USE OF VISCOSITY-MODIFYING ADMIXTURE TO ENHANCE STABILITY OF FLUID CONCRETE

The placement of concrete in congested areas requires rile use of a hi ghly fluid mixture that can spread readily into place with minimal con solidation. The incorporation of a high-range water reducer along with a viscosity-modifying admixture can enable the production of fluid co ncrete having sufficient cohesiveness to reduce bleeding segregation. and settlement. Such stability can be secured er en,then the concrete is subjected to high shearing action resulting from pumping, casting, and consolidation. This paper presents the results of a study carried out to investigate the effects of viscosity-modifying admixture concen tration placement height, and mode of consolidation on enhancing the s tability of mixtures made with various water-to-cementitious material ratios and consistency levels. In the first phase, bleeding and settle ment are determined using 70-cm high columns cast with concrete contai ning various viscosity-modifying admixture dosages, water-to-cementiti ous material ratios (0.50 to 0.70), and slump values (140 to 220 mm). In the second phase, bleeding, settlement, and segregation are evaluat ed for concretes with 220-mm slump cast in 50-, 70-, and 110-cm high c olumns. The mixtures are made,with a water-to-cementitious material ra tio of 0.50 and various contents of viscosity-modifying admixture. The effect of excessive external vibration on stability is also evaluated . Regardless of the water-to-cementitious material ratio, slump, casti ng height, and mode of consolidation, the incorporation of a viscosity -modifying admixture is shown to significantly enhance the resistance to bleeding, settlement, and segregation. Concrete containing 0.07 per cent viscosity-modifying admixture and no silica fume can secure great er stability than similar concrete made with 0.035 percent viscosity-m odifying admixture and 8 percent silica fume. A simple and accurate me thod for measuring surface settlement is proposed. Such a method can b e useful in optimizing highly stable, yet flowable mixtures.