Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
ISSN-L : 1346-8014
Volume 17, Issue 6
Displaying 1-7 of 7 articles from this issue
Scientific paper
  • Hailong Ye, Zhijian Chen
    2019 Volume 17 Issue 6 Pages 269-281
    Published: June 07, 2019
    Released on J-STAGE: June 07, 2019

    Alkali-activation of high-volume fly ash (HVFA) is a viable approach to produce durable cementitious binders with faster and stronger strength development than its water-activated counterparts. However, the use of alkaline activator increases the risk of alkali-silica reaction (ASR) in these systems. In this work, the compressive strength and ASR susceptibility of alkali-activated fly ash-OPC mortars containing reactive aggregate are studied. The results show that in comparison to plain water-activated fly ash-OPC mixture, the alkali incorporation at a low concentration improves strength development only when the fly ash replacement ratio is higher than about 80%; however, excessive alkali has an adverse influence. Regardless of activator type and dosage, alkali-activated fly ash-OPC mortars are ASR innocent as assessed in the accelerated mortar bar test and scanning electron microscopic analysis, provided that the fly ash percentage higher than about 40%. The mechanism for the insignificant ASR expansion and damage in alkali-activated HVFA mortars is likely attributed to the low calcium content that prevents gelation of deleterious and expansive ASR products.

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  • Ya Wei, Wei-Kang Kong, Cheng Wan, Ya-Qiong Wang
    2019 Volume 17 Issue 6 Pages 282-294
    Published: June 15, 2019
    Released on J-STAGE: June 15, 2019

    Fast and accurate assessment of fire-damaged concrete structures is of great significance for later maintenance and reuse. The traditional methods require large amount of experimental efforts, and some other new technologies are expensive and their applicability still needs further investigation. In view of this, a colorimetric method based on the optical analysis is proposed to evaluate the fire damage of the concrete in terms of the translation of the color coordinates in the chromaticity diagram. Fire damage experiment was first conducted on concrete cubes with two different strengths. Photos were then taken under the conditions of daylight vs. fluorescent light, and manual white balance vs. auto white balance. The chromaticity diagram is constructed to represent the relationship between the coordinates of the concrete colors and the maximum temperature that concrete was subject to. The conditions under the daylight and the manual white balance are recommended for taking photos to construct the chromaticity diagram, and a linear equation was obtained to estimate the heating duration and the maximum temperature that the concrete exposed to from the coordinates of the concrete color. The results of this study will advance the technology of non-destructively assessing the fire-damaged structures.

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  • Quang Dieu Nguyen, Mohammad Shakhaout Hossain Khan, Tengfei Xu, Arnaud ...
    2019 Volume 17 Issue 6 Pages 295-308
    Published: June 20, 2019
    Released on J-STAGE: June 20, 2019

    A concrete mix (FNS25) including 50% natural sand replacement by ferronickel slag (FNS) sand and 25% ordinary portland cement (OPC) substitution by fly ash (FA) was considered to mitigate the risk of early-age cracking in fly ash blended cement-based concrete. Experiments were carried out to accurately quantify early-age shrinkage and tensile creep and assess their influence on early-age cracking in reinforced concrete members. The results show the free shrinkage strain is not influenced by either fly ash or FNS significantly, whereas the tensile creep of FNS25 is significantly larger than that of both OPC100 and FA20. Both restrained ring test and simulations on reinforced concrete members confirm that partly replacing conventional sand by FNS sand reduces the risk of early-age cracking. Microstructural analysis of the Interface Transition Zone (ITZ) of FNS sand shows that excess in Portlandite is absent in FNS sand ITZ leading to a higher early-age tensile strength of FNS25 concrete.

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  • Brice Delsaute, Stéphanie Staquet
    2019 Volume 17 Issue 6 Pages 319-334
    Published: June 25, 2019
    Released on J-STAGE: June 25, 2019

    This paper aims at identifying the effect of the substitution of natural coarse gravel and sand by recycled gravel and sand on the early age development of the volume change and the mechanical properties since setting. For this purpose, a new experimental testing protocol for the characterization of cementitious materials at early age is used. This new approach is based on the repeated application of thermal variation and loading using a newly developed testing device. The high porosity and absorption of the recycled aggregate and sand induce a strong reduction of the autogenous deformations, the modulus of elasticity and the strength during the hardening process. A significant increase of the basic creep phenomenon is observed when using recycled aggregate, especially with recycled sand and at very early age. An elastic and viscoelastic calculation of the restraint of the free deformations shows that the use of recycled gravel and sand decreases the risk of cracking in sealed condition.

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  • Dirk Schlicke, Lýdia Matiašková
    2019 Volume 17 Issue 6 Pages 335-349
    Published: June 28, 2019
    Released on J-STAGE: June 28, 2019

    The distribution of restraint stresses in bottom-restrained walls is an important information for the efficient crack control of wall-like concrete members. Practical examples are retaining walls, bridge abutment walls or tank walls, for which the results can be used in order to assess the risk and intensity of harmful separating cracks over the wall height.

    Different solutions exist for the determination of these stress distributions, ranging from advanced computational methods over analytical and semi-analytical solutions up to empirical approaches. The aim of the present contribution is twofold. On the one hand, the general applicability as well as commonalities and differences of the investigated solutions were demonstrated by using them for the analysis of a given demonstration example. On the other hand, a para-metric study was carried out in order to assess the dependence of the prediction quality of the applied solutions on changing conditions. Altogether it was found that advanced computational methods and analytical or semi-analytical solutions showed a good agreement for common design tasks. Solutions with empirical modifications, however, were proved to be less satisfying from engineering perspective due to predefined parameters or mechanically inconsistent modifications.

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  • Qiang Zeng, Zhendi Wang
    2019 Volume 17 Issue 6 Pages 350-364
    Published: June 28, 2019
    Released on J-STAGE: June 28, 2019

    Most concrete structures service under external loads and the studies of the external-loading effects on chloride diffusivity in these porous media remain insufficient. This paper reports a relationship between porosity variation and external load inspired by poroelastic theory. This porosity-load relationship, together with an empirical equation for chloride diffusivity versus porosity, provides an explicit diffusivity-load model for saturated porous media. Without the specific assumptions of geometries of the pores and the matrix phases, the present model shows flexible expressions. Comprehensive analyses are performed to demonstrate the effects of external load and initial porosity on the porosity variation, chloride diffusion coefficient, penetration depth and durable time of specific cement-based samples. Two models reported in the literature are employed for the purpose of comparison. Overall, initial porosity is a primarily dominative factor affecting the chloride diffusivity, penetration profile and durability of cement-based porous materials. Within the elastic regime, external loads only influence the outcomes in limited degrees.

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Technical report
  • Ukyo Musya, Yuki Katagiri, Yuya Takase, Takahide Abe, Keita Sakamoto, ...
    2019 Volume 17 Issue 6 Pages 309-318
    Published: June 22, 2019
    Released on J-STAGE: June 22, 2019

    When buildings are seismically retrofitted, new members are connected to existing members through a roughened concrete surface, which is created using a vibration drill. However, there are few studies on such roughened concrete. When the roughened concrete area ratio is small, bearing failure occurs. On the other hand, shear failure occurs when the roughened concrete area ratio is large. In this paper, the focus was on bearing failure. When the roughened concrete area ratios were 0.1 to 0.3, the failure mode was bearing failure. To evaluate shear strength, the shapes of roughened concrete were measured using a laser displacement sensor and 3D scanner. Moreover, shear loading tests were conducted. Finally, a shear strength formula was proposed considering the concrete compressive strength, Young’s modulus, and vertical projection area. By comparing the test results with the calculated values, it is concluded that the proposed formula estimated the test results well. Finally, this paper is an extension of the authors’ previous work [Musya et al., (2019). “Supported Strength Formula of Roughened Concrete Using Shape Measurement Value by 3D-scanner.” AIJ Journal of Technology and Design, 25(59), 55-60].

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