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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

18-524

Date: 

January 1, 2020

Author(s):

Dipayan Jana

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

Extensive cracking in thousands of residential concrete foundations in eastern Connecticut is found to be due to two-stage expansions associated with oxidation of pyrrhotite in crushed gneiss coarse aggregate of concrete used from a local quarry that sits on a hydrothermal vein of significant pyrrhotite crystallization, followed by internal sulfate attack in concrete from the sulfates released by pyrrhotite oxidation. Microstructural, chemical, and mineralogical evidences of pyrrhotite oxidation and the resultant internal sulfate attack in concrete are presented from a case study. A five-step laboratory testing protocol is suggested for assessment of aggregates from the area to prevent pyrrhotite-related deterioration for future construction.

DOI:

10.14359/51718059


Document: 

14-012

Date: 

May 1, 2012

Author(s):

Seamus F. Freyne, Mitchell L. Watkins, and Adam Browne

Publication:

Materials Journal

Volume:

112

Issue:

3

Abstract:

Vibrations are potentially harmful to green concrete in shaft foundations, and many states, including Mississippi, cautiously established limits in terms of compressive strength, distance boundary, and wait time to protect early-age concrete. These limits, however, could be overly conservative with respect to experimental evidence, and perhaps unnecessarily impede construction schedules and add to project cost. The objective of this study was to quantify the effects of early-age vibrations on concrete performance. Concrete cylinders were exposed to several combinations of vibration magnitudes and durations that were representative of shaft construction, and at ages coincident with the sensitive period between initial and final set. The vibrations had no consistent influence on compressive strength and electrical resistivity. There was also no discernable difference between limestone and river gravel coarse aggregates.

DOI:

10.14359/51687393


Document: 

105-M62

Date: 

November 1, 2008

Author(s):

Xiaodan Ren, Weizhong Yang, Yong Zhou, and Jie Li

Publication:

Materials Journal

Volume:

105

Issue:

6

Abstract:

A systematic experimental research was carried out to investigate the mechanical properties of high-performance concrete (HPC). A total of 91 plate specimens were tested in four different loading conditions including uniaxial tension, uniaxial compression, biaxial compression, and tension compression with the help of a closed-loop testing machine. Uniaxial and biaxial complete stressstrain curves were obtained under a strain control loading scheme. Based on the stochastic process theory, the average curves and standard deviation curves were obtained for uniaxial loading conditions. The rehardening of concrete after having entered the softening stage was observed in this experiment. The ultimate strength envelopes in both stress and strain space were developed through parameter identification of the complete stress-strain curves. This research laid a foundation for further research on the multiaxial constitutive law of concrete.

DOI:

10.14359/20196


Document: 

97-M44

Date: 

May 1, 2000

Author(s):

Kamal H. Khayat, John Bickley, and Michel Lessard

Publication:

Materials Journal

Volume:

97

Issue:

3

Abstract:

The construction of foundation and basement walls in residential and small building construction often involves the use of low-quality con-crete. Such concrete can exhibit excess cracking and low impermeabil-ity, hence affecting the quality of habitation. This paper reports the results of a field-oriented study carried out to demonstrate the suit-ability of high-performance, self-consolidating concrete for the con-struction of basement and foundation walls. Two optimized mixtures were first used to cast 4 m 3 L-shaped experimental walls measuring 15 x 1.2 x 0.2 m. The easy-flowing yet cohesive concrete was shown to spread through the narrow unrein-forced formwork and fill it in. The mean spacing factor and rapid chloride ion permeability were determined along the walls and were shown to vary between 120 and 175 µm and 575 and 900 coulomb at 56 days, respectively. The mean compressive strength of such con-crete ranged between 8 and 16 MPa after 1 day, and 50 to 60 MPa after 56 days The in-place compressive strength after 56 days varied between 30 and 40 MPa for the self-consolidating concrete made with 20% fly ash and 3% silica fume replacements (w/cm of 0.45), and 42 and 50 MPa for the richer mixture with 40% slag and 3% silica fume replacements (w/cm of 0.42). The strength decreased slightly near the top of the walls and away from the casting position. The silica fume slag concrete was used in the casting of the perimeter foundation walls of a three-townhouse complex at the Canadian Centre for Housing Technology in Ottawa. A total of 36 m 3 of self-consolidating concrete was used to fill the basement walls measuring 12 x 18 m in plan, approximately 2.5 m in height, and 0.2 m in thickness. The concrete was cast from opposite corners and was shown to spread readily into place and self-level, resulting in a high-quality surface finish.

DOI:

10.14359/4630


Document: 

97-M45

Date: 

May 1, 2000

Author(s):

Zdenek P. Bazant and Drahomir Novak

Publication:

Materials Journal

Volume:

97

Issue:

3

Abstract:

The size effect on the nominal strength of quasibrittle structures failing at crack initiation, and particularly on the modulus of rupture of plain concrete beams, is analyzed. First, an improved deterministic formula is derivedfrom the energy release due to a boundary layer of cracking (initiating fracture process zone) whose thickness is not negligible compared to beam depth. To fit the test data, a rapidLy converging iterative nonlinear optimization algorithm is developed. The formula is shown to give an excellent agreement with the existing test data on the size effect on the modulus of rupture of plain concrete beams. The data range, however, is much too limited; it does not cover the extreme sixes encountered in arch dams, foundations, and retaining walls. Therefore, it becomes necessary to extrapolate on the basis of a theory. For extreme sizes, the Weibull type statistical effect of random material strength must be incorporated into the theory. Based on structural analysis with the recently developed statistical nonlocal model, a generalized energetic statistical size effect formula is developed. The formula represents asymptotic matching between the deterministic- energetic formula, which is approached for small sixes, and the power law size effect of the classical Weibull theory, which is approached for large sixes. In the limit of infinite Weibull modulus, the deterministic-energetic formula is recovered. Data fitting with the new formula reveals that, for concrete and mortar, the Weibull modulus m = 24 rather than 12, the value widely accepted so far. This means that, for extreme sixes, the nominal strength (modulus of rup-ture) decreases, for two-dimensional similarity, as the -I / 12 power of the structure size, and for three-dimensional similarity, as the -I /8 power (whereas the -I /4 power has been assumed thus far). The coefficient of variation characterizing the scatter of many test results for one shape and one size is shown not to give the correct value of Weibull modulus because the energetic size effect inevitably intervenes. The results imply that the size effect atfracture initiation must have been a significant contributingfactor in many disasters for example, those of Malpasset Dam, Saint Francis Dam, and Schoharie Creek Bridge.)

DOI:

10.14359/9879


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