Siliceous Aggregates Research Articles

Caracterización Macroscópica De Morteros Romanos De Tipo Industrial En Villamanta (Madrid). Primeros Datos

The objective of this article is to show the results obtained from the physical and macroscopic characterization of the mortars sampled by Isabel Marqués and Alejandro Bermúdez, archaeological directors of the intervention carried out in El Tejar settlement, in the municipality of Villamanta (Madrid, Spain). The results of this work have determined a relevant typological classification among the samples, highlighting the presence of siliceous aggregates, ceramics in some mortars, a very varied grading and a distribution of the components that have conditioned the conservation. Of the four samples taken -VMT1 to VMT4- one of them has an aqueous pigmentation, belonging to an inside plaster, while the others correspond to lime mortars with aggregates from hydraulic surfaces. The archaeological investigation of the deposit of Villamanta is complemented by an implementation check of lime mortars, being one of the most important Roman context of Madrid. This research add a sequence of new results around the Roman mortars and implements a methodology in the study of the historical mortars.

Mechanical and durability performance of concrete produced with recycled aggregates from Greek construction and demolition waste plants

Greece has to recycle 70% of Construction and Demolition Waste (CDW) by 2020, in the context of the enforcement of Waste Framework Directive (WFD) 2008/98/EC. CDW recycling has started only recently to a small extent and is restricted to road works. The reuse of CDW in new concrete production could contribute to the construction sector sustainability through minimizing landfill and the need for new raw materials. Literature data are found regarding the performance of recycled concrete, but limited knowledge is available regarding the chemical and mineralogical properties of recycled aggregates (RA) and how these affect concrete. Moreover, Greek aggregates are not siliceous aggregates as are most of the aggregates investigated in literature. Against this background, this study aims to evaluate for the first time mechanical and durability performance of concrete made with RA from different Greek recycling plants. All recycled materials used were characterized in terms of chemical and mineralogical composition and certain chemical and physical properties have been determined. It was found that all RA are enriched in Si, Al, and alkali oxides, which was mineralogically verified by the identification of quartz and minor quantities of mica and feldspars. They proved though innocuous to alkali aggregate reaction. Higher water absorption of coarse RA is their most negative physical characteristic. Fine fractions of RA have low Sand Equivalent and significantly high water absorption values, which make them unsuitable to replace natural sand. Water soluble ions are at the same level to that of natural aggregates.Furthermore, concrete mixtures were prepared using an RA percentage ranging from 0% to 75%. Results indicate that the compressive strength of recycled concrete ranges from significantly lower (37% reduction) to equal, compared to conventional concrete, depending on the composition of RA. The majority of literature data relate the inferior quality of RA to their high water absorption, the findings of the present research though indicate that the presence of clay minerals has a more pronounced adverse effect to concrete's strength. As for the durability properties examined, i.e. water absorption, sorptivity, frost and carbonation resistance, the recycled concrete mixtures exhibited somewhat lower performance than reference concrete.

Artificial neural networks approach to predicting rut depth of asphalt concrete by using of visco-elastic parameters

Performing comprehensive research on the functional behavior of asphalt pavements under the influence of various environmental and structural parameters can better assist the engineers in the design and maintenance of asphalt pavements. Using a solution that can reduce the cost and time of assessment is very important. Using artificial neural networks in many facilitates operations on data engineering sciences. It is necessary to ensure that a comprehensive study is performed through considering all or most of the parameters affecting the behavior. The aim of this study is to provide an experimental model to estimate the rut depth of asphalt concrete by using viscoelastic parameters and artificial neural networks. Accordingly the asphalt concrete specimens containing 3, 5 and 7 percent void with two types of limestone and siliceous aggregates and PG64-22 and PG58-28 bitumens were made and exposed to dynamic creep tests under 50–60 °C and the stress range of 100–300 kPa. Then the viscoelastic parameters of asphalt specimens were extracted from the creep diagrams and eventually the asphalt concrete’s rut depth prediction model was trained and provided by artificial neural network. Comparing the output results with the experimental test results show that by using this model it is possible to estimate the creep behavior and rut depth of asphalt concrete pavements based on the effective parameters without the need for costly and time-consuming tests.

Influence of Granulometric Composition of Batch on Technological and Physical-Chemical Properties of Granular Porous Silicate Aggregate

It was shown that ash-slag wastes from TPP can be used in the production of heat-insulating glass materials. Compositions with different granulometric composition of batch were developed and underwent heat-treatment. The primary properties of the synthesized samples were determined. The effect of the particle size on the foaming-up of granules was determined and the optimal dispersity of the batch found.

Radiocarbon dating of mortars: Contamination effects and sample characterisation. The case-study of Andalusian medieval castles (Jaén, Spain)

Since 1960s, mortars have been exploited as a potential material for radiocarbon dating and, despite the fact that this methodology appears very simple in its principles, some measured radiocarbon ages were definitely different from the expected historic ages.The paper concerns to the characterisation of mortars from three Andalusian castles (Spain) by means of different mineralogical techniques in order to control “contamination effect” that could affect age estimation. Several mixtures of binders and aggregates composed the archaeological mortars; lime-based or gypsum-based binders were distinguished whereas the aggregates varied from carbonates to intrusive igneous rocks. The radiocarbon dating provided good results for lime-based mortars with silicate aggregate; conversely, for other specimens the method for sample preparation (Cryo2SoniC) was improved increasing the ultrasonic time and decreasing the mesh size. The research points out the importance of a multi-analytical approach aimed at improving a widely accepted protocol for 14C dating of archaeological mortars.

Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-µm sized cosmochemical analogues

Laboratory spectral measurements of relevant analogue materials were performed in the framework of the Rosetta mission in order to explain the surface spectral properties of comet 67P. Fine powders of coal, iron sulphides, silicates and their mixtures were prepared and their spectra measured in the Vis-IR range. These spectra are compared to a reference spectrum of 67P nucleus obtained with the VIRTIS/Rosetta instrument up to 2.7 µm, excluding the organics band centred at 3.2 µm. The species used are known to be chemical analogues for cometary materials which could be present at the surface of 67P. Grain sizes of the powders range from tens of nanometres to hundreds of micrometres. Some of the mixtures studied here actually reach the very low reflectance level observed by VIRTIS on 67P. The best match is provided by a mixture of sub-micron coal, pyrrhotite, and silicates. Grain sizes are in agreement with the sizes of the dust particles detected by the GIADA, MIDAS and COSIMA instruments on board Rosetta. The coal used in the experiment is responsible for the spectral slope in the visible and infrared ranges. Pyrrhotite, which is strongly absorbing, is responsible for the low albedo observed in the NIR. The darkest components dominate the spectra, especially within intimate mixtures. Depending on sample preparation, pyrrhotite can coat the coal and silicate aggregates. Such coating effects can affect the spectra as much as particle size. In contrast, silicates seem to play a minor role.

Effect of Aggregate Type on Properties of Natural Hydraulic Lime-Based Mortars

In the current restoration practice, the mortars based on aerial or hydraulic lime with siliceous aggregate are used on repair / reconstruction of historical plasters. The resulting properties of lime mortars do not depend only on the type of aggregate, but also on its contamination, origin and a degree of hardening. For this reason, it is needed to know a detailed characteristic of the aggregate and the results obtained for the particular aggregate cannot be generally applied for the similar type of aggregate. This work presents the applicability of Czech local crushed limestone aggregate and limestone fines as a filler to natural hydraulic lime-based mortars. The role of aggregate and limestone fines on the properties of mortars is examined by comparing the mechanical strengths, porosity and frost resistance of the mortars with pure quartz sand and limestone aggregate and its quantity in the mortar. It was found that the limestone aggregate has produced lower strengths, higher total porosity of natural hydraulic lime-based mortars. It has resulted in low frost resistance of the mortars.

Effects of Irradiation on Albite's Chemical Durability.

Albite (NaAlSi3O8), a framework silicate of the plagioclase feldspar family and a common constituent of felsic rocks, is often present in the siliceous mineral aggregates that compose concrete. When exposed to radiation (e.g., in the form of neutrons) in nuclear power plants, the crystal structure of albite can undergo significant alterations. These alterations may degrade its chemical durability. Indeed, careful examinations of Ar+-implanted albite carried out using Fourier transform infrared spectroscopy (FTIR) and molecular dynamics simulations show that albite's crystal structure, upon irradiation, undergoes progressive disordering, resulting in an expansion in its molar volume (i.e., a reduction of density) and a reduction in the connectivity of its atomic network. This loss of network connectivity (i.e., rigidity) results in an enhancement of the aqueous dissolution rate of albite-measured using vertical scanning interferometry (VSI) in alkaline environments-by a factor of 20. This enhancement in the dissolution rate (i.e., reduction in chemical durability) of albite following irradiation has significant impacts on the durability of felsic rocks and of concrete containing them upon their exposure to radiation in nuclear power plant (NPP) environments.

Fe–Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites

Fe–Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites

Influence of aggregate type on conversion and strength in calcium aluminate cement concrete

Calcium aluminate cement (CAC) is gaining popularity in North America as a rapid repair material due to its ability to quickly gain strength, even at low curing temperatures. Use of CAC has been limited due to a lack of understanding of the process of conversion and the role of aggregates in CAC concrete. Conversion, which occurs only in 100% CAC systems, is a chemical process in which metastable hydrates convert into denser, stable hydrates. Presented is an examination of aggregate source impacts on this conversion process and converted CAC concrete strengths. Nine different concrete systems with fifteen varying aggregate sources were examined. Results indicated that carbonate limestone and siliceous limestone aggregate systems had significantly less strength reduction due to conversion compared to siliceous aggregate systems. Microstructural analysis of systems suggested that the carbonate limestone system had less porosity and better-formed aggregate/paste interfacial transition zones compared to the siliceous systems. Chemical analysis of the concrete pore solution indicated that the carbonate limestone system's pH and ionic concentrations of aluminum, sodium, and potassium were significantly higher than that of a siliceous system, indicating more dissolution of unhydrated cement in the carbonate limestone system. These studies are presented along with a proposed theory explaining the cause of the significant converted strength differences in CAC concrete systems made with limestone aggregates compared to siliceous aggregates.

A 10,400-year-old sunken lime kiln from the Early Pre-Pottery Neolithic B at the Nesher-Ramla quarry (el-Khirbe), Israel

The Pre-Pottery Neolithic B (PPNB) is the first period in human cultural evolution that is characterized by the extensive production of lime plaster for architectural, decorative and ritual purposes. The production of large quantities of lime plaster requires the operation of a lime kiln, a structure where limestone cobbles are heated to high temperatures (>600°C) to obtain quicklime, which is then mixed with water to form a moldable lime putty. However, little is known about lime kilns and plaster production processes during the PPNB. This may be because the technology used at that time was simple and left few traces that are unique to lime plaster production. These include combustion features rich in lime plaster and heat-altered sediments, which are difficult to identify through only a visual inspection of the archaeological context. Here we report the study of a small sinkhole at the Nesher-Ramla quarry in Israel, which yielded Early PPNB artifacts. Using infrared spectrometry and micromorphology of sediments, we identified in-situ deposits of heat-altered sediments rich in fragments of burnt limestone, lime plaster, and wood ash in the form of charcoal, phytoliths and siliceous aggregates, which are features consistent with the operation of a lime kiln. Charred botanical remains were characterized and used for radiocarbon dating, which determined the age of the site at 10,400cal BP. We therefore conclude, based on the examination of the microscopic archaeological record, that this sinkhole was used as a lime kiln during the Early PPNB.

Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content

Abstract The present work investigated alkali-activated mortars with high ceramic waste contents. Tile ceramic waste (TCW) was used as both a recycled aggregate (TCWA) and a precursor (TCWP) to obtain a binding matrix by the alkali-activation process. Mortars with natural siliceous (quartz) and calcareous (limestone) aggregates, and with other ceramic waste materials (red clay brick RCB and ceramic sanitaryware CSW waste), were also prepared for comparison purposes. Given the lower density and higher water absorption values of the ceramic aggregates, compared to the natural ones, it was necessary to adapt the preparation process of the recycled mortars by presaturating the aggregate with water before mixing with the TCWP alkali-activated paste. Aggregate type considerably determined the mechanical behaviour of the samples cured at 65 °C for 3 days. The mortars prepared with the siliceous aggregate presented poor mechanical properties, even when cured at 65 °C. The behaviour of the limestone aggregate mortars depended heavily on the applied curing temperature and, although they presented the best mechanical properties of all those cured at room temperature, their compressive strength reached a maximum when cured at 65 °C, and then decreased. The mechanical properties of the mortars prepared with TCWA progressively increased with curing time (53 MPa at 65 °C for 28 days). An optimum 50 wt% proportion was observed for the limestone/TCWA mortars (≈43 MPa, 3 days at 65 °C), whereas the mechanical properties of that prepared with siliceous particles (10 MPa) progressively increased with the TCWA content, up to 100 wt% substitution (23 MPa). Limestone particles interacted with the binding matrix, and played an interesting beneficial role at the 20 °C curing temperature, with a slight reduction when cured long term (28 days) at 65 °C. The results demonstrated a potential added value for these ceramic waste materials.

Fuel remains in archaeological contexts: Experimental and archaeological evidence for recognizing remains in hearths used by Iron Age farmers who lived in peatlands

In the archaeological record, ash and charred organic material are the only indications of the type of fuel used by ancient societies to feed their fires. This potential source of information may help further understanding of past human behaviour in relation to fuel selection, applied type of fire and function of fires lit in hearths. This study examined ash from reference samples and ash and char samples recovered from an Iron Age peatland site in Vlaardingen, the Netherlands. Local availability and abundance made it possible for the occupants of the site to choose from different fuel resources. Peat and cattle dung were readily available, while wood was less abundant. Reference samples from various locations were collected to investigate the properties of ash. Different types of wood, peat and cattle dung were accordingly ashed and analysed. In total, two techniques were used, that is, chemical analyses (x-ray fluorescence (XRF)) for the determination of the elemental composition and microscopic studies on field images of these ashes, mounted on glass slides, to investigate phytoliths quantitatively (Si and Ca types), siliceous aggregates and spherulites. The properties of the archaeological samples were compared with these results. The archaeological char samples were used for identification and analysed using reflective microscopy to study structure and temperature by reflectance (%Ro). It provided the necessary information to determine the type of fuel used by the Iron Age farmers and obtain more information on the function of the present fire structures. The results are strong indications that Iron Age farmers used all available fuels, that is, peat, cattle dung and wood, to feed their fires. The integrated application of phytolith, geochemical and char analyses has a high potential for the identification of the fuel selected by ancient societies.

Determining the Condition of Reinforced and Prestressed Concrete Structures Damaged by Elevated Temperatures

This paper focuses on the effect that high temperatures generated during a fire have on reinforced and prestressed concrete structures. Fire is one of the common reasons for rehabilitations and reconstructions during the service life of a building. Before these can be started, however, it is necessary to assess the structure's technical condition. It is therefore necessary to know the physico-chemical changes occurring in the concrete due to fire. Rising temperatures effect the evaporation of all water contained and cause the dehydration of CSH compounds. Transformations in the crystalline structures of siliceous aggregate minerals result in an increase of volume and crack formation. The decarbonation of limestone aggregate produces escaping gases which damage the concrete as well. Additional mechanical stress caused by the sum of the volume changes is another important factor. In addition, the different thermal expansion of steel and concrete severs the bond between the two. Changes in the material structure are then detrimental to the mechanical parameters. Concrete sees significant changes at temperatures as low as 300°C. A structure's load-bearing capacity is often determined by reinforcement bars or prestressing tendons, which reach their critical limits at temperatures lower than concrete. The paper draws on knowledge about the condition of materials damaged by elevated temperatures and discusses the assessment of a concrete skeleton structure after a fire. The main problem was presented by the ceiling, which was built from Spiroll prestressed ceiling slabs. The grouting between the slabs had disintegrated, the bottom faces of the slabs fell off and the prestressing tendons often lost tension. A renovation procedure for the structure was suggested.

Deformational behaviour of fly-ash based geopolymer concrete at temperatures of up to 150°c

The use of Geopolymer Concrete (GP * C) has been on the rise over the last few decades owing to its lower carbon emissions as compared to Ordinary Portland Cement Concrete (OPC). Recent research has also established the superior thermal properties of GPC and makes it an ideal construction material for specialized application. However, the deformational behaviour of GPC at elevated temperatures has not fully understood. If GPC is to be used as a main stream construction material for specialized applications, the exact deformational behaviour of the material under thermal loading needs to be investigated. This paper looks into the deformational characteristics of GPC (with natural crushed siliceous aggregates) when dry heated up to 150°C at near zero loading. The deformations recorded using a clip-on extensometer are used to determine the strains developed in the GPC samples due to thermal loads. Coefficient of thermal expansion (CTE) for the tested GPC samples was found and was comparable to OPC concrete at the tested temperatures. Between ambient (20°C) and 80°C the CTE for GPC was determined to be between 10.3-10.9x10 −6 mm/mm/°C which is similar to OPC concretes. CTE for temperatures between 80°C and 150°C was determined to be 9.3-10.0x10 −6 mm/mm/°C. First heating cycles resulted in much lower CTE which may be due to the presence of evaporable water in the samples. Like OPC, GPC is a non-homogeneous material and the variation in the materials between samples account for the slight variation in the CTE values determined.

Effect of aggregate and water to cement ratio on concrete properties at elevated temperature

SUMMARYProperties of concrete during and after fire exposure are of significant importance for serviceability and rehabilitation of buildings. This article presents an experimental investigation on the effects of elevated temperature on physical and mechanical properties of concrete made using two types of locally available coarse aggregates (crushed and wadi aggregates) and water‐to‐cement (w/c) ratios of 0.50 and 0.70. Temperature range from 200 °C to 1000 °C was used with intervals of 200 °C. Test results indicate that the weight of concrete reduced with increase in temperature. This reduction was quite sharp beyond 800 °C. Minor spalling was observed in concrete with Wadi aggregates at temperatures beyond 800 °C. The results also reveal that relative strength of concrete decreased as exposure temperature increased. The effect of high temperatures on the strength of concrete was more pronounced in concrete with Wadi aggregates. w/c ratio had insignificant effect on weight loss after exposure to elevated temperatures, but it increased the rate of strength degradation irrespective of aggregate type used. Comparison of results with Eurocode (EC‐2) and American Concrete Institute (ACI) standards indicate that the concrete with both aggregate types can satisfy the limits of siliceous aggregates set by ACI, but concrete made with Wadi aggregates with w/c ratio of 0.50 failed to satisfy limits of EC‐2. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental investigation of the effect of using different aggregate types on WMA mixtures

In recent years, production of warm mix asphalt (WMA) mixtures with the help of chemical additives has been developed due to obvious advantages, such as reduction of pollution emissions, construction temperature and the possibility of carrying asphalt in long distances. Various additives can have positive or negative effects on the performance characteristics of WMA mixtures made from different types of aggregates. Although, effects of different types of aggregates have been more investigated on the performance of hot mix asphalt (HMA), the effects on WMA have been less studied. Therefore, in this study, three types of aggregates including: limestone (Li), siliceous (Si) and slag (Sl) from the metal production factories together with Sasobit and Zeolite additives were provided to be used for the WMA mixtures. After constructing the asphalt samples and determining the optimum binder, Marshall Stability, indirect tensile strength tests and resilient modulus test and the durability parameter determination were performed. Test results indicated that WMA-Sasobit mixtures have the greatest impact on reducing consumed percentage of binder in slag and siliceous aggregates compared to limestone aggregates. For both additives, WMA mixtures containing limestone aggregates showed higher resilient modulus and siliceous aggregates showed lower resilient modulus. Moreover, the results of indirect tensile strength of specimens containing limestone aggregates showed the highest value and siliceous aggregates showed the lowest one. TSR in the limestone and slag aggregates was improved using both additives, but Zeolite additives reduce TSR in the siliceous aggregates.

Recycling and reuse of chosen kinds of waste materials in a building industry

The article describes the current state of knowledge and practice in Poland concerning recycling as a method of reuse of chosen groups of waste materials in building industry. The recycling of building scraps is imposed by environmental, economic and technological premises. The issue of usage of sewage residues is becoming a problem of ever -growing gravity as the presence of the increasing number of pernicious contaminants makes their utilization for agricultural purposes more and more limited. The strategies of using waste materials on Polish building sites were analyzed. The analysis of predispositions to salvage for a group of traditional materials, such as: timber, steel, building debris, insulation materials, plastics, and on the example of new materials, such as: artificial light aggregates made by appropriate mixing of siliceous aggregates, glass refuses and sewage residues in order to obtain a commodity which is apt for economic usage also was made in the article.The issue of recycling of waste materials originating from building operations will be presented in the context of the binding home and EU legal regulations. It was proved that the level of recycling of building wastes in Poland is considerably different from one which is achieved in the solid market economies, both in quantity and in assortment. The method of neutralization of building refuses in connection with special waste materials, which are sewage sludge that is presented in the article may be one of the alternative solutions to the problem of recycling of these wastes not only on the Polish scale.

High temperature behaviour of a wide petrographic range of siliceous and calcareous aggregates for concretes

This study aims to characterize the physical and chemical transformations of aggregates undergoing high thermal solicitation in order to better understand their deterioration in this context. Twenty one (21) aggregates of various mineralogical compositions are exposed to heating/cooling cycle up to 750°C. The thermal behaviour of siliceous and calcareous aggregates depends on several parameters related to mineralogical structure including granular texture, crystallinity of minerals, porosity and density. Thermal properties like expansion and weight loss related to chemical reactions show important variations among the siliceous aggregate category. The thermal behaviour of aggregate is dependant of its mineralogical and chemical compositions.

Damage evaluations of oven-dried mortar subjected to one-directional fire

Concrete structures can be damaged by various factors in extreme service conditions. Analytical methods that can predict the strength of structural concrete after exposure to fire are needed to facilitate decisions regarding whether to repair, strengthen, or demolish fire-damaged buildings. However, appropriate and widely applicable material models have not yet been proposed. This paper presents an experimental study in which we assess damage, including changes in flexural strength, porosity and residual cement hydrates, to oven-dried mortar that has been fired and immediately cooled in the air. Mortars were made from calcareous and siliceous aggregates, and one face of each specimen (100×100×400 mm) was exposed to fire curves of ISO 834 and ASTM E119. Specimens for quantitative assessment were hewed to ten layers from the original specimens. Experimental results indicate that the in-depth flexural strength of a thin specimen is substantially diminished by fire exposure, especially for specimens with existing fire cracks. In addition to the loss in strength, changes in porosity and chemical properties occur. Based on the experimental evidence obtained from this study, the relationships between each property are discussed.