Evaluating polycyclic aromatic hydrcarbon-free binders in taphole clays - a possible alternative to coal tar pitch
CAMERON I. 1, GARBERS-CRAIG A. 1
1 University of Pretoria, Hatfield, Pretoria, South Africa
Coal tar pitch has over many years been used as the bulk of the binder in taphole clays. The main disadvantage associated with coal tar pitch is the generation of polycyclic aromatic hydrocarbon (PAH) species on thermal decomposition, which are classified as a Group I carcinogen. The work in this paper investigates two possible PAH-free alternatives, namely a processed petroleum waxy oil (PWO), and a research grade glycerine. The binder systems consisted of the PAH-free alternative mixed with a phenolic resole resin. Taphole clay samples were constituted from laboratory scale mixing of the different binders, aggregate and matrix components, after which the process properties as well as high temperature properties of the clays were monitored and evaluated. The coal tar pitch (sourced from a coke oven) was used as binder in the reference material against which the PAH-free binders were compared. The process properties that were evaluated included workability (plasticity), Marshall extrusion pressure (MEP, simulating the ramming process) and strength development profile (SDP) tests. The workability and MEP were evaluated during ageing at 20°C (mud gun barrel temperature) over a 21-day period, and during a drying test at 60°C, which simulated the change in these properties through continuous heating. The SDP test consisted of cold crushing strength (CCS) measurements from samples heated at 200°C for different periods of time ranging from 10-120 min. Volatile loss of the clay samples during the SDP evaluation, was also recorded. Lastly, the high temperature properties which included loss on ignition (LOI), volatile organic compounds (VOC), as well as CCS and apparent porosity (AP) after firing to 800°C in reducing atmosphere, were determined. This was done to examine the effect of changing binder composition on the high temperature properties of the clay.