The effect of increasing amounts of each of Al203, MgO and MnO in synthetic slag glasses corresponding to Indian slag compositions, on their hydraulic behaviour after activation with cement clinker has been studied. Results showed lowering of strength of cements at all ages with increase in Al2O3 content in glasses beyond 22 percent in spite of the progressive increase in chemically combined water. Presence of MgO up to 2.5 percent improved the strength but a higher content was found to be detrimental. High MgO in glass did not cause unsoundness in cement. MnO up to 2.5 percent was beneficial but a higher content affected the early strength adversely.The hydration products identified were mainly calcium silicate hydrate and tetracalcium aluminate hydrate. Magnesium or manganese containing hydration products could not be identified. These ions appear to go into solid solution in the hydration phases. The study explained the pattern of strength development in Indian granulated slags.

Role of Alumina, Magnesia and Manganese Oxides on the Hydration and Hardening of Slag Glasses

Slags having three different SiO2: Al2O3 ratios (1.2,1.9 and 2.6) and three different CaO contents (44%, 39% and 34%) were prepared. These slags were classified into nine series, in each of which Al2O3 and SiO2 were kept constant and CaO was replaced by MgO in molecular proportion. The hydraulicity of these slags was estimated from the compressive strengths of 1:3 mortars, the cements being prepared from 1.8 parts slag and 1 part hydrated lime by volume. The soundness of the cements produced from some of these slags and portland cement was also measured. Hydraulicity of slag had a tendency to decrease when CaO was molecularly replaced by MgO and it practically did not change when CaO of slag was replaced by MgO on weight basis. Compressive strength increased with the increase of CaO and Al2O3 content of slag and decreased with increase of SiO2 content. The cements produced from high-magnesia slags were perfectly sound and did not show any dimensional instability.

Durgadas Lahiri

Papers

Effect of MgO on Hydraulicity of Slag in the System CaO-Al2O3-SiO2-MgO