Quality Control of Hot Mix Asphalt Type MDC-2 Produced in High Mountain Batch Plant By Quantitative Extraction of The Binder and Granulometric Analysis: Case Study in Pasto, Colombia

Abstract

This paper presents a comprehensive quality control case study of dense-graded hot mix asphalt (HMA) type MDC-2 produced by a batch plant (Barber-Greene KA-40) located at 2,495 m above sea level in Pasto, Colombia. The quantitative binder extraction method (INV E-732, Method A) and aggregate gradation analysis (INV E-782) were applied to evaluate compliance with Marshall design specifications and Colombian highway standards (INVIAS). Three production lots were sampled during field operations in June 2011, yielding 18 specimens: nine tested at the plant's quality control laboratory and nine at Universidad de Nariño's soils laboratory for independent verification. This dual-laboratory approach enabled statistical comparison of procedures, equipment, variability, and systematic biases in asphalt content determination and mineral gradation. Statistical treatment included descriptive statistics, interlaboratory variability assessment, and tolerance verification based on INVIAS specifications. Results indicate that plant laboratory asphalt contents deviated significantly from the optimal design value (6.25%) and exhibited high inter-specimen variability, primarily associated with deficient sampling practices, insufficient solvent-mix contact time, and use of manual centrifuge equipment. Conversely, university laboratory results demonstrated lower dispersion and closer approximation to optimal content. Aggregate gradations from extracted materials fell within the MDC-2 band but often exceeded allowable deviations from the target gradation curve, revealing deficiencies in aggregate proportioning and process control. The study confirms that integration of INV E-732 and INV E-782 methods with robust statistical analysis provides an effective diagnostic framework for HMA quality control performance in Andean region plants.