Long-Term Strength, Chloride Permeability, Acid Resistance, and Microstructural Analysis of Quaternary High Performance, Concrete: OPC + Silica Fume + Fly Ash + GGBS Systems

Abstract

Quaternary High Performance Concrete (HPC) systems incorporating Ordinary Portland Cement (OPC) with three supplementary cementitious materials (silica fume SF, fly ash FA, and GGBS) simultaneously exploit the synergistic pozzolanic reactions of all three SCMs to achieve exceptional combined strength and durability. This paper presents the comprehensive characterisation of three quaternary HPC mixes (Q1: OPC+SF+FA+GGBS at w/b = 0.32; Q2: optimised at w/b = 0.30; Q3: high performance at w/b = 0.28) and five ternary/binary reference mixes, focusing on long-term strength (3, 7, 28, 56 days), chloride permeability (RCPT per ASTM C1202 [8])) at 28 days, acid resistance after 30 days in 5% H₂SO₄ solution, water absorption, and SEM microstructural analysis. Mix design follows ACI 363R [1]) and IS 10262: 2019 [11]). Key findings: Q2 (OPC 350 + SF 50 + FA 50 + GGBS 60 kg/m³, w/b 0.30) achieves 28-day f'c = 72.8 MPa and 56-day f'c = 85.4 MPa (+17.3% continued gain from GGBS/FA late pozzolanic reaction) [43]); RCPT = 312 coulombs (approaching NEGLIGIBLE per ASTM C1202 [8])) 92.5% reduction from NSC; acid resistance: 88.2% strength retained after 30-day H₂SO₄ exposure [10]). Q3 achieves 92.6 MPa at 56 days and RCPT = 288 coulombs the best combined performance in the study. SEM analysis confirms near-elimination of the ITZ in quaternary HPC and virtual absence of Ca(OH)₂ crystals the densest microstructure observed [30],[34]). The quaternary system outperforms binary and ternary HPC in durability while achieving equivalent or superior long-term strength, providing the optimal HPC system for aggressive exposure structural applications.