Acidic Rocks as Aggregates in Concrete: Engineering Properties,Microstructures and Petrologic Characteristics

In this research, the possibility of replacing different portions of the normally used aggregate by acidic rocks was investigated. These rock types outcrop at the northern part of Eastern Desert, southwest Ras Gharib area where large quantities of good quality acidic rocks are available their. Portland cement concrete is a composite material made up of the hydrated cement matrix, fine aggregate and coarse aggregate. The scanning electron microscope equipped with an energy dispersive X-ray analysis system (EDX) has been applied to investigate several aspects of Portland cement concrete microstructure. The topics investigated so far include the influence of aggregate composition on the development of the cement paste-aggregate interface and the formation of calcium silicate hydrate CSH/calcium silicate aluminate CSA formation. The silicate gel coated the aggregates in the concrete paste and crystallized into well defined needle like shape, cotton shape as well as euhedral to subhedral crystals of silicate/alumiante and ettringite minerals with free lime librated from the hydrolysis process. The free lime can react again with the aggregates leading to the formation of cementing materials which increase strength and durability of the concrete paste by increasing the interfacial bonds between the used aggregates.     

Comparative carbon emission assessments of recycled and natural aggregate concrete:Environmental influence of cement content

This work examines the environmental and geochemical impact of recycled aggregate concrete produc-tion with properties representative for structural applications.The environmental influence of cement content,aggregate production,transportation,and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region.To obtain a detailed insight into the optimum life cycle parameters,a sensitivity study is carried out in which supplementary cementitious materials,different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered.The results show that carbon emissions were between 323 and 332 kgCO2e per cubic metre of cement only natural aggregate concrete.These values can be reduced by up to 17％by replacing 25％of the cement with fly ash.By contrast,carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50％and 100％,and trans-portation is not included in analysis.However,the concrete with 50％recycled aggregate presented lower increase,only 0.3％and 3.4％for normal and high strength concrete,respectively.In some cases,the rel-ative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25％,and case-specific transportation distances were considered.In absolute values,the concrete mixes with 100％recycled aggregates and 25％fly ash had lower carbon emissions than concrete with cement and natural aggregates only.Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short(15-25 km)and the cement replacement by fly ash is equal or higher than 25％,considering that the mechanical properties are adequate for prac-tical application.The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete,recommending them as an alternative to achieving global sustainability standards in construction.     

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.     

Geotechnical and mineralogical properties of weak rocks from Central Greece

Thirty bulk samples of hard soils-soft rocks such as marls, originating from Euboea Island and Peloponnesus area, were investigated to evaluate their geotechnical behavior. Specifically, by conducting a series of physical and geotechnical tests, such as liquid limit and plastic limit tests, along with the estimation of the grain size fraction, Slake Durability and Point Load Test. Certain parameters were determined and used for empirical correlations with their mineralogical characteristics. The mineralogical composition was determined by X-ray diffraction, thermo-gravimetric and thermal analysis, succeeded by textural analysis performed by Optical Microscope. With the help of the above mentioned tests, we interpreted the observed geotechnical behavior of the examined weak rocks by means of mineralogical composition and texture. Durability and the unconfined compressive strength was found to be influenced by high percentages in carbonate minerals. In addition, it was found that a decrease in clay content resulted in higher strength and durability values. The concluded empirical correlations verified the influence of these parameters and gave a general overview of the engineering behavior of the examined weak rocks.     

Assessment of Durability and Weathering State of Some Igneous and Metamorphic Rocks Using Micropetrographic Index and Rock Durability Indicators: A Case Study

Weathering and durability are the key factors of the rock in the suitability and usefulness of different construction materials, building materials and engineering structures. A single test never predicts the entire factor for suitability of rock stone and aggregate in different uses. Thus, variety of physical, mechanical and chemical tests and indices of rocks are widely used to estimate and evaluate the rocks for the suitability of the required purpose. In all the cases, knowledge of durability and weathering properties are the most important along with the strength of the rock. Micropetrographic index and rock durability indicators (dynamic and static) are the one of the best methods to evaluate the rock for weathering and durability. To estimate these indices, variety of tests are performed such as petrographic examination test, point load index, sulfate soundness test, water absorption test, modified aggregate impact value test and test for specific gravity. Slake durability index and impact strength index tests were also performed for correlation with static and dynamic rock durability indicators due to its application and usefulness in the durability and strength of the rock materials. Micropetrographic index was obtained by petrographic examination test and correlated with all the physical and mechanical properties used for find out the durability indicators. The present study is to express the usefulness of these three indices in the classification of weathering and durability classes and estimation of durability indices by slake durability index, impact strength index and micropetrographic index.     

Salt weathering in dual-porosity building dolostones

The influence of rock fabric on physical weathering due to the salt crystallization of selected brecciated dolostones is discussed. These dual-porosity dolostones are representative of heterogeneous and anisotropic building rocks, and present highly complex and heterogeneous rock fabric features. The pore structure of the matrix and clasts is described in terms of porosity and pore size distribution, whereas the relative strength for each textural component is assessed using the Knoop hardness test. The whole characterisation process was carried out using the same samples as those used in the standard salt durability test (EN-12370), including connected porosity, the water saturation coefficient, fissure density, compressional wave velocity and waveform energy.

Results show the most important rock fabric elements to be considered are the matrix and clast properties and the nature of fissures. Firstly, a relatively weak matrix was the focus of major granular disintegration as it presents high porosity, low pore radius and reduced strength. Secondly, narrow micro-fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth. On the contrary, macro-fissures do not contribute greatly to rock decay since they act as sinks to consume the high supersaturations caused by growth of large crystals. Additionally, an analysis of stress generated by crystallization was carried out based on the general situation of a lenticular crystal geometry. Finally, the relationships between whole petrophysical properties and durability were established using a principal component analysis. This analysis has clearly established that the durability of rocks affected by salt crystallization mechanisms diminishes in weaker and anisotropic rocks with high porosity and fissure density.     

Quantitative assessment of rock texture and correlation with drillability and strength properties

Summary A dimensionless quantitative measure of rock texture, describing grain: —shape, orientation, degree of grain interlocking and relative proportions of grains and matrix (packing density) has been developed. Data required for the model are obtained by image analysis of thin sections and concerns percentage areas of grains and matrix, length, breadth, perimeter, orientation and area of each grain in the viewing window. The results of rock strength, diamond and percussion drillability tests in eleven sandstones, marbles and igneous rocks are reported, and correlated with the developed texture coefficient. The texture coefficient returns highly statistically significant correlations with rock strength and drillability data. Sandstones have low texture coefficients and high drillability whereas igneous rocks have high texture coefficients and low drillability. With particular reference to percussive drillability it is suggested that extensional crack propagation in the sandstones in an energy efficient process since fracture paths propagate through the weak phyllosilicate matrix. Extensional crack propagation in the igneous rocks is an energy intensive process since a significant proportion of the available drilling energy is consumed in the formation of intra-granular fracture paths. Observational and correlated data are supportive of the suggestion that the texture coefficient is a measure of the resistance of the microstructure of a rock to crack propagation, whether it be inter-or intra-granular. The texture coefficient can be used as a predictive tool for the assessment of drillability and rock strength properties. The technique offers a useful approach in understanding fracture initiation and growth as controlled by the texture of intact rock samples.     

Evaluation of selected basalts from Niğde, Turkey, as source of concrete aggregate

Basaltic rocks have been widely used as aggregate for various purposes. They show a variety of textural and mineralogical characteristics that may affect their physico-mechanical properties as well as their use as construction material. The study presented in this paper was carried out on basalts that are widespread in the Middle Anatolian Region of Turkey and that comprise the major source of local crushed rock aggregates. To determine the suitability of the basalts as alternative aggregate resource, Early Quaternary Melendiz Volcanites, Quaternary Karataş volcanites andİğredağ basalts were selected around the Niğde Region. The experimental studies were conducted on these rocks. The samples were collected as being representative of 11 different types of basalt. The physico-mechanical properties of the basalts of different compositions and textures, and the properties of their aggregates were determined. The results were then compared with the typical acceptance limits in international usage. Although olivine basalts have better aggregate quality compared to other basalts, most of the basalts were found to be suitable for production of crushed rock aggregates for concrete production.     

Alkali-aggregate reactions in concrete

Concrete durability is adversely affected by expansive reactions between cement alkalies and certain rocks and minerals sometimes used as aggregates. Present trends towards production of portland cements containing higher alkali contents than formerly indicate that the problem may become more acute. Recent work shows that the rocks and minerals involved fall into three groups which leads logically to a three-fold subdivision of the reactions termed here: (I) the alkali-silica reaction, (II) the alkalicarbonate rock reaction, and (III) alkali-silicate reactions. A clearer understanding of the mechanisms of these reactions has practical implications particularly because of the light thrown on the criteria for recognition of potentially expansive rocks and minerals in aggregate source materials. Appropriate preventive measures prior to concrete placing make it possible to avoid the worst effects of these reactions. These include use of low-alkali cement, incorporation of a suitable pozzolan, design to reduce wetting and beneficiation of aggregate. The effectiveness of these measures varies however, depending on the mechanism and severity of the reaction.     

Water absorption process effect on strength of Ayazini tuff,such as the uniaxial compressive strength (UCS), flexural strength and freeze and thaw effect

Tuffs have been used as a construction material possibly since ancient times. In Afyonkarahisar, Turkey, there are numerous buildings constructed by tuff. Tuff has been a local construction material, during the Roman, Seljuk and Ottoman periods. Even though tuffs have relatively low durability and low strength values compared to marble, etc., they have survived with no major deterioration failures on many historical buildings. It has also been preferred because of its high porous texture, lightweight and easy shaping and process properties in the building sector. Naturally, it would be easily affected by water and humidity because of its porous structure. However, having this kind of structure leads to poor durability properties due to keeping water in it. The main objective of this study was to evaluate the physical and mechanical properties of the tuff quarried from the region and possible water effect, which may lead to degradation of its strength and durability of the material, thereby shortening the life span of the building structure used. Samples, which were tested after exposing to water and the freeze and thaw effects, were measured at a certain time. In this study, uniaxial compressive strength and flexural strength tests were conducted on test samples. The test results indicate that water may deteriorate the tuff’s strength properties and durability of the materials in due time.     

Engineering characteristics of road aggregates from northern Pakistan and the development of a toughness index

This paper summarizes an extensive series of common durability, shape and strength tests carried out on road aggregates from quarries in northern Pakistan by Sharif et al. at the University of Engineering and Technology, Taxila. The data from these standard tests have been correlated for a particular aggregate type to show the close relationship between these measured physical characteristics. The paper outlines how, once these relationships have been established for a particular aggregate source, it is feasible to simplify the testing or quality assurance regime and monitor only some of these characteristics to assess the overall quality of the aggregate. The physical characteristics have then been combined into a linear relationship, using coefficients estimated from the extensive data set in the paper, to give a single characteristic for an aggregate type known as the Toughness Index (TI). The TI is therefore based on the main strength and durability characteristics of the aggregates and can be used as an indicator of the overall quality of the aggregate.     

桂北元宝山宝坛地区约825Ma镁铁-超镁铁岩的地球化学及其地质意义

镁铁－超镁铁岩的岩石学和地球化学特征表明，元宝山超镁铁岩中橄榄石的Fo为78－83，岩石具有明显的包橄结构，具有LREE亏损，低Th/Nb和La/Nb比值以及高（t)值（约＋5），是来源于亏损地幔低程度部分熔融的岩浆堆晶的产物；宝坛地区镁铁－超镁铁岩富集LREE，具有高的Th/Nb,La/Nb比值和低的（t)值（－0．45－7．01），是镁铁质岩浆上升，结晶过程中与地壳物质混染（AFC）的结果，超镁铁岩与澳大利亚Garidner岩脉群具有相似的不相容元素分布型式和Nd(t) 值，是导致新元古代Rodinia超大陆裂解的地幔柱熔融的产物。     

Eocene magmatism(Maden Complex) in the Southeast Anatolian Orogenic Belt: Magma genesis and tectonic implications

The origin and geodynamic setting of the Maden Complex, which is situated in the Bitlis-Zagros Suture Zone in the Southeast Anatolian Orogenic Belt, is still controversial due to lack of systematic geological and geochemical data. Here we present new whole rock major-trace-rare earth element and Sre Nd isotope data from the Middle Eocene volcanic rocks exposed in Maden Complex and discuss their origin in the light of new and old data. The volcanic lithologies are represented mainly by basalt and andesite, and minor dacite that vary from low-K tholeiitic, calc-alkaline, high-K calc-alkaline, and shoshonitic in composition. They exhibit enrichments in large ion lithophile and light rare earth elements, with depletions in high field strength elements. Basaltic rocks have uniform Sr and Nd isotope ratios with high εNd(t) values varying from t5.5 to t6.7, in contrast to, andesitic rocks are characterized by low εNd(t) values ranging from à1.6 to à10. These geochemical and isotopic characteristics indicate that two end-members, a subduction-related mantle source and a continental crust, were involved in the magma genesis. Considering all geological and geochemical data, we suggest that the Eocene Maden magmatism occurred as a post-collisional product by asthenospheric upwelling owing to convective removal of the lithosphere during an extensional collapse of the Southeast Anatolian ranges.     

Engineering Properties, Microstructure and Strength Development of Lightweight Concrete Containing Pumice Aggregates

Lightweight aggregate concretes are widely incorporated in construction and development. This study presented an experimental investigation on the engineering properties of volcanic pumice lightweight aggregates concretes. Three groups of lightweight concretes: 1—coarse pumice aggregates (2–6 mm), 2—course pumice aggregates (2–6 mm)/sand size pumice aggregates and 3—course pumice aggregates (2–6 mm)/sand fraction were built and the physical/mechanical aspects of them were studied. The results of the compressive strength, density, water absorption, pH and shrinkage showed that these lightweight concretes were affected by the type of aggregates, the cement paste and the interfacial zone between cement and aggregates. One grain size pumice (2–6 mm) showed best compressive strength (65 kg/cm²), density of 0.60 g/cm³, linear shrinkage 0.4 % and high water absorption 29.73 %. Strength minerals represented by calcium-silicate-hydrate (CSH) and calcium-aluminate-hydrate (CAH) leading the concrete strength.     

Natural aggregates in the performance and durability of concrete: physical characteristics

The production of rock aggregates for construction is the largest of the extractive industries in Britain. Natural aggregates form the main component, by volume, in the manufacture of concrete but the part played by aggregates in the durability and performance aspects of concrete is still only moderately understood. This feature summarizes the main characteristics of common aggregate in concrete, especially those leading to cracking and deterioration. Physical and mechanical causes of concrete cracking are of immense importance but are omitted from the following. The feature expands on the earlier one: ‘Concrete: a man‐made rock?’ (Geology Today, 2010, v.26, n.2). To follow is another that will continue the story by looking at chemical reactivity in concretes.     

扬子西缘祥云响水花岗岩体的成因:锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素制约

滇西至滇中一带新元古代镁铁质岩类、花岗岩类等岩浆岩有广泛分布,前人利用不同岩石组合指示这些岩浆岩形成于不同的地质构造背景.通过对祥云一带调查研究,新确定了南华纪花岗岩体,花岗岩体中含有大量的超镁铁质岩（橄榄辉长岩）、闪长岩类包体,包体与花岗岩不规则边界呈成分渐变,混合形成为花岗闪长岩、石英闪长岩、英云闪长岩类岩石.对花岗岩和铁镁质包体进行锆石U-Pb LA-ICP-MS同位素测年,获得了相近的206Pb/238U平均年龄:761.9±4.1 Ma、761.7±4.2 Ma、761.3±3.7 Ma和757.5±5.9 Ma.花岗岩主量元素显示具有高碱（alk）、中等Mg#（38~57,平均值为50）、低TiO₂、P和亏损Ta、Nb、Sr特点,展现了富集轻稀土元素（LREEs）、亏损重稀土元素（HREEs）和选择性富集大离子亲石元素（LILEs）等特点,并且其ε_Nd（t）为负值（-2.73~-4.90）,表明花岗岩浆的物质应为早期古老地壳部分熔融的产物;橄榄辉长岩包体地球化学特征为:低K₂O,低稀土总量,LREEs和LILEs略富集或不富集,具明显P负异常,Nb-Ta和Zr-Hf无亏损,具有非常高的Mg#（71~83）等特点,这些特征都指示这些橄榄辉长岩来源于幔源,应为地幔边缘岩浆熔融的产物.花岗闪长岩、闪长岩具有略富集LREE和LILE、亏损HREE,其Mg#（45~71）较高,P亏损、负ε_Nd（t）值等特征,Ta、Nb、Ti、Sr、P略亏损或不亏损,组分介于花岗岩和橄榄辉长岩之间,显示了幔源和古老地壳部分熔融混合特点.这些岩石都展示陆源弧岩浆岩的构造背景,大洋板块向扬子板块俯冲导致幔源物质重熔的结果.      

The effect of pH of water and mineralogical properties on the slake durability (degradability) of different rocks from the Lesser Himalaya, India

Slake durability is an important geotechnical parameter and is a measure of degradability of rocks due to the process of mechanical and chemical breakdown. It is closely related to the mineralogical composition and the texture of the rocks. In this paper, mineralogical examination along with slake durability tests under variable pH conditions, both in acidic and alkaline environments, on the limestone, shale and siltsone were evaluated to understand the relationship between mineralogy and the degradability of rocks. The study revealed that rocks rich in calcium carbonate and or magnesium carbonate are adversely affected in the acidic environment, whereas, the rocks rich in quartz, feldspar and muscovite are independent of the pH of the slaking fluid, which in turn, is more influenced by the texture of the constituent minerals. It has also been observed that fine grained rocks are more susceptible to degrade in comparison to the coarse grained rocks.     

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of Potential Alkali Aggregate Reactivity for Siliceous and Carbonate Aggregates: A Case Study

Alkali-aggregate reactivity (AAR) involves a reaction between the pore solution of concrete and certain minerals found in some aggregates. To assess the potential AAR various physical and chemical tests are available and extensively used. The petrographic examination is the initial assessment that decides the further investigation for potential reactivity of an aggregate. A chemical approach is another option to assess the aggregate for potential AAR. The accelerated mortar bar method and concrete prism tests are other very important tests for determination of potential AAR of aggregates samples. However, a combination of the results of all the techniques provides most reliable results for potential AAR in aggregates. Moreover, each test represents the stepwise investigation and provides the decision for the test of next approach. Petrographic examination and chemical test methods are the quick decision-making methods for the estimation of potential AAR. In some cases, by these two methods, the aggregate can be selected and rejected confidently. However, for critical values or doubtful aggregates, further tests are necessary to develop a higher confidence level of the results. The present study comprises of the assessment of the alkali-reactivity of siliceous and carbonate aggregates using petrographic and chemical approaches. X-ray diffraction analysis was used as a complementary method to the petrographic evaluation. Moreover, under chemical approach, two separate test methods were used for siliceous and carbonate aggregates. The study also included a comparison between the petrographic examination and chemical analysis for the same aggregate samples and found significant results.