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Showing 1-5 of 63 Abstracts search results

Document: 

SP153-47

Date: 

June 1, 1995

Author(s):

G. J. Osborne and B. Singh

Publication:

Symposium Papers

Volume:

153

Abstract:

A rapid-hardening cement was made by blending mixtures of high- alumina cement (HAC) and ground granulated blast furnace slag (GGBS). The addition of slag alters the course of hydration reactions in HAC. A chemical compound 2CaO.Al 2O 3.SiO 2.8H 2O (gehlenite hydrate or stratlingite), only seen in plain HAC in small amounts, readily forms and becomes the main stable hydrate in the blended cement concretes in the temperature range of 5 to 38 C, replacing the metastable hydrates which lead to loss of strength in HAC through the conversion reaction. The properties of mortars and concretes made with this cement were assessed in a series of durability studies carried out by the Building Research Establishment. Mortars made with the blend have shown excellent sulfate resistance. Concrete specimens were compared with those from HAC concretes of similar proportions, following exposure for two years in aggressive sulfate, marine, and soft acid water environments. The findings, at this relatively early stage, are very encouraging. Longer term tests will be carried out at five and 10 years. Concretes made with the blend have shown a greater tolerance of high water-cement ratio mixtures in forming stable products with reduced temperature rises and enhanced durability in terms of their excellent sulfate, seawater, and soft acid water resistance.

DOI:

10.14359/1103


Document: 

SP153-12

Date: 

June 1, 1995

Author(s):

A. Xu and S. L. Sarkar

Publication:

Symposium Papers

Volume:

153

Abstract:

As focus increasingly shifts to protecting the environment through recycling of industrial byproducts and wastes, as well as conserving energy and resources, corresponding restructuring of conventional production technology and practices has become imperative. Because of these considerations, mixtures of kiln dust and fly ash were hydrothermally treated and calcined to produce a new type of beta-C 2S rich cement. Fly ash, which is the most abundantly generated industrial byproduct, is still largely disposed of as waste; kiln dust is the waste product of the cement industry, vast quantities of which are discarded due to its high alkali content. The former is composed of alumino-silicate glass, while the latter has a composition similar to that of partially calcined cement raw meal. This study demonstrates that it is possible to produce C 2S cement of dequate 28-day strength by suitably proportioning fly ash and kiln dust. The results of variations in factors such as the CaO:SiO 2 ratio and two different precalcination treatments are presented. Prehydration-dehydration (sintering at 950 C) processes were specially applied for the production of this cement, in contrast to the direct calcination method in the presence of a mineralizer. The cement was constituted of beta-C 2S and calcium aluminates. The formation of these minerals in relation to the clinkering sequence is discussed. The cement is sufficiently hydraulic, and its strength development largely depended on the CaO:SiO 2 ratio of the raw mix and the precalcination process.

DOI:

10.14359/1071


Document: 

SP153-51

Date: 

June 1, 1995

Author(s):

J. P. H. Frearson and D. D. Higgins

Publication:

Symposium Papers

Volume:

153

Abstract:

Various accelerated test methods have been proposed for the assessment of sulfate resistance of cements. A majority of these methods measure the expansion of mortar prisms in sulfate solution. Differences in test procedure can have a significant effect on the expansion observed and may possible affect the ranking of cement types. The different performance in sulfate solutions of cements containing different slag percentages and water- cement ratios and the lesser influence of different slag alumina contents have been reported previously. This paper summarizes data from various test works which demonstrate the effect on expansion of variations in the following test parameters: aggregate- cement ratio (at constant water-cement ratio), specimen shape, initial curing period, specimen compaction, initial curing deficiencies, early carbonation, concentration of sulfate solution, and type of sulfate solution. The first three of these parameters had comparatively little influence on expansion; the remainder had more significant influences on expansion. Sieving mortar for test specimens from production concrete provided a useful and comparable method of assessment. The test programs were principally concerned with slag cement blends, but as any test method had to be applicable to all types of cement, a number of sulfate-resisting portland cements were tested. The wide range of expansion characteristics suggest that a "typical" control SRPC may not be easily defined.

DOI:

10.14359/1044


Document: 

SP153-50

Date: 

June 1, 1995

Author(s):

T. Tomisawa and M. Fujll

Publication:

Symposium Papers

Volume:

153

Abstract:

Describes test results obtained on the heat of hydration, strength development, hydration products, pore structure, and combined water of blended cements with high fineness and large amounts of ground granulated blast furnace slag (GGBS) and discusses the relationship between them, comparing them with ordinary portland cement (OPC) and blended cement with smaller amounts of GGBS. The following conclusions were drawn from this study. 1. The heat of hydration of blended cement with over 70 percent content of GGBS reduces significantly. The blended cement incorporating a large amount of GGBS with high fineness can have the properties of lower heat of hydration and relatively high compressive strength required for massive concrete generally used in Japan. 2. The blended cement with high fineness and high content of GGBS results in a more compact pore structure than OPC due to the formation of finer hydration products.

DOI:

10.14359/1106


Document: 

SP153-46

Date: 

June 1, 1995

Author(s):

M. D. Luther and W. Halczak

Publication:

Symposium Papers

Volume:

153

Abstract:

The first two abrasion-erosion concrete repair projects in the United States that used silica fume (SF) concrete started in 1983. One was the stilling basin rehabilitation of the Kinzua Dam, in northwestern Pennsylvania. The other was the Los Angeles River low-flow channel rehabilitation project (completed in 1985). The first known application of SF concrete (SFC) addressing cavitation resistance occurred in 1985, also at the Kinzua Dam, but for a sluice repair. This paper largely summarizes long term performance information relating to the 1983 to 1985 SFC placements. Other, more recent, SFC projects in which abrasion-erosion or cavitation was a concern are mentioned. Also presented are two mixtures featuring portland cement with ground granulated blast furnace slag and SF that were recently used in a very severe environment. Overall, after up to 10-1/2 years in service, the various SFCs are performing very well. The 1983 Kinzua Dam stilling basin SFC wear after 10-1/2 years is only a small fraction of that seen in previously utilized concretes. For the Los Angeles River SFCs, all of the three different SFC mixtures that were employed are performing comparably as of March 1994. Overall erosion was uniform and to an estimated 4 to 12 mm depth. The 1985 Kinzua Dam sluice repair concrete showed no evidence of cavitation damage by 1994.

DOI:

10.14359/1102


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