PSI - Issue 70

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

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k 7 d = 0.90- 0.10 ln(P) k 28 d = 1.20- 0.14 ln (P)

(4)

(5)

The model was validated on 27 different FAC mixes (S1 – S27), with predicted strengths deviating by no more than ±11.2% from actual values, suggesting high accuracy and reliability. The model also proved effective when applied to datasets from prior studies by Dhir et al. (2000), Mangaraj and Krishnamoorthy (1994), Siddique (2003) confirming its broader applicability. The novelty of this work lies in its ability to predict strength even when the quantity of FA added exceeds the amount of sand replaced — a condition not typically addressed in conventional models given by Ganesh Babu and Sivanageswara (1993). 3. Regression analysis of strength values for HVFAC mixes: a new rational and innovative mix proportion 3.1 Research methodology: Preparation of materials in this current research In this paper, authors have tried to implement regression analysis on compressive strength (σ comp ) values for HVFA concrete mixes with a new, rational and innovative mix proportioning technique. This technique which is developed is modified from latest IS code guidelines. In order to implement high-volume fly ash, fly ash replacement levels kept varying from 40% till 70%, to increase the reduction of CO 2 emission factor. The increased percentage of pulverized fuel ash is attempted to reduce the carbon footprint in the environment due to concrete production (1 tonne cement production leads to ~ 1 tonne of CO 2 ).

Fig. 1. Rational approach for mix proportion HVFAC concrete suitable for ASTM class F fly ash content

As shown in fig.1, cement is partially replaced by class F fly ash (F ash ) in assorted amounts (such as 40%, 50%, 60% and 70%) in a fixed proportion of Cem: F Ash (i.e. 1:1 by wt.). In this experimental setup, F Ash is partially substituted with traditional Portland cement while the remaining unreacted F Ash substitutes as filler material in the form of fine aggregate. Attempt is made so compressive strength at standard curing regime can be compared with the same of ordinary control concrete. With incremental content of fly ash i.e. 40%, 50%, 60% and 70% (CRL), modified lignosulphonate-based admixture is used in required dosage (~ 1- 2%) by weight of total cementitious material or binder. The cement replacement level (CRL) starts from 40% by weight of OPC. The total fly ash content which is used as substitution (w Fash ), 75% of that weight takes part in chemical hydration of cement (i.e.0.75 w Fash ) and remnant 25% behaves as filler material in the form of fine aggregate (i.e. 0.25 w Fash ). This mode of percentage distribution can be attributed to long term performance of fly ash concrete.