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Showing 1-10 of 66 Abstracts search results

Document: 

SP145-65

Date: 

May 1, 1994

Author(s):

P. Schiebl, W. breit, and M. Raupach

Publication:

Special Publication

Volume:

145

Abstract:

First results of the investigation of the corrosion behavior of steel in concrete after local repair measures are described. The examinations in this research project refer to construction practice where local damage due to reinforcement corrosion, e.g., spalls and cracks, is repaired in the area of visible surface damage only. When dealing with damage in this way, the carbonated or chloride contaminated concrete is often not removed completely, thus avoiding stability problems with the structure. Following such a repair measure, reinforcement areas consequently remain, in which there is no guarantee of sufficient corrosion protection and which, therefore, are subject to a higher corrosion risk. With the help of macrocell current measurements between different steel electrodes embedded in concrete, the study investigated circumstances and extent of corrosion problems before and after local repair measures. Further investigation dealt with the measures that have to be taken to guarantee corrosion protection after local repairs.

10.14359/4513


Document: 

SP145-64

Date: 

May 1, 1994

Author(s):

R. K. Dhir, M. R. Jones, E. A. Byars, and I. G. Shaaban

Publication:

Special Publication

Volume:

145

Abstract:

Paper discusses the current approach for specifying concrete durability in structures. The shortcomings of the use of bulk parameters such as strength, water-binder ratio, and binder content to specify durability are discussed. Studies carried out over the last 10 years at Dundee University, using simple permeation tests, which are sensitive to curing, cement type, and concrete grade, have shown close association between permeation properties and concrete durability. Paper deals with the measurement of concrete durability by the Dundee-modified initial surface absorption test (ISAT). A wide range of concrete mixes made with ordinary portland cement and blends with pulverized fuel ash (PFA) and ground granulated blast furnace slag were designed. The duration of moist-curing was varied from 0 to 28 days, and the maximum aggregate size ranged from 5 to 40 mm. All mixes were tested for absorptivity and durability, including freeze-thaw resistance, carbonation, chloride ingress, and mechanical wear. Results show that the absorptivity of concrete, measured with the ISAT, can be used as an accurate specification for concrete durability, irrespective of curing, grade, or mix constituents. A tentative surface absorptivity classification for durability has been proposed.

10.14359/4437


Document: 

SP145-63

Date: 

May 1, 1994

Author(s):

B. K. Marsh and M. A. Ali

Publication:

Special Publication

Volume:

145

Abstract:

Paper describes a number of research programs on assessment of the effectiveness of practical on-site curing techniques; in addition, it reviews the need for curing of structural concrete, for which carbon-induced corrosion of reinforcement is the most likely cause of deterioration. It is demonstrated that, while compressive strength of small specimens such as 11- or 150-mm cubes are sensitive to curing, the same has not been shown true in larger elements. Carbonation depths from 4-year exposure tests for a range of concrete types suggest that the influence of ambient conditions in a temperate climate may be greater than that of most curing methods, even when the concrete is sheltered from rainfall. Limitations on the validity of the use of small specimens and water storage to assess the effect of curing, or predict the performance of concrete, are discussed, together with the possibility of developing a suitable in situ test for curing effectiveness. It is concluded that, except in conditions of very dry air, little evidence was found of easily measurable curing effects on durability-related properties of formed surfaces, in temperate climates, for concretes made with normal portland cement in conditions where carbonation-induced corrosion is the most likely form of deterioration.

10.14359/4435


Document: 

SP145-62

Date: 

May 1, 1994

Author(s):

A. P. Barker and J. D. Matthews

Publication:

Special Publication

Volume:

145

Abstract:

The European prestandard for concrete, ENV 206, includes durability requirements framed principally in terms of maximum water-cement values for various exposure classes. Minimum cement contents are also given, but the values are relatively low. No minimum concrete strength grades are included, and no distinction is made between cements of different strength classes or different types. It is clear that the variety of cement types specified in the European prestandard for cement, ENV 197-1, will produce a wide range of concrete strengths when fulfilling the limiting specification requirements for a given exposure category. Previous work has suggested that, although water-cement ratio may be the most suitable specification parameter within a single cement type, strength should also be specified if comparable concrete durability is to be achieved with a range of cement types. To test this proposition, two series of concrete mixes were prepared with a variety of cements, including slag, fly ash, and limestone filler: one series had equal cement contents and water-cement-ratio and the other had equal strength grade and workability. The results to date show that durability, as measured by permeability, carbonation, and freeze-thaw resistance, is not equal for all cements at the same water-cement ratio, and suggest that concrete strength grade is a better specification parameter if similar durability is required from the wide range of cement types defined in ENV 197-1.

10.14359/4433


Document: 

SP145-61

Date: 

May 1, 1994

Author(s):

J. M. Scanlon and J. D. Conolly

Publication:

Special Publication

Volume:

145

Abstract:

In 1980, dead-burned dolomite particles removed from a cement kiln were inadvertently distributed in aggregates that were later used in concrete. These particles were of coarse aggregate size (38 mm) and contained approximately 55 percent calcium oxide (CaO) and 35 percent magnesium oxide (MgO). When this contaminated aggregate was used to make concrete in 1980, it caused some relatively large popouts (up to possibly 230-mm-diameter). Subsequent periodic visual evaluations of this contaminated concrete were performed to verify the acceptability of the concrete and the durability of popout repairs. To the authors' knowledge, only one structure was removed and repaired. In 1989, another such incidence occurred, but this time the portland cement was contaminated with smaller (<9.5-mm) dead-burned dolomite particles with approximately the same proportions of CaO and MgO. Paper reports on how data developed from the 1980 incident was extended for use in evaluating the concrete contaminated in 1989, and how instrumentation was used to effectively determine the actual volume of dead-burned dolomite in the contaminated concrete and degree of hydration of the particles. Such information is being used to predict the long-term effects of the contamination.

10.14359/4431


Document: 

SP145-60

Date: 

May 1, 1994

Author(s):

I. R. De Almeida

Publication:

Special Publication

Volume:

145

Abstract:

Abrasion resistance of 10 concrete mixes with compressive strength ranging from 0.24 to 0.42 MPa was evaluated. Mixes studied contained silica fume, fly ash or natural pozzolan, and addition of superplasticizer in some cases to reduce mixing water. Concrete workability remained constant. Tests were carried out following a Portuguese standard similar to a Brazilian standard and German Standard DIN 52108, using the Dorry apparatus. Porosity and compressive strength of concrete were also determined. The main conclusions are as follows: 1) cement replacement by mineral admixtures always reduced the abrasion resistance at rates between 10 and 25 percent, while less satisfactory results were obtained with condensed silica fume concretes; 2) addition of superplasticizer increased the abrasion resistance about 25 percent; 3) abrasion resistance varied inversely with water-cement ratio, cement paste volume, and concrete porosity; 4) general correlation was poor between abrasion resistance and compressive strength, indicating a strong influence from cementing material type, mainly in the case of silica fume; 5) there was evidence that poor performance of condensed silica fume concrete can be ascribed to self-desiccation; 6) even the worst results obtained in this test series were equivalent to abrasion resistance at least six times higher than that of ordinary concrete with 20 MPa compressive strength.

10.14359/4429


Document: 

SP145-59

Date: 

May 1, 1994

Author(s):

E. I. Tazawa, T. Morinaga, and K. Kawai

Publication:

Special Publication

Volume:

145

Abstract:

An underground concrete structure in Japan was severely damaged. The structure was located in a soil that contained considerable hydrogen sulfide and the effects of various microorganisms could not be disregarded. In this study, several types of bacteria in the soil around the structure were isolated and cultured, and simulation tests of mortar deterioration were performed to clarify effects of bacteria on concrete deterioration. Hydrogen sulfide-producing bacteria or sulfur-oxidizing bacteria or both were used. Calcium ion was dissolved out of mortar soaked in the culture medium inoculated with hydrogen sulfide-producing bacteria. The value of pH was decreased and the quantity of hydrogen sulfide was increased in the culture medium as growth of the bacteria proceeded. Since this dissolution of calcium ion from mortar was not observed in the control medium, metabolites of these bacteria could be one of the reasons. From the results of TG-DTA, CaCO 3 content in the mortar surface increased and Ca(OH) 2 content decreased. This is because carbon dioxide produced by the bacteria caused carbonation of the mortar. It has already been established that concrete can be severely damaged by anaerobic bacteria, but this study suggests that concrete can also be damaged by metabolites of aerobic bacteria.

10.14359/4427


Document: 

SP145-58

Date: 

May 1, 1994

Author(s):

S. I. Pavlenko and V. S. Bogusevich

Publication:

Special Publication

Volume:

145

Abstract:

The Siberian Metallurgical Institute (SMI) has developed low-cement concrete with acid and basic slags from a Russian foundry. The concrete contains neither natural aggregates (crushed stone, gravel, or sand) nor artificial porous aggregates (claydite, aggloporite, polystyrene, or others). It includes the following materials: 680 to 1140 kg/m 3 of acid slag sand form PTP with a particle size of 0 to 5 mm used as fine aggregate; cementitious materials (340 to 400 kg/m 3 of fine-grained basic slag and 100 to 170 kg/m 3 of M500 portland cement); 260 to 290 kg/m 3 of water; 0.3 percent by weight of cement of plasticizing admixture (technical grade lignosulfonate); and 1 to 2 percent of air-entraining admixture (secondary sodium alkyl sulfate). To make the wide application of this concrete possible in construction (mainly for low-rise cottages), deformation properties, protection of reinforcement from corrosion, frost resistance, and water and gas permeability were studied during a 1-year period. The investigation shows that concrete developed in this way complies with Russian international standards for low-strength concrete and can be used in housing construction. Air-entrained concrete for external walls should be protected by mortar or some other finishing material.

10.14359/4425


Document: 

SP145-57

Date: 

May 1, 1994

Author(s):

M. S. Akman and H. Gulseren

Publication:

Special Publication

Volume:

145

Abstract:

The effects of steam-curing at atmospheric pressure were investigated on three kinds of concrete: pozzolanic portland cement concrete, high-strength portland cement concrete, and high-performance concrete manufactured with high-strength portland cement containing a superplasticizer and retarder. The early and final compressive and flexural strengths, coefficients of capillary absorption, and apparent porosities were determined on prismatic specimens stored for 140 days in water and ammonium nitrate solution. The dynamic moduli of elasticity were also measured every week during the storage period. Two steam-curing cycles with maximum temperature of 60 and 80 C, respectively, were used. The steam-curing processes were found to be suitable and less detrimental for high-performance concrete compared to pozzolanic portland cement and high-strength portland cement concretes.

10.14359/4424


Document: 

SP145-56

Date: 

May 1, 1994

Author(s):

G. Mathieu and J. Sari

Publication:

Special Publication

Volume:

145

Abstract:

In France, water towers, reservoirs, tanks, and basins constitute extensive facilities requiring inspection and maintenance. The survey recently conducted on the performance and durability of waterproofing in these structures is of considerable importance at the present time, with the publication of the new French professional recommendations, the revision of Section 74 of the CCTG (general technical specifications governing public contracts entered into in the name of the state), and the negotiation of future European Community regulations. This survey enables us to better understand existing facilities and to obtain precise information on such structures, with details on capacities, heads, and commissioning dates, but also on the selection of the initial waterproofing used, which may be a sealed structure itself or a support for waterproofing.

10.14359/4529


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