Evaluation of cleaning methods for granite based on petrographic examinations

The decay of granite blocks in buildings results in microfracturing, mineral alteration and salt crystallisation. The conservation of granite historic buildings involves the application of cleaning methods to reduce these effects and to improve the general condition of the stone. Strong cleaners applied without any control have sometimes caused damage to the materials. This study determines the effect of various cleaning methods on microfractures, mineralogy and soluble salt content in granite. Samples of weathered granite from buildings in Trinity College, Dublin and unweathered freshly-quarried granite were cleaned by physical and chemical methods. The condition of the granite was assessed before and after cleaning by examining thin sections under a petrographic microscope. Fracturing, mineral transformation and soluble salt content were used as indicators of the condition of the stone. This paper concludes that the cleaning methods tested do not significantly alter the intensity and depth of fracturing in weathered granite. It also concludes that chemical cleaning does not cause significant mineralogical alteration to weathered granite and that salts remaining after cleaning are remnant weathering products and not reaction products. Finally, the paper highlights the effectiveness of a poultice containing detergent and chelating agents in removing salts from weathered granite.     

Artificial weathering and non-destructive tests for the performance evaluation of consolidation materials applied on porous stones

The evaluation of consolidation treatment efficiency in terms of improving the resistance of treated lithotypes to deterioration phenomena caused by soluble salts crystallisation, is taking place through dynamic artificial weathering accelerated tests of marine salt spray. Quarried biocalcarenites from Greece and Cyprus have been treated with four consolidation materials (diversified according to their deposition mechanism). The materials applied are colloidal dispersion of silica, pre-hydrolysed ethyl silicate with amorphous silica, ethyl silicate in ethanol and acrylsiliconic resin in organic solvents. The treated stone samples are placed in an artificial weathering chamber, where they remain for nearly two months, being attacked by severe quantities of marine salt spray. The application of non-destructive techniques (weight and ultra sonic velocity measurements, deteriorated surface analysis by a camera-laser scanning system) during the salt spray simulations verified the improvements presented to the consolidated biocalcarenite samples in comparison to the untreated ones. Consolidated samples present weight stability during the tests, increase in ultra sonic velocity and minor fluctuations on it, and less roughness increase and grain detachment during the simulations. Deductions among the consolidants are made indicating the superiority of ethyl silicate as an appropriate consolidant for those biocalcarenites, as it has arisen from these certain tests.     

华南风化花岗岩劈拉断裂行为的试验与细观模拟研究

为研究不同风化程度花岗岩在劈拉受载下的破损行为,该文对广东从化地区新鲜、微风化、中风化三种风化程度的花岗岩进行微观特征测量及巴西圆盘试验研究。分别基于考虑空间相关特征的随机模型和数字图像技术两种方法实现对岩样细观结构的表征,结合细观参数反演技术,建立反映岩石细观非均质组构特性的颗粒离散元模型,对花岗岩劈拉试验进行数值仿真试验研究。结果表明,随着风化级别的提高,花岗岩中粘结力较强的长石等矿物向粘土矿物转化,结晶强度降低,微孔隙等软弱结构增多,岩石宏观力学性能不断劣化,劈拉破坏由单一裂纹主导转为多条分叉状裂纹,岩样脆性也逐渐减弱。基于两种方法建立的细观随机力学模型仿真结果均表明岩样的劈拉强度随风化级别的提高逐渐降低,与试验结果变化趋势相符,分析得到不同风化花岗岩的劈拉破裂响应特征与试验结果一致,且从细观层面对花岗岩样受劈拉作用的渐进破裂响应提供了深入认识。     

Accelerated weathering of cementitious matrix for the development of an accelerated laboratory test of biodeterioration

Cement based materials are porous, may contain organic adjuvants, and thus possesses an important primary bioreceptivity. To preserve constructions from fungal colonization and to act efficiently against fungal biodeterioration, it is necessary to have a better understanding of biodeterioration mechanisms and its effects on materials properties. An accelerated laboratory test which allows us to compare the growth of three fungal strains and the aesthetic biodeterioration of a cementitious matrix was developed. As the surface pH of the fresh cement specimen is too high to allow fungal growth (pH ~12), accelerating weathering of the matrix, consisting of the combination of carbonation and leaching, was performed to reduce the matrix alkalinity. XRD analyses and SEM observations pointed out that the matrix surface is progressively covered by a calcium carbonate layer as the weathering increases. Results point out that the microbial growth occurs on matrix with a surface composition more like a limestone than a cementitious one.     

Modification of the porous network by salt crystallization in experimentally weathered sedimentary stones

The aim of this study is to understand how the porous network of a stone is modified by the crystallization of sodium sulphate. Samples of five different stones have been experimentally weathered and evaluated thanks to mercury porosimetry in three different states: fresh, weathered by salt and weathered cleaned from the salts. Optical and electronic microscopy observations have also been led to complete these measurements. The results show that porosity and the general aspect of the porous network remain quite similar after weathering. Nevertheless, crystals tend to grow on all the grains regardless of the size of the related voids (pores or cracks), and these crystallizations seem to be harmful for the stone: a lot of voids of different entry sizes (from 10 nm to 20 μm) have been affected by the accelerated ageing tests. This study confirms that generally stones with a high amount of small pores (up to several μm) are the most susceptible to suffer from salt damage. Nevertheless, the influence of a few other features (high porosity, pore shape and pre-existent intragranular cracks) on the long-term behaviour of the stones suffering from salt decay is discussed.     

Mineralogical study of the deterioration of granite stones of two Portuguese churches and characterization of the salt solutions in the porous network by the presence of diatoms

Two Portuguese churches were built with stones of different types of two-mica fine to coarse grained granites. The stones in both monuments were previously submitted to a natural weathering process in the quarries leading to a homogeneous and very well interconnected porous network composed of very thin fissures, allowing a fast capillary transfer of rain water and salt solutions. Therefore, the stones presently exhibit several types of stone decay. A mineralogical study of the deteriorations was carried out in the two churches that permitted the identification of several minerals of soluble salts responsible for stone decay. Some forms of diatoms have been identified in samples of deteriorated stones in both monuments. Several ions in the salt solutions present in the porous networks of the granites, which are in conformity with the minerals of soluble salts associated with the deterioration of the granite, permit the development of several forms of diatoms.     

Water and salt migration through a sandstone coping

A section of decayed sandstone coping was removed from the parapet of Sydney's (Australia) 90-year old Central Railway Station and subjected to a number of tests to confirm whether salts migrating through the stone from the upper surface contribute to the deterioration on the underside. Tests included the measurements of water absorption, bulk density, ultrasonic velocity through the stone and the depth and rate of water and salt migration. As well, the composition and concentration of salts within the stone were determined. The results indicate that the porosity and water absorption capacity of the stone have increased with time of weathering and that the salts present in the stone are primarily sulfates of calcium and magnesium. The salts do readily migrate through Sydney sandstone, and they concentrate on the underside of external cornices and coping where they contribute to the deterioration of the stonework, as they crystallize. It is suggested that lead flashing on the top surface of new (replacement) stone would alleviate this problem. It is not evident whether flashing on weathered stone would be of any benefit.     

Preparation and properties of cast aluminium alloy-granite particle composites

With a view to develop light weight, low cost and abrasion resistant material cast aluminium alloy composites dispersed with granite particles were prepared and their properties were evaluated. Natural mineral granite was crushed and treated prior to its incorporation in the aluminium alloy. Liquid metallurgy techniques was used to prepare composites involving the following steps: melting of aluminium alloy in graphite crucible, stirring of the melt, addition of granite particles and reactive metal in the melt and pouring the composite melt into permanent moulds. Physical, mechanical, tribological and metallographic properties of composites were studied. It was observed that there was reasonably uniform dispersion of granite particles in the matrix. Hardness and tribological (abrasive wear) properties of the base alloy improved considerably due to addition of the granite particles into it. This clearly indicates that these cast aluminium alloy based composites can be used as wear resistant materials.     

基于原子力显微镜技术对全气候老化沥青的老化非线性预测

采用全气候加速老化箱对马歇尔成型的SMA-13、AC-13沥青混合料分别进行0、1000、2000及3000h的老化,对混合料中的老化沥青进行抽提。沥青老化后的形貌高度(Height)、粘附力(Adhesion)以及模量(Modulus)用原子力显微镜(AFM)进行量化。选用Verhulst模型,采用1stOpt的LM+通用全局优化法对试验数据进行非线性拟合,分别建立AFM试验指标与老化时间(t)之间的非线性微分模型。结果表明:在全气候老化条件下,非线性方程可以精确地从微观角度对沥青混合料中沥青的老化规律进行描述,模型参数L和r对老化状态和老化速率进行量化。随着老化时间的增长,形貌粗糙度值降低,粘附力和模量的粗糙度值增加。     

Short-term natural weathering of MSWI bottom ash

The release of heavy metals from MSWI bottom ash has been the key concern in the management of this material. The leaching distribution values obtained from 100 freshly quenched bottom ash samples, according to the German DIN 38414-S4 procedure test, showed the release of lead, zinc and copper to be the main hazards associated with bottom ash utilisation as a secondary building material. Currently, natural weathering of MSWI bottom ash, for an estimated period of 1-3 months, is the most economic treatment available to ensure the eventual utilisation of this material. The leaching of natural weathered bottom ash in the short-term (up to 9 months) was studied. The most significant changes in the bottom ash were found to occur in the first 90 days. At pH values greater than 12, lead, zinc and copper were the main heavy metals to be released from the MSWI freshly quenched bottom ash samples studied. Natural weathering for a period of about 90 days reduced the leaching of heavy metals, stabilising the bottom ash pH to minimise the solubility of metal hydroxides, and enabled the residue to be used as secondary building material. The profile of the pH neutralisation curve is similar to that described by carbonates, which would suggest that the reaction is controlled by CO(2). The formation of insoluble oxides as well as carbonates control the immobilisation of certain heavy metals, e.g. lead and zinc. The leaching of aluminium increases during this short natural weathering stage due to elemental metal oxidation. Aluminium solubility is controlled by the precipitation of gibbsite or other aluminium-sulphate neoformations. The latter may contribute to the immobilisation of heavy metals.     

Sample preparation techniques for nano-mechanical characterization of glass fiber reinforced polyester matrix composites

Glass fiber reinforced plastics are widely used in a host of engineering applications. In these two component materials, the region around the boundary where the components meet is known as the ‘interphase’. The size of the interphase is typically of the order of few microns and understanding the mechanical properties of this microscopic region is central to understanding the mechanical behavior of the composite. Such a small region is amenable to nanomechanical investigation using nanoindentation techniques. For nano length scale investigation it is imperative to have a surface with a roughness of the order of 10s of nanometers. In this investigation techniques have been developed to obtain very low surface roughness in both monolithic polyester and glass fiber reinforced polyester composite samples using a combination of abrasion and etching.     

循环冲击下风化花岗岩渗透性演化规律

针对低渗透离子型稀土矿体回采效率低的缺点,提出利用爆炸应力波改变岩体内部孔隙结构进而提高渗透性的设想,并通过试验进行验证。选取赣南某离子型稀土矿弱风化层花岗岩为研究对象,利用改进的SHPB装置进行等速循环冲击,结合GDS-VIS三轴渗流试验,分析风化花岗岩循环冲击后的破坏模式,并研究有效孔隙度对循环动荷载前后岩石渗透性变化规律的影响。研究结果表明:随着冲击次数的增加,风化花岗岩抗冲能力逐渐减弱,其破碎程度与冲击速度呈正相关;冲击速度为4 m/s和5 m/s的等速循环冲击会使风化花岗岩渗透性呈现先减后增的趋势,而冲击速度为6 m/s的等速循环冲击会使风化花岗岩渗透性持续增大至岩样损坏;岩体渗透性受其有效孔隙度的影响,随有效孔隙度的增大整体呈现上升趋势,同时风化花岗岩初始有效孔隙度越大,冲击后其内部孔隙结构更易发生改变,后续循环冲击荷载下增渗效果更明显。     

Review Melt crystallisation of polymer materials: The role of the thermal conductivity and its influence on the microstructure

Even though many characteristics of the quiescent crystallisation process of polymers have been deeply investigated in the long run, some subjects are still open. Indeed, the theory of nucleation and growth, originally developed for metals and low molecular weight materials, have been extended to polymers without taking into account all the characteristics of macromolecules that can induce a crystallisation behaviour different from that of atoms or small molecules. This paper, within the framework of nucleation and growth, reviews the main aspects of the crystallisation process of polymers and discusses its influence on the microstructure, also in comparison with metallic and ceramic materials. Additional factors, often neglected, affecting the crystallisation process have been also identified. In particular, consideration is given to heat flow from solid to melt during polymer crystallisation that can provide an explanation for modified spherulitic morphologies found in fibre based composite materials and blends. Moreover, the circumstances under which thermal gradients within polymer samples may play a dominant role in crystallisation are underlined. Finally, several examples of polymer textures, that could have been originated by heat transfer anisotropy inside samples, are shown.     

非晶态Ni—Si—B系合金在FeCl3溶液中的腐蚀行为

用失重法研究了几种Ｎｉ－Ｓｉ－Ｂ系合金在ＦｅＣｌ３溶液中腐蚀行为，分别考查了腐蚀速率与材料组分，表面状态，溶液温度，浓度及ｐＨ值的关系。结果表明：随着Ｎｉ含量增加，表面状态越粗糙，溶液浓度增加，温度升高，ＰＨ值降低，均将使腐蚀速率增加。     

加固材料在石质文物保护中应用的研究进展

阐述了石质文物风化机理及加固材料在石质文物保护中的地位和作用,分析了目前广泛使用的无机加固材料、有机加固材料的保护原理、方法特点及其应用,并提出了在石质文物保护中有发展前景的加固材料.     

Multi-attribute optimization of end milling epoxy granite composites using TOPSIS

Epoxy granite composites are identified and recognized as better materials for machine tool applications due to inherent damping properties. However, end milling of these composites has not been explored much. Milling of epoxy granite composites presents a number of problems, namely, cutting forces and surface roughness appear during machining. This research work focuses on end milling of epoxy granite composite specimens using high-speed steel end mill cutter by varying the cutting conditions such as spindle speed and feed with a uniform depth of cut and selection of optimal machining parameters. The experimental runs of 27 different trials were carried out and three different attributes such as thrust force, tangential force, and surface roughness were analyzed. This research work presents a sequential procedure for machining parameters selection. Selection of optimal machining parameters is done on the basis of Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method.     

The Flin Flon paleosol and the composition of the atmosphere 1.8 BYBP

Within the 1800 to 1900 my old Flin Flon-Snow Lake greenstone belt, Amisk Group volcanics are overlain by Missi Group fluvial sediments. Several localities along the Missi-Amisk contact, the volcanics show evidence of subaerial weathering. Field relationships, mineralogical evidence, and chemical analyses confirm that this alteration zone is a paleosol. Pedogenic fabrics and mineralogy were somewhat obscured by greenschist-grade metamorphism associated with the Hudsonian orogeny (1750 my). This is especially true in the upper meter of the paleosol, where metamorphic paragonite and sericitic micas developed in a crenulated fabric. This metamorphism did not, however, obliterate the imprint of weathering on the Amisk volcanics. Features characteristic of well-drained modern soils are evident in the paleosol. Corestones of spheroidally weathered pillow lavas occur at depth within the paleosol (Cr horizon). The corestones decrease in size upward and eventually disappear into a hematite-rich horizon at the top of the paleosol. These macroscopic changes are accompanied by a decrease in CaO and MgO and by an increase in Al2O3, TiO2, and total iron toward the paleosol-Missi contact. Ferrous iron decreases upward toward the contact; FeO was apparently oxidized to ferric iron and retained within the paleosol during weathering. The oxidation and retention of iron within the Flin Flon paleosol indicates that PO2 was probably > or = 10(-2) P.A.L. at the time of weathering. The behavior of iron in the Flin Flon paleosol contrasts sharply with its behavior in the 2200 my Hekpoort paleosol, which is strongly depleted in iron. This difference suggests that a significant increase in the ratio of PO2/PCO2 in the atmosphere took place between 2200 and 1800 mybp.     

Study of Abrasive Wear Volume Map for PTFE and PTFE Composites

The potential of this work is based on consideration of wear volume map for the evaluation of abrasive wear performance of polytetrafluoroethylene (PTFE) and PTFE composites. The fillers used in the composite are 25% bronze, 35% graphite and 17% glass fibre glass (GFR). The influence of filler materials, abrasion surface roughness and applied load values on abrasive wear performance of PTFE and PTFE composites were studied and evaluated. Experimental abrasive wear tests were carried out at atmospheric condition on pin-on-disc wear tribometer. Tests were performed under 4, 6, 8 and 10 N load values, travelling speed of 1 m/sec and abrasion surface roughness values of 5, 20 and 45 μm. Wear volume maps were obtained and the results showed that the lowest wear volume rate for PTFE is reached using GFR filler. Furthermore, the results also showed that the higher is the applied load and the roughness of the abrasion surface, the higher is the wear rate. Finally it is also concluded that abrasive wear process mechanism include ploughing and cutting mechanisms.     

Effects of Lubricant Condition and Tool Wear in Hard Turning of Novel-Abrasion-Resistance (N-AR) Cast Iron

Advanced materials, such as high abrasion resistant cast iron, have great applications for abrasive and erosive environments. Since the amount and the hardness of the microstructural carbides constituents in this material is extremely high, the abrasion-resistance cast iron is generally difficult to be machined with traditional cemented carbide tool. The hard and abrasive particles in this material can remarkably shorten the cutting tool life through abrasion of tool face and deterioration of cutting edge. In this article, Cubic Boron Nitride (CBN) cutting tool has been used to machine a novel-abrasion-resistance (N-AR) cast iron. The performances of CBN tool under different lubrication conditions were evaluated in view of tool wear, cutting force, and surface roughness (Rz). Further more, the wear rate of CBN tool under different machining condition and the mechanism of the CBN tool in machining of this type of work materials has also been investigated.     

20SiMn低合金钢和0Cr13Ni5Mo不锈钢的多相流损伤行为

对水轮机用金属材料20SiMn低合金钢和0Cr13Ni15Mo不锈钢进行旋转圆盘仪空蚀和冲刷磨损单元和组合多相流损伤实验。结果表明，20SiMn低合金钢和0Cr13Ni15Mo不锈钢的冲刷磨损及空蚀和冲刷磨损联合作用损伤累积质量损失－时间曲线均呈线性关系，空蚀和冲刷磨损联合作用对材料造成的损伤显著高于空蚀和冲刷磨损单独作用，空蚀和冲刷磨损的交互作用在空蚀和冲刷磨损联合作中起重要的作用；在空蚀和冲刷损联合作用中，液体空化及随后的空泡溃灭改变了流体中固相颗粒的运动方向，引起固相颗粒的流速增加和攻角改变，从而加剧了固相颗粒对材料表面的损伤。