محمدمحسن توفیق

Stabilizing weak and poorly graded soils in engineering projects is commonly achieved using lime and cement. However, the cement production process requires significant energy and generates a substantial volume of carbon dioxide, which presents considerable environmental risks. As an alternative to cement and lime, alkali-activated aluminosilicates have gained recognition due to their cost-effectiveness and environmental compatibility. This study aims to investigate the feasibility of utilizing metakaolin as a stabilizing agent for sandy soil, with Calcium carbide residue (CCR) serving as an alkaline activator. To this end, factors such as the concentration of alkaline activator, metakaolin content, curing time, and temperature of treated soil samples were examined through unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests. The results were then compared to those of sand stabilized with Portland cement. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the microstructures formed during the soil stabilization process. The findings indicate a significant increase in the stabilized soil samples' compressive strength and ductile behavior. Moreover, the analysis of the developed microstructures in the stabilized soil samples demonstrates a noticeable bond between the binding gel and sand particles and the filling of intergranular space with alkali-activated binding gel. Overall, the findings of the present study suggest that the introduced binding gel has the potential to be an environmentally compatible stabilizing agent for stabilizing sandy soils.

Nowadays, the ordinary Portland cement (OPC) industry causes to extensive environmental consequences due to consuming huge amounts of fossil fuels. This necessitated researchers to introduce a novel group of binders called “Geopolymer cements” or “Green cements” with higher performance and lower pollution compared to the OPC. Thus, in this research, the effect of using two types of alkaline activators such as sodium hydroxide (NaOH) and calcium carbide residue (CCR), for stabilization of clay soil (CL) has been investigated. Initially, the chemical compositions of soil, recycled glass powder, calcium carbide residue, and sodium hydroxide were obtained via X-ray fluorescence (XRF) test. Then, the mechanical behavior of different unstabilized, geopolymer-stabilized, and OPC-stabilized samples has studied using unconfined compressive strength (UCS) test. The effects of several parameters such as the type and concentration of alkaline activators, the curing times (7, 28, and 91 days), and the initial synthesis temperature (25 and 70 ˚C) on the UCS and failure strain of samples have been assessed. Moreover, in order to studying the microstructure of samples, the scanning electron microscope (SEM) images and energy dispersive X-ray (EDX) analysis of selected samples have been used. Results showed the effective stabilization of soil geopolymer, using both alkaline activators. However, the CCR will be more appropriate if environmental and economic problems considered.

Glass powder is one of the increasing solid wastes in the world and clay usually needs improvement for use in construction projects. In the present study, the modification of the toughness parameters of fine-grained soils was studied by a geopolymer based on recycled glass powder (RGP). For this purpose, uniaxial strength (UCS) and California bearing ratio (CBR) tests were performed on the modified specimens. Processing time, weight percentage of RGP use and activator concentration (M) were among the variables studied in the study. For comparison, experiments were performed on samples modified with 10% Portland cement. The results of increasing the geopolymer to soil samples showed that the optimal use of RGP is 9%. Also, except for the 0day samples in the CBR experiment, other UCS and CBR samples had the optimal amount of activator concentration (NAOH), which indicates the effect of processing conditions on the behavior of the modified soil. Examination of scanning electron imaging (SEM) images showed the effect of the correction method on soil mass. Analytical comparison of UCS and CBR experiments showed a mathematical relationship between the results of UCS and CBR-7day experiments with a good relative correlation that was expected due to the same storage conditions of the samples in the first 7 days. A slight correlation was observed in the results of UCS and CBR-0day tests due to the difference in processing conditions of the two tests in the first 7 days.

Portland cement is one of the most common materials for improving the mechanical properties of soils; however, it has a lot of detrimental effects on the environment. Cement production releases million tons of carbon dioxide gas (CO2) to the air and uses million tons of raw material such as clay and limestone. For this purpose, geotechnical engineers are looking forward to using a new friendly environment material instead of cement. Geopolymers are new alternative materials that have some advantage such as high resistance, friendly environment, long durability, and low cost. Two materials need to make a geopolymer matrix. First, any materials have silicate and Aluminium oxide and Second Alkaline activators. In this study, a geopolymer based on rice husk ash and iron ore tailings (IOT) are used for sandy soil stabilization. Two types of alkaline activators are used: 1) Type I sodium hydroxide and 2) Type II carbide calcium residue. Various parameters such as type of material consumed, percentage of compound composition, type of alkaline activator, and processing time are considered as influencing factors in the behavior of the stabilized specimens. Unconfined Compressive Strength (UCS) and splitting tensile strength tests (Brazilian test) are the main criteria for a comparison of the specimens to evaluate the effect of a geopolymer on the mechanical behavior of the specimens. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses are performed to investigate the microstructures of the stabilized soil. The results show that by adding the optimum amount of additives and handling the specimens under ambient conditions, the unconfined compressive strength of the specimens increased. The optimum percentage of selected specimens is a combination of 10% of rice husk ash and 24% of iron ore tailings for activator I and 18% of iron ore tailings for activator II. The use of type I activator indicates that it is highly effective in the formation of aluminosilicate gels in geopolymer compounds.

Today, Portland cement is used as the most common material for construction purposes and stabilizer forbuilding bases and substrates in civil engineering. However, engineers are looking for a replacement of cementdue to adverse environmental impacts. Geopolymer and alkali activated materials as environmentally friendlymaterials are a suitable alternative to cement. In this study, geopolymers based on Taftan natural pozzolan and nanomaterials (nanoclay and nanosilica) were used to stabilize sandy soil. Various parameters such as type ofnanomaterial, amount of nanomaterial, alkaline activator solution ratio and curing time were taken intoaccount as the affecting factors on the behavior of stabilized specimens. To evaluate the effect of geopolymerand nanomaterials on sandy soil stabilization, in addition to testing of the unconfined compressive strength(UCS) and the tensile strength, which is the main criterion for comparison of specimens, X-ray diffraction andscanning electron microscopy were performed to verify the microstructure of the stabilized soil. Based on thisstudy, natural pozzolan and nanomaterials are appropriate and beneficial alternative materials in stabilizationof earth structures. The results showed that the addition of pozzolan and nanomaterials to soil and increasingthe amount of alkaline solution caused an increase in the unconfined compressive strength and the tensilestrength of the soil and thus the soil stabilization. Additionally, the results of the microstructural analysisindicate a strong reaction of chemical additives and the formation of aluminosilicate gel in geopolymercompounds, which itself increases the load-bearing capacity of the soil and stabilizes it.