Parallel Session 2A

Aggregate quality during crushed stone manufacturing does not rely only on characteristics of the source rock but is also influenced by mechanical settings of the crushing machinery. The current research examines how the combined effect of crusher type and Closed Side Setting (CSS) influences two important characteristics of aggregates, that aggregate morphology (angularity) and aggregate toughness. Aggregate samples were collected from a full scale quarry crusher plant under controlled and documented CSS conditions. Angularity was measured with the help of an innovative image based digital method using a composite Angularity Index including gradient angularity, sharp corner density, curvature concentration and convexity deficit. Aggregate toughness was assessed with the help of aggregate impact value (AIV) test in compliance with BS 812-112. A total number of ten sampling situations was considered for both five different CSS situations from a main crusher plant and five different CSS conditions from a mobile crusher plant. Research results show that angularity indices as well as AIV of aggregates manufactured using jaw crushers always were significantly higher than those of aggregates manufactured using cone crushers. A strong positive quadratic relationship (R² = 0.8965) was established between Angularity Index (AI) and AIV across all samples and also, increase in CSS resulted in increased values of AI and AIV in both types of crushers.

Aruwakkalu red soils in Sri Lanka contain economically significant titanium-bearing heavy minerals, yet these materials are presently used as quarry fill. This study investigates the depth-wise mineralogical and geochemical variations of Aruwakkalu red soils and evaluates the recovery of titanium-bearing heavy minerals using a Humphreys spiral concentrator. A total of 20 bulk samples from three quarry locations (SA, SB, and SE) and different depths were characterized by X-ray Fluorescence (XRF). The XRF results reveal that SiO2, Al2O3, Fe2O3, and TiO2 dominate these red soils. These dominant oxides are broadly similar spatially, whereas small fluctuations occur depth-wise. The XRD analysis revealed the presence of kaolinite, metahalloysite, quartz, ilmenite, rutile, hematite, and magnetite. TiO2 was selected as the primary recovery target due to its abundance and association with dense heavy minerals such as ilmenite and rutile. Particle size analysis confirmed that approximately 78.4% of the feed material lies within the optimal range for effective spiral concentration. Beneficiation trials using a Humphreys spiral concentrator produced an average TiO2 enrichment ratio of 4.1 and an average recovery of 74.7%. The findings validate the utilization of spiral concentration as the primary rougher stage for recovery of titanium from Aruwakkalu red soils.

Coarse aggregates constitute 60–75% of total concrete volume and their mechanical properties directly govern compressive strength of concrete. This study investigates the effect of jaw and cone crusher settings on Aggregate Impact Value (AIV), Aggregate Crushing Value (ACV), and Los Angeles Abrasion Value (LAAV), and their relationship with Grade 25 (M25) concrete strength using the same quarry source. Aggregates were collected from four jaw and cone crusher Closed Side Setting (CSS) combinations and were tested AIV, ACV and LAAV according to BS 812-112, BS 812-110 and ASTM C131 respectively. A fixed mix design (w/c = 0.60, ratio 1:2.46:2.9) was maintained throughout, and 150 mm cubes were tested at 7, 14 and 28 days. Logarithmic regression was used to evaluate the relationships, and R² was used to assess the goodness of fit. The 110 mm jaw and 22 mm cone CSS combination produced the best aggregate quality (AIV = 20.8%, ACV = 20.8%, LAAV = 22%) and the highest 28-day strength of 32.8 MPa. AIV and ACV showed strong negative relationship with strength of concrete at 7 and 28 days, while LAAV showed a weak relationship with the concrete strength under the conditions of this study.

The mechanical quality of the coarse aggregate determines the cement demand and the concrete compressive strength needed to meet the specified performance. This study identified the optimum cement content for Grade 25 concrete using aggregates characterized by Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), and Ten Percent Fines Value (TFV) collected from five crusher configurations at Doratiyawa quarry, Kurunegala. ACV groups aggregate into three quality levels. The Taguchi L9 orthogonal array was used for four control factors, namely cement content, water-cement ratio, ACV category, and fine aggregate percentage. Fifty-four concrete cubes were tested on 14 and 28 days. ANOVA revealed that water-cement ratio (42.43%), ACV category (20.92%), cement content (15.22%), and percentage of fine aggregate (7.66%) were the factors contributing to variation in strength.

Underground mining requires precise ventilation control to enable a safe work environment, yet complex multi-fan networks often suffer from unmanaged shaft leakage that compromises deep-level safety. To address this issue, this study evaluates the impacts of primary surface fan frequency variations (50 - 20 Hz) on airflow stability across the critical 240 fm and 275 fm horizons of the Bogala mine. By executing 100-step simulation sweeps within a VentSim DESIGN model, four operational configurations were systematically evaluated by changing the booster fan and sealing status. The simulations reveal that operating an inline booster fan alongside unsealed landings causes substantial loss of aerodynamic coupling at the lowest workings, as fresh air short-circuits through upper elevations before reaching active zones. While sealing these upper landings restores primary fan control, it triggers local airflow volatility due to pressure competition at opposing airway T-junctions. To stabilize the network, permanently bypassing the inline booster fan while fully sealing the upper shafts delivers a highly predictable airflow response and a more consistent airflow distribution across both deep production levels, and provides a basis for future investigations to test this scenario in the real mine, which could lead to automated ventilation control strategies.

This final segment invites reflections from presenters and attendees, synthesizing key insights from the session. The session chair will conclude the discussion by summarizing thematic threads, highlighting interdisciplinary contributions, and outlining potential collaborative directions.