Abstract: Fine powders from crushed waste concretes have high water absorption and their reuse is limited. In this research the fine powders with diameter of less than 4.75mm were activated by using grinding method and hydrothermal synthesis method, and then the specimens were manufactured from these activated fine powders by mechanically compacting at the pressure of 80MPa. The experimental results show that the instant maximum compressive strengths are 9.65MPa and 16.8MPa respectively for the specimens from the ground powders and the hydrothermal synthesis powders. Their apparent densities are low and they can be used as wall materials. The results also show that the optimal grinding time ranges from 80 min to 90 min when using the grinding activation method. When using hydrothermal synthesis method the proportion of lime as an admixture affects the compressive strength and the constant temperature period should be less than 7 hours as the temperature is 120 °Cfor the powder made from gravel concrete.
Abstract: In this study, coarse fly ash was ground with laboratory ball mill, vibration mill and jet mill respectively. The powder characteristic of ground fly ash was tested by laser particle size analyzer and scanning electron microscope. And the performance of cement containing different ground fly ash was also studied. It was observed that the characteristic value of fly ash ground by ball mill, vibration mill and jet mill was 13.543 μm, 13.403 μm and 17.344 μm, respectively, when average particle size was about 25μm. And the uniformity coefficient of fly ash ground by ball mill, vibration mill, and jet mill was 1.26, 1.24 and 1.38, respectively. Specially, the mortar strength was increased when 10 to 20 percent of ground fly ash was added. And the highest fluidity of mortar was obtained when 30 percent of fly ash ground by jet mill was added.
Abstract: This paper presents an experimental research on mechanical properties and permeability of recycled aggregate concrete (RAC). Concretes at a water/binder ratio of 0.255 were broken into recycled aggregates (RA). A type of thermal treatment was employed to remove mortar in RA. Tests were conducted on aggregate to measure water absorption and crushed values, and on RAC and natural aggregate concrete (NAC) to measure compressive strength, tensile splitting strength, and fracture energy. The results revealed that both gravel damage and mortar attached can significantly influence the water absorption and crushed value of RA. The mechanical properties RAC were obviously lower than those of NAC at an identical mix proportion. Moreover the removal of mortar caused a decrease in mechanical properties. The behavior of the chloride ion penetration of RAC under compressive loading is different that of NAC, which may be related to the flaws of RA. Further experimental research is needed to identify its mechanism.
Abstract: Warm-Recycled Mix Asphalt (WRMA) is a new type mixture that can not only reduces the mixing temperature and exhausting gas emissions but also includes some waste materials (Reclaimed Asphalt Pavement, RAP).The compaction characteristics of WRMA were tested, while the compaction temperatures were 140°C, 130°C, 120°C, 110°C, 100°C and the RAP contents were 0%, 15%, 30%, 45%, and 60%, respectively. The compaction temperature for each WRMA was recommended according to the test results. Furthermore, this paper also evaluated the performances of each WRMA.
Abstract: Durability improvement of concrete in the complex environments of chloride, sulfate and freeze-thaw, by incorporating compound mineral additives of fly ash, slag, diatomite and zeolite in concrete, was studied through the approach of orthogonal array testing and related analysis. The results show that zeolite and diatomite play a dominant role in improving the durability of concrete in the complex environments, but the role of fly ash and slag should not be ignored. A reasonable combination of the mineral additives can effectively improve the durability of concrete in the complex conditions without lowering or even increasing the early and later strength of concrete.
Abstract: Concretes of C30 and C60 were prepared with iron mine tailings as fine aggregate and coarse aggregate and with natural sand and common crushed stone separately. The drying shrinkage of concretes cured under the natural condition in the laboratory was tested. The results showed that whether C30 or C60 the drying shrinkage of concrete prepared with iron mine tailings was a little smaller than that of concrete with natural sand and common crushed stone. It was also found that whether the concrete with iron mine tailings or the concrete with natural sand and common crushed stone the drying shrinkage of C60 concrete was larger than that of C30 concrete.
Abstract: The electroplating sludge is a kind of solid waste material in the process of handling electroplating waste water, which has indefinite amount of harmful heavy metals hard to dissolute. The electroplating factory must seek economical and valid technology to deal with the sludge harmlessly, along with the reinforcement of the country law administer power to the discharge of the solid wastes. Since the last ten years, the handling technique to electroplating sludge has rapid advance, which mainly include solidification or stabilization technique, filling into the sea or pile-up, creature method, recycling heavy metal[2,3], iron-oxygen method, burning brick[8,9] and agriculture function and so on. A key handling technique is the recycling heavy metals from electroplating sludge in recent years, whose research fruits are no mature quietly from an area of technique view and the oddments still need to cope with harmlessly come from recycling heavy metals. This is a kind of technique of low economic yield ratio, low scale benefit and higher production costs from a point of economic view. It is difficult to accept for a mass of small electroplating enterprise in China if there is not encouragement and support from the government. The solidification method is the final handling method for harmful and dangerous waste in west country in recent years. Cementing solidification method is adopted the most effectively at present. It is satisfied with the aim of harmlessly handling electroplating sludge but unsatisfied with the requirement of utilizing electroplating sludge as a resource and disadvantageous to build recycling type economics. Making use of the electroplating sludge to product building materials may be an economical and valid approach to handle it harmlessly as a resource. The solidified effects on heavy metals of electroplating sludge at 1200°C high temperature burnt were analyzed in the paper, at the basis of feasible studies on the technology of burning ceramsite by the composite of electroplating sludge and seabeach sludge.
Abstract: Two kinds of the representative artifactitious aggregates, namely the calcium-base and silicon-base, were chosen in the experimental study. Through analysis of SEM, it was found that the former’s main chemical component is calcium carbonate with a structure of crystal granules, the later might be a rock of silicon-base in a state of sandwich. Through experiments of the paste fluidity, ZETA potential and concrete test with different water-reducers, it was shown that the calcium-base aggregate, which could be easily used to prepare high workability and high strength concrete with the polycarboxylic water-reducer, bears a lower water-sobbing ability and has a well adaptability with any water-reducer, and that the silicon-base aggregate, a higher water-sobbing ability, a higher ZETA potential value of its powders, a bad adaptability that there might be a problem of producing HPC though using the high property polycarboxylic water-reducer.
Abstract: In recent years, recycled aggregate concrete has been used in reinforced concrete structures. Concrete structures exposed to chloride environment often encountera premature deterioration due to corrosion of steel reinforcement. In order to avoid unplanned maintenances or repairs, it is necessary to develop a reliable prediction model for the chloride diffusion in concrete. The basic formulation of the transport theory will be presented first and then its application to Recycled Aggregate Concrete (RAC) will follow. Chloride diffusion in RAC is different from the diffusion in regular concrete, because the material parameters of RAC such as chloride diffusion coefficient are different from those of regular concrete. In this paper, a multi-scale and multi-phase model will be developed to characterize theinternal structure of the recycled aggregate with a layer of residual cement paste on the surface of natural aggregate and another layer of surface treatment material on the surface of the residual cement paste. The multi-scale and multi-phase model will also be used to characterize the chloride diffusion coefficient of RAC. The numerical analysis of the diffusion equations is performed by using finite element method.