Papers by Keyword: Dynamic Elastic Modulus

Abstract: The use of natural fibers has a great interest due to their damping properties, low density and moderate strength. The effect of incorporating chopped natural fibers, as disperse reinforced phase, on the dynamic or quasi-static elastic modulus of glass fiber laminates is presented. Squares of 32 cm² plain wave glass fiber prepreg with epoxy resin were used in a stacking sequence [0]4. Short length chopped (1-3 mm) natural coir fiber was placed in between of each glass fiber prepreg sheet (4) and laminates were prepared by the vacuum bag technique. The volume fraction of natural fiber was 30% (mass fraction of 10%) and samples of 254 mm length and 25.4 mm width were cut and tested at vibration conditions in a cantilever beam arrangement. The vibration frequency was measured by an accelerometer ADXL335 at z-axis, perpendicular to the sample test plane and the elastic modulus was estimated with the cantilever model. The results showed that the samples with coir fiber showed an increase in the dynamic elastic modulus value of 150 to 171% with regard to that one of glass fiber samples without fiber. Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials (ASTM D3039) was also used to further characterize the thin samples (≈0.75 mm) with an Instron machine 8800, 25kN. The tensile properties obtained are lower for coir fiber samples than the ones without.

Abstract: Self-Compacting Concrete (SCC) incorporating a blend of normal aggregate and waste rubber or expanded clay aggregate were prepared in present paper. And then the properties of SCC incorporating combined aggregates in fresh state and hardened state, including workability, dynamic elastic modulus, compressive strength and chloride ion permeability were investigated by experiments. Results indicate that utilization of rubber particles as a fine aggregate or expanded clay particles as a coarse aggregate by partially replacing sand or coarse aggregate of the same volume can successfully produce the SCC with suitable workability. The addition of rubber or expanded clay particles results in a remarkable reduction of mechanical strength and dynamic elastic modulus of SCC. And the compressive strength and dynamic elastic modulus of SCC with expanded clay aggregate replacing coarse aggregate is higher than that of SCC with the same volume rubber replacing sand. The incorporation of rubber or expanded clay aggregate in concrete exhibits a reduction in chloride ion permeability as compared to normal concrete. It is of great importance for further understanding the effect of waste rubber and expanded clay aggregate on workability, mechanical properties and durability of SCC.

Abstract: The uniaxial cyclic fatigue tests on granite coming from the ChangJiang of Hainan nuclear power first-stage construction conventional island were done on the RMT-150B multi-function automatic rigid rock servo material testing machine. Stress amplitude of 10 MPa and sine wave cyclic loads with five different frequencies of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 Hz were adopted as dynamic disturbance. The law between cyclic frequency and dynamic stress-dynamic strain hysteretic curve, dynamic elastic modulus and damping ratio are researched. The results showed that the curves of strain and stress for loading and unloading are not superposition under cyclic loading, but hysteretic loops. When cyclic frequency changes between 0.01 and 1.0 Hz, the granite hysteretic loop area, dynamic elastic modulus and damping ratio are increased with frequency increasing. The research result offered great reference value to seismic response analysis and site safety evaluation of the changjiang nuclear power.

Abstract: Carbon nanotubes (CNTs) were modified by alkali, and carbon nanotubes epoxy composites samples were prepared by the hot pressing method. Dynamic characteristics of the composites were studied by experiments. The results suggest that carbon nanotubes can hardly enhance the first natural frequency of epoxy composite, but the change of second and third order natural frequencies are obvious compared with the first one. Damping properties of the composites are improved, and with the mass ratio of CNTs increasing, the first three order damping properties of composites are all increased initially followed by the decrease. The results also indicate that flexural elastic modulus of the composites is enhanced, the first and the second order dynamic elastic modulus is greater than it but the third order is opposite. The first three order dynamic modulus of elasticity moments of CNTs composites whose mass fraction is two percent are all high.

Abstract: Basalt fiber reinforced concrete has excellent basic mechanical properties. It has become a hot topic of engineering studies. Based on the freeze-thaw resistance of durability indices, through the comparative experiment on the dynamic elastic modulus and mass loss of plain concrete and basalt fiber reinforced concrete in the freeze-thaw cycles, this paper had discussed the impact of basalt fiber on the freeze-thaw resistance of concrete, and have considered whether the specimens were mixed with fly ash. The results showed that basalt fibers can improve the freeze-thaw resistance of concrete specimens significantly. After 100 freeze-thaw cycles, the dynamic elastic modulus of basalt fiber reinforced concrete specimens was 1.47 times as much as that of plain concrete specimens, and mass loss of basalt fiber reinforced concrete specimens was 0.64 times as much as that of plain concrete specimens. Fly ash had an influence on the freeze-thaw resistance of basalt fiber reinforced concrete. In engineering applications, the mixing amount of fly ash should be taken into consideration. This research had a certain reference value on the engineering applications of basalt fiber reinforced concrete.

Abstract: In this paper based on the foundation construction of Datong Xian high-speed railway, a large number of test samples have been taken. The order and contribution rate of every experiment factor like cement commingle ratio, depths, water dipping conditions, compacting factor and vibration frequency on the dynamic characteristics of cement-improved loess such as dynamic elastic modulus, dynamic deformation, damping ratio by dynamic triaxial test, which orthogonal test method has been applied to. The dynamic load was calculated according to the train vibration attenuation rule of different depth. The dynamic characteristics of cement-improved loess such as dynamic deformation, dynamic elastic modulus, damping ratio were got form the dynamic tests of long time and large number of cycles. The results showed that with the increase of cement ratio, the dynamic characteristics of cement-improved loess are more better, there is no optimal ratio of cement.

Abstract: For exploring the attenuation law of limestone dynamic elastic modulus (DEM) under fatigue cyclic loading, 24 limestone specimens were used to conduct dynamic uniaxial cyclic compressive tests under different loading frequencies and stress amplitudes on MTS Test System. The tests results confirmed that the decrease of DEM goes through three different stages with the increase of cyclic numbers. And, there is no distinct correlation between three-stage evolution rule of DEM and frequencies as well as stress amplitudes. The degeneration of DEM is caused by accumulation of micro-cracks and damage increase in rock specimen. Thus, based on attenuation rule of DEM, a fatigue damage evolution model which can depict the first two stages of limestone fatigue damage development was proposed.

Abstract: Water content is one of key effect factors on the dynamic elastic modulus, which is an important damage assessment index of concrete structures induced by freeze-thaw cycles, fire and chemical attacks. Through the ultrasonic and bending vibration test, the regularity of dynamic elastic modulus changed with the water content of concrete specimens was analyzed in this paper. The results show that the ultrasonic velocity has a low sensitivity to water content when it is below 1.5%. The bending vibration method can better reflect the effect of water content change on dynamic elastic modulus. The regression equation of dynamic elastic modulus and water content was set up by introducing the index function. The research results offer technical reference for the predicting of actual concrete dynamic elastic modulus in different humidity environment.

Abstract: This paper tested the capillary water absorption, impermeability and cracking of cement mortars modified with three polymers respectively and founded the correlation of cracking with the waterproof performance. The results show that with the polymer content increasing, especially as the polymer/cement ratio (mp/mc) increases from 0% to 5%, the reduction in the capillary water absorption and the penetration depth of water into mortar is significant. When the mp/mc is more than 15%, the increase of the mp/mc in all mortars has little effect on the capillary water absorption and the penetration depth. For the purpose of reducing the cracking weighted value, the styrene-butadiene rubber (SBR) dispersion and the styrene-acrylic copolymer (SAE) powder are superior to the SAE dispersion. Regardless what kinds of polymers, the capillary water absorption and the penetration depth of water into mortar show exponential growth with the increasing cracking weighted value.

Abstract: Aiming at determining the durability of concrete in very salty regions, this study examines the performance of various high performance fine aggregate concretes in a sulfate environment, such as high performance concrete inside a composite additive, and Portland cement concrete and sulfate resistant cement concrete, all of which experienced dry-wet cycles in sodium sulfate solutions. By examining the changes of elastic moduli and analyzing the SEM of the concrete, this paper has found that the salt resistance of sulfate resistant cement concrete is no better than that of Portland cement concrete in the extremely aggressive dry-wet cycle environment but high performance concrete containing a composite additive has better resistance in a sulfate environment. Besides, the composite additive can create the environment for a second hydration to reduce the amount of Ca(OH)2 inside the concrete, and build additional C-S-H gel to reform the microstructure of concrete effectively. Finally, the paper offers some advice for mixing concrete in salt regions.