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International Concrete Abstracts Portal

Showing 1-5 of 370 Abstracts search results

Document: 

19-158

Date: 

September 1, 2020

Author(s):

Faez Sayahi, Mats Emborg, Hans Hedlund, and Andrzej Cwirzen

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This research studies the effect of retarder, accelerator, stabilizer, air-entraining agent, and shrinkage-reducing admixture (SRA) on plastic shrinkage cracking in self-consolidating concrete (SCC). The main objective is to identify the dominant cracking cause—that is, plastic settlement or plastic shrinkage—in an SCC containing a particular admixture. During experimentation, crack-free concretes were achieved by adding air-entraining agent and SRA, while accelerator and retarder increased the crack area. The impact of admixtures on the cracking mechanism was identified by comparing the respective vertical and horizontal deformations. It was observed that the crack-free concretes had moderate settlement and horizontal shrinkage, while the cracked specimens exhibited significant deformation either vertically or horizontally.

DOI:

10.14359/51724623


Document: 

19-306

Date: 

September 1, 2020

Author(s):

Rachel E. Henkhaus, Sandra Villamizar, and Julio A. Ramirez

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The allowable range of epoxy coating thickness specified by ASTM A775/A775M is 175 to 400 μm (7 to 16 mils). This study investigates the impact on structural performance of increasing the upper limit of epoxy coating thickness to 460 μm (18 mils) with respect to deflections, cracking, and bond strength of tension splices. Twenty beam specimens containing single splices as well as splices of bundled bars were tested to failure. The experimental parameters were ranges of epoxy coating thicknesses (300 to 380 μm [12 to 15 mils] and 460 to 530 μm [18 to 21 mils]) and bar sizes No. 16 and 29 [No. 5 and 9]). Test results confirmed the applicability of current code requirements for development and splice length of epoxy-coated bars in tension in ACI 318-14 and AASHTO LFRD 2014, including bars in bundles, up to a coating thickness not to exceed 460 μm (18 mils).

DOI:

10.14359/51727018


Document: 

19-385

Date: 

September 1, 2020

Author(s):

Tan Li and Jianzhuang Xiao

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The uniaxial compression behavior of concrete with 0.98 to 3.15 in. (25 to 80 mm) large-size recycled coarse aggregate (LRCA) was numerically studied. Most of the errors between results of experimental and numerical simulation are within 5 to 10%. The finite element method was used to compare with the discrete element method (DEM). The results show that with a higher replacement rate of LRCA, the DEM has higher accuracy. Failure image of models shows that when the strength of LRCA is lower, the influence of LRCA content is more obvious to cracking patterns of concrete. Kinetic curves show that the cracking resistance of concrete with LRCA is lower than normal concrete and the logarithm of the box-counting dimension has a good linear relationship with the replacement of LRCA, which shows that cracks in the concrete with LRCA have obvious fractal features.

DOI:

10.14359/51725976


Document: 

19-374

Date: 

September 1, 2020

Author(s):

D. Marcon Neto, C. Effting, A. Schackow, I. R. Gomes, G. Aurélio Cifuentes, and D. Ganasini

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

In this work, concretes with high levels of fly ash replacing portland cement were elaborated. The concretes’ properties in the fresh state (consistency, workability, and heat of hydration) and in the hardened state (compressive strength, modulus of elasticity, conductivity, void index, water absorption, and density) were measured. Microstructural and thermal characterization were performed. Numerical simulations were performed to analyze the heat exchange during the cement hydration process. Statistical analysis was adequate, and a proposed regression model was validated for the high-volume fly ash concrete, with 60% replacing the portland cement. This concrete presented values of mechanical strength (33.38 ± 3.99 MPa) and modulus of elasticity (38.58 ± 0.81 GPa) which confirms its use as structural concrete. This concrete showed low heat of hydration, a reduction of 23% in relation to the reference concrete (without fly ash) during its curing process, and its microstructure presented a lower level of cracking.

DOI:

10.14359/51725783


Document: 

19-320

Date: 

July 1, 2020

Author(s):

Bruce Menu, Thomas Jacob-Vaillancourt, Marc Jolin, and Benoit Bissonnette

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The experimental program reported in this paper sought to evaluate the efficiency of a range of curing methods in view of minimizing the evaporation rate at the surface of freshly placed shotcrete and preventing the detrimental consequences of early-age shrinkage. CSA A23.1-14 states that severe drying conditions should be considered to exist when the surface moisture evaporation rate exceeds 0.50 kg/m2/h (0.1 lb/ft2/h). In fact, the environmental conditions that lead to such evaporation rates are regularly experienced on construction sites, requiring that adequate protection of the concrete surface be carried out in a timely manner after placement. This research effort is aimed at quantifying the influence of selected curing methods upon the early-age moisture loss and the resulting shrinkage. The results show that early-age volume change of freshly sprayed shotcrete can be significantly reduced by adequate surface protection. Among the investigated methods, moist curing is found to be the most effective.

DOI:

10.14359/51724624


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