International Concrete Abstracts Portal

For the repair and strengthening of historical masonry structures, high penetrability injection grouts which use lime, natural pozzolan, portland cement and some with silica fume have been developed. The type, morphology and evolution of the microstructure and hydration products as evidenced by mercury intrusion porosimetry and X-ray diffraction are presented. Furthermore, the evolution of the insoluble residue and soluble silica contents is also presented. The results of mechanical and bonding tests are presented. Grout mixtures at different ages up to 180 days are compared. The results indicate that ternary blends of the type lime-natural pozzolan-normal portland cement with or without addition of silica fume are highly sensitive to curing conditions. If appropriate curing and quality control are applied, the grout mixtures developed very good mechanical properties and address both durability and economy issues.

Both material and fiber rebound in dry-mix shotcrete are high, and the use of an appropriate mineral admixture is known to alleviate the problem. However, the exact influence of the admixture particle size, gradation and shape on the rebound and the ultimate mechanical properties of shotcrete are poorly understood. This study is divided into two parts: in the first part, the effectiveness of four mineral admixtures-fly ash, silica fume, high reactivity metakaolin (HRM) and carbon black-with varying particle size gradations and shapes was investigated from a rebound reduction point of view. In the second part, HRM and silica fume were compared on the basis of hardened mechanical properties with special emphasis on flexural toughness in the presence of fiber reinforcement.

Conditioning coal-burning power-plant flue gases with ammonia reduces the emission of nitrous oxide compounds. But the ammonia often combines with available sulfur and other compounds that attach to the fly ash. If the ammoniated fly ash is then used in concrete, the high-pH environment causes a release of ammonia and a strong, objectionable ammonia smell. This can make the fly ash unmarketable. What’s the solution? Fly ash beneficiation processes that can remove ammonia and also reduce the unburned carbon content. Some of the processes are described in one of the 54 papers included in ACI SP-199, Seventh CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete. Other papers deal with effects of fly ash and admixture combinations on setting time, use of slag concrete to reduce corrosion of reinforcement, and the role of chemical and mineral admixtures in concrete made with recycled concrete as aggregate. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP199

It is now established that the incorporation of industrial byproducts, such as fly ash (FA), ground granulated blast furnace slag (GGBFS) and silica fume (SF), in concrete mixtures as partial cement replacement materials (CRMs) significantly enhances the durability related properties of concrete, besides improving its mechanical properties.. Such concretes are termed as High Performance Concretes (HPCs). In HPC mixtures, it is possible to have low W/C with reduced cement content by judicious choice of mineral and chemical admixtures. The assessment of the flexural behavior of reinforced HPC beams is a subject of ongoing research. Standards and codes of practice differ in the definition of compressive stress block parameters of reinforced HPC beams. Hence, investigations were undertaken at the Structural Engineering Research Centre (SERC), Chennai, to investigate the behavior of reinforced HPC beams under flexural loading. The beam specimens for the test programme were designed as under reinforced, balanced and over reinforced sections as per the guidelines given in the Indian code of practice for reinforced concrete, IS:451 978. The influence of supplementary cementitious materials (SCMs) used as cement replacement materials (CRMs), viz., fly ash (25% as CRM) and GGBFS (40% as CRM), on the flexural behavior of reinforced HPC beams was studied. The paper presents the details of the investigations and discusses the results obtained.

Two silica-manganese slags containing about 11 % MnO were ground to Blaine finenesses of 360 to 600 m*/kg. Their C/S (CaO/SiO2) modulus was very low (0.47 to 0.58) and, for this reason, these slags were considered likely to be unsuitable for use in the preparation of blended cements. They were therefore introduced in concrete instead of either fly ash or silica fume. The cement content of these concrete mixtures was in range of 2 1 0 kg/m3 t o 4 5 0 kg/m3. The quantity of each supplementary cementing material was adjusted according to the French standards and varied from 50 to 80 kg/m3. The slags behaved as well in concrete as fly ash or silica fume: no decrease in strength was observed and the water permeability was the same.