Estudo de critérios de dosagem para melhoria de desempenho mecânico de brita graduada tratada com cimento

Abstract

In the middle of 20th Century, Graded Gravel treated with cement (BGTC) was widely used in the main high-traffic Brazilian highways. However, it presents several limitations related to the properties of the material, due to its almost fragile composition, because as soon as the large variations in the tensile strain occur along loading cycle, critical and accelerated degradations also occur leading to fatigue rupture. Several factors stand out as probable causes for the intense and rapid process of fatigue, being the main ones: granulometry and type of aggregates, contente e type of cement, moisture content and curing time. This study aims to propose technical recommendations for dosage to improve the mechanical performance of cemented material such as Graded Gravel Treated with Cement for paving. For this, an experimental plan was defined and it consisted on the factorial analysis, from three selected factors (granulometry, cement content and moisture content) to examine the effects of the components of the mixtures and their proportions to obtain a satisfactory mechanical performance. In this way, it was defined two types of granulometry that were dosed for 3%, 4% and 5% of cement, for the optimal humidity and for -1% of the optimal humidity. These mixtures were submitted to mechanical tests (simple compression strength, indirect tensile strength, resilience modulus, modulus of elasticity, dynamic modulus). In the sequence, the mixture that presented the best mechanical performance was chosen, defined by the relationship between indirect tensile strength and other mechanical tests, and then was submitted to fatigue life analysis (tensile strength in flexion at four points, flexural modulus and flexion fatigue rupture). With the results, it was possible to verify the behavior of each mechanical parameter of the BGTC mixtures studied, with a better performance mix with the one with the highest percentage of sand, higher cement content and molded with -1% of the optimum moisture. Fatigue performance prediction models were determined for this mixture, involving the number of cycles for rupture and the specific deformation of traction, tensile stress and percentage of tensile strength in flexion. However, laboratory models must be calibrated to the field, defining transfer function. Some recommendations were made for the dosage of BGTCs, like the definition of a granulometric range that considers the analysis of the small/large aggregate ratio in order to obtain greater maximum specific apparent dry mass gain, to define corrections in the optimal humidity from the compaction test to avoid excess water, that damages the mechanical performance of the BGTC mixture, as well as to use a cement content of 4% or more, because lower percentages would be insufficient. In addition, optimized ratios (aggregate + cement + water) should be defined by performing the mechanical analyzes listed in this study, in order to select the best performance mix to be applied in the field.