摘要：
UHPC tensile strength is often measured indirectly through splitting tests and flexural tests substituted for direct tensile tests. However, the tensile strain-hardening and multiple cracking performance of UHPC is highly sensitive to the testing techniques and the specimen shape used. In this paper, the double-edge wedge splitting (DEWS) test and direct tensile test were performed to evaluate the tensile strain-hardening properties and damage evolution of UHPC. The digital image correlation (DIC) technique was utilized to detect the cracking opening displacement (COD) and evaluate the damage evolution in the tensile stress vs. crack opening response. The results show that the tensile strength between DEWS and direct tensile tests in UHPC strain-hardening and strain-softening stages had a high correlation value of 0.98. Moreover, the difference in cracking strengths in the DEWS and direct tensile tests was less than 5 %, and those of peak strengths were fewer than 5.23 MPa. An improvement in relative COD increment was observed in DEWS and direct tensile tests before 90 % of the peak load at the post-peak branch. Results indicate that the DEWS testing is an efficient way to evaluate the UHPC tensile failure properties.
摘要：
Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature var-iations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the nu-merical analysis. Various temperature ranges (-20 to-10 degrees C,-10 to 0 degrees C), cyclic cooling rates (10 degrees C/h, 20 degrees C/ h), low-temperature performance cooling rates (10 degrees C/h, 8 degrees C/h, 6 degrees C/h, 4 degrees C/h, 2 degrees C/h) and pre-crack di-mensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.
通讯机构：
[Wu, H ] C;[Zhu, P ] T;Cent South Univ, Sch Civil Engn, Changsha 410075, Hunan, Peoples R China.;Tongji Univ, Coll Civil Engn, Shanghai 200092, Peoples R China.;Tongji Univ, Key Lab Performance Evolut & Control Engn Struct, Minist Educ, Shanghai 200092, Peoples R China.
关键词：
Introduction;Materials and Methods;Results;Discussion;Conclusion;Abstract;Data Availability;Additional Points;Ethical Approval;Consent;Disclosure;Conflicts of Interests;Authors’ Contributions;Funding Statement;Acknowledgements;Acknowledgments;Supplementary Materials;Reference;Dataset Description;Dataset Files;Abstract;Introduction;Introduction and Materials;Introduction and Methods;Materials;Materials and Methods;Methods;Results;Discussion;Results and Discussion;Discussion and Conclusion;Results and Conclusion;Conclusion;Conclusions;Data Availability;Additional Points;Ethical Approval;Consent;Disclosure;Conflicts of Interest;Authors’ Contributions;Funding Statement;Acknowledgements;Supplementary Materials;References;Appendix;Abbreviations;Preliminaries;Introduction and Preliminaries;Notation;Proof of Theorem;Proofs;Analysis of Results;Examples;Numerical Example;Applications;Numerical Simulation;Model;Model Formulation;Systematic Palaeontology;Nomenclatural Acts;Taxonomic Implications;Experimental;Synthesis;Overview;Characterization;Background;Experimental;Theories;Calculations;Model Verification;Model Implementation;Geographic location;Study Area;Geological setting;Data Collection;Field Testing;Data and Sampling;Dataset;Literature Review;Related Works;Related Work;System Model;Methods and Data;Experimental Results;Results and Analysis;Evaluation;Implementation;Case Presentation;Case Report;Search Terms;Case Description;Case Series;Background;Limitations;Additional Points;Case;Case 1;Case 2 etc.;Concern Details;Retraction Details;Copyright;Related Articles
摘要：
Permeable pavement materials are attracting great attention due to the superior benefits in fast drainage, driving safety, and noise reduction effectiveness. This study investigated the sound absorption behaviors of permeable pavement materials, including permeable cement concrete (PCC) and open-graded friction course asphalt mixture (OGFC). The sound absorption coefficients (SACs) of dense-graded cement concrete and dense-graded asphalt mixture were also measured for comparison. The sound absorption test was conducted by the impedance tube method according to ASTM E1050-19. Computed tomography (CT) scanning tests were conducted to obtain the pore characteristics of PCC and OGFC, including porosity distribution, pore size, and coordination number (CN). The porosity distribution, pore size distribution, and CN distribution presented a symmetrical trend of decreasing, then increasing, and then decreasing with the increase of specimen height. When OGFC and PCC showed similar porosities, the pore number of PCC was significantly larger than that of OGFC. Comparisons of the peak SAC and the average SAC were made between PCC and OGFC. Correlations were made between the SAC and the pore characteristics. Results indicated that with increasing porosity, the peak SAC and the average SAC both increased significantly for PCC and OGFC. The characteristic pore size, pore number, and CN distribution together affected the SAC. At the same porosity, OGFC mixtures presented larger average SAC compared to PCC, which was ascribed to the fact that more pores with larger size and a better pore connectivity existed in OGFC mixtures.
期刊：
Construction and Building Materials,2022年357:129376 ISSN：0950-0618
通讯作者：
Yin, Jian(csuyj700930@163.com)
作者机构：
[Li, Yuelin; Li, Jiabin; He, Jiaguo] Katholieke Univ Leuven, Dept Civil Engn, Res Grp RecyCon Mat & Construct, Campus Bruges, B-8200 Brugge, Belgium.;[Yin, Jian] Cent South Univ Forestry & Technol, Sch Civil Engn, Changsha 410004, Hunan, Peoples R China.;[Yuan, Qiang; Huang, Tingjie] Cent South Univ, Sch Civil Engn, Natl Engn Lab High Speed Railway Construct, Changsha 410075, Peoples R China.
通讯机构：
[Jian Yin] S;[Jiabin Li] R;Research Group RecyCon, Materials and Constructions, Department of Civil Engineering, KU Leuven, Campus Bruges, 8200 Bruges, Belgium<&wdkj&>School of Civil Engineering, Central South University of Forestry and Technology, 410004 Changsha, Hunan, PR China
摘要：
The search for eco-friendly grouting materials with excellent workability performance to strike a balance between environmental protection and manipulability is a popular topic in underground engineering. This paper presented a practical and efficient strategy for producing a composite grouting material with microbial polysaccharide gum (CGMG) for pre-reinforcement of shallow underground excavation in a vegetation protection area. The CGMG grout is formulated based on excellent synergistic interactions among cement, water, xanthan gum and sodium aluminate, and an optimal weight proportion of 1, 1.5, 0.01 and 0.004 for cement, water, sodium aluminate and xanthan gum is proposed by orthogonal experimental design. The obtained CGMG shows a fluffy mass structure and high stability (bleeding rate less than 5%), satisfactory early compressive strength (1.5 MPa), and a pumping period of more than 30 min. In particular, the pot experiment results shows that the germination, root growth characteristics, root activity and chlorophyll content were similar in the study group (plant soil injected with CGMG as the growing media) and the control group (plant soil as the growing media) at different growing stages. Moreover, the effectiveness and eco-friendly characteristics of the CGMG were verified by a field grouting application for shallow tunnel excavation in a vegetation protection area. This work provides a new option for grouting in ecologically sensitive areas.
摘要：
The purpose of this paper is to investigate the effect of different methods on reducing the pH value of soil in Porous Sea Sand Concrete Mixtures (PSSCM) through a series of experiments. Thereinto, the X-ray diffraction (XRD) technology was applied to analyzing the mechanism of pH value change, and the relationship between the fundamental performance (effective porosity, sound absorption coefficient and compressive strength) and the optimum mixture proportion of PSSCM successfully. In all experiments, plant varieties which have a high matching degree with PSSCM were screened out, and the vegetation performance of PSSCM was verified by field investigation. Consequently, it is showed that the content of calcium hydroxide in PSSCM was positively correlated with the pH value of soil in PSSCM. The four approaches, adding mineral admixtures, appending acid-modified materials, accelerating carbonization, and immersing Deep penetration sealer (DPS), help reduce the pH value. Among them, the lowest pH value (7.8) was obtained by the addition of 10% silica fume, accelerating carbonization for 28 days, and subsequently immersing in DPS for 28 h. Besides, these methods all reduce PSSCM pore and soil pH value by consuming calcium hydroxide. In addition, the best fundamental performance was obtained on the condition that the water-cement ratio of PSSCM was 0.26 and the effective porosity of PSSCM was 25.95%. Likewise, the matching degree between tall fescue and PSSCM was the best under this pH condition. After 120 days of sowing, their stems were thick and strong, and leaves were green and lush. In the meantime, their rhizomes length exceeds 8 cm. (C) 2020 Elsevier Ltd. All rights reserved.
摘要：
Due to material requirements for grouting in loose deposits, a new polymer-modified cement grout (PMCG) material was designed by addicting polyethylene glycol (PEG), polycarboxylate superplasticizer (PS) and sodium silicate into the cement grout. Then, the properties of PMCG were predicted statistically by using the response surface method (RSM) and the effects of the four parameters (w/c, PEG content, sodium silicate content and PS content) as well as their interaction on the response variables (fluidity, bleeding rate, gel time, and early strength) were investigated. Furthermore, the optimal formulation of PMCG (w/c of 0.9, 8.7% sodium silicate, 4% PEG and 1% PS) can be obtained using a multi-objective optimization technique considering the multi-performance requirements of grouting material in loose deposit. Finally, the macro-performance of the grouting material formed by optimal formulation was validated by a set of experiments. The results demonstrated that the proposed designing method can work effectively in determining the optimal formulation of the grouting material to meet various engineering demands. (C) 2020 Elsevier Ltd. All rights reserved.
作者：
Chunning Deng;Weiqun Cai;Jian Yin;Fen Yang;Linchen Li
期刊：
International Journal of Transportation Engineering and Technology,2019年5(4):97-102 ISSN：2575-1743
作者机构：
[Chunning Deng; Weiqun Cai; Jian Yin; Fen Yang; Linchen Li] College of Civil Engineering, Central South University of Forestry and Technology, Changsha, China
摘要：
Autoclaved aerated concrete (AAC) is a new type of green building material rapidly developed nowadays. Moisture content plays a significant effect on its mechanical properties. In this study, a series of uniaxial compression tests were conducted to evaluate the effect of moisture content on the mechanical behaviors. During the tests, full stress-strain curves were obtained. The influence of water content on AAC stress-strain full curve shape, elastic modulus, peak stress, peak strain and ultimate strain was analyzed. The fitting equations of water content with peak stress, peak strain and elastic modulus were established. The results show that the brittleness of AAC decreased with the increased of water content, and the failure mode gradually transited from brittle to ductile failure. When the water content increased from 0% to 10%, obvious difference in the stress-strain curves can be observed. The peak stress decreased by 20.00% and 11.63% when the moisture content was 5% and 10%, respectively. However, when the water content increased from 10% to 40%, the peak stress decreased slowly. The rising section relation model of AAC stress-strain full curve can be fitted by cubic polynomial, which provided reference basis for finite element analysis.
期刊：
International Journal of Transportation Engineering and Technology,2019年5(4):103-110 ISSN：2575-1743
作者机构：
[Weiqun Cai; Jian Yin; Songyun Wu; Chunning Deng; Fen Yang; Linchen Li; Jiongjun Yuan] College of Civil Engineering, Central South University of Forestry and Technology, Changsha, China
关键词：
Cement Mortar;Flexural Strength;Compressive-flexural Ratio;Polypropylene Fiber;Orthogonal Test
摘要：
In this study, laboratory tests were conducted to investigate the mechanical behaviors of cement mortars incorporated with different admixtures, such as polypropylene fiber (PP), slag, silica fume and fly ash. Orthogonal tests were designed to evaluate the effects of the admixtures on the brittleness. The flexural strengths and the compressive-flexural ratios were selected to evaluate the brittleness. The optimal proportion can be obtained when PP content was 1.6 kg/m3, and the content of fly ash, slag and silica fume was 10%, 20% and 3% of the cement content respectively. Using the optimal proportion, the 3d flexural strength of cement mortar was 5.65 MPa, which was 19% larger than the specimens without the addition of admixtures; the compressive-flexural ratio was 4.1, which was reduced by 19% in contrast to the control group. The flexural strength at 28d was 9.04 MPa, which was 13% higher than the control group; and the compressive-flexural ratio was 4.21, decreasing 24% compared to the control group. SEM technology was utilized to characterize the evolution of the microstructure induced by the addition of mineral admixtures and PP fiber. Results showed that mineral admixtures made the mortars denser, and the PP fiber formed a cross-linking structure, improving the brittle-resistance. The test results provided some guidance for the mixture design of pavement concrete with a high flexural strength and a low brittleness.
