PSI - Issue 70

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

676

To develop a predictive model, a linear regression analysis was applied by Gauch et al. (2003) using the least squares method, which optimizes the fit by lowering the total squared residuals. The resultant model matches with eqn. (1). ≈ 0.00237x + 24.17 (1) Eqn. (1) provides an empirical relationship between replacement percentage (x) and compressive strength (y), demonstrating a low mean squared error of approximately 0.0254, indicative of a strong model fit. The study by Siddique (2006) adopts a mechanistic modelling approach, wherein the relationship is derived based on physical interpretation and statistical fitting rather than purely empirical curve fitting. While the regression model is suitable within the tested replacement range, the authors caution against extrapolating the predictions beyond this limit due to the assumption of linearity as given by Rodríguez Viacava (2012). In addition, compressive strength, tensile and flexural strengths were also evaluated by Al-Harthy (2003), with 25% replacement showing the highest tensile strength (3.7 MPa) and OPC exhibiting the best flexural performance (4.2 MPa). These mechanical properties help in determining the performance thresholds for structural applications using cement kiln dust and similar materials. The findings support earlier work emphasizing the viability of kiln dust as a sustainable cement substitute, provided that optimal percentages are maintained as mentioned by Abukhashaba (2014). Analytical study Agwa and Ibrahim (2019) highlights the regression model could act as a preliminary tool for mix proportioning, allowing engineers to estimate compressive strength outcomes with minimal experimental input. However, the authors such as Utsev (2022) also acknowledge limitations — particularly the narrow data range, assumption of homoscedasticity, and lack of long term durability validation — requiring further investigations under different environmental conditions and material types. 2.2. Prediction of Compressive Strength of Concrete with Fly Ash as Sand Replacement Material Rajamane et al. (2007) addressed a less-explored domain in concrete technology — using pulverised fuel as a sand replacement material (SRM) instead of the conventional role as a binder substitute. While the pozzolanic behaviour of Fash in cement replacement has been extensively researched by Neville et al. (1987) and Mehta (1997), its role as a direct fine aggregate replacement had limited predictive methodologies. The authors formulated a strength prediction equation based on a modified version of Bolomey (1935), given in equation below. Traditionally, Bolomey’s (Brandt) model relates compressive strength ( f c ) to the water – cement ratio ( w/c ) via: f c =A× ( w 1 ⁄c − 0.50) (2) In order to account for FA acting as partial fine aggregate, they introduced the cementing efficiency factor ( k ) and binder replacement fraction ( p ), yielding: f c =A × ( 1−p ( 1−k ) w⁄c − 0.50) (3) Values of A correspond to 14.42 and 19.23 for 7-days and 28-days strength. Experimental investigations were conducted utilizing concrete mixes with fly ash replacing 20%, 40%, and 60% of sand by weight. At each level, three different water – cement (w/c) ratios were used. Interestingly, Fash was added in amounts exceeding the sand reduction to study the impact of fly ash addition factor (m) on strength prescribed by Dattatreya (2002). The study introduced a generalized predictive formula that included the binder composition, w/b ratio, replacement fraction (p), and the calculated cementing efficiency (k). Values of k were shown to vary logarithmically with FA content in binder, and specific equations for 7- and 28-day strengths as proposed in eqn. (4) and eqn. (5).