ABSTRACT
The use of recycled aggregates in concrete can bring social and environmental benefits to society. In concrete precast industry, the rejects from the production contain a high potential for recycling, however its feasibility depends on the realization of tests in order to know its physical and mechanical properties. One of the affected properties is the modulus of elasticity, which tends to decrease with the replacement of natural aggregates by the concrete recycled aggregates (ARC). This work aims to: compare the results of the concrete modulus of elasticity by two different methods: the static (MEE), obtained by compression, and the dynamic modulus of elasticity (MED) performed by means of an ultrasonic apparatus for specific use in concrete; analyze the influence of the substitution of natural aggregate by the ARC at the values of MEE, MED, compressive strength, water absorption, voids index and dry density; and verify the existence of relationships between the modulus of elasticity and concrete properties, aiding in understanding the behavior of concrete modulus of elasticity. ARC was obtained after pretreatment of concrete waste from a precast industry, resulting in recycled aggregates of three different sizes: 2.4 mm, 4.8 mm and 6.3 mm. The recycled aggregates showed higher values of water absorption and powder material, besides lower dry density in comparison with the natural aggregates. The substitutions were carried out on reference concrete (C-ref) produced daily by the industry: in the C1-ref concrete of fluid consistency and in the concrete C2-ref, of dry consistency. Concretes were made from the replacement of fine natural aggregates by the recycled aggregates in percentages of 30% and 50% in the C1-ref concrete, respectively named C1-30 and C1-50, and from the substitution of 100% of the whole weight of natural aggregate in the concrete C2-ref, named of C2-100. Cylindrical test specimens were used and MEE, MED, compressive strength (RCS) and water absorption tests were performed. Through the water absorption data, it was possible to obtain the values of voids index and the dry density. The intensity of the correlations was analyzed by the comparison between the correlation (R) and determination coefficients (R2). The results of MEE and MED were close to each other, the reasons between the MEE and the MED varied between 0.86 and 1.04, and a relationship between the values of the two methods was determined, with R2 = 0.9821. The results showed a decrease of both modulus of elasticity (MEE and MED) to the pro-portion of the percentage of recycled fine aggregates (AMR). C2-100 obtained a significant decresing in its modulus of elasticity, reaching a decrease of 35% of the value in the MEE. The compressive strength was not affected by the incorporation of recycled aggregates, nor did it obtain a good correlation with the modulus of elasticity. Strong correlations were obtained between the modulus of elasticity and some properties, with coefficients of determination (R2) greater than 0.90. It is concluded that both methods for obtaining the modulus of elasticity may have representative results. The modulus of elasticity of the concrete was so affected by the presence of ARC. The modulus of elasticity was shown to be a property so affected by the characteristics of the recycled aggregates as the absorption and the dry density.
Keywords:
Concrete recycled aggregate; concrete; modulus of elasticity
