International Concrete Abstracts Portal

The research goal of this project was to measure silica fume particle size distribution and conduct dispersion tests, using measured levels of ultrasound as a method to evaluate the relative agglomeration "strength" and de-agglomeration [dispersability] of the undensified and densified product forms of silica fume. Scanning Electron Microscopy (SEM) testing of silica fume samples was performed, showing combinations of individual particles (0.02 to 0.25µm) along with loose agglomerate clusters (25 to 120µm), which could not be quantified in size distribution analysis. A specially modified laser scattering particle size distribution analyzer, with a built in digitally controlled ultrasonic processor, was developed to measure particle size distribution statistics such as mean, medium and standard deviation. Ultrasonic energy levels were determined for complete de-agglomeration of undensified and densified material, which allows the measurement of the primary un-agglomerated material particle size. A test method was developed to evaluate the dispersability or relative agglomerate "strength" of the different silica fume forms by measuring the various particle size distributions, with and without ultrasound. Through the application of ultrasound, at specific energy levels and time periods, the relative agglomerate dispersability at different bulk density levels were determined. Mortar and shotcrete performance tests were conducted to evaluate the dispersability of different silica fume product forms, for different bulk loose density levels. The mortar laboratory evaluation tests included pozzolanic strength activity index ratios and electrical resistivity measurements. The test method’s ability to evaluate product dispersability and quality assurance was further verified through a field shotcrete test program, conducted with various bulk loose densities, measuring rebound percentages, thickness before bond break and compression strength.

The influence of silica fume (SF) on performance of cementitious systems like concrete is due to physical (i.e. improved particle packing) and chemical (i.e. pozzolanic reaction) effects. Since silica fume particles are much smaller than cement grains they will pack in the voids between cement grains. In this way the system is densified already at the time of setting. SF is an active pozzolana that leads to strength increase. When SF is not used to obtain equal strength at higher w/cm than reference, but to obtain high performance concrete with lower w/cm including plasticizers, no durability problems should occur unless adequate precautions are not taken to prevent cracking from autogenous shrinkage and high heat of hydration. In general, the use of SF in concrete mixtures reduces the permeability to waterborne aggressive ions (e.g. alkalis, chlorides, sulfates), thus mitigating the potential for sulfate attack, alkali-aggregate reactions, and corrosion of reinforcing steel in concrete.

Industrial waste clay materials, which are good pozzolans, can be used in place of cement in the manufacture of mortars and concretes. During the manufacturing process, which involves dehydration followed by firing at controlled temperatures ranging from 700 °C to 1000 °C, the clay minerals found in high proportions in the natural materials used to make bricks and similar products acquire pozzolanic properties. The present study examines the microstructure and morphology of the industrial concrete made with standard portland cement containing fly ash partially substituted with waste clay material, by backscattered electron images (BSE) and mercury porosimetry (MP) techniques. The microstructure of concrete test samples is not altered by the inclusion of clay discards and the pore size did not vary too, the only difference found was a slight decline in the proportion of larger diameter pores (over 0.1 micron).

When used as a constituent of raw meal for cement kiln, electric arc furnace (EAF) slag, being a source of non-carbonated lime, can contribute to a sustainable development in as much as both the kiln thermal requirement and CO2 generation are reduced. Ternary mixtures containing limestone, clay, and EAF slag (up to 35%), as a partial substitute for both natural materials, were submitted to laboratory and industrial tests. Burnability indexes better than that given by the reference mix (without EAF slag) were obtained. Chemical, physical and mechanical parameters of cements made with EAF slag-derived clinkers met the European standard EN 197-1. The kiln emissions of SO2, CO, HCl, HF, metals, total solid particles, and organic carbon were lower than the concentration limits in the exhaust gas prescribed by the national environmental standards. Keywords:

In Japan, sea sand is used frequently as fine aggregate for concrete. The mining of sea sand has been more difficult year by year for environmental reasons. This would be a serious problem in manufacturing concrete. The amount of fly ash has been increasing gradually in Japan, therefore the utilization of fly ash as the substitution of fine aggregate has a significant advantage. In this study, bending fatigue test of roller compacted concrete was carried out, in which all fine aggregate was replaced with fly ash. The obtained S-N curve was compared with that of normal concrete and general roller compacted concrete. Scatter of fatigue strength was also determined.