ABOUT THE 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.

International Concrete Abstracts Portal

Showing 1-5 of 10 Abstracts search results

Document: 

SP256-01

Date: 

October 1, 2008

Author(s):

A. Durán-Herrera, N. Petrov, O. Bonneau, K. Khayat, and P.-C. Aïtcin

Publication:

Symposium Papers

Volume:

256

Abstract:

The partial substitution of natural sand by lightweight sand has been used to reduce autogenous shrinkage in concretes with a low water/binder ratio, but when this substitution is combined with quasi-adiabatic curing conditions during the first 24 hours, it has been found that autogenous shrinkage can be mitigated and controlled. During an experiment done at Sherbrooke University on large concrete blocks measuring 0.6 × 0.6 × 0.6 m (2 × 2 × 2 ft) where 28% by volume of the natural sand in the concrete was replaced by the same volume of saturated lightweight sand, with absorption of about 20%, it was found that autogenous shrinkage was mitigated within the concrete blocks. Moreover, it has been found that the compressive strength and the elastic modulus of the substituted concrete were not affected by this substitution. For the first time in large concrete specimens, it can be reported that autogenous shrinkage can be mitigated and controlled without the help of any chemical product added to the concrete to induce an initial expansion to neutralize autogenous shrinkage. It seems that quasi-adiabatic conditions favor the development of large crystals that result in swelling of the apparent volume of the concrete block, and that the temperature increase also contributes to reduce chemical shrinkage. This could explain why Le Chatelier found more than 100 years ago that when a paste was cured under water, after a certain time, it swells enough to break the vase in which it had been placed.

DOI:

10.14359/20227


Document: 

SP256-09

Date: 

October 1, 2008

Author(s):

D. Cusson

Publication:

Symposium Papers

Volume:

256

Abstract:

The effects of internal curing, type of blended cement and coarse aggregate size on earlyage expansion, autogenous shrinkage, and strength of high-performance concrete were investigated. To do so, 12 high-performance concrete mixtures were developed and tested under sealed and room temperature conditions. The results were statistically analyzed using the paired comparison design method. It was shown that internal curing of HPC with presaturated porous lightweight aggregate allowed signifi cant autogenous expansion and resulted in considerable reduction in net autogenous shrinkage. The type of cement used in concrete, which was either ordinary portland cement, silica fume blended cement, or slag/silica fume blended cement, had a strong effect on early-age expansion, autogenous shrinkage, and the effectiveness of internal curing. For instance, the concrete specimens made with silica fume blended cement, which yielded the largest autogenous shrinkage strains under sealed conditions, obtained the best reductions in autogenous shrinkage when tested under an internal curing condition.

DOI:

10.14359/20235


Document: 

SP256-03

Date: 

October 1, 2008

Author(s):

Y. Wei and W. Hansen

Publication:

Symposium Papers

Volume:

256

Abstract:

High-performance concrete (i.e. water-cementitious ratio below 0.40) for bridge-deck applications has been shown to develop shrinkage-related cracking. This study explores the concept of internal curing using pre-soaked lightweight fine aggregate (LWFA) as partial replacement of sand for mitigating autogenous shrinkage and moisture warping. Concretes with water-cementitious ratios (w/c) of 0.35 and 0.45 containing LWFA to sand ratios of 20% and 40% by volume were investigated. Results show that pre-soaked LWFA is effective in mitigating autogenous shrinkage but also reduces slab uplift from moisture warping due to combined drying shrinkage at the top surface and wetting at the bottom surface.

DOI:

10.14359/20229


Document: 

SP256

Date: 

October 1, 2008

Author(s):

Editors: Benjamin J. Mohr and Dale P. Bentz

Publication:

Symposium Papers

Volume:

256

Abstract:

SP-256CD In the absence of adequate curing, early-age self-desiccation and consequent autogenous shrinkage may be problematic, particularly in concretes with a low water-to-cementitious material ratio. In 2003, a Federal Highway Administration survey regarding the most common distresses in high-performance concrete estimated that up to 60% of bridge decks have experienced early-age cracking, most likely due to autogenous shrinkage. Internal curing has been proposed as a potential technique to mitigate autogenous shrinkage and earlyage cracking. Internal curing is accomplished by the incorporation of water-absorptive materials in low permeability (that is, high performance) concretes, where external curing may not be sufficient to maintain saturation of the concrete member. Within the past decade, internal curing techniques have begun to move from laboratory research to field applications, with tremendous success. The papers contained in this publication were presented at the Fall 2007 American Concrete Institute Convention in Fajardo, Puerto Rico. The two half-day technical sessions brought together engineers and material scientists from around the world to discuss laboratory research, case studies, and practical applications related to internal curing of high-performance concretes. This publication, co-sponsored by ACI Committees 236, Material Science of Concrete, and 231, Properties of Concrete at Early Ages, offers a unique state-of-the-art perspective regarding this evolving topic.

DOI:

10.14359/20094


Document: 

SP256-04

Date: 

October 1, 2008

Author(s):

V.H. Villarreal

Publication:

Symposium Papers

Volume:

256

Abstract:

The benefits of using lightweight aggregate (LWA) to replace a portion of the normalweight aggregates in concrete mixtures have been investigated by many researchers. The main purpose of this substitution has been to provide a source of moisture for internal curing that will promote more complete hydration of the cementitious materials. The adequate initial moisture conditioning of the LWA is the most crucial step in the ready mixed concrete production cycle. Once the LWA has been satisfactorily saturated, the potential for field problems is insignificant. Any shortcuts in this fundamental procedure can result in the failure of the concept and reluctance on the part of the concrete contractor to adapt this technology. The problems can range from yield issues to slump loss, segregation, finishability, and pumpability. The slow release of moisture from the lightweight aggregate to the concrete matrix has resulted in the mitigation or elimination of plastic and drying shrinkage cracking, as well as limiting the effects of self-desiccation. Enhanced workability and better consolidation due to an improved total grading provided by the use of an intermediate aggregate is also evident; contractors have reported that it reduces the total placing time.

DOI:

10.14359/20230


12

Results Per Page 




Please enter this 5 digit unlock code on the web page.