Rock Aggregates Research Articles

Soft computing implementations for evaluating Los Angeles abrasion value of rock aggregates from Kütahya, Turkey

The Los Angeles abrasion value (LAAV) of rocks is a critical mechanical aggregate property for designing road infrastructures and concrete quality. However, the determination of this critical aggregate property is labour-intensive and time-consuming and thus, in the literature, there are many predictive models to estimate the LAAV for different rock types. However, most of them are based on classical regression analyses, limiting their broader usage. In this study, several soft computing analyses are performed to develop robust predictive models for the evaluation of LAAV of rocks in the Ilıca region (Kütahya – Turkey). The main motivation for implementing soft computing analyses is that precise predictive models might be useful when exploring suitable rock types that are manufactured in crushing–screening plants. For this purpose, a comprehensive laboratory schedule was established to obtain some inputs for the evaluation of LAAV. As a result of the soft computing analyses, four robust predictive models are developed based on artificial neural networks (ANN), multiple adaptive regression spline (MARS), adaptive neuro-fuzzy inference system (ANFIS) and gene expression programming (GEP) methodologies. The performance of the proposed models is investigated by some statistical indicators such as R2 and RMSE values and scatter plots. As a result, the ANFIS-based predictive model turns out to be the best alternative to estimate the LAAV of the investigated rocks.

Studies on durability, thermal and morphological property with partial replacement of single use waste plastic and complete recycled aggregate in eco-friendly self-compacting concrete

This study focuses on creating an eco-friendly self-compacting concrete (EF-SCC) by recycling waste materials like plastic and construction debris. The researchers collected High-Density Polyethylene (HDPE) and Polypropylene (PP) plastics, cleaned and shredded them, then used them to partially replace fine sand at different levels, from 5% up to 20%. They also replaced all the traditional coarse rock aggregate with recycled materials from construction waste. The concrete’s flow and ease of pouring (workability) were tested, and it was found that mixes with recycled aggregates flowed faster, with the best result being a 6-second flow time when using 10% HDPE. Durability tests were done by exposing the concrete to acid and sulphate attacks over several weeks, showing that the recycled concrete with plastics held up well, with only minor weight loss after 56 days in acid. Thermal tests showed that adding plastic lowered the concrete’s heat conductivity by 30-35%, making it better at insulating. Microscopic analysis showed that the plastic was well integrated with the cement mixture, and chemical tests confirmed there were no harmful reactions between the plastic and the cement. Overall, the study suggests that EF-SCC made with recycled aggregates and plastic waste can keep key properties needed for construction, making it a promising, sustainable building material

Mechanical Properties and Penetration Characteristics of Mudstone Slag-Based Waterproof Composites under Cyclic Loading

In this study, ground polymers were prepared from mudstone and slag. NaOH and water glass were used as alkaline exciters and mine waste rock aggregate was used as the aggregate for mudstone slag-based waterproof composites (MSWCs). A series of laboratory tests, including a uniaxial compression test, uniaxial cyclic loading and unloading test, scanning electron microscope test, and rock penetration test were conducted for macrostructural and microstructural analysis. The effect of the coupling between the mudstone proportion and the number of uniaxial cyclic loading and unloading tests was investigated. The results showed that it is feasible to use mudstone and slag to synthesize geopolymers, and that MSWCs fulfil the conditions for use as a reconstituted water barrier. The permeability of MSWCs with the different mudstone proportions set in this study fulfils the requirement of being used as a material, and the permeability and uniaxial compressive strength of the MSWCs gradually decreased with increases in the mudstone proportion. Considering the UCS and permeability of the MSWCs, the optimal mudstone proportion of the MSWC is r = 0.6. In this test, cyclic loading and unloading times of 0, 25, 50, and 100 were set, and with an increase of cyclic loading and unloading times, the UCS of the MSWCs showed a tendency of increasing first and then decreasing. In the SEM test, with an increase of cyclic loading and unloading times, microfractures and pores appeared in the MSWCs, which led to a gradual increase in its permeability and a decrease in its waterproofness.

Geotechnical Suitability of Soils in Road Construction for Sustainable Development in Tropical Africa: Case of Lateritic Graveled Soils of Bandjoun (West, Cameroon)

The environmental impact of the exploitation of geomaterials and their relatively high cost, coupled with the increasingly low financial capital in developing countries, are pushing road actors to turn to inexpensive local ecological materials. The present study is conducted on lateritic graveled soils of Bandjoun (LGSB) in the West Cameroon Region. The aim is to determine whether lateritic gravel soils, particularly those in Bandjoun, can be an ecological and economical alternative to rock aggregates in road construction, considering their geotechnical parameters and environmental impact. These soils were described in the field and were also subjected to complete geotechnical identification in the laboratory. The LGSB presents Californian bearing ratio indices ranging from 26% to 83.3%, a plasticity index of 10.11%, a fines content of 12.05%, an average methylene blue value of 4.25, a water content at the Proctor optimum of 27.6% and a dry density of 1.75 g/cm3. They are silty or clayey gravels and sands of subgroup A-2-7 according to the Highway Research Board classification; sandy and gravelly soils with fines of class B according to the classification of the Road Construction Guide; and silty gravels according to the classification of the Central Laboratory of Bridges and Highways. These soils can be used naturally in pavement layers, in particular in subgrade for all traffic classes and in subbase for low traffic. The tonnage of these soils has been estimated at 18,389 t. The global warming index shows that the use of these soils (18,389 t) in road construction can reduce 31,629–62,706 kg of carbon emissions. The use of lateritic soils in road construction is a very interesting alternative to reduce the environmental impacts associated with the manufacture of rock aggregates. So, lateritic soils should be used instead of rock aggregates for cleaner, more environmentally friendly road construction. The present work presented a specific evaluation of the geotechnical properties and ecological impact of lateritic graveled soils for road construction, as well as their potential for ecological and economic utilization.

Particle morphology characterization of waste-tyre-stabilized rock aggregates via computational geometric modellings

This study offers a comprehensive understanding of the most important geometrical concepts for concave shape particles with very low sphericity. Study of concave hulls in three-dimensional space is performed with an emphasis on accurate and asymptotically fast algorithms. Based on that a three-dimensional concave hull algorithm is designed to generate the actual shape of irregular particles through a set of 3D surface coordinate data points captured by 3D handy laser scanner and photogrammetry. The algorithm is utilized for a wide range of large-scale waste tyre and rock aggregates to assess several fundamental theoretical hypotheses related to geometric parameters, including surface texture with concavity/convexity, concave hull volume, perimeters of projected area, and concavity computation that have not been tested before for highly irregular concave shape particles. As a result, the morphological characteristics of the waste-tyre-stabilized rock aggregate mixtures are analysed for mining operations. We also provide the details on how the application of the resulting particle morphology is employed in cloning particles with wide range of concavity distribution. The paper identifies the accuracy by implementing the proposed 3D concave hull algorithm for morphology analysis of concave particles and comparing the morphology analysis results against those of Finite Element Method (FEM), polar representation approach (PRA), and experimental data.

Experimental Study on the Interface Characteristics of Reinforced Crushed Rock Cushion Layer Based on Direct Shear Tests.

Through indoor large-scale direct shear tests, the interface characteristics of the crushed rock cushions layer reinforced with ParaLink geogrid were studied. The test results indicate that the shear strength of the crushed rock aggregate and the interface strength parameters have a non-linear relationship with the normal stress. The addition of the geogrid reduces the shear strength of the crushed rock aggregate and the interface strength parameters, which is mainly due to the relatively large size, small thickness, and high smoothness of the geogrid. The reinforced geogrid has a significant impact on the deformation and fragmentation characteristics of the crushed rock aggregate. It effectively suppresses the shear contraction and shear dilation effects of the crushed rock aggregate, reducing its peak compression and peak dilation angle. Furthermore, it inhibits the tendency of particle fragmentation in the crushed rock aggregate.

Effect of rock gradation in Stone Matrix Asphalt using Coir Fibre

Stone Matrix Asphalt (SMA) was introduced to counter heavy traffic and loading due to its better rut resistance. This study aims to determine the effect of rock gradation on SMA, water susceptibility, tensile strength, and retained tensile strength. The methods adopted for testing include the physical properties of rock and bitumen, the Marshall Stability Test, and the Water Sensitivity Test. Coir fibre is used in SMA to prevent draining as an alternative to cellulose fibre. The study shows that coir fibres satisfy the drain-down requirement for both 13 mm and 19 mm gradations, respectively. Laminate sedimentary rock aggregate used in SMA is susceptible to water. A larger size of gradation has achieved higher retained tensile strength, mainly due to the lesser degradation that develops in bituminous concrete

Quantifying the Degree of Binder Availability in Recycled Asphalt Mix Design Using White and Black Rock Mixes

Quantifying recycled asphalt binder availability in recycled asphalt pavement (RAP) mix design is very essential, as the widely adopted 100% RAP binder availability assumption in RAP mix design never holds correct. Depending on the mix production condition, recycled binder stiffness, and virgin binder properties, the degree of binder availability in the mix is always partial. The present study proposes a simple procedure to estimate the degree of recycled binder availability in RAP mix design. In the proposed methodology, the designer needs to compare optimum binder content of bituminous mixes prepared using white rock aggregate gradation and virgin aggregates, along with mixes designed by blending black rock gradation and virgin aggregates blended in proportion to achieve the target white rock gradation. The binder content in the RAP fraction used in the blending exercise was determined using ignition oven method. RAP mix designs were performed for RAP material collected from two different sources, and design was performed for three mixing durations in a laboratory pug mill—60, 120, and 180s. The mixes were prepared with 50% RAP incorporation level. RAP material was conditioned at 110°C for 2 h, whereas virgin aggregates were superheated to 175°C. Using the methodology proposed, RAP binder availability was found to vary between 92.5% and 96.6% for softer RAP material, 75.9% to 91.5% for mixes incorporating stiffer RAP. With increasing mixing time, even though the total active binder content did not change significantly, a mixture performance test quantified the implication of increased RAP binder availability in mixes. A higher degree of binder activation resulted in mixes being rut resistant, while the same mixes exhibited relatively higher cracking susceptibility.

Rock Aggregate Size Influence on Physical Degradation of Laminate Sedimentary Rocks in Flexible Pavement

Rock aggregates are the most fundamental material of highways, railroads, and other construction activities. Degradation of aggregate is the disintegration of aggregate due to the wheel load and moisture saturation causing loss of support in unbound granular layer and reduction of drainage in pavement materials. Sedimentary rocks from different quarries were evaluated to determine the influence of aggregate size on the degradation of materials. This study is to find out the effect of size on physical parameters of aggregate used in flexible and rigid pavement. The performance of river rock and crushed rock physical properties has been tested and compared. In order to determine the effect of aggregate size on their degradation properties, different sieve ranges were selected. The sieve sizes are graded into four categories according to Indian Standard sieve: R1 (20 mm-16 mm), R2 (16 mm-12.5 mm), R3 (12.5 mm-10 mm), and R4 (10 mm-4.75 mm) for degradation test such as, aggregate impact value (AIV), aggregate crushing value (ACV), water absorption (WA) and weathering test such as soundness and slake durability. It is observed that the larger size of aggregate has given better resistance against impact load, abrasion, weathering action and water absorption compare to smaller size over the same volume of rock. The rate at which aggregate degradation occurs is influenced by size. Along with the wheel load, environmental factors including moisture and temperature changes are the primary causes of the early degradation of aggregate. The river rock has a better resistance against degradation and weathering action as it has lesser lamination (a small scale sequence of fine rock layer). Adoption of larger size aggregate in the pavement base course is suggested to withstand the effect of environmental action and wheel load, especially on the friable and quickly disintegrated rock. Arating value, rating index and regression equation have been developed for aggregate degradation. Keywords: Particle Size, Properties of Rock, Weathering, Slake Durability, Degradation Index

Strategy to minimize induced 24Na, 56Mn activity in concrete composites used for fast neutron shielding: impact of cement and rock aggregates

Strategy to minimize induced 24Na, 56Mn activity in concrete composites used for fast neutron shielding: impact of cement and rock aggregates

Dielectric characterisation of rock aggregates with different grain size distributions

Aggregates largely influence a road's dielectric properties, which is an important physical parameter when using non-destructive methods such as ground penetrating radar to evaluate a road's geometry. Due to the irregular shapes, the direct measurement of an aggregate piece by piece in the microwave domain is not easy. To address this problem, an epoxy-based composite is used to estimate the dielectric constant of the aggregates by resonant test and mixing law calculation. As a water-free binder, the epoxy composite eliminates the water effect on the dielectric properties. Meanwhile, the distribution of each component can be studied by X-ray computed tomography, which allows knowing the composite's morphology. Moreover, the composite has a smooth surface that avoids the texture effects on the dielectric measurement. In addition, the impedance analysis of individual aggregates at low frequencies was used to evaluate the results obtained with composites and mixing laws.

Machine learning models for predicting unconfined compressive strength: A case study for Precambrian basement complex rocks from Ado-Ekiti, Southwestern Nigeria

This study investigates the applicability of four distinct machine learning (ML) models – Random Forest (RF), Relevance Vector Machine (RVM), Support Vector Machine (SVM), and Artificial Neural Network (ANN) - for predicting the unconfined compressive strength (UCS) values of Precambrian basement rocks. The models employ input parameters such as rock aggregate index (Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), and Los Angeles Aggregate Value (LAAV)) and mechanical test index values (Schmidt Hammer Rebound Number (SHR) and Point Load Strength Index (IS(50)) for prediction purposes. Additionally, a multilinear regression (MLR) model was implemented to compare the predictive performance of the ML models against the traditional linear regression model. The developed models were validated using performance metrics such as Mean Absolute Error (MAE), Root Mean Squared Error (RMSE), and Adjusted R-Squared (Adj.R2). The Friedman statistical test was also employed to investigate the significance of the differences in the performance of the models. The results indicate that all the models performed well and showed better predictive performance compared to the MLR model during both the training and testing phases, except for the ANN model, which exhibited slightly poorer performance than the MLR model in the testing phase. However, the SVM model demonstrated the best predictive accuracy among all the models with MAE, RMSE, and Adj.R2 scores of 0.76 and 1.45; 1.16 and 1.8; 0.98 and 0.90, respectively, for the training and testing phases. The difference in the performance of the predictive models was statistically significant, as revealed by the Friedman statistical test. A feature importance analysis was conducted to verify the significance of each input parameter, revealing that all input features had a positive effect on the output of all the models. However, IS(50) had the most significant impact on the models.

Experimental Study on Effect of Partial Replacement of Waste Aggregate by Over Burnt Brick in Concrete

The most popular building material in the world, according to experts, is concrete. Water, sand, cement, and a rock aggregate are the main components of standard concrete compositions. The coarse aggregate in concrete is the main topic of this project.The other substance will be utilized in place of the normal concrete's coarse rock aggregate. Burn brick will be a part of this. They were picked because they were readily available. The brick production location has burn brick available. Numerous bricks are also rejected throughout the brick-making process because they do not meet the necessary requirements. The warped shape of brick created as a result of the kiln's uneven temperature regulation is one such significant non conformity. Additionally, these rejected bricks may be a source of coarse material. Key Word: over burnt brick in concrete, work ability, compressive strength, tensile strength, flexural strength.

Inhibitory mechanism of fly ash on alkali-silica reactivity of siliceous rock fine aggregate: A case study of Yangxi concrete dam

The fine aggregate of siliceous rock has the advantages of high production efficiency, stable yield and low construction and transportation cost. The Yangxi concrete dam was firstly apply siliceous rock as fine aggregate to a large concrete project of three million m3. However, siliceous rock aggregate has high SiO2 content, which is easy to trigger alkali-silicate reactivity. To investigate the alkali-silica reactivity characteristics of siliceous rock fine aggregate and its inhibitory measures, in this work, we used fly ash, ordinary silicate cement, and siliceous rock fine aggregate to prepare cement mortar. The effects of fly ash admixture on the expansion rate, as well as the flexural and compressive strength of the mortar were investigated by the mortar rod rapid method and mechanical tests. The inhibition mechanism of fly ash on the siliceous rock fine aggregate was analyzed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. The results showed that the addition of 30 % fly ash to the siliceous rock mortar could effectively limit the mortar expansion and its late strength growth was the most rapid. Compared to siliceous rock mortar without fly ash, the FA30 specimen mixed with 30 % fly ash had a denser structure, the hydration products at the ITZ were more closely arranged, and the C-A-S-H gel with a low calcium-silica ratio was generated internally, which could effectively inhibit the ASR of the siliceous rock fine aggregate.

Research and Application of Key Technologies for the Construction of Cemented Material Dam with Soft Rock

In order to safely and efficiently use soft rock aggregate cemented dams in red bed regions and promote the development of widely sourced cemented sand and gravel dam materials, the Jinjigou project in China applied soft rock for the first time in the construction of cemented material dams. This article further explores the concept of cemented material dams from conducting on-site direct shear tests and research on soft rock material ratios and explores and invents a new structure and construction method by combining soft rock cemented sand and gravel with cemented rockfill. This article also proposes a digital mixing and intelligent dynamic control method for cemented material dams with soft rock. The research results show that soft rock aggregate content not exceeding 60% can produce soft rock cemented gravel with a compressive strength of no less than 6 MPa. The stress on the dam body is small and does not produce tensile stress. The dam body with added soft rock has certain shear-bearing capacity, with a shear friction coefficient of 0.99~1.10 MPa, cohesion of 0.26~0.53 MPa, and high residual strength, accounting for 60~80% of the peak strength. At the same time, the problems of large fluctuations in moisture content and the uneven grading of the soft rock and riverbed gravel mix during the mixing and production process, and the significant influence on safety caused by the large strength dispersion of the cemented sand and gravel, are resolved, ensuring the quality of soft rock cemented sand and gravel preparation. The successful application of soft rock cemented material dams in Jinjigou has achieved a breakthrough in key technologies for soft rock cemented dam construction in red bed regions, proving the feasibility of soft rock cemented material dam construction and having broad prospects for application and promotion.

Microstructural transformations of swelling clay minerals

An original model of microstructural transformations during clay swelling is considered, a thermodynamic and physical-mechanical description of the properties of clays during the process of swelling in vapors and aqueous solutions is given. The model proposed to explain these properties is based on the concept of mutual displacement of clay particles in clay rock aggregates during swelling with the formation of new pores between clay particles forming crystallites and aggregates. The model is based on the mechanism of utilization of the excess surface energy of clay particles during hydration, taking into account the influence of certain environmental parameters, for example, the concentration of the solution, through a change in the mutual orientation of clay particles, mainly due to rotations or shifts relative to each other, with the formation of an area available for further wetting free surface. In the thermodynamic description, such a process will manifest itself in a change in the surface interaction energy on the wetted areas of the particles when moving during mutual shifts and rotations. At the same time, one of the most important parameters of clay rock, microporosity, also changes. In this work, this phenomenon was experimentally studied using the methods of static moisture capacity and Mössbauer (NGR) spectroscopy. The proposed model makes it possible to explain the features of the clay hydration process and to compare the observed experimental data with the theoretical description of the clay swelling process.

Hydration characteristics of tailing mud–42.5 OPC composite cementitious system and its application to dry-mixed mortar

This study investigated the influence of the raw material ratio on the product quality of tailing mud with type-I 42.5 ordinary Portland cement (OPC) in a binary cementitious system. In particular, this research aimed to expand the applicability of tailing mud and tailing waste rock while minimizing the production cost of dry-mixed mortar. The results demonstrated a synergistic reaction between the tailing mud and 42.5 OPC, which was beneficial for enhancing hydration and gelation, increasing the production of calcium silicate hydrate (C–S–H) and calcium hydroxide (C–H), promoting more free magnesium oxide (MgO) in the cement to participate in the hydration reaction, and improving the structure of the composite gelation system. When the concentration of tailing mud in 42.5 OPC was 20%, the cementitious block attained a 28-day compressive strength of 44.85 MPa. To manufacture the dry-mixed mortar product, 80% mud and 20% 42.5 OPC were mixed with equal amounts of tailing mud and waste rock aggregate. For the dry-mixed mortar, the 28-day compressive strength was 7.32 MPa, 2-h consistency-loss rate was 12.4%, and water retention rate was 99.2%. To further explore the synergistic reaction mechanism between the tailing mud and 42.5 OPC, the energy calculations, geometric optimization, and dynamic modeling of the tailing mud–42.5 OPC cementitious system were performed using the Forcite module in Materials Studio software. Overall, the results indicated that including tailing mud improved the mechanical strength of 42.5 OPC.

Petrography and Geochemical Relationships of the Ultramafic Rocks in Galalah area within Erbil Governorate, NE Iraq

The current research to study the petrography, mineralogy and geochemical relationships of the ultramafic rocks in the Galalah area within Erbil Governorate, at the Unstable Shelf in the Imbricate Zone, to determine the origin of the ultramafic rocks. Dunite and Harzburgite are the most abundant rock bodies in the study area, and they represent most of the outer surface exposure of the ultramafic rock aggregates. The dunite rocks are characterized by pale brown color on the altered surface that is broken into olive green and dark green lithic. Dunite represents a homogenous lithologic feature that mainly consists predominately of olivine with accessory spinel and traces of orthopyroxene. While the harzburgite appears as a massive rock body consisting of olivine, orthopyroxene, and clinopyroxene. These rocks are mainly characterized by alteration to serpentinite, with accessory chromian spinel, secondary magnetite, chlorite, and talc. The studied ultramafic rocks are predominately rich in ferromagnesian minerals of less silica content, and other major elements affected by serpentinization are causing the deviation of elements. They have a strong decrease in sodium and calcium oxides relative to MgO and verified the silica and alumina with MgO and a slight increase in iron oxide. The low values of TiO2 in dunite and harzburgite are characteristic property of the Alpine type ophiolites during the primary process of the mantle in its upper part, before the tectonic emplacement of the ultramafic rocks, and also due to partial melting degree for the asthenospheric mantle. The MREE depletion relative to HREE and LREE may be attributed to the hornblende absence and the presence of olivine and pyroxenes minerals and/or to the source rock features. The U-shaped patterns of REE and their ratios are typical properties of ophiolitic ultramafic rocks, which are compatible with the supra-subduction zone. During the partial melting, the negative anomalies of Nb in ultramafic rocks with sequestration of the Nb concentration by sphene and ilmenite in various types of the source rocks have also been attributed to the crust contamination. These are also characterized by island arc conditions, and its depletion in the studied rocks may indicate the fore-arc tectonic environments

Enhancing the properties of lightweight aggregates using volcanic rock additive materials

The aim of the research was to investigate the applicability of different volcanic rocks as additives materials in lightweight aggregates (LWA) production. This study explains how the high amorphous content can improve the bloating properties of expandable clays and the properties of the LWAs produced. Ten different expandable clays, suitable for lightweight aggregate production, were collected and tested from clay deposits in Egypt and Hungary. Perlite and rhyolite tuff were used as volcanic rock aggregates. The composition of the samples was investigated by X-ray fluorescence spectroscopy (XRF) and X-ray powder diffraction (XRD, Rietveld method), while their expandability was characterized by heating microscopy (HM). The ideal amount of volcanic rock additives (10 wt%) and the required firing temperatures (1225 °C for the Hungarian clays and 1275 °C for the Egyptian clays) were determined and the LWAs were then produced. The LWAs produced (by hand rolling) by mixing of 90 wt% of expandable clay with 10 wt% of the additive materials (10 wt% perlite or 10 wt% rhyolite tuff) as green pellets then fired for different temperature. The LWAs made by mixing 10 wt% perlite or 10 wt% rhyolite tuff were characterized by their density, compressive strength, mineral composition, and pore structure. All samples had a density of less than 1.2 g/cm3, so they can be used as LWA. The results show that the additives helped some clay samples produce LWA with higher strength but lower density than the reference sample which was used, enabling the construction of lighter but stronger structures. Compositional analysis of the LWAs showed that there is a strong correlation between the amorphous content of the samples and their density, with higher amorphous content resulting in lower density.

Performance assessment of a rock aggregate heat exchanger exposed to daily temperature variation

Opportunities exist to utilize rock aggregate to condition ventilation air at mine sites in humid continental climates. Vale’s Creighton mine in Canada proved that a natural heat exchanger offered significant energy savings; however, the system was not suitable to establish design guidelines. A novel prototype-scale outdoor 30 m3 rock pile heat exchanger experiment was constructed to characterize the thermal response to measurable aggregate parameters with insight shared regarding their sensitivity. This paper validates an unsteady 3D CFD numerical methodology involving the thermal non-equilibrium porous zone model with lab-scale-derived correlations against weather-influenced temperature data and proposes guidelines for improving performance: Increasing pile flatness was beneficial for damping whereas increasing hemispericality was beneficial for phase shifting. A CFD case study requiring 47 m3/s (100,000 cfm) ventilation flow found that a rock pile constructed using traditional methods could achieve 100% damping with 6,000 m3 of granitic rock aggregate at a pressure penalty of 2,500 Pa.