Aggregates Of Grains Research Articles

Impact of Aggregate Grain Size on ASR-Induced Expansion.

Alkali-silica reaction (ASR) is a sequence of complex chemical processes, resulting in the formation of alkali silica gels with high swelling ability. ASR leads to the expansion of concrete and the degradation of its microstructure. The susceptibility of aggregates to alkali reaction depends, among other factors, on the type and origin of the aggregate, the presence of reactive forms of silica, the mineral composition, and the geometric properties of the aggregate, such as shape and grain size. This study aimed to investigate the impact of the grain size of polymineral post-glacial gravel aggregate, originating from the northern regions of Poland, on its susceptibility to ASR. The expansion of mortars made from polymineral aggregate and the cracking of grains and cement matrix due to the occurring reactions were analyzed. Based on the conducted research, it was observed that the expansion of mortars depends on the grain size of the aggregate. It was demonstrated that the fraction of reactive aggregate generating the most significant elongation of mortars is in the range of 1.0-2.0 mm. The reaction of silica with alkalis continued until the depletion of reactive components in the aggregate. The relationship between the progress of corrosive processes and the grain size of the aggregate was evident in the form of different linear elongation increments of mortars over time. The expansion of mortars was caused by the swelling ASR gel, inducing stress in the grain and the surrounding cementitious paste.

ANALYSIS OF MARSHALL CHARACTERISTICS WITH FLY ASH MATERIAL FOR STONE DUST SUBSTITUTION AS FILLER IN HRS-WC MIXTURE

Lataston asphalt mix is a thin layer of asphalt concrete that is often used on light-traffic roads because it produces roads with good flexibility and durability. An economical way of doing this is to vary the asphalt mix, especially by modifying fillers, to improve the quality of the road pavement and asphalt mix. So, an alternative was found, namely the use of fly ash, residue from the Asam-Asam PLTU. The filler material for fly ash which will be varied with the filler for stone dust, plays a role in filling the voids between aggregate grains in the Hot Rolled Sheet-Wearing Course (HRS-WC) mixture with each predetermined composition. This study aims to determine the characteristics of the HRS-WC asphalt mixture with respect to the utilization rate of rock dust and fly ash fillers. To find out the characteristics of a HRS-WC mixture with mixed variations of the two fillers, the method that will be used is the Marshall Test by analyzing each characteristic of the parameters to be obtained in accordance with the 2018 Revised Highways Specifications II Year 2018 to make the mixture hot asphalt. The bitumen content used in this study was 4.5%, 5.0%, 5.5%, 6.0%, and 6.5%, with varying levels of fly ash and rock dust filler, namely 100%: 0%, 80%: 20%, 50%: 50%, 20%: 80%, and 0%: 100%. The results of the Marshall characteristic calculation analysis show that the asphalt mixture with lataston is very influential in the substitution of rock ash as a fly ash filler. Lataston asphalt mixture tends to be stiff and easily cracked because it has a high stability value of 1,615.38 kg and the lowest flow value of 4.10% in the 100% fly ash filler variation. At optimal asphalt content, the HRS-WC asphalt mixture for each variation in the range of fly ash and rock dust produces a decreased asphalt content because the water absorption capacity of rock dust is less than that of fly ash filler, so less asphalt is needed. In addition, the HRS-WC asphalt mixture also shows increasing durability, along with the replacement of rock dust filler with fly ash filler, which can be seen from the increased stability values, MQ values, and VFB values.

Finite Element Analysis of Tyre Contact Interaction Considering Simplified Pavement with Different Aggregate Sizes

This study considered the effect of pavement aggregate grain size on tyre–pavement contact interaction during the late stages of pavement skid resistance. First, hemispherical shells 7, 9, and 13 mm in diameter were used to simulate coarse pavement aggregates. Subsequently, a three-dimensional finite element tyre–pavement contact model developed using ABAQUS was employed to analyse the contact interaction between each simplified pavement type and the tyre under steady–state rolling and braking conditions. Finally, the concept of occlusal depth was proposed and applied to characterise pavement skid resistance. The results showed that under steady–state rolling conditions, the peak contact stress of the simplified pavement increased with the pavement mean texture depth, whereas the contact area decreased. Under steady–state braking conditions, the effect of the contact interaction between the tyre and simplified pavement aggregates was ranked in order of superiority as aggregate grain sizes of 9, 7, and 13 mm, indicating that aggregate grain size did not exhibit any correlation with tyre–pavement contact interaction. Additionally, the squares of linear correlation coefficients between the pavement cumulative occlusal depth and horizontal braking force reached 0.921, 0.941, 0.889, and 0.894 for vehicle speeds of 30, 60, 90, and 120 km/h, respectively, indicating that they could be used to assess pavement skid resistance.

Elastic behaviour of orientation-correlated grains in multiphase aggregates.

Diffraction elastic constants (DEC) describe the elastic response of a sub-set of orientation correlated grains which share a common lattice vector. DEC reflect the elastic behaviour of the single crystal constituents through their dependence on grain orientation. DEC furthermore depend on the behaviour of the polycrystal aggregate both through the dependence on preferred orientation and through the average elastic interaction of the grains in the sub-set with their surroundings. The latter is also known as grain-matrix interaction which is grain shape dependent. Both dependencies can make the DEC uniquely sensitive to the elastic effects of the grain shape, texture, and phase composition. Several micro-mechanical models are explored with respect for use both in calculating diffraction elastic constants and overall elastic constants. Furthermore, it is shown how discrete data from electron backscatter diffraction on grain shape, grain orientations, and neighbouring grains can be used for DEC calculations. Lastly, the inverse problem of calculating single crystal elastic constants from DEC is discussed in detail. All calculations discussed in this work can be verified using the freely available computer program IsoDEC.

Effects of different grain size of expanded perlite aggregate and content of silica aerogel on the characteristics of lightweight cementitious composite

In this research, an attempt was made to investigate effects of expanded perlite aggregate grain size on consistency, density, compressive strength, thermal conductivity and microstructure of 15 different composite mixes with silica aerogel. As for the samples preparation, expanded perlite aggregate of 5 different groups based on grain size, were used for sample preparation, then partially replaced by volume for 20% and 40% of hydrophobic silica aerogel particles. The results showed, that density of the samples varied between 0.35 g/cm3 and 1.5 g/cm3, flexural strength varied between 3.4 MPa and 7.4 MPa, compressive strength was in the range between 12.3 MPa and 55 MPa, thermal conductivity coefficient was in the range between 0.130 W/mK and 0.190 W/mK. Scanning electron microscopy showed that expanded perlite aggregates and silica aerogel particles are capable of being mixed and formed homogenous mixture. Nevertheless, microscope images indicated weaker adhesion of silica aerogel particles at interfacial zone as compared with expanded perlite aggregate particles. Results revealed, that both of the factors: grain size of expanded perlite aggregate particles silica aerogel content influenced the density, compressive strength and thermal conductivity. The study also indicated feasibility of expanded perlite aggregate and silica aerogel for achieving homogeneous mixture of the lightweight cementitious composites. Study demonstrated that using different size fractions of expanded perlite aggregate affects differently physical, mechanical and thermal characteristics of the lightweight cementitious composite with silica aerogel.

Analysis probes and statistical parameters affecting the OSL ages of mortar samples; a case study from Italy

Mortars stand among the very few materials that theoretically cannot be reused due to irreversible hardening processes. Among the various dating techniques, radiocarbon and Optically Stimulated Luminescence (OSL) struggle for being selected as the most robust and reliable dating technique for the specific material. The principle of mortar OSL dating depends on the bleaching of the quartz grains of the sandy aggregate while mixing and laying the mortar to daylight. Thus, the OSL ages strongly depend on the effective bleaching of the quartz. Here, we deal with OSL ages from the old Roman Theatre of Padua. Preliminary OSL results based on Single Aliquot Regeneration (SAR) protocol using three regenerated doses to multigrain (MG) quartz aliquots, indicated distributions of ED (Equivalent Dose) leading to significant mismatch of these results compared to the expected ages. The present work attempts to discuss the influence of various data analysis approaches such as (a) exclusion criteria like recycling ratio and recuperation values, (b) selection of the suitable region of interest in the signal's integral along with the correct background (late or early) subtraction technique and (c) appropriate statistical analysis by selecting the suitable age model (descriptive statistics, Central Age Model, Minimum Age Model) on the final distribution as well as both value and precision of the ED, enabling thus to obtain ages that are not only more accurate, but also closer to what was expected. Alternative statistical indicators of either the symmetry of the ED distributions (like skewness, kurtosis, etc) or the OSL signal itself (residual distribution analysis, kinetic parameters and percentage contribution of each OSL component to the overall signal) will be assessed in an effort to investigate possible correlations.

Research on the evolution of adsorption behavior of asphalt and aggregate surface and its influencing factors

The adsorption between asphalt and aggregate surfaces is a crucial factor in the formation of the asphalt mixture structure, directly affecting the strength, stability, and aging rate of the mixture. This study aims to explore the physical-chemical bonding process between asphalt and aggregates and establish a reliable expression for asphalt adsorption on aggregate surfaces. The optimal wavelength and concentration of asphalt-toluene solutions were determined through Strategic Highway Research Program (SHRP) net adsorption tests. Then the aggregates' composition, shape, and texture properties were evaluated using a scanning electron microscope (SEM), needle-like content, and gray-level co-occurrence matrix. Finally, the impact of temperature, asphalt type, aggregate grain size, and surface texture on the adsorption evolution was studied based on the SHRP net adsorption test. Results showed significant differences in surface morphology among the four types of aggregates. Quartz exhibited the highest smoothness, while albite showed a high degree of roughness despite its complex surface morphology. Increasing temperature led to a decrease in the total adsorption capacity of the aggregates, especially for quartz and elpidite. The inflection points of the adsorption amount of calcite and albite shifted backward with 90# asphalt compared to 70# asphalt, indicating both physical and chemical adsorption. Additionally, changes in specific surface area had a more pronounced effect on the adsorption amount. The presence of a rich texture structure significantly increased the pre-sorption rate of the aggregates and ultimately influenced the adsorption amount. The research findings provide insights to more fully understand the evolution of adsorption behavior between asphalt and aggregate surfaces.

Evaluation of the Performance of Low-Cement Strain-Hardening Cementitious Composites Containing Desert Sand and Ground Scoria Rocks.

Fine aggregates are the main ingredients that control the success of the preparation and performance of strain-hardening cementitious composites (SHCCs). Worldwide deserts can be used as eternal sources of fine aggregates for the preparation of SHCCs. Arabian Peninsula desert sand spreads over the largest desert area in the world, covering an area of 2,300,000 km2 among the Arabian Gulf countries. White and dune desert sands were procured for use in this study. The morphological structure is important in selecting the appropriate sand for use in the preparation of SHCCs. The utilization of microfibers such as polyvinyl alcohol (PVA) has become common practice for the preparation of SHCCs. The presence of desert sand is proven to enhance the dispersibility of PVA due to its spherical structure, which alleviates the friction among the ingredients forming SHCCs. Two mechanisms are defined under the tensile force at the interface of microfibers and natural sand, namely, a strong frictional force leading to rupture or a weaker force causing pullout. The synergy between fibers and fine aggregate grains depends on their surface characteristics, which can be modified using different types of mineral admixtures. In this research, the alignment of microfibers as an indication of the quality of dispersion could be evaluated using a proposed approach based on an advanced technique of microstructural analysis. PVA dispersion and its relation to strain-hardening properties are visually correlated to the surface interaction of the mineral admixture and dune sand. The microdurability and cost effectiveness of SHCCs could be assessed using the proposed approach, as depicted by the results obtained in this research work.

Strains of high-performance and ordinary concretes depending on the cement paste volume and the w/c ratio

The test results of 15 high performance concretes (HPCs) and ordinary concretes allowed to explain the influence of different volumes of cement paste on shaping the deformation properties of concrete under temporary compressive load. Increasing the volume of the paste by 100 dm3/m3 and reducing the volume of coarse aggregate at the same time reduces the modulus of elasticity and significantly increases the compressive strain at the peak stress. When increasing the volume of cement paste, smaller changes in properties were observed in ordinary concretes than in HPCs, modulus of ordinary concrete elasticity decreased by 4–9%, and compressive strains at the peak stress increased by 18–23%. However, in HPCs the changes are greater. Modulus changes are 7–28% and strains at the peak stress changes are from 19% to 41% at w/c = 0.25. It was found that the compressive strength of all concretes with the smallest volume of cement paste at each w/c ratio from 0.25 to 0.60 was the highest. Increasing the volume of cement paste in concretes for each w/c ratio causes a large increase in the compressive strains at peak stress.Hence, the likely causes of changes in the examined properties are the reduced adsorption of water on the smaller surface area of the aggregate, which dries less bulk cement paste, increasing the aggregate-cement paste interfacial transition zone (ITZ) width, which is visible on the scanning electron microscopy (SEM) images taken. When the volume of the aggregate is larger and the volume of the paste is smaller, as a result of water adsorption by the larger surface area of the aggregate grains, the actual (effective) w/c ratio in bulk paste decreases, resulting in improved strength and deformation properties.

Protective Аbility of Cement Concrete with Polyfunctional Additive in Relation to Steel Reinforcement

The paper presents the results of studies of the influence of the components of a complex polyfunctional additive on the protective ability of concrete in relation to steel reinforcement of reinforced concrete building structures. In accordance with modern trends in the use of chemical additives in concrete with the aim of a complex effect both on the processes of hardening and the formation of its structure, and on the final physical, mechanical and operational properties of concrete, the additive in question consists of a number of components. It consists of a plasticizing component, accelerating hardening and compacting the structure of hardening concrete, as well as amorphous ultrafine microsilica. The presence of the latter is accompanied by a reaction with calcium hydroxide and its transfer to a bound state in hardening concrete, which creates prerequisites for a decrease in alkalinity (pH factor) in its volume and, accordingly, can create a risk of corrosion of steel reinforcement of reinforced concrete structures. Taking into account this circumstance, studies have been carried out in order to establish the degree of influence of the amorphous ultrafine microsilica present in the composition of the additive on the properties of concrete, including an assessment of its protective properties in relation to steel reinforcement, as well as a change in strength over time (in this paper up to the "age" of concrete in three years from the moment of manufacture of samples of compositions without chemical additives and with the introduction of a complex polyfunctional additive). As a result, an increase in the density, strength of concrete and its operational properties, including the protective ability in relation to steel reinforcement, due to the complex effect of the additive components, has been revealed, including a decrease in the initial water content and an increase in the density of the cement stone and transition zones of its contact with the surface of the aggregate grains in concrete.

Effect of Coarse Aggregate Grading on Mechanical Parameters and Fracture Toughness of Limestone Concrete

This work presents a discussion of the basic properties of broken mineral limestone aggregates with the specification of the properties affecting the fracture toughness of concretes made with these aggregates. To determine the influence of the grain-size distribution of coarse aggregates for each concrete series, two types of aggregate grain were used, with maximum grain sizes of 8 mm (series of concrete L1) and 16 mm (series of concrete L2). Fracture-toughness tests were carried out using mode I fractures in accordance with the RILEM Draft recommendations, TC-89 FMT. During the experiments the critical stress-intensity factor (KIcS) and crack-tip-opening displacements (CTODc) were determined. The main mechanical parameters, i.e., the compressive strength (fcm) and splitting tensile strength (fctm), were also assessed. Based on the obtained results, it was found that the grain-size distribution of the limestone aggregate influenced the concrete’s mechanical and fracture-mechanics parameters. The obtained results showed that the series-L2 concrete had higher strength and fracture-mechanics parameters, i.e.,: fcm—45.06 MPa, fctm—3.03 MPa, KIcS—1.22 MN/m3/2, and CTODc —12.87 m10−6. However, the concrete with a maximum grain size of 8 mm (series of concrete L1) presented lower values for all the analyzed parameters, i.e.,: fcm—39.17 MPa, fctm—2.57 MPa, KIcS—0.99 MN/m3/2, and CTODc —10.02 m10−6. The main reason for the lower fracture toughness of the concretes with smaller grain sizes was the weakness of the ITZ in this composite compared to the ITZ in the concrete with a maximum grain size of 16 mm. The obtained test results can help designers, concrete producers, and contractors working with concrete structures to ensure the more conscious composition of concrete mixes with limestone aggregates, as well as to produce precise forecasts for the operational properties of concrete composites containing fillers obtained from carbonate rocks.

Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material

Strap reinforcement is very commonly used as reinforcement material in mechanically stabilized earth walls (MSEW). Metal straps are mostly used as reinforcement material. However, in humid climates, where the risk of damage to metal straps due to corrosion is high, the use of geosynthetic straps is quite justified. In the Croatian coastal region, geosynthetic straps were used as reinforcement for two very high MSEWs. In both cases, the backfill material crushed stone aggregate from the neighboring site was used. According to the relevant standards, it is recommended that the backfill material should have a uniformity coefficient of Cu ≥ 4.0. To meet these requirements, it is usually necessary to sieve and crush the backfill material. To evaluate the influence of the uniformity coefficient on the friction interaction coefficient between a geosynthetic strap and a crushed stone aggregate, a series of pullout tests with different confining stresses and aggregate grain size distributions were conducted. The pullout tests were performed for three different uniformity coefficients of the crushed stone aggregate. The results confirmed the justification to use backfill material with a uniformity coefficient higher than 4.0. The pullout tests were performed with one strap, two closely spaced straps, and two separated straps. The results showed that lateral friction contributes to the pullout force in the amount of 16.1% of the total force.

Analysis of The Effect of Variations in Mud Content on Stability and Flow Values in Asphalt Concrete Mixtures Layer Aus (AC-WC)


 
 
 
 Aggregat mud affect the weakening of asphalt adhesion and bonds between aggregate grains which will cause damage more quickly before reaching the design age, one of which is the formation of holes in the road surface layer.The purpose of this study was to measure the effect of variations in silt content on the stability and flow values ​​of Asphalt-coated concrete mix (AC-WC). All tests were carried out using the Marshall test method and each test object became the basis for calculations to analyze the stability and flow values ​​of the AC-WC asphalt concrete mixture with variations in silt content of 0%, 5%, 10%, 15% and 20%. The optimal bitumen content used is 6.7%. Furthermore, marshall testing was carried out on variations in silt content in the aggregate to obtain stability and flow values, stability values ​​tended to decrease from 1048.64 kg to 798.96 kg, this affected the minimum stability value of ≥ 800 kg and flow values ​​tended to increase from 1.54 mm to 3.05 mm, but the discharge value still meets the required limit of ≥ 3 mm with a mud content of 13%. Based on the results of the ANOVA analysis obtained from the test, the stability value shows a significant decrease in the level of stability and the flow value shows an insignificant effect on the proportion of sludge.
 
 
 

Phase separation of recycled concrete powder during grinding and consequent influences on its hydration behaviors in cement paste

Recycled concrete powder (RCP) collected from waste concrete recycling presents significant variation in both composition and hydration behavior, while available literatures were mainly carried out on RCPs derived from target concrete, mortar, or cement paste, RCPs collected from actual waste concrete is totally different from RCPs reported, their roles has not been clarified yet due to its complexity in components, leading to substantial deviation in understanding the roles of RCP in cement-based materials. In this study, RCP collected from a waste concrete reutilization plant was classified into five fractions, then effects of RCP fractions on heat evolution and mechanical properties of cement pastes were investigated. The results showed that hydration products and un-hydrated clinker were predominantly concentrated in fine RCP fraction, while higher proportion of aggregate grains (mainly quartz, anorthite, and dolomite) in coarse RCP fraction, indicating that cement paste was pulverized or milled into finer particles prior to fine and coarse aggregates due to its diminished elastic modulus. Compared with coarse RCP fraction, fine RCP fraction showed significant acceleration of cement hydration and higher strength contribution, which can be attributed to the remarkable pore refinement of fine particle and conspicuous seeding effect of C–S–H in RCP. Furthermore, increased dissolution of Si4+ and Al3+ from the fine RCP fraction was observed, then more hydration products were generated to densify the microstructure of cement paste. The results provided a deeper insight into the roles of RCP in cement-based materials, and then facilitate the efficient utilization of RCP to achieve resource-conservation development.

Railway ballast aggregate characterization through a new strength index: Preliminary suitability evaluation of an industrial by-product for a railway application

Ballast is a layer of the railway infrastructure that ensures the correct geometric position of track equipment, distributing vertical loads on the underlying layers. Ballast is composed by aggregate grains of adequate grading, containing a consistent number of voids and a medium–low fine content.The aggregates of ballast must be tested in the laboratory to ascertain the suitability for their use under construction or maintenance. In this work, the physical–mechanical characteristics of different types of aggregate (natural and “artificial”) were evaluated to verify their acceptability as ballast under the Italian specifications. All the aggregates came from Italian production plants. One “artificial” aggregate (steel slag) was used to assess if it can be used instead of the natural aggregate on a railway line in Italy. A mixture of natural and artificial aggregates was also tested for comparison purposes. An index from Point Load Test was also assessed to predict the main physical–mechanical characteristics provided by the laboratory tests.The artificial aggregate shows excellent physical–mechanical properties, compared to the natural one, indicating that the tested by-product can replace the natural aggregate. The mixture of natural and artificial aggregates can guarantee the preservation of natural resources and solve supply difficulties of by-products, maintaining very good physical–mechanical characteristics.In general, the Los Angeles index (both before and after the freeze-thawing cycles) shows a good correlation with the Point Load Strength Index for the tested ballast aggregates. Starting from this result, the Point Load Test could be used to characterize ballast aggregates. A statistical analysis was also performed on the other physical–mechanical parameters: a good correlation was found in some cases, indicating that the Point Load Strength Index can provide a first indication of the other physical–mechanical characteristics of ballast aggregates.

AGGREGATE AS A COMPONENT IN THE PROCESS OF CONCRETE MAKING

<p style="text-align: justify;">By modern design of the concrete system, proper selection of cement and aggregates with appropriate additives as well as other concrete production procedures, satisfactory properties of the finished concrete mass can be achieved. When making concrete, aggregate makes up approximately three-quarters of its volume, which has a great influence on the properties of fresh and hardened concrete. Due to its significantly greater stiffness than that of cement stone, large aggregate grains form the basis of concrete through which forces are transmitted. Small aggregate grains together with cement paste make up the mortar. Although the role of coarse grains and sand in fresh and hardened concrete is different, they are observed together in all tests. The choice of aggregate depends on several factors, where we would especially emphasize its availability. Its characteristics such as: plasticity, workability, strength, density, durability, permeability, texture and color largely depend on the type and quality of the aggregate used in the process of making concrete. It is available to everyone because it is actually a composite material whose basic ingredients are aggregate, cement, water and other necessary additives. This paper will deal with the division of aggregates as well as the most frequently investigated properties of aggregates. </p>

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Volumetric stability and elastic properties of concrete subjected to simulated service exposure conditions on road pavements

Expressway and highway pavements are exposed to intensive impacts of exploitation, including heavy vehicle traffic and environmental factors such as temperature and moisture along with the aggression of de-icing agents. Proper selection of mineral aggregates and design of the concrete mixture composition are important for the durability of the concrete pavement. Experimental tests were conducted on concrete under simulated service exposure conditions with external exposure to a 3% sodium chloride solution. The subject of the research was the expansion and elastic properties of air-entrained concrete made with siliceous aggregates from rocks containing moderate amounts of reactive minerals. The category of reactivity of coarse aggregates was uncertain, and in the fine aggregate was moderately reactive quartz sand. Under simulated service exposure conditions on road pavements, the significant expansion of concrete specimens and a significant decrease in the resonance elastic modulus up to 12.5% were observed. The tendency of concrete to expand was related to the presence of reaction products of reactive silica in the aggregate grains with sodium and potassium hydroxides in the cement paste [ASR], confirmed by microscopic observations. Replacement of Portland cement with CEM II/A-V 42.5 N cement and CEM II/B-S 42.5 N cement significantly reduced concrete expansion and improved the stability of elastic properties. In two of the nine concrete mixtures, the selected content of siliceous fly ash and granulated blast furnace slag, 18% and 30%, respectively, turned out to be sufficient to counteract the deleterious effects of the ASR under conditions of external contact with sodium chloride solution. A practical method for predicting the durability of concrete in the conditions in which the reactivity category of the aggregate from local natural resources is uncertain was established.

A Comprehensive Model of Morphologically Realistic Cosmic Dust Particles: An Application to Mimic the Unusual Polarization Properties of the Interstellar Comet 2I/Borisov

The cosmic dust particles found in space are mainly porous aggregates of smaller grains. Theoretically, these aggregates are replicated using fractal geometry, assuming a cluster of spheres. Although the light scattering response of cosmic dust aggregates has been thoroughly studied using clusters of spherical grains in the past few decades, the effect of irregularities on the surface of each grain in an entire aggregate has mostly been neglected. We introduce, for the first time, a visually realistic cosmic dust model that incorporates a mixture of rough fractal aggregates (RFA) and agglomerated debris (Solids) to replicate the unusual polarization–phase curve observed in the case of the interstellar comet 2I/Borisov at multiple wavelengths. The authenticity of the RFA structures has been verified by replicating light scattering results of circumstellar dust analogs from the Granada Amsterdam Light Scattering Database. We demonstrate that the light scattering response from the RFA structures has a very close resemblance to the experimental values. Finally, we model the observed polarization–phase curve of the interstellar comet 2I/Borisov using a mixture of RFA and solid particles. The best-fit data indicate the presence of a higher percentage of porous RFA structures (80%) owing to the fact that the comet carries a higher percentage of small and highly porous pristine cosmic dust particles. Further, the model indicates that the unusually steep polarimetric slope and the high dust-to-gas ratio in newer comets are mainly due to a higher porous-to-compact ratio.

Suitability of the Lower Zab River Sediments for Concrete Works / Southwest of Kirkuk - Northern Iraq

An Engineering study was carried out for five stations in the Lower Zab basin, southwest of Kirkuk, to determine the viability of the Quaternary age sediments for concrete works. The geotechnical evaluation results included that the coarse aggregate's grain size analysis is identical to the gradient class (63.0 mm) according to the [1] classification. As for the gradation of fine aggregate for the sediments of the study area, the results of the granular gradient of the samples after matching them with the limits of AASHTO specification showed that they are identical to the specification with slight differences on some sieves. The elongation and flatness tests showed that the highest percentage of the longitudinal shape is (19.2%) and flat-shaped particles is (28.8%), within permissible limits according to British standard [2], the specific gravity for coarse aggregate was between (2.60 - 2.64) and saturated specific gravity (2.61 - 2.65), and the values of specific weight for fine soil ranged from (2.72 - 2.64) which is suitable for use in concrete works. The results of the laboratory test of the durability tests - The Los Angeles test for the samples showed that the highest percentage for weight loss was (20%), which is suitable for use in the concrete according to the Iraqi standard [3], the results of the laboratory test for stability showed that the percentage of weight loss for coarse aggregate (gravel) by the effect of sodium sulfate solution and for the number of 5 cycles of the samples ranged between (8.3% - 4.1%), which is valid for use in concrete works according to the American specification [4]. The results of the resistance tests - the point load test for stations (S1, S3, S4) within the classification range of very strong - extremely strong, and the two stations (S2, S5) within the class strong - very strong - extremely strong compared to the classification of [5], and they are good for concrete works. It was found from the results of the chemical tests the gypsum content, organic matter content, Total soluble salts, and the sulfate content of the samples of the study area are suitable to for concrete works according to British Standard [6], which is suitable for concrete works, testing the compressive strength of concrete cubes ranged between (24.93 - 18.22 MPa) for age seven days and ranged between (33.02 - 29.76 MPa) for 28 days for reference mixture, Which is (4:2:1 by weight). According to the Iraqi standard specification [7], the compressive strength values of the samples are suitable for regular unreinforced concrete, and in comparison with [8] classification, it was apparent that the concrete produced is of moderate endurance. And suitable for concrete works According to [9].