PSI - Issue 70

Saurav Kar et al. / Procedia Structural Integrity 70 (2025) 674–681

678

3.2 Hardened properties of concrete: Compressive strength development After preparation of various concrete mixes, basic workability tests were conducted. Workability tests include slump cone test, compacting factor test and flow table test. The slump values for all the mixes showed satisfactory values ranging from 100 mm to 200 mm, compacting factor (C.F.) values ranged from 0.9 to 0.98 and flow spread values ranged from 300 mm to 450 mm. Table 1 shows the compressive strength values for varied concrete mixes for curing age of 28-days (pond curing). With progress in age, it can be seen that with incremental content of F Ash , compressive strengths reduced even after incorporation of chemical admixture. Due to pozzolanic reaction of F Ash with increased curing ages, the % of strength gain at 28-days, 90-days and 180-days, increased. Table 1. Compressive strength development on HVFA concrete specimens cured under standard conditions for series 1, 2,3,4,5 and 6 Series F ash (%) (Cem:F ash 1:1) Compressive strength σ comp ( MPa ) Series F ash (%) (Cem:F ash 1:1) Compressive strength σ comp ( MPa )

Age of curing ( days ) 7 days

Age of curing ( days ) 28-days

Age of curing ( days ) 7 days

Age of curing ( days ) 28-days

1

0 40 50 60 70 0 40 50 60 70 0 40 50 60 70

25.7 17.0 15.3 15.7 13.2 27.0 17.9 16.5 17.8 15.3 28.3 37.5 38.1 21.6 18.6

37.2 26.7 24.7 25.2 20.8 39.1 28.0 28.3 30.5 24.7 41.0 48.8 50.4 32.1 25.7

4

0 40 50 60 70 0 40 50 60 70 0 40 50 60 70

29.8 19.7 48.3 21.0 18.6

43.1 30.9 66.6 34.0 30.5 42.5 45.2 32.5 30.0 28.1 55.6 52.3 27.6 34.8 29.5

2

5

45.6 31.2 20.7 18.6 17.76

3

6

52.4 36.2 23.9 21.5 18.8

As evident from the fig. 2, for series 1, compressive strength values subsequently decreased from 37.2 MPa to 20.8 MPa for fly ash content from 0% to 40%, 50%, 60% and 70% (≈ 78% decrease). Series 1,2,3,4,5 and 6 are prepared with concrete mixes with water/binder ratios of 0.38, 0.36, 0.32, 0.30, 0.28 and 0.25 respectively. For series 2, compressive strength values subsequently decreased from 39.1 MPa to 24.7 MPa (≈ 58% decrease). For series 3, compressive strength values subsequently drop from 41.0 MPa to 25.7 MPa (≈ 59% decrease). For series 4, compressive strength values subsequently decreased from 43.1 MPa to 30.5 MPa for fly ash content from 0% to 40%, 50%, 60% and 70% (≈ 41% decrease). Series 5 and 6 showed, compressive strength values decreased from 51% decrease and 88% decrease in strength from 0% to 70% fly ash respectively. In Fig. 2 and Fig. 3., it can be observed that, good linear relationships between strength and F Ash content for all these HVFA concrete mixes are obtained. For 28- days σ comp strength, much better correlation coefficients (R 2 ) of 0.9831 is obtained for series 1, 2 and 3. Computed standard errors (S xy ) determined as 0.61 to 0.67 MPa. For series 4, 5 and 6, R 2 values obtained as 0.974, 0.843 and 0.768 respectively. Computed standard errors (S xy ) determined as 1.1 to 2.5 MPa. Since the measured strength values are between 30 to 60 MPa, standard error of 1.1 MPa can be considered good (~ 2 to 5%) while 2.5 MPa error is