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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 study examined the effects of using a high range water reducer (HRWR) on concrete with pozzolan replacement. The HRWR was used in two ways: 1) to increase the workability of mixtures with otherwise unchanged mixture proportions, 2) to pro-duce mixtures with workability similar to those without HRWR but with lower w/cm. For the first goal, HRWR dosages were determined that would increase the slump of mixtures to approximately 150 mm. For the second goal, concretes were produced with water to cementitious material ratio (w/cm) reduced by 0.03 (as compared to the control mixtures) but with slumps in the 25 to 75 mm range. Comparisons were made between the HRWR mixtures and with control mixtures without HRWR. Only two types of mixtures were studied: 1) 15 percent Class C fly ash replacement and 2) 25 percent slag replacement. The research results showed that use of HRWR in mixtures containing ground granulated blast furnace slag and in mixtures containing fly ash generally improved compressive, flexural, and tensile strengths (to varying degrees), even for mixtures with unchanged w/cm.

Most modern high performance concretes contain supplementary cementitious materials such as silica fume, slag or fly ash. However, highly reactive silica fume adversely affects the autogenous shrinkage properties and increases the risk of cracking at early ages. In order to compensate for the adverse effects of silica fume, ultrafine fly ash was also incorporated into the binder phase of the concrete. Part of cement and part of silica fume were replaced by ultrafine fly ash and early age properties of the mixtures with these ternary binders were compared. Strength gain was followed by compression testing and, autogenous shrinkage properties were measured under free conditions. It is seen that ternary binders can decrease the autogenous shrinkage strains, while keeping the early strength gain at a comparable level. Results of the thermogravimetric analysis showed that mixtures with ternary binders had a similar hydration rate compared to the mixture with silica fume only. Mercury intrusion porosimetry proved that the amount of finer pore volume, one of the major reasons of autogenous shrinkage, was decreased with the incorporation of ultrafine fly ash.

In this study, the influence of moist curing on strength development of high-strength concrete containing fly ash was investigated. The fly-ash concrete was prepared with a w/c and w/cm of 0.40 and 0.30, respectively. To evaluate the relative contribution of fly ash to strength development, two reference concretes (w/c=0.40 and w/c=0.30) without fly ash were also tested. The specimens were kept in three basic curing conditions: underwater-, sealed-, and exposed to atmosphere. At ages of 7 or 28 days, specimens were subjected to various curing conditions. Fifteen types of curing sequences were adopted in all. The changes in the density and compressive strength were measured at ages of 7, 28, 91,182, 273, and 358 days. It was concluded that, when the fly-ash concrete was kept in moist conditions, the contribution of fly ash to the long-term strength exceeds 0.8. However, when specimens were allowed to air dry, the contribution of fly ash to the long-term strength was around 0.4, as low as its contribution to the early-age strength.

The paper deals with fly ash as the by-product from coal-combustion electricity power plants. This type of fly ash (also classified as ASTM class F fly ash) can be utilized as a raw material in cement production, as a filler material in concrete and as a pozzolanic material that can partly replace cement. This paper examines the use of fly ash in concrete and stabilisations. Fly ash cement stabilisation are used in some road projects and compared to fly ash containing concrete the stabilisation contain a large pro-portion of fly ash relative to the amount of cement. The pH of such mixtures is lower than the pH of the pore water in concrete. The pozzolanic reaction of fly ash with lime needs a sufficient supply of pore water and a high pH because at a low pH the glass of the fly ash will not break down at the molecular level, thus cannot dissolve easily. For enhancement of the pozzolanic reaction, mixtures of fly ash and portland cement have been made with a 2% NaOH solution as mixing water. The stabilisations have been tested on strength, leaching and freezing and thawing durability. The strength increases due to the addition of NaOH. The freezing and thawing durability is investigated with the Fagerlund method and also with a simple freezing and thawing test with thawing under water. The freezing and thawing behaviour however is not improved by the addition of the NaOH solution. Also the leaching of heavy metals and SO4 is not diminished by the addition of the NaOH solution. The use of fly ash cement stabilisations should be under the restriction of protection against rainwater and groundwater, which is easily accomplished in the case of bituminous road constructions.