International Concrete Abstracts Portal

International Concrete Abstracts Portal

The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

Showing 1-5 of 112 Abstracts search results

Document: 

SP100-31

Date: 

April 1, 1987

Author(s):

Van Begin

Publication:

Symposium Papers

Volume:

100

Abstract:

The Belgian Public Works Ministry manages about 5200 important bridges--3640 (70 percent) of them are concrete bridges of which 40 percent are reinforced and 30 percent are prestressed. The average bridge has a surface of 1200 mý, 22 m long spans, and is 22 years old. After seven years of systematic inspection, it is possible to make a balance of the noticed shortcomings and of the reasons why they appeared. Dirty concrete surfaces (graffiti, water trails, moss, etc.) occur very often but generally don't influence the good behavior of the structures. Geometric faults are noticed in 2 to 4 percent of the cases, mainly for cantilever bridges. Concrete cracks are very frequent (30 to 80 percent of the concerned structures). Most of them don't affect the safety but have an influence on the durability. Corrosion of reinforcements and prestressing steel also occurs frequently (20 to 80 percent of the concerned structures). Steel in concrete is naturally protected, but two main factors disturb that favorable situation: carbonation of concrete by CO2 reduces the pH of the concrete and also the protective effect, and cracks and lack of closeness in the protective coating lead to penetration of corrosive agents like deicing salts and acid rain. The deicing salts (chlorides) also attack hardened cement and transform the surface of the concrete into gravel. Although all our bridges are provided with a protective waterproofing, water containing salts remains the most aggressive element. The maintenance, rehabilitation, and reinforcement of the bridges are an important technico-economical problem in Belgium.

DOI:

10.14359/3617


Document: 

SP100-46

Date: 

April 1, 1987

Author(s):

Robert E. Philleo

Publication:

Symposium Papers

Volume:

100

Abstract:

Recent developments have made a new generation of high-strength concrete a viable material for routine construction. The two principal developments are high-range water-reducing admixtures, which permit the placement of concrete of very low water-cement ratio, and silica fume, a pozzolan of extremely high fineness. There are those who argue that high-strength concrete is of such a quality that entrained air is unnecessary. The resistance to freezing is directly dependent on the concrete's capacity for and its probability of containing freezable water if ambient conditions permit continuous hydration for a long period of time so that all the available space is filled with hydration products; or, short of complete space filling, they may become so impermeable that saturation by water is unlikely in most natural exposures. High-range water-reducing admixtures do not alter the pore structure of cement paste; they merely extend traditional cement technology into a range of low water-cement ratios that were previously impractical. The addition of silica fume does alter the pore structure and places more of the pore volume in pores that are so small that water cannot freeze in them at ordinary atmospheric temperatures. It offers some hope of achieving frost resistance without entrained air. The normal test for evaluating frost resistance, ASTM C 666, exposes specimens to freezing at an intermediate level of maturity with no opportunity for drying by loss of water to the surroundings prior to test and exposes them to a very rapid freezing cycle. High-strength specimens without entrained air that may ultimately become durable cannot be expected to do well in the test. While the test is excellent for assessing the frost resistance of young saturated specimens to severe exposure, the resistance of mature specimens to more typical exposures might better be assessed by altering the age-at-test and specimen-conditioning requirements in C 666 or by replacing it with a critical dilation test such as ASTM C 671.

DOI:

10.14359/3708


Document: 

SP100-51

Date: 

April 1, 1987

Author(s):

Micheline RegourdI

Publication:

Symposium Papers

Volume:

100

Abstract:

The use of unconventional aggregates, which includes several sulfide minerals, in making concrete in the Canadian Arctic aroused the interest of the authors to investigate the durability of such a concrete subjected to a very cold environment. Compressive strength measurements on concrete samples three and nine years old, cored in a dock, show that the concrete is still very strong--at least 28 MPa (4000 psi). A close examination of the aggregates and concrete microstructure suggests the concrete is durable. The presence of these aggregates does not give rise to any deleterious effect. The concrete is found to be a dense one. Only a superficial layer of a few millimeters thick has been transformed by carbonation. This zone, enriched in potassium, does not contain any Ca(OH)2 crystal. Its C-S-H has a low CaO/SiO2 ratio and is sometimes replaced by a siliceous gel. Penetration of chloride and sulfate ions is also observed but is not related to any concrete damage. The presence of a large amount of Ca(OH)2 and calcium rich C-S-H (C/S ÷ 1.7) below the thin carbonated layer corresponds to a high chemical stability of the concrete.

DOI:

10.14359/3718


Document: 

SP100-52

Date: 

April 1, 1987

Author(s):

Lauri Kivekas and Markku Leivo

Publication:

Symposium Papers

Volume:

100

Abstract:

Concrete is a suitable material for arctic offshore oil and gas drilling and for production platforms. In the splash and tidal zone of these structures concrete is subjected to severe frost-salt attack, chemical attack of sea water, and ice abrasion. In the test series, a method for accelerated testing of arctic freeze-thaw durability in sea water was developed. High-strength air-entrained superplasticized concretes made with blended cement were tested. The test was found to be very severe.

DOI:

10.14359/3728


Document: 

SP100-106

Date: 

April 1, 1987

Author(s):

M. Berra and G. Baronio

Publication:

Symposium Papers

Volume:

100

Abstract:

Some different degrees of alteration have been found in a concrete tunnel lining affected by dissolved calcium sulfate in water due to the oxidation and solubility of the pyrites contained in the rock. In some cases the damage has been so extensive that the concrete has changed into a plastic mass. Measurements taken inside the tunnel over many years showed a range of temperature from 4 to 6 C. The chemical analysis of the concrete, the diffractometric analysis, and the scanning electron microscope analysis performed on some alteration products all clearly showed the presence of thaumasite and calcite, while no ettringite was found. The recorded thermal conditions, the presence of silica due to feldspar alteration, and the free carbon dioxide in the water lead to the conclusion that the ettringite has been transformed completely into thaumasite. To understand this transformation, some laboratory tests were carried out on mortar immersed in a water mixture containing calcium sulfate, calcium carbonate, calcium hydroxide, and amorphous silica in an environment rich in carbon dioxide, at 5 and 20 C, respectively.

DOI:

10.14359/2305


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