Avaliação e determinação de parâmetros para otimização de esqueleto granular em atendimento à autoadensabilidade de concretos

Abstract

Self-compacting concrete (SCC) is a composite material consisting by paste and granular skeleton phases, being the first obtained by measuring the water / cement ratio, additions and additives, which ensure flowability between aggregates. In the second, the compositions of the aggregates are formulated aiming at the best performance of self-compactability properties. The packing theory of aggregate grains, which relate the lowest void content with the best particle size distribution and lower paste volume, has been applied to obtain the optimization of aggregate compositions for SCC. However, no studies have been identified that have shown that a composition of aggregates with larger concentrations of small and large particle sizes, in a continuous distribuction, have a smaller distance from each other, providing a granular arrangement with higher voids content, contributing, to this, for better performance in the fresh state of SCC. Thus, the present study aims to propose aggregate grading parameters in order to optimize these compositions by evaluating particle size distributions of large and fine aggregates, seeking to “ideal” packing for SCC. To meet the proposed, the following aggregate grading parameters (PGA) were determined: particle diameter predominance (PDP), uniformity coefficient (CU) and coarse aggregate percentage (PAG). Different binary, ternary and quaternary aggregate compositions based on the lowest void content were developed using natural, industrial, and concrete recicled aggregates. In addition, different SCC granular skeletons obtained in the literature were analyzed. In the production of concretes, the composition of the cement paste remained fixed. Fresh performance was evaluated using slump flow, apparent plastic viscosity (t500), box L and funnel V test methods in order to associate the results obtained with the grading parameters. Of these, only the scattering diameter (SF), V-funnel time (VF) and passing ability (HP) measurements were response variables. Assurance of hardened properties was obtained from the test methods of compressive strength, initial tangent modulus of elasticity e physical indices of the concrete such as water absorption and concrete voids and real specific gravity. In general, the continuous particle size distributions predominated in meeting SCC properties, with a PAG of around 50%. In the statistic application of the parameters with the statistical technique Principal Component Analysis (PCA), the results showed significant evidence regarding the interpretation of the variability of the data of SCC mixtures encompassing the six variables referring to the grading parameters (PDP, CU and PAG) and the response variables (SF, VF and HP). An indication of a higher discontinuity and predominance ratio of large and small particles negatively affected the uniformity of the mixtures. Finally, based on the establishment of relationships between the six variables, the following PDP and CU intervals can be proposed: 6 < PDP < 25; 9 < CU < 23. The relationships between the PGA and the proposed particle size zones served as performance indicators of the fresh SCC mixtures, with guaranteed of the performance in the hardened state.