International Concrete Abstracts Portal

This paper presents an empirical equation representing the relation between the amount of air laden chlorides reaching a concrete surface and the rate of chloride ions penetrating into concrete. By using this proposed equation as a boundary condition, an analytical diffusion model is presented, where various factors such as water-cement ratio (w/c), carbonation depth, and lapse of time after construction are considered. Comparing the analytical results obtained from the proposed model with the experimental results, the effectiveness of this proposed model is confirmed.

The relationship between the neutralization depth determined by a phenolphthalein 1% ethanol solution and the concentration distribution of CaCO3 - Ca(OH)2 in carbonated concrete is discussed, based upon accelerated carbonation and outdoor exposure tests, and field - survey research by making use of powder X - ray diffraction and thermal analytical methods. It was found that the neutralization depth exists in the partly - carbonated zone of concrete where both CaCO3 and Ca(OH)2 are observed, and that carbonation front depth from which CaCO3 is not detected, exists much deeper in concrete. Further, it was confirmed that the neutralization depth is about half of the carbonation front depth. This fact is interpreted by theoretical research of unsteady state dynamic analysis for the diffusion of CO2 from the surface inwards into concrete accompanied by carbonation reaction with Ca(OH)2 . Computer simulation was done for the converted CO2 concentration in carbonated concrete by using the effective diffusion coefficient estimated as a function of water cement ratio. If the converted CO2 concentration in the neutralization depth is assumed to be 10% of the surface concentration, the neutralization depth is almost the same as the depth calculated using Hamada's law which is considered to be adequately applicable for the progress of neutralization of concrete with a water cement ratio of 60% exposed outdoors in the rain. It is concluded that the relationship between the neutralization depth (X,,) and the carbonation front depth (X;) is expressed by the following equation : Xn = (l/2) Xf

When high-strength concretes are conveyed by pumping, the pumping pressure may increase and the flowability of high-fluidity concrete may be greatly decreased. This is a problem for construction of concrete-filled tubular steel columns. In this study, pumping tests and filling tests of steel tubular model columns with several kinds of high-fluidity concrete having a water: cementitious ratio of 30% were conducted. Silica fume results in better pumpability. The pressure loss reflects good correlation to the plastic viscosity of the concrete calculated from the time taken for it to discharge from an inverted slump cone. When the concretes used in the tests were pumped into tubular columns, the cavity area under the diaphragm plates was less than 10% and the core strength obtained at 91 days was over 80 N/mm*. If the slump flow of concrete at the top of the column is mote than 45cm, it can be expected that the column will be filled well. The pressure of concrete at the bottom of the column is approximately 1.2 times the head pressure.

A comprehensive experimental program was designed in order to investigate the mechanical and durability properties of high performance lightweight concrete. The concrete mixture was prepared in order to obtain a specific value of the compressive strength at 28 days of age (fCz75MPa). Testing was carried out on a large number of lightweight concrete specimens. The following properties were investigated: compressive, flexural and splitting-tensile strength, modulus of elasticity, fracture parameters, concrete-steel bond properties, drying shrinkage and durability properties. The test results show that high-performance lightweight concrete has considerable potential for the precast/prestressed industry.

Meeting the needs of urban development, high strength concrete has made remarkable progress where the standard concrete strength of 60 MPa level is attained with the help of high performance AE water-reducing agents. High strength lightweight concrete could be more advantageous with respect to the reduction of dead load and resulting construction cost reduction, and has been successfully applied to marine concrete constructions. This paper deals with the high strength, high fluidity lightweight concrete with bulk densities from 1.8 to 2.0 t/m3 and compressive strength from 60 to 90 MPa manufactured with belite-rich low heat cement and silica fume cement, and discusses the influences of materials and mixture proportions upon the properties of fresh and hardened concretes. Compressive strength with a water-cement ratio of 0.23 was 65 to 79 Mpa when silica fume blended cement was used, and was 59 to 68 MPa when belite-rich low heat cement was used.