关于港湾围堰中泥水混合物流动的计算

围堰充填是近代港湾建设的一种新型方法，海底泥水混合物在围堰中边流动、边沉降，是一个复杂的两相流动．本文以大连港大窑湾港区充填沉降流动为基础，用流网法对围堰中混合物的速度分布与浓度分布进行了预估计算，所得结果与模型实验结果吻合很好．

城市型河道清淤泥水混合物的絮凝效果试验探讨

絮凝剂添加量对于河道底部泥水混合物加速分离效果影响显著,为提高河道清淤效果文章对絮凝剂的添加量进行试验。试验表明当絮凝剂投加量达到0.79mg/g时,泥水混合物分离效果可达到最佳,分离后的出水水质浓度显著减少。

泥水混合物充填型岩溶电磁波反射特性研究

泥水混合物充填型岩溶的准确预测可以大幅度的减小隧道施工安全隐患。利用地质雷达探测系统对泥水混合物充填型岩溶构造进行探测,对电磁波的形态和频谱特性进行分析,结果表明:(1)当电磁波在通过岩溶构造前缘时发生强反射,形成较为连续的同相轴界面,电磁波波幅明显变宽,子波为负相位;(2)可以得到较完整灰岩相对准确的介电常数,据此推算出岩溶构造前缘位置;(3)泥水混合物充填型岩溶构造会出现一定的低频现象,可为充填物形态判定提供依据。为泥水混合物充填岩溶预测解译提供依据,也为探测隧道泥水混合物充填岩溶不良地质体积累经验。

CPAM对河道泥水混合物的絮凝效果研究

河道淤泥使水体变黑发臭,严重影响水体环境。近年来,利用清淤船吸取河道底部泥水混合物,然后添加絮凝剂加速泥水分离,从而达到清淤效果的应用研究已初步展开。但絮凝剂投加量对河道泥水混合物絮凝效果的影响尚未有系统的研究,严重影响了清淤船的设计。基于此,通过絮凝实验研究了阳离子型聚丙烯酰胺(CPAM)投加量对泥水混合物分离沉降效果的影响,以及分离后的出水水质。结果表明,当CPAM投加量达到0.79 mg/g时,泥水快速分离效果明显,出水浊度和COD值显著降低。

双轴旋转超滤膜组件过滤厌氧泥水混合液

设计开发了一套中试规模的双轴旋转超滤膜组件系统.系统容器容积120 L,内装填的有效膜面积为4 m2.试验选用两种不同截留分子量(5万和10万)的PVDF超滤膜,采用该系统处理厌氧生物反应器内泥水混合液,研究了膜截留分子量、膜渗透通量、过膜压差、膜旋转速度之间的相互关系.结果表明,一定膜旋转速度下,随着过膜压差的提高,存在一个膜极限渗透通量;随着膜旋转速度的降低,膜极限渗透通量明显下降,且膜极限渗透通量出现时对应的过膜压差往低压方向迁移;截留分子量大小对膜过滤行为的影响在高压、高转速区有减弱趋势.

海底取排水工程玻璃钢管受力特性试验研究

利用物理模型试验手段,结合越南沿海二期2×660 MW燃煤电厂取排水工程,开展了新型玻璃钢管材质的管道受力特性试验研究。通过在试验室配置不同密度泥水混合物的组合方式,验证玻璃钢管处于自由静载状态疏浚物回填施工期和运营期密实固定状态下,受力、上浮过程等内容。试验揭示了不同密度回填土中管道上浮由初期缓慢阶段、中期快速阶段、最终震荡动态平衡阶段的规律,得到各上浮阶段的受力结果,并推导出利于实际工程应用的经验公式。结果可为海底管道的安全施工和运行稳定性提供重要的技术保障,以及为同类工程应用提供参考。

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.

Mechanical properties of pervious cement concrete

Compressive and flexural strength,fracture energy,as well as fatigue property of pervious cement concrete with either supplementary cementitious materials (SCMs) or polymer intensified,were analyzed.Test results show that the strength development of SCM-modified pervious concrete (SPC) differs from that of polymer-intensified pervious concrete (PPC),and porosity has little effect on their strength growth.PPC has higher flexural strength and remarkably higher flexural-to-compressive strength ratio than SPC at the same porosity level.Results from fracture test of pervious concrete mixes with porosity around 19.5% show that the fracture energy increases with increasing the dosage of polymer,reflecting the ductile damage features rather than brittleness.PPC displays far longer fatigue life than SPC for any given failure probability and at any stress level.It is proved that two-parameter Weibull probability function describes the flexural fatigue of pervious concrete.

Formation mechanisms of water inrush and mud burst in a migmatite tunnel：a case study in China

This paper presents a case study of water inrush and mud burst occurring in a migmatite tunnel to study its formation mechanisms. The geological investigation and mineralogical analysis showed that water inrush and mud burst in the migmatite was closely related to the component of the host rock. High content of soluble minerals,e.g.,calcite and dolomite,would make the migmatite rock prone to be fragmentized,isintegrated and eventually form different sorts of connected or semi-connected veins. The field exploration revealed most cavities in the magmatite tunnel were eroded by groundwater and formed large interconnected networks. The two faults and the dike in the magmatite tunnel became the preferred paths and provided great convenience for plenty of precipitation and mud slurry. Due to high water pressure and blast disturbance,the cavities can soon connect each other as well as all sorts of veins,forming a complex ground channel for water inrush and mud burst. To estimate the potential occurrenceof water inrush and mud burst,the water bursting coefficient was employed. The results showed the water bursting coefficient of the magmatite tunnel was much bigger than the threshold values and it can be used to explain the accident of water inrush and mud burst occurring in the magmatite tunnel.

Utilization of Concrete Waste Aggregates Using Geopolymer Cement

Reuse of concrete waste, especially in large quantity, can save not only material but also cost for its disposal. This paper presents experiment results on the use of fine and coarse aggregates from concrete waste in geopolymer mortars and concretes. Geopolymeric cement is an inorganic compounds of aluminosilicates synthesized from precursors with high content of silica and alumina activated by alkali silicate solutions. Geopolymer in this experiment was synthesized from fly ash as the precursor and sodium silicate solution as the activator. Hardening of geopolymers was performed by heating the casted paste in an oven at -60~Cfor 3 to 36 hours. Compressive strength of geopolymer pastes and mortars using either fresh or waste fine aggregates were in the range of 19-26 MPa. Hardening time of 3 hours at 60~C followed by leaving the test pieces at room temperature for 7 day before testing results in similar strength to that of mortars cured for 36 hours at 60~C followed by leaving the samples at room temperature for 3 days. It suggests that optimum strength can be achieved by combination of heating time and rest period before testing, i.e the specimens age. Applying mix design with a target strength of 40 MPa, conventional Portland cement concretes using fresh aggregates reached 70% of its target strength at day-7. Compressive strength of geopolymer concretes with waste aggregates was -25 MPa at day-3 while geopolymer concretes with fresh aggregates achieved -39 MPa at day-3. It can be concluded that geopolymer concretes can achieve the target strength in only 3 days. However, the expected reinforcing effect of coarse aggregates in concrete was ineffective if waste coarse aggregates were used as the strength of the concretes did not increase significantly from that of the mortars. On the other hand, waste fine aggregates can be reused for making geopolymer mortars having the same strength as the geopolymer mortars using fresh aggregates.

Characterization of Stabilized Earth Blocks with Incorporation of Cement Expanded Polystyrene for Use in Buildings

This work focuses on the development of local building materials in Benin for their efficient use in buildings. It aims to make mud bricks lightened with good mechanical, thermal and sound properties and enhance the waste polystyrene. This article is the result of experimental work on a broad field of applied sciences： building mechanics. The study is focused on BTS （blocks of stabilized earth） chosen as reference materials to which we linked polystyrene. The percentage of polystyrene varies from 0% to 100% starting from a constant volume of each reference material. The results showed that the increase in polystyrene percentage lowers mechanical properties. These results also showed that the gradual addition of polystyrene to the laterite-cement mixture has a significant influence on the density and mechanical resistances of the final composite material.

Use of Chemical Admixtures to Modify the Rheological Behavior of Cementitious Systems Containing Manufactured Aggregates

The use of local materials is an important part of sustainability for the concrete industry. The declining availability of aggregate resources in many areas has the potential to result in the use of alternative aggregates of lower quality, which can require higher cementitious materials contents, or the use of aggregates shipped from greater distance. In some markets, manufactured sands are replacing natural sands, which can adversely impact the rheology of cementitious mixtures. The use of certain chemical admixtures has been found to often minimize the need to increase cement and water contents in order to overcome the loss of workability that can accompany aggregate sources which feature flat, elongated, angular, and rough particles. In this study, a wide range of natural and manufactured sands were characterized for gradation, mineralogy, shape, texture, and cleanliness, and also evaluated for their effect on mortar rheology with and without a VMA （viscosity modifying agent） type chemical admixture. Use of the VMA is shown to mitigate the rheological effect of certain sands, and in some cases can allow for optimizing the mixture to lower paste contents. In the case of PCP （polycarboxylate）-based superplasticizers, attention is drawn to the increased dose required to achieve target workability versus superplasticizers based on NSFC （naphthalene sulfonate condensate） when swellable clays are present in the very fine fraction of certain aggregate sources. The use of sands with higher fines contents are also shown to increase the workability provided the fines are of appropriate quality.

Low-temperature Synthesis of Belite Cement from Reactive Mixtures Based on Coal Fly Ash

This paper summarizes the selected results of an extensive investigation of application of two methods （hydrothermal and mechanochemical） assisted by calcination for synthesizing belite cement from reactive mixtures （CaO/SiO2 molar ratio of 2） consisting of various waste kinds from fluidized brown coal combustion in Slovakian power plant and CaO addition. Based on XRD diffraction patterns and infrared spectra ofpre-treatment products, the formation of the new profiles corresponding to CSH phases with low degree of ordering as belite precursors after hydrothermal treatment as well as metastables calcium silicates and aluminosilicates in mechanosynthesized products was confirmed. Calcination of hydrothermally treated products led to transformation of CSH phases to wollastonite （CS）, belite and gehlenite phase, whereas creation oft^- and I^-C2S or wollastonite in milled reactive mixture took place. Differences in phase composition of products before and after calcination depend upon waste quality and precursor＇s synthesis conditions. Bottom ash isn＇t suitable as raw material for synthesizing belite phase because of high CaO content fixed in anhydrite form （44.1%）. Coal fly ash with low CaO content in anhydrite form （4.2%） and its mechanochemical or hydrothermal treatment in combination with subsequent heating offer opportunities for the utilization of coal fly ash as raw material for belite production.

Experimental Study of Concrete Column Shape Modification Using Fiber Reinforced Polymer Composite Shells and Expansive Cement Concrete

Fiber Reinforced Polymer （FRP） composites are an effective material for strengthening circular concrete columns. The effectiveness of FRP confinement for square and rectangular columns is greatly reduced due to stress concentrations at the sharp comers and loss of the membrane effect at the fiat sides of the cross-section. Shape modification can eliminate the effects of column comers and flat sides, and thereby restore the membrane effect and improve the compressive behavior of FRP-confined square and rectangular concrete columns. Shape modification using chemical post-tensioning, achieved by using expansive cement concrete, is described and several mix designs for obtaining the optimal level of expansion are presented. In addition, parametric studies regarding the optimal geometry of the shape-modified cross-section are presented utilizing the analytical model.

Influence of Mineral Admixtures on Essential Properties of Ternary Cement Blends

Two CaCO3-based materials （limestone and clamshells） and steel slag were used as mineral admixtures in cement to produce ternary blends and their influences on hydration and portlandite formation were analyzed. Additionally, mechanical properties were determined. These properties were determined using X-ray diffraction and scanning electron microscopic/energy dispersive X-ray analytical techniques as well as applying methods specified by EN （European Standards） and ASTM （American Standards for Testing and Materials）. The portlandite （Ca（OH）E） content was considerably reduced from 36.9% of reference cement to between 13.79% and 15.5%. With the water demand and setting times of the cements containing up to 10%, admixtures did not change significantly. The mechanical tests results showed that ternary blends produced 2-day strengths higher than that specified by EN 197-1 and that blends containing up to 20% admixtures can be used to produce both Class 32.5N and 42.5N cements.

Experimental Study on the Use of Trass as a Supplementary Cementitious Material in Pervious Concrete

Abstract： The purpose of this paper is to evaluate the suitability of using trass as a supplementary cementing material in pervious concrete. OPC （Ordinary Portland Cement） was replaced in the concrete mix by 15%, 25% and 35% weight percentages and the results were compared with reference mixtures with 100% Portland cement. The variables in this study were trass content, aggregate size and water to cement ratio. Sixteen eases of concrete mixtures were tested to study physical and mechanical properties of hardened concrete, including porosity, permeability, compressive strength, splitting-tensile strength and flexural strength at various ages. Results indicated that mechanical properties of the pervious concrete marginally decreased with the increased content of trass when compared to the reference mixtures. However, at later ages the differences were insignificant.

The Study of Resistance of Cement Composites against Microbial Attack

The start and the course of bio-corrosion are conditioned by many factors which include biological effects like the influence of vegetation and microorganisms causing the deterioration of materials. The influence of bacteria causing the deterioration of concrete has been linked to the generation of biogenic sulphuric and nitric acids which originate in corrosion process by dissolution of calcium containing minerals from the concrete matrices. This paper primarily focuses on the investigation of influence of sulphur-oxidising bacteria Acidithiobacillus thiooxidans and sulphate-reducing bacteria Desulfovibrio desulfuricans at the resistance degree of cement composites. Various concrete composites with 5% addition of black coal fly ash as cement replacement as well as the reference samples without coal fly ash addition were studied in the experiments environments of sewage system proceeded during 90 days. The The laboratory experiments as well as experiments in situ in real corrosion was manifested by surface changes and weight changes of cement composites samples as well as changes in pH values of leachates. Considerable surface changes were detected in all investigated samples by microscopic methods. Crystals precipitated on concrete samples surface were identified by EDX as mixture of gypsum and ettringite. The roughness increases of surface of cement microscopy. composites were determined by confocal laser scanning