Performance evaluation of cement-stabilized pond ash-rice husk ash-clay mixture as a highway construction material

This paper reports the results of an investigation carried out on clay soil stabilized with pond ash (PA), rice husk ash (RHA) and cement. Modified Proctor compaction tests were performed in order to investigate the compaction behavior of clay, and California bearing ratio (CBR) tests were performed to determine the strength characteristics of clay. For evaluation purpose, the specimens containing different amounts of admixtures were prepared. Clay was replaced with PA and RHA at a dosage of 30%–45% and 5%–20%, respectively. The influence of stabilizer types and dosages on mechanical properties of clay was evaluated. In order to study the surface morphology and crystallization characteristics of the soil samples, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were carried out, respectively. The results obtained indicated a decrease in the maximum dry density (MDD) and a simultaneous increase in the optimum moisture content (OMC) with the addition of PA and RHA. Multiple linear regression analysis (MLRA) showed that the predicted values of CBR tests are in good agreement with the experimental values. Developed stabilized soil mixtures showed satisfactory strength and can be used for construction of embankments and stabilization of sub-grade soil. The use of locally available soils, PA, RHA, and cement in the production of stabilized soils for such applications can provide sustainability for the local construction industry.     

The potentials of some stabilizers for the use of lateritic soil in construction

Lateritic soil was stabilized with various percentages of rice husk ash (RHA), lime and cement. Atterberg limits, standard Proctor compaction, unconfined compression and California bearing ratio tests were carried out on lateritic soil with various percentages of these stabilizers in order to examine their influence. The required amounts of ash, lime and cement were determined for economical stabilization. This paper presents the potentials of rice husk ash compared to lime and cement in lateritic soil stabilization. For road construction, it recommends 7% cement for base materials, 5% lime for sub-base materials and 18% rice husk ash for sub-base materials.     

Coupling effect of pond ash and polypropylene fiber on strength and durability of expansive soil subgrades: An integrated experimental and machine learning approach

This study explores the coupling effect of pond ash(PA) and polypropylene(PP) fiber to control the strength and durability of expansive soil. The PA is used to chemically treat the expansive soil and PP fiber is adopted as reinforcement against tensile cracking. The sustainable use of PA and PP fiber are demonstrated by performing mechanical(i.e. unconfined compressive strength, split tensile strength and ultrasonic pulse velocity), chemical(p H value, electrical conductivity and calcite content), and microstructural analyses before and after 2 nd, 4 th, 6 th, 8 th and 10 th freezing-thawing(F-T) cycles. Three curing methods with 7 d, 14 d and 28 d curing periods are considered to reinforce the 5%, 10%, 15% and20% PA-stabilized expansive soil with 0.25%, 0.5% and 1% PP fiber. In order to develop predictive models for mechanical and durability parameters, the experimental data are processed utilizing artificial neural network(ANN), in association with the leave-one-out cross-validation(LOOCV) as a resampling method and three different activation functions. The mechanical and durability properties of the PA-stabilized expansive soil subgrades are increased with PP fiber reinforcement. The results of ANN modeling predict the mechanical properties perfectly, and the correlation coefficient(R) approaches up to 0.96.     

Sugarcane press mud modification of expansive soil stabilized at optimum lime content:Strength,mineralogy and microstructural investigation

This study attempted to investigate the potential of sugarcane press mud(PM) as a secondary additive in conjunction with lime for the stabilization of an expansive soil.The physico-mechanical properties of an expansive soil,such as plasticity,shrink-swell behavior,unconfined compressive strength(UCS),mineralogical and microstructural characteristics were investigated.The expansive soil was stabilized at its optimum lime content(7%) for producing maximum strength,and was modified with four different quantities of PM in small dosages(0.25%-2%).Cylindrical soil samples,38 mm in diameter and 76 mm in height,were cast and cured for varying periods to evaluate the strength of the amended soil.The spent samples after strength tests were further used for determination of other properties.The test results revealed that PM modification led to a substantial improvement in 7-d strength and noticeable increase in 28-d strength of the lime-stabilized soil(LSS).The addition of PM does not cause any detrimental changes to the shrink-swell properties as well as plasticity nature of the stabilized soil,despite being a material of organic origin.Mineralogical investigation revealed that the formation of calcium silicate hydrate(CSH) minerals,similar to that of pure lime stabilization with only the type of mineral varying due to the modification of PM addition,does not significantly alter the microstructure of the LSS except for superficial changes being noticed.     

Stabilization of residual soil with rice husk ash and cement

Stabilization of residual soils is studied by chemically using cement and rice husk ash. Investigation includes the evaluation of such properties of the soil as compaction, strength, and X-ray diffraction. Test results show that both cement and rice husk ash reduce the plasticity of soils. In term of compactability, addition of rice husk ash and cement decreases the maximum dry density and increases the optimum moisture content. From the viewpoint of plasticity, compaction and strength characteristics, and economy, addition of 6–8% cement and 10–15% rice husk ash is recommended as an optimum amount.     

膨胀土地基承载力研究

根据非饱和膨胀土的分形结构模型,导出了非饱和膨胀土的吸力强度公式,讨论了非饱和膨胀土强度公式的有线性,根据膨胀土的强度特性提出了膨胀土地基承载力公式,运用所提出的承载力公式估算了邯郸和宁夏膨胀土地基承载力值,与实测结果一致,这种膨胀土地基承载力公式可以直接应用于工程实践中。     

A comparative study of the potentials of rice husk ash on cohesive and cohesionless soils

In this study, the effects of rice husk ash (RHA) on various geotechnical properties of cohesive (A-7-6 group) and cohesionless (A-1-b group) soils were determined and compared. Atterberg limits, dry density, optimum moisture content, unconfined compressive strength, California bearing ratio, cohesion and angle of internal friction of A-1-b and A-7-6 group soils were studied with different percentages of rice husk ash (0, 4, 8, 12, 16, 20, and 24). Optimum moisture content, compressive strength, California bearing ratio and cohesion of both soils increased with increase in RHA. Maximum dry density decreased with RHA contents. Angle of internal friction of A-7-6 soil increased while that of A-1-b soil decreased with RHA contents. From the point of view of economy and CBR value, A-1-b soil with 16% RHA is recommended for base materials for field trials in the first instance while A-7-6 soil with 17% RHA may be recommended only for sub-base materials.     

红层泥岩改良土特性室内试验研究

宜巴高速公路穿越巴东组紫红色泥岩地层。直接将泥岩风化物作为路基填料填筑,产生了路面鼓包,翻浆冒泥和路基不均匀沉降、承载力不足等工程问题。为了消除泥岩路基土不良特性,采用石灰、水泥、粉煤灰对泥岩风化物进行改良试验研究。开展击实、承载比、无侧限抗压强度试验,利用自制崩解仪、大环刀进行改良土崩解试验及土水特性测试,利用环境电镜扫描改良土微观结构,研究分析泥岩改良土的工程特性及改良机制。在综合评价改良效果及分析膨胀指标、承载比、无侧限抗压强度等常规改良效果评价指标基础上,尝试结合耐崩解性、土水特性指标全面对比分析改良效果。结果表明：改良剂消除泥岩路基土的膨胀特性,大幅提高其承载力及抗压强度指标,其耐崩解性及水稳定性也得到提高和改善;水泥改良路基土效果最佳,掺比5%为最优;石灰改良效果次之,最佳掺比为7%;粉煤灰改良效果最差,掺比11%为最优,适当提高粉煤灰掺量改良效果会更佳。     

不同改良材料对膨胀土工程性能影响的对比试验

以石灰、水泥、粉煤灰、风化砂四种材料改良同一种膨胀土,掺入不同的比例后,进行室内试验研究。试验表明:四种材料的掺入均能改善膨胀土的抗剪强度,其中掺水泥能大幅度提高膨胀土的黏聚力和内摩擦角;其次,掺石灰也能显著提高膨胀土的抗剪强度指标;掺入风化砂和粉煤灰后,膨胀土的黏聚力会有所下降,内摩擦角会随着掺量的增加,先逐渐增大后缓慢降低。掺入这四种材料均能有效改善膨胀土的膨胀特性,从对有荷膨胀率的影响效果来看,掺石灰对抑制膨胀效果最好,其次是水泥,而后是粉煤灰和风化砂。     

The role of carbide lime and fly ash blends on the geotechnical properties of clay soils

Carbide lime is a by-product obtained during the manufacturing of acetylene from the reaction of calcium carbide and water. A major portion of carbide lime is dumped in waste deposition areas, creating an environmental problem. Carbide lime and fly ash have possible applications in slope stabilization, subgrade improvement of roads, and soil treatments under shallow foundations. A series of Atterberg limits tests, compaction tests, unconfined compressive strength tests, ultrasonic pulse velocity tests, and wetting–drying tests were performed on carbide lime and fly ash treated clay soils to evaluate the effects of additive content, curing time, strength development, and the effects of wetting and drying. A total of 8% of carbide lime constituted the fixation point, and peak strength was achieved at 12% carbide lime content. A total amount of 25% additive was found as a threshold changing the Atterberg limits. Test results indicated that the strength of the treated soil improved by the existence of carbide lime and fly ash; best performance was observed in 28-day specimens with 10% carbide lime and 20% fly ash content reaching to 8 times larger strength than untreated soil. The failure patterns of the specimens reflected the curing time and wetting–drying effects. Although, the application of wetting–drying cycles deteriorated the treated soil, the presence of carbide lime partially prevented the strength loss. New relationships between normalized strength and curing time depending on carbide lime content were proposed. Furthermore, a linear relationship between the unconfined compressive strength and the ultrasonic pulse velocity of the treated soils was established.

     

Unconfined compressive strength prediction of soils stabilized using artificial neural networks and support vector machines

This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models. The soils used in this study are stabilized using various combinations of cement, lime, and rice husk ash. To predict the results of unconfined compressive strength tests conducted on soils, a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement, lime, and rice husk ash is used. Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement, lime, and rice husk ash under different conditions. The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering. This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks. The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models. Moreover, based on sensitivity analysis results, it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.     

Engineering characteristics of the compressed-stabilized earth brick

Utilization of lime and rice husk ash for soil stabilization produced considerable strength gain and other geotechnical properties of the stabilized soils. Its application could be also superior for construction materials as compressed-stabilized earth (CSE) or unfired-brick. This paper presents the investigation result of the application of lime and rice husk for unfired brick or compressed stabilized earth. The compressive and three-point flexural strength tests including compressive strength after water submersion were carried out in this present study. The investigation results show that compressive and flexural strength of clay brick are improved by adding of lime and RHA. The best quantity of lime and RHA in this study, is obtained by ratio 1:1 of lime and RHA. The addition of sand in stabilized clay resulted in more improvement in the water retention ability.     

Significance of compaction time delay on compaction and strength characteristics of sulfate resistant cement-treated expansive soil

The addition of cement for stabilization of expansive soils is one of the most commonly used methods. As with every calcium-based stabilizer, the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization. However, a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established. Furthermore, the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay. The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite, which deteriorates the stabilized soil matrix. In view of this, the present study is aimed at using the sulfate resistant cement (SRC) as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil. To bring out the above effects, three periods of time delays (0 h, 6 h and 24 h) and three sulfate concentrations of 5000 parts per million (ppm), 10,000 ppm and 20,000 ppm were adopted. The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil. Upon sulfate addition to SRC-stabilized expansive soil, the formation clogs was not curtailed and resulted in the formation of ettringite clusters. These formations were captured with the help of scanning electron microscope (SEM) images and validated with electron dispersive X-ray spectroscopy (EDAX) analysis. Further, an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry (MIP) studies.     

Correlation between one-dimensional consolidation coefficients and different basalt fiber lengths and RHA-cement contents in fiber-reinforced stabilized expansive soils

Recently, environmentally friendly soil reinforcement and stabilization techniques, used to reconstitute weak expansive soils, are on the rise, calling for an in-depth analysis of the consolidation projections on the engineering structures built on them. This study investigated one-dimensional consolidation coefficients by conducting a series of oedometer tests on expansive soils reinforced with basalt fibers of different lengths, stabilized with rice husk ash (RHA) as an environmentally friendly cement-reducing aggregate, and nominal dosages of cement in specified combinations. The correlation between the coefficients of consolidation (c_v), volume change (m_v), and permeability (k) and different basalt fiber lengths and RHA-cement contents in ultimate soil composite material was quantified using equations and graphical forms. Furthermore, scanning electron microscopic imagery (SEM) was conducted to examine the structural modifications within the reinforced and stabilized soil specimens upon one-dimensional consolidation. The results showed that basalt fiber-reinforced specimens, comprised of 5% RHA and 3% cement mixtures, showed the lowest one-dimensional consolidation coefficients with a notably greater reduction at high-stress states than the control specimen. Additionally, the coefficients of volume change (m_v) and permeability (k) decreased with the increased compactive effort, with a clear and significant reduction in the basalt fiber-reinforced stabilized soil composites. This study also proposed the best material combination scheme and analytical equations for evaluating the c_v, m_v, and k considering basalt fiber lengths at different pressure levels. The ultimate soil composites had superior properties, and thus, can be used as fill or subbase material for such engineering structures as embankments, pavements, and foundations.     

Assessment of the effects of rice husk ash particle size on strength,water permeability and workability of binary blended concrete

This study develops the compressive strength, water permeability and workability of concrete by partial replacement of cement with agro-waste rice husk ash. Two types of rice husk ash with average particle size of 5 micron (ultra fine particles) and 95 micron and with four different contents of 5%, 10%, 15% and 20% by weight were used. Replacement of cement up to maximum of 15% and 20% respectively by 95 and 5 μm rice husk ash, produces concrete with improved strength. However, the ultimate strength of concrete was gained at 10% of cement replacement by ultra fine rice husk ash particles. Also the percentage, velocity and coefficient of water absorption significantly decreased with 10% cement replacement by ultra fine rice husk ash. Moreover, the workability of fresh concrete was remarkably improved by increasing the content of rice husk ash especially in the case of coarser size. It is concluded that partial replacement of cement with rice husk ash improves the compressive strength and workability of concrete and decreases its water permeability. In addition, decreasing rice husk ash average particle size provides a positive effect on the compressive strength and water permeability of hardened concrete but indicates adverse effect on the workability of fresh concrete.     

Expansive soil modified by waste steel slag and its application in subbase layer of highways

Steel slag is a waste by-product of the steel industry. The recycling usage of steel slag is limited due to the mutative chemical compositions it contains and its low cementation. In this investigation, the composition adjustment and activation of steel slag were studied to produce an optimal slag-based composite with improved cementation efficiency. The controlling moduli of cement clinker were introduced to standardise the composite. Subsequently, the composite was used to modify Hefei expansive soil (a kind of engineering waste for swelling properties) in embankment construction. The basic physical properties including free swelling ratio, California bearing ratio, unconfined compressive strength, microstructure, and mineral evolution were evaluated to understand the engineering performance and mechanism of modified expansive soils. The results show that the cementation of the slag was significantly improved after the composition adjustment and activation. Furthermore, the treated soil can satisfy the requirement of the Chinese standard for first-class road/highway when the composite incorporation ratio is more than 5%. The microstructural and mineralogical analysis shows that the component adjustment and activation enrich the cementation of the slag, resulting in the suppression of the swelling potential and improved strength. The above findings improve the reuse efficiency of steel slag, especially in expansive soil modifications.     

Pozzolanic properties of rice husk ash, burnt clay and red mud

In this paper materials like rice husk ash, burnt clay and red mud are examined for their pozzolanic properties. Rice husk ash, obtained from various sources, is analysed by X-ray diffraction. Compressive strength properties of lime-pozzolana mortars with rice husk ash, burnt clay and red mud as pozzolana are studied. Influence of grinding of rice husk ash and intergrinding with lime are also investigated. Combination pozzolana with partial replacement of burnt clay and red mud by rice husk ash are examined for their pozzolanic properties. Long term strength behaviour of lime-pozzolana mortars is investigated to understand the durability of lime-pozzolana cements.     

Bearing ratio of reinforced fly ash overlying soft soil and deformation modulus of fly ash

This paper presents the laboratory study on the bearing ratio of unreinforced and reinforced fly ash overlying soft soil beds of a total of 11 fly ash samples collected from different thermal power plants located in the Eastern part of India. The thickness of the bottom clay layer (H_c) was maintained as 100 mm in the bearing ratio mould. The upper layer thickness of compacted fly ash (H_f) was varied. The values of the ratio H_f/H_c used were 0.75, 1.00 and 1.25 in this study. The fly ash layer was reinforced with single layer and double layers of geotextiles. The effects of (i) position and number of layers of geotextiles, (ii) thickness of the compacted fly ash layer overlying soft soil layer, and (iii) moulding water content of the soft soil, on the bearing ratio of fly ash are highlighted. The inclusion of geotextile into the compacted fly ash bed enhances the bearing ratio. An increase in the thickness of compacted fly ash layer over the soft soil layer also increases the bearing ratio of the compacted fly ash bed. The values of unconfined compressive strength and deformation modulus of all the fly ash samples are also presented. Empirical relationships to estimate deformation modulus of fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus of fly ash are presented. It may be concluded from this research study that reinforced compacted fly ash overlying soft soil with a geotextile layer at the interface can find potential application in the construction of roads over soft soil.     

An investigation into the effects of lime on compressive and shear strength characteristics of fiber-reinforced clays

To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP) fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E_(50)) and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT) under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM) analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.     

空军汉口新机场试验路段石灰改性膨胀土试验研究

空军汉口新机场试验路段石灰改性膨胀土（简称灰土）试验研究包括室内和现场试验研究。室内试验研究包括：天然膨胀土与击实膨胀土的基本物理特性和胀缩特性试验、灰土击实试验以及膨胀土掺石灰改性试验等。室内试验结果表明：击实膨胀土比天然膨胀土的膨胀潜势更大；在道面下一定范围内，填料不能采用膨胀土，而必须用灰土；石灰能有效地对场区内的膨胀土进行改性，最优石灰掺合比为6％～8％：不同灰土层的最大干密度与最佳含水量差异较大，现场施工填料不能混填。现场试验包括：碾压试验、压实灰土基本物理特性和胀缩特性试验、浸水载荷试验、测定路基回弹模量和回弹弯沉试验等。现场试验结果表明：在有效控制灰土的石灰掺量和含水量情况下，采用激振力为450kN的碾压机对松铺厚度为50和30cm的灰土进行碾压，分别需碾压8和6遍，路基压路度才能达到95％，表面沉降才趋于稳定；现场压实灰土的膨胀潜势很低，仍有明显失水收缩特性，在施工时应注意采取保水措施；压实灰土具有较高承载能力、强度特性和吸水稳定性。