International Concrete Abstracts Portal

This paper analyzes the mechanical behavior and its relation with the development of the hydration reaction in concretes with low water-to-cementitious material ratio made with binary and ternary cements containing limestone filler and blast furnace slag. It explores the maximum level of replacement of portland cement by both additions to obtain high early strength concrete. At 3 days, the compressive strength was 43 to 45 MPa and it was greater than 60 MPa at 28 days. All studied concretes present a very similar strength development. Results show that the combination of limestone filler and blast furnace slag is complementary: the limestone filler improves the early strength of concrete while the slag improves the later strength achieving to an optimal strength development. The concrete performance analyzed in terms of water penetration test also classified these concretes as very low permeability.

The results of an experimental investigation of the effects of short steel fibers on the shear behavior of reinforced concrete beams are presented. Two types of steel fiber with different shapes, lengths and cross sections were used. Two series of reinforced concrete beams were cast and tested in the laboratory. Each series had a different ratio of transverse reinforcement as well as the addition or not of steel fibers in the concrete mix. The test results indicate the better performance of the beams made with fibers. These beams exhibited smaller crack width and spacing and consequently more stiffness and load carrying capacity. The results also show that the steel fibers improve the shear resisting mechanisms of the concrete represented by the aggregate interlocking and dowel action and behave as an additional transverse ireinforcement, consequently reducing the stresses in the stirrups. This finding suggests a code revision of the concrete contribuition for the shear design of beams when steel fibers are used. Their use can reduce the labor costs in the fabrication of these beams.

Mortar joints are commonly used in precast concrete structures as connection between columns, walls and load bearing precast concrete facade elements. Usually, the mortar joint has a lower strength than precast elements and its deformability tends to be larger than the ones, which causes a non-uniform distribution of stress in the joint. The mortar joint represents the weakest link in the structural system and the mortar bearing capacity limits the bearing capacity of the precast concrete elements. This paper reports on the development of an experimental program to analyze the bearing capacity of precast high strength concrete columns connected by mortar joints produced with commercially available materials, with the purpose of making better use of the columns’ bearing capacity. It was found that the thicker the joint, the lower the system’s bearing capacity, and that different strains are produced, depending on the type of material used to fill the joint - grout or dry mortar, even when the same thickness and the same relation between strengths is maintained. The conclusion reached was that it is always advisable to adopt a relation equal to or higher than one, and that a 20mm mortar layer produces an optimal behavior, in terms of both strength and ductility.

This paper deals with the properties of styrene butadiene latex (SBR)-modified lightweight aggregate concrete (LWAC) for thin precast components, made with two Brazilian lightweight aggregate (LWA). Water reduction capacity, air content, flow table after 2 h, compressive strength, splitting-tensile strength, flexural strength, modulus of elasticity, stress-strain behavior and water absorption were tested. The 7-day compressive strength and the dry concrete density varied from 39.7 to 51.9 MPa and from 1460 to 1605 kg/m3, respectively. The modulus of elasticity at 7 days, which varied from 17.9 to 22,6 GPa, was lower than that typically observed for normal-weight concrete at the same compressive strength level. The inclusion of SBR in the LWAC decreased W/(C+S) and water absorption level. The inclusion of SBR in the LWAC decreased W/(C+S) and water absorption and increased splitting-tensile and flexural strengths.

In this work, some experimental results for determination of fracture energy and brittleness number for high-performance concrete are presented. Three-point bend tests were conducted for different concrete mixture proportions, with compressive strengths of 70 MPa to 90 Mpa. The tests were performed using crack mouth opening displacement control in a closed-loop servo-hydraulic system. The experiments involved the testing of 75 single-notched beams of four different sizes in order to study the size effect. The compositions of the concrete were established according to, those specified by IBRACON (Brazilian Concrete Institute) in order to match the concrete commonly used by companies that operate in Brazil. The results found in this work by the method proposed by RILEM show that the size of the specimens influences the value of the obtained fracture energy, it being larger as the size of influences the value of the obtained fracture energy, it being larger as the size of the specimen increases, thus suggesting that the RILEM method is not valid in characterizing fracture energy as a material parameter. The results from this work found that the fracture energy obtained by the method proposed by Bazant and Pfeiffer can be adopted as a fracture parameter of the material, since its value is independent of the size of the specimen.