Drying Cycle Tests Research Articles

Study on properties of alkali activated titanium gypsum artificial aggregate concrete

Abstract In order to solve the problem of raw material shortage and solid waste disposal in the construction industry, titanium gypsum was used as raw material to prepare titanium gypsum artificial aggregate by alkali-activated cold bonding. The physical properties and microstructure of aggregates were studied, they were used to replace natural aggregates in unfired bricks. The unburned aggregate of ternary cementitious material system (titanium gypsum, cement, silica fume) was designed, and the best artificial aggregate ratio was selected by physical performance analysis, XRD and SEM analysis. The unburned bricks were prepared by replacing natural gravel with different replacement rates. The physical properties and durability were analyzed by physical test, dry and wet cycle test, and the best utilization method was sought. Main research contents and conclusions: (1) When the ratio of titanium gypsum: cement: silica fume = 7: 2: 1, NaOH: CaO = 1: 1 as the activator, the comprehensive performance of artificial aggregate is the best. According to XRD and SEM analysis, the main products in the titanium gypsum artificial aggregate system are C-S-H and AFt. (2) The compressive strength of the unburned brick prepared by titanium gypsum artificial aggregate completely replacing natural gravel reached 31.40 MPa, and the water absorption rate was 10.18 %. The unburned brick specimens with different substitution rates showed good dry-wet cycle resistance after 15 dry-wet cycles.

Study on durability of concrete under alternating positive and negative temperature curing in plateau area

In order to investigate the durability of concrete under alternating curing from −20℃ to 20℃, different antifreeze (JB-1 type/HD-type) and different dosages (1.5 wt%/2 wt%) were chosen to carry out the study. This study used a variety of tests such as rapid freeze-thaw test, freeze-thaw-sulfate coupling test, dry and wet cycle test, electrical flux test, and drying shrinkage test, combined with NMR techniques, to comprehensively evaluate the properties and pore structure of the concrete. The results show that adding antifreeze can optimize concrete durability and pore structure under alternating curing from −20°C to 20°C. This study showed that 1.5 wt% was the optimal dose to maximize the improvement of concrete durability. Comparative analysis revealed that JB-1 type antifreeze is superior to HD-type antifreeze in enhancing the frost resistance, the freeze-thaw-sulfate coupling resistance, and the chloride ion permeation resistance of concrete, which is manifested in the relative dynamic modulus of elasticity increase of 1.5 %, compressive strength increase of 1.5 MPa, mass loss decrease of 0.12 % and electric flux decrease of 86 C. In-depth investigation reveals that the JB-1 type antifreeze agent promotes the generation of C-S-H gel by accelerating the hydration process of concrete, fills and shrinks the micropores of concrete, reduces the porosity, and improves the microstructure. However, over-addition has a reverse effect, which enhances the content of tiny bubbles and leads to a 2.4 % decrease in the relative dynamic modulus of elasticity of concrete. Meanwhile, the increase in porosity leads to an increase in the electrical flux of concrete by 151 C and shrinkage by 17.2 μm.

Investigating combined effects of saturation–desaturation cycles and cyclic stress resistance of reinforced biopolymer-treated soil

Throughout their service life, subgrades endure significant stress from cyclic traffic and seasonal moisture fluctuations. This study aims to evaluate the moisture variation and cyclic stress resistance of reinforced and biopolymer-treated soils, which were treated with varying percentages (0.25%, 0.5%, 0.75%, and 1.0%) of xanthan gum (XG) and sisal fiber, to determine the level of tolerance a subgrade can sustain. Wetting–drying (W-D) cycle tests, unconfined compressive strength (UCS) tests, and dynamic resilient modulus (DRM) tests were conducted to assess the resistance of the treated soils to moisture variation and cyclic stress. The findings indicate that biopolymer-treated specimens retained over 95% of their original mass after 15 cycles, whereas fiber-reinforced soil exhibited a 9.1% loss in mass. Furthermore, the DRM of the reinforced soil improved, demonstrating greater resistance to cyclic stress compared to biopolymer-treated soils. Fiber-reinforced soils exhibited strain-hardening responses at low cyclic stress levels and maintained stress tolerance even at high cyclic stress levels without signs of strain deformation. Conversely, the UCS of the biopolymer-treated soil surpassed that of the fiber-reinforced soil due to the brittleness of the specimens.

Analysis of the Mechanical Properties of Cured Sludge by Alkaline Excitation of Phosphogypsum

Engineering slag is a green building material that meets the requirements of contemporary sustainable development, and the solidification technology of residue is particularly important in the practical engineering of resource utilization and environmental protection. In order to reuse the waste soil and industrial waste and reduce the construction cost, the stabilization effect of adding different contents of calcium oxide, blast furnace slag and phosphogypsum to the waste soil of a township road reconstruction project was studied. The unconfined compressive strength test of calcium oxide further clarified the solidification mechanism of residual soil and helped us to obtain the optimal curing ratio. The dry and wet cycle test simulated the influence of temperature and humidity changes on the appearance, quality, strength and water resistance in actual engineering. The experimental results show that the unconfined compressive strength of the sample reaches 1.273 MPa after 7 days of curing when the mixture of 4% calcium oxide (ratio to 100% plain soil) and 16% blast furnace slag (ratio to 100% plain soil) is mixed. When the three materials were mixed, the unconfined compressive strength of 4% calcium oxide (the ratio of 35% phosphogypsum and 65% plain soil) and 16% blast furnace slag (the ratio of 35% phosphogypsum and 65% plain soil) reached 1.670 MPa and 3.107 MPa at 7 and 28 days, respectively. The curing age has a significant promoting effect on the stability of loess. The dry and wet cycle test results conclude that the specimens have good durability and stability. The results of microstructure analysis shows that a large number of ettringite and C-S-H gel were formed in the gelling system, which not only makes the original soil more stable, but also acts as a part of filling pores, and the two work together to support the soil and improve the strength.

A PINN-based modelling approach for hydromechanical behaviour of unsaturated expansive soils

Hydromechanical behaviour of unsaturated expansive soils is complex, and current constitutive models failed to accurately reproduce it. Different from conventional modelling, this study proposes a novel physics-informed neural networks (PINN)-based model utilising long short-term memory as the baseline algorithm and incorporating a physical constraint (water retention) to modify the loss function. Firstly, a series of laboratory tests on Zaoyang expansive clay, including wetting and drying cycle tests and triaxial tests, was compiled into a dataset and subsequently fed into the PINN-based model. Subsequently, a specific equation representing the soil water retention curve (SWRC) for expansive clay was derived by accounting for the influence of the void ratio, which was integrated into the PINN-based model as a physical law. The ultimate predictions from the PINN-based model are compared with experimental data of unsaturated expansive clay with excellent agreement. This study demonstrates the capability of the proposed PINN in modelling the hydromechanical response of unsaturated soils and provides an innovative approach to establish constitutive models in the unsaturated soil mechanics field.

Factors Affecting the Strength Formation Mechanism and Water Stability of Geopolymer Stabilized Phosphogypsum in Road Construction

By adjusting the content of geopolymer in geopolymer stabilized phosphogypsum (GSP) as roadbed filler, along with the mixing ratio, this paper mainly explores tendencies in the mechanical properties and water stability of GSP. This research is based on macro-mechanical properties such as unconfined compressive strength, resilience modulus, California bearing ratio and shear strength. It is also based on water stability tests, such as the water soaking test, dry and wet cycle test and expansion test, to explore changes in water stability. As for the durability of GSP, this paper is mainly based on the realization of a long time observation of mechanical properties and water stability. In the existing research, most of the stabilized phosphogypsum (PG) base material or roadbed filler consists of cement, lime, etc. In this paper, a new exploration is carried out on the composition of stabilized PG material, realized without the participation of cement. The 28 d compressive strength of GSP reaches 2.5 MPa, and over time this strength grows, which prevents the phenomenon of strength inversion that may occur in conventional cement-stabilized PG. In addition, a long-term soaking experiment was designed in this study based on the material after the strength was stabilized for up to 90 d. After the strength was steady, the GSP with the best water stability still had a softening coefficient of 80% after experiencing water immersion for 7 d. After determining the feasibility of the mechanical properties and water stability of GSP as roadbed filler, we further explored the strength formation mechanism of GSP by microscopic tests (XRD and SEM). This shows that geopolymer can stabilize PG in two main ways: one is the hydration reaction with PG to generate C-S-H gel and ettringite, and the other is to connect PG not involved in the chemical reaction to form a dense whole through generated hydration products. Geopolymer, stabilizing a high amount of PG, not only provides a new method for the consumption of PG, but also has more stable performance than cement, and has certain advantages in economy. In addition, the advantage of this study is that good performance can be achieved by simply sieving PG and adjusting the geopolymer ratio in practical engineering projects.

Reuse of Abandoned Shield Residues Stabilized by a Sustainable Binder: Assessment of Strength, Durability, and Environmental Properties

The resourceful reuse, construction, and environmental and safety hazards of shield residues in underground construction have received a lot of attention. This paper reports the assessment of shield residues generated with the underground space development through stabilization. The variations of strength, durability, and environmental properties of magnesium oxide (MgO)-activated ground granulated blast furnace slag (GGBS)-fiber material stabilized shield residues are tested by unconfined compressive strength test, direct shear test, pH test, and modified dry and soaking cycle test (acidic sulfate ion condition, pH = 5.0). Portland cement (PC)-stabilized shield residues are selected as the control group. The optimal ratio of MgO-activated GGBS-fiber-stabilized material is recommended. The test results show that the basalt fiber with 12 mm length and 0.1% ratio is designed as the optimal value. The MgO-activated GGBS-fiber-stabilized shield residues specimens with the ratio of MgO to GGBS of 1:7 display higher unconfined compressive strength (qu) and shear strength (τ). After ten dry–soaking cycles, the qu, τ, and pH of the MgO-activated GGBS-fiber-stabilized shield residues specimens decreased by 21%, 8%, and 12%, respectively, compared to those corresponding to the standard curing time. In contrast, the qu, τ, and pH of the control group were reduced by 46%, 39%, and 13%.

Study on Composite Improvement of Silt Sites by Lignin and Sodium Methylsilicate and Its Micro Mechanism

Kaifeng Zhouqiao site is located in the traffic trunk line in Gulou District of Kaifeng City. The dynamic load of urban traffic is large. In addition, the silt has poor stability of its particle skeleton structure, large porosity and poor mechanical performance. Under the action of dynamic load, the soil of the site will suffer from cracking, collapse, unstable deformation and overall stability damage. In order to enhance the stability of the soil, this paper uses sodium methylsilicate and lignin fiber to modify the site soil, evaluates the mechanical properties of the improved soil through the compression and shear tests, evaluates the durability of the improved soil through the dry wet cycle test, and reveals its modification mechanism through the micro experiment, so that the mechanical properties of the site soil can be improved, so as to achieve the purpose of repair and reinforcement. The experiment shows that the effect of improving the compressive strength of soil is the best when the content of sodium methylsilicate is 0.3%–0.5%, and the effect of improving the shear strength of soil is the best when the content of lignin is 0.5%–2%. The maximum mass loss rate of the composite modified sample after 10 dry and wet cycles is only 0.71%. The comprehensive analysis determines that the best proportion of the composite is 0.5% sodium methylsilicate and 2% lignin fiber. The modified soil has good waterproof and mechanical properties.

Damage Characteristics of Argillaceous Quartz Sandstone Mesostructure under Different Wetting-drying Conditions

Extensive water–rock interaction in the Three Gorges Reservoir area of the Yangtze River leads to rock mass deterioration along the reservoir banks. However, mineral evolution behavior and its effect on the mesostructure deterioration of rocks under the wetting–drying cycle condition remain unknown. So, the wetting–drying cycle tests were conducted on peculiar argillaceous quartz sandstone in TGRA under neutral (pH = 7) and alkaline (pH = 10) water environments. Here, we provided detailed physical and microscopy images data to determine the control mechanism of mineral behavior on the evolution of sandstone’s mesostructure. Under the neutral condition, repeated “absorption and swelling–dehydration and contraction” of clay minerals leads to the repeated physical action of “squeezing–unloading” in the interior of a rock. This results in the initiation and gradual expansion of cracks in the framework mineral quartz, exhibiting failure mode from the interior to the exterior. In contrast, under the alkaline condition, the dissolution on the surface of quartz particles leads to the expansion and connection of pores, implying that the sandstone exhibits failure mode from the exterior to the interior. Moreover, the internal mechanical analysis indicates the minerals are at high pressure because of the expansion of clay minerals in the neutral solution. However, in an alkaline water environment, the extrusion pressure of framework mineral quartz decreases significantly and is not easily broken due to increased porosity. Thus, the evolution behavior of minerals in different water environments plays an important role in the damage of the rock.

Analysis and Optimization of Hybrid Soil Properties for Gel Based Roof Tiles

Our current 21st century has seen more drastic changes in terms of environmental conditions due to global warming, climate change and deforestation. This has shown a great rise in the global temperature throughout the world. Normally, the roof top of a building is provided with tiles to protect the structural components and to create a comfortable environment. The tiles can be made of materials like clay, concrete, fly ash, lime etc. Due to the prevailing environmental challenges, there is a need for the tiles to be made as with more energy efficient material that supports thermal insulation and cost effectiveness. Aerogel and hydrogel are the gel based product that are used in our current work to enhance the thermal insulation property of the tiles. Various tests such as water absorption test, wet and dry cycle test, bending strength test, thermal conductivity test, wear and tear test are carried out on the tile to quantify its characteristics. All the above shows better value than the normal commercial tile product.

Analysis and Optimization of Hybrid Soil Properties for Gel Based Roof Tiles

Our current 21st century has seen more drastic changes in terms of environmental conditions due to global warming, climate change and deforestation. This has shown a great rise in the global temperature throughout the world. Normally, the roof top of a building is provided with tiles to protect the structural components and to create a comfortable environment. The tiles can be made of materials like clay, concrete, fly ash, lime etc. Due to the prevailing environmental challenges, there is a need for the tiles to be made as with more energy efficient material that supports thermal insulation and cost effectiveness. Aerogel and hydrogel are the gel based product that are used in our current work to enhance the thermal insulation property of the tiles. Various tests such as water absorption test, wet and dry cycle test, bending strength test, thermal conductivity test, wear and tear test are carried out on the tile to quantify its characteristics. All the above shows better value than the normal commercial tile product.

Experimental Investigation of Mechanical, Permeability, and Microstructural Properties of PVA-Improved Sand Under Dry-Wet Cycling Conditions

To improve the stability of sand slopes in Southeast Tibet, the wet–dry cycle test, immersion test, and permeability test were carried out using polyvinyl alcohol (PVA) as the improving material. The improvement effect was evaluated by considering the unconfined compressive strength. The results have revealed that the unconfined compressive strength of the improved soil significantly increased with the PVA content, while the degradation of the improved soil by wet–dry cycling and water immersion weakened. However, the permeability of the improved soil slightly decreased compared with that of unmodified soil. Through scanning electron microscopy (SEM), it was found that PVA only forms an elastic network structure in the sand to wind and connect the soil particles, but pores remain in the sand. This indicates that the addition of PVA does not affect the permeability to a great extent but greatly increases the strength. The findings of this study provide a useful reference for the practical application of PVA.

Improved testing procedures to assess the physical and mechanical properties of ceramic blocks

In Brazil, ceramic blocks have a significant share of the masonry construction market. Thus, an experimental testing program was devised to determine the physical and mechanical properties of ceramic blocks from different regions of Brazil. The experimental program included blocks from five Brazilian states and ten different producers, and the properties studied were absorption, material density, efflorescence, abrasion, compressive strength, and resistance towet-dry cycles. The purpose of determining these material properties is to set guidelines to standardize the performance of same-geometry blocks. The material density test method and the wet- and dry cycle test method are being proposed as new tests and are not usually specified in international codes. The objective of the wet and dry cycle test is to determine a durability parameter for blocks that are not subjected to freeze-thaw cycles. The analysis of the results identified important relationship between these properties. Keywords: masonry, clay, ceramic blocks, test in blocks.

Study on the Mechanical Properties of Red Clay under Drying‐Wetting Cycles

To study the mechanical properties of red clay under repeated dry and wet cycle test conditions, in this paper, the disturbed red clay in an engineering area in Liuzhou, Guangxi Province, was taken as the research object. By artificially controlling different dry and wet cycles in the laboratory, a direct shear test and triaxial consolidation drainage test were carried out on the red clay samples after different dry and wet cycles. The stress‐strain curve and change rule of corresponding c and φ values were obtained. The results showed that, in both the direct shear test and the triaxial test, the shear strength parameters of red clay decreased with an increase in the number of dry and wet cycles and the attenuation was most obvious during the first cycle. With an increase in the number of dry and wet cycles, the attenuation gradually decreased. The constitutive model of the deviatoric stress and strain curve of red clay under dry and wet cycles was a plastic‐hardening type. By analyzing the variation in parameters in the P‐H model, the relationship between c, φ, and the number of dry and wet cycles n was obtained. The results showed that the parameters had different degrees of attenuation with the action of dry and wet cycles. To explain the above rules, some samples under different drying‐wetting cycles were selected for environmental electron microscope scanning, and appropriate assumptions were made based on the microstructure.

Wetting–drying cycles enhance the release and transport of autochthonous colloidal particles in Chinese loess

Soil columns packed by Chinese loess were tested under stimulated wetting–drying cycles. The results of leaching tests showed that ACPs concentration, although changed with initial peak concentration and secondary peak concentration, eventually tended to a stable level at about 6.0 mg L−1 within 48 h. The results of wetting–drying cycle tests showed that the initial peak concentration, cumulative mass and mean size of ACPs increased with the length of drying period with the drying period. The initial peak concentration of ACPs after 90-d drying period was about nine times of that after 1 d. In addition, the release and transport of ACPs increased with the wetting–drying cycles having the same drying duration. After ten wetting–drying cycles, the initial peak concentration of ACPs for 30-d drying period increased by 35.35% and that for 15 d increased by 18.33%. The preliminary mechanisms to enhance the release and transport of ACPs include physical mechanisms of the air–water interface scouring, the shear stress of preferential flow and the collapsing pore walls by capillary pressure, and chemical mechanism of the salts dissolving of loess matrix. These findings are helpful to evaluate the risk of soil and groundwater pollution.

The impact of dry unit weight and cement content on the durability of sand–cement blends

Increasing the dry unit weight (γd) through vibration/compaction and the addition of Portland cement are among promising ground improvement procedures to enhance the endurance performance of granular materials. The present investigation intends to compute the impact of cement content (C) and γd on the durability of Osório sand–Portland cement blends. An experimental programme of wetting–drying cycle tests considering distinct γd and C was carried out to assess that influence. A steadiness of the characteristic loss of mass (CLM) during 12 wetting–drying cycles for distinct specimens (of each particular γd and C) is observed and suggests a possibility of carrying out just a few cycles, making possible to extrapolate the results up to the required 12 cycles, reducing the time needed to assess the durability of such blends. It is also shown that the CLM of each specimen is reduced on increasing the γd and C. The CLM and accumulated loss of mass of compacted sand–cement mixes during wetting–drying cycles were originally perceived in the present research to be directly associated with the porosity/cement index. This broadens the applicability of such index, demonstrating that it controls not only the strength but also endurance performance of sand–cement blends.

Experimental Research on the Durability of Stabilized Gravel Soil

This paper systematically studied the durability of stabilized gravel soil (SGS) based on the gravel-poor regions of Liaoning province. This paper focused on water stability and frost resistance of SGS from home and abroad. Two gradation schemes were designed: one is natural gravel soil (NGS), the other one is NGS with coarse aggregate. Moreover, the NGS was stabilized by cement of different contents and soil stabilizer. On the basis of the two gradation schemes, three groups of test material schemes were designed: (1) Cement-stabilized natural gravel soil (CSNGS); (2) Cement and soil stabilizer stabilized natural gravel soil; (3) Cement-stabilized natural gravel soil of skeleton dense structure. Water saturated time simulation test, dry and wet cycle test and frost resistance test were done. The results of the tests indicate that it can improve the water stability and frost resistance of SGS by the ways of adding soil stabilizer and coarse aggregate and increasing the dosage of cement properly.

Work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays

A mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory. In this approach, the adsorbed and the capillary water, as well as the micropores and macropores, are two distinct phases. An interaggregate stress considered as the work-conjugate of the macrostructural strain increment has been defined. Both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level. Other work-conjugate variables relevant for the constitutive modeling of double-porosity unsaturated media have also been identified, consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment. A hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro- and the macrostructures in expansive clays can thus be built. Based on the bounding surface concept, an anisotropic loading – collapse yield surface has been introduced to reproduce the three-dimensional mechanical behavior. To analyze the model capabilities, two series of laboratory tests consisting of multiple wetting and drying cycle tests on Boom clay and triaxial tests on Zaoyang (ZY) expansive clay were simulated. The comparisons between numerical and experimental results show that the model can reproduce with reasonable accuracy the mechanical behavior and the water retention characteristic of unsaturated expansive clays.

Electrochemical and Mechanical Durability of Cast Membranes and a Reinforced Membrane Based on Sulfonated Poly(arylene ether sulfone) for Polymer Electrolyte Fuel Cells

Abstract In this study, the electrochemical and mechanical durabilities of two types of cast membranes and a reinforced composite membrane based on sulfonated poly(arylene ether sulfone) were evaluated by OCV test and wet–dry cycle test. The composite membrane with electrospun microporous polyimide substrates showed higher mechanical stability than the cast membranes. Also, the higher the molecular weight of polymer membrane, the greater the electrochemical stability.

Weathering of Lead in Fort Irwin Firing Range Soils

This paper investigates the physical and chemical transformation of metallic lead (Pb) in Ft. Irwin firing range soils. Soil samples were collected from berms of two small arms firing ranges, an active one and an abandoned one, located in the Mojave desert. Pb bullet fragments found in field samples were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine the mechanism of metal breakdown in desert climates. Moreover, in order to further elucidate metallic Pb surface reactions, the process by which Pb fragments are subjected to field weathering conditions was simulated in the laboratory by performing wetting and drying cycle tests on the surface of metallic Pb specimens. Results indicated that metallic Pb bullet fragments recovered from the active range field samples were primarily covered by surface layers of cerussite and hydrocerussite, but litharge was also identified. In the abandoned range, hydrocerussite and metallic Pb were the predominant Pb species, but laurionite was also identified. The wetting and drying test results also confirmed the predominant presence of cerussite and hydrocerussite. In addition, the presence of copper (Cu). Overall, it seems that in these high pH desert environments, Pb would eventually form insoluble secondary minerals and therefore, its mobility is expected to be quite limited.