Search Results (6)

The management of unutilized fly ash poses challenges due to concerns about storage and its potential groundwater contamination. Within the road industry, where the bulk utilization of fly ash is feasible, its unsuitability for use in the base and sub-base layers of pavements due to its low strength and a high proportion of fine particles has been a limitation. The incorporation of stone dust alongside fly ash, treated with lime or cement, yields superior strength and stiffness. Apart from strength, the stabilized mix’s durability, capillary rise, and water absorption properties are crucial for determining its suitability for pavement applications. Observations from this study reveal that fiber-reinforced cement-stabilized fly ash–stone aggregate specimens treated with 4% and 6% cement, with and without fibers, met the limiting mass loss of 20%, as specified in IRC SP: 89. The mass loss decreases with an increase in cement and fiber content. However, the capillary rise in the mixes increases with a higher percentage of fly ash and fiber content but decreases with increased cement content. Cement addition results in a reduction in water absorption; however, the addition of fibers results in an increase in water absorption. A linear correlation has been established between mass loss and UCS and IDT, which can be used to evaluate the suitability of materials for the structural layer without conducting a wet–dry durability test, which typically takes one month. This study proposes that cement-stabilized fly ash and stone aggregate mixtures with 4% and 6% cement can be used as the subbase and base of pavement based on wet–dry mass loss criteria and water absorption criteria. Observations from this study reveal that fiber-reinforced cement-stabilized fly ash–stone aggregate specimens treated with 4% and 6% cement, with and without fibers, met the limiting mass loss of 20%, as specified in IRC SP: 89. The mass loss decreases with an increase in cement and fiber content. However, the capillary rise in the mixes increases with a higher percentage of fly ash and fiber content but decreases with increased cement content. Cement addition results in reduction in water absorption. However, the addition of fibers results in increase in water absorption. A linear correlation is established between mass loss and UCS and IDT, which can be used to evaluate the suitability of materials for the structural layer without conducting wet–dry durability tests, which take one month. This study proposes that cement-stabilized fly ash and stone aggregate mixtures with 4% and 6% cement can be used as the subbase and base of pavement based on wet–dry mass loss criteria and water absorption criteria. Full article

The utilization of waste fly ash in road construction is primarily confined to its use in embankment filling or as a stabilizer when combined with lime and cement. Its application in structural pavement layers, such as the base and subbase, faces a challenge due to the high volume of fine particles, which renders it brittle when stabilized. In this study, fly ash was blended with stone dust and aggregated to enhance its gradation. Subsequently, it was stabilized with cement to bolster its strength, rendering it suitable for pavement use. Additionally, polypropylene (PP) fibers were introduced to mitigate the brittleness of the mixture. An extensive experimental investigation was conducted to assess the strength and stiffness properties, including compressive strength, indirect tensile strength, flexural strength, cyclic indirect tensile modulus, and flexural modulus of fiber-reinforced cement-stabilized mixtures of fly ash, stone dust, and aggregate. The experimental results reveal that the addition of PP fibers up to 0.25 wt.% enhances compressive strength, but any further increase in fiber content leads to a reduction in strength. However, indirect tensile strength and flexural strength show improvement, with an increase in fiber percentage up to 0.5 wt.%. It was observed that cement content plays a dominant role in stabilizing these materials. Appropriate relationships have been established between strength and modulus parameters for stabilized mixtures. Based on the strength and stiffness study, a combination of 70% fly ash and 30% stone dust aggregate with 6% cement can be considered for the base layer. Regarding the behavior of indirect tensile strength and flexural strength, an optimum fiber percentage of 0.35% is recommended. Full article

In the past few decades, solidification/stabilization (S/S) technology has been put forward for the purpose of improving soil strength and inhibiting contaminant migration in the remediation of heavy metal-contaminated sites. Cement, lime, and fly ash are among the most common and effective binders to treat contaminated soils. During S/S processing, the main interactions that are responsible for improving the soil’s behaviors can be summarized as gelification, self-hardening, and aggregation. Currently, precipitation, incorporation, and substitution have been commonly accepted as the predominant immobilization mechanisms for heavy metal ions and have been directly verified by some micro-testing techniques. While replacement of Ca²⁺/Si⁴⁺ in the cementitious products and physical encapsulation remain controversial, which is proposed dependent on the indirect results. Lead and zinc can retard both the initial and final setting times of cement hydration, while chromium can accelerate the initial cement hydration. Though cadmium can shorten the initial setting time, further cement hydration will be inhibited. While for mercury, the interference impact is closely associated with its adapted anion. It should be pointed out that obtaining a better understanding of the remediation mechanism involved in S/S processing will contribute to facilitating technical improvement, further extension, and application. Full article

For asphalt pavement structures, semi-rigid road base course has to sustain repeated high-axle load during its service life and the performance of semi-rigid road base materials directly influences the durability of pavement structures. The dynamic compressive resilience modulus of two commonly used semi-rigid road base materials, cement stabilized aggregates (CSG) and lime-fly ash stabilized aggregates (LFSG) were evaluated at different frequencies using a Universal Testing Machine (UTM). The results showed that LFSG had higher dynamic modulus than that of CSG and the load frequency had less influence on the dynamic modulus of these two semi-rigid road base materials. The four-point bending test was applied to measure the flexural-bending strength and the fatigue life of these two semi-rigid materials. A higher flexural-bending strength of LFSG indicated its better bearing capacity than that of CSG. The fatigue life of LFSG and CSG decreased with the increase of stress–strength ratio and the LFSG performed better in terms of fatigue resistance. The fatigue damage models of CSG and LFSG based on Stress-Life (S-N) curve are established. As per incremental-recursive mechanics, a general modulus degradation model was established and verified by the results of full-scale accelerate loading test. This model cannot only be used to predict the fatigue deterioration of semi-rigid road base materials under different stress levels, but is also able to calculate the current bending elastic modulus based on its initial modulus value. Full article

One of the important aspects of highway design is aggregates. Aggregates strength and consistency has an effect on pavement structure’s overall performance. The consistency of the base material near the site of the construction doesn’t always match the requirements of pavement construction and carrying quality aggregate raises the cost of construction. Stabilizing agents such as asphalt cement, lime, fly ash were used to improve the strength of these materials in order to make greater use of locally available materials. Layer materials present in the pavements and the structure of them influence pavement performance. The compressive strain and the tensile strain in the layer of subgrade and asphalt layer respectively are influenced by the stiffness of the base layer. The important aspects causing rutting and fatigue cracking are compressive strain in the top region of the subgrade layer and tensile strain at the bottom of the asphalt layer, respectively. In this research study, field performance (cracking, rutting, and surface roughness) of pavement sections with untreated and treated bases were collated to assess the impact of the stabilizing agents. The treated sections performed well significantly compared to the untreated sections in terms of pavement surface roughness and fatigue cracking. The treated sections performed higher than the untreated sections in terms of the cumulative average values of all 3 distresses with fatigue cracking averaging 5 times lower than the untreated sections. The combined IRI and rutting of treated sections averaged about 1.5 times and 0.11 inches smaller, respectively than those of untreated sections. Full article

The application of construction waste as an aggregate in subgrade backfilling is an important recycling option. This study analyzed a subgrade backfill material consisting of lime-fly ash construction waste mixture (LFCWM). Compaction and California bearing ratio (CBR) tests were performed on LFCWM under different cement-aggregate ratios (CARs, 3:7, 4:6, 5:5, 8:2). Different normal stresses (100, 200, and 300 kPa) and aggregate sizes (20%, 40%, 60%, 80% of P_4.75) were also evaluated. The experimental results indicated that: (1) when the CAR was 4:6, the optimum water content and the maximum dry density reached their maximum values of 10.1% and 2.03 g/cm³, respectively, the maximum CBR value was 42.5%, and the shear strength reached its maximum value. (2) With an increase in shear displacement, the shear stress showed a rapid initial increase, then a slow decrease, and finally tended to stabilize. (3) Normal stress had a positive effect on the shear strength of the mixture. (4) When P_4.75 was 40%, the shear strength of LFCWM was the maximum. The research results have been successfully applied to road engineering, providing an important reference for the application of construction waste aggregate in roadbed engineering. Full article