Increase In Sand Content Research Articles

A comprehensive experimental study on the monotonic behavior of clay-sand mixtures

The main object of this research is the investigation of the behavior of clay-sand mixtures in undrained condition. For this purpose, the behavior of clay mixed with the different percentage of sand (i.e., 0%, 20%, 40%, and 60%) was studied by carrying out undrained triaxial tests on normally consolidated and overconsolidated specimens under different effective stresses. The results showed that sand inclusion up to 20–40% (depend on sand size) does not affect considerably the shear strength of the clay, but when the amount of sand is more than 40%, the shear strength raises 74 to 260%. Maximum pore water pressure at low confining pressures remains unchanged by changing sand content from 0 to 60%. At high confining stress, this parameter for specimens consists of 40% sand is higher than the corresponding values of the other ones. For overconsolidated specimens, irrespective of some exceptions, dependent on sand size, the values of shear strength improve 43 to 73% when sand content varies from 0 to 60%. In addition, deformation modulus of both normally consolidated and overconsolidated mixtures increases 9 to 136% by an increase in sand content from 0 to 40%, and, then, the values diminish rapidly by changing sand content from 40 to 60%.

Global convergence in correlations among soil properties.

The correlations among major soil properties at a global scale are essential for explaining the global convergence of ecological processes in terrestrial ecosystems but have never been assessed. In this study, a global soil database was analyzed to determine whether correlations among soil properties were consistent and how such correlations varied among continents and land use types. Across the entire dataset, the electrical conductivity of soils increased significantly with increasing pH; additionally, the total nitrogen and cation exchange capacity increased significantly with increasing organic carbon content, while the organic carbon content and cation exchange capacity decreased significantly with increasing sand content in soil. The correlations between paired soil properties were consistent among continents and land use types. The slopes of the relationships, however, varied significantly by continent and land use type. The results indicated a global convergence of correlations among soil properties and variation in the slopes of specific relationships between paired soil properties among continents and land use types. Such consistent global correlations and different slopes of specific correlations can have important implications in explaining the global patterns of biogeochemical processes and can provide some basis for linking soil resources with ecological processes on a global scale. Keywords: continent, land use, organic carbon, electricity, pH, CEC DOI: 10.25165/j.ijabe.20201303.4547 Citation: Xie B C, Zhang C X, Wang G D, Xie Y G. Global convergence in correlations among soil properties. Int J Agric & Biol Eng, 2020; 13(3): 108–116.

Soil reconstruction after mining fails to restore soil function in an Australian arid woodland

The biogeochemical properties of soils drive ecosystem function and vegetation dynamics, and hence soil restoration after mining should aim to reinstate the soil properties and hydrological dynamics of remnant ecosystems. The aim of this study is to assess soil structure in two vegetation types in an arid ecosystem, and to understand how these soil properties compare to a reconstructed soil profile after mining. In an arid ecosystem in southeast Australia, soil samples were collected at five depths (to 105 cm) from remnant woodland and shrubland sites, and sites either disturbed or totally reconstructed after mining. We assessed soil physico‐chemical properties and microbial activity. Soils in the remnant arid ecosystem had coarse‐textured topsoils that overlay clay horizons, which allows water to infiltrate and avoid evaporation, but also slows drainage to deeper horizons. Conversely, reconstructed soils had high sand content at subsoil horizons and high bulk density and compaction at surface layers (0–20 cm). Reconstructed soils had topsoils with higher pH and electrical conductivity. The reconstructed soils did not show increased microbial activity with time since restoration. Overall, the reconstructed soil horizons were not organized in a way that allowed rainfall infiltration and water storage, as is imperative to arid‐zone ecosystem function. Future restoration efforts in arid ecosystems should focus on increasing sand content of soils near the surface, to reduce evaporative water loss and improve soil quality and plant health.

UV light and temperature induced fluridone degradation in water and sediment and potential transport into aquifer

Fluridone is widely used in ambient water bodies to control the spread of invasive aquatic plants. While the ability of fluridone to control aquatic weeds such as water hyacinth is well reported, an improved understanding of fluridone persistence in water and sediment is still needed to determine potential residues of fluridone in the water column and bed sediment of ambient water bodies. In this study, experiments were conducted over a three-month period to examine the degradation of fluridone in saturated sediment and water under various levels of UV-light (0–1000 μW/cm2), and temperature (4–40 °C). Results showed a large decrease in the half-life of fluridone in water with increasing UV light intensity, but in saturated sediment the impact of UV light exposure on fluridone degradation was minimal. At low temperature (4 °C), the degradation of fluridone in both water and sediment was minimal. At elevated temperature (20–40 °C), fluridone degradation was increased in water and sediment. Additionally, the persistence of fluridone in sediment was reduced by increasing sand content in the sediment matrix. Possible fluridone transport through the subsurface was estimated over a range of initial concentrations, groundwater velocities, fluridone half-lives, and fluridone sorption coefficients which may be seen in a field environment. A form of the Ogata-Banks equation which accounts for 1st order decay was used for describing the dispersion of fluridone, while a related equation from Bear, 1979 was utilized to quantify advection. In all tested scenarios, maximum transport was less than 10 m over one month of observation. Results of this study will improve our existing understanding of fluridone persistence and in water and sediment.

Mechanical Behavior of Mode I Fractured Concrete Repaired by Polymethyl Methacrylate (PMMA)

This paper attempts to investigate the fracture toughness of the cracked concrete repaired by polymethyl methacrylate (PMMA) - a thermo-plastic polymer resin. A single-edged notch beam in three-point bending test was conducted to examine the performance of cracked concrete beam after reparation. Three concrete crack widths of 1 mm, 5 mm, 10 mm were designated to be repaired and examed. The fracture properties include critical stress intensity factor KIC by Jenq and Shah and fracture energy GF by Hillerburg, were evaluated for the concrete before cracking and after reparation. Four sand contents of 0%, 10%, 20% and 40% by volume were used in the PMMA mortars. From the testing results, it appears that the load capacity and fracture toughness of repaired concrete increased with the increasing sand content. And, the PMMA mortar made repaired concrete better strength and fracture toughness as well.

Effects of Soil and Water Conservation Measures on Runoff and Sediment Yield in Red Soil Slope Farmland under Natural Rainfall

This paper analyzes the relationship between runoff, soil erosion, sediment particles, and natural rainfall characteristics on sloping farmland in the red soil region of southern China. The surface runoff and soil loss data were measured on runoff plots during 66 natural rainfall events from 2015 to 2018 in Jiangxi Province. The results show that the maximum 30-min rainfall intensity (I30) is positively related to the runoff depth, soil erosion modulus, and sediment mean weight diameter (MWD). With the increase in I30 during rainfall, the coarse sand content increases, and the fine sand content decreases. The average annual runoff of slope tillage, hedgerows with slope tillage, straw mulching with conventional tillage, and contour tillage decreased by 32.56%, 65.87%, 83.99%, and 87.30%, respectively, compared with that of bare land. Soil and water conservation measures can significantly reduce slope runoff. The flow-reduction effect of contour tillage and straw mulching with conventional tillage increases as I30 increases, and the flow-reduction effect of hedgerows with slope tillage first increases and then decreases as I30 increases. The coefficients of variation and standard deviations of the flow-reduction effects of different soil and water conservation measures decrease with increasing I30. The average annual soil erosion moduli of slope tillage, hedgerows with slope tillage, contour tillage, and straw mulching with conventional tillage decreased by 59.33%, 91.29%, 97.17%, and 98.45%, respectively, compared with that of bare land. Soil and water conservation measures can significantly reduce the sediment yield on slopes. The flow-reduction effects of hedgerows with slope tillage, contour tillage, and straw mulching with conventional tillage all increase with I30, and their coefficients of variation and standard deviations decrease with I30. The average single rainfall erosion sediment MWD of decreased by 5.91%, 8.33%, 9.69%, and 13.32%, respectively, compared with that of bare land. Straw mulching with conventional tillage can significantly reduce the MWD of erosion sediment, effectively reduce the content of coarse sand, and increase the content of fine sand. Straw mulching with conventional tillage is a very good soil and water conservation measure for sloping farmland. It not only has the best effect on reducing flow and sediment, but also can effectively intercept coarse sand and reduce the MWD of erosion sediment.

The Impact of Various Soil Proportions Towards the Strength of Interlocking Compressed Earth Brick

An interlocking compressed earth brick (ICEB) is a dry-stacked masonry brick with a similar production process to the Compressed Earth Brick (CEB). ICEB mainly consists of clay soil, sand, ordinary Portland cement (OPC) and water. This paper studies the properties of a combined soil (clay soil and sand), which affects the optimum moisture content (OMC) of the mixture and compressive strength of the produced specimens. There are five types of combined soils with mixture ratios of clay(C) soil to sand (S) of C55:S45, C50:S50, C45:S55, C40:S60, C35:S65 and C30:S70. Every mixture ratio shows a different OMC and varies in its compressive strength. The combination soil ratio of C45:S55, which means 45% of clay soil + 55% of sand, produced the highest compressive strength. The compressive strength increases as the clay content decreases and sand content increases. However, as the clay soil content decreased to lower than 45%, the compressive strength starts to decrease. It is due to the lack of plasticity properties from the clay which are responsible for bonding the material particles.

Evaluation of models for fitting soil particle-size distribution using UNSODA and a Brazilian dataset

The mineral soil Particle Size Distribution (PSD) is a fundamental and very useful soil characteristic widely used to support soil classification, soil management and soil processes modeling. An important limitation of PSD is the lack of standardization for granulometric fractions obtained from different soil classification systems, making difficult to compare and combine data. To overcome this drawback several attempts have been made to mathematically fit PSD data in order to allow soil texture data conversion among soil databases. Parametric equations have been proposed and/or evaluated for particular systems, but none of them has been studied, compared and proved being effective for soils of different types, regions and textural classes. Thus, the purpose of this work was evaluating and comparing performances of several PSD equations on a more comprehensive soil database as well as providing a method capable of fitting a general model for any soil texture. Cumulative PSD data of 221 soil samples, carefully selected from UNSODA and Brazilian/Embrapa datasets to include 12 soil textural classes mapped in the texture triangle, were used in this study to evaluate the fitting performance of commonly applied PSD equations with three and four parameters for unimodal data (SKAG-3p, ANDE-4p, BEST-3p, FRED-4p) and a seven-parameters equation (FRED-7p) used for gap-graded bimodal shaped data. The FRED-7p equation showed outstanding fittings accuracies with average RMSE (100*g g−1) of 0.53 for all soils, about twice as low as the second best fitted equation (ANDE-4p). FRED-7p fitting accuracy was slightly influenced by soil texture, showing a small increase as sand content increases and a decrease as silt content increases. The FRED-7p equation, originally proposed to fit cumulative gap-graded bimodal PSD, performed properly and accurately for all textural classes, including both unimodal and bimodal shaped PSDs. As a result of that, it is strongly recommended as a general model for any kind of soil PSD.

Laboratory characterization and modelling of the thermal-mechanical properties of binary soil mixtures

Binary soil mixtures are extensively used in the construction of geothermal-related earth structures such as geothermal energy piles (GEP), ground source heat pumps (GSHP) and earth air tunnel heat exchangers (EATHE). An evaluation of the binary soil’s thermal-mechanical properties is the key process in determining the final performance of geothermal-related projects. Therefore, the thermal-mechanical properties of binary soil mixtures were systematically investigated in this paper. A series of thermal and mechanical property tests was conducted on five sand-kaolin clay mixtures with sand contents ranging from 0% to 100% by dry weight. The experimental results indicated that the sand-clay mixtures achieved the theoretically densest state when the sand content reached the critical threshold. The further the binary mixture’s sand content was from the critical threshold, the lower the mixture’s density was. As the sand content increased, the shear stress-strain curves gradually shifted from strain-softening behavior to strain-hardening behavior due to the decrease in suction stress. The relationship between the sand content and the shear strength of the mixtures exhibited an “S” shape, which is attributed to the interaction between the sand and clay particles and varied with the sand contents. The shear wave velocity of the sand clay mixtures was found to decrease continuously with the increase in sand content until the sand skeleton had formed. In addition, the thermal conductivity of the binary mixed soil changed linearly with the sand content, and the upper bound of the critical threshold interval (77%) was found to separate the two different heat conduction modes. Finally, an elastic shear modulus (G0) model, which correlated to the tangent elastic modulus of the binary mixture (Em), and a more generalized thermal conductivity (K) model were formulated for the binary sand-clay mixtures, and the effectiveness and feasibility of the proposed models were validated by comparing the values predicted with the model and the experimental data.

Influence of Increasing Fines on Soil Physical Properties of U.S. Golf Association Sand

Drainage is important to golf and athletic facilities trying to avoid lost play time. Native soil containing clay is sometimes incorporated into sand profiles with the intent to increase water and nutrient holding capacities. However, mixes high in silt and/or clay often have drainage problems. Research was conducted on soil physical properties from incremental 10% v/v additions of silt and clay (fines) to a U.S. Golf Association (USGA)-specification sand. Soils were evaluated based on volumetric water retention from 0 to 50 cm matric potential, saturated hydraulic conductivity (Ksat), porosity, and bulk density. The soil water characteristic (SWC) for 100:0 (sand:fines) had lower volumetric water content (θv) throughout the profile than any other mixture. Addition of 10% fines increased θv to more than 0.17 cm3·cm–3 throughout the 0- to 50-cm matric potential range, whereas 20% fines increased θv to more than 0.26 cm3·cm–3. The 70:30 mixture had greater θv throughout the profile than mixtures containing more than 70% sand. Mixtures with less than 70% sand produced similar SWCs. Increasing sand content increased bulk density, which altered saturated volumetric water content. Ksat was reduced from more than 265 cm·h–1 in 100:0 mixtures to 43 cm·h–1 for 90:10 mixtures, and to less than 5 cm·h–1 with ≥20% fines. The addition of ≥20% by volume of fines to a USGA sand increased water content in the soil to the point it was rendered unacceptable for trafficked turf sites. This research illustrates the influence fine particles, even in small amounts, can have on a USGA sand, and why they should not be added without prior evaluation.

Silicon Dioxide (SiO2) Is the Most Important Component of Spots on the Inner Surface of Mactra veneriformis Shells

Yellow-brown spots are often observed on the inner shell surface of the clam Mactra veneriformis sampled in Binhai New Area, Lijin County, Shandong Province, China, negatively impacting its commercial value. In this study, SEM-EDS, X-ray diffraction (X-rd), laser Raman spectrum, and Fourier infrared spectrum scanning (FT-IR) were used to detect and analyze the composition of spots on the inner shell surface of these clams. Compared with shells without spots, the shells with spots showed significant differences in their silicon contents but no differences in the content of other basic elements; Laser Raman spectroscopy and X- rd examination revealed that, in addition to calcium carbonate particles, there were traces of silica bonds; after the removal of calcium carbonate by using hydrochloric acid, the spectral trend of particles was similar to that of sea sand, which was consistent with the spectral characteristics of SiO2. Therefore, the spots on the inner shell surface of M. veneriformis are sea sand. These are likely to result from the increased sand content in seawater in the Yellow River Delta, whereby the grains of sand have fallen into the gap between the mantle and shell; thus, the sand becomes encased in the shells as they grow.

After Hurricanes Irma and Matthew: Living Shorelines Stabilize Sediments

Constructed intertidal oyster reefs, an example of a “living shoreline”, can protect against erosion and loss of habitat, but can they prevent erosion during high-energy storm events such as hurricanes? Oyster reefs were constructed in 2012 within the Guana Tolomato Matanzas National Estuarine Research Reserve in Northeast Florida to stabilize the shoreline sediment and prevent erosion of an archeological site. Sediment cores were collected behind constructed oyster reefs before and after hurricanes Matthew (2016) and Irma (2017) to study changes in sediment particle size due to these high-energy storms. Pre-hurricane data were collected in 2016 from three different constructed reefs, as well as three control sites where no reef was present. Pre-hurricane sediment profiles behind the constructed reefs consisted of finer sediments, ~36% silt and clay, in the surface ~10-12 cm, with decreasing silt and clay and increasing sand content as depth increased. This was different than the sediment from the control sites with ~4% silt and clay in all depths sampled. Like the sediment profiles before the high energy storms, the post-hurricane sediment data showed a clear layer of finer sediment ~10-12 cm over coarser sediment. Although they were high-energy storms, the storms did not appear to significantly affect the sediment behind the constructed oyster reefs. Sediment profiles remained consistent after these storms but may not remain undisturbed during the next storm without some intervention because the oyster reefs have been degrading. KEYWORDS: Oyster Restoration; Living Shorelines; Hurricanes; Coastal Erosion; Sedimentation; Salt Marsh

Influence of gradations on performance of emulsified asphalt cold recycled mixture produced using vertical vibration compaction method

In this study, the effects of virgin aggregate content, such as mineral filler, machine-made sand, and coarse aggregate, on the performance of emulsified asphalt cold recycled mixtures (ECRMs) produced using the vertical vibration compaction method (VVCM) are evaluated. The optimum virgin aggregate contents are proposed based on the results. The results show that with increasing mineral filler content (mass fraction <5%), the mechanical strength, rutting resistance and crack resistance of the ECRMs gradually increase, whereas the moisture sensitivity increases initially but gradually decreases, and 3% mineral filler demonstrates the optimum moisture sensitivity compared to reclaimed asphalt mixtures. Further, as machine-made sand content increases, the mechanical strength, rutting resistance, crack resistance and moisture sensitivity of the ECRMs increase initially and decrease gradually, and the aforementioned performance of the ECRMs reaches the peak values when 20% machine-made sand is added, compared to mixtures without the machine-made sand. The mechanical strength, rutting resistance, crack resistance and moisture sensitivity of the ECRMs initially increase and then gradually decrease with the addition of the coarse aggregate. When the coarse aggregate content is 10%–30%, the ECRMs show a good performance, compared to mixtures without the coarse aggregate. To effectively improve the engineering properties of the ECRMs, the proposed optimum content of the mineral filler, machine-made sand and coarse aggregate are 3%, 20% and 10–30%, respectively.

Influence of sand content on the flow characteristics of soft soil under cyclic and high-frequency vibration

The flow characteristics of foundation soils subjected to train loads can present engineering hazards in high-speed railways. In order to verify the feasibility of blending coarse sand in modifying soft subsoil, undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies. Laboratory testing results indicate that the flow characteristics of soft soil can be significantly enhanced by high-frequency vibration; meanwhile the continuous increase in flow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil. The influence of sand content on flow characteristics is also studied in detail, and it is shown that the addition of coarse sand can weaken the flow characteristics of soft soil induced by sudden vibration at lower than 50 Hz. Under the condition of cyclic vibration, the growth of the flow characteristics of sand-clay mixtures is mainly caused by the first-time vibration in the cycle, and the increase in sand content can make the flow characteristics present a faster convergent tendency.

Effects of sand and water contents on the small-strain shear modulus of loess

Characterizing soil properties at small-strains (<10−5) is a subject of long-standing interest for geotechnical engineers at both academic and practical levels. Compared to conventional soil types, such as sand or clay, the small-strain properties of loess are less extensively studied and remain poorly understood. This paper presented an experimental study to investigate the influence of sand and water content on the small-strain shear modulus (G0) of Yan'an loess. A specifically designed experimental program was conducted for a sequence of sand-loess mixtures under unsaturated conditions using the resonant column technique. It was found that, in general, the G0 of loess decreases with the water content. By using the water content as a state variable, its dependence on G0 was established. The study also showed that under otherwise similar conditions, the G0 of the sand-loess mixture is lower than that of loess without sand. However, a further increase of sand content beyond a threshold value (15%) induces no remarkable difference in terms of G0. These findings suggested that the presence of sand plays an important role in the small-strain behaviours of loess. The underlying reasons behind these observations were provided, along with a detailed interpretation at the micro-scale level. To enhance the practicability, an empirical model was also proposed for sandy loess, and it could provide reasonable estimates of G0 for both loess samples in the current study and loess data in the literature.

Transitional behavior in well-graded soils: An example of completely decomposed granite

This study presents the results of a series of isotropic compression tests and drained and undrained triaxial shearing tests on naturally graded and reconstituted completely decomposed granite soils to investigate their compressive response and transitional behavior. Naturally graded soils exhibited unique isotropic compression and critical state lines within the stress levels studied. Soils reconstituted by increasing the sand content by 5% and 10% revealed non-unique isotropic compression lines; however, unique critical state lines were present in the e-log p' space. The degree of non-convergence increased as the sand content increased. The value of the m parameter, which is used to quantify the transitional mode and is defined as the ratio between the changes in the final and initial specific volumes (i.e., m = ∆v2/∆v1; see Fig. 1), increased from 0 in the case of naturally graded soil to 0.3 and 0.73 for reconstituted soils with increased sand content of 5% and 10%, respectively. For naturally graded soils, the initial void ratio affects only the initial compression response, and its influence does not extend to the normal compression line. In the case of reconstituted soils, the fabric that results from various compaction efforts exerts a significant effect on the soil′s compressive response. However, this fabric cannot withstand large strain during the shearing path and is completely destroyed, producing a unique fabric in the critical state. Both natural and reconstituted soils revealed isotropic responses during the loading and unloading compression paths with unrecoverable volume change. The transitional behavior is no longer limited to gap-graded soils, and grading is no longer the only dominant factor in this behavior. The transitional mode occurs due to relatively inconsiderable changes in soil mineralogy, grading, and microstructure.

Yielding behaviour of cemented binary mixture

Cement stabilization is commonly used for improving soft soils and the mechanical behaviour of cemented pure clay has been well documented. However, limited studies have investigated the effect of sand in a cement-clay matrix because the conventional water to solid (solid includes soil and cement) ratio cannot be simply used to characterize the behaviour of cemented binary mixture. The water holding capacity of the mixture reduces with increase in sand content, when the water to solid ratio is kept constant. In this study, the ratio of water to clay and cement is kept constant, so that the effect of sand content could be studied. The materials used in this study are kaolin clay, sand with D50 of 0.71 mm and Ordinary Portland cement type 1. Sand content varies from 0% to 50% and curing time is kept constant at 7 days. We used three ratios of water to clay and cement which correspond to 139%, 104% and 78%. The isotropic yield point increases with increase in sand content and cement content, while it reduces with increase in water content. A power function captures the variation of yield point with the ratio of water to cement and clay.

Micro-aggregate Indices and Structural stability of Soils under Different Management

Low water stability of soil micro-aggregates accentuated by increased intensity of cultivation and soil degradation are among the significant issues that draw the atten- tion of Soil Scientists due to their effects on soil physical conditions. The study was carried out to quantify changes in micro-aggregate stability indices of soils on coastal plain sands under contrasting land use and management. Soil samples were collected from cassava plots, plantain, maize, rubber plantation, oil palm and 2-season fallow plots with Calapogonium mucunoides. Results revealed significant changes in micro-and macro-aggregate stability indices. Clay dispersion index (CDI) was 0.46 and 0.39 respectively in cassava and maize plots. Parameters such as aggregated silt and clay (ASC), clay flocculation index (CFI) and saturated hydraulic conductivity (Ksat) used as estimates of soil structural stability were significantly (p &lt; 0.05) increased due to 2-season fallow and 10-year oil palm plantation. Two-year fallow increased ASC and CFI by 57 % and 86.5% respectively compared with continuous maize culti- vation. Ten-year cultivation to cassava and maize increased sand content by 18 and 9% respectively and decreased the mean weight diameter (MWD) of water stable aggregates and Ksat. Relationships showed significant (p &lt; 0.05) positive correlation between ASC and CFI and Ksat. Two-year fallow with Calapogonium mucunoides and 10-year oil palm plantation improved the soil micro- and macroaggregate indices. They could be used to conserve the soil and reduce the degradation of soil resources.

Influence of temperature on swelling deformation characteristic of compacted GMZ bentonite-sand mixtures

Laboratory swelling deformation tests were carried out on compacted GMZ bentonite and bentonite-sand mixtures with 30% and 50 % sand contents at 20, 40, 60, 80 and 90 °C with infiltration of distilled water. Influence of temperature, initial dry density, and quartz sand content on the swelling deformation characteristic of compacted bentonite specimens was analyzed. Results indicate that the swelling deformation process is accelerated, and the maximum swelling strain increases with the increase in temperature, while the maximum swelling strain tends to be stable with increasing temperature. In the meantime, the temperature effects depend on both of the sand content and the initial dry density of the specimens, the increases of the maximum swelling strain induced by increasing temperature, are enlarged by increasing sand content or initial dry density. Adding of quartz sand to bentonite not only influences the integrality of bentonite specimen, but also increase the microfissuring in area on quartz sand, which are advantageous to the heat transfer, leading to the increase of swelling deformation capacity of the specimen. The increased dry density relatively increases the bentonite content, so the swelling property is enhanced. However, no change on mineral composition of bentonite was observed when temperature was changed from 20 to 90 °C.

Compaction and CBR properties of RAP/sand blends in Iraq

Nowadays, Iraq is experiencing a rapid reconstruction process during which a significant amount of construction waste material is generated. One of such materials is RAP (reclaimed asphalt pavement) which is obtained from the removal of surface pavement of roads and used especially as an aggregate substitute in asphalt mix, granular base and sub-base material for roads, or as road fill material. From this point of view, the primary objective of this study was to evaluate the possible effects of adding sand to RAP in terms of compaction and strength properties and to suggest a possible recycling application. For this purpose, RAP and sand samples were collected from Iraq. Then, RAP/sand blends were prepared by mixing RAP with 5%, 10%, 15%, 20%, 25%, and 50% sand by weight. Modified Proctor Compaction and California Bearing Ratio (CBR) tests were performed on these samples. The results have revealed that the compaction properties of the RAP/sand blends were significantly improved as compared to RAP samples resulting in increased maximum dry density and optimum moisture content. CBR values of the tested mixtures had also increased with increasing sand content similar to the results of previous studies. The primary finding of this study was that RAP/sand blends with a sand content of 20% or more were defined to be suitable for use as road fill material according to the American Association of State Highway and Transportation Officials (AASHTO) standards in terms of tested parameters, providing a new field for recycling of RAP in the studied region.