Environmental Ecology and Technology of Concrete

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Authors: Zhi Feng Zhang, Hong Ding, Jun Wang, Zhan Min Zhang
Authors: Nai Qian Feng, Jian Hua Yan, Gai Fei Peng
Authors: Piet Stroeven, J. Hu, Martijn Stroeven
Abstract: The computer simulation study of Portland cement blending confirmed the major mechanism to be size segregation in the Interfacial Transition Zones around the aggregate particles. Fine particles tend to move through the skeleton of larger particles towards the surface of the aggregate grains, improving local density. But the most interesting feature is a disproportionately larger internal bond capacity (based on van der Waals forces between nearby particles). In this contribution, we have isolated the mechanism of internal diffusion capacity of particles, on which blending efficiency relies, for a simulation study on the migration of fine sand articles into the network of coarse aggregate grains. The influences of technical parameters (including gap in size between fine sand and coarse aggregate, as well as the workability conditions) have been investigated on the migration capacity of fine sand particles. This paper will report briefly the outcomes of this computer simulation study on aggregate mix systems.
Authors: Feng Xing, Xiang Yong Guo, Fa Guang Leng, Ren Yu Zhang
Abstract: In this paper, the main characteristic of definition, property, requirement of raw material, mix proportion design and performance improvement of high volume fly ash concrete (for short HVFAC) are summarized. The applications of HVFAC in dam, highway, building and port are introduced. The research results have shown that HVFAC have outstanding properties of physical mechanics, but some problems need to be further studied. It is believed that an operable strict corresponding technical criterion would be set down as soon as possible for engineering practice.
Authors: Dario Rosignoli, Giovanni Martinola, Martin Bäuml
Abstract: Reinforced concrete structures are often conceived for a certain time span of serviceability. Due to the superposition of different kinds of loads and particularly due to the presence of aggressive substances the resistance of construction materials is insufficient in numerous cases. Hence, many structures have to be repaired before the end of their designed life span. In case of reinforced concrete structures these repair measures are not only very expensive but they also consume high amounts of energy and materials which causes strong environmental impacts. The main challenge in developing reliable concrete technologies is the capability to enhance the life span of new and already repaired structures to a reasonable maximum. When aiming this objective not only durability related material properties have to be accomplished but their environmental impact has to be minimized simultaneously. This paper evaluates different concrete technologies and materials from diverse perspectives: Durability (simulating expected life span using numerical analyses), ecology (product life cycle and environmental impact assessments) and economy (estimating life cycle costs by investment appraisals). This kind of combined analysis facilitates the efficient design of structural elements and repair measures and provides the possibility to significantly increase the life span of new and repaired concrete structures.
Authors: Rokuro Tomita, Hiroshi Hirao, Takashi Tochigi, Takamiki Tamashige
Abstract: In Japan, a majority of urban waste is incinerated to reduce the volume and the residue (incineration ash) is land filled. Japanese municipalities, however, are confronted with serious shortages of waste landfill sites. To mitigate this situation, Taiheiyo Cement Corporation has developed two technologies, which are Ash Rinsing Process and Ecocement. Incineration ash is a suitable material for cement production because it primarily contains essential chemical components of cement clinker. The problem is that chlorine and heavy metals accompanying primary components cause operational trouble and deteriorate quality and material safety of cement. Ash rinsing technology will be effective to remove chlorine and heavy metals in the ash. Therefore, for municipalities closely located existing Ordinary Portland cement plants, it is the simplest way to use waste incineration ash as a raw material in those cement plants. Ecocemet, on the other hand, will be an attractive option for the municipalities distant from cement plants. Ecocement is defined as cement that is produced from over 500 kg (dry base) waste incineration ash supplemented with other wastes (sludge, etc) per ton of Ecocement. According to the discharged amount of ash, correspondingly scaled Ecocement plant is needed. In Ecocement production process, chlorine in the ash is combined with intentionally added alkalis or heavy metals and is extracted. Extracted metal chlorides are recycled as metal sources. Two types of Ecocement can be used in the fields of ready mixed concrete, concrete blocks or soil stabilizer. The first commercial plant of Ecocement constructed in Chiba prefecture started operation in April 2001. In July 2002, Japanese Industrial Standard of Ecocement was published. Consequently, Ecocement has become an authorized product in Japan. The second Ecocement plant is now under construction in Tokyo.
Authors: Quan Lin Niu, Nai Qian Feng
Abstract: Effect of a combination of alkali ions, sulfate ion and chloride ion on durability of concrete structures was analyzed, and the effect of different mineral admixtures on deterioration caused by Cl- penetration, sulfate attack and alkali-silica reaction was investigated. It is shown from wetting-drying test that sulfate attack on concrete was greatly relieved in high Cl- concentration solution, but diffusion test showed that Cl- diffusion was accelerated by SO4 2- ion existence as SO4 2- may incorporate with aluminum phase prior to Cl- ion. Replacement of cement with mineral admixtures such as ground blast furnace slag (SL) and metalaolin (MK) were beneficial for absorption of Cl- ion penetrated into paste, while ASTM C441 showed that fly ash (FA), metakaolin and natural zeolite (NZ) exhibited effectiveness in controlling Alkali-silica reaction (ASR).
Authors: Quan Lin Niu, Nai Qian Feng
Abstract: ASTM C1012 and GB2420 method were employed to evaluate the inhibiting effect of different mineral admixtures on sulfate attack of cement mortar, and the mass loss of mortar specimens after drying-wetting cycles was measured for comparison. It is shown that all the mineral admixtures, including ground blast furnace slag (SL), fly ash (FA), natural zeolite (NZ) and metakaolin (MK) were effective in decreasing the 15-week expansion and increasing the corrosion resistance coefficient of the specimens immersed in Na2SO4 solution. The wetting and drying test however, showed inconsistent result, as both physical and chemical attack may soon occur due to quick accumulation of sulfate by capillary absorption instead of diffusion mechanism.

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