Effect of substitution of lime stone in CPJ45 by Jorf Lasfer fly and bottom ash on the hydration of cement and on the mechanical proprieties of mortar

Abstract

The study undertaken in this work indicates that it is possible to exploit the industrial by products such as fly ash and bottom ash from the combustion of coal in Jorf lasfar thermal power and valorize them as additive in the construction materials. Because in addition to their poozolanic activity, these ashes have technical, economical and ecological compelling interests. In this work we have studied the effects of substitution of limestone in the CPJ45 cement by fly ash or bottom ash on the mechanical properties of prepared mortars, on the grinding time and on the hydration of the new cements. Different analysis techniques were undertaken to determine the physico-chemical characteristics of the starting materials. X-ray fluorescence (XRF) had permitted the classification of fly ash and bottom ash in the class F from their levels on major oxides. Rietveld quantitative phase analysis (RQPA) allowed us to compare the percentages of clinker phases with that calculated with bogue formulas. The result showed that the values found by RQPA of C3S and C3A were much higher than those calculated, while for the C2S the values given by RQPA were much lower. The isothermal conduction micro calorimeter was used to measure the heat evolution during the hydration of the cements prepared. We noticed that the additions of fly ash or bottom ash have accelerated the hydration of C3A and have delayed that of C3S. The tests performed by substituting limestone in CPJ45 by different proportions of fly ash or bottom ash have shown that the effect of these ashes on the mechanical properties of cement CPJ45. We have observed that the 28days mechanical strengths of the mortar went for a maximum with the substitution of lime stone by 6% of fly ash and 7% of bottom ash; We have also observed that increasing the amount of substitution of lime stone by fly ash had decreased the grinding time and had eliminated the clogging of the cement on the mill balls.