Small to intermediate strain properties of fly ashes with various carbon and biomass contents

Abstract

High-carbon-content fly ashes with biomass particles are typically landfilled in accordance with the ASTM C618 regulation. To quantify their geotechnical properties relating to storage and disposal, this study evaluates the small to intermediate strain properties of fly ashes with various carbon and biomass contents. Tested fly ashes had carbon contents ranging from 1.1% to 9.6%, resulting from co-combusting coal with biomass (biomass contents ranging from 0% to 8.2% by weight). The small-strain stiffness and intermediate-strain constrained modulus were evaluated using consolidation tests performed in a modified oedometer cell equipped with bender elements. It was found that initial void ratio governed the compressibility (or constrained modulus) of fly ashes, and with an increase in carbon and biomass contents, the small-strain stiffness of fly ashes decreased due to the decrease in number of direct contacts between microspheres. In addition, the interfine void ratio, ef, was employed instead of global void ratio to capture the alteration of interparticle contact or interparticle coordination between microspheres, due to the change in carbon and biomass contents. Finally, the stiffness in an overconsolidated state and the stiffness anisotropy of fly ashes were evaluated.

Experimental investigation on dynamic behavior of silt-rich fly ash using cyclic triaxial and bender element tests

“…This wide range variation is due to the different methods available for the identification of travel time in bender element test. Also, the small strain shear modulus (G max ) of present silt-rich fly ash was found to be in the range of G max of fly ash reported by Choo et al [111] and Chattaraj and Sengupta [63]. The normalized shear modulus (G/G max ) of the present fly ash represents broadly from 0.9 to 0.3 using cyclic triaxial and bender element test when compared with resonant column test, G/G max value was found to be 1 to 0.82 [17] and 1 to 0.5 [112].…”

Shear wave velocity of granular mixtures of silica particles as a function of finer fraction, size ratios and void ratios

“…This experimental observation supports the validity of the concept of intergranular void ratio reflecting contacts between large particles are active force chain or structural skeleton determining the mechanical behavior of granular mixtures with low FC. The velocity results at FC = 20-40 % (∼ FC * , Table 3) follow a separate trend, which indicates the stiffness of mixed materials is governed by the stiffness of particles in the active force chain [9]. At, or near, FC * , the active force chain is in a transitional zone that deviated from the behavior of either the large particles or the small particles.…”

“…The critical fines content (FC * ) is defined as the ratio of the mass of finer particles to the mass of the total mixture when the voids between coarser particles are fully filled with finer particles [9,20]. Consequently, the following relation can be established for the condition of FC * (Fig.…”

“…In this aspect, a significant decrease in the stiffness of the mixture with d s /d L = 0.014 can be explained by comparing the mixture with d s /d L = 0.157 (Figs. 5,8,9). The mixture with d s /d L = 0.014, which has much smaller size ratio than that of d s /d L = 0.157 mixture, has less developed active grain contacts between large grains at a given FC, leading to a significant decrease in stiffness.…”

“…In addition, the mixture with d s /d L = 0.282 has a somewhat greater stiffness than that of the mixture with d s /d L = 0.157 (Figs. 5,8,9).…”