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International Concrete Abstracts Portal

Showing 1-5 of 26 Abstracts search results

Document: 

SP253-04

Date: 

July 31, 2008

Author(s):

H. Justnes, F. Wuyts, and D. Van Gemert

Publication:

Symposium Papers

Volume:

253

Abstract:

The heat of hydration in massive concrete structures can raise the temperature to a level where thermal cracks can pose a problem. Hardening retarders are admixtures that lower the rate of hydration, distribute the heat release over time, and lower maximum temperature in concrete. Such admixtures will inherently lead to lower early strength, but should lead to comparable 28-day strength to reference concrete. Relative large amounts of urea works, in particular when the additional retardation of setting (not hardening) is counteracted by the set accelerator calcium nitrate. However, these dosages are high, and urea will also slowly decompose to ammonia that may limit the urea application to outdoor use, if any. The latest potential admixtures are combinations of minor amounts of strong setting retarders like organic acids (0.1-0.3 %) with the setting accelerator calcium nitrate (1-3%), where a true synergy between the two leads to hardening retardation.

DOI:

10.14359/20166


Document: 

SP253-05

Date: 

July 31, 2008

Author(s):

W.G. Moravia, C.S. Rodrigues, A.G. Gumieri, and W.L. Vasconcelos

Publication:

Symposium Papers

Volume:

253

Abstract:

Durability is one of the key factors considered in the specification of concrete for most of its applications. When applied to industrial floors, road pavements, and sidewalks, abrasion wearing impairs the concrete performance. This work is focused on the abrasion resistance of lightweight concrete produced with expanded clay, comparing it to the performance of a conventional concrete produced with normal-weight aggregates, and with mixture proportion for an estimated compressive strength of 30 Mpa. The lightweight aggregate structure was investigated through mercury intrusion porosimetry and water absorption tests. The parameters used to evaluate the abrasion phenomena were thickness and mass loss of the concretes, which resulted from the friction between the specimens and an abrasive material. Although the expanded clay presents lower abrasion resistance than the normal-weight aggregate, due to its higher porosity; for example, both concretes behaved similarly regarding their wearing resistance. The denser interfacial transition zone between the expanded clay and the cement paste in the lightweight concrete seems to compensate for the lower wear resistance of the aggregate.

DOI:

10.14359/20167


Document: 

SP253-08

Date: 

July 31, 2008

Author(s):

G.P. Gava and L.R. Prudêncio Jr.

Publication:

Symposium Papers

Volume:

253

Abstract:

This paper investigates if the ASTM C1399-02 procedure minimizes the post-peak instability, and if it is able to measure the fiber-reinforced beam response at low displacements. The load and mid-span displacement curve, the crackmouth opening displacement and mid-span displacement curve and the average residual strength obtained from ASTM C1399-02 test results were compared with those obtained from ASTM C1018-94b, both conducted in an servo-controlled test machine. The results from ASTM C1399-02 were similar to those obtained according to ASTM C1018-94b. Additionally, the neutral axis value and the crack-mouth opening displacement obtained from ASTM C1399-02 were similar to those determined by ASTM C1018-94b, showing that ASTM C1399-02 test procedure did not minimize the effect of post-peak instability.

DOI:

10.14359/20170


Document: 

SP253-21

Date: 

July 31, 2008

Author(s):

M. Nepomuceno and L. Oliveira

Publication:

Symposium Papers

Volume:

253

Abstract:

This paper reports an experimental study on the mortar phase for selfcompacting concrete. A series of mortars were produced with similar fl ow properties, measured by spread and v-funnel tests, adequate to produce self-compacting concrete. The water content and the modifi ed carboxylic superplasticizer dosage were determined experimentally for each mortar. Different percentages of cement replacement materials were used in binary blends, each one combining one of the two types of cement with one of the three mineral additions selected: limestone powder, granite fi ller, and fl y ash. Each of the binary blends of powders was combined in fi ve different proportions in volume with the fi ne aggregate (Vp/Vs). Mortars were tested for compressive strength at 28 days and this value was related to the water/cement ratio, the percentage of replacement materials, and Vp/Vs parameter. The analysis revealed the possibility of establishing adequate mortar parameters to obtain simultaneously the self-compactability and the required compressive strength of self-compacting concrete.

DOI:

10.14359/20183


Document: 

SP253-12

Date: 

July 31, 2008

Author(s):

G. Camarini, P.S. Bardella, D.C. Barbosa, and V.M. Pereira

Publication:

Symposium Papers

Volume:

253

Abstract:

Steam curing at atmospheric pressure is an important technique for obtaining high early strength values in precast concrete production. The aim of this work was to explore the potential benefits of steam curing in concrete products made with different cements types and with supplementary cementitious materials. All concretes mixtures had the same workability and were produced with two cements both with and without silica fume replacement (10% by mass): highearly-strength portland cement and blast-furnace slag portland cement. For each mixture, specimens were subjected to three curing conditions. Immersion curing until the age of 7 days, curing in air and steam curing at temperatures of 60°C and 80°C maximum temperature over 4 h. Concretes were prepared and tested for initial surface absorption and air permeability. Compressive strength was also determined. The concretes were tested at different ages: 1, 3, 7, 28, 90, and 180 days. The results showed that the concretes with silica fume presented a lower air permeability and capillary absorption, mainly in later ages, when compared with concretes without silica fume for all curing procedures and both portland cements used. The inclusion of silica fume improved performance of concrete produced with blast-furnace slag portland cement at temperature of 80°C. High-early-strength portland cement had a good performance with silica fume replacement. The curing method adopted had significant effects on the near-surface properties of concrete incorporating silica fume.

DOI:

10.14359/20174


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