International Concrete Abstracts Portal

This paper give some results of flowing and high strength concretes using type F fly ash (FA) and naphthalene based superplasticizer (SP). In series S.Sp was used only to produce flowing concrete and in series H was used to reduce W/C and to cause the concrete to flow. In each studied series the portland cement content was maintained fixed of 250 kg/m3. Fly ash was added as a percentage of the normal portland cement from 10% up to 150%. For reference series a .8 W/C was used, and for series S. 200 liters of water was used to attain a nominal consistency of 60.0 cm DIN. For reference series H a reduction of 35% of mixing water of series S was used (70 L). To find the maximum amount of FA and SP dosage in series S, SP admixture was used to obtain the reference consistency of 60.0 cm DIN. In series H where the admixture was used as high-range water-reducing-retardant admixture (HRWRRA) in large dosages, the concrete becomes very cohesive and significant slump loss was noted. When superplasticizer-retardant admixture (SPRA) was used as HRWRRA to produce flowing concrete under established conditions, it was possible to obtain a very significant compressive strength gain at 56 days, which was the upper limit of the age covered in this study. An increment of 160% (from 25 to 65 Mpa) at 56 days was attained for series H in relation to the reference mixture without FA and SP. To obtain high strength concretes using high volumes of fly ash, it is essential to use SP admixture.

High-strength concrete columns, usually reinforced, require high rates of confined transverse reinforcement to obtain ductile fracture. In this paper it the composite columns of steel pipes with square and rectangular sections, and cores consisting of high-strength concrete, are analyzed with the objective to of changing the usual confining reinforcement. The metal pipes were fabricated with steel plates with 5,0 mm and 6,9 mm thickness, on cold cutting and folded in "U" form, and then subsequently compounding pipes with transverse sections of 60mm by 60mm and 60mm by 100mm, and 460mm height. The wall cross-section of steel pipes was determined by section of transverse and longitudinal reinforcement used in the square and rectangular columns reinforced conventionally. In the design the differences between yield strain of steel plates and yield strain of the reinforcement concrete columns were computed. To define the yield of strain of steel plates, specimens were tested and analyzed under axial tension. With the mechanical properties of the metal pipes and the mixture o the high-strength concrete core, eight models were tested, four with square transverse section and four with rectangular transverse section. The specimens were tested under concentric compression loading, on a ridged hydraulic press with load controlled capabilities, having a maximum compression load of 10.000 kN. It is concluded from the investigation that composite columns with square section was efficient in the confinement of high-strength concrete columns with rectangular section presented, localized instability near the extremities probably due to compression of the concrete core.

The chlorides from the sea and the marine breeze are the main source of corrosion in marine environments. Their penetration into concrete occurs through capillary absorption, diffusion or a mix of both. A chloride threshold for producing reinforcement corrosion can be predicted through mathematical models but no reliable results may be obtained if the action of environmental agents as the RH, temperature, winds, rains, and drying periods are not well known. Although these limitations are recognized in several works, there are few field data in the literature to support, according to different exposure conditions, the form of the chloride penetration profiles. This work presents the form of chloride profiles from different exposure conditions. It discusses their behavior and justifies the results according to the presence of the environmental conditions. Some of the results indicate that the environments with chloride saturation produce profiles with a well defined concentration gradient, while those with strong periods of rains, drying, winds, as well as strong variations of RH and temperature show a two-zone profile. In the last case, one zone is close to the concrete nucleus where the supposed reinforcement is positioned and that stays dampened due to the high chloride concentration, and the other one is close to the concrete surface, in which continuous wetting and drying cycles take place. It was also found that, under this research trial, the chloride penetration mechanism did not change with the micro-climate but nucleus concentration changed with the distance from the sea and concrete quality.

Attempts to study the effect of vibration of fresh concrete have mainly been based on visual observation of, for example the radius of influence of the insertion vibrator, or the rate of flow of concrete down a tube when vibration is applied. The reason for this has been the difficulty of measuring the sinusoidal wave form created by mechanical vibrators. Advances in electronic equipment have made devices for measuring this wave form commercially available, and they have therefore been used in this research project to gain a better understanding of the consolidation process. The amplitude of the sinusoidal signal was calculated from the acceleration measured at distances up to 250mm from the surface of the insertion vibrator. Preliminary tests indicate that the amplitude of the vibratory wave decays exponentially with distance. The damping coefficient is greater for superplasticized high-strength concrete mixtures with low W/C than it is for normal-strength concretes. An attempt was made to relate the damping coefficients to the rheological properties, yield (g) and plastic viscosity (h) values determined from tests carried out with Tattersall's two point test apparatus. Both the yield (g) and plastic viscosity (h) values were found to increase by decreasing the W/C, despite the concrete having an equal slump of 150 mm. This shows that the slump values obtained by the use of high dosages of superplasticizers, as is the case with low W/C, are not directly comparable to those resulting from high water contents, with respect to the rheological behavior of concrete.

This paper presents the results of laboratory studies conducted to determine freezing and thawing and scaling resistance of high-performance concrete. High-performance concretes were made using a combination of different cementitious materials (Blast-furnace slag and silica fume). The water-to-cementitious materials ratio was .27, and the bulk volume of coarse aggregate and fine aggregate per unit volume of concrete were fixed at .50 and .60, respectively. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were cast for testing in compression at 1 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A. and for resistance to scaling from deicing chemicals according to ASTM C 672. The curing methods were water curing and steam curing. The air-void parameters of the hardened concrete were determined on the sawn sections. The test results indicate that non-air-entrained, high-performance concrete with steam curing showed low durability factors. High-performance concrete with water curing performed satisfactorily when subjected to up to 1500 cycles of freezing and thawing. Water-cured, high-performance concrete showed no appreciable scaling after 100 freezing and thawing cycles, showing high resistance to scaling.