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International Concrete Abstracts Portal

Showing 1-5 of 13 Abstracts search results

Document: 

SP218-05

Date: 

February 1, 2004

Author(s):

J. A. Ramirez, J. Olek, and B. J. Malone

Publication:

Symposium Papers

Volume:

218

Abstract:

An experimental investigation was conducted to compare the shear strength of lightweight reinforced concrete beams with that of normal-weight concrete companion specimens. The experimental variables were type of coarse aggregate, concrete compressive strength, and distribution of transverse and longitudinal reinforcement. A total of twelve specimens with shear reinforcement were tested. Seven specimens were made with normal-weight aggregate concrete and five specimens were made with lightweight aggregate concrete. The target concrete strengths were 41 MPa and 69 MPa. Measured shear capacities were compared with calculated values according to the 1998 AASHTO LRFD Bridge Specifications (Interim 2001) and ACI 318-02 Building Code. The experimental findings have shown that both code-based methods produce conservative estimates of shear strength within the range of variables considered in the study.

DOI:

10.14359/13055


Document: 

SP218-07

Date: 

February 1, 2004

Author(s):

C. L. Tasillo, B. D. Neeley, and A. A. Bombich

Publication:

Symposium Papers

Volume:

218

Abstract:

In initiating the final phase of modernizing the locks and dams on the Monongahela River, the U.S. Army Corps of Engineers, Pittsburgh District, used float-in and in-the-wet technology to build the new Braddock dam. This is the first use of such technology for an inland navigation project in the United States, and was employed to eliminate the cost and construction time associated with a conventional cofferdam for mass concrete construction. The new Braddock dam design was fabricated as two large, hollow-core segments. Unlike such applications used for offshore structures, the inland application was limited by navigational draft, and lock and bridge clearances. This restricted the overall dimensions and mass of the segments. The use of lightweight concrete in a significant portion of the two large dam segments was central to the success of the design. Good planning, an understanding of the concrete materials, and quality control were critical to project success.

DOI:

10.14359/13057


Document: 

SP218-11

Date: 

February 1, 2004

Author(s):

M. A. Caldarone and R. G. Burg

Publication:

Symposium Papers

Volume:

218

Abstract:

Structural lightweight concrete is defined as concrete made with low-density aggregate having an air-dry density of not more than 115 lb/ft3 (1850 kg/m') and a 28-day compressive strength of more than 2500 psi (17.2 MPa). This paper presents the test results of very low-density structural lightweight concrete mixtures developed in the laboratory for the purpose of finding a suitable mixture for use on a historic building rehabilitation project. Mixture parameters included a specified compressive strength of 3000 psi at 28 days and an air-dry density approaching 70 lb/ft3. Various constituent materials, mixture proportions and curing methods were examined. The result of this research exemplifies the feasibility of achieving very low densities with structural concretes.

DOI:

10.14359/13062


Document: 

SP218-09

Date: 

February 1, 2004

Author(s):

M. R. Geiker, D. P. Bentz, and O. M. Jensen

Publication:

Symposium Papers

Volume:

218

Abstract:

The use of internal curing is a highly effective means of mitigating autogenous shrinkage in cement mortars (w/cm=0.35, 8 % silica fume). Two different sources of internal water supply are compared: 1) replacement of a portion of the sand by partially saturated lightweight fine aggregate and 2) the addition of superabsorbent polymer particles (SAP). At equal water addition rates, the SAP system is seen to be more efficient in reducing autogenous shrinkage at later ages, most likely due to a more homogeneous distribution of the extra curing water within the three-dimensional mortar microstructure. A comparison of the water distribution in the different systems, based on computer modeling and direct observation of two-dimensional cross sections, is given.

DOI:

10.14359/13060


Document: 

SP218-08

Date: 

February 1, 2004

Author(s):

T. A. Hammer, 0. Bjontegaard, and E. J. Sellevold

Publication:

Symposium Papers

Volume:

218

Abstract:

The 3 main factors determining the efficiency of lightweight aggregate (LWA) as internal curing agents in concrete are discussed with reference to published papers: I) total amount of water in LWA, 2) LWA particle spacing factor and 3) the LWA pore structure. A desorption method is suggested to characterize factor 3) directly as the ability of the LWA to release water. The method is applied to two LWA types and the results demonstrate clear differences. The role of water in ordinary aggregates is discussed with reference to autogenous shrinkage measurements in concrete and the equivalent paste. It is concluded that the aggregate with 0.8% water absorption indeed serves as internal curing agent by reducing and delaying the autogenous shrinkage. Finally, it is shown that sealed curing does reduce and delay both the cement and pozzolanic reactions.

DOI:

10.14359/13059


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