International Concrete Abstracts Portal

Concrete is an essential material for creating infrastructures. However, with the growing awareness of environmental problems in recent years, concrete is now required to function in harmony with nature and help preserve ecosystems. Porous concrete has received a great deal of recent attention. It is believed that porous concrete has water purification functions in flowing water through organism membranes created in a series of inner voids, and that it also creates a new environment for organism because aquatic organisms and algae adhere to the insides and surface of porous concrete. This paper describes changes over time in the type and number of organisms adhering to porous concrete placed in streams of a river. In addition, the physical properties ofporous concrete exposed in a river are discussed. It was concluded that porous concrete can be used as an environmentally-friendly concrete.

About 20 million cubic meters used-timbers are discharged every year from demolished buildings, mainly wooden houses in Japan. The authors have carried out a study on recycling used timber as wood-chip concrete. The experiment was carried out as follows. First, the wood-chips were filled into a steel mold to achieve the desired packing ratio with a compressive stress of 0.5-l .OMPa. Then, the fresh cement paste was injected into the mold to make the specimens. The densities of the wood-chip concrete in this case generally fall into the range of 920kg/m3 to 1250kg/m3. To evaluate the performance of the wood-chip concrete, bending strength, compressive strength, drying weight loss and shrinkage, thermal conductivity, and thermal expansion were tested. Furthermore, two types of artificial light-weight aggregate were added to the wood-chips mold and cement paste simultaneously to reduce the densities of the concrete, and the compression of the wood-chips for packing was not needed in the production process. The densities of the wood-chip concrete with the light weight aggregates were about 780kg/m’ to 92Okglm’. After these tests, it became clear that the wood-chip concrete will be suitable for use as a building material, for partition walls, floor joists, floor boards, etc.

This paper presents the results of an experimental investigation of RPC (Reactive Powder Concrete) on shrinkage and creep under uniaxial compressive loading. The RPC are ultra-high strength concretes characterized’ by high silica fume content and steel fibers reinforcement. The present study focuses on RPC with a very low water/binder (0.17) ratio and a compressive strength at 28 days of 160 and 200 MPa after a 90°C heat-treatment. The thermogravimetric analysis shows that in RPC a high proportion of cement remains unhydrated, and the pozzolanic reaction becomes predominant two weeks after mixing. The autogenous shrinkage and creep of RPC were measured on sealed specimens. The stress level on the creep specimens represented 20 % of the concrete compressive strength at the time of loading. The basic creep kinetics of RPC is very rapid and does not differ from high strength concrete, whereas its magnitude can be twice as much. The basic creep amplitude and kinetics of RPC are strongly affected by the age of loading. After a heat-treatment of RPC at 9OC, the shrinkage becomes insignificant, and the basic creep is highly reduced.

In the past decades, cement-based materials have been increasingly used for the construction of radioactive-waste barriers. The design of durable structures for this specific application requires a precise knowledge of the evolution of the material engineering properties over a 1000-year period. Among the wide range of degradation phenomena to which the structure can be exposed upon its service life, the leaching of calcium appears to be the most critical. Given the intricate nature of the leaching process, a reliable prediction of the long term behavior of the concrete barriers can only be made through numerical modeling. In order to generate more quantitative information on the subject, a new accelerated leaching test has been developed. The operating principle of the test is quite simple. The leaching process is accelerated by applying an external electric field through the material. This paper details the different electrochemical phenomena involved during a LIFT experiment. It also presents several experimental data obtained for various neat paste samples. In this series of tests, the evolution of the hydrated cement paste microstructure was studied using various experimental techniques such as X-ray diffraction, DTA/TG analyses and scanning electronic microscopy. The advantages and limitations of this new procedure are discussed.

High fluidity concrete has been used to meet requirements for the marine construction thanks to its superior durability and ease of placing. High-fluidity concrete is, however, so viscous and has less bleeding to have the cold joint that may harm the uniformity of the structure. We have executed series of experiments to study the effect of interval and method of making joints on the strength of placing-joint of 5 types of high-strength and high-fluidity concrete and high-fluidity lightweight concrete for the marine construction . The strength of the placing-joint has shown no substantial degradation compared to those without placing-joint by rodding the joint within 120 minutes after the first placing under an ambient temperature of 20 C, while specimens without rodding, cured under the standard water bath, have shown 2/3 of the strength of those without placing-joint at an interval of placement less than 60 minutes.