Improvement of Pavement Subgrade by Adding Cement and Fly Ash to Natural Desert Sand

Soil characteristics are paramount to design pavements and to assess the economic viability of a road. In the desert, such as that found in southern Libya, the very poor quality of soils leads to important pavement distress such as cracks, rutting, potholes, and lateral shear failure on the edges. To improve the strength of desert sand, an innovative approach is proposed, consisting of adding manufactured sand, ordinary Portland cement (OPC), and fly ash (FA) as a binder. OPC and FA improve the characteristics of mixes of crushed fine aggregate (CFA) and natural desert sand (NDS). These results are based on a gradation of two sand sources to determine the particle distribution and X-ray fluorescence (XRF) to determine their chemical and physical properties, respectively. This research assesses the effect of cement and fly ash on the geotechnical behavior of two mixtures of fine desert and manufactured sands (30:70% and 50:50%). The mix composed of 26% of CFA, 62% of NDS, 5% of OPC, and 7% of FA shows optimal results in terms of strength, compaction, and bearing capacity characteristics.

Research on the Effect of Desert Sand on Pore Structure of Fiber Reinforced Mortar Based on X-CT Technology

Concrete is a multi-phase, porous system. The pore structure has an important influence on the properties of the concrete. In this paper, a kind of fiber reinforced mortar was prepared with desert sand and its pore structure was studied. The MIP technique was used to investigate the pore structure characteristics between 1 nm and 500 μm (in diameter). Meanwhile, the μX-CT technique was used to study the pore structure characteristics above 200 μm. It was found that the total porosity tends to decrease first and then increase as the dosage of desert sand increased. The porosity decreased gradually from the upper to bottom area inside the sample, and the diameter of the air voids near the upper area became larger. After curing for 28 days, the compressive strength of fiber reinforced mortar reached the maximum when the content of desert sand was 50%. In conclusion, the appropriate amount of desert sand can reduce the porosity of the fiber reinforced mortar to some extent and the number of large size air voids can be significantly reduced, which improves the pore structure and the mechanical properties of the fiber reinforced mortar.

A comprehensive research in chemical consolidator/stabilizer agents on sand production control

Sand or fine is a typical product in many processing of oil production from unconsolidated and weakly consolidated formations. High variation of in situ stress, fluid production rate above maximum sand-free rate, and water production are main primary sources of the sand production. Sand production can cause hazardous operational problems to the facilities, pipes, and wellbore. Hence, it is a significant problem that requires to be managed and studied. To minimize the operational impacts of particle migration, chemical consolidators/stabilizers can be utilized to alter surface properties of sand and formation particles. The decreasing zeta potential besides increasing the cohesion between sand and formation particles could result in controlled sand production. However, understanding the mechanism and application of chemical methods to alleviate sand production is not well-discussed. This study presents and discusses chemical consolidator/stabilizer agents, which may be applied for managing sand production in the petroleum industry. This was achieved through a comprehension review of the literature and the application of chemical consolidators/stabilizers in other fields such as bauxite residue (red mud and red sand) control, desert sand, mine reclamation, wind erosion control, unpaved road modification, and enhancement of water retention and soil infiltration properties that are similar to formation sand. Standard experimental methods in various fields, for performance analysis of chemical consolidator/stabilizer agents, are compared and summarized. The consolidation/stabilization mechanisms of various types of chemical consolidator/stabilizer agents are discussed and compared. This review potentially can be used to inhibit blind usage of chemicals and functions as a reference to additional research in sand production control in petroleum engineering. The results are appropriate for extending quantitative approaches for performance evaluation of sand consolidator/stabilizer agents.

Effect of Desert Sand on the Mechanical Properties of Desert Sand Concrete (DSC) after Elevated Temperature

Building fires and shortage of medium sand resources have become two major issues in building domain. Desert sand was used to produce desert sand concrete (DSC), which was suitable for engineering utility. The mechanical properties tests of DSC with different desert sand replacement ratio (DSRR) were carried out after elevated temperature. The effects of elevated temperature and DSRR on DSC mechanical properties were analyzed. DSC microstructure was investigated by SEM and XRD. Research studies’ results showed that the relative compressive strength increased gradually with increasing temperature. The maximum value appeared at 200°C–300°C, and it began to decrease at 500°C. Compared with room temperature, the compressive strength at 700°C was about 70% of that at room temperature. Relative splitting tensile strength increased first and then decreased, and the value reached the maximum at 100°C. DSC relative flexural strength decreased with the temperature. Relative compressive strength, splitting tensile strength, and flexural strength of DSC enhanced first and then decreased with DSRR, and the maximum values were obtained with 40% DSRR. Based on the regressive analysis, the relative compressive strength was a quadratic polynomial with relative porosity. Relative splitting tensile strength and relative flexural strength were linear with relative porosity. Research results can provide the technical support for DSC engineering application and postfire assessment.

Association with Ambient Air Pollutants and School Absence Due to Sickness in Schoolchildren: A Case-Crossover Study in a Provincial Town of Japan

The effect of ambient air pollutants and Asian dust (AD) on absence from school due to sickness has not been well researched. By conducting a case-crossover study, this study investigated the influence of ambient air pollutants and desert sand dust particles from East Asia on absence from school due to sickness. From November 2016 to July 2018, the daily cases of absence due to sickness were recorded in five elementary schools in Matsue, Japan. During the study period, a total of 16,915 absence cases were recorded, which included 4865 fever cases and 2458 cough cases. The relative risk of overall absence in a 10-μg/m3 increment of PM2.5 and a 0.1-km−1 of desert sand dust particles from East Asia were found with 1.28 (95%CI: 1.15–1.42) and 2.15 (1.04–4.45) at lag0, respectively. The significant influence of PM2.5 persisted at lag5 and that of desert sand dust particles at lag2. NO2 had statistically significant effects at lag2, lag3, and lag4. However, there was no evidence of a positive association of Ox and SO2 with absence from school. These results suggested that PM2.5, NO2, and AD increased the risk of absence due to sickness in schoolchildren.

Frost Resistance of Desert Sand Concrete

Demand for medium sand has increased greatly with increasing infrastructure construction items. The shortage of construction sand resources has become a serious problem in many districts. It not only increases the engineering cost, and the overexploitation of river sand and mountain as medium sand also brings a series of serious environment problems. There are abundant desert sand (DS) resources in western China. If DS resources can be used to substitute medium sand to produce desert sand concrete (DSC), which was suitable for engineering practice, the environment can be improved and engineering cost can be reduced. Although many researchers had focused on the mechanical performance of DSC, there were few documents on the frost resistance of DSC. Frost resistance experiments of DSC with 50% desert sand replacement ratio (DSRR) and ordinary concrete (OC) were performed in this paper. Influence of freeze-thaw cycles on the mechanical properties of OC and DSC was analyzed. Experimental results showed that, with increasing freeze-thaw cycles, the damage, peak strain, and porosity increased, while elastic modulus, Poisson's ratio, and peak stress declined, the stress-strain curves tended to be flat. Under the same condition of freeze-thaw cycles, the frost resistance of DSC with 50% DSRR was higher than that of OC. Constitutive model of DSC after different freeze-thaw cycles was formulated. The results predicted by constitutive model agreed well with experimental results, which can provide technical support for DSC engineering practice.