International Concrete Abstracts Portal

In 2004, the Canadian Centre for Mineral and Energy Technology (CANMET), in association with the American Concrete Institute, the Electric Power Research Institute, Palo Alto, CA, UWM Center for By-Products Utilization, Milwaukee, WI, and several other organizations in Canada, sponsored the Eighth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete. The conference was held in Las Vegas, Nevada, U.S.A., May 23-29, 2004. The proceedings of the conference containing 56 refereed papers from more than 20 countries were published as ACI Symposiuml Publication SP-221. 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. SP221

This paper presents results of a study that compared ASTM C 1202 test, a steady-state migration test, a conductivity test, and a non-steady-state diffusion test for deter-mining the chloride-ion penetrability of control portland cement concrete and concretes incorporating fly ash, ground granulated blast-furnace slag, silica fume, metakaolin, and rice-husk ash. The water-to-cement ratios of the control portland cement concretes ranged from 0.31 to 0.60. The content of fly ash and slag was 20, 40, or 60% by mass of total cementitious materials as cement replacement. Silica fume, metakaolin, and rice-husk ash was used as 8% cement replacement. Most of the concrete mixtures were made from normal-weight aggregate except for two concrete mixtures that were made from light-weight aggregate. In general, the results from the four test methods led to similar conclusions regarding the penetration of chloride ions into concrete. Therefore, ASTM C 1202 test method can be used for evaluating the resistance to chloride-ion penetration for concrete with or without supplementary cementing materials in spite of its short comings. The conductivity test is another rapid and convenient method, and has potential for wide acceptance by the construction industry for determining ingress of chloride ions into concrete.

Macro- and micro-cell corrosion of steel bars in pre-cracked prism specimens ex-posed to marine environment for 15 years are summarized here. The size of the specimens was 100xlOOx600 mm. W/C were 0.45 and 0.55. The specimens were made with ordinary portland, slag (Types A, B and C), and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded at the center in each specimen. Crack widths were varied from 0.1 to 5.0 mm. Chloride concentrations in the concrete, micro- and macro-cell corrosion, passivity grade, anodic polarization curve, deposits in the crack, and pit depths over the steel bars were investigated. Dense microstructure of concrete made with a large amount of slag (SCB, SCC) causes accumulation of more chloride in the vicinity of the unhealed cracks (>0.5 mm). However, it does not lead to a remarkable amount of corrosion at the cracked region compared to the other cements after 15 years of exposure. Narrower cracks (5-0.5 mm) as well as the debonded areas in the vicinity of the root of the crack over the steel bars heal irrespective of the cement types. It improves the passivity of the steel bar at the cracked region. Relations between pit depth and crack widths; and macro-cell and micro-cell corrosion are proposed.

Self-compacting concretes (SCC) represent a move toward a sustainable material since they encourage the use of waste and recycled materials. The high volume of very fine powder necessary to achieve deformability and passing ability properties, in fact, permits SCC to consume large amount of fly-ash, very fine particles generated by the re-cycling of demolished concrete structures, and huge amount of calcareous filler avail-able from the marble quarries. Moreover SCC turn out to be materials with an extended durability with respect to conventional concretes. Since fresh properties of self-compacting concretes (SCC) are significantly different from those of conventional concretes (CC) durability can be significantly improved when a SCC is used due to a modification of the microstructure of the interfacial transition zone between aggregates and cement matrix. This paper presents results of an experimental study carried out to evaluate changes in microstructure of interfacial transition zone (itz) and of bulk paste for both SCC and CC. Data on the influence of the calcareous filler, a fundamental ingredients to achieve self-compactability, on the hydration process of cement are also presented. Data indicate that the decrease in internal bleeding, when self-compacting concrete is used, seems to favour the formation of a stronger transition zone characterized by a less porous structure and with a limited amount of microcracking responsible for higher compressive strength values for SCC with respect CC. No differences were detected by EDAX analysis in the chemical nature of itz with respect the bulk matrix both for SCC and CC. Finally, observations of the cement hydration by analysis of the temperature pro-file vs time seem to indicate the calcareous grains promote formation of heterogeneous nucleation responsible for the increased crystallinity of ettringite, for a shorter normally dormant period and, hence, for higher strength values at early ages, when the calcareous filler is used.

A technology for comprehensive utilization of high volumes of coal ashes for production of lightweight concrete was developed at The Research Institute of The College of Judea and Samaria, Ariel, Israel. The technology is based on the combined use of bottom ash and fly ash in lightweight concrete, which enables the advantages of each kind of the ashes to be realized. The features of the suggested technology were con-firmed under laboratory and field studies. The obtained binary concrete (with respect to coal ashes) is a beneficial material for production of masonry units. The current paper describes the results of testing the effect of concrete proportions on properties of the binary lightweight concrete and of combined use of coal ashes with waste fines from stone quarries as additive for ternary lightweight concrete. The use of these materials both controls the strength of the lightweight concrete containing highly porous bottom ash and lowers the concentrations of radionuclides 226Ra, 232Th and 40K in the lightweight concrete.