Search Results (17)

Mechanical soil parameters are not constants and can be defined in various ways. Therefore, determination of their values for engineering practice is difficult. This problem is discussed based on results of piezoceramic element tests and triaxial tests (unconfined and confined) on loess specimens improved by compaction and sand admixture (20% by weight). The study indicated also the effectiveness of this simple method of loess stabilization. The influence of specimen size, draining conditions, stress and strain state, and different calculation methods on the evaluation of basic mechanical parameters were analyzed. The initial shear and Young’s moduli, the degradation of secant moduli with strain, tangent moduli, and Poisson’ ratio were determined. The results showed that the shear strength parameters are much less sensitive to the test variables than the stiffness parameters are. In triaxial tests, the strength criterion adopted, the sample size, and the drainage conditions influenced the measured value of cohesion, with a much smaller impact on the angle of internal friction. On the other hand, the adopted definition of the parameter and the range of strains had the greatest influence on the value of the stiffness modulus. Moreover, larger specimens were usually found to be stiffer. Full article

To improve the performance of shotcrete in high-altitude and low-temperature environments, emulsified asphalt shotcrete (EASC), which can be used in negative-temperature environments, was prepared by using low-freezing-point emulsified asphalt, calcium aluminate cement, and sodium pyrophosphate as modified materials. The effect of emulsified asphalt on the performance of shotcrete was investigated through concrete spraying and indoor tests. Then, the modification mechanism of emulsified asphalt with respect to EASC was analyzed by combining scanning electron microscopy images and the pore structure characteristics of EASC. The results showed that in a negative-temperature environment, the incorporation of emulsified asphalt delayed the formation of the peak of the cement hydration exotherm, slowed the rate of the cement hydration exotherm, reduced the thermal perturbation of permafrost by EASC, increased the cohesion of the concrete, improved the bond strength between EASC and permafrost, and reduced the rate of rebound. The mechanical strength of the studied EASC decreased upon increasing the amount of emulsified asphalt in the admixture, and its resistance to cracking gradually improved. A content of less than 5% emulsified asphalt could improve the internal pore structure of EASC, thus improving its durability. Increasing the content of emulsified asphalt affected the hydration process of the cement, and the volume content of the capillary pores and macropores increased, which reduced the durability of the EASC. Full article

The feature of self-cleansing in sewer pipes is a standard requirement in the design of drainage systems, as sediments deposited on the channel bottom cause changes in channel geometric properties and in hydrodynamic parameters, including the friction caused by the cohesive forces of sediment fractions. Here, it is shown that the content of cohesive fractions significantly inhibits the transport of non-cohesive sediments. This paper presents an advanced calculation procedure for estimating flushing flows in channels. This procedure is based on innovative predictive models developed for non-cohesive and granulometrically heterogeneous sediment transport with additional cohesive fraction content to estimate the magnitude of increased flow necessary to ensure self-cleansing of channels. The computations according to the proposed procedure were carried out for a wide range of hydrodynamic conditions, two grain diameters, six cohesive (clay) fraction additive contents and two critical stress values. The trend lines of calculations were composed with the results of experimental studies in hydraulic flumes. Full article

Expansive soil exhibits significant swellings and shrinkages, which may result in severe damage or the collapse of structures built upon it. Calcium-based admixtures, such as lime, are commonly used to improve this problematic soil. However, traditional chemical additions can increase significant environmental stress. This paper proposes a sustainable solution, namely, the use of lignin fiber (LF) from the paper industry to partially replace lime as an amendment for expansive soils. Both the macroscopic and microscopic characteristics of the lignin fiber-treated expansive soil are extensively studied. The results show that the mechanical properties of expansive soil are improved by using lignin fiber alone. Under the condition of an optimal dosage of 8%, the compressive strength of lignin fiber-modified soil can reach 193 kPa, the shear strength is increased by 40% compared with the untreated soil, and the water conductivity is also improved with the increase in dosage. In addition, compared with 2% lime-modified soil, the compressive strength of 8% lignin fiber- and 2% lime composite-treated expansive soil increased by 50%, the cohesion increased by 12%, and the water conductivity decreased significantly. The microstructure analysis shows that at an 8% lignin fiber content, lignin fibers interweave into a network in the soil, which effectively enhances the strength and stability of the improved soil. Simultaneously, the fibers can form bridges across the adjacent micropores, leading to the merging of pores and transforming fine, dispersed micropores into larger, connected macropores. Lime promotes the flocculation of soil particles, forming larger aggregates and thus resulting in larger pores. The addition of fibers exerts an inhibitory effect on the flocculation reaction in the composite-improved soil. In conclusion, lignin fibers are an effective addition used to partially replace calcium admixture for the treatment of expansive soil, which provides a sustainable and environmentally friendly treatment scheme for reducing industrial waste. Full article

Treating peat soil foundations around Dianchi Lake and Erhai Lake in Yunnan is a complex problem in practical engineering projects. Peat soil solely reinforced with ordinary cement (OPC) does not satisfy demand. This study aims to solidify soil to achieve better mechanical properties. The preparation of peat soil incorporates a humic acid (HA) reagent into cohesive soil, and cement and ultra-fine cement (UFC) are mixed by stirring to prepare cement soil samples. They are then immersed in fulvic acid (FA) solution to simulate cement soil in the actual environment. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and pores and cracks analysis system (PCAS) tests are used to study the impact of the UFC on the microscopic pore structure of cement soil in a peat soil environment. The unconfined compressive strength (UCS) test is used for verification. The microscopic test results indicate that incorporating UFC enhances the specimen’s micropore structure. The XRD test results show the presence of C–S–H, C–A–S–H, and C–A–H. SEM and PCAS tests show that the UFC proportion increases by between 0% and 10%, and the percentage reduction in the macropore volume is the largest, at 38.84%. When the UFC admixture is 30%, the cumulative reduction in the percentage of macropore volume reaches 71.55%. The MIP test results show that the cumulative volume greater than 10 µm in pore size decreases from 7.68% to 0.17% with an increase in the UFC proportion. The UCS test results show that the maximum strength growth of cement soil is 12.99% when the UFC admixture is 0–10%. Incorporating UFC to form a compound curing agent solves the problem of the traditional reinforcement treatment of peat soil foundation being undesirable and decreases the amount of cement. This study provides practical guidance for reducing carbon emissions in actual projects. Full article

Bridges’ expansion joints are prone to damage during operation, and repairing them often requires interruption of traffic, the impact of which can be minimized by using fast-hardening and early-strength expansion joint materials. In this study, a fast-hardening polymer cement composite (PCC) was developed using sulfate aluminate cement and ordinary silicate cement as binding agents and polymer powder as admixture. To improve the crack resistance of the material, several types of fibers were added and the effects of different fiber types and admixtures on the crack resistance of the material were compared using SCB tests. The results showed that the best effect of improving the crack resistance of concrete was achieved with a volume fraction of 0.5% of basalt fibers. Then, a test method for the interfacial shear properties of PCC materials and ordinary concrete was established, and the cohesive force model was selected as the interface simulation parameter for finite element analysis and compared with experimental data to verify its feasibility. Finally, based on the previously obtained PCC material parameters, a solid model of the expansion joint anchorage zone was established to study the mechanical properties of the expansion joint anchorage zone with the application of fast-hardening PCC material. This research provides a new way to develop fast-hardening and early-strength expansion joint materials with high crack resistance. Full article

Although lignin improves the strength and modulus of soil, it is less active when unmodified, and it exhibits more limited effects on soils in combination with traditional Ca-based curing agents. Lignin-solidified soil also exhibits deficiencies, such as poor durability under dry–wet cycling conditions, and thus, the amelioration effect is limited. This study investigated the enhancement of cement-solidified soil using hydroxylated lignin with sodium silicate and quicklime used as activators to improve the engineering performance and durability of the treated soil. Using respective cement, sodium silicate, quicklime, and lignin contents of 7%, 0.4%, 0.2%, and 0.2% with respect to the dry mass of the slag soil, the strength and cohesion of the composite-solidified soil were 1.5 times those of cement-solidified soil, whereas the internal friction angle increased by 5.1°. At a solidifying age of 14 d, the penetration resistance almost doubled, indicating a significant improvement in the bearing capacity of the soil. The results suggest that modified lignin-based admixtures may significantly enhance the performance of cement-solidified soil. The cement curing admixture used in this study provides theoretical and technological support for curing agent preparation and the utilization of slag. Full article

Self-compacting concrete (SCC) is a highly flowable, self-leveling, and non-segregating type of concrete that requires no form of vibration to maintain its uniformity throughout the mixture as well as being able to perform in an outstanding manner in densely reinforced structures. The main objective of this study is to investigate the primary differences in the engineering properties of SCC using CEM-I, CEM-II/A-M, and CEM-II/B-M types of cement as the primary binding material. The properties of SCC, such as cohesiveness, stability, flowability, etc., can be modified by selecting definitive amounts of aggregates, cementitious materials, and viscosity-modifying admixtures. Therefore, it will highlight the effects of the mechanical and flow properties of the concrete mix due to the change in cement type with a similar composition and volumetric ratio to other constituent materials. The flow properties were validated using the V-funnel test, L-box test, T-500 test, and slump flow test. A comparative result highlighting the strength response, i.e., the compressive, tensile, and flexural strength of the mix designs, was recorded at 28 days, and correlations among these values were established and analyzed. Full article

A decisive aspect of site evaluation for construction is the presence of anthropogenic materials occurring in the geological environment. The geotechnical properties of blast-furnace slag were investigated as a potential substitute for aggregates in the construction industry. The basic geotechnical parameters of the slag were determined, which are critical for evaluating its stability, environmental impact, and usability in geotechnical construction. The research focused on monitoring the physical and mechanical properties of the two samples, and also included mineralogical analysis. The obtained results demonstrated that the slag belongs to the category of poorly graded gravel, G2/GP, and gravel with an admixture of fine-grained soil, G3/G-F. In addition, other important parameters, such as the water disintegration of the slag aggregate, the minimum and maximum bulk densities, the California bearing ratio (CBR), the oedometric modulus (E_oed), and shear tests (the angle of internal friction φ and cohesion c), were determined. The results from this paper provide important information for the proper management of blast-furnace slag so to minimize its environmental impact and achieve sustainability in the mining industry. At the same time, it enables a better understanding of the use of slag as a substitute for aggregates in geotechnical tasks. Despite its local importance in relation to the investigated case, the presented study has significant educational and scientific value for the construction sector, where it is necessary to evaluate anthropogenic activities and materials. Full article

The mechanical properties of the subgrade have a significant impact on the service life and pavement performance of the superstructure of pavement. By adding admixtures and via other means to strengthen the adhesion between soil particles, the strength and stiffness of the soil can be improved to ensure the long-term stability of pavement structures. In this study, a mixture of polymer particles and nanomaterials was used as a curing agent to examine the curing mechanism and mechanical properties of subgrade soil. Using microscopic experiments, the strengthening mechanism of solidified soil was analyzed with scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XDR). The results showed that with the addition of the curing agent, small cementing substances on the surface of soil minerals filled the pores between minerals. At the same time, with an increase in the curing age, the colloidal particles in the soil increased, and some of them formed large aggregate structures that gradually covered the surface of the soil particles and minerals. By enhancing the cohesiveness and integrity between different particles, the overall structure of the soil became denser. Through pH tests, it was found that the age had a certain effect on the pH of solidified soil, but the effect was not obvious. Through the comparative analysis of elements in plain soil and solidified soil, it was found that no new chemical elements were produced in the solidified soil, indicating that the curing agent does not have negative impacts on the environment. Full article

Rubber concrete (RC) exhibits high durability due to the rubber admixture. It is widely used in a large number of fatigue-resistant structures. Mesoscale studies are used to study the composition of polymers, but there is no method for fatigue simulation of RC. Therefore, this paper presents a finite element modeling approach to study the fatigue problem of RC on the mesoscale, which includes the random generation of the main components of the RC mesoscale structure. We also model the interfacial transition zone (ITZ) of aggregate mortar and the ITZ of rubber mortar. This paper combines the theory of concrete damage to plastic with the method of zero-thickness cohesive elements in the ITZ, and it is a new numerical approach. The results show that the model can simulate reasonably well the random damage pattern after RC beam load damage. The damage occurred in the middle of the beam span and tended to follow the ITZ. The model can predict the fatigue life of RC under various loads. Full article

The paper presents results of experimental and theoretical studies on transport of water-sand mixtures in steady flow with small amounts of cohesive fractions. The experiments were carried out for sand alone and with cohesive admixtures in the form of clay in the amount of 5, 10, 15 and 20% by weight. The amount of sand fractions retained in the trap and along the control area was measured. The experimental results were compared with the calculation results for transport rate of sand fractions. An intended model of the vertical structure of both sand velocity and concentration as well as vertical mixing and sorting is proposed here in order to determine the influence of cohesive admixtures on the transport of sand fractions. Hence the reduction of sand fractions transport due to cohesion forces is included. The agreement of sand transport calculations according to the extended model with measured results and experimental data from literature was achieved within plus/minus a factor of 2. Full article

Epoxy plastic, a form of epoxy resin, is widely employed in a variety of sectors due to its superior mechanical qualities and adaptability. The application of waste epoxy plastic in urban highway construction has been a major topic of study. To conduct this study, epoxy polymers are mixed with concrete to enhance the thermal and compressive resistance and tensile strength, which acts as a substitute for conventional cements. The experimental results indicate that ER concrete has good cohesive qualities since it does not collapse or peel, and the nature of the epoxy plastic guarantees that ER concrete has great mechanical capabilities due to the strong bond between the epoxy resin and the fibres. In terms of frost resistance, granular concrete with a 10% ER additive has a mass loss rate between 0.3% and 0.12% and a strength loss rate between 3.55 and 9.4%, outperforming conventional concrete. When often loaded by traffic, ER concrete exhibits no substantial permanent deformation, and its fatigue damage rate is superior to that of ordinary concrete. In total, 10% admixture of ER concrete may efficiently fulfil BPN (British Pendulum Number) and structural depth standards, while greatly improving the road’s skid resistance. In addition, its modulus of elasticity, deformation capacity, and high-temperature stability are superior to those of conventional concrete. Full article

In the context of the global pandemic of COVID-19, the use and disposal of medical masks have created a series of ethical and environmental issues. The purpose of this paper is to study and evaluate the high temperature properties and thermal storage stability of discarded-mask (DM)-modified asphalt from a multi-scale perspective using molecular dynamics (MD) simulation and experimental methods. A series of tests was conducted to evaluate the physical, rheological, thermal storage stability and microscopic properties of the samples. These tests include softening point, rotational viscosity, dynamic shear rheology (DSR), Fourier transform infrared (FT-IR) spectroscopy and molecular dynamics simulation. The results showed that the DM modifier could improve the softening point, rotational viscosity and rutting factor of the asphalt. After thermal storage, the DM-modified asphalt produced segregation. The difference in the softening point between the top and bottom of the sample increased from 2.2 °C to 17.1 °C when the DM modifier admixture was increased from 1% to 4%. FT-IR test results showed that the main component of the DM modifier was polypropylene, and the DM-modified asphalt was mainly a physical co-blending process. MD simulation results show that the DM modifier can increase the cohesive energy density (CED) and reduce the fractional free volume (FFV) of asphalt and reduce the binding energy between base asphalt and DM modifier. Multi-scale characterization reveals that DM modifiers can improve the high temperature performance and reduce the thermal storage stability of asphalt. It is noteworthy that both macroscopic tests and microscopic simulations show that 1% is an acceptable dosage level. Full article

In this paper, the effect of a newly developed superfine basalt powder (SB) on the fresh and mechanical properties of cement paste was studied. The concept of water film thickness (WFT) was cited to explain the influence of SB on fresh and mechanical properties and related mathematical model formulas were established. In addition, the relationship between the fresh properties and mechanical properties of paste was also explored. The results indicated that SB can improve the segregation resistance and cohesiveness. The maximum improvement rate relative to the control cement paste was 75.4% and 50.4%, respectively. The 5% SB and 10% SB reduced the fluidity in the range of 4.1–68.7% but increased the early and late compressive strength in the range of 1.2–25.7% compared to control cement paste under different water/cementitious materials (W/CM) ratios. However, the influence of 20% SB on fluidity and compressive strength was opposite to the above behavior, and the increase rate and decrease rate were 1.8–11.8% and 1.1–13.9% respectively. The WFT was the most important factor that determined the compressive strength, rheological parameters, and flow parameters of paste containing SB, while the substitute content of SB and WFT together determined the bleeding rate and cohesiveness. Among them, the correlation between bleeding rate and WFT increased with time. The empirical mathematical models between WFT, fresh properties, and compressive strength were established and verified by other mineral admixtures, which were successfully extended and applied to the entire field of cement-based materials Full article