ABSTRACT

In this study, the effect of equivalent Na₂O (Na₂O_eq) ratio of cement on fresh properties and compressive strength of paste and mortar mixtures containing polycarboxylate ether-based high range water reducing (HRWR) admixture was investigated. A low and a high alkali cement were used. Five mixtures having five different Na₂O_eq ratios were prepared with increasing alkali content of the cement by incorporating three different amounts of NaOH solution to the low alkali cement-bearing mixtures. Irrespective of the absence or presence of HRWR, Na₂O_eq content of the mixtures was found to have a considerable adverse effect on the fresh properties of the mixtures, particularly on their flow loss. NaOH addition increased 1-day compressive strength of the mortar mixtures, however, reduced the compressive strength at later ages. In spite of having a lower fineness and a longer setting time, low alkali cement showed slightly higher 1-day strength than high alkali cement. This seems to have occurred, to some extent, from the higher HRWR admixture demand (0.4 wt.%) of the high alkali cement-bearing mixture than that of the mix containing low alkali cement (0.25 wt.%). At later ages, both of the cements showed equivalent strength values.