THE ROLE OF NA2OEQ RATIO ON THE FLOWABILITY AND STRENGTH DEVELOPMENT OF CEMENTITIOUS SYSTEMS IN THE PRESENCE OF A POLYCARBOXYLATE ETHER-BASED ADMIXTURE

Abstract

In this study, the effect of equivalent Na2O (Na2Oeq) 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 Na2Oeq 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, Na2Oeq 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.