Φ118标准试验发动机压强-时间曲线下降段要求的研究

利用大量的Φ118标准试验发动机压强-时间曲线,针对下降段要求中tb/ta≥0.87对燃速数据的准确性的影响做了大量而全面的比较和分析,得出tb/ta<0.91就会较大地影响到燃速数据的准确性、tb/ta≥0.87已不合适的结论,并研究出tb/ta在0.87～0.91范围内对燃速数据的修正方法。

真空系统的压强—时间曲线诊断法

应用真空系统的静态压强与时间的 Ｐ－Ｔ曲线，可以诊断出真空系统存在的问题：漏气、放气和蒸汽源，这为真空设备的调试和运行提供了简便和实用的诊断手段。

Mechanical properties of anti-seepage grouting materials for heavy metal contaminated soil

Cement-based composite grouting materials were used to construct grouting cutoff wall for heavy metal contaminated soil in non-ferrous metal mining areas. Cement, fly ash, and slag as principal ingredients were mixed with water glass in different ways to produce three composite grouting materials. In order to investigate the effect of water glass mixing ratio, Baume degree, fly ash and slag contents on the mechanical properties of the composite grouting materials, particularly their gel time and compressive strength, the beaker-to-beaker method of gel time test and unconfined compressive strength test were conducted. In addition, the phase composition and microstructure of the composite grouting materials were analyzed by the X-ray diffraction（XRD） and scanning electron microscope（SEM） techniques. The test results show that their gel time increases when water glass mixing ratio and Baume degree increase. The gel time increases dramatically when fly ash is added, but decreases slightly if fly ash is partly replaced by slag. When the mixing ratio of water glass is below 20%, their compressive strength increases with the increases of the ratio; when the ratio is above 20%, it significantly decreases. The compressive strength also tends to increase as Baume degree increases, and improves if fly ash and slag are added.

Workability Tests on Fresh Concrete Formulated with Eco-friendly Admixture

Extra-cellular compounds, secreted by microorganisms into their surroundings, can be integrated in concrete composition as admixtures. These substances are important in biofilm formation and some of them can be used as corrosion inhibitor of concrete reinforcement. This paper deals with products made with biological surface active compounds/agents allowing the development of more eco-friendly concrete. The influence of this environmentally friendly bio admixture on setting time, workability, bending and compressive strengths of various mortar based materials made of CEM I, CEM III and CEM V was studied. Mechanical tests were carried out to highlight the influence of admixture in workability and hardening of samples containing the biological product with ratio in the range of 0-2.5%. It was demonstrated that the presence of the new bio-compound admixture in mortar decreases their compressive strength after 28 days of standard curing, in spite of remaining higher than standard minimal strength. Furthermore, Vicat needle experiments have shown a tendency of this admixture to decrease the setting time. A discussion was finally proposed in order to correlate the setting times and the decrease of the mortar compressive strength, corresponding in fact to a hardening delay. This setting time delay could be linked to a delay of the admixtured mortar to increase its resistance. The slump results highlight the action of bio-admixture as a plasticizer on mortars because it increases their workability for a same water-cement ratio. This effect seems variable according to the added amount.

Particle Size Effect on Shear Properties of Bottom Ash Added-Geocomposite Soil

It is well known that the finer particle of cementing material has more pozzolanic reaction than the coarser. This paper investigates the shear properties of geocomposite soil with various particle sizes of bottom ash. The geocomposite soil （GCS） in this study consists of dredged soil, bottom ash and cement for recycling dredged soil and bottom ash. Three different particle sizes of bottom ash passing No. 4 sieve, No. 40 sieve, and No. 140 sieve were added into soil mixtures, namely as GCS 4, GCS 40, and GCS 140, respectively. These bottom ashes have the same chemical component except for different particle sizes. Several mixtures were prepared with various contents of bottom ash ranging from 0 to 100% at 50% intervals by the weight of dry dredged soil. In this study, several series of unconfined compression test were carried out on the mixtures with various curing times. It is found that the unconfined compressive strength is a function of curing time and bottom ash content. For the curing time less than 28 days, the GCS 4 has higher unconfined compressive strength than the GCS 40 and GCS 140 due to the interlocking effect and friction between the particles with angular shape of coarse bottom ash. For the curing time larger than 28 days, the GCS 140 has higher strength due to the pozzolanic reaction. However, the ratios of secant modulus to unconfined compressive strength of three mixtures are almost the same, and in range of （46-100）, regardless of mixing condition and curing time.

不稳定结构设计对足部动力学的影响

选取22名步态稳定的健康男性作为受试者,分别用控制鞋和实验鞋以自选速度沿10m长实验室跑道行走,对足底不同区域的峰值压强、压强-时间积分和接触面积进行研究.结果表明:实验鞋在后跟区域的峰值压强和压强-时间积分比控制鞋明显升高,说明不稳定结构元素在前脚掌冠状面上的调整可以显著地改变足底压力的分布.

Mechanism of high pressure roll grinding on compression strength of oxidized hematite pellets

The mechanism of high pressure roll grinding on improvement of compression strength of oxidized hematite pellets was researched by considering their roasting properties. The results indicate that oxidized hematite pellets require higher preheating temperature and longer preheating time to attain required compression strength of pellets compared with the common magnetite oxidized pellets. It is found that when the hematite concentrates are pretreated by high pressure roll grinding （HPRG）, the compression strengths of preheated and roasted oxidized hematite pellets get improved even with lower preheating and roasting temperatures and shorter preheating and roasting time. The mechanism for HPRG to improve roasting properties of oxidized pellets were investigated and the cause mainly lies in the increase of micro-sized particles and the decrease of dispersion degree for hematite concentrates, which promotes the hematite concentrate particles to be compacted, the solid-phase crystallization, and finally the formation of Fe203 bonding bridges during subsequent high temperature roasting process.

Influence of specimen uniformity on mechanical behaviour of unsaturated soil

Pressure plate instrument is employed during drying, and unconfined compressive strength test is performed on the unsaturated specimen. Curves of shear force versus shear displacement, and curves of saturation degree versus time are investigated. The results show that the specimens with similar curves of saturation degree versus time have nearly identical mechanical behavior. In particular, the uniform specimens should be chosen within the lower equilibrium saturation degree because steady test results are presented. Further, the conclusion is verified by the repeated test. Thus, the method for distinguishing the uniform unsaturated specimen is obtained. In the light of the method, an improved test process is proposed. The uniform specimens should be chosen by this method under the specific matric suction, and then shear tests are carried out on the chosen unsaturated specimen. Namely, initial value of unsaturated soil is not zero matric suction but a specific suction.

Experimental study on improving collapsible loess with cement

The collapsibility of loess ground can directly affect stability of subgrade. Therefore, how to adopt practical technical measures to reduce or eliminate its collapse deformation is an important content in foundation design in collapsible loess zone. Selecting collapsible loess from Fuxin-Chaoyang highway in Liaoning, the authors conducted a series of tests for improving loess with cement. The loess in different water content was mixed with the cement in varying proportions, unconfined compression strength for the samples at four different curing periods were tested, and the relationships of improved soil strength among cement mixture ratio and curing periods were analyzed. When the curing periods are certain, the strength of loess increases along with the mixture ratio increases; when the cement mixture ratio is 5%-15%, the scope of increases is quite obvious; when the mixture ratio is greater than 15%, the tendency of intensity increases turns slow. When the mixture ratio for the specimen is certain, the intensity of the test specimen increases along with the curing period increases, the intensity grows obviously in 28 days, and the growth rate is small in 28-90 days, the intensity tends to be steady in the curing period of 90 days.