Abstract
The effect of CBA/CBA-L ratio and the cement replacement on the Loss on ignition (LOI) of ternary cement blends was investigated using central composite design approach in the prediction of LOI of ternary cement blend comprising of Ordinary Portland cement, coal bottom ash and Limestone. LOI is an essential technique employed in the determination of the quality of the cement blend which can be achieved by heating a sample strongly at a specified temperature to enable release of volatile components until the weight remains constant. In this study, monitoring of the LOI of the various cement blends conducted dependent on cement replacement and coal bottom ash to coal bottom ash-limestone ratio (CBA/CBA-L ratio) via thermogravimetric analysis (TGA) and X-ray fluorescence (XRF) analysis. The CBA/CBA-L ratio was varied from 0.25-0.75 while the cement replacement ranges from 20-40%. The significance of these factors within the specified ranges considered was evaluated using analysis of variance. The aim of the study was to evaluate the effect of CBA/CBA-L ratio and cement replacement in the prediction of LOI for ternary cement blends by employing Face Central Composite Design. Analysis of variance results indicated that the LOI prediction via XRF analysis was better than that of TG analyses in which both satisfied Two-Level Factorial model. It was observed from the predictive models that the LOI of the ternary cement decreased as the CBA/CBA-L ratio was increased while LOI of the ternary cement blend increased as the cement replacement was increased. An increase in both CBA/CBA-L ratio and cement replacement resulted in a decrease in the LOI of ternary cement. The cement replacement level of the ternary cement blends indicated a stronger influence on LOI compared to the CBA/CBA-L ratio which was indicated by a significantly high F value for cement replacement compared to CBA/CBA-L ratio. The LOI results from XRF analysis were also found to significantly predict the LOI of the ternary cement blend compared to TGA with Regression value of 99.96% against 97.36% respectively. The CBA/CBA-L ratio and cement replacement were found to have a significant and interactive effect on the LOI of ternary cement blend for both XRF and TGA analyses.
Highlights
The continuous generation of waste which possesses both hydraulic and pozzolanic properties via pyro processes along with environmental concerns has given rise to the need to effectively utilize ashes as pozzolana to improve the physico-mechanical properties and durability of cement [1, 2, 3]
It was observed from the predictive models that the Loss on ignition (LOI) of the ternary cement decreased as the CBA/CBA-L ratio was increased while LOI of the ternary cement blend increased as the cement replacement was increased
The high F value is a strong indication that the effect of the CBA/CBA-L ratio has a far more significant compared to the cement replacement while the product of interaction terms obtained very low F values of 9.47 while for X-ray fluorescence (XRF) analysis obtained a relatively high F value of 1129.34 respectively with p values of > 0.05 respectively
Summary
The continuous generation of waste which possesses both hydraulic and pozzolanic properties via pyro processes along with environmental concerns has given rise to the need to effectively utilize ashes as pozzolana to improve the physico-mechanical properties and durability of cement [1, 2, 3]. It is a key cement property that affects the quality of cement blends containing pozzolanas like slags, coal bottom ash, rice husk ash, corn cob ash [9] etc., which are associated with the amount of moisture and carbonates present [10, 11]. Loss on ignition of coal bottom ash or cement blends can be determined by heating a sample strongly at a specified temperature to enable release of volatile components until the weight remains constant [12]. The weight losses of cement blends during heating could be due to the evaporation or volatilization of a variety of components of the sample and some of the components lost include water at 100–105 ̊C, organic material which is burnt off at about 550 ̊C, while most of the carbonates decompose between 800–1000 ̊C [15]
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