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International Concrete Abstracts Portal

Showing 1-5 of 109 Abstracts search results

Document: 

20-011

Date: 

November 1, 2020

Author(s):

Xiao-Yong Wang

Publication:

Materials Journal

Volume:

117

Issue:

6

Abstract:

Carbonation of concrete can cause the uptake of CO2 and alleviate the CO2 emissions burden of the concrete industry. This study shows a procedure for evaluating the CO2 uptake of fly ash (FA)-blended high-strength concrete, considering both the service and recycling stages. First, a blended cement hydration model is proposed to evaluate the contents of carbonizable substances, porosity, and CO2 diffusivity. In the service stage, a one-dimensional carbonation model is proposed for evaluating carbonation depth. In the recycling stage, an unreacted core model is proposed for evaluating the carbonation process of spherical crushed concrete. Second, CO2 uptake models are proposed for the service and recycling stages, considering concrete materials, structural elements, and environmental exposure. The total CO2 uptake ratio is determined as the sum of CO2 uptake in the service and recycling stages. The calculation results show that, as the FA replacement ratio increases from 0 to 40%, the CO2 uptake ratio in the service stage increases from 2.78 to 4.72%, and the total CO2 uptake ratio increases from 18.9 to 20.8%. As the surface to volume ratio of the structural element increases, or the size of particles of crushed concrete decreases, the rate of CO2 uptake increases but the total CO2 uptake ratio does not change.

DOI:

10.14359/51725982


Document: 

18-535

Date: 

September 1, 2020

Author(s):

Jun-Zhi Zhang, Xiao-Yun Zhou, Jing Zhao, Meng Wang, Yan-Hong Gao, and Yu-Rong Zhang

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

According to the main meteorological parameters and chloride concentration of field exposure tests, indoor artificial climate and dry-wet cycle simulated tests were designed to investigate the similarity of apparent and instantaneous diffusion coefficients in different ambient environments. Results show that chloride diffusion coefficients increased with water-cement ratio (w/c) and decreased with exposure time, regardless of the environment. Besides, instantaneous diffusion coefficients are all less than the corresponding apparent diffusion coefficients; their differences decrease with the increasing of w/c and show first a decrease and then gradually an increasing trend with exposure time. Environmental factors have little effect on the similarity constant of instantaneous diffusion coefficients. A quadratic function can be used to describe the relationship between age reduction factors of apparent and instantaneous diffusion coefficients and w/c in different environments. According to the Second Similarity Theorem, specimens exposed to a natural tidal environment for 240 days can be simulated by that exposed to an artificial climate simulated environment for 80 days effectively.

DOI:

10.14359/51727021


Document: 

18-512

Date: 

July 1, 2020

Author(s):

Mahdi Valipour and Kamal H. Khayat

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

DOI:

10.14359/51724613


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


Document: 

19-253

Date: 

May 1, 2020

Author(s):

K. Tamanna, M. Tiznobaik, N. Banthia, and M. Shahria Alam

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Using recycled scrap tire and construction and demolition waste as aggregates in concrete will not only facilitate an environmentally sustainable solution to solid waste disposal but also will significantly contribute to alleviating the ever-growing demand for natural aggregates in concrete production. However, only limited studies focused on the use of rubberized recycled aggregate concrete (RRAC), which lacks in-depth scrutinization of its material behavior with respect to conventional concrete. The first stage of this study is focused on investigating the effect of pre-treatment of crumb rubber (CR) with three levels of NaOH concentration on rubberized mortar specimens. The second stage consists of an experimental investigation on the mechanical behavior of concrete comprising CR and recycled concrete aggregate (RCA) each at three replacement levels of natural fine and coarse aggregates, respectively, at a water-cement ratio (w/c) of 0.34. The results indicate RRAC yields satisfactory compressive and flexural behavior for use in structural concrete.

DOI:

10.14359/51722409


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