Unsoaked California Bearing Ratio Research Articles

The Use of Dynamic Cone Penetrometer to Predict California Bearing Ratio Value of Subgrade Soils

California Bearing Ratio (CBR) is an indirect method mostly used to investigate the strength of subgrade material for highway design. The CBR of subgrade materials can be determined from costly and time-taking laboratory or in situ CBR tests. These limitations suggest the need for an easy and low-cost in situ direct method to estimate the CBR of subgrade materials. Dynamic cone penetration (DCP) is easy, quick, and economical in situ test in geotechnical uses. However, the use of DCP test to evaluate the CBR of subgrade material is condition specific i.e., local conditions should be considered before adopting existing correlations in engineering design. The objective of this study is therefore to develop a correlation that can predict the CBR of subgrade material from the dynamic cone penetration index (DCPI). Several laboratory and field tests including Plasticity index (PI), Liquid limit (LL) and Plastic limit (PL), in situ density, and classification (sieve analysis and hydrometer analysis), CBR (unsoaked), in situ moisture content, and DCP were conducted. The suitability of the existing model to predict CBR from DCPI was checked. The prediction model was then developed using Statistical Package for the Social Sciences (SPSS) software. The result of the SPSS analysis is log (CBR) = 2.954 – 1.496log (DCPI) with R2 = 0.943. The result shows that a good correlation exist between the dynamic cone penetration indexes (DCPI) and unsoaked CBR values.

The Use of Waste Materials Red Mud and Fly Ash as Road Embankment Fill

This study provides a comprehensive evaluation of red mud as a sustainable material for road base construction, particularly in combination with bottom ash. Red mud, a by-product of the Bayer process used in alumina extraction, is known for its high alkalinity and heavy metal content. For this reason, this waste material causes environmental challenges. Red mud sourced from the Eti Aluminum Factory in Seydişehir, Konya (Turkey), was stabilized with bottom ash. Then, these waste materials were tested through a number of experiments, such as in relation to their Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), California bearing ratio (CBR), and microstructure through a scanning electron microscopy (SEM) analysis. The results highlight that the UCS of stabilized red mud samples significantly improved with the addition of bottom ash and longer curing periods. Specifically, the UCS values increased from 0.5 MPa to 2.5 MPa after 28 days of curing. Moreover, RM specimens stabilized with 25% bottom ash achieved a CBR value of 146.64% after 28 days, far exceeding Turkey’s road fill material requirement, which mandates a minimum unsoaked CBR value of 15%. These findings indicate that red mud stabilized with bottom ash not only meets but exceeds the structural requirements for road base materials. This approach provides a sustainable solution for the environmental management of red mud while contributing to infrastructure development. Through the recycling of these industrial by-products, this study presents a viable method to reduce waste and support economic and environmental sustainability in road construction projects.

Application of Gum Arabic on the Geotechnical Properties of Subgrade Materials

This study investigates the impact of Gum Arabic on the geotechnical properties of subgrade soil materials, a non-traditional soil stabilization technique. Given the need for sustainable and locally available alternatives in road construction, the study aims to assess how different percentages of Gum Arabic affect the physical and mechanical behavior of soil. The research aims to provide sustainable and locally available alternatives in road construction. Three soil samples were treated with varying percentages of Gum Arabic, (1.5%, 3%, 6% and 12%), and standard geotechnical tests were conducted under both soaked and unsoaked conditions. The results showed that the average natural moisture content of the soils was 7.9%, 2.2%, and 4.6%. The addition of Gum Arabic increased the peak maximum dry density of the soil samples by 8.02%, 1.88, and 7.88%. The maximum unsoaked California Bearing Ratio (CBR) values of soil samples were 32.1%, 81.7%, and 48.7%, respectively. Whereas, maximum soaked CBR values of soils S1, S2 and S3 obtained at 1.5%, 6% and 1.5% additions of gum Arabic were 8.4%, 28.7% and 16.9% respectively. The study recommends using 3% Gum Arabic to improve the CBR property of soil samples. The application of Gum Arabic showed significant improvements in soil behavior under both soaked and unsoaked conditions.

The Effect of Adding Bamboo Leaf Ash and Cement on the Stability of Clay Soil

Subgrade soil or clay subgrade is a type of soil with very high pore water characteristics, causing problems for civil structures, both buildings and road pavements. Bamboo leaf ash contains several compounds such as silica (SiO2) at 77.24%, while cement contains several calcium oxide (CaO) compounds at 60%. Bamboo leaf ash has a high silica content which functions as a support for pozzolanic reactions with clay soil. The variations in the mixture of bamboo leaf ash and cement used are 2%, 3%, 4%, 5% and 6% for bamboo leaf ash and 20% for cement by weight of soil, with a curing time of 4 days. From the two tests that have been carried out, namely soil compaction (Standard Proctor) and Unsoaked CBR (California Bearing Ratio), the optimum values ​​obtained for soil compaction (Standard Proctor) and CBR (California Bearing Ratio) Unsoaked are in the variation of soil + cement addition of 20% + Bamboo Leaf Ash 3%. In the soil compaction test (Standard Proctor), the dry volume weight value was 1,728 gr/cm3 and the optimum water content value was 16.02%, while in the Unsoaked CBR (California Bearing Ratio) the optimum CBR percentage value was 10.25%.

Effect of Scrap Tyre Crumb Rubber (STCR) and Lime on the California Bearing Ratio (CBR) of Non-Lateritic Soil

Nigeria is one of the countries generating many used tyres with only small quantity utilized for different local use and the remaining large quantity dumped in different areas as waste. In this study non – laterite soil was stabilized with 3 % Scrap Tyre Crumb Rubber (STCR) and 5.0, 7.5, 10.0, 12.5 and 15.0 % lime for use as road construction material. Atterberg limit tests, compaction (using West African Standard energy) and California Bearing Ratio (CBR) tests were carried out using standard methods, on the natural non-lateritic soil and the treated soil specimens. Preliminary test on the soil was carried out which classified the soil as A-6 (9) and CL in accordance with ASHTO and USCS classification systems respectively. Compaction and California Bearing Ratio (CBR) parameters of the treated non-lateritic showed a great improvement as the MDD increased from 1.68 Mg/m3 to 1.88 Mg/m3 while the OMC reduced from 17.1 % to 14 %. Both soaked and unsoaked CBR values equally increased to 109 % and 103 % respectively with the addition of lime up to 15% plus 3% STCR waste. Based on results obtained from the study, the use of a mixture of 15% lime and 3% STCR waste, are recommended for the treatment of non-lateritic soil for road construction purposes.

Impact evaluation of polypropylene fibres on the engineering behaviour of Siwalik clay

In the Kashmir region of Pakistan, the presence of Siwalik clays engenders serviceability issues to the infrastructure causing substantial loss of property. In this study, an attempt has been made to address these issues using polypropylene fibres (PPFs) as a sustainable modifier. These fibres were used in five different proportions, namely 0.25, 0.5, 0.75, 1 and 1.25% as partial replacement of base soil to analyse their impact on the engineering behaviour of matrices. Classification, compaction, indirect tensile, unconfined and triaxial compression, swell potential, consolidation and California bearing ratio (CBR) tests were conducted on controlled as well as reinforced-clay samples for comparative analyses. The maximum improvements were observed in unconfined compressive strength (109%), tensile strength (300%), cohesion (13%), friction angle (110%), soaked CBR (800%) and un-soaked CBR (550%). Besides, the reduction in swelling strain by 92% was also recorded corresponding to 1 kPa effective vertical stress. The capital cost analyses showed that PPFs reduced the costs of backfill behind the retaining wall and foundation soil beneath isolated footing by 21 and 44.5%, respectively. Moreover, the modifier had no adverse effect on the aqueous media. Conclusively, PPFs can be used as sustainable modifiers leading to a potential solution for serviceability issues.

Geotechnical appraisal of failed sections of some highway pavements in parts of Northcentral Nigeria

Purpose The purpose of this study was to investigate the likely causes of failure of some sections of road pavements in Ajaokuta, Northcentral Nigeria. This was achieved through a geotechnical assessment of subgrade soils in affected areas. Design/methodology/approach The methods entailed field and laboratory methods and statistical analysis. Subgrade soil samples were retrieved from a depth of 1,000 mm beneath the failed portions using a hang auger. The soils were analyzed for natural moisture content (NMC), Atterberg limit (liquid limit, plastic limit and linear shrinkage), grain size distribution, compaction and California bearing ratio (CBR), respectively. Findings The results of the geotechnical tests ranged from NMC (12.5%–19.4%), sand (84%–98%), fines (2%–16%), LL (16.0%–32.2%), PL (17%–27.5%), LS (2.7%–6.4%), PI (2.5%–18.4%), maximum dry density (1756 kg/m2–1961 kg/m2), optimum moisture content (13.2%–20.2%), unsoaked CBR (15.5%–30.5%) and soaked CBR (8%–22%), respectively. Pearson’s correlation coefficient performed on the variables showed that some parameters exhibited a strong positive correlation with r2 > 0.5. Research limitations/implications Funding was the main limitation. Originality/value Comparing the results with Nigerian standards for road construction, and the AASHTO classification scheme, the subgrade soils are competent and possess excellent to good properties. The soils also exhibited very low plasticity, a high percentage of sand, high CBR and low NMC, which implies that it has the strength required for road pavement subgrades. The likely causes of the failures are, therefore, due to the use of poor construction materials, technical incompetence and poor compaction of sub-base materials, respectively.

Evaluation of citric acid-treated natural fibres as sustainable additives for improving expansive soil performance in highway construction

This study addresses the evaluation of citric acid-treated natural fibres as sustainable additives for improving soil performance in highway construction. A series of tests were conducted on the soil to assess its baseline properties. The natural soil exhibited a Plasticity Index (PI) of 30 and Linear Shrinkage of 12%, along with a Liquid Limit (LL) of 65 and Plastic Limit (PL) of 35. Additionally, the fines content (<0.075 mm) and sand content (0.075–4.7 mm) were determined to be 79.6% and 20.4%, respectively. The soil's mineral composition included Quartz (5%), Orthoclase (3–5%), Montmorillonite (2.6%), and Illite (18.2%), with key components identified through chemical analysis: SiO2 (52.721 wt%), Fe2O3 (16.132 wt%), and Al2O3 (15.202 wt%). Subsequently, a range of tests were performed with varying additives to assess their impact on the soil's engineering properties. The sample containing 6% Sawdust (SD) additive exhibited notable improvements in multiple aspects. This sample achieved a maximum dry density (MDD) of 1856 kg/m³, surpassing the control (1900 kg/m³) and the 10% Rice Husk Ash (RHF) sample (1698 kg/m³). Furthermore, the 6% SD sample demonstrated enhanced Unconfined Compressive Strength (UCS) of 320 kPa, as opposed to the control's 121 kPa. Triaxial shear strength followed a similar pattern, peaking at 41 kPa for the 6% SD sample. The California Bearing Ratio (CBR), the 6% SD sample showcased significant improvements, achieving 41% for Unsoaked CBR and 36% for Soaked CBR. These results outperformed the control (25%) and the 4% RHF sample (37%). Additionally, the hydraulic conductivity of the 6% SD sample was notably lower at 4.98 ×10–8 cm/s compared to the control (3.35 ×10–8 cm/s) and the 4% RHF sample (4.58 ×10–8 cm/s). The Coefficient of Volume Change (Mv) further supported the superior performance of the 6% SD sample with a value of 0.6, indicating reduced settlement potential compared to the 4% RHF sample (Mv: 0.7). Based on the results, the 6% Sawdust (SD) additive consistently demonstrated the most favourable engineering properties for the expansive clay soil. hence, it is recommended that the 6% SD sample be considered as an optimal choice for enhancing subgrade material, leading to improved performance and sustainability in highway construction.

Harnessing waste glass powder for soil modification

The challenge posed by weak soil, characterized by low bearing capacity and shear strength, is significant in civil engineering, impacting road construction, structural foundations, and irrigation systems. Recycling non-biodegradable waste, especially glass waste, presents a promising solution for environmental sustainability and cost-effectiveness in construction. This study aims to improve the geotechnical properties of weak soils by stabilizing them with Waste Glass Powder (WGP) and exploring novel construction applications. The experimental investigations determined the optimal incorporation of glass powder into soil samples, ranging from 2% to 10% by dry weight. Geotechnical tests, including sieving analysis, Atterberg limits determination, California Bearing Ratio (CBR) tests, and Unconfined Compressive Strength (UCS) assessments, were conducted to assess the effect of glass powder addition. At a 10% glass powder content, the Plasticity Limit (PL), Liquid Limit (LL), and Plasticity Index (PI) were 18.4%, 33.9%, and 15.5%, respectively. The addition of glass powder significantly improved CBR values, reaching peaks of 10.5% (soaked CBR) and 22.3% (unsoaked CBR). Moreover, UCS increased to 135.6 kN/m2 with 8% glass powder, decreasing slightly to 120.8 kN/m2 with 10% glass powder. These findings highlight waste glass as a viable additive for enhancing the engineering properties of weak soils, promoting sustainable construction practices.

INTEGRATED GEOLOGY AND ENGINEERING GEOLOGICAL PROPERTIES OF LATERITIC SOIL AT ITA – ONIYAN AREA, SOUTHWESTERN NIGERIA

This study investigates the geology and the engineering geological properties of lateritic soil of Ita – Oniyan area of Ondo state, Southwestern, Nigeria. Twenty soil samples were collected from twenty test pits at depth of about 1.0m and were air–dried for two weeks and, thereafter were subjected to laboratory analyses which include natural moisture content, particle size analysis, consistency limits, linear shrinkage, specific gravity, standard compaction, shear strength, and unsoaked California Bearing Ratio (CBR) tests. Results showed that the natural moisture content of the soils ranged from 7% to 28%, the liquid limit ranged from 30.2% to 69.1%, the plastic limit ranged from 17.5% to 43.4%, while the plasticity index ranged from 8.6% to 36.9%. The soils were grouped into CL (low plasticity), CI (medium plasticity), and CH (high plasticity). Linear shrinkage ranged from 3.7% to 11.9%. Grain size analysis gave coarse contents varying from 30.4% to 98.1% and fine contents from 27.4% to 86.9%. The unsoaked CBR ranged from 18% to 72%, for compaction, MDD ranged from 1482kg/m3 to 1981kg/m3, and OMC from 13.7% to 32.5%. Geologic mapping showed that the major rock types in the study area were biotite gneiss, charnockite, quartzite and granite parent rocks from which the soil was formed. The soil samples are made up of lateritic soil with high clay content mainly illite, since the soil samples in the study area have poor engineering properties therefore the soil needed to be stabilized to improve their engineering properties.

Mechanical Properties of Expansive Soil Stabilized by Sand

Expansive clay soils have swelling and shrinkage properties and somehow reduce the mechanical properties required for soils to be used in civil engineering works. One method to improve the soil is by mechanical stabilization, namely mixing expansive clay soil with sand material. The sand material used in this research varied by 7.5%, 15%, and 22.5% of the total dry weight of expansive clay. The results shows that changes in mechanical properties were observed from the compaction test and California Bearing Ratio (CBR) both for soaked or unsoaked test. Based on these variations, in the compaction test, the addition of sand variations increases the maximum dry unit weight value and generally reduces the optimum water content value. The same results were also seen in the soaked and unsoaked CBR tests. In the swelling potential test, the addition of sand material succeeded in reducing the swelling value in expansive clay soils.

Soil strength improvement by reinforcing soil with geotextiles

In recent times, geosynthetic products are widely utilized in the construction sector and particularly in the field of Geotechnical Engineering. Geosynthetics are the synthetic products used mainly within the soil to perform various functions. In this paper, an attempt has been made to utilize Woven geotextiles (WG) and Non-woven geotextiles (NWG) as reinforcement within soil to enhance the strength of subgrade soil. 2 types of coarse-grained soil, soil with high fines content and soil with low fines content were utilized in the experimental work. WG and NWG were placed at varying depths of H/5, 2H/5, 3H/5 and 4H/5 from top of the soil specimen (where H is the height of soil specimen), to find the enhancement in soaked & unsoaked California Bearing Ratio (CBR) strength of soil with respect to that of unreinforced soil. Based on the experimental results, improvement in CBR strength of soil reinforced with geotextile and the ideal location of placement of geotextile within the soil thickness varied according to the soil type and this may be attributed to the presence of varied percentages of fines within soil. Also, the soil reinforced with WG was observed to be more effective in terms of strength gain as compared to that of soil reinforced with NWG. Improvement in CBR strength of subgrade soil reinforced with geotextiles leads to reduced pavement thickness thus resulting in a cost-effective construction.

A Study on Crushed Coconut Shells as Stabiliser to Soil

Road construction over soft subgrade soil is a major issue affecting cost and scheduling of highway projects. Many techniques have been conducted to strengthen the highway soil subgrade. One of them are using additives such as coconut shells, rice husk ash, stone dust, and fly ash. to strengthen the soil. The strength of the subgrade is commonly expressed as California Bearing Ratio (CBR). In this study, the crushed coconut shells (CCS) of 65 mm to 10 mm ranges of size was mix with the laterite soil. A series of unsoaked CBR test were conducted with an addition of 1, 2, 3, 4, 5, 6, 7 and 8% of CCS to determine the strength of the stabilized laterite soil. The laterite soil is classified as sandy SILT of high plasticity (MH) according to British Standard Classification System (BSCS). The results show that the CBR values of the stabilized soil increase with an increasing percentage the CCS. The stabilized soil with 4% CCS is the highest CBR value, 27.5%. The CBR% then decreasing as further additional of CCS %. The stabilised soil with an 8% CCS content had the lowest CBR value at 5.25%, which is lower than the unstabilised laterite soil’s CBR value. It is concluded that the additions of CCS have greatly improved the soil strength with the increment increase of CBR value. Hence CCS has a good potential for upgrading the CBR value of subgrade soil.

Investigation of Soil Sample Using Triaxial Test and Detailed CBR Test

California Bearing Ratio (CBR) value of subgrade is utilized in accordance with IRC recommendation.in order to create flexible pavements. A crucial soil parameter for the design of flexible pavements and runways at airports is the California Bearing Ratio (CBR) value. It might also utilize to calculate the soil's subgrade reaction via correlation. It is among the most significant engineering characteristics of soil for designing road subgrade. CBR value is depend upon optimal dry density (MDD), maximum moisture content (MC), and other variables liquid limit (LL), plastic limit (PL), plasticity index (PI), moisture content (OMC), and type of soil, soil permeability, etc. Additionally, the soil's condition—whether it's damp or not—affects the value. The method of determining CBR is quite drawn-out and time-consuming. This study aims to link the soaked or unsoaked CBR value with the MDD, OMC, LL, PL, PI along with triaxial of various soil samples collected from Qila Road in Aligarh, Uttar Pradesh, India.

Sustainable Binary Blending for Low-Volume Roads—Reliability-Based Design Approach and Carbon Footprint Analysis

The utilization of industrial by-products as stabilizers is gaining attention from the sustainability perspective. Along these lines, granite sand (GS) and calcium lignosulfonate (CLS) are used as alternatives to traditional stabilizers for cohesive soil (clay). The unsoaked California Bearing Ratio (CBR) was taken as a performance indicator (as a subgrade material for low-volume roads). A series of tests were performed by varying the dosages of GS (30%, 40%, and 50%) and CLS (0.5%, 1%, 1.5%, and 2%) for different curing periods (0, 7, and 28 days). This study revealed that the optimal dosages of granite sand (GS) are 35%, 34%, 33%, and 32% for dosages of calcium lignosulfonate (CLS) of 0.5%, 1.0%, 1.5%, and 2.0%, respectively. These values are needed to maintain a reliability index greater than or equal to 3.0 when the coefficient of variation (COV) of the minimum specified value of the CBR is 20% for a 28-day curing period. The proposed RBDO (reliability-based design optimization) presents an optimal design methodology for designing low-volume roads when GS and CLS are blended for clay soils. The optimal mix, i.e., 70% clay blended with 30% GS and 0.5% CLS (exhibiting the highest CBR value) is considered an appropriate dosage for the pavement subgrade material. Carbon footprint analysis (CFA) was performed on a typical pavement section according to Indian Road Congress recommendations. It is observed that the use of GS and CLS as stabilizers of clay reduces the carbon energy by 97.52% and 98.53% over the traditional stabilizers lime and cement at 6% and 4% dosages, respectively.

A comparative study of stabilising collapsible soil using different types of biopolymers

This paper presents a comprehensive study of using xanthan gum (XG), sodium alginate (SA) and gelatin (G) to stabilise collapsible soil. Modified Proctor, one-dimensional collapse, unconsolidated-undrained triaxial and California bearing ratio (CBR) tests were conducted to estimate the engineering characteristics of the untreated and treated soil. Additionally, x-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were utilised to demonstrate the changes in the microstructure of the treated samples. It was found that biopolymers decreased the maximum dry density and increased the optimum water content. The results also indicated that a 4% content of XG, SA and G significantly reduced the collapse index by 96, 95 and 82%, respectively. Shear tests showed that biopolymers slightly reduced the internal friction angle and significantly increased the cohesion intercept, which led to shear strength improvement. The results also indicated that 4% XG-treated, 4% SA-treated and 4% G-treated samples exhibited higher shear strengths by 145, 106 and 73%, respectively, than the untreated samples under the same conditions. The findings also indicated that when the soil was mixed with a 4% concentration of XG, SA and G, the unsoaked CBR value increased by about 185, 157 and 141%, respectively.

Utilization of coal fly ash to enhance the bearing capacity of road base

Coal is responsible for the generation of around 38 percent of the power that is used throughout the entire planet. In the last two decades, there has been a rise in the number of chances for recycling and usage of fly ash from coal combustion due to its hydrophobic and cementitious properties. However, there is still limited commercialization of coal fly ash (CFA) in road construction. The focus of this research is to determine the bearing capacity of a CFA-treated crusher run used as a road base course. In order to determine the appropriate percentage of CFA, the crusher run was mixed with various percentages of Class F CFA, including 10%, 15%, 20%, and 25%. The proctor Compaction test (PCT), soaked and unsoaked California Bearing Ratio (CBR) tests, and Unconfined Compressive Strength Test (UCST) were then used to evaluate the bearing capacity of the CFA-treated crusher. The result shows that as the percentage of CFA increased, the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) decreased compared with the control specimen. The soaked and unsoaked CBR of the CFA-treated crusher run with 20% CFA increased by approximately 32% and 26% respectively that of the control specimen. Therefore, it is proven that utilization of CFA up to 20% into crusher run could enhance the bearing capacity of the road base.

Effect of sodium silicate and cement on the improvement of engineering properties of organic soil

The study is aimed at evaluating the effect of adding sodium silicate and cement to organic soil. Geotechnical properties of organic soil are determined before and after the addition of the stabilizing materials, which in this case are cement and sodium silicate. The results obtained after treatment were analyzed and evaluated to determine whether the strength values reached are adequate for strong subgrades for pavement, and airports construction. Organic soil samples used in this study were obtained from Kayseri Free Area in Turkey. Index properties and geotechnical properties of organic soil, which was identified as sample P, were determined and this formed the reference upon which strength improvements of each mix design sample were obtained. Optimum moisture content and maximum dry density of the soil and the various mixes were obtained using standard proctor test. Unconfined compressive tests (UCS), California bearing ratio (CBR), and Falling head permeability tests were used to determine geotechnical properties. UCS tests were conducted on air cured samples for 1, 7, and 28 days. Soaked and unsoaked CBR samples were tested after 1, 7 and 28 days. Hydraulic conductivity was determined using the falling head permeability test. From the experiments, sodium silicate and cement were seen to improve the strength of organic soil and provide acceptable subgrade strength and CBR values. CBR and UCS tests indicated that longer curing periods improved strength even more. Higher values were obtained for 7 days cured samples than for 1-day samples with the highest values being obtained for 28 days cured samples. Design mixes with higher cement and sodium silicate compositions gave the highest values of strength. In conclusion, sodium silicate and cement give positive results when it comes to stabilizing organic soil.

The Effect of Diatomaceous Earth Addition on CBR Values of Glee Geunteng Soil in Aceh Besar, Aceh Province, Indonesia

The soil which is the platform often used for construction activities needs the strength to resist loads. However, its physical and mechanical properties are sometimes naturally limited and this implies there is a need for improvement and stabilization. Therefore, this study uses diatomaceous earth, which is a natural pozzolanic material classified as a type of Supplementary Cementing Materials (SCM), as an additive. The chemical stabilization was conducted by mixing the soil with stabilizing materials such as cement, lime, fly ash or others that have the ability to change the chemical composition and combination of soil. It is important to note that diatomaceous earth has similar properties as other pozzolanic materials such as fly ash and metakaolin powder and this is the reason it is expected to function as a soil stabilizing agent needed to improve soil properties. This study was conducted using the soil from Glee Geunteng in Peukan Bada as well as the diatomaceous earth obtained from Lambeureunut Village, Aceh Besar Regency, Aceh Province, Indonesia. The main purpose was to determine the California Bearing Ratio (CBR) value of the Glee Geunteng soil mixed with diatomaceous earth at 5, 10, 15, and 20% dry weight of the soil. The CBR test consisted of unsoaked CBR, soaked CBR testing at 4 days, and swelling properties of CBR with a variety of diatomaceous earth mixtures. Glee Geunteng soil was classified as A-6 Group Index 3 based on the AASHTO soil classification and as the SC (silty clay) soil according to the USCS classification. The results showed that the unsoaked CBR value reduced from 35.96% for the natural Glee Geunteng soil to 31.65% for the soil mixed with 20% diatomaceous earth material. A similar trend was observed for the soaked CBR value with a reduction from 15.57% to 6.98%. The decrease in CBR value was perceived to be caused by the very small silica content (SiO2 ) in diatomaceous earth material with 42.09% compared to the 86% in the material obtained from another source in the previous research by Hidayati.

The Effect of CKD and RAP on the Mechanical Properties of Subgrade Soils

The construction of pavement layers on subgrade soil with good characteristics decreases the thickness of these layers, which in turn lowers the cost of building and maintaining roadways. However, it is impossible to avoid constructing pavements on unsuitable subgrade due to a number of limitations. Using conventional additives like lime and cement to improve subgrade properties results in additional costs. As a result, utilizing by-products (cement kiln dust and reclaimed asphalt pavement) in this field has benefits for the environment, economy, and technology. Large amounts of cement kiln dust (CKD), a by-product material, are produced in Portland cement factories. On the other hand, large amounts of reclaimed asphalt pavement (RAP) are accumulated as a result of the rehabilitation of old roads. This paper discusses using CKD and RAP to improve the characteristics of poor subgrade layers by conducting a series of Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests on samples of natural soil and soil stabilized with different percentages of CKD and RAP with different curing times to investigate their impacts on soil properties. The curing was carried out by wrapping the stabilized samples with several layers of nylon and then placing them in plastic bags at room temperature. The compaction results illustrated that the addition of CKD increases OMC and decreases MDD, in contrast to RAP, which decreases OMC and increases MDD. The addition of CKD and RAP led to a significant and unexpected increase in the CBR values. The results show that the soaked and unsoaked CBR values improve from 3.4% and 12.1% for natural soil to 220.1% and 211%, respectively, after adding 20% CKD and curing the samples for 28 days. Also, the addition of 25% RAP to soil-20% CKD blend increased the soaked and unsoaked CBR values to 251% and 215%, respectively. All the additions resulted in a significant reduction in swelling.