Influence analysis of foamed asphalt mixture gradation based on mechanical properties
In order to determine the influence and rules of the gradation of foamed asphalt on the mechanical properties, three typical gradations of foamed asphalt including the continuous gradation AC-20, the discontinuous gradation SMA-20 and the skeleton embedded crowded structure FAC-20 were taken for dry and wet splitting strength test, besides the mechanical properties of asphalt mixture under different gradations were systematically researched. The gradation composition fluctuation of four key sieve pores consisting of 0.075 mm, 0.3 mm, 1.18 mm and 4.75 mm affecting the mechanical properties of the foamed asphalt mixture gradation were systematically researched. The experimental results showed that foamed asphalt mixture was not suited for the stable discontinuous gradation; the Wittgen stable recommended gradation of foamed asphalt had better mechanical properties; the passing rate of sieve pore size bellow 0.075mm was the key factor affecting the gradation properties of the foamed asphalt mixture, and the rate between five percent and twelve point five percent had better mechanical properties foamed asphalt mixture; the smaller sieve pore size was, the influence of the fluctuation of the passing rate on the mechanical properties of gradation was greater; among others
STRUCTURAL RESPONSE OF FOAMED-ASPHALT--SAND MIXTURES IN HOT ENVIRONMENTS
This research project was conducted to investigate the ability of foamed-asphalt to stabilize local marginal sand aggregates for use as base or subbase pavement materials. The variables measured were intended to give indications of the quality of performance of these mixtures as well as aid in the development of design procedures for the use of foamed-asphalt as a stabilizing agent under the relatively high temperature conditions in the Arabian Gulf. Quantitative information is given about the effects on mixture response of significant factors such as sand type and gradation, quality and quantity of the fine fraction, asphalt grade and its percentage, moisture content, and curing condition. Both moisture and temperature susceptibilities of foamed-asphalt mixes were found to be significantly reduced by the addition of limestone powder to modify the fine fraction of sand. Structural response of foamed-asphalt mixes was compared with that of other hot-asphalt-sand mixes commonly used as base material in Kuwait. It appears that properly designed foamed-asphalt--sand mixes have a structural thickness that corresponds to that of hot asphalt and much less susceptibility to permanent deformations under traffic loads in hot environments.
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.