International Concrete Abstracts Portal

Six reinforced concrete beams and four slabs with different reinforcement ratios were tested to failure. The behavior of specimens manufactured with normal strength concrete (fc = 36 MPa) and high-strength concrete (fc = 83 MPa) was compared with respect to cracking and deflections. It was found that crack widths and crack spacings were fairly comparable for both concrete types in the region of stabilized cracking. Deflections decreased by using high-strength concrete due to the increased modulus of elasticity and cracking moment. However, for the beams, this gain diminishes at higher load levels.

A series of 28 reinforced concrete beams without shear reinforcement have been tested in shear by two-point loading. The main test parameters were: longitudinal reinforcement ratio (1.8 and 3.2 percent); shear span ratio (2.3, 3.0, and 4.0); size (b/h = 150/250 and b/h = 300/500 mm); and concrete type (normal density concrete of cylinder strength 54, 78, and 98 MPa and lightweight aggregate concrete, 58 MPa). The results are compared with other test results and concrete codes. For members made of normal density concrete of compressive cylinder strength exceeding 80 MPa, the diagonal cracking strength remained constant or showed a minor decrease in spite of the increasing tensile splitting strength of the concrete. A more significant decrease in ultimate shear strength was observed. A probable explanation is the increasing brittleness of the material with increasing strength. The new Norwegian Concrete Code, which includes provisions for high-strength concrete, predicts the influence of concrete compressive strength and aggregate types on the diagonal cracking shear strength fairly well. The influence of dimensional scale was, however, larger than expected. The shear strength formula in CEB-FIP Model Code generally overestimates the diagonal cracking strength of high-strength concrete slabs or beams with moderate longitudinal reinforcement ratios. An improved shear strength prediction formula for high-strength concrete has been adopted by the Norwegian Code. The lightweight aggregate concrete beams had relatively low diagonal cracking strength, as expected, but high ultimate shear strength. The tests confirm the results (except for one test series) found by Ahmad et al.

An equation is proposed for predicting the ultimate shear capacity of reinforced concrete columns and beams composed of high-strength concrete having a compressive strength of up to 90 MPa, and high-strength reinforcing bars having a tensile strength of 1000 MPa. Six beams and ten columns with and without shear reinforcement were tested to determine their diagonal cracking strengths and ultimate shear capacities. The shear span-depth ratio was 1.0 for the beams and 1.14 for the columns. The quantity pw åy (pw: shear reinforcement ratio; åy: yield strength of shear reinforcement) was varied from 0 to 11.2 MPa. The axial stress in the columns was varied at 0, 18.4, and 36.8 MPa. The current ACI Building Code equation for predicting shear capacity of deep beams was found to be applicable to the beams fabricated with high-strength concrete. However, it cannot be applied to the members with high axial load stress. The equation proposed in this paper accurately predicts the ultimate shear capacity of reinforced concrete columns as well as the beams made with high-strength concrete and high-strength steel bars.

In Norway, almost every car is equipped with tires that have small steel studs to improve the traction between the tire and the road for driver control during the winter season. These studded tires have an enormous wearing effect on ordinary asphalt pavement. Roads with the heaviest traffic near the major towns need to be resurfaced at intervals of 1 to 2 years. To improve the abrasion resistance, application of high-strength concrete instead of asphalt has been started. The national Norwegian cement producer has performed a large-scale investigation to determine the relation between concrete composition and abrasion resistance. The results prove that a 100 MPa concrete might approach the same properties as massive granite. The paper describes a number of projects performed by an independent company, where this high-quality material has been utilized in practical construction.

Use of silica fume is important to produce high-strength concrete. Possible negative effects on long-term properties are, therefore, of vital interest for the future development of high-strength concrete. It has been reported that silica fume concrete stored in air showed strength loss from 90 days to 5 years, but courses are not discussed. The report was based on a limited number of results. Similar results are not found in high-strength concrete up to 10 years old either in laboratory tests or testing samples from existing structures in Norway. Results from two major research projects showed that, for laboratory-stored specimens, the strength increased or was constant for concrete stored in water or air, respectively. No difference was found between high- and normal strength concretes. The increase was somewhat higher for concretes without silica fume compared to concretes with up to 20 percent silica fume by weight of cement. Furthermore, the strength increase was somewhat higher for water-stored concretes than for air-stored. However, high-strength silica fume concrete was not more sensitive to early drying than concrete without silica fume. High-strength concrete from several existing structures did not exhibit the same consistent pattern in strength development, however. This is probably due to insufficient documentation at an early age. However, the results did not show any significant negative long-term strength development.