Search

Currently, fire in building is one of the most serious disasters. With the increase of basic construction items in western China, ordinary medium sand resource no longer met with the need of engineering. Compressive strength experiments of concrete produced with desert sand after elevated temperature were carried out in this paper. The effects of desert sand replacement rate (DSRR), temperature and cooling regime on the mechanical performances of concrete produced with desert sand were analyzed. XRD and SEM experiments were also conducted to study the microstructure of concrete produced with desert sand after elevated temperature. Experimental results showed that the cubic compressive strength of concrete produced with desert sand increased firstly, and then declined with temperature. Whereas, the prismatic compressive strength and elasticity modulus of concrete produced with desert sand under static compression declined with temperature. With the enhancement of DSRR, the elasticity modulus under static compression, cubic compressive strength and prismatic compressive strength of concrete produced with desert sand after elevated temperature increased firstly, and then declined, the maximum value of which was reached when DSRR amounted to 40%. Regression models were established to predict the mechanical performances of concrete produced with desert sand after elevated temperature, which were in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Polymer-modified concrete and fiber concrete are two excellent paving materials that improve the performance of some concrete, but the performance of single application material is still limited. In this paper, polymer-modified concrete with strong deformation and fiber concrete with obvious crack resistance and reinforcement effect were compounded by using the idea of composite material design so as to obtain a high-performance pavement material. The basic mechanical properties of high-content hybrid fiber–polymer-modified concrete, such as workability, compression, flexural resistance, and environmental durability (such as sulfate resistance) were studied by using the test regulations of cement concrete in China. The main results were as follows. (1) The hybrid fiber–polymer concrete displayed reliable working performance, high stiffness, and a modulus of elasticity as high as 35.93 GPa. (2) The hybrid fiber–polymer concrete had a compressive strength of 52.82 MPa, which was 31.2% higher than that of the plain C40 concrete (40.25 MPa); the strength of bending of the hybrid concrete was 11.51 MPa, 191.4% higher than that of the plain concrete (3.95 MPa). (3) The corrosion resistance value of the hybrid fiber–polymer concrete was 81.31%, indicating its adjustability to sulfate attack environments. (4) According to cross-sectional scanning electron microscope (SEM) images, the hybrid fiber–polymer concrete was seemingly more integrated with a dense layer of cementing substance on its surface along with fewer microholes and microcracks as when compared to the ordinary concrete. The research showed that hybrid fiber–polymer concrete had superior strength and environmental erosion resistance and was a pavement material with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Aims Atmospheric nitrogen (N) deposition influences tree hydraulic architecture and thus the growth and survival; but the responses of leaf hydraulic traits remain uncertain, and may vary with species or plant functional types. Methods We used the 16-year N addition experiment (10 g N m−2 year−1) on Fraxinus mandshurica (ash, broadleaf angiosperm) and Larix gmelinii (larch, conifer gymnosperm) plantations in northeastern China and examined the effect of N addition on their leaf hydraulics. We measured the leaf pressure–volume traits by the bench drying method and quantified the maximum leaf hydraulic conductance (K leaf_max) and resistance to embolism (P 50leaf) by the timed rehydration method. Important Findings Larch had higher K leaf_max and stronger drought tolerance (i.e. lower relative water content at turgor loss point (RWCtlp) and modulus of elasticity (ε), and more negative P 50leaf) than ash. N addition increased the leaf osmotic potential at turgor loss (π tlp) and full turgor (π 0), and leaf capacitance (C leaf_mass) for ash but not for larch, indicating that ash is more sensitive to N addition. N addition consistently increased K leaf_max and P 50leaf values for both species. π tlp and π 0 were positively while C leaf_mass was negatively correlated with leaf density (LD) for ash. K leaf_max was positively but P 50leaf was negatively related with LD for larch. There were negative relationships between K leaf_max and P 50leaf for both species. Overall, our findings suggest that long-term N addition decreases the leaf drought tolerance for these two important tree species, which improve the understanding of the tree hydraulic performance under N deposition. [ABSTRACT FROM AUTHOR]

Use of mangrove ecosystems for coastal flood protection requires reliable predictions of mangrove wave attenuation, especially if this capacity lessens due to storm‐induced forest damage. Quantifying and understanding the variation in drag forces and mechanical properties of mangrove vegetation can improve assessment of mangrove protective capacity. We studied five mangrove species common in the subtropical Pearl River Delta, south China. The studied species range from typically landward‐occurring to more seaward‐occurring pioneer species. We sampled across seven sites in the delta to study the impact of salinity on mechanical properties. We quantified strength and flexibility of branches (branch strength and flexibility related to branch diameter, modulus of rupture and modulus of elasticity), leaf strength (leaf attachment strength related to leaf size, and leaf mass per area) and drag properties (drag force related to surface area and drag coefficient). For all tested species, larger branch diameters resulted in higher mechanical strength. Larger leaf size resulted in larger peak pulling forces and larger branch surface area resulted in stronger drag forces. Notably, species that generally occur lower in the intertidal zone, where exposure to wind and waves is higher, had relatively stronger branches but more easily detachable leaves. This may be regarded as a damage‐avoiding strategy. Across the seven field sites, we found no clear effect of salinity on mangrove mechanical properties. This study provides a mechanistic insight in the storm damage process for individual mangrove trees and a solid base for modeling storm (surge) damage at the forest scale. [ABSTRACT FROM AUTHOR]

• 52 tensile coupons of high-performance bolt material are tested. • Effects of test strain-rate on the elevated temperatures are clarified. • Elevated-temperature behaviour of the steel is elucidated at microstructure level. • Prediction equations are proposed for elevated-temperature performance. • Constitutive model of full-range stress-strain relation is developed. Mechanical properties of steel at elevated temperatures are critical to the fire-resistant analysis and the fire safety design of steel structures. Thus, one solution for improving the fire resistance is use of high-performance (HP) steel, such as fire-resistant (FR) steel. However, practical use of the FR steel in steel structures implies requirements of sufficient fire resistance for the high-strength (HS) bolts as well, so that the loading capacities of bolted connections commonly used in steel structures can be guaranteed in case of fire. In this paper, material properties of grade 10.9 HP bolts recently developed in China, possessing both fire resistance and corrosion resistance, are tested at various elevated temperatures. Their stress-strain curves, modulus of elasticity, yield strength, ultimate tensile strength (UTS), and elongation percentage after fracture are obtained. These results are compared with that of conventional HS bolts and with reduction factors given in national standards. Constitutive models and prediction equations of the HP bolts at elevated temperatures are proposed. Besides, the relationship between degradation in macro mechanical properties and change in microstructure is clarified. The research outcomes may provide essential bases for the fire response analysis of steel structures applying the FR steel and the HP bolts. [ABSTRACT FROM AUTHOR]

Study of frozen rock mechanical properties is necessary for safe application of the artificial ground freezing method in excavation of Chinese western water-rich soft rock layers. Triaxial compression tests and NMR test for samples from the western Jurassic sandstone were performed to investigate rock mechanical properties affected by low temperature and confining pressure. The results show mechanical parameters such as peak strength, cohesion, internal friction angle, residual strength, and elasticity modulus increased with the decreasing temperature under stable pressure, and the above parameters increased with the increasing confining pressure at a certain temperature. In particular, the growth rate of the rock strength would decline when the temperature was below −10°C in this study. Strength attenuation coefficients increased with the decreasing temperature, which indicated higher brittleness, whereas plastic characters got more obvious with the increasing confining pressure at a stable temperature. Furthermore, during the first two freezing stages, porosity decreased sharply with obvious increase of pore (crack) ice content, while porosity varied little at the third stage, which was the reason for the growth rate of rock strength declining with continuous low temperature from microcosmic point of view. [ABSTRACT FROM AUTHOR]

Mudstones of Bayanhua Formation are characterized by high porosity, large content of swelling clay minerals, and weak cementation due to its late diagenesis in Wujianfang Basin, eastern Inner Mongolia, China. Mechanical properties heavily deteriorate during water absorption or dehydration, resulting in underground engineering instability. To study water absorption/dehydration and mechanical response for weakly cemented mudstones, two sets of weathering routes, namely, higher relative humidity (RHs) and lower RHs, are performed by using a self-developed weathering instrument, which can achieve environmental control and real-time weight measurement. The water migration is logged by nuclear magnetic resonance (NMR). Finally, uniaxial compression tests are carried out on weathered samples to study their mechanical properties. The results show that dehydration occurs even under the 70% RH condition, due to their higher initial water content of more than 10%, and the dehydration content is exponential over time under the 60% RH condition. Variations of T2 spectrum reflect the water migration when the surrounding humidity changes. The maximum peak of the transverse relaxation time (T2) moves left during dehydration and shifts to the right when adsorbing water. The uniaxial compressive strength (UCS) does not increase with the decreasing RH at any time, which is distinct from elasticity modulus (E). There is a critical RH at 50%, indicating that damages accumulate when the RH is lower than 50%. Tensile fracture occurs for the most types of weathered samples, and shear failure only occurs under the drying condition. [ABSTRACT FROM AUTHOR]

In this study, 145 poplar (Populus × euramericana cv.'74/76') seedlings, a common plantation tree species in China, were selected and their ultrasonic velocities were measured at four timepoints during the first growth year. After that, 60 poplar seedlings were randomly selected and cut down to determine their acoustic velocity, using the acoustic resonance method. The effects of influencing factors such as wood green density, microfibril angle, growth days, and root-collar diameter on acoustic speed in seedlings and the relationship between ultrasonic speed and acoustic resonance speed were investigated and analyzed in this work. The number of specimens used for investigating growth days and root-collar diameter was 145 in both cases, while 60 and two specimens were used for investigating wood density and the microfibril angle, respectively. The results of this study showed that the ultrasonic speed of poplar seedlings significantly and linearly increased with growth days, within 209 growing days. The ultrasonic velocity of poplar seedlings has a high and positive correlation with growth days, and the correlation was 0.99. However, no significant relationship was found between the ultrasonic velocity and root-collar diameter of poplar seedlings. Furthermore, a low and negative relationship was found between wood density and ultrasonic speed (R2 = 0.26). However, ultrasonic velocity significantly decreased with increasing microfibril angle (MFA) in two seedlings, and thus MFA may have an impact on ultrasonic speed in poplar seedlings. In addition, ultrasonic velocity was found to have a strong correlation with acoustic resonance velocity (R2 = 0.81) and a good correlation, R2 = 0.75, was also found between the dynamic moduli of elasticity from ultrasonic and acoustic resonance tests. The results of this study indicate that the ultrasonic technique can possibly be used to measure the ultrasound speed of young seedlings, and thus early screen seedlings for their stiffness properties in the future. [ABSTRACT FROM AUTHOR]

Moso bamboo (Phyllostachys edulis (Carriere) J. Houzeau), native to China, is one of the most economically and ecologically important bamboo species. Since the economic interests and the strong clonality, it has been widely cultivated in southern China, which inevitably reduces the natural stands and leads to gene loss in this species. In this study, three natural populations of Moso bamboo distributed in Anhui, Guangxi, and Zhejiang province, were used to analyze the correlation between phenotypic traits, cell structure, and material properties from the perspective of phenotypic, genetic, and environmental. Among those traits and properties, fiber width was correlated with wall thickness at breast height and average nodes length under branch positively. Leaf length was correlated positively with fiber lumen diameter and parenchyma lumen diameter. Furthermore, it showed a very close correlation between moisture content, bending strength, modulus of elasticity, and diameter at breast height, clear height, and leaf length. The lumen diameter of fiber cell wall thickness is positively correlated with bending strength and modulus of elasticity. Density is positively correlated with parenchyma cell wall thickness. The experimental design is relatively detailed and representative, and the workload is huge. This study reflects the research objectives with scientific and rational experiments and data. This study will analyze the differences of various indicators from the perspective of genetic to build a bridge between micro-structure and macro-structure for rational utilization of the whole area of Moso bamboo resources in China. [ABSTRACT FROM AUTHOR]

The density and modulus of elasticity (MOE) distribution can provide information on the effectiveness of parametric and non-parametric methods in calculating the characteristic value of MOE. In this study, we aim to determine the optimal distribution model of the actual measured data of the lumber. We also estimate the lumber's MOE characteristic value and compare the difference in density and MOE between natural and planted larch. Approximately 1200 pieces of dimension lumber of 4 m × 140 mm × 40 mm in size, made from larch and planted larch, were obtained, tested, and the corresponding standard MOE value was calculated. Results revealed the 3-parameter Weibull distribution to be optimal in fitting the natural and planted larch distributions. The parametric method proved effective in calculating the characteristic value of both larch groups, with characteristic MOE values of 9.73 kN/mm2 and 8.84 kN/mm2, and characteristic density values of 530 kg/m3 and 460 kg/m3 for natural and planted larch, respectively. Moreover, the MOE and density values followed grades C40 and C35. Thus, the conclusion is that the parametric method should be used to determine these characteristic values for natural and planted larch. [ABSTRACT FROM AUTHOR]