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.

Some of the most recent developments related to the production of concrete have focused on the addition of components which can improve the mechanical, wokability and durability properties of concrete and whenever possible, to solve environmental problems in a simple and economical way. This is research work fits in this field, trying to contribute to the clearing up of the advantages and disadvantages of concrete production with the addition of fly ash (FA). High-performance concrete (HPC) is usually produced using high quality materials. These constituents drastically increase the initial cost of HPC, thus hindering its more widespread usage. This research work intends to investigate the possibility of producing low cost enhanced performance concrete or even low cost HPC, with 90 day strengths in the range of up to 60 MPa, using low quality fly ash and locally available crushed aggregates. The effect of the amount of fly ash was evaluated using 0, 20%, 40% and 60% cement replacement with different quantities of total binder of 400 kg/m3, 500 kg/m3 and 600 kg/m3, Workability, mechanical and durability properties were also studied. The results obtained indicate that it is possible to, produce HPC with up to 60 MPa by replacing up to 40% of cement by fly ash and using local available crushed granite aggregates. Furthermore, it was observed that the workability and the durability, as measured by the chloride-ion difision coefficient, increased drastically when fly ash partially replaced Portland cement. Based on the results obtained, it is possible to conclude that the use of fly ash in concrete is beneficial in terms of the workability and durability properties but was some disadvantages because early strengths are reduced.

High performance concrete is generally specified to meet special requirements such as higher compressive strength, lower permeability, higher resistance to aggressive environments and longer durability. The design of structures must be based on the knowledge of all concrete properties and the determination of creep values of paramount importance in several cases. This paper presents the influence of water-cement ratio and level of hydration for concretes with compressive strengths ranging from 20 MPa to 75 MPa. Creep of four mixtures with water-cement ratios of 0.29, 0.37, 0.52 and 0.75 with 6% of silica fume and a fixed slump was determined. Specimens were loaded at ages 3, 7, 28 and 90 days and maintained with a constant load for 90 days. Concrete testing included creep, compressive strength, modulus of elasticity, autogenous deformation and drying shrinkage. The paper presents creep coefficients, autogenous volume changes, drying shrinkage and their correlation with age and water-cement ratio. Test results showed that high performance concrete presents lesser creep if compared with concretes with lower compressive strength and that differences between specific creep values range from 12% to 43%. High performance concrete presented significantly higher values of autogenous volume changes. Tests confirmed that drying shrinkage is directly related to the water content of the mixture, whereas similar values were obtained from tests performed on several specimens representing different mixtures with various compressive strengths but containing approximately the same amount of water.

This paper presents the result of the work performed by the Norwegian Defence Estates Agency on the development of a low cost ultra high performance concrete (UHPC) for protective structures. The aim has been to develop a high strength concrete, about 150 MPa, based on commonly available materials, with workability suitable for traditional construction practice, and produced at a reasonable cost. The documentation program includes studies of the hardened properties of the concrete, in addition to full scale production tests, full scale realistic impact tests and large-scale beam tests. It is verified that concrete with a 2%day compressive cube strength of 150 MPa, based on commonly available high quality materials, may be produced without any major modifications to standard production facilities or procedures. For practical application, the autogenous shrinkage of the concrete may be a critical property whenever the hardening concrete is subject to restraint. The penetration resistance of UHPC is significantly better than normal strength concrete. Increasing the concrete strength from 30 MPa to about 200 MPa the penetration depth will be reduced by a factor of approximately 2.5.

The use of high strength concrete has increased progressively over the past years not only for benefits of strength but also for significant improvements in service life. Nevertheless increases in strenght lead to a more brittle behavior of the material. Steel fiber reinforcement is probably the best way to improve its performance when higher toughness is required. This paper discusses the contribution of fiber reinforcement in high strength concretes. Load-deformation curves under compressive and flexural loads of concretes prepared with different types and contents of fibers are compared. The behavior of sound and microcreacked concretes exposed to high temperatures is also studied. The effect of fiber reinforcement on the compressive behavior of high performance concrete was similar to that observed on normal concrete. Fibers incorporation enhance crack control and produced significant benefits in toughness. Flexure tests performed on fiber reinforced concretes were very stable. It was possible to use different specimens sizes and loading configurations to evalute the effct of the type and content of fibers. There were some improvements when high carbon steel fibers were employeed.