Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ratios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm （Nos. 7, 6 and 5 according to JIS A 5001） were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

Study on the packed volume and the void ratio of idealized human red blood cells using a ?nite-discrete element method

Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The packed volume and the void ratio of a large number of randomly packed RBCs are clari?ed,and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the ?at or thick cells used in this study. Such information is bene?cial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.

Inversion and Prediction of Consolidation Settlement Characteristics of the Fluvial Sediments Based on Void Ratio Variation in the Northern Modern Yellow River Subaqueous Delta, China

The modern Yellow River delta is formed near the estuary of the Yellow River with the characteristics of short formation time, efficient sedimentation rate and loose structure which make sediments prone to be compacted and consolidate under the geostatic stress and overburden stress. It is one of the key areas with land subsidence disasters in China, bringing a series of safety hazards to production and living. Based on the data of massive surface cores and ten drill holes ranging from 12 to 40 m obtained from the northern modern Yellow River subaqueous delta, the inversion method suitable for the calculation of consolidation settlement characteristics of the modern Yellow River subaqueous delta is discussed, and the consolidation settlement characteristics of the delta sediments are inversed and predicted in this paper. The actual void ratio of the delta sediments at the depth from 3 to 15 m shows a significant power function relationship with the depth, while the void ratio of the sediments below 15 m changes little with depth. The pre-consolidation settlement(from deposition to sampling) of the delta sediments is between 0.91 and 1.96 m, while the consolidation settlement of unit depth is between 9.6 and 14.0 cm m^(-1). The post-consolidation settlement(from sampling to stable) of the subaqueous delta sediments is between 0.65 and 1.56 m in the later stage, and the consolidation settlement of unit depth is between 7.6 and 13.1 cm m^(-1) under the overburden stress. The delta sediments with a buried depth of 3 to 7 m contribute the most to the possible consolidation settlement in the later stage.

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity(h), dry unit weight(gd) of molding, cement content(C)and porosity/volumetric cement content ratio(h/Civ) or void/cement ratio on the unconfined compressive strength(quor UCS) of silty soileroof tile waste(RT) mixtures. Soil samples are molded into four different dry unit weights(i.e. 13 kN/m^3, 13.67 kN/m^3, 14.33 kN/m^3 and 15 kN/m^3) using 3%, 6% and 9%cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT esoil mixtures increases in a linear manner. On the other hand, the addition of RT decreases quof the samples at a constant percentage of cement, and the decrease in porosity can increase qu. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio(h/C_(iv)) where the control variables are the moisture content, crushed tile content, cement content and porosity.

Factors Affecting the Relation of Fracture Toughness V_(GC) with Critical Void Growth Ratio R_C/R_O

The relationship between fracture toughness VGC and critical void growth RC/RO was studied for ten kinds of Steel. The macroscopic fracture toughness VGC was determined by using notched tensile specimens. and the microscopic parameters of critical void growth ratio RC/RO were quantitatively measured under SEM. Then, the coefhcient C in the relation VGC = C In(RC/RO) proposed in author's past work was specifically explored. The correlation of C with tensile proderty parameter φ=σyδ/(Eφn) was presented for the Steel investigated, and the effects of low temperature on C were also discussed. Results show that the coefficient C is linearly related to the parameter and insensitive to low temperature.

Ratio of In-Sphere Volume to Polyhedron Volume of the Great Pyramid Compared to Selected Convex Polyhedral Solids

The architecture of the Great Pyramid at Giza is based on fascinating golden mean geometry. Recently the ratio of the in-sphere volume to the pyramid volume was calculated. One yields as result RV = π ⋅ φ5, where is the golden mean. It is important that the number φ5 is a fundamental constant of nature describing phase transition from microscopic to cosmic scale. In this contribution the relatively small volume ratio of the Great Pyramid was compared to that of selected convex polyhedral solids such as the Platonic solids respectively the face-rich truncated icosahedron (bucky ball) as one of Archimedes’ solids leading to effective filling of the polyhedron by its in-sphere and therefore the highest volume ratio of the selected examples. The smallest ratio was found for the Great Pyramid. A regression analysis delivers the highly reliable volume ratio relation , where nF represents the number of polyhedron faces and b approximates the silver mean. For less-symmetrical solids with a unique axis (tetragonal pyramids) the in-sphere can be replaced by a biaxial ellipsoid of maximum volume to adjust the RV relation more reliably.

Primary Breeding Ratio Analysis of an Improved Supercritical Water Cooled Fast Reactor

The purpose of the study is to analyze the breeding ratio of a supercritical water cooled fast reactor (SCFR) and to increase the breeding core of SCFR. The sensitivities of assembly parameters, core arrangements and fuel nuclide components to the breeding ratio are analyzed. In assembly parameters, the seed fuel rod diameter has higher sensitivities to the conversion ratio (CR) than the coolant tube diameter in blanket. Increasing heavy metal fraction is good to CR improvement. The CR of SCFR also increases with a reasonable core arrangement and Pu isotope mass fraction reduction in fuel, which can achieve more negative coolant void reactivity coefficient at the same time. The breeding ratio of SCFR is 1.03128 with a new core arrangement. And the coolant void reactivity coefficient is negative, which achieves a fuel breeding in initial fuel cycle.

Numerical Investigation into the Effect of Air Voids on the Anisotropy of Asphalt Mixtures

The aim of this study is to investigate the asphalt mixture anisotropy of both the modulus and Poisson＇s ratio due to air voids using a discrete element modeling simulation method. Three three-dimensional cubic digital samples of asphalt mixture with different shapes of single air void were built using discrete element software PFC^（3D）. The aggregate gradation, air voids and mastic included in the digital samples were modeled using different contact models, with due consideration of the volumetric fractions of the different phases. Laboratory uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. Simulation of the uniaxial cyclic compressive tests was performed on the three cubic samples loaded in three different directions. Dynamic modulus in three directions and Poisson＇s ratio in six directions were calculated from the compression stress-strain responses. Results show that both the modulus and Poisson＇s ratio are dependent on the preferential orientation of air voids. The anisotropy of the modulus and Poisson＇s ratio increases as the pressure loading on the asphalt mixture increases. Compared to the modulus, Poisson＇s ratio due to air voids has been shown to be more anisotropic. The maximum of Poisson＇s ratio and modulus is shown to be up to 80% and 11% higher than the minimum, respectively.

考虑孔隙比影响的堆石料湿化试验及湿化模型

对某堆石坝的坝壳料进行了不同密实状态下的单线法三轴湿化试验,分析了湿化变形随围压、应力水平以及初始孔隙比的变化规律。结果表明:在围压和应力水平相同条件下,随着初始孔隙比的减小,堆石料湿化轴向应变和体积应变均明显降低;初始孔隙比对湿化应力剪胀规律影响不大,采用对数形式的湿化剪胀方程可对不同初始孔隙比条件下的湿化应力剪胀关系进行统一描述。对指数形式的湿化轴向应变经验模型进行修正,构建了考虑初始孔隙比及应力状态影响的湿化轴向应变计算模型,并联立湿化剪胀方程推导了湿化体积应变的计算公式,通过对三轴湿化试验结果进行模拟验证了该公式的合理性。

橡胶混合黏土小应变剪切模量特性试验研究

为了研究橡胶混合黏土(混合土)的动变形特性,对不同橡胶掺量、橡胶粒径和围压的混合土开展共振柱试验,分析动剪切模量G和阻尼比λ的发展规律,并基于二元介质模型,提出了表达混合土接触状态的骨架孔隙比e_(sk)计算方法,进一步依托骨架孔隙比e_(sk)对混合土的最大动剪切模量G_(max)进行评价。结果表明:掺入橡胶颗粒后,混合土的G减小,λ增大,且橡胶掺量增大时,混合土的G减小、λ增大;围压增大时,混合土的G增大、λ减小;橡胶粒径增大时,混合土的G增大、λ减小。随着橡胶掺量增大,骨架孔隙比e_(sk)增大,G_(max)降低;在相同橡胶掺量时,随着橡胶粒径的增大,e_(sk)增大,G_(max)升高。在Hardin公式的基础上,基于骨架孔隙比e_(sk)提出了考虑橡胶掺量和橡胶粒径的G_(max)表征模型,该模型具有较好的准确性,可为评价橡胶混合黏土G_(max)提供依据。

长江漫滩相超固结软土最大动剪切模量试验研究

为探究长江漫滩相超固结软土最大动剪切模量G_(max)变化特征,利用弯曲元对原状长江漫滩相软土开展了系列试验研究,探讨了不同超固结比H_(OCR)、初始有效固结围压σ'_(3c)及孔隙比e对漫滩相软土G_(max)的影响规律。试验结果表明,当σ'_(3c)和H_(OCR)均相同时,G_(max)随e的增大而减小;H_(OCR)的增大会导致G_(max)随e的衰减速度逐渐降低,而σ'_(3c)的增大不会引起G_(max)衰减速度的变化。孔隙归准化最大剪切模量G_(max)/F(e)随归准化初始有效围压σ'_(c0)/Pa的增大而增加,但其增长速率逐渐降低,G_(max)/F(e)与σ'_(3c)/Pa呈幂函数关系。基于回归分析,提出了合理表征具有不同超固结状态、初始应力条件及密实程度的长江漫滩相软土G_(max)预测方法,并通过独立试验验证了该方法的有效性。

电渗透系数试验装置研制及其影响因素

为深入探讨饱和土的电渗透系数及其影响因素,自制了一种简单便捷的电渗透系数试验装置。该装置可以保证在电渗试验过程中试样含水率和孔隙比相对稳定,并排除由于试样两端水头差引起水力渗流的影响。利用该试验装置对5种不同孔隙比的饱和重塑黏性土试样进行电渗试验,结果表明,在低电压和小孔隙比条件下排水量与时间成正比。在此基础上,探讨了电势梯度及孔隙比对电渗透系数的影响规律。试验结果表明,电渗透系数随着电势梯度或孔隙比的增大而增大,且与电势梯度和孔隙比均近似呈线性关系。其中,孔隙比对电渗透系数的影响较大。

砂-粉混合料颗粒接触状态的临界条件确定

砂-粉混合料被广泛应用于高速铁路路基、人工筑岛及海底沉管隧道垫层等重大工程,如何科学地表征砂-粉混合料复杂的颗粒接触状态及连续演变的力学行为特征,并深入揭示其对混合料静/动力学特性的影响已是一项紧迫的基础性科学研究任务。本文基于代表性砂-粉混合料的基本物理性能指标及力学特性指标试验数据,验证Rahman等提出的区分“细粒填充砂粒”和“砂粒悬浮细粒”的阈值细粒含量FCth半经验公式预测能力。基于理想二元介质材料的理论最小孔隙比计算方法,提出确定中间性态土颗粒接触状态临界条件参量FC_(in-min)和FC_(in-max)的方法,分析各参数对FC_(in-min)和FC_(in-max)的影响规律,建立基于基本物理性能指标的FC_(in-min)和FC_(in-max)预测方法,最终提出全FC范围(FC=0~100%)的砂-粉混合料各颗粒接触状态临界条件参量的有效评价方法。

饱和珊瑚砂体应变发展模式与预测模型试验研究

珊瑚砂具有较好的排水条件,地震、波浪荷载作用下饱和珊瑚砂产生的排水变形易引起海床和附近结构物的破坏。利用GDS循环三轴仪,针对南沙岛礁饱和珊瑚砂试样进行了一系列循环排水加载试验,以探究细粒含量FC、相对密度D_r及循环应力比CSR对饱和珊瑚砂变形特性的影响。试验结果表明,饱和珊瑚砂的累积体应变ε_(vp)的发展速率和变形程度随FC、CSR的增大而增大,随D_(r)的增大而减小。饱和珊瑚砂ε_(vp)-N关系曲线呈现出循环平稳和循环蠕变两种发展模式。引入潜在破坏系数DP表征FC对ε_(vp)发展模式的影响,建立了DP×CSR-D_(r)框架的饱和珊瑚砂体应变发展模式评价方法。为表征FC及D_(r)对饱和珊瑚砂ε_(vp)-N关系曲线的影响,引入了骨架孔隙比e_(sk)*,发现两种发展模式下ε_(vp-s)与e_(sk)*均存在良好的相关性,遂建立了排水循环加载条件下饱和珊瑚砂的体应变发展模型,可以较好地预测饱和珊瑚砂的累积体应变发展规律。

覆岩离层注浆采空区自燃“三带”分布规律

覆岩离层注浆技术通过压实采空区内的破碎岩体,改变了采空区的流场特性和自燃“三带”的分布情况。为了探讨屯兰矿22301综采工作面离层注浆件下采空区遗煤自燃风险范围,基于实测和数值模拟相结合的方法,对该工作面采空区内存在的自燃“三带”进行准确划分;并提出了注浆钻孔的空隙率三维数学模型,评估不同注浆钻孔位置对采空区流场的影响。结果表明:修正后的空隙率三维数学模型能更好地反映注浆后采空区的气体流场,其模拟结果与现场实测结果的残差精度提高22%;相比于未注浆情况,离层注浆后采空区受到压实作用,有效抑制采空区自然发火的危险性,并导致工作面漏风风流向上汇聚,使采空区垮落带较高位置的氧气体积分数增加;注浆钻孔的布置参数对采空区流场将产生影响,其影响关联度依次为钻孔间距、钻孔排数、钻孔影响半径。

结构性对软黏土次固结特性影响的试验研究

【目的】分析软黏土原状样和重塑样次固结系数随固结压力的演化规律,比较不同试样的孔隙比和孔径分布曲线,探究结构性影响软黏土次固结特性的内在机理。【方法】对上海和温州软黏土的原状样和重塑样开展不同固结压力下的次固结试验及相同孔隙比下的压汞试验,得到试样在对应固结压力下的次固结系数及孔径分布曲线。【结果】原状样的次固结系数随固结压力的增大呈先增大后减小的变化规律,重塑样的次固结系数基本不受固结压力的影响。相同孔隙比下的原状样和重塑样在孔径分布上存在明显差异,而两者的次固结系数基本一致。但是,相同压力下的原状样和重塑样的次固结系数差值与孔隙比差值具有良好线性关系。【结论】固结压力对原状样次固结系数具有重要影响,但对重塑样次固结系数的影响可忽略不计。此外,相同压力下的原状样和重塑样的次固结系数差异,主要是结构性引起两种试样的孔隙比不同所致的,而孔隙结构对次固结系数的影响可忽略不计。

地铁车站下水平冻结过程中冻胀的热−水−力耦合模型研究

随着地下空间大规模开发利用,人工冻结法在隧道下穿上覆结构工程中得到广泛应用,但上覆结构对冻胀变形控制要求也越来越高,而上覆既有结构与冻结法工艺的相互作用规律尚不明晰。为此,提出多物理场耦合冻胀变形计算方法。依托上海地铁18号线国权路站下穿既有10号线上部运营车站的盾构隧道工程,以上海第⑤_(1)层灰色黏土为对象,研究新建隧道冻结法施工对上部运营车站主要结构的扰动作用。以孔隙比、冻结温度和平均水压力为耦合变量,考虑水分迁移,推导冻胀变形公式,改进热−水−力耦合的冻胀计算模型。基于黏性土的冻胀试验,获得冻胀试样的应力−应变关系,描述黏性土孔隙结构的变化规律。利用软件COMSOL Multiphysics的弱形式模块,开展热−水−力三场耦合数值模拟。结果表明:模拟结果与监测数据具有较高的拟合度,并小于预定的控制值,验证了耦合理论的正确性。研究成果可为类似冻结下穿隧道工程,提供一种多物理场耦合作用的上覆结构变形计算方法;为下穿隧道工程冻结法设计及施工提供有效的计算参数;为制定下穿隧道工程冻结法加固施工的安全控制指标,提供科学依据。

振动排水条件下软黏土的渗透特性试验研究

为研究振动排水条件下软黏土的渗透特性,采用振动排水固结仪和变水头渗透试验装置,对软黏土进行振动排水条件下的渗透试验,分析了荷载幅值、频率以及孔隙比对软黏土渗透性的影响规律。研究结果表明:软黏土的渗透系数随着加载时间的增加呈现先减小后增大再减小的趋势;随着载荷幅值的增大,渗透系数的增幅亦相应增大;不同频率下的渗透系数在加载中期增幅不同,1 Hz时对应的增幅最高;提出了适用于振动排水条件下e-k非线性表达式,渗透系数随着孔隙比的减小而减小。研究结论可为振动排水固结法的设计及应用提供参考。

硬沥青改性沥青混凝土黏结层路用性能研究

选择硬沥青作为一种天然沥青添加剂,通过在沥青混凝土黏结层中添加6%,7%,8%的硬沥青,与未添加硬沥青的混合物进行比较,评估硬沥青对沥青混凝土性能的影响。结果表明:添加硬沥青的混合物稳定性提高的同时,流动性增加,导致混合物具有更大的变形性;当硬沥青添加比例为6%时,混合物具有最优路用性能,表明在沥青混凝土黏结层中添加适量的硬沥青可有效提升道路铺装的质量和耐用性。

考虑孔隙比的冻胀弱敏感性土修正PCHeave模型研究

针对我国严寒地区高速铁路路基填料和机场填方等工程具有严格的压实度要求,而考虑孔隙比的冻胀弱敏感性土冻胀影响研究尚未有系统性的理论分析,采用理论与经验分析相结合的方法,基于冻胀弱敏感性土的孔隙比与渗透系数和未冻水含量之间的关系,建立考虑孔隙比的修正PCHeave模型。基于该模型分析孔隙比与冻胀量、冻结深度和冻胀率之间的关系,并进行试验对比验证。研究结果表明:孔隙比与冻胀弱敏感性土的未冻水含量之间存在很好的线性关系;冻胀弱敏感性土的冻胀量和冻胀率均随孔隙比先增大再减小,即存在一个最不利孔隙比使得冻胀量和冻胀率均达到最大值;冻胀弱敏感性土的冻结深度随孔隙比增大而逐渐增大;若仅考虑孔隙比对饱和渗透系数的影响,冻胀量和冻胀率均随孔隙比显著增加,若仅考虑孔隙比对未冻水含量的影响,冻胀量和冻胀率均随孔隙比减小,但减小幅度很小。冻胀弱敏感性土通常被认为不能产生显著冻胀,在一定孔隙比下也能产生较大冻胀,同时考虑孔隙比对饱和渗透系数与未冻水含量的影响要更合理。冻胀弱敏感性土的冻胀不能忽略孔隙比的变化,与试验结果对比,该模型能够较好地描述孔隙比对冻胀弱敏感性土的冻胀影响。