Time-dependent atmospheric degradation of building stone in a polluting environment

Weathered facing stone of Durham Cathedral is undergoing a program of progressive replacement. The durability characteristics of the original stone and the replacement stone are examined, and those factors that are responsible for atmospheric weathering are discussed. Results of a field survey into relative weathering rates in the Durham area using local gravestones also are reported.     

岩石强度时效性演化模型

在一定的外界荷载作用下,岩石材料的强度会随时间不断降低,在工程上常表现为由于强度的弱化而导致岩体的突发性破坏行为以及岩体的长期强度等不同现象和问题。因此,岩石强度的时间效应研究对岩体工程施工安全和工程长期稳定性都具有重要的指导意义。在对大量试验结果分析的基础上,总结了岩石强度演化规律与内在机制,发现岩石强度的损失与岩石本身的固有强度、所受应力状态（屈服接近度）以及应力作用的持续时间有关,在此基础上,提出了以岩石凝聚力和内摩擦角随上述因素变化为核心的岩石强度时效性演化模型。通过对多组试验数据的模拟分析表明,提出的岩石强度时效性演化模型能很好地描述岩石强度的演化规律,可以较好地定量反映不同应力水平下岩石强度弱化过程,且物理意义明确,为岩石强度的时间效应研究开拓了一个新的思路和方法。     

三维裂纹布置角度对砂浆材料强度的影响

利用伺服控制试验系统及声发射设备对含有单椭圆裂纹的非均质砂浆材料进行物理试验,获得了单轴加载作用下不同布置角度的三维内部裂纹试样的全应力-应变曲线和声发射数据。找到了声发射数据与应力-应变曲线的对应关系。根据对应关系,判断出试样的起裂应力及破坏应力。分析了裂纹布置角度对材料强度的影响,分析表明：裂纹与加载方向为45º夹角时最难破坏,与加载方向成60º夹角时最容易破坏。此外,裂纹尖端起裂应力为试样极限强度的86.07 %～87.42 %。     

Time-dependent changes of the electrical conductivity of basaltic melts with redox state

The electrical conductivity of basaltic melts has been measured in real-time after fO₂ step-changes in order to investigate redox kinetics. Experimental investigations were performed at 1 atm in a vertical furnace between 1200 and 1400 °C using air, pure CO₂ or CO/CO₂ gas mixtures to buffer oxygen fugacity in the range 10⁻⁸ to 0.2 bars. Ferric/ferrous ratios were determined by wet chemical titrations. A small but detectable effect of fO₂ on the electrical conductivity is observed. The more reduced the melt, the higher the conductivity. A modified Arrhenian equation accounts for both T and fO₂ effects on the electrical conductivity. We show that time-dependent changes in electrical conductivity following fO₂ step-changes monitor the rate of Fe²⁺/Fe³⁺ changes. The conductivity change with time corresponds to a diffusion-limited process in the case of reduction in CO-CO₂ gas mixtures and oxidation in air. However, a reaction at the gas-melt interface probably rate limits oxidation of the melt under pure CO₂. Reduction and oxidation rates are similar and both increase with temperature. Those rates range from 10⁻⁹ to 10⁻⁸ m²/s for the temperature interval 1200-1400 °C and show activation energy of about 200 kJ/mol. The redox mechanism that best explains our results involves a cooperative motion of cations and oxygen, allowing such fast oxidation-reduction rates.     

Characterization of natural stone material used in the Nordic eastern urban and costal environment

The report analyses the main properties pertaining to the durability of Finnish granitoid rocks, based upon extensive field and laboratory data collected during the past ten years. Commercial materials have been tested and compared along ten years of production and their frost resistance assessed according to European standards. Laboratory tests have been coupled with non-destructive methods most used on site assessment as ultra-pulse velocity and Schmidt hammer in order to compare the results of commercial materials with materials on construction site. Evaluation of durability has included petrographic analysis, crack density, and for site exposed material, chemical analysis, to understand the environmental effects on it. The material has generally maintained its original properties. It has natural heterogeneity, and it presents higher interlocked cracking network on the surface of the exposed materials. Site samples in some cases have shown chemical changes due to environmental actions.     

Compression strength properties of the hardened cement mortar mixed with municipal incineration fine bottom ashes

In order to recycle the incineration fine bottom ash generated from municipal solid waste as a fine aggregate construction material(<4.75 mm), a series of uniaxial compression tests were carried out according to the mixing ratio of bottom ash, the curing temperature, the water–cement ratio, the mixing ratio of expanded poly styrene (EPS), and the curing time. As the results of tests, the compression strengths cured 28 days of all specimens prepared with different mixing ratios are ranged between 87 and 220 kg/cm². The water content of the hardened cement mortar is not much different with the curing time. Also, the water content is increased with increasing the mixing ratio of bottom ash, the water–cement ratio, and the mixing ratio of EPS. The unit weight of the hardened cement mortar is decreased with increasing the mixing ratio of bottom ash and the mixing ratio of EPS. The compression strength of the hardened cement mortar is decreased with increasing the mixing ratio of bottom ash. The compression strength of the hardened cement mortar cured at 30 ± 2°C and 40 ± 2°C is bigger than that of the cement mortar cured at normal temperature (20 ± 2°C). However, the compression strength of the hardened cement mortar cured at 30 ± 2°C is bigger than that of the cement mortar cured at 40 ± 2°C. The compression strength is increased at the range from 0.55 to 0.6 of water–cement ratio, and then the compression strength is decreased over 0.65 of water–cement ratio. Meanwhile, the compression strength of the hardened cement mortar is decreased with increasing the mixing ratio of EPS.     

国内外航磁补偿技术历史与展望

笔者从飞机干扰场构成、数学模型建立、模型系数求解3个方面概要介绍了航磁补偿技术的基本原理,回顾了国内外航磁补偿方法研究历程和航磁补偿仪器更新换代的历史,对比了两种航磁补偿质量评价方法,并在分析航磁补偿技术研究现状的基础上,对航磁补偿技术的发展趋势进行了分析与预测.     

Effect of strain rate on strength properties of low-calcium fly-ash-based geopolymer mortar under dry condition

This paper presents the mechanical and elastic properties of inorganic polymer mortar under varying strain rates. The study includes a determination of the compressive strength, modulus of elasticity and Poisson’s ratio at 0.001, 0.005, 0.01 and 0.05 mm/s strain rate. A total of 21 cylindrical specimens having 100 mm length and 50 mm diameter were investigated, and all tests were carried out pursuant to the relevant Australian Standards. Although some variability between the mixes was observed, the results show that, in most cases, the engineering properties of geopolymer mortar compare favourably to those predicted by the relevant Australian Standards for concrete mixtures. It was found that the change in the strain rate causes different behaviour related to the percentage of the ultimate load. The ultimate strength, Young’s modulus and Poisson’s ratio of the geopolymer mortar depend on the strain rate. It was also found that as the strain rate increases, mechanical and elastic properties of geopolymer mortar substantially increase in logarithmic manner.     

Time-dependent stratification in the Gauthami-Godavari estuary

The time-dependent salinity stratification in an environment of highly variable turbulence of Gauthami-Godavari estuary is described. From time series observations at three stations over two tidal cycles each in the winter (December 1989) and the dry (April 1990) seasons in the Gauthami-Godavari estuary, the development of stratification is correlated with periods of substantially reduced velocity shear. Stratification is observed to be greatest around the low water slacks and least around the high water slacks. The formation of stratification relaxes viscous constraints and a buoyancy circulation rapidly develops. The breakdown of stratification drastically modifies the circulation and largely removes the vertical shear associated with the density driven flow. Destratification occurs around the high water slacks in the lower reaches fairly close to the mouth of the estuary. The variations in the fields of mass will strongly affect the response of the velocity field.     

改性糯米灰浆的室内研究及在九寨沟钙华地质裂缝修复中的应用

我国有着大面积的钙华地区,国内外学者对钙华的形成及影响因素进行了大量的研究,但针对钙华地区地质裂缝生态修复材料及工艺还鲜有研究。文章以九寨沟风景区震后地质裂缝为研究对象,结合水文条件及钙华颗粒的性质,在传统糯米灰浆的基础上,通过掺入不同比例的原料、改性剂及一定级配的钙华颗粒,研制出一种性能优良的灌浆材料,并对其流动性、凝结时间、抗压强度及抗折强度进行测试。室内试验表明:该材料具有流动性好、凝结时间可控、强度高、可水下浇筑等特点;空气中养护试样的各项指标均优于水中养护的试样。优选裂缝修复配合比为:糯米浆0.6~0.64份、石膏1.19份、石灰0.29份、钙华颗粒1份、改性剂1# 0.07份、改性剂2# 1.19%份,浆液可泵期63~86 min,初凝时间74~98 min,终凝时间92~125 min。改性糯米灰浆在九寨沟修复裂缝、加固崖体现场修复试验中取得了良好的效果,将流水漏失量由原来的50%降低至3%,较好的恢复了瀑布景观。应用表明改性糯米灰浆与钙华颗粒具有较好的相容性,可改善钙华颗粒的原生孔隙结构,促进钙华景观的生长。     

Time-dependent behaviour of the rock mass

Summary The strength of intact rock and the rock mass is time-dependent. For intact rock experimental verification is available, for the rock mass the scale of time-dependence is a matter of judgement. Rock mass classifications do however emphasize the effect of time on tunnel stability. This paper examines the source of time-dependence in rocks and the rock mass and suggests a technique for estimating the long term strength. The long term strength of the rock mass is controlled by the time-dependent weakening of intact rock. Frictional resistance, a major source of rock mass strength, increases rather than decreases with time. Lifetime estimation for rocks can be accomplished phenomenologically or mechanistically. The first is a statistical process of wide applicability, the second is more restrictive in usage as its applies only to materials that suffer time-dependent strain (creep). Although the mechanistic route is more appealing, it has a major drawback as it concentrates on steady state creep. There is no strong evidence for steady state creep in rocks. The technique for long term prediction is developed through the analysis of the failure rate under constant load. The failure rate for a given load and environment is established from the frequency distribution of time-to-failure data as measured in static fatigue tests. As expected, the failure rate is strongly affected by both the loading and the environmental condition. The influence, however, is systematic and predictable.     

Quantitative evaluation of stability changes in historical stone bridges in Kagoshima,Japan, by weathering

This study deals with a weathering problem of historic arch stone bridges built of welded tuff about 150 years ago in Kagoshima, Japan. Based on a detailed comprehensive weathering evaluation we previously carried out, the way in which the weathering affects the structural stability of the bridges is quantitatively evaluated herein by using a distinct element method (DEM).The suitability of this method of analysis was confirmed through a comparison of the numerical analysis results with the in situ load testing data. The analysis results show that when considering the stability of a stone bridge, the slide safety factor and eccentric safety factor are more important than the compressive safety factor. That is, the types of possible failure include sliding and openings between arch blocks. In 150 years of weathering, the shear stress in the arch ring generally increased about 20%. The eccentric safety factor decreased about 9%, from 4.35 to 3.97, and the slide safety factor decreased about 20%, from 8.02 to 6.46. Deflections at the arch crown increased about two times, from 0.60 to 1.28 mm. Despite these changes, the stone bridges are considered to be still in a good condition after 150 years of weathering.     

干密度和细粒含量对砂卵石及碎石抗剪强度的影响

通过对河床砂卵石及爆破碎石的无黏性粗粒土直接剪切试验,对比分析了在不同试验状态下两种粗粒土的细粒含量和干密度分别对其抗剪强度参数的影响以及抗剪强度参数变化规律;试验结果表明,两种粗粒土的抗剪强度参数基本是随着干密度的增大而增大,摩擦角在细粒含量较小时稳定在某一特定值,随着细粒含量的增加而迅速减小;而当干密度增加到一定程度后不同试料在不同试验状态下,咬合力各自都将趋于某一稳定值。从两种试料的试验状态来看,非饱和固结抗剪强度参数相应地比饱和固结的大,河床砂卵石的抗剪强度参数比爆破碎石的大;对同一级配的河床砂卵石在不同相对密度下进行的直接剪切试验结果表明,其抗剪强度参数随着干密度的增大而增大,最终有趋于某一稳定值的趋势。     

The influence of binder/aggregate ratio on the pore properties and strength of repair mortars

Repair mortars with different B/Ag (binder/aggregate) ratios and natural stone were studied in order to understand the influence of limestone aggregate on the properties of mortar and to check the compatibility of repair mortar with a porous limestone. Three different types of mortars with three different aggregate contents were evaluated by using mercury intrusion porosimetry (MIP) and water saturation method (WSM). Changes in density and uniaxial compressive strength as a function of aggregate content were also recorded. For comparison the properties of the porous limestone were also tested, since it is used in monuments and also as aggregate in the mortar. Tested mortars had average porosities of 27.0 % (±2.0), while oolitic limestone has higher average porosity of 32.2 % (±1.9). The limestone has mainly medium and large pore radii (1–100 μm) while the repair mortars even with high aggregate content has predominantly smaller pores. All but one pure repair mortars have higher uniaxial compressive strength than that of the oolitic limestone. The strength decreases while porosity increases with increasing aggregate content.     

论冰碛石的形态特征及其与泥石流石的区别

长期以来流行的球度和圆度概念不足以刻画冰碛石及其他成因砾石的细微特征,需要在其基础上进一步挖掘有判别价值的标志性特征。针对冰碛石与泥石流石辨识的疑难问题,提出外接圆特征、粗糙度特征、圆度-体积特征以及混杂堆积砾石形态构成特征等几个概念。通过这些特征研究,结合真实的冰川擦痕、颤痕等标志,可更加准确地进行冰川沉积物与其他成因沉积物的判定。     

Geochemical evidence for abrupt changes in relative strength of the Arabian monsoons during a stadial/interstadial climate transition

The occurrence and propagation of abrupt climate change between the high and low-latitudes has become an important focus of paleoclimatic and paleoceanographic research. The causes of abrupt change have significant implications for understanding future manifestations of similar forcings under late Holocene (‘Anthropocene’) boundary conditions. Of particular interest are signals indicative of sub-millennial scale climate change in the sub-tropics of similar magnitude and frequency to those recorded in Greenland ice cores. Earlier research in the Arabian Sea has highlighted the sensitivity of sedimentary organic carbon and nitrogen isotope measurements for recording the state of the SW monsoon and associated Arabian Sea Oxygen Minimum Zone. In this study, we exploit the unprecedented fidelity of the sedimentary δ¹⁵N record to identify a 20 cm interval at ODP Site 723 containing a stadial/inter-stadial interval between 43-42 Kyr BP. We employ sedimentary nitrogen isotopes, chlorin pigment and alkenone abundances, major and minor element analyses of highly-resolved (2 mm ≈ 10 yr) samples across this interval to compare a comprehensive, multi-proxy data set to understand (a) the processes contributing to the δ¹⁵N signal in the longer records of denitrification; and (b) the associated climatic events, especially the relative intensity of summer and winter monsoons at these times. A lack of evidence for bioturbation in excess of our 2 mm sampling resolution facilitates decadal-scale oceanographic and climatic reconstructions. Using a four-component flux-dilution model, we show that the deposition of carbonate decreased in parallel with an increase in Total Organic Matter flux from stadial to inter-stadial time. This interval is also marked by a significant drop in lithogenic (dust) accumulation, analogous to a similar decrease noted during deglaciation in the Western Arabian Sea. Combined with alkenone U₃₇^K′-derived estimates for sea surface temperature (SST), we conclude that the climatological shift from stadial to inter-stadial conditions at low latitudes was characterized by repeated switches in mean monsoon state approximately every 200 yr. The winter monsoon was the dominant mode during maximum stadial conditions; conversely the summer monsoon was dominant during maximum interstadial-like conditions. However, each interval was separated by a distinct ‘inter-monsoon’ mode, indicated by a higher continental dust flux but warmer SST. Proxy records for changing bottom-water oxygenation show near-identical results down to the mm-scale, but hint at increased export production leading the onset of anoxia during the stadial/inter-stadial transition. The coherence of all sedimentary signals depicts a wholesale reorganization of the Arabian Sea climate and marine ecosystem over approximately 200 years, a period that may be associated with monsoon modulation by small oscillations in solar irradiance.     

Manuel Rocha Medal Recipient Simulating the Time-dependent Behaviour of Excavations in Hard Rock

Summary Although hard rock is not usually associated with large creep deformation, data collected from the tunnels and stopes of the deep South African gold mines illustrates significant time-dependent behaviour. Apart from application in mining, a better understanding of the time-dependent behaviour of crystalline rock is required to analyse the long term stability of nuclear waste repositories and to design better support for deep civil engineering tunnels in these rock types. To illustrate the subtle problems associated with using viscoelastic theory to simulate the time-dependent behaviour of hard rock, a viscoelastic convergence solution for the incremental enlargement of a tabular excavation is discussed. Data on the time-dependent deformation of a tunnel developed in hard rock further illustrates the limitations of the theory, as it is unable to simulate the fracture zone around these excavations. To simulate the rheology of the fracture zone, a continuum viscoplastic approach was developed and implemented in a finite difference code. This proved more successful in modelling the time-dependent closure of stopes and squeezing conditions in hard rock tunnels. A continuum approach, however, has limitations in areas where the squeezing behaviour is dominated by the time-dependent behaviour of prominent discontinuities such as bedding planes. To overcome this problem, a viscoplastic displacement discontinuity technique was developed. This, combined with a tessellation approach, leads to more realistic modelling of the time-dependent behaviour of the fracture zone around excavations. Received January 15, 2002; accepted June 3, 2002 Published online September 2, 2002     

Zr/Rb ratio in the Chinese loess sequences and its implication for changes in the East Asian winter monsoon strength

The long-term dust accumulation sequences on the Chinese Loess Plateau (CLP) provide a valuable opportunity to study the evolution of East Asian winter monsoon strength. Grain size of bulk samples of loess deposits, though widely used, is a modified measure of the strength of winter monsoon wind due to modification by post-depositional weathering and pedogenesis. This study proposes a new and reliable geochemical climate proxy that records the variability of the East Asian winter monsoon on the CLP. Six loess-paleosol sections on the Plateau were selected for measuring concentrations of the trace elements Zr and Rb as well as grain size. Variations of the Zr/Rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples (MGSB). Though a positive correlation exists between the Zr/Rb ratio and MGSB, the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates. Long-term Zr/Rb variation in the Lingtai section exhibits amplitudes and frequencies similar to those in MGSB and the mean grain size of quartz particles (MGSQ, accepted as a more reliable proxy than MGSB) in the upper loess-paleosol sequence over the past 2.6 Ma. However, for the underlying Red Clay formation, in the interval from about 7-2.6 Ma B.P., the MGSB record is relatively stable, whereas both the Zr/Rb ratio and MGSQ show distinct variability and display amplitudes similar to those observed in the overlying loess-paleosol sequence. These results demonstrate that the Zr/Rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of East Asian winter monsoon winds.