Florida-produced fine aggregates are generally of suitable quality, and deleterious effects associated with organic matter are uncommon. However, naturally occurring organic constituents can affect cement hydration and early-age strength development depending on their concentration, composition, and interaction with cementitious phases. The sands evaluated in this study contained relatively low organic contents, making establishment of a universal organic-content threshold impractical. FDOT currently uses AASHTO T 21 as the primary screening method for potentially deleterious organic impurities and requires AASHTO T 71 testing when screening results indicate concern. This framework should be maintained. AASHTO T 21 provides effective statewide screening, while AASHTO T 71 provides performance-based confirmation. However, AASHTO T 21 is qualitative, and AASHTO T 71 requires extended testing that can delay aggregate acceptance decisions. Neither elemental analysis nor the Modified Walkley-Black method demonstrated sufficient precision, consistency, or correlation with AASHTO T 21 to support statewide acceptance criteria. However, MWB may be used to establish minespecific organic-carbon baselines, and isothermal calorimetry may be used to establish mine-specific hydration-response baselines. Deviations from these baselines may indicate the need for additional evaluation, including AASHTO T 71 testing. Organic-carbon contents below approximately 0.015% did not measurably affect hydration or compressive strength. Alkaline washing reduced measured organic content and increased pH but did not consistently improve strength. The ASTM C109 hand-tamped consolidation procedure is recommended for AASHTO T 71 mortar cube fabrication. Trace inorganic constituents, including phosphorus, did not produce measurable strength effects.

Infrastructure Assets: Highway Assets
Resource Types: Research Report
Capabilities: Tools & Technology
Management Processes: Performance Based Planning & Programming