Fracture Behaviour of Real Coarse Aggregate Distributed Concrete under Uniaxial Compressive Load Based on Cohesive Zone Model.

Two-dimensional meso-scale finite element models with real aggregates are developed using images obtained by digital image processing to simulate crack propagation processes in concrete under uniaxial compression loading. The finite element model is regarded as a three-phase composite material composed of aggregate, mortar matrix and interface transition zone (ITZ). Cohesive elements with traction-separation laws are used to simulate complex nonlinear fracture. During the experiment, digital image correlation (DIC) was used to obtain the deformation and cracks of the specimens at different loading stages. The concept of strain ratio is proposed to describe the effectiveness of simulation. Results show that the numerical strain ratio curve and stress-strain curves are both in good agreement with experimental data. The consistency between the cracks obtained by simulation and those obtained by DIC shows the good performance of cohesive elements as well as the effectiveness of simulation. In summary, the model is able to provide accurate predictions of the whole fracture process in concrete under uniaxial compression loading.

On Phase Identification of Hardened Cement Pastes by Combined Nanoindentation and Mercury Intrusion Method.

The micro-mechanical properties of hardened cement paste can be obtained by nanoindentation. Phases at different locations can generally be determined by using the Gaussian mixture model (GMM) method and the K-means clustering (KM) method. However, there are differences between analysis methods. In this study, pore structure and porosity of hardened cement paste aged three, seven, and 28 days were obtained by mercury intrusion porosimetry (MIP), and their micro-mechanical properties were obtained by the nanoindentation method. A new method, GMM-MIP and KM-MIP, was proposed to determine the phase of hardened cement paste based on the pore structure and nanoindentation results. The results show that GMM-MIP and KM-MIP methods are more reasonable than GMM and KM methods in determining the phase of hardened cement paste. GMM-MIP can be used to obtain reasonable phase distribution. If the micro-mechanical properties of each phase in hardened cement paste do not satisfy the normal distribution, the GMM method has significant defects.

Influence of Parent Concrete Properties on Compressive Strength and Chloride Diffusion Coefficient of Concrete with Strengthened Recycled Aggregates.

Parent concrete coming from a wide range of sources can result in considerable differences in the properties of recycled coarse aggregate (RCA). In this study, the RCAs were obtained by crushing the parent concrete with water-to-cement ratios (W/Cparent) of 0.4, 0.5 and 0.6, respectively, and were strengthened by carbonation and nano-silica slurry wrapping methods. It was found that when W/Cparen was 0.3, 0.4 and 0.5, respectively, compared with the mortar in the untreated RCA, the capillary porosity of the mortar in the carbonated RCA decreased by 19%, 16% and 30%, respectively; the compressive strength of concrete containing the carbonated RCA increased by 13%, 11% and 13%, respectively; the chloride diffusion coefficient of RAC (DRAC) containing the nano-SiO2 slurry-treated RCA decreased by 17%, 16% and 11%; and that of RAC containing the carbonated RCA decreased by 21%, 25% and 26%, respectively. Regardless of being strengthened or not, both DRAC and porosity of old mortar in RCAs increased with increasing W/Cparent. For different types of RCAs, DRAC increased obviously with increasing water absorption of RCA. Finally, a theoretical model of DRAC considering the water absorption of RCA was established and verified by experiments, which can be used to predict the DRAC under the influence of different factors, especially the water absorption of RCA.

Functional self-assembled peptide scaffold inhibits tumor necrosis factor-alpha-induced inflammation and apoptosis in nucleus pulposus cells by suppressing nuclear factor-κB signaling.

Although nucleus pulposus (NP) tissue engineering has achieved tremendous success, researches still face the huge obstacles in maintaining cell survival and function. A novel functional self-assembled peptide RADA-KPSS was constructed by conjugating BMP-7 short active fragment (KPSS) to the C-terminus of RADA16-I that displays anti-inflammatory and anti-apoptosis effects. However, whether this functional self-assembled RADA-KPSS peptide can alleviate inflammation and NPC apoptosis induced by tumor necrosis factor-alpha (TNF-α) has not been studied. Therefore, we cultured NPCs treated with TNF-α for 48 h with the RADA-KPSS peptide, and compared the results to those with RADA16-I peptide. The cell apoptosis rate, inflammatory mediator secretion, expression of matrix-degrading enzymes, and extracellular matrix (ECM) protein levels were evaluated. The expression of nuclear factor-κB-p65 (NF-κB-p65) protein was also tested. TNF-α-treated NPCs cultured with the RADA16-I peptide showed up-regulated gene expression for matrix-degrading enzymes, such as matrix metalloproteinases-3 (MMP-3), MMP-9, and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-4), and down-regulated gene expression for ECM proteins such as aggrecan, collagen II, and Sox-9. The RADA-KPSS peptide could attenuate the expression of MMP-3, MMP-9, and ADAMTS-4, promote accumulation of ECM proteins, and increase secretion of glycosaminoglycan as compared with the RADA16-I peptide. Moreover, the TNF-α-damaged NPCs was further demonstrated to inhibit NF-κB-p65, IL-1, IL-6, and prostaglandin E-2 proteins and decrease cell apoptosis in RADA-KPSS peptide. In conclusion, the functional self-assembled RADA-KPSS peptides have anti-inflammatory and anti-apoptotic effects by promoting anabolic processes and inhibiting catabolic processes in intervertebral disk degeneration. These peptides may be feasible for clinical applications in NP tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1082-1091, 2018.