International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

Document: 

SP207-29

Date: 

October 7, 2002

Author(s):

G.C. Isaia, M. Vaghetti, and A.L.G. Gastaldini

Publication:

Symposium Papers

Volume:

207

Abstract:

Most of the carbonation studies are carried out by means of accelerated tests in conditioned chambers in order to obtain data in a shorter time, although the results are not always well correlated with field or laboratory data in natural tests. This work presents a comparative study between a reference portland cement concrete and pozzolanic mixtures with 10% to 50% fly ash, rice husk ash and silica fume in binary and ternary mixtures. Accelerated tests in a conditioned chamber with carbonation depth readings after 4, 8, 12 and 16 weeks, and natural tests with similar specimens exposed to the lab air environment with readings after 0.5, 1 and 2 years, were performed. The calculated rate between the carbonation coefficient of accelerated and natural tests was approximately 1 mm.week0.5 = 1 mm.year0.5 for concrete with w/cm < 0.45 and pozzolan contents up to 25%. For higher w/cm rates and w/cm < 0.45 and pozzolan contents up to 25%. For higher w/cm rates and pozzolan contents, the accelerated tests showed coefftcients 2 to 6 times higher than those observed in the natural test. This work presents preliminary data and it will be continued for 5 years more, in order to obtain readings after exposure to lab air for 4 and 8 years, after casting.

DOI:

10.14359/12407


Document: 

SP207-30

Date: 

October 7, 2002

Author(s):

G. Giaccio and R. Zerbino

Publication:

Symposium Papers

Volume:

207

Abstract:

The characteristics of cement paste are very important for the workability, the mechanical properties and the durability of concrete, particularly in High Performance Concrete (HPC). Several problems of concrete such as slump loss, retardation in setting time or excessive heat of hydration, are directly related with some characteristics of the cement paste. This paper presents the results of a study made on cement pastes to select cementitious materials and chemical admixtures, and adjust mixture proportions before the concrete mixture design. Changes in the fluidity and the behavior of different super-plasticizers combined with cementitious materials including cements of different fineness, and different types or contents of mineral additions (calcareous fillers, natural pozzolans or silica fume) were comparatively studied by using the Marsh cone. It was found that the saturation point (defined as the dosage of superplasticizer over which the flow is not substantially modified) may change significantly with the type of superplasticizer, the fineness of the cementitious material and the incorporation of mineral additions (especially silica fume). Moreover, a quick and easy procedure was applied to analyze the behavior of different cement pastes regarding hydration process, setting time and heat development during the first ages.

DOI:

10.14359/12408


Document: 

SP207-27

Date: 

October 7, 2002

Author(s):

G. Menendez, V.L. Bonavetti, H. Donza, M. Trezza, and E.F. Irassar

Publication:

Symposium Papers

Volume:

207

Abstract:

This paper analyzes the mechanical behavior and its relation with the development of the hydration reaction in concretes with low water-to-cementitious material ratio made with binary and ternary cements containing limestone filler and blast furnace slag. It explores the maximum level of replacement of portland cement by both additions to obtain high early strength concrete. At 3 days, the compressive strength was 43 to 45 MPa and it was greater than 60 MPa at 28 days. All studied concretes present a very similar strength development. Results show that the combination of limestone filler and blast furnace slag is complementary: the limestone filler improves the early strength of concrete while the slag improves the later strength achieving to an optimal strength development. The concrete performance analyzed in terms of water penetration test also classified these concretes as very low permeability.

DOI:

10.14359/12405


Document: 

SP207-28

Date: 

October 7, 2002

Author(s):

J.M.Calixto, L.V. Filho, and C.M. Goncalvez

Publication:

Symposium Papers

Volume:

207

Abstract:

The results of an experimental investigation of the effects of short steel fibers on the shear behavior of reinforced concrete beams are presented. Two types of steel fiber with different shapes, lengths and cross sections were used. Two series of reinforced concrete beams were cast and tested in the laboratory. Each series had a different ratio of transverse reinforcement as well as the addition or not of steel fibers in the concrete mix. The test results indicate the better performance of the beams made with fibers. These beams exhibited smaller crack width and spacing and consequently more stiffness and load carrying capacity. The results also show that the steel fibers improve the shear resisting mechanisms of the concrete represented by the aggregate interlocking and dowel action and behave as an additional transverse ireinforcement, consequently reducing the stresses in the stirrups. This finding suggests a code revision of the concrete contribuition for the shear design of beams when steel fibers are used. Their use can reduce the labor costs in the fabrication of these beams.

DOI:

10.14359/12406


Document: 

SP207-25

Date: 

October 7, 2002

Author(s):

A. Da Silva Ramos Barboza and M.K.El Debs

Publication:

Symposium Papers

Volume:

207

Abstract:

Mortar joints are commonly used in precast concrete structures as connection between columns, walls and load bearing precast concrete facade elements. Usually, the mortar joint has a lower strength than precast elements and its deformability tends to be larger than the ones, which causes a non-uniform distribution of stress in the joint. The mortar joint represents the weakest link in the structural system and the mortar bearing capacity limits the bearing capacity of the precast concrete elements. This paper reports on the development of an experimental program to analyze the bearing capacity of precast high strength concrete columns connected by mortar joints produced with commercially available materials, with the purpose of making better use of the columns’ bearing capacity. It was found that the thicker the joint, the lower the system’s bearing capacity, and that different strains are produced, depending on the type of material used to fill the joint - grout or dry mortar, even when the same thickness and the same relation between strengths is maintained. The conclusion reached was that it is always advisable to adopt a relation equal to or higher than one, and that a 20mm mortar layer produces an optimal behavior, in terms of both strength and ductility.

DOI:

10.14359/12403


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