STUDY OF THE BEHAVIOR OF DIFFERENT MINERAL AND POZZOLANIC ADMIXTURES IN CONVENTIONAL AND ROLLER-COMPACTED CONCRETE WITH RESPECT TO THEIR MICROSTRUCTURE AND DURABILITY

摘要

The use of mineral and pozzolanic admixtures in concrete may contribute to the improvement of its properties such as workability, permeability loss with resulting increase in durability and, in general, increase in mechanical strength. Several of the admixtures generally employed in conventional concrete (CVC), such as fly ash, blast-furnace slag and silica fume, have been used in roller compacted concrete (RCC). However, other materials like powdered aggregate, rice husk-ash and metakaolin are under study with a view to improving the properties of both CVC and RCC, with considerable cost effectiveness. In this paper, the focus is on assessing, by means of laboratory tests, the influence of different admixtures in the durability and microstructure of CVC and RCC. The experimental program comprised the study of seven different types of admixture, as follows: powdered aggregate, ground blast furnace slag, calcined clay pozzolan, silica fume, fly-ash, metakaolin and rice husk-ash, totaling 15 combinations for CVC and 26 for RCC. Water permeability tests under pressure were performed, along with compressive strength tests in concrete test specimens and accelerated reactivity tests on mortar bars featuring the different admixtures. Microstructural observations of the concrete samples with the various admixtures were performed after 90 days of curing, by using a scanning electron microscope. The results obtained indicate that the admixtures analyzed display differing behaviors and may have a considerably positive influence on the durability and on the microstructures of conventional and roller compacted concrete, provided the former are employed in adequate proportions.