|M.Sc Student||Keren Binyamin|
|Subject||The Use of Fly Ash as Hydraulic Road Binder for Production|
and Strengthening of Structural Pavement Layers
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Ishai Ilan|
|Dr. Mario Hoffman|
This research thesis examined the use of fly ash, a by-product of coal combustion in the generation of electricity, as a main constituent of hydraulic road binder (HRB) used to strengthen or manufacture pavement. HRB is a relatively new application in road construction, and has been used increasingly for the past decade, mainly in Europe. According to a draft of the European standard for HRB (2000), the binder is defined as an industrial powder consisting of a blend of different constituents, which may include industrial waste, such as fly ash, as a main constituent.
The two main objectives of the study were to examine the practicability of using South African fly ash as the main constituent of HRB (90% content), and the contribution to the binder of hydrated lime and hemi-hydrate gypsum as additives (combined content 10%). Five combinations of fly ash, lime and gypsum, at different percentages, were tested. In addition, the influence on the properties of HRB of fly ash source (Indonesian vs. South African) and of fly ash treatment and storage before usage was investigated.
Laboratory tests conducted included dry density-moisture content CBR, unconfined compressive strength, indirect tensile (splitting), durability of soil cement, moving wheel, and XRD and SEM tests. Experiments were carried out at different curing times (1, 7, and 28 days). Specimens were stored at 90% relative humidity and 23 + 2 0C.
Tests results showed that South African fly ash (with a calcium oxide content of 10.33%), stored in a silo (in dry condition), fulfills the requirements of various standards and specifications for stabilized road materials from around the world. South African fly ash has high durability, does not crack when subjected to vehicular traffic, has high compressive strength, and can therefore be used as the main constituent of HBR (even with no additives). An addition of 8% lime and 2% gypsum to HRB can improve its properties. This effect was also observed in the SEM and XRD tests after 28 days of curing and is due to chemical reactions that take place.
In summary, research results show that HBR can be combined effectively with fly ash as a main constituent, and with lime and gypsum as additives. The efficiency of the binder depends on its engineering and economic properties, type of fly ash and its properties, fly ash storage conditions, relative content of the other binder constituents, and curing time of the applied product.