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Showing 1-10 of 1687 Abstracts search results

Document: 

18-401

Date: 

November 1, 2019

Author(s):

Yail J. Kim, Yongcheng Ji, and Troy Butler

Publication:

Structural Journal

Volume:

116

Issue:

6

Abstract:

This paper presents a novel modeling approach to predict the response of parameters constituting the strength of concrete cylinders confined with carbon fiber-reinforced polymer (CFRP) sheets under an acidic environment (pre-conditioned concrete is strengthened). Contrary to conventional modeling that requires specific parameter values to solve for the strength of the confined concrete, the stochastic inverse method mathematically infers individual parameter values without prior information based on a known confined strength. Accordingly, the implications of each parameter on the strength development of the confined concrete are quantified. The modeling approach is validated against a previously conducted experimental program and is employed for parametric investigations with various geometric and material properties as well as with variable sulfuric acid exposure periods. The cylinder diameter affects the surety of the strength variation in terms of occurrence probability. The rate of strength decrease in the confined concrete is pronounced when the core concrete has been initially exposed to sulfuric acid, while the rate slows down as the exposure time progresses. High-strength CFRP materials noticeably increase the strength of the confined concrete; however, the efficiency of enhancement diminishes with the CFRP strength. The functionality of the concrete confined by multiple CFRP layers is examined. Upon assessing the empirically calibrated factors of existing design guidelines, new factors are proposed for strength prediction of the confined concrete. To substantiate the distinct effects of the sulfuric acid exposure time, the strength of the confined concrete is characterized by a Euclidean distance-based clustering technique. The uncertainty associated with the CFRP-confinement is elucidated and contributing attributes are identified.

DOI:

10.14359/51716761


Document: 

18-393

Date: 

November 1, 2019

Publication:

Materials Journal

Volume:

116

Issue:

6


Document: 

18-241

Date: 

November 1, 2019

Author(s):

Mostfa Al Azzawi, Gray Mullins, and Rajan Sen

Publication:

Structural Journal

Volume:

116

Issue:

6

Abstract:

This paper investigates the influence of concrete porosity on durability of the bond between fiber-reinforced polymer (FRP) and concrete. Twenty-four slab specimens were cast using three different concrete mixtures with water-cementitious materials ratios (w/cm) of 0.53, 0.41, and 0.21, representing high, medium, and low porosities, respectiviely. The slabs were preconditioned by oven-drying and two commercially used carbon fiber-reinforced polymer (CFRP) materials bonded to surfaces that had been sand-blasted to provide a concrete surface profile (CSP) 3 rating. Repaired specimens were submerged in 30°C (86°F) potable water for 15 weeks and residual bond was evaluated through pulloff tests. Results showed 1 to 3% bond reduction in the high-porosity, low-strength concrete compared to a reduction in excess of 20% in its low-porosity, higher-strength counterpart. The likely reason for the better performance was deeper epoxy penetration into the more porous concrete substrate. Findings suggest that surface preparation and installation methods that allow epoxy to penetrate deeper into low-porosity, high-strength concrete can result in increased durability under moisture exposure.

DOI:

10.14359/51716801


Document: 

18-010

Date: 

November 1, 2019

Publication:

Materials Journal

Volume:

116

Issue:

6


Document: 

18-490

Date: 

September 1, 2019

Author(s):

Marisol Tsui-Chang, Chunyu Qiao, Luca Montanari, Prannoy Suraneni, and W. Jason Weiss

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Chloride binding is typically studied by exposing a certain quantity of powdered hydrated cement paste to chloride salt solutions, and by comparing the differences in final and initial chloride concentrations after equilibrium is achieved. Chloride concentrations are generally determined by titrating the solutions using manual or automatic titration. Chloride-binding isotherms are obtained by repeating this process for a range of chloride concentrations. While titration produces accurate results, the process can be labor-and time-intensive. In this work, chloride-binding isotherms are obtained by testing chloride solutions using a calibrated X-ray fluorescence (XRF) device and were evaluated by comparison with titration. Testing was performed on a cement paste with a water-cement ratio of 0.42, exposed to sodium chloride salt solutions ranging from 0 to 5 mol/L at 23°C. Chloride concentrations determined by titration and XRF were similar (differences averaged approximately 3% for the various solutions tested); however, chloride-binding isotherms obtained using the two methods showed significant differences (differences averaged approximately 49% for different chloride binding contents) due to assumptions regarding solution density. When the solution density was accurately measured using a pycnometer, chloride-binding isotherms obtained using titration and XRF were very similar, with differences averaging less than 6%. The importance of accurate density measurements for such calculations is demonstrated mathematically. While these results are preliminary and need to be verified for other salt solutions and cementitious paste compositions, they suggest that the use of XRF may provide a promising alternative to determine chloride-binding isotherms in cementitious materials.

DOI:

10.14359/51716996


Document: 

18-415

Date: 

September 1, 2019

Author(s):

C. Gunasekera, Z. Zhou, M. Sofi, D. W. Law, S. Setunge, and P. Mendis

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

The increase of carbon emissions due to the annual growth of portland cement (PC) production has promoted research into the development of sustainable green concrete using a range of readily available industrial waste materials. The present study is focused on developing two high-volume fly ash (HVFA) concretes with cement replacement levels of 65% (HVFA-65) and 80% (HVFA-80). The required lime for both HVFA concrete mixtures was initially determined and the optimized mixture designs identified, based on the 28-day compressive strength, by varying the low-calcium Class F fly ash-hydrated lime composition. The optimized concrete mixtures achieved a compressive strength of 53 and 40 MPa (7.69 and 5.80 ksi) for HVFA-65 and HVFA-80 concretes, respectively. The early-stage strength development is dependent on the matrix produced in the specific HVFA concrete, which is itself dependent on the number of unreacted fly ash spheres. The increase of fly ash and hydrated lime dosage in HVFA concrete increases the rate of hydration of the C3A and C4AF phases, but decreases the hydration of the C3S phase, which resulted in lower early-age strength development than occurs in PC concrete. It was noted that the initial setting time of HVFA concretes increase with an increase of fly ash content. However, addition of hydrated lime accelerates the hydration and decreases the final setting time for HVFA concretes.

DOI:

10.14359/51716815


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: 

18-349

Date: 

September 1, 2019

Author(s):

Alok A. Deshpande and Andrew S. Whittaker

Publication:

Structural Journal

Volume:

116

Issue:

5

Abstract:

The effect of elevated temperature on the mechanical behavior of concrete and the seismic behavior of reinforced concrete walls was investigated through materials and component testing. Tests were performed on concrete cylinders at temperatures between 70 and 600°F (21 and 316°C). The planar walls had web reinforcement ratios of 0.93% and 2.0%; the concrete compressive strength was approximately 6 ksi (41 MPa) for all walls. The maximum surface temperature for the tests of the walls was 450°F (232°C). Fully reversed, in-plane, inelastic cyclic loading was imposed on the walls in heated and ambient conditions to establish the effects of elevated temperature on peak strength and elastic stiffness. For temperature between 68 and 450°F (20 and 232°C), the materials tests showed a reduction in concrete uniaxial compressive strength and compression modulus of elasticity of no more than 10% and 30%, respectively. The wall tests showed no meaningful effect of temperature on either peak strength or secant stiffness to peak strength in both heated (up to 450°F [232°C]) and residual (tested at room temperature after cooling from 450°F [232°C]) conditions.

DOI:

10.14359/51715636


Document: 

18-338

Date: 

September 1, 2019

Author(s):

Karthik H. Obla

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Past research showed a correlation between the measured apparent chloride diffusion coefficient determined in accordance with ASTM C1556 and the ASTM C1202 rapid indication of chloride ion penetrability test (RCPT) results. Based on that research, a combination of RCPT and strength criteria was proposed to categorize mixtures based on their resistance to chloride ion penetration. This article proposes specification criteria based on a formation factor to categorize mixtures. The efficacy of using both approaches to categorize 44 concrete mixtures prepared from different portland cements, types and dosages of supplementary cementitious materials, and w/cm is examined. It is found that either approach can be used to categorize mixtures based on their resistance to chloride ion penetration. Specimens from 10 mixtures, moist-cured for over 8 years, were tested for surface and bulk resistivity. The same specimens were immersed in chloride solutions in accordance with ASTM C1556, and chloride-ion contents at specific depths from the exposed surface were measured and compared with the later-age bulk resistivity, early-age RCPT, and estimated formation factor.

DOI:

10.14359/51716835


Document: 

18-310

Date: 

September 1, 2019

Author(s):

M. Moini, K. Sobolev, I. Flores-Vivian, S. Muzenski, L. T. Pham, S. Cramer, and M. Beyene

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Durability and long-term performance of concrete exposed to deleterious ions and environmental conditions are major concerns. The rapid chloride permeability (RCP) test is commonly used in specifications in the United States to evaluate the permeability of concrete. To evaluate the critical factors that control the service life of structures, the investigation of various concrete mixtures is required. In this paper, the performance of 54 concrete mixtures containing three types of water-reducing admixtures, two types of aggregates, and two levels of cement contents are evaluated in the RCP and freezing-and-thawing tests and the air void structure of selected mixtures are analyzed. It was found that the use of supplementary cementitious materials (SCMs) significantly enhances the performance of concrete mixtures in the RCP test. In addition, mixtures containing up to 30% of Class C fly ash and 50% slag content achieved exceptional durability performance in both RCP and freezing-and-thawing (F-T) tests. The “very-low” RCP values were found for mixtures containing Class F fly ash and polycarboxylate ether (PCE) admixture.

DOI:

10.14359/51716828


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