Search

For evaluating the resistance performance of cement-stabilized soils in cold regions, the variation of the strength of the cemented sand–gravel (CSG) mixture concerning the hydration process should be explored. This paper aims to study the effect of freeze–thaw (F–T) cycles on the strength and microstructure of a CSG mixture with 10% cement that is subjected to 12 cycles of freezing at a temperature of −23°C for 24 h and then melted at room temperature of 24°C for the next 24 h. The uniaxial compressive strength (UCS), California bearing ratio (CBR), and weight volume loss of the samples were measured after individual F–T cycles. Furthermore, the change in the microstructure of the CSG mixture in various F–T cycles was explored. The results showed a considerable reduction in the UCS up to Cycle 3, then a slight increase for Cycles 3–6, and finally a gradual decrease for further cycles. However, the CBR and weight loss slightly fluctuated up to Cycle 6, and then gradually decreased for subsequent cycles. The majority of compounds of hydrated cement were damaged in the first three cycles. In the following cycles, between Cycles 3 and 6, the portlandite compound was dissolved and recrystallized within the microvoids. Depending on the environmental conditions, carbonation may be generated from the hydrated cement fraction, which fills the microvoids and improves the strength and structure of the mixture. During further cycles after the sixth cycle, the mechanical action of the ice lenses coupled with the disintegration of the hydrate compounds imposed many new microvoids and cracks with considerable length and width, which intensified the strength reduction of the moisture and weakened the adhesion between grains. Since cement is widely used in pavement and dam engineering for stabilizing soils, the durability of cemented soils is of prime concern. This study may help improve the durability and resistance of cemented soils in cold climates. The F–T action not only influences the macrostructure of cement-stabilized soils by imposing a wide crack and ice lens but also induces a considerable change in the complexes existing in the hydrated cement paste of the mixture. Three patterns govern the change of the mixture microstructure in various F–T cycles that correspond to the observed trend in strength. The mentioned trend for the microstructure change and, consequently, the strength variation of the CSG mixture are associated with many factors such as pH, cement content, CO2 content, moisture content within the mixture, and relative humidity within the environment. Accordingly, the pattern of microstructural changes in the CSG mixture after the middle F–T cycles may vary depending on environmental conditions. [ABSTRACT FROM AUTHOR]

The volumetric instability of steel slag hinders its use in pavement layers and embankments. Accordingly, evaluating the swelling potential of steel slag and designing volumetrically stable steel slag mixtures is required to promote its sustainable utilization. This paper focuses on the comparison of the swelling response of basic-oxygen-furnace steel slag (BOFS), electric-arc-furnace steel slag (EAFS), BOFS-fly ash and BOFS-glass powder mixtures based on the results of three different types of tests: (i) long-term California bearing ratio (CBR) swelling, (ii) heated water bath swelling and (iii) autoclave tests. BOFS mixtures were prepared using glass powder or class F fly ash with 5%, 10%, and 20% replacement ratios. The compaction characteristics, permeability, and California bearing ratio (CBR) of steel slag and steel slag mixtures were also assessed within the framework of a detailed discussion of their swelling response. At the end of swelling tests, the measured maximum 1D strains of EAFS were all at negligible levels. Based on the test results, BOFS and BOFS-glass powder mixtures had ∼5.0–5.5% swelling strains after 20.5 months without signs of stabilization. 20% class F fly ash replacement stabilized the swelling strains of the mixture at about 0.75% after ∼3 months of monitoring in long-term tests. 1D swelling rates measured for all BOFS-class F fly ash mixtures decreased with increasing fly ash content. CBR and swelling response of BOFS-class F fly ash mixtures were more favorable compared to those of BOFS. The heated water bath tests provided higher estimates of the swelling strains compared to those obtained from autoclave tests for the steel slag mixtures that contain 15% or more fines. The results of this study showed that glass powder replacement is not effective in alleviating the swelling of BOFS. The volumetrically stable BOFS-class F fly ash mixtures indicated favorable mechanical properties for their use in pavement layers. [Display omitted] • Glass powder replacement is not effective in alleviating the swelling of BOF slag. • 20% class F fly ash replacement can suppress the 1D strains of BOF slag. • Autoclave may provide relatively low estimates of strain for steel slag with 15% or more fines. • Separate handling of EAF and ladle steel slag in the plants can help their utilization. • BOF steel slag-class F fly ash mixtures show potential to be used in bound pavement layers. [ABSTRACT FROM AUTHOR]

This research investigated the effect of Waste Marble Dust (WMD) and Corncob Ash (CCA) on expansive soil's engineering and microstructural properties. Various laboratory experiments were performed on the natural soil to ascertain its characteristics. The corncobs underwent pre-water treatment for fourteen days to remove excess potassium and increase their silica content, resulting in a rise in the silica level from 0% to 50%. At first, only WMD was added to the soil in increments of 5% to 30% using compaction and California bearing tests. The optimum dosage of 15% WMD addition yielded the best result. CCA was then incorporated by the weight of the soil from 2% to 10% in increments of 2% to the first optimum (15% WMD) to obtain the overall optimum for the study (15% WMD and 8% CCA). Stabilization of the natural soil using both materials led to the modification and solidification of the soil mass, evident by the rise in California bearing ratio values from 1.68% to 15.53% and unconfined compressive strength from 41.33 kN/m2 to 174.68 kN/m2. There was also a decrease in the soil's free swell from 120% to 15% as well as reductions in the liquid limits from 56.23% to 36.01% and in the plasticity index from 29.74% to 8.72%, respectively. The microstructural images showed the formation of cementitious compounds in the form of calcium silicate hydrate and calcium aluminate hydrate gels. The findings indicate that using WMD and CCA as a unit has great potential in enhancing engineering properties, like strength parameters and the swell potential of expansive soils. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Use of by-product materials, such as steel slag and cathode ray tube glass, as alternative recycled materials in the construction of roads, could reduce the demand for natural aggregates. Measurements of the physical properties (specific gravity, water absorption, Los Angeles abrasion value and soundness) and microstructure characteristics were made to evaluate the effectiveness of using these materials in pavement road base. The laboratory assessments were also conducted using California bearing ratio, unconfined compression strength and indirect tensile strength tests. Leaching tests were performed on six elements (arsenic, barium, cadmium, lead, silver and mercury) to determine the leaching potential of hazardous metals. Element concentration release limits were determined based on the Toxicity Characteristic Leaching Procedure (TCLP). The results indicate that the alternative recycled materials are suitable for use in aggregates and meet the requirements for natural aggregates used for similar purposes. Microstructure analysis shows that the steel slag is more porous and rougher than granite and cathode ray tube glass. The higher percentage of steel slag produces higher California bearing ratio test values for both the soaked and unsoaked samples. Findings from unconfined compression strength and indirect tensile strength tests show that the performance of the mixture was enhanced significantly upon incorporating a higher percentage of steel slag. The samples show a significant strength improvement between 2 and 17%. The concentration of leached barium and lead is higher than that of the other elements, however it is still less than 1% of the TCLP regulatory limit, hence the concentration of the leached elements does not pose an environmental risk. The laboratory test results indicate that mixtures consisting of granite, steel slag and cathode ray tube glass are both environmentally safe and suitable for use as aggregate in pavement road base. [ABSTRACT FROM AUTHOR]

Expansive soils are susceptible to ground movements and are problematic to overlying geotechnical structures. There is a growing shift to use nontraditional sustainable and economical alternatives. To date, limited research is available on investigating the reaction mechanism of nontraditional soil stabilization; thus, this research aims to fill this gap in the knowledge. A series of experiments was conducted to assess the mechanical and hydraulic behavior of field expansive soil with the enzyme-based soil stabilizer. Moreover, the reaction mechanism of enzyme soil stabilization was studied using microstructural-driven analytical techniques. The results indicate substantial increase in California bearing ratio, unconfined compressive strength, and resilient modulus with a considerable reduction in permeability with the addition of enzymes into the expansive soil. The enzyme additive is adsorbed by the clay particles, which reflects a reduced affinity for water, an improved density, and a reduced ingress of water within the soil. Adding enzymes causes the expansive clay mineral lattices to relax, as the enzyme stabilizers penetrate the inner layers leading to expansion and subsequent moisture entrapment of the inner layers, emphasizing densification and a reduced affinity for water. The outcomes from the study are beneficial for the understanding of enzyme-based ground improvement to inhibit the expansive nature of reactive soils. [ABSTRACT FROM AUTHOR]