PSI - Issue 70

K. Navin Balaji et al. / Procedia Structural Integrity 70 (2025) 295–302

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3.2.2. Compressive Strength (CS) The 7-day CS of the mixes measured between 30.2 MPa (CC) and 36.0 MPa (RHA-15). RHA contributed to strength improvements through its addition up to 15% replacement levels. The strength measurements at 28 days reached from 33.25 MPa (CC) to 40.12 MPa (RHA-15). The strength showed a moderation of decline beyond 15% RHA addition. Concrete strength behaviours showed improvement at early ages and later ages when cement was partially substituted with RHA. The CS of all SCC mixtures exhibited a distinct upward trend with the incorporation of RHA up to 15%, thereafter followed by a slight decline. At 28 days, the CS varied from 33.25 MPa for the control concrete (CC) to a maximum of 40.12 MPa for the mixture containing 15% RHA. The enhancement is attributed to the pozzolanic interaction of RHA, which produces more calcium silicate hydrate (C–S–H), which leads to pore refinement and better microstructure (Khan et al.,2019). The inclusion of LSP at 15% and CSA at 20% enhanced early hydration and strength development. The test findings are illustrated in Fig.4.

Fig.4. Development of CS for SCC mixes

3.2.3. Split Tensile Strength (STS) The addition of RHA to the mixture increased the STS to a maximum of 15%. The values of STS at day 28 reached their maximum at 3.80 MPa when using RHA-15 but dropped to 3.10 MPa for the CC sample resulting in about 22.5% better tensile strength. At 15% RHA incorporation a strength increase occurred because both better paste-aggregate contact and improved particle arrangements develop from RHA's fine texture. The resistance to tension improved through additions of LSP which facilitates hydration product nucleation together with CSA permitting early-age strength development (Sandhu & Siddique.2021). The addition of 20–25% RHA caused a decrease in tensile strength to result in 3.45 MPa and 3.20 MPa because unreacted RHA particles created weak areas in the material. 3.2.4. Flexural Strength Similar trends developed in FS testing corresponded with the observed outcomes from the compressive and tensile strength tests. At 28 days the mix with RHA-15 achieved the highest FS value of 5.98 MPa. The addition of RHA pozzolanic properties while incorporating LSP filler effect led to denser microstructures which improved flexural performance of SCC (Wang et al.,2018; Courard et al.,2011). The combination of RHA at 15% with constant LSP at 15% and CSA at 20% improves SCC mechanical property performance strongly. When the RHA content surpasses the optimal level, it causes reduced strength because the cementitious material proportions become diluted. Previous studies demonstrated that RHA improved the concrete strength (Sandhu & Siddique.2021; Khan et al.,2015; Msinjili et al.,2018) 3.2.5. Modulus of elasticity (MOE) The MOE of SCC mixes ranged from 27.1 MPa to 30.1 MPa after 28 days, as illustrated in Fig. 5. When RHA reached 15% incorporation in the mixture the elasticity modulus achieved its highest level because of improved