International Concrete Abstracts Portal

Canada Centre for Mineral and Energy Technology (CANMET) has an ongoing project dealing with the role of supplementary cementing materials in concrete. As a part of this program, a new type of concrete known as high-volume fly ash concrete has been developed. In this type of concrete, the water and cement contents are kept very low, i.e. about 115 and 155 kg/n?, respectively, and the proportion of low-calcium fly ash is about 56 per cent of the total cementitious materials. This type of concrete has excellent mechanical properties and durability characteristics. The objective of this study was to investigate the application of the high-volume fly ash system to the production of structural lightweight concrete. In this study, high-volume fly ash concrete mixtures were made using ASTM Type I portland cement, fly ashes from sources in the U.S.A. and lightweight coarse aggregates from four different producers, three from the U.S.A., and one from the U.K. A reference concrete mixture without fly ash was also made for comparison purposes. A large number of test specimens were cast to determine the mechanical properties and durability characteristics of the concrete. The test results show that the structural high-volume fly ash concrete had mechanical properties similar to those of the reference concrete. The fly ash concrete generated significantly less heat of hydration, and showed noticeably better resistance to chloride-ion penetration than the reference concrete of similar 2%day strength. All concretes investigated demonstrated an excellent resistance to the freezing and thawing cycling

A large proportion of concrete placed in Australia contains one or more supplementary cementing materials (SCM’s; either fly ash, ground granulated blast-furnace slag or silica fume). Despite this, specifications for technically advanced projects often restrict their use even though Australian research data justifying their application dates back to the early 1960’s for fly ash and slag, and the early 1970’s for silica fume. World-wide research on SCM’s in concrete dates back even longer. It is the task of the researcher together with the technical marketer to provide effective transfer of this knowledge to the specifier. In most cases, the specifier is either a civil or structural consultant, or a design team within a major public authority or contracting firm. The specifier increasingly needs to seek up-to-date knowledge in concrete technology, a task that is ever more difficult with imposed time constraints. This study maps the processes whereby research and development data are put into practice. A three-stage process is used to investigate this. First, measurements of the technology transfer process are obtained through targeted surveys of concrete specifiers with the objective of determining their attitudes and knowledge regarding SCM’s Second, recent Australian specifications for SCM concrete comprising Standards, Codes of Practice and selected project specifications are reviewed. Third, the data generated is examined to highlight present shortcomings in the technology transfer process in Australia, specifically relating to the use of SCM’s. It is concluded that many project specifications with respect to the use of SCM’s in concrete can be significantly improved from the standpoint of the supplier, the specifier and the facility owner. This can be facilitated through improved technology transfer. Discussion in the paper focuses on increasing the efficiency of the process for taking research into field application.

This paper reports the results of an investigation on the effect of the water- to-(cement+fly ash) ratio, fly ash content, fly ash type, and curing compounds on the de-icing salt scaling resistance of concrete, and attempts to explain why fly ash when used in large amounts in air-entrained concrete reduces its resistance to the de-icing salt scaling. Fourteen air-entrained concrete mixtures were made in this investigation. The water-to-cementitious materials ratio of the concrete mixtures ranged from 0.32 to 0.45. Two ASTM Class F and one Class C fly ashes were included in this investigation, and the fly ash content ranged from 2.5 to 58% by mass of the total cementitious materials. Two control portland cement concrete mixtures with the water-to- cement ratios of 0.40 and 0.45 were included in this study for comparison. The type and the amount of fly ash used and the water-to-cementitious materials ratio of the concrete affect considerably the de-icing salt scaling resistance of concrete. In general, the resistance to the scaling decreases with increasing amounts of fly ash and increasing water-to-cementitious materials ratio. When cured with the curing compounds, both the control concrete and the concrete incorporating fly ash showed substantially less scaling than the concretes cured in the moist room. The water absorption of the moist-cured concrete seems to be related to its resistance to the de-icing salt scaling; the scaling increased with increasing water absorption. However, the concrete cured with the curing compounds had much less scaling than the concrete cured in the moist room even though the water absorption of the former concrete was higher than the latter. The microstructure of the cement paste at the on-set of the freezing and thawing appears to affect the de-icing salt scaling of the concrete.

A pressurized fluidized-bed combustion power plant (PFBC) is a coal-fired thermal power plant specially developed for the enhancement of generating efficiency and the reduction of environmental loads. The physico-chemical properties of coal ash produced from this type of power plant (PFBC ash) are different from those of ordinary fly ash, because coal is mixed with pulverized limestone and burnt at a lower temperature than that in the conventional power generation system. This study explores the feasibility of utilizing PFBC ash as a concrete mineral admixture. It has been found that the coal ash from a secondary cyclone dust collector enhances the strength of concrete although it cannot improve the fluidity. A series of tests, including those for durability and changes in length, show that the durability of concrete containing the coal ash so produced is adequate for practical applications.

Concrete containing fly ash has been used in many parts of the world for several decades. Various standards and codes have generally limited the use of ASTM Class F fly ash from 20 to 25 percent. Laboratory studies and field demonstration projects sponsored by CANMET during the last 12 years have shown that concrete containing 55 to 60 percent fly ash has excellent structural and durability characteristics when proportioned with superplasticizers and at low water to cementing materials ratios. This paper presents some results of research performed under contract to CANMET and some of the practical uses for which the high-volume fly ash concrete system has been utilized in Eastern Canada. The applications discussed include structural concrete, relatively massive machinery foundations, a roller compacted dam, environmental applications such as impermeable shotcrete covers and encapsulation/solidification, and design of mine backfills. The high-volume fly ash system has proven to be an economical construction material which can be mixed, placed and consolidated with conventional concrete construction equipment. Some unique properties such as very low heat generation, low cost, and the possibility to use large quantities of fly ash will expand the future use of the high volume fly ash system.