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International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

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: 

SP207-11

Date: 

October 7, 2002

Author(s):

A.T.C. Guimaraes and P.R.L. Helene

Publication:

Symposium Papers

Volume:

207

Abstract:

The application of deterministic models based only on Fick's Laws can show considerable differences compared to the effective chloride profiles in existing marine structures. An important factor to be taken into consideration is the influence of the concrete saturation degree (SD). In the research, a laboratory test method for the influence of the SD on chloride diffusion in hardened cement paste was developed. Test results were applied to an existing marine structure with 22 years old. Results indicate that the concrete SD has a great influence on chloride diffusion and requires further research. It also shows that the SD should be taken into account when estimating the service life of concrete structures and a model is proposed.

DOI:

10.14359/12389


Document: 

SP207-12

Date: 

October 7, 2002

Author(s):

H. Donza, O. Cabrera, E.F. Irassar, and V. Rahhal

Publication:

Symposium Papers

Volume:

207

Abstract:

In this paper, the effects of physical and mineralogical characteristics of fine aggregate particles on mechanical properties of high-strength concrete (HSC) are evaluated. Two different sand types were used: natural and granitic crushed sand. Proportions 0, 25, 50, 75 and 100 % were selected to obtain blended sands with continuous changes in their physical and mineralogical characteristics. The properties of concrete were evaluated with these five blended sands. From the research and studies performed up to five years, it was shown that the use of granitic crushed sand in high-strength concrete, (strength range around 80 MPa) is possible. The results show that the influence of fine aggregate on compressive strength is not significant at early age, when rounded particle percentage in sand is increased and the paste volume is keep constant. However, at five years the compressive strength of concrete was higher when the natural sand content was greater than 50 %.

DOI:

10.14359/12390


Document: 

SP207-26

Date: 

October 7, 2002

Author(s):

J.A. Rossignolo and M.V.C. Agnesini

Publication:

Symposium Papers

Volume:

207

Abstract:

This paper deals with the properties of styrene butadiene latex (SBR)-modified lightweight aggregate concrete (LWAC) for thin precast components, made with two Brazilian lightweight aggregate (LWA). Water reduction capacity, air content, flow table after 2 h, compressive strength, splitting-tensile strength, flexural strength, modulus of elasticity, stress-strain behavior and water absorption were tested. The 7-day compressive strength and the dry concrete density varied from 39.7 to 51.9 MPa and from 1460 to 1605 kg/m3, respectively. The modulus of elasticity at 7 days, which varied from 17.9 to 22,6 GPa, was lower than that typically observed for normal-weight concrete at the same compressive strength level. The inclusion of SBR in the LWAC decreased W/(C+S) and water absorption level. The inclusion of SBR in the LWAC decreased W/(C+S) and water absorption and increased splitting-tensile and flexural strengths.

DOI:

10.14359/12404


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