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Compressive deformation/failure of cement–asphalt mortars

Liu Yongliang, Mu Mulan, Wang Junjie

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e174, 2023

EN

Cement–asphalt mortar (CAM) has been widely used as a cushion layer in prefabricated concrete slab tracks. However, the deformation and failure of different CAMs under compression are scarcely understood. In this study, therefore, we studied the compressive deformation and failure modes of CAMs with different asphalt–cement ratios (A/Cs or m(A)/m(C) = 0.2 ~ 1.0) together with the temperature effects, to understand the mechanisms behind their mechanical behaviour. Results indicated that, at room temperature, CAMs with low A/Cs (0.2 ~ 0.4), namely CAM-Ls, deformed and failed in a quasi-brittle manner, whereas CAMs with high A/Cs (0.8 ~ 1.0), namely CAM-Hs, were more like ductile materials. The temperature effect could be negligible for CAM-Ls, but significant for CAM-Hs. Low temperatures would cause a ductile-to-brittle transition in CAM-Hs and high temperatures would pose an adverse effect on their deformation and failure under compression. To understand the deformation and failure mechanisms of different CAMs and the temperature effects, microstructural models for CABs with relevant A/Cs were proposed. The microstructural models of CABs demonstrated that the compressive deformation and failure of CAMs depend primarily on their CABs. It is also indicated that, experimentally and theoretically, the boundary A/C value between CAM-Ls and CAM-Hs might be around 0.6, below which the hardened cement paste (hcp) form the matrix of the CAM, whilst above which the asphalt binder turns to the primary continuous phase in the CAB. Due to the microstructure change in CABs with the increasing A/C, the CAMs transitioned from quasi-brittle to ductile materials under compression.

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Anisotropy on the ductile-to-brittle transition for rock in process of drilling

He Mingming, Wang Jing, Yuan Zhuoya, Wang Haoteng, Ma Xudong, Luo Bo

Acta Geophysica

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2023

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Vol. 71, no. 5

2107--2124

EN

Anisotropy is an inherent property of rocks. It refers to the different response of the rock properties in each direction. Understanding the anisotropy characteristics of rock failure by drilling has practical applications in improving drilling efficiency, especially for engineering applications. In this paper, a criterion is established to clarify the ductile-to-brittle transition in the drilling process of rock. Moreover, a new anisotropy index has been proposed to evaluate the effect of anisotropy on the critical state of the ductile-to-brittle transition. The digital drilling tests are conducted on six types of rock to study the drilling mechanical performance in the X, Y, and Z directions. The anisotropy characteristics of drilling parameters and mechanical specific energy (MSE) are analysed at the critical state of ductile–brittle failure. The results show that the critical state of ductile–brittle failure is manifested as an inflection point of the depth of cut. The evolution of MSE is fitted as two linear functions, which corresponds to the two stages. The order of anisotropy in MSE is obtained as: gneiss > slate > red sandstone > granite > argillaceous sandstone > sandstone. The anisotropy in the uniaxial compressive strength and MSE for different rock types has the same sequences. The advantages of the proposed method in determining rock anisotropy are illustrated.

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Analysis of estimation of parameters in 3P-Weibull Kjc distribution: sample size effect

Allas Diego Omar, Perez-Ipiña Juan Elías, Berejnoi Carlos

Engineering Transactions

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2021

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Vol. 69, iss. 2

195--210

EN

The minimum sample size for a good estimation of the parameters in both three-parameter Weibull KJc distribution (3P-W) and ASTM E1921 methods was analyzed. Additionally, the estimations provided by maximum likelihood (ML) and linear regression (LR) were compared. Fracture toughness sets with different sample sizes were randomly generated following a 3P-W with parameters corresponding to experimental datasets from the Euro round robin fracture toughness test. Then, LR and ML were applied to the sets and the parameters were estimated. Standard deviation (SD) and interquartile range (IQR) were employed to analyze the goodness of fit. The results of this paper were consistent with the necessity of large sample sizes (over 30) to find a representative value of the threshold and shape parameters. However, the scale parameter showed a lower scatter and can be estimated with a smaller sample size (around six samples), as used in the standard ASTM E1921-19b