Crushed Rock Research Articles

Deep Subseafloor Biogeochemical Processes and Microbial Populations Potentially Associated with the 2011 Tohoku-oki Earthquake at the Japan Trench Accretionary Wedge (IODP Expedition 343).

Post-mega-earthquake geochemical and microbiological properties in subseafloor sediments of the Japan Trench accretionary wedge were investigated using core samples from Hole C0019E, which was drilled down to 851‍ ‍m below seafloor (mbsf) at a water depth of 6,890 m. Methane was abundant throughout accretionary prism sediments; however, its concentration decreased close to the plate boundary decollement. Methane isotope systematics indicated a biogenic origin. The content of mole-cular hydrogen (H2) was low throughout core samples, but markedly increased at specific depths that were close to potential faults predicted by logging-while-drilling ana-lyses. Based on isotopic systematics, H2 appeared to have been abundantly produced via a low-temperature interaction between pore water and the fresh surface of crushed rock induced by earthquakes. Subseafloor microbial cell density remained constant at approximately 105‍ ‍cells‍ ‍mL-1. Amplicon sequences revealed that predominant members at the phylum level were common throughout the units tested, which also included members frequently found in anoxic subseafloor sediments. Metabolic potential assays using radioactive isotopes as tracers revealed homoacetogenic activity in H2-enriched core samples collected near the fault. Furthermore, homoacetogenic bacteria, including Acetobacterium carbinolicum, were isolated from similar samples. Therefore, post-earthquake subseafloor microbial communities in the Japan Trench accretionary prism appear to be episodically dominated by homoacetogenic populations and potentially function due to the earthquake-induced low-temperature generation of H2. These post-earthquake microbial communities may eventually return to the steady-state communities dominated by oligotrophic heterotrophs and hydrogenotrophic and methylotrophic methanogens that are dependent on refractory organic matter in the sediment.

ОБҐРУНТУВАННЯ ЗАХОДІВ ЩОДО БЕЗПЕЧНОЇ РОЗРОБКИ КРУТИХ ВУГІЛЬНИХ ПЛАСТІВ

Purpose. Justification of measures regarding the safe development of steep coal seams to ensure the safe efficiency of coal mining and increase the safety of miners in deep coal mines. Methodology. In order to achieve the goal, laboratory studies of the deformation properties of protective constructions were carried out on the models subjected to uniaxial compression, and field studies of the stability of preparatory mining products with various methods of protection. Results. It was found that for coal cinders within the limits of the established deformation resource (0,10,25)) at the same time as their stiffness increases, the potential energy of deformation reaches a critical level, on which the short-term stability of protective constructions is realized. At the same time, there is a relative change in volume in the range of 0,05V0,1. With the increase in static use and the transition of the critical level of deformations, when 0,25 і V0,1, the loss of cylinder stability remains. For protective constructions made of crushed rock when they are uniaxially compressed, the change in the behavior of the deformed body is separated from the compaction of the primary material. Within the limits of the deformation resource (0,40,7), a relative change in the volume of crushed rock of 0,2V0,35 has been recorded. According to the number of sizes of such protective constructions, when the work of compression increases, the value of V decreases. At the same time, the bearing capacity of protective constructions increases. Scientific novelty. The deformation resource of protective constructions of preparatory mine workings determines the effectiveness of the protection method used. Within the limits of the deformation resource, a stable state of protective constructions is ensured, which operates under conditions of single-height compression until the critical level of the specific potential energy of deformations is reached. Practical significance. To ensure the stability of the pits in the coal-bearing massif and the operational condition of the prepared products in the mining areas, it is advisable to use partial or full laying of crushed rock or wooden chock with sleepers in the mined space.

Soil-atmosphere interaction: cracking of a compacted soil under the effect of a thermo-hydric stress

Reusing excavated material in geotechnical engineering reduces the carbon impact of a project. Such materials are usually placed in a compacted state in order to achieve the mechanical and hydric characteristics required to guarantee the safety of the structures. A good geotechnical knowledge of the materials is therefore necessary as well as a good anticipation of their behaviour over time. Indeed, in some situations, as in the case of waste storage, a low hydraulic conductivity is required. The use of crushed rocks rich in clays (argillite), possibly improved by adding bentonite, could be interesting. However, this addition, beneficial in terms of hydraulic conductivity, could be damaging from a mechanical point of view by the development of cracks at the interface atmosphere-compacted soil. For this purpose, samples compacted at the normal Proctor optimum are exposed to a relative humidity of 46% and a temperature of 22.5°C. The thickness, mass and surface condition (cracking) were monitored during the drying process, and measurements were taken in the thickness of the specimen after 29 hours of exposure. The results make it possible to compare the two materials at the same compaction energy. The argillite sample shows a significant shrinkage but no cracks at this scale. On the different hand, with the addition of bentonite, a significant cracking was observed and analysed. These results provide information on the hydromechanical behaviour of unsaturated fine soils at the atmosphere-compacted soil interface.

Evaluation of CBR of Graded Crushed Stone of Flexible Base Structural Layer Based on Discrete Element Model

In order to study the mechanical properties of graded crushed stone, the discrete element method is used to simulate the CBR test of graded crushed stone. Aiming at the composition structure of graded crushed stone material, the PFC3D simulation software is used to construct the test model, and the process of constructing the virtual specimen model of the graded crushed stone discrete element model is discussed in detail. A servo mechanism is used to control the speed of the wall in the software, so as to control the virtual confining pressure imposed on graded crushed stone by the wall and simulate the real CBR test environment. The micro-parameter calibration of the virtual test is carried out by comparing the indoor and virtual CBR specimens of a single particle size specimen and three groups of graded crushed stone specimens. The comparison result shows that the stress-strain characteristics of the graded crushed rock obtained by the discrete element simulation during the uniaxial penetration process have a high degree of similarity, which can verify the accuracy of the model establishment. With the increase in the penetration depth, the penetration force of the aggregates of various particle sizes gradually increases, and the penetration force and the penetration depth are basically linear, and when the particle size is greater than 9.5 mm, the increase in particle size has little effect on the CBR test results. Under the certain conditions, the contact stiffness of graded crushed stone particles with particle sizes of 4.75 mm, 9.5 mm, 13.2 mm, 16 mm, and 19 mm should be 0.88 × 107 (N/m), 0.98 × 107 (N/m), 1.10 × 107 (N/m), 1.25 × 107 (N/m), and 2.05 × 107 (N/m), respectively. The recommended value of the contact stiffness of the small spherical particles increases with the increase in the particle size. This model can provide a basis for studying the micromechanical state of graded crushed stone and physical mechanics tests.

Substantiation of research results on energy efficiency of basalt crushing

Purpose. To experimentally determine the main design and operational parameters of the influence of rock mass properties on the Roller Crusher performance when processing basalt rock mass. Methodology. The crushing and grinding of basalts are studied by the methods of mathematical statistics in order to identify the results obtained and determine the dependences of technological parameters on the mechanical impact factors. Experimental studies are carried out on the example of basalts from the Rafalivskyi quarry in the Rivne region. Findings. It has been revealed that the elemental composition of rocks in the benches of basalt quarries has a different mineral composition. Experimental studies of the rock crushing results have determined the efficiency of using screening for crushing basalts. The experimental dependences of the roller crusher performance in crushing and grinding modes on the properties of the rock mass have been obtained. Originality. The value of crushed rock fractal joints has been found, when using cone and centrifugal crushers, which is characterized by the shape factor and fractal dimension D. For cone crusher Kf=2.15.0 and D=1.4. For centrifugal crusher Kf=1.51.8 and D=1.17. These parameters testify to the energy feasibility of using centrifugal crushers. The high value of the multiple correlation coefficients R2 and Fisher criterion F, whose value at a significance level of 0.05 is higher than the critical one, indicates a sufficient convergence between the experimental and theoretical results and the accuracy of the obtained analytical dependences. Practical value. The generalized models for determining the Roller Crusher performance, obtained for each rock type, based on significant factors, greatly facilitate the choice of parameters for crushing and grinding processes, and also allow choosing a rational mode of crusher operation.

Who Was Buried at the Petit-Chasseur Site? The Contribution of Archaeometric Analyses of Final Neolithic and Bell Beaker Domestic Pottery to the Understanding of the Megalith-Erecting Society of the Upper Rhône Valley (Switzerland, 3300–2200 BC)

Abstract The Petit-Chasseur megalithic necropolis is a key archaeological context for analyzing the social and ideological changes at the end of the Neolithic in the Alpine region of Central Europe. The link between the funerary monuments and settlement sites was established by means of ceramic archaeometric analysis. Domestic pottery from settlement sites were thoroughly characterized using multiple spectroscopic and microscopic techniques. Twelve ceramic fabrics were identified along with three types of clay substrate: illitic, muscovitic, and kaolinitic. Reconstructed paste preparation recipes largely involved the tempering of the raw clays with crushed rocks or coarse sediments. Types of raw material were not picked up randomly but were selected or avoided due to their particular compositional properties and attest to the exploitation of glacial, gravitational, eolian, and fluvial deposits. Compositional correspondence between ceramic grave goods and domestic pottery allowed identification of a link between the megalithic tombs and settlement sites, thus providing new data contributing to the investigation of the social dimension of monumental burials. Ceramic grave goods were revealed to be intertwined with the social instability affecting the 3rd millennium BC communities of the Upper Rhône Valley.

Thermal performance analysis of hollow cellular concrete block air convection embankment for cold regions

Crushed-rock air convection embankment (ACE) is an excellent passive cooling technique that uses open-graded crushed rocks as a “thermal semi-conductor” to prevent roadbeds from thawing in summer and enhance the cooling effect in winter in permafrost regions. However, the desired crushed rocks needed for ACE are not readily available in interior Alaska, resulting in extremely high construction costs. Previous studies indicated that using the cost-effective cellular concrete for ACE could effectively enhance the cooling performance of ACE and mitigate moisture warping and temperature curling of the asphalt concrete layer. It is promising to be an alternative to crushed rocks for ACE to mitigate pavement distresses. However, the design of cellular concrete ACE needs to be further studied to maximize performance and facilitate future implementation. Hence, two design configurations of cellular concrete block ACEs were proposed in this study. The thermal performance of pavement structures with these two designs was investigated by comparing them with the other four. A total of six pavement structures were analyzed, including a typical flexible pavement in the Northern Region of Alaska and five pavement structures reinforced with different paving interlayers, i.e., silty sand/gravel, crushed rocks, cast-in-place cellular concrete (full insulation), and two types of precast cellular concrete blocks. The thermal profiles, air pressure gradients, and velocities were numerically analyzed in ANSYS Fluent. The numerical results indicated that the two proposed cellular concrete ACEs exhibited a significant heat insulation effect in summer and a desired cooling effect in winter, which raised the permafrost table significantly. The maximum thaw depth of the two proposed cellular concrete ACEs was only 15% of the thaw depth of traditional silty sand/gravel embankment.

Weathered quartite sandstones of the Kursk magnetic anomaly as a raw material for construction industry

Introduction. The features of composition and structure of quartzitic sandstones of the Kursk Magnetic Anomaly affected by weathering processes, which do not meet the requirements of normative documents for obtaining crushed rock, are considered. The reserves of these rocks have not been approved as minerals and are currently stored in the form of large-tonnage dumps on the territory of the plant.The main challenge to be solved within the framework of the work is aimed at solving the issue of expanding the raw material base of the construction industry.Materials and methods. Efficiency evaluation of the weathered quartzite sandstone use is based on the study of indicators of physical and chemical properties. The analysis of mineral rocks was carried out using digital microscopy, the method of X-ray phase analysis. The experimental studies of the kinetics of grinding raw materials have been carried out. The activity of composite binders using weathered quartzite sandstone was studied in accordance with GOST 30744-2001.Results. It is shown that genetic features of weathered quartzitic sandstones are caused by defective crystal structure of quartz, they are also characterised by low frost resistance and strength. The grinding efficiency of weathered quartzite sandstone is 4 times higher in comparison with untethered. It has been established that the use of these raw materials to produce composite binders makes it possible to reduce the proportion of Portland cement in the mixture by up to 50% and increase the strength of the composite binder by 20%.Discussion and Conclusions. In consideration of current trends in the transition of the construction industry to multicomponent compositions, it is advisable to use weathered quartzite sandstone as an unconventional quartz raw material in obtaining energy-efficient building composites of a new generation.

The Effect of Using Ceramic Waste Powder as a Filler on the Performance of Bitumen Mastic and Hot Asphalt Mix

The use of raw resources is increasing due to the continuous increase of world population and rapid industrialization; while natural resources are being depleted day by day. The use of waste or manufactured materials in road construction has significant environmental and economic benefits. In this study, the use of ceramic powder as mineral filler in hot asphalt mix as an alter- native method to traditional crushed stone was investigated. The optimal amount of bitumen was determined using Marshall Mix Design method or using four different amounts of bitumen 4.5%, 5% and 5.5%. With the optimal amount of bitumen, two different types of corroded mineral fillers, ceramic and stone powder with three different filler ratios (4%, 6%, and 8%) were used to prepare asphalt mixture samples. The samples were subjected to Marshall Resistance Test, flow, determination of empty space percentage and percentage of empty space filled with bitumen and the results were compared. Also, to evaluate the type and amount of filler on the performance of bitumen, penetration degree test, softening point and ductility test of pure bitumen and bitumen containing two materials of calcareous filler and ceramic powder with different percentages were performed. The results show that the Marshall and flow strength of mixtures containing calcareous filler is about 5% higher and 12% less than the mixture containing the waste filler, respectively, and with increasing the percentage of filler in asphalt samples, the average degree of penetration and elasticity are about 30% and 4.5%, respectively decreases and softening point increases 7%; These changes are more severe in asphalt samples containing calcareous fillers. In general, it can be concluded that ceramic waste powder can be used in asphalt mixture as a mineral filler to replace crushed rock dust, because the use of this material as filler in road construction is appropriate in terms of economic and environmental factors.

Utilizing Tunnel Boring Machine (TBM)-Crushed Limestone as a Construction Material.

Tunnel boring machine (TBM) materials are usually crushed powder obtained during tunnel excavations for subways and transportation networks. Huge quantities of crushed rock powder are generally treated as waste. This study is aimed at assessing proposed mixtures of TBM and granular material for use in construction. This approach will help in a greener environment and reduce the need for crushed aggregates used in sub-base and subgrade layers of pavements. Assessment is executed using dynamic and static strength tests, including the modulus of resilience and the California bearing ratio (CBR). The TBM-crushed material can be sorted and screened on site to optimize its use as a construction material. The blending ratios for the 3/8-inch aggregate (G1) to the material-passing sieve number 4 (P4) were found to influence the pavement design parameters. This study recommends sorting the TBM-crushed limestone by an on-site sieving operation. A guide to optimizing the quality of the material is suggested by blending 3/8-inch aggregate with the crushed limestone fine-powder material at a specified percentage ranging from 5 to 10% by weight. The stability and durability tests conducted on the TBM-crushed powder material confirmed its suitability as a pavement construction material for subgrade and sub-base layers. Modulus of resilience, CBR values and compressive strength tests were carried out for different suggested mixtures.

Macro-level economic and environmental sustainability of negative emission technologies; Case study of crushed silicate production for enhanced weathering

Enhanced weathering (EW) involves application of crushed silicate rocks on croplands to capture CO2. Although research on EW is gaining traction, the missing elements in the literature however are the supply chain sustainability impacts associated with large-scale production and deployment of crushed silicates for EW purposes. The need to conduct sustainability assessments for EW systems in addition to validated technical feasibility remains a relevant research gap. In this work, the potential economic and environmental impacts associated with production of crushed silicates is assessed for eight countries, belonging to two separate groups: emerging economies (Brazil, Russia, India, and China) and developed economies (USA, UK, France, and Germany).A total of six economic and environmental impact categories are included in the assessment; gross domestic product (GDP), gross operating surplus (GOS), imports, greenhouse gas emissions, energy, and material use. The input-output model is used to estimate the economy-wide and macro-level sustainability impacts derived from producing crushed silicates. Findings show developed economies have relatively high levels of positive economic benefits and may experience less negative environmental impacts within their national boundaries by ‘leaking’ such impacts via imports. Imported consumption for crushed silicate production in developed countries were found to be substantially higher than that of emerging economies. For the emerging economies, imported consumption associated with crushed silicate production constitutes on average, less than 10% whereas for developed economies, imported consumption averages 20%. The UK mining and quarrying sector has the highest imported consumption at approximately 30%. The results of the study provide insightful outlook into the opportunities and challenges surrounding EW sustainability and is important in informing both national and global policy decisions regarding this technique.

Temperature and settlement characteristics of graded crushed-rock layer for runway engineering in permafrost regions.

To maintain the temperature and settlement stability of a subgrade, a combination of graded crushed rock layer and insulation layer may be applied to optimize pavement structures. This study verifies a proposed numerical model of pavement and subgrade design in permafrost regions and evaluates temperature and settlement characteristics at different particle size and thickness of graded crushed rock layer and different thickness and location of insulation layer. The results show that the temperature and settlement of the combination of graded crushed-rock layer and insulation layer decrease significantly as the particle diameter and thickness of graded crushed-rock layer increase, and vary little when the thickness of insulation layer is more than 0.15 m. The location of installation layer has significant influence on the temperature of the subbase layer, but has little influence on the temperature of the subgrade. The maximum settlement of the pavement structure and subgrade decreases when the installation layer varies from the top of the subbase layer to the bottom of the subbase layer. The optimal combination of graded crushed-rock layer and insulation layer is that the 0.15 m-thickness installation layer is at the bottom of the 0.50 m-thickness graded crushed-rock layer with the particle size of 6–8 cm. This study provides a theoretical basis for the design, construction, operation, maintenance, and safety management of airport runways in permafrost regions.

Nano- to Global-Scale Uncertainties in Terrestrial Enhanced Weathering.

Enhanced weathering (EW) is one of the most promising negative emissions technologies urgently needed to limit global warming to at least below 2 °C, a goal recently reaffirmed at the UN Global Climate Change conference (i.e., COP26). EW relies on the accelerated dissolution of crushed silicate rocks applied to soils and is considered a sustainable solution requiring limited technology. While EW has a high theoretical potential of sequestering CO2, research is still needed to provide accurate estimates of carbon (C) sequestration when applying different silicate materials across distinct climates and major soil types in combination with a variety of plants. Here we elaborate on fundamental advances that must be addressed before EW can be extensively adopted. These include identifying the most suitable environmental conditions, improving estimates of field dissolution rates and efficacy of CO2 removal, and identifying alternative sources of silicate materials to meet future EW demands. We conclude with considerations on the necessity of integrated modeling-experimental approaches to better coordinate future field experiments and measurements of CO2 removal, as well as on the importance of seamlessly coordinating EW with cropland and forest management.

Enhancing Property of Concrete Using Styrene Butadiene Rubber (SBR) Latex with Waste Ceramic Tile Powder

Abstract: The cement Concrete is a mixture of cement, water, sand, pebbles, or crushed rocks (the aggregate or fillers), which when used to build structures and then allowed to cure, hardens into stone. Water, aggregate, and cement are the three main ingredients. Plastic and polymer are the least priced materials as compared to steel and are widely accessible. One of the three main manufacturers of carbon dioxide, a significant greenhouse gas, is the cement industry. Its contribution to the global human CO2 emissions as of 2011 is 7%, primarily as a result of the sintering of clay and limestone at 15000 C. Because Styrene Butadiene Rubber (SBR) latex emulsions have advantages in terms of flexure strength, compressive strength, adhesion, and impermeability, they are increasingly used in the construction and repair of concrete. When used in a certain ratio between old and new concrete layers, SBR emulsion can increase the compressive and flexural strength of concrete members. There is demand on the ceramic industries to find a solution for the disposal of the growing amount of ceramic waste. Therefore, using ceramic waste powder in many industrial sectors, particularly the building industry, would aid in environmental protection. Consequently, the use of eco-friendly concrete has increased. Concrete can be made more environmentally friendly by using waste ceramic tile powder as a partial replacement for cement. Thus, the goal of this study is to develop an affordable and environmentally friendly concrete replacement using waste ceramic tile powder and SBR latex

Cultural Composition of the Muroma Based on the Study of the Pottery Traditions

Purpose. To reveal the cultural composition of the Muroma tribe at different stages of its history, two aspects of research of the pottery were included: the traditions of making specific shapes and preparation of pottery paste.Results. Analysis of the shapes of 679 vessels from the Muroma burial grounds allowed us to distinguish three traditions of shaping. The first shape dominates at the early and middle stages and represents the original cultural core of the Muroma. The second shape marks the spread of the population of another culture in the Muroma area. The analysis of the pottery pastes of 137 vessels from Podbolotevo burial ground has shown that Muroma pottery developed as a result of contacts between potters with different skills, such as tempering clay (C) with crushed rock (CR) and chamotte (Ch). For Muroma of a middle stage such mixed recipe of pottery paste as C + CR + Ch + Org is typical. At the later stage, the tradition of C + Ch + Org begins to dominate in the Muroma, and the addition of crushed rock almost disappears. A comparison of the data on the shapes of the vessels and the pottery pastes from which they were made distinguished a connection between the first shape tradition and the C + CR + Ch + Org recipe, and the second tradition – with the C + Ch + Org recipe.Conclusion. Both aspects of pottery technology allow reconstruct a whole picture of a quick change in the Muroma cultural composition at the late stage. This change was associated with the influx of the new population.

Water Retention Characteristics of Various Sizes of Expanded Perlite Produced from Two Different Types of Rocks

This study presents the results of the water retention characteristics of six groups (0.25 mm to 8.35 mm) of expanded perlite (EP) produced from two crushed raw perlite rocks of Turkey (A) and China (B). The particle size proportions of EPs showed that the particle size less than 1.68 mm was higher in B than that of A and the particle size distribution curves (PSDC) of three samples of EP A and B were similar, while the percent finer value (DN) of B was higher than that of A in all corresponding particle sizes. Volumetric water content (θv) for EPs of A and B were obtained at 11 levels of matric potentials between 0 to −50 kPa (sandbox with kaolin-plate) and −50 to −1500 kPa (pressure chamber), respectively, after fully saturating the uniformly packed EP in open-ended metal round rings. The results showed that the shapes of measured WRCs and particle size distribution curves of EP A and B were similar, while the percent values of PSDC were higher than those values of θv corresponding to each water potential greater than 0.1 kPa. The WRCs of respective EP showed that a substantial decline started at about −1 kPa and approached the residual water content (θr) observed at −500 kPa for all measurements. θv for all particle sizes of the EP A and B was not only decreased with the increasing matric potential but also distinctive with increasing particle size greater than 2.36 mm. θr was increased with decreasing particle size. For these results, we assumed that θv of the different particle sizes of EP A and B could be determined by actual pore volume excluding occluded pore volume depending on size and surface area in the EP particles.

Influence of particle size distribution on fractal characteristics of waste rock backfill materials under compression

Broken waste rock as backfill materials is filled into the underground goaf and will encounter particle breakage under the overburden pressure. The damage degree of the crushed waste rock materials directly affects the compression properties of the backfill body and the control effect of strata movement and surface subsidence. Fractal theory can be used to quantify the breakage degree of waste rock particles. In this study, compression tests are carried out on the broken waste rock materials with different particle size distributions to investigate the influence of the particle size distribution on the fractal characteristics of waste rock backfill materials under compression. The results show that the waste rock specimens with discontinuous size grading and containing more coarse particles have higher stress when entering the stable deformation stage, larger strain if at the same stress level and larger breakage ratio after compression. The particle size distribution of the crushed waste rock specimens after compressive loading has superior fractal characteristics and the fractal dimension increases with the content of fine particles and decreases significantly under discontinuous size grading. The fractal dimension has significant negative exponential function regression relationship with the strain and the breakage ratio. The strain and the breakage ratio decline with the growing fractal dimension. If the waste rock specimens have continuous particle size gradation and higher content of fine particles, the fractal dimension, the strain and the breakage ratio of the waste rock backfill materials tend to be optimal and stable, proving a desirable initial particle size distribution of the waste rock backfill materials.

Strength, durability and shrinkage behaviours of steel fiber reinforced rubberized concrete

Many studies have recently been conducted to reduce the environmental influences of construction in industrial sectors. Recycling rubber as aggregate in concrete helps to reduce the environmental effects of waste automobile tires, and enhances the deformability of the concrete in structural applications such as slabs on grade and concrete pavements. This study aims at examining the reinforcement of rubberized concrete by a hybrid system of fibers comprising industrial steel fibers and steel fibers from waste tires. Six concrete mixtures with/without steel fibers were investigated, using 0, 20% and 40% by volume of waste tire rubber (WTR) particles as a substitute for natural aggregates. The fresh properties of these concrete mixes were evaluated using concrete slump and air content tests, as well as unit weight. Compressive and splitting tensile strengths at 7 and 28 days and flexural strength at 28 days were used to evaluate the hardened concrete properties. Concrete porosity and rapid chloride permeability tests were conducted to evaluate the concrete’s permeability, and its volume stability was assessed by examining free-drying shrinkage and restrained shrinkage. The results showed that, although the mechanical properties of the concrete were negatively impacted when a portion of the crushed rock and sand aggregates were replaced by rubber particles, it was possible to produce rubberized concrete with comparable mechanical properties and durability to conventional concrete when 40 kg/m3 of steel fibers was used in conjunction with 20% rubber. The flexural strain capacity and post-peak properties of the rubberized concrete containing 20% rubber and 40 kg/m3 steel fibers were substantially better than conventional concrete. In addition, the free drying shrinkage strain after 56 days for all mixes was low, below 457 micro-strain or 0.046%, and the presence of high quantities of rubber particles and/or steel fibers in the concrete ring specimens subjected to restrained shrinkage testing prevented the initiation and propagation of cracks. The outcome of this study highlights the potential of these combinations for use in concrete pavement and slab on grade applications.

Experimental Study on Compaction Characteristics and Mechanical Behavior of Crushed Rock Masses

The compaction and consolidation process of a regenerated roof can be divided into two stages, namely, secondary fragmentation of crushed rock masses and pore structure adjustment. Therefore, the mechanical properties of the regenerated roof differs significantly from those of the primary roof. We performed confined compression tests of crushed mudstones and sandy mudstones using a self-developed compression testing apparatus. We studied the influence of the moisture content, compression ratio, particle size, and volume-based degradation on the compression and consolidation characteristics based on the microscopic morphology of the crushed rock masses. Further, the degrees of influence of these factors on the stability of the consolidated bodies were determined. Therefore, the influence mechanism of each factor on the compressive and shear strengths of the consolidated bodies was revealed. The results indicated that the compaction and consolidation of the crushed rock masses involved a constant adjustment of the contact and stress states of the rock masses. Under uniaxial compression and shearing, the consolidated bodies presented the features of ductile failure. The compression ratio and particle size were the most important influencing factors in the compressive and shear strengths of the consolidated bodies. Further, we carried out an orthogonal experiment and built a multivariate nonlinear regression model to quantitatively characterize the combined influence of these factors on the compaction characteristics of the crushed rock masses and the mechanical behavior of the consolidated bodies.

Experimental Study on the Influence of Mogadishu Manufactured Sand on the Engineering Properties of Concrete

Due to the increasing demand for sand for construction activities across the world including Mogadishu Somalia, natural sand resources are growingly used up and its price is becoming increasingly high. This study aimed to research the influence of Mogadishu-manufactured sand on the engineering properties of concrete. Manufactured sand refers to fine aggregate which is less than 4.75mm. In this research, Mogadishu Manufactured sand was refined from the crushed limestone rock as a replacement for river sand. The overall objective of the study was to evaluate the influence of Mogadishu manufactured sand on the engineering properties of concrete; the specific objectives were to examine the properties of plastic and hardened concrete; to investigate the durability of concrete with Mogadishu manufactured sand. The study used manufactured sand in incomplete or complete replacement for natural sand. The basic aggregate tests considered were sieve analysis for fine and coarse aggregate, specific gravity, and water absorption was also done. Design mix of class 30 concrete having mix amount for both natural and manufactured sand was considered for the workability test (slump test and compaction factor test). The splitting tensile strength test and compressive strength test for 28 and 56 days was done. The study, in addition, considered durability testing by exposing the concrete to sodium chloride, magnesium sulphate, and sulphuric acid. Then final assessment was done to determine how these chemicals affected the concrete after 28 and 56 days of immersion. It was found that the slump and compaction factor values of the concrete mix with Mogadishu manufactured sand decreased compared to that of conventional concrete. Concrete with Mogadishu manufactured sand significantly improves the strength properties of the concrete up to 25% replacement and reduces as replacement increases. This was attributed to the presence of micro fines in the Mogadishu manufactured sand generated from limestone rock. When exposed to sulphuric acid, magnesium sulphate, and sodium chloride, the durability of concrete with manufactured sand were improved as compared to that of normal concrete with river sand. Hence from the experimental investigations, it is concluded that Mogadishu manufactured sand can be partially utilized as fine aggregate in concrete production of construction activities.