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International Concrete Abstracts Portal

Showing 1-5 of 32 Abstracts search results

Document: 

18-356

Date: 

September 1, 2019

Author(s):

Jussara Tanesi, Haejin Kim, and Ahmad Ardani

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Deicing chemical solutions can profoundly affect concrete’s physical and chemical properties. It is a known fact that salt solutions are highly conductive in comparison with pure water and are expected to alter concrete’s electrical resistivity as well as other transport properties. In this study, the influence of NaCl, CaCl2, and MgCl2 on transport properties of cementitious materials was investigated. The first part of the project evaluated the continuous exposure for 1 year, while the second part evaluated the wetting-drying cyclic exposure for 6 months (27 cycles). This paper presents the results of the cyclic exposure. Results obtained with standard testing methodologies can be misleading and should be interpreted with caution because transport properties were influenced by different factors, especially the exposure history. In addition, each salt affected each individual transport property differently. Cyclic exposed samples presented similar results as those subjected to 1 year of continuous exposure.

DOI:

10.14359/51716837


Document: 

16-100

Date: 

September 1, 2017

Author(s):

L. A. Sbia, A. Peyvandi, I. Harsini, J. Lu, S. Ul Abideen, R. R. Weerasiri, A. M. Balachandra, and P. Soroushian

Publication:

Materials Journal

Volume:

114

Issue:

5

Abstract:

A pilot-scale field investigation was conducted through which: 1) a refined ultra-high-performance concrete (UHPC) mixture was prepared in a ready mixed concrete plant; 2) a large reinforced UHPC block was constructed through placement, consolidation, and finishing of UHPC; and 3) a commonly available concrete curing (insulating) blanket was applied for field thermal curing of the UHPC block using the exothermic heat of hydration of the cementitious binder in UHPC. Monitoring of the reinforced UHPC block temperature over time confirmed the development of a reasonably uniform temperature and a viable temperature time history, which suited thermal curing of UHPC without any heat input. In-place nondestructive inspection of the reinforced UHPC structure pointed at timely setting and strength development, leading to achievement of ultra-high-performance status. Specimens were cored from the large reinforced concrete block and subjected to laboratory testing. The experimental results indicated that the field thermal curing was more effective than the laboratory thermal curing considered in the project, and that the pilot-scale production of the UHPC mixture produced compressive strengths approaching 170 MPa (24.7 ksi).

DOI:

10.14359/51689677


Document: 

13-053

Date: 

November 1, 2014

Author(s):

Luis Orta and F. Michael Bartlett

Publication:

Materials Journal

Volume:

111

Issue:

6

Abstract:

The stresses, strains, and curvatures due to the shrinkage restraint of new concrete bridge deck overlays by the underlying older substrate are investigated. A time history analysis method is derived that, for each time increment, computes free-shrinkage and creep strains, enforces compatibility and equilibrium using a time-dependent stiffness matrix, and determines incremental mechanical and total strains. A new model for tensile creep strains has test-predicted ratios for experimental results reported by others that average 1.00, with a coefficient of variation of 11%. The resulting stresses and mechanical strains are nonlinear across the depth of the member, with large stress gradients in the top and bottom faces of the overlay at early ages of drying. Simplified analytical methods proposed by others are often not accurate: neglecting swelling of the substrate underestimates the mechanical strains, neglecting tensile creep markedly overestimates the mechanical strains, and assuming uniform free shrinkage through the overlay thickness initially overestimates the mechanical strains but subsequently underestimates them at older ages. The studies also found that application of a waterproofing membrane at the top of the overlay 3 days after the end of curing has very little effect on the maximum tensile stresses in the overlay. The age-adjusted equivalent modulus method accurately estimates the overlay tensile stress at early ages, but fails to predict the time of cracking.

DOI:

10.14359/51687183


Document: 

109-M50

Date: 

September 1, 2012

Author(s):

Shengxing Wu, Yao Wang, Dejian Shen, and Jikai Zhou

Publication:

Materials Journal

Volume:

109

Issue:

5

Abstract:

A series of dynamic axial tensile tests were performed on concrete and its three components using a servo-hydraulic testing machine. The dynamic mechanical properties of approximately 200 specimens were tested under a dynamic load at strain rates that ranged from 10–6 to 10–2 s–1, different initial static loads, and cyclic variable-amplitude loads with different frequencies. The results indicated the following: 1) tensile strength is sensitive to strain rate in all these materials and the rate sensitivity of strength for concrete was close to the composite material with the lowest sensitivity factor k; 2) the elastic modulus is less sensitive to strain rate than strength in all the materials. The rate sensitivity of the modulus for concrete was close to its component material with the lowest sensitivity factor m. The interfacial transition zone (ITZ) had the highest m among the composites; 3) the stress-strain relation for mortar is almost completely linear before peak stress. In contrast, the stress-strain relations of the concrete, granite, and interface appear nonlinear when the stress is set at more than approximately 50% of the peak value, and the nonlinear section showed a linear trend with increasing strain rate; 4) an initial static load within certain limits increased the dynamic tensile strength. The critical initial static loads for the mortar, granite, interface, and concrete were 70%, 50%, 50%, and 30%, respectively; and 5) the cyclic loading history had the least influence on the mortar and the most influence on the interface. The influence of fatigue damage decreased when the loading frequency increased.

DOI:

10.14359/51684083


Document: 

109-M06

Date: 

January 1, 2012

Author(s):

Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, and Nemat Hassani

Publication:

Materials Journal

Volume:

109

Issue:

1

Abstract:

One of the important factors in the use of portland cement concrete is its durability, and most of the situations where durability is lacking have been identified and strategies to manage durability have been implemented. Geopolymer concrete, made from an alkali-activated natural pozzolan (AANP), provides an important opportunity for the reduction of carbon dioxide (CO2) emissions associated with the manufacture of concrete but has a limited history of durability studies. Until its different properties are well understood there is no desire to adopt this new technology of unknown provenance by the concrete industry. This paper presents an experimental study of oxygen and chloride permeability of AANP concrete prepared by activating Taftan andesite and Shahindej dacite (Iranian natural pozzolans), with and without calcining, and the correlations between these properties and compressive strength. The results show that compared to ordinary portland cement (OPC) concrete, AANP concrete has lower oxygen permeability at later ages; but it shows moderate to high chloride ion penetrability.

DOI:

10.14359/51683570


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