S. J. Jung

REVIEW OF CURRENT HIGH DENSITY PASTE FILL AND ITS TECHNOLOGY

Backfilling techniques are widely used in large-scale underground mines. Massive pillars, which have been left in place for stability, limit mining activity. Backfilling allows for safe recovery of the ore remaining in pillars and assures long-term stability. The high rock stresses which result from deep mining operations can be relieved by backfilling. Initially, waste rock was used to fill the openings left by mining operations, though with mixed results. The need to improve safety and reduce costs has prompted the mining industry to investigate alternative backfill methods. Hydraulic filling with Portland cement has shown considerable promise, but little has been done to define the parameters for an effective design. The objective of this paper is to enhance the understanding of current paste backfill practice. Sixty to seventy weight-percent solids-cemented backfill slurries are currently being used in the mining industry (as a matter of practicality). However, deficiencies in this particular ratio need to be examined. Physical properties of mine tailings are unique based on their geology and the milling process. Flaws in the cemented backfill slurries are usually a result of poor hydration and slime build-up to levels that cause additional dewatering, high equipment/operating costs, and work delays. Furthermore, the required strength and quality of the fill may be affected by high water-cement ratios, as well as by its consolidation time, permeability, and volume changes.

Development and evaluation of hot mix asphalt stability index

This paper addresses the development and evaluation of a mix stability index referred to as the gyratory stability (GS). GS is calculated from the compaction data by summing the cumulative energies dissipated in the compaction of a gyratory sample. A wide range of commonly used mixes in the State of Idaho were selected for evaluation. Mixes were tested for dynamic modulus (E*) and flow number (F N); rutting was measured with the asphalt pavement analyser (APA). Furthermore, E* test results were used in the AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG) as level 1 inputs, to predict rutting for these mixes; GS ranked mixes similarly to the APA and F N tests and MEPDG results. Furthermore, results indicated that the GS has the potential to be used as a screening tool for asphalt mix design, especially to decide upon the acceptance of the mix aggregate structure, and as a quality control tool.

Effects of Asphalt Mix Design Properties on Pavement Performance: A Mechanistic Approach

The main objective of this study was to investigate the effects of hot mix asphalt material properties on the performance of flexible pavements via mechanistic approach. 3D Move Analysis software was utilized to determine rutting and cracking distresses in an asphalt concrete (AC) layer. Fourteen different Superpave mixes were evaluated by utilizing results of the Dynamic Modulus () Test and the Dynamic Shear Modulus () Test. Results showed that with the increase of binder content, the tendency of rutting in AC layer increased. However, with the increase of binder content, the cracking of AC layer lessened. Furthermore, when different binder grades were evaluated, results showed that with the increase of the upper binder grade number, rutting decreased, and with the increase of the lower binder grade number, rutting increased. Furthermore, analysis showed that with the increase of the lower binder grade number, higher percent of bottom up cracks would result. As a result of the analysis, binder grade should not be solely considered for cracking in AC layer; binder content and aggregate structure play a big role. Finally, results illustrated that the mechanistic approach is a better tool to determine the performance of asphalt pavement than commonly used methods.