorptivity, 2) to evaluate the concrete surface resistivity, 3) to evaluate and compare the total porosity of specimens with different mixes, and 4) to obtain correlations between resistivity and sorptivity. All of these experimental tests were carried out according to ASTM International Standards (Sorptivity, Porosity) and Florida Method of Test (Resistivity). The tests were performed on concrete samples at various ages. Moreover, The results provided a fast and reasonable approximation of the concrete durability over time. Ordinary portland cement was partially replaced with supplementary cementitious materials including: fly ash (20%), silica fume (8%) and blast furnace slag (50%). These SCMs are highly effective in creating more durable concrete design mixtures. The water-to-cementitious (w/cm) ratios of 0.41 and 0.35 were investigated. The concrete that contains pozzolanic materials has demonstrated progress in extending the time for initiation of corrosion. The test results obtained indicate that the concurrent inclusion of fly ash and silica fume greatly reduced water penetration. The mixes containing slag also showed lower porosity and water absorption result, when compared to specimens containing fly ash only. Ternary concrete mixtures specimens showed much higher surface resistivity values than binary mixture specimens. These results suggest that reducing w/cm ratio, adding SCMs to concrete mixtures improved the concrete durability. The possibilities for the risks of corrosion initiation would be minimized (delayed) by prescriptive and then performance-based concrete blends with SCM materials optimized for service exposure in aggressive environments.

Geopolymer concrete (GC) is a sustainable construction material and a great
alternative to regular concrete. GC is a zero-cement material made from a combination of
aluminate, silicate and an activator to produce a binder-like substance.
This investigation focused on the effects of wet and dry cycles on the strength and
durability of fly ash-based recycled aggregate geopolymer concrete (RAGC). The wet-dry
cycles were performed approximately according to ASTM D559 standards.
RAGC specimens with nearly 70% recycled materials (recycled aggregate and fly
ash) achieved a compressive strength of approximately 3600 psi, after 7 days of heat curing
at 60ºC. Although the recycled aggregate is prone to high water absorption, the
compressive strength decreased by only 4% after exposure to 21 wet-dry cycles, compared
to control specimens that were not exposed to the same conditions. Accordingly, the RAGC
material developed in this study can be considered as a promising environmentally friendly
alternative to cement-based regular concrete.

Three vital factors, namely environmental protection, savings in energy, and technical benefits, make it advantageous to incorporate fly ash of controlled quality and composition in all concrete construction. The specific objective of this research was to compare the performance characteristics of fly ash-modified concrete with that of normal concrete in the coastal environment. To make this comparison, a series of tests using appropriate ASTM standards were conducted. First, the compressive strength development of five mixes was studied. Reinforced beam specimens were then subjected to varying periods of accelerated corrosion with sea water as electrolyte. These were tested under flexure and impact. An attempt was made to predict remaining life. Finally, permeability tests were carried out. Results indicate that fly ash increases compressive strength, improves both moment carrying capacity and impact resistance, and increases watertightness.

This thesis presents the experimental investigation of durability and fracture toughness (K IC) of fly ash concrete in the marine environment. The findings indicate that the deterioration rate of durability parameters, such as compressive strength, weight loss, and dynamic modulus of elasticity, due to 450 wet and dry cycles exposure (the Accelerated Durability Testing), was inversely proportional to the amount of fly ash replacement. On the other hand, tensile strength properties, such as modulus of rupture and fracture toughness, were independent of fly ash replacement, but increased with the period of accelerated testing. The mean K IC values of fly ash concrete mixes showed that they are closely related to their compressive strengths and size effects. According to AE, unstable crack propagation initiated at 93-97% maximum load. With SEM observations, it was found that crystallized particles were precipitated in the void spaces due to chemical reaction between the cement paste and seawater.

Coal fly ash and wood ash were added singly to asphalt mixes as partial replacements of the asphalt cement. Mechanical property testing and cost analysis were carried out with the following percentages: 0, 10, 15, 20, and 25. The objective of the investigation was to determine the changes in mechanical properties and cost-effectiveness of ash modification. The softening point, penetration, creep displacement, and modulus of elasticity indicated stiffening of the mix with increased ash proportion. The indirect tensile and compression strengths reached peak values for the 10 and 15% mixes. The Marshall stability, the bulk density, and the maximum density, decreased with ash addition. The cost analysis indicated a saving of 6% for ash replacement of 15%. Therefore, the replacement of 10 to 15% of asphalt cement is an excellent solution to decrease the mix costs and to reduce the amount of ash in landfills without compromising the mechanical properties of the mix.

This paper presents the comparison of shrinkage and corrosion characteristics of optimized hybrid Rice Husk Ash (RHA)/Fly Ash (FA)-modified Concrete, with those of normal concrete in the marine environment. Uses of both FA and RHA have numerous environmental benefits. Shrinkage performance was determined by subjecting the mixes to restrained shrinkage testing per ASTM C1581. The time to cracking of the specimens improved an average of 18% with the hybrid mixes. Corrosion testing of reinforced columns was performed in a simulated tidal cycle Marine Environment. Corrosion potential improved by as much as 35% for the mix with the highest FA/RHA replacement, and corrosion activity as measured with potentiostat equipment improved by an average of 34% . These results indicate a clear performance improvement of the modified concrete that is proportional to the percent replacement of cement.