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International Concrete Abstracts Portal

Showing 1-5 of 26 Abstracts search results

Document: 

SP148-15

Date: 

September 1, 1994

Author(s):

S.A. Austin and PJ. Robins

Publication:

Symposium Papers

Volume:

148

Abstract:

This paper reports on part of a substantial research programme on properties of condensed silica fume (CSF) concretes cured in temperate and climates, carried out in the Department of Civil Engineering at Loughborough. The hot The research approach was to investigate mixtures proportioned to have equal workability and 28 day strength (when water cured at 20°C). This paper examines the effect of superplastizer, curing method (water and polythene) and curing environment (temperate and hot) on the compressive strength, permeability and pore structure of 40 MPa concretes. More specifically, the paper contrasts the performance of two 15% CSF mixtures (replacement by weight of cement) where workabilities were controlled by the addition of extra water or superplasticizer. The development of the concretes’ strength and subsurface permeability index (air and water) with age (from 7 to 180 days) is described, together with the intrinsic permeability (air and water) and pore structure of their equivalent mortar fraction. The use of superplasticizer to control workability increased the compressive strength of CSF concrete mixtures by around 18% and 10% in the temperate and hot environments respectively. The super-plasticized concrete had lower air and water permeabilities which is attributed to an improved pore structure as confirmed by mercury intrusion porosimetry date. The improvements were more marked in the CSF concretes cured in a hot environment.

DOI:

10.14359/10049


Document: 

SP148-20

Date: 

September 1, 1994

Author(s):

H. Wang, S. Tysl, and J. E. Gillott

Publication:

Symposium Papers

Volume:

148

Abstract:

Two well-understood and defined reactions in concrete are known as alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). These two reactions are extremely detrimental to the integrity of concrete structures. It is known that lithium-based chemical compounds can control and/or eliminate the expansion caused by ASR. Based on this technology, a commercial chemical admixture has been developed. The admixture is a ready-to-use liquid product formulated to meet ASTM C 494 requirements as a Type A water-reducing admixture. This product is not intended to control ACR-induced expansion. Therefore, identification of the types of alkali-aggregate reactions is necessary to effectively control concrete expansion.

DOI:

10.14359/4111


Document: 

SP148-01

Date: 

September 1, 1994

Author(s):

R. N. Swamy, M. Sakai, and N. Nakamura

Publication:

Symposium Papers

Volume:

148

Abstract:

Presents a detailed investigation of the role and effectiveness of ground granulated blast furnace slag and a high-range water reducer (HRWR) on the quality of concrete in terms of bleeding, setting times, heat evolution, strength development, and pore structure. The tests were carried out in two parts. In the first, a slag of normal fineness was used, and both the replacement level and water-binder ratio were varied. It was found that both the slag and HRWR acted as set retarders in terms of setting times and heat evolution. The water-binder ratio was the predominant factor affecting the rate of bleeding. The presence of slag, on the other hand, caused low-early strength and slow strength development, but had significant beneficial influence on the total pore volume and pore size distribution. In the second part, fineness of slag was varied from 453 to 1160 m 2/kg and the replacement level was kept constant at 50 percent. It was then possible to obtain compressive strength in excess of 30 MPa at 3 days and 100 MPa at 28 days, with substantial reductions in total porosity and water permeability. The bleeding rate was also reduced and the setting times also improved. The overall conclusion of this study is that a judicious combination of HRWR and slag fineness can lead to a very effective synergic interaction to produce concretes of high strength, high modulus, and low porosity.

DOI:

10.14359/4100


Document: 

SP148-13

Date: 

September 1, 1994

Author(s):

N. Nishiyama, Y. Kasai, N. Yuasa, and Y. Nakata

Publication:

Symposium Papers

Volume:

148

Abstract:

Flowing concrete is characterized by high flowability, requiring only slight consolidation by vibrating and easy control in a plant. An experimental model structure using flowing concrete was made. Paper deals with placing capability on site and properties of hardened flowing concrete in the structure. Pumpability, flowability, and capability to fill forms were investigated for the fresh flowing concrete, and distribution of compressive strength, carbonation depth, cement content, air permeability, and water absorption were measured. Compressive strength of core samples taken from the model structure and standard cylinder specimens from the plant mixture were approximately 24 Mpa. The average estimated cement content was 333 kg/m 3 and the standard deviation was 15 kg/m 3 within a wall of 3 x 4.2 m. Measured carbonation depth was smaller in the freely flowed portions than in the upper portion of vibrated parts.

DOI:

10.14359/4280


Document: 

SP148-24

Date: 

September 1, 1994

Author(s):

G. Mantegazza, A. M. Penn, and S. Tattoni

Publication:

Symposium Papers

Volume:

148

Abstract:

Reports the results of an experimental research program on polypropylene fiber reinforced cement mortars. The purpose of the work was to define the effects produced on a basic mortar by addition to the mixture of various synthetic polymers in the form of latexes. The significant features considered that characterize a cement mortar formulated for repairing concrete structures include workability, low permeability, dimensional stability, mechanical resistance (compressive and flexural strength), Young's modulus of elasticity, ductility, toughness, and durability. The test results suggest that optimal characteristics have been obtained (given a minimum percentage of fibers) with a content of 10 percent silica fume by weight of cement and by using acrylic acid copolymer water dispersion at the rate of 9 percent of the solid polymer to cement. For protective use, it is possible to modify the basic mortar by a styrene-butadiene copolymer water dispersion; however, the modification of the basic mortar by using styrene-acrylic polymer latex generates a product suitable either for repairing or coating of reinforced concrete structures. The reliability of this last modified mortar as a protective coating has also been investigated. The most significant results relate to the penetration of Cl- and SO 4-ions, variation of bond strength between mortar and concrete, and effectiveness of a thin layer of such a cement composite, correlated to rate of steel corrosion. Equivalent criteria have been described comparing different mortar covers, with the minimum cover thickness of concrete as prescribed by European codes, by using an electrochemical test procedure.

DOI:

10.14359/4284


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