Keywords: fly ash, ground ganulated blast furnace slag, pozzolanic activity, compressive strength, mineralogical and morphological features.

The research described in this paper focuses on evaluating the influence of fly ash (FA) and ground granulated blast furnace slag (BFS) as supplementary pozzolanic materials on the mortar and concrete strength using destructive and non-destructive test methods. The evaluations were carried out through monitoring the strength development rate and values for ninety one days. The admixture of 50% OPC, 25% FA and 25% BFS showed the most significant strength development rate and values, indicating that the ternary system was much better and would improve the values of strength with time.

The BFS pozzolanic reaction would be activated earlier than the FA and the fineness of the BFS could play a role for enhancing the matrix homogeneity of the mortar or the concrete specimens to be more compacted than that of the FA [1,2]. The fly ash had little adverse effect on the bending and compressive strength when used with the BFS. The FA enhanced the bending strength [3] while the BFS enhanced the compressive strength.

On the other hand, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observation were used to investigate the mineralogical and morphological features of FA and BFS. The XRD and SEM confirmed that the incorporation of 50% OPC, 25% FA and 25% BFS was the most appropriate proportions. Also, the higher glassy phase of the BFS indicated a higher consumption of free calcium hydroxide [1] than the FA which better enhanced the early strength than the FA. The hydrated particles of the BFS at the early age enhanced the pozzolanic activity of the FA particles which were merged and superimposed in the matrix.

Therefore, the incorporation of FA and BFS as cement replacement in concrete as in the admixture of 50% OPC, 25% FA and 25% BFS was preferred to the sole use of either material for obtaining high performance concrete. In addition, the CaO content of the BFS was relatively high and only enhanced the early strength more than the FA but the hydration of the BFS did not release free CH as cementitious materials as demonstrated by XRD analysis. Therefore, the BFS could be classified as a fully pozzolanic material.

1

ACI Committee 226: Granulated blast-furnace slag as a concrete constituent, ACI materials journal, No.84, p. 327-342, 1987.

2

ACI Committee 226: Use of Fly ash in concrete, ACI materials journal, No.84, p. 381-409, 1987.

3

R.C. Joshi and R.P. Lohtia: Fly ash in concrete production, properties and uses, The Univ. of Calgary Alberta, Canada, p. 269, 1997.

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