Leaching Depth Research Articles

Effect of mineral admixtures on the calcium leaching resistance of porous cement stabilized macadam

Porous cement stabilized macadam has a good drainage property, but the loss of strength due to calcium leaching can significantly reduce its road performance. The effect of the dosage of fly ash, silica fume, and slag powder on the calcium leaching resistance of porous cement stabilized macadam base material was investigated using the accelerated leaching method with 4 mol/L ammonium chloride. The results show that calcium leaching occurs simultaneously at multiple contact points between the internal cement paste and the leaching solution, and the leaching depth has exceeded the average thickness of the layered cemented paste within 3d. The dissolution of CH crystals and the decalcification of C-S-H gel increase the porosity of cement and reduce the strength of the base material. Volcanic ash reaction of silica fume and fly ash as well as slag powder by alkali excitation and sulfate excitation will consume CH and generate low alkalinity C-S-H gel with better dissolution resistance, which can reduce calcium leaching and delay the loss of strength. The optimum dosages of fly ash, silica fume, and slag powder are 20%, 15%, and 30%, respectively, and their optimum dosages can be estimated on the assumption that the mineral admixtures completely consume CH.

Pore evolution in extrusion-based 3D printed cementitious materials due to calcium leaching

Extrusion-based 3D printed cementitious materials (3DPC) require specific parameters to be met that will substantially impact printed part durability, particularly when exposed to aggressive external conditions. Due to the specificity of the spatial distribution of the pores, 3DPC are reported to exhibit performance anisotropy compared to cast materials. A fundamental understanding of the discrepancy in the pore evolution between the printing direction, lateral direction, and top direction is essential for calcium leaching from 3DPC in aggressive water. This research investigates pore structure evolution in 3DPC with the three directions in a 6 mol/L ammonium chloride solution. The leaching depths of the samples in the three directions were tested and compared. In addition, their porosity, maximum, median, and average pore diameters, pore size distribution, and pore morphology are investigated using optical microscope (OM) and mercury intrusion porosimetry (MIP) analysis. Significant differences were found between the leaching depths in the different directions of the 3DPC. Samples leached in the top direction show less leaching depth than in the other two directions, indicating the anisotropic nature of 3DPC. This was attributed to the different pore structures of the sample in the top direction compared to the other directions, as confirmed by OM and MIP analysis. Furthermore, the pore morphology is more irregular and elongated in the printing and lateral directions than in the top direction. In turn, the calcium leaching increases the porosity and coarsens the pore structure of 3DPC. The results of this study can be used as a reference for the application of 3DPC in aggressive water environments.

The leaching-deterioration properties and leaching mechanism of cement mortar under dry-wet cycles

The dry–wet cycle in cement mortar is essential for accelerating ion transport; however, it results in an increase in severity of durability damage. Leaching damage is a primary-contributing factor that reduces durability. Studies on calcium corrosion degradation of cement-based materials and its inhibition process during dry–wet cycles are lacking. In this work, the frequency of dry–wet cycles, concentration of soaking liquid, reduction of water–cement ratio, and incorporation of silica fume on the corrosion deterioration of cement mortar were studied. Using NH4Cl solution as the corrosion medium, the variation in leaching depth, calcium-ion dissolution, compressive strength, flexural strength, phase composition, and microstructure was analyzed. The results showed that calcium dissolution occurs during dry–wet cycles, hence the mechanical properties of the cement mortar declines, and pore expansion occurs. With the shortening of the dry–wet cycles, leaching damage increased and the dissolution rate gradually deviated from Fick's law. Increasing the concentration of NH4Cl solution significantly increased the leaching depth of mortar and accelerated the reduction of the compressive flexural strength. Reducing the water–cement ratio or adding a proper amount of silica fume effectively inhibited the dissolution rate of cement mortar and the deterioration of compressive strength and flexural strength. The results of this study provide a new insight and deeper understanding of the leaching-degradation properties and mechanisms of cement-based materials during dry–wet cycles. Furthermore, the results may be used for the inhibition of cement-based material dissolution during dry–wet cycles.

Effect of ultra-fine limestone powder on leaching resistance of cement mortar

This study investigated the effect of ultrafine limestone powder on the calcium leaching performance of cement mortar. Ammonium chloride solution (3 mol/L) was used as the accelerated medium with a controlled pH disposal, and leaching tests of cement mortar were conducted using continuous immersion and wet/dry cycles. The evolution laws of the leaching depth, calcium ion dissolution, compressive strength, flexural strength, porosity, physical phase composition and microstructure were analyzed. The results show that with the expansion of the leaching area, the mechanical properties of the mortar in the leaching environment deteriorate and the porosity increases. The coupling effect of wet/dry cycles and leaching can significantly increase the deterioration rate of mortar, and the dissolution rate gradually deviates from Fick's law. An appropriate amount of ultrafine limestone powder can reduce the porosity and improve the density of the micro-structure, thus inhibiting the leaching damage of mortar in an immersion environment. However, this degrades the structural properties of the wet/dry leaching coupling environment, and the structural properties of the mortar deteriorate faster with an increase in the ultrafine stone powder admixture.

Desalination of saline fields by soil leaching in the Karkhehnur Watershed, Iran

Abstract Since large parts of agricultural fields are saline or subjected to salinity stress, practical and efficient methods may be used for recycling fields, worldwide. The effects of the type and amount of soil leaching on the quality of saline fields, in different parts of the world have yet to be investigated. The objectives were to investigate: (1) the optimum depth of water required to decrease soil salinity of saline fields to the levels, suitable for crop production in the Karkhehnur Watershed, Khuzestan province, Iran, and (2) the most suitable method of soil surface leaching. Four different regions were selected for the experiment, and a wide range of soil-related parameters as well as water properties was determined. Soil leaching was conducted by surface continuous irrigation (three regions), and surface alternative irrigation (one region). The depths of soil leaching were equal to 0–25, 25–50, 50–75, 75–100, 100–125, and 125–150 cm. The class of salinity was changed to S2 (EC = 24 dS/m) from an initial class of S4 (EC = 87 dS/m) using a water depth of 25–125 cm in different experimental regions. If soil is highly saline, continuous irrigation may be a more effective method, however, under less stressful conditions, alternative irrigation can also be recommendable.

Investigation of leaching in steel fiber-reinforced shotcrete exposed to fresh and saline groundwater in a subsea road tunnel

The field and laboratory investigations performed in the Frøya subsea road tunnel, constructed between 1998 and 2000, focus on the degree of leaching undergone by steel fiber-reinforced shotcrete in fresh and saline groundwater. Shotcrete samples were extracted by core drilling at two locations: in the middle of the tunnel approximately 150 m below sea level, and near one of the portals. Leaching is only evident in the first location identified by portlandite reduction, potassium reduction, shotcrete density reduction, and suction porosity increase towards the traffic room. The leached depth is approximately 9 cm.

Evaluating soil water and salt transport in response to varied rainfall events and hydrological years under brackish water irrigation in the North China Plain

• Responses of soil water and salt dynamics to varied rainfall events and hydrological years were evaluated. • Salt leaching and deep drainage occurred mainly due to summer-concentrated rainfall during wet year. • Salt decrease percentage in the CL was greater than that in the GL in all hydrological years. • One brackish water irrigation application is avail salt leaching both in cropland and grassland. Soil salination challenges sustainable agricultural production and management in the lowland area of the North China Plain (NCP). This study investigated the effect of varied rainfall events and hydrological years on deep drainage and salt leaching in Nanpi County in the NCP. Field experiments were conducted to measure soil matric potential (SMP) and soil water electrical conductivity (EC w ) in 300 cm profiles of an irrigated cropland (CL) and unirrigated grassland (GL). The HYDRUS-1D model was calibrated and validated to optimize soil water and salt transport parameters using the SMP and EC w data obtained in 2015 and 2016, respectively. The results showed that the HYDRUS-1D model was reliable to simulate soil water and salt migration in 300 cm profiles at both sites. The salt leaching depths and degrees were positively correlated with precipitation amount. The heavy rain (45 mm) and rainstorm (68 mm) favored salt leaching within 100 cm, and severe and extreme rainstorms resulted in salt leaching within 150–200 cm both in the CL and GL. The SDP in the CL was greater than that in the GL in all hydrological years owing to agricultural cultivation and irrigation. Salt leaching in the 300 cm profiles mainly occurred in the rainy seasons of wet year, with the salt decrease percentage (SDP) being 61% in the CL and 42% in the GL. Salt leaching due to precipitation was sufficient in the irrigated CL in all hydrological years, and precipitation in normal rainfall years could remove 70–80% of soil salts within 50–63 cm soil depth. Grass growth without irrigation led to water deficits and salt accumulation when the annual precipitation amount was less than that in wet years. The results demonstrated that precipitation, combined with irrigation using of brackish and freshwater, could be usefully for soil salt leaching. A recommended irrigation scheme for water saving and salt control in CL and GL is one brackish water irrigation application and three freshwater irrigation applications each year in the NCP.

Effect of Leaching Behavior on the Geometric and Hydraulic Characteristics of Concrete Fracture.

The leaching of material from concrete fracture surfaces has an impact on the structural concrete in service, but the number of studies that consider the effect of the coupling of the leaching, fracture geometry and hydraulic processes on concrete fractures is insufficient. In this study, a series of experiments was conducted, and a leaching model proposed, to investigate the mechanism of leaching behavior on the geometric and hydraulic characteristics of concrete fractures. Following the leaching experiment, the evolution of fracture geometric characteristics was observed by a three-dimensional (3D) laser scanning technique, finding that the fracture produces residual leached depth and local uneven leaching, which results in a decrease in roughness. The hydraulic characteristics were then investigated by permeability tests, and it was found that the fracture hydraulic aperture and permeability increase monotonically with leaching time. A simulation of fluid flow in a numerical fracture revealed the effect of residual leached depth and a decrease in roughness on the hydraulic characteristics. Finally, based on the analysis of the chemical composition of the leaching solution, a leaching model of concrete rough fracture surface is proposed and the mechanism of leaching behavior is discussed. These new findings are useful for the understanding of the development of leaching, local to concrete fracture surfaces.

Study on vibratory leaching behavior and damage evolution of cement stabilized macadam (CSM)

Leaching is one of the main causes of water damage to the highway base, which can aggravate under the vibrations of the highway load and substantially deteriorate the durability of highway. To investigate the effect of the leaching of cement stabilized macadam (CSM) under vibration condition, a new method was reported in this study accelerate the leaching of CSM in a laboratory by changing the parameters such as vibration frequency, vibration time, leaching medium, etc. The vibration leaching behavior and damage evolution of CSM were studied by comparing the results of the vibration non-leaching test and the vibration leaching test. The main test indexes were calcium ion concentration, pH, leaching depth, ultrasonic wave velocity, unconfined compressive strength, splitting strength and acoustic emission amplitude. The results indicated that vibration could accelerate the leaching efficiency, and the acceleration effect can be changed by changing the vibration frequency. The performance of CSM considerably deteriorated due to leaching. With the increase in the leaching time, the leaching depth increased continuously, and the unconfined compressive strength and splitting strength decreased considerably; moreover, the damage accumulation increased. The durability of CSM was substantially reduced. The effect of the leaching of low-dose CSM is more obvious than that of high-dose CSM.

Leaching potential of S-metolachlor in a medium-textured Oxisol soil with bioindicator plants

ABSTRACT Information about the impact of herbicides in the soil based on the growth of bioindicator species is extremely useful in developing crop management strategies. Therefore, this study aims to evaluate the leaching potential of the herbicide S-metolachlor under different natural precipitations in medium-textured Oxisol using bioindicator plants. A completely randomized experimental design was adopted, with four replicates and treatments arranged in a 3 × 8 factorial scheme [three indexes of precipitation occurred in the environment before the collection of the samples (50, 91, and 131 mm) and eight depths in the soil profile (0-0.03; 0.03-0.06; 0.06-0.09; 0.09-0.12; 0.12-0.15; 0.15-0.20; 0.20-0.25; 0.25-0.30 m)]. PVC columns were used, maintaining the original soil integrity during sampling after accumulating the stipulated natural precipitation. Longitudinal sections separated the columns to sow the bioindicator species (cucumber, lettuce, Alexander grass, and sorghum). The phytotoxicity symptoms of bioindicator plants were evaluated, adopting a phytotoxicity visual scale between 0 and 100%, at 5, 7, 9, and 11 days after seeding. The responses of the bioindicator species to the residual effect of the herbicide S-metolachlor were variable and depended on the rainfall level. Generally, in a medium-textured Oxisol, the higher values of concentration of S-metolachlor occurs in depths ranging between 0 and 0.06 m. The maximum leaching depth detected was 0.12-0.15 m with 131 mm of precipitation. Cucumber was the most sensitive species to the presence of S-metolachlor in an Oxisol of medium-texture since it presents symptoms of phytotoxicity at higher depths.

Chloride profiles with a peak – why and what are the consequences for predictions?

Chloride ingress profiles do almost always have a peak at some depth but most prediction models are missing this peak. Some prediction models, such as the fib model, simply “cut off” a slice of the concrete up to the peak in further predictions. Other prediction models use data only from the profiles beyond the peak but include the concrete up to the peak as if it has the same properties as the rest of the concrete. A physical model has been developed to quantify the local changes because of leaching and the consequences of these changes with time. The model uses Fick’s 1st law for chloride diffusion and linear chloride binding. The depth of leaching with time is modelled with a simple square-root equation. The consequences of leaching are assumed to be linear from the surface into the maximum depth of leaching. The consequences of leaching are modelled as depth-dependent changes of porosity, chloride binding and the diffusion coefficient in Fick’s first law.

Influence of temperature history on calcium leaching resistance of hydraulic concrete

In order to find out how temperature history affect leaching resistance, the leaching depths and compressive strength loss rate of pastes under three different temperature histories have been studied, the result shows that, with the progress of leaching, the compressive strength of samples continue to decrease, but the rate of decrease gradually slows down, and the leaching resistance of temperature match curing cured sample is better than that of standard curing cured, while the leaching resistance of circadian cycle curing cured sample is worse than that of standard curing cured.

Experimental and numerical study of the effects of solution concentration and temperature on concrete under external sulfate attack

The work reports on an experimental programme, conducted to validate comprehensively our previously proposed coupled chemo-transport model for external sulfate attack on concrete. Specifically, the effects of the concentration of sulfate solution and temperature on the distribution of sulfate ions in concrete are experimentally investigated and used to demonstrate the accuracy of the modeling framework. Further, the profile of aluminate depletion and the leaching depth numerically are investigated. For all cases the model predictions are in good agreement with the experimental results, showing increases of the concentration of sulfate ions in concrete with higher concentrations of sulfate solution and higher temperatures. It is concluded that higher sulfate solution concentration and temperature enhance the processes involved in the external sulfate attack on concrete, namely diffusion of sulfate ions and their chemical reactions with concrete. It is found that these parameters affect the external sulfate attack predominantly via the chemical reaction process.

Evaluating the saline water irrigation schemes using a distributed agro-hydrological model

Quantitatively assessing the practicality and sustainability of saline groundwater for irrigation at the regional level could provide a valuable reference for macro decision-making and management in terms of alleviating the severe contradiction between freshwater shortages and food production. In this study, the distributed agro-hydrological SWAP-WOFOST (Soil-Water-Atmosphere-Plant-WOrld FOod STudy) model was applied in the east-central North China Plain (NCP). The model was used to simulate the five saline water irrigation scenarios for a 20-year period, and the effects on the spatiotemporal variations in crop yield, water productivity (WP), and soil water and salt balances were analyzed. Furthermore, appropriate saline water irrigation schemes were solved considering crop yield reduction and soil salt accumulation. Finally, spatial matching between the appropriate irrigation schemes and saline groundwater resources from the perspectives of “water quality” and “water quantity” was evaluated. The main results were as follows. (1) The average yield and WP of winter wheat during the simulation period remained stable or increased slightly under saline water (2–6 g L−1) irrigation for winter wheat compared with that under freshwater irrigation, whereas the average yield and WP of the following summer maize decreased to varying degrees. (2) When the sum of seasonal precipitation and irrigation of summer maize was >450 mm, 401–450 mm, 351–400 mm, 200–350 mm and <200 mm, the average soil salt leaching depth was approximately 120 cm, 100 cm, 80 cm, 60 cm and 40 cm, respectively. (3) On the premise that the average salt content of the 2-m soil profile at summer maize harvest during the simulation period was less than 3 g kg−1, if the average crop yield reduction of the rotation system in the range of ≤500 kg hm−2, ≤1000 kg hm−2, ≤1500 kg hm−2 and ≤2000 kg hm−2 was permitted, the dominant maximum irrigation water salinity in the study area was 3 g L−1, 4 g L−1, 6 g L−1 and 6 g L−1, respectively. (4) The average saline water amount needed for winter wheat irrigation during the simulation period was approximately 22.78 × 108 m3, which was approximately 9% more than the exploitable amount of saline groundwater. The results could support decision-making related to developing and using shallow saline groundwater for irrigation.

Rheology of Pastes Containing High-Volume Fly Ash and Their Permeability Because of Calcium Leaching Procedure in Ammonium Chloride Solution

Abstract This article presents the findings of a research program that concern the rheology of fresh paste containing high-volume fly ash and its permeability because of calcium leaching procedure after 90 days’ curing. In a fresh state, the combined influence of fly ash content and water addition time on Herschel–Bulkley parameters was investigated. The critical value of fly ash content and water addition time was defined. In a hardened state, ammonium chloride (NH4Cl) was chosen as the accelerate leachant based on the comparison of microscale effect of ammonium nitrate (NH4NO3) and NH4Cl solution as well as leaching mechanism establishment. At specified leaching durations, the leached depth and porosity and permeability coefficient of both sound and deteriorated paste specimens were tested. It was indicated that both the porosity increment and permeability coefficient increment have a linear relation to the square root of leached ratio. Additionally, the velocity of the porosity increment declines with fly ash content, whereas the velocity of permeability coefficient increment declines with fly ash content at first and increases slightly when the fly ash dosage ranges from 40 % to 60 %. It can be concluded that fly ash was effective in improving leaching resistance. Finally, the relevance of fresh and hardened behavior was proposed.

Soil salinity and moisture content under non-native Tamarix species

This study investigated, soil salinity and moisture content under the exotic Tamarix in the Olifants River, South Africa, where they predominantly occur. Soil electro-conductivity (EC) was mapped using the electromagnetic induction (EMI) device (EM38 sensor), in three transects laid along the river from as close to the water source outward towards the bank of the River at 50 m apart. This was supported by three soil EC and moisture measurements from each of the three transects at a soil depth of 0–100 cm at intervals of 10 cm using soil EC meter and Amplitude Domain Reflectometry (ADR) sensor, respectively. The highest salt concertation (3,000 mS/m or 19,500 ppm) was found at a depth of 30–40 cm under the dense Tamarix species. The highest soil moisture (20–40%) was also found at the same depth under the Tamarix, suggesting a hydraulic lift of water to the top 30–40 cm, where the Tamarix fine roots for water absorption occur. It also confirms that the distance from water point and Tamarix plant density affect salt leaching depth and amount of litter decomposition, respectively, which is the main source of salt deposition in soil.

Experimental study on leaching-abrasion behavior of concrete in flowing solution with low velocity

In order to study the influence of flowing velocity of solution on the leaching-abrasion behavior of concrete, this paper conducts a series of accelerated corrosion experiments on specimens in 1 M ammonium chloride solution with 0.0, 0.5, 1.0 and 2.5 m/s. The leaching-abrasion behavior of the specimens, characterized by the leaching depth, porosity, phase composition, microstructure morphology and hydration product of its surface, was investigated by using the phenolphthalein indicator, saturation-drying weighing, X-ray diffraction (XRD), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). Additionally, the boundary movement of specimen caused by the abrasion of flowing solution was also studied. Results showed that, higher flowing velocity of solution results in higher leaching depth and porosity in specimen. With the increase in flowing velocity of solution, the compactness of microstructure and the content of cement-hydrated products on the surface of specimen decrease first and then increase, but at a certain flowing velocity, the content of C-S-H gel is basically constant at its surface when the boundary of specimen moves. Finally, the boundary movement condition of specimen in flowing solution was proposed.

Influence of Nano-silica on the Leaching Attack upon Photocatalytic Cement Mortars

Photocatalytic cementitious materials are used in the exterior of the buildings and infrastructure for self-cleaning and air-purifying purposes. These materials are exposed to the aggressive exposure conditions like acid rain, runoff water and are subjected to the deterioration due to the leaching of calcium. The knowledge of leaching attack upon photocatalytic cementitious materials after the addition of nano-materials is necessary. In the current study, the influence of nano-silica addition on the leaching attack upon photocatalytic cement mortars was thoroughly investigated. For this purpose, photocatalytic mortars were made by adding 3% TiO2 and variable amount (0–2%) of nano-silica. Accelerated leaching environment was created by immersing mortars in 6 M ammonium nitrate (NH4NO3) solution. The progressive development of the leaching depth in mortars was measured. The loss of hardened properties was monitored by evaluating the compressive strength, flexural strength, porosity, and dynamic modulus of elasticity. X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy, scanning electron microscopy tests were conducted to know the microstructural deteriorations. Results indicated that the leaching attack induced mechanical and microstructural damages in the mortars, but the addition of nano-silica decreased mechanical and microstructural damages in the photocatalytic mortars and increased the resistance of photocatalytic mortars to leaching attack.

Effects of calcium leaching on the physical and mechanical properties of aerial lime-cement mortars

PurposeThis paper aims to assess the effects of chemically accelerated leaching on the physical and mechanical properties of aerial lime–cement mortars (LCMs).Design/methodology/approachTwo aerial LCMs, differencing mainly in their calcium hydroxide content, were degraded by the use of an ammonium nitrate solution as a leaching agent. The leaching effects were studied by evaluating the rate of change in physical (sorptivity and mass loss) and mechanical (flexural and compressive strength) characteristics of aerial LCMs. To quantify the evolution and kinetics of degradation, the leached depth was then characterized at different levels of degradation by means of a phenolphthalein solution.FindingsThe experimental results showed that the dissolution of binder decreases the mass, alkalinity and strength of aerial LCMs but increases their sorptivity. A linear relationship was derived by plotting the values of leached depth against the square root of immersion time in an aggressive solution. It was found that the leached depth followed diffusion-controlled kinetics.Originality/valueIt was found that the global loss of compressive strength of aerial LCMs because of complete dissolution of calcium hydroxide can reach up to 80 per cent.

Electrochemical Characterization and Inhibiting Mechanism on Calcium Leaching of Graphene Oxide Reinforced Cement Composites.

Calcium leaching is a degradation progress inside hardened cement composites, where Ca2+ ions in cement pore solution can migrate into the aggressive solution. In this work, calcium leaching of graphene oxide (GO) reinforced cement composites was effectively characterized by combined techniques of electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). Inhibiting mechanism of GO on calcium leaching of the composites was also examined. The obtained results show that the diameter of the semi-circle of the Nyquist curves of leached samples with GO addition decreased less than that of controlled samples. After leaching for 35 days, loss rate of model impedance RCCP of leached samples with 0, 0.05, 0.1, 0.15, and 0.2 wt.% GO addition was 94.85%, 84.07%, 79.66%, 75.34%, and 68.75%, respectively. Therefore, GO addition can significantly mitigate calcium leaching of cement composites, since it can absorb Ca2+ ions in cement pore solution, as well as improve the microstructure of the composites. In addition, coupling leaching depth and compressive strength loss were accurately predicted by using the impedance RCCP.