Water Sorptivity Research Articles

Use of recycled mortar as fine aggregates in pavement concrete applications

The use of recycled aggregates derived from construction and demolition wastes increased in the concrete construction industry. While the coarse fraction (i.e., from 5 to 20 mm) was successfully recycled, the fine fraction (i.e., from 0 to 5 mm) is hardly recyclable given its heterogenous nature and poor physical properties. This paper assesses the feasibility of recycled mortar aggregate (RMA) in pavement concrete applications requiring superior resistance to weathering and wearing effects. Three concrete strength grade categories prepared with different water-to-binder ratios (w/b) of 0.4, 0.5, and 0.6 are investigated; the natural sand replacement levels by RMA varied from 0 % to 60 % by volume, at 20 % increment rates. Test results showed that the detrimental RMA effect on durability depends on the concrete strength category, requiring proper adjustment of the maximum replacement rate to maintain acceptable losses in performance. Hence, the higher strength grade mixtures prepared with 0.4 w/b were found to yield significant drops in durability reaching 25 % in water sorptivity, 18 % in abrasion, and 22 % due to freeze/thaw (F/T) cycles. In contrast, the lower strength grade concrete made with 0.6 w/b exhibited marginal degradation in strength and durability, despite the incorporation of 60 % RMA. The resulting losses in sorptivity, abrasion, and F/T cycles were limited to 13 %, 8 %, and 12 %, respectively.

Preparing hydrophobic alkali-activated slag mortar with lotus-leaf-like microstructure by adding polydimethylsiloxane (PDMS)

In this study, polydimethylsiloxane (PDMS) was applied for overall hydrophobic modification of alkali-activated slag (AAS) mortars aiming to reduce its high water sorptivity. The effects of the amount and viscosity of PDMS on the water absorption characteristics and mechanical properties of AAS mortars were investigated. Meanwhile, MIP, the surface contact angle of AAS mortars and SEM-EDS, Inverse gas chromatography (IGC), FT-IR, XRD of hardened AAS pastes were performed for analyzing the modification mechanisms. The results indicated that the water sorptivity of PDMS-modified AAS mortar decreased by 90 %, and the contact angle of the inner surface increased from 14° to 128° when the dosage of PDMS reached 8 % (by weight of binder). The main modification mechanisms of PDMS in AAS system can be summarized as: Firstly, the formation of hydrophobic coatings on the surface due to the cross-linking reaction between C-S-H gel and PDMS reduces the surface energy and the hydrophilicity of hardened AAS pastes, achieving chemical modification; Secondly, the hierarchical structures formed by micro papillary increases the surface roughness, thus enhancing the hydrophobic effect further through physical modification. Moreover, the coarsening of capillary pores also reduces the capillary force during water absorption process. Meanwhile, the addition of PMDS maintains comparable strength development of AAS mortars, which is beneficial for the practical application.

Assessment of Water Transport and Chemical Attack of Meta-Illite Calcined Clay Blended Cement in High-Performance Concrete.

Rapid urbanisation causes a rise in the need for infrastructure, which in turn fuels the creation of additional concrete and further increases cement supplies. Activation of illite-based clay mineral and usage in concrete production is one of the sustainable ways to address the cement industry anthropogenic issues. This study evaluates the durability properties of water transport (water absorption, and capillary water absorption), and resistance to aggressive environments (5% solutions of hydrochloric acid, HCl; sodium sulphate, Na2SO4; and calcium chloride, CaCl2) of meta-illite calcined clay (MCC)-based high-performance concrete (HPC). For this purpose, concrete was produced with 5, 10, 15, 20, 25 and 30% MCC content in partial substitution of CEM II. Results from the water absorption tests indicate an average percentage value of 3.57%, 3.35% and 2.52% for all the observed mixes at 28, 56 and 90 days, respectively, with MCCC-10 HPC having an average best value of 2.23% across the curing ages. On all observed days, the 5 to 15% cement replacements had very close average water sorptivity value of 0.125 ± 0.001 mm/min0.5 with the control mix (0.113 ± 0.011 mm/min0.5). The aggressive environments exposure findings of the hardened MCC-based HPC specimens of 10 to 20% recorded an approximately 15% compressive strength loss in HCl, Na2SO4 and CaCl2 solutions over the 90 days of curing. In all, the HPC mixes of 5 to 15% MCC content obtained an average durability performance factor of 89%. As a result, these findings imply that MCC can replace cement in up to 15% of HPC production.

Influence of multi-stage processing and mechano-chemical treatments on the hydration and microstructure properties of recycled aggregate concrete

On account of the shortage of naturally occurring coarse aggregate, recycled aggregate (RA) made from crushed concrete debris is now used in the construction industry. With this rise in the utilisation of recycled aggregate in the construction sector, there has been extensive research into ways to improve its quality. The significant fraction of mortar remains that are left on the RA surface is the primary factor that affects its quality. Concrete made from RA loses strength and mechanical performance due to the attached mortar's increased porosity and water absorption values and the frailer transition region between the new mortar and aggregates. In order to minimise the old cement fractions and increase the quality, this paper studies the effect of concrete incorporating multi-stage processed RA from demolished concrete waste, followed by treatment with mechanical abrasion and sodium silicate immersion. The recycled aggregates were produced through multi-stage jaw crushing, followed by utilising natural aggregate, recycled aggregate, and recycled aggregate obtained after mechanical abrasion, followed by sodium silicate treatment for concrete mix design at various substitution percentages as coarse aggregates. The experimental investigation further progresses with the evaluation of mechanical and durability properties of concrete mixes, which is additionally followed by microstructural studies such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetry-differential thermal analysis (TG-DTA). The outcomes demonstrate that two-stage treatment, such as mechanical abrasion followed by sodium silicate immersion, yields superior-quality RA. Recycled aggregate concrete (RAC) made with these treated aggregates illustrated an increase in workability and density with respect to an untreated RAC mix. Furthermore, comparable strengths in compression, flexure, and tension are found in treated RAC mixes, particularly at 35% replacement levels, with respect to concrete mixes comprised of natural aggregates. A similar trend is detected in the chloride penetration tests and water sorptivity tests. In addition, the microstructural investigation confirmed the formation of additional calcium silicate hydrate for treated RAC mixes, particularly for the 35% substituted RA mix. On the basis of the results, it is suggested that multi-stage jaw crushing followed by treatment through mechanical abrasion and sodium silicate can potentially enhance the mechanical, microstructural, and durability performance of RAC.

Investigation on the surface hardness and durability-related properties of concrete containing coconut shell as partial substitute to coarse aggregates

Purpose Using coconut shell aggregates (CSA) in concrete benefits agricultural waste management and reduces the demand for mineral resources. Several studies have found that concrete containing CSA can achieve strengths that are comparable to regular concrete. The purpose of the present work is to evaluate the concrete’s durability-related properties to supplement these earlier findings. Design/methodology/approach Cylindrical specimens were prepared with a constant water–cement ratio of 0.50 and CSA content ranging from 0% to 50% (at 10% increment) by volume of the total coarse aggregates. The specimens were cured for 28 days and then tested for density, surface hardness, electrical resistivity and water sorptivity. The surface hardness was measured to describe the concrete resistance to surface wearing, while the resistivity and sorptivity were evaluated to describe the material’s resistance to fluid penetration. Findings The results showed that the surface hardness of concrete remained on average at 325 Leeb and did not change significantly with CSA addition. The distribution of surface hardness was also similar across all CSA groups, with the interquartile range averaging 59 Leeb. These results suggest that the cement paste and gravel stiffness had a more pronounced influence on the surface hardness than CSA. On the other hand, concrete became lighter by about 9%, had lower resistivity by 80% and had significantly higher initial sorptivity by up to 110%, when 50% of its natural gravel was replaced with CSA. Future work may be done to improve the durability of CSA when used as coarse aggregate. Originality/value The present study is the first to show the lack of correlation between CSA content and surface hardness. It would mean that the surface hardness test may not completely capture the porous nature of CSA-added concrete. The paper concludes that without additional treatment prior to mixing, CSA may be limited only to applications where concrete is not in constant contact with water or deleterious substances.

Influence of graphene oxide on the long-term durability behaviour of high-strength rubberised concrete

Applying waste tire rubber as rubber aggregate (RA) in concrete is advantageous from the perspective of environmental sustainability. This study examines the action of graphene oxide (GO) on the durability properties of high-strength rubberised concrete (RC). The durability characteristics of concrete were assessed with the help of acid attack, water sorptivity, and rapid chloride penetration test (RCPT) on the hardened concrete specimens for the test periods of 7, 28, 56, and 90 days each. Acid attack tests (mass loss and compressive strength loss) were performed after immersing the concrete specimens in hydrochloric (HCl) and sulphuric (H2SO4) acids for the stipulated periods. The increased mass and compressive strength losses were observed with the incorporation of RA in concrete, which was finally mitigated by the action of GO in concrete. Water absorption was increased by RA alone but was reduced after the incorporation of GO in this RC. It was also observed that the chloride penetration was reduced after the incorporation of RA and GO in conventional concrete (CC). This study concludes that GO excellently strengthens the long-term durability properties of the RC.

Microstructure and Water Retention Kinetics in Autogenous Cured Self-Compacting Concrete Blends Using Super Absorbent Polymer.

This research aimed to determine how a super absorbent polymer affects the microstructural characteristics and water retention kinetics of a new composite made by substituting granite pulver (GP) and fly ash (FA) for cement. Understanding the mechanics of water movement is crucial for comprehending the effectiveness of autogenous curing. Several experiments were conducted to analyze the water mitigation kinetics of super absorbent polymer (SAP) in the hydrating cement paste of autogenous cured self-compacting concrete (GP-ACSSC) mixtures. In the first hours following casting, water sorptivity, water retention, and hydration tests were carried out. The effects of various concentrations of SAP and GP, which was utilized as an alternative cement for the production of sustainable concrete that leads to reduction in carbon footprint, on the autogenous cured self-compacting concrete with reference to the abovementioned properties were explored. The investigation showed that releasing the curing water at a young age, even around the beginning of hydration, allowed homogenous and almost immediate distribution of water across the full cured paste volume, which improved the water retention kinetics. Compared to the control mixtures, the addition of SAP up to 0.6% and the substitution of cement with GP up to 15% had favorable impacts on all water kinetics parameters.

Assessing Microplastic-Induced Changes in Sandy Soil Properties and Crop Growth

An ever-increasing amount of microplastics enters the environment and affects soil properties and plant growth. Investigating how the interactions between microplastics and soil properties vary across different soil types is crucial. In sandy soil, the subcritical SWR induced by microplastics may affect other soil properties. The objective of this study was to assess the impact of adding three types of microplastics (high-density polyethylene, polyvinyl chloride, and polystyrene) at a concentration of 5% (w/w) to sandy soil on the persistence and severity of SWR, as well as on various soil properties (bulk density, water sorptivity, and hydraulic conductivity) and plant characteristics (fresh and dry weight, maximum photochemical efficiency of PSII, and nutrient content) of radish (Raphanus sativus L.). It was found that microplastic contamination increased the persistence and severity of SWR and decreased soil bulk density, water sorptivity, and hydraulic conductivity. The total biomass measurements did not reveal a significant difference between the microplastic treatments and the control group. This study did not confirm any significant influence of microplastic contamination on the maximum photochemical efficiency of PSII, a measure of crop photosynthesis. Even though the value of photosynthetic efficiency changed with time, the values for all treatments stabilised at the end of the experiment. Microplastic contamination did not significantly alter crops’ nitrogen, phosphorus, potassium, or zinc contents. However, the copper content was reduced in all treatments, and magnesium and iron were reduced in the PVC and PS treatments compared to the control. The microplastic-induced changes in biomass or photosynthetic efficiency do not correspond to the changes in crop element concentrations.

Assessment of Wood Bio-Concrete Properties Modified with Silane-Siloxane.

Bio-based materials, such as wood bio-concrete (WBC), hold promise in reducing energy consumption and carbon footprint of the construction industry. However, the durability of these materials is not well understood and can be negatively affected by the high water absorption capacity of wood bio-aggregates. In the field of cement composites, for example, silane-siloxane-based water repellent has been used to protect such materials from natural environmental attack. Nevertheless, there is still a limited understanding of various aspects related to this type of treatment, including its performance when applied to the bio-concrete substrate. This research aimed to investigate the influence of silane-siloxane on the rheology and hydration of cementitious paste through isothermal calorimetry and thermogravimetric analysis. Additionally, the impact of silane-siloxane on the physical and mechanical properties of WBCs was examined by conducting tests at fresh state (flow table and entrained air content) and hardened state (compressive strength and capillary water absorption). The composites were produced with a volumetric fraction of 45% of wood shavings while the cement matrix consisted of a combination of cement, rice husk ash, and fly ash. Silane-siloxane was applied in three ways: as coating, incorporated as an admixture, and in a combination of both methods. The results indicated that by incorporating silane in the cementitious pastethe viscosity increased by 40% and the hydration was delayed by approximately 6 h when compared to the reference. In addition, silane improved the compressive strength of WBCs by 24% when incorporated into the mixture, expressively reduced the water sorptivity of WBCs (93%), and was more effective if used as coating.

Effect of silica fume and PCE-HPMC on LC3 mortar: Microstructure, statistical optimization and life cycle Assessment

With immense carbon emissions, the cement and concrete industries account for nearly eight percent of the world’s total. As the demand for urbanisation increases, the carbon footprint of the industry will also increase rapidly. A sustainable and greener low carbon cement called limestone calcined clay cement (LC3) is being developed as a promising alternative to ordinary Portland cement (OPC). The present study investigates the effects of silica fume (SF) on LC3 with variable dosages of polycarboxylate ether-based superplasticizer (SP) and hydroxypropyl methylcellulose (HPMC) admixtures. Using three level-three factorial (33) Box Behnken Design and response surface methodology (RSM), SF content, SP content, HPMC content, and flow value were set as input parameters to optimise and evaluate the eight output response parameters, namely, water binder (w/b) ratio, compressive strength (7 and 28 days), modulus of rupture, porosity, water absorption, ultrasonic pulse velocity, and water sorptivity. With a combined desirability of 90.8% for an optimised mix, the model showed that with 0% SF, 0.811% SP, 0.923% HPMC, and 124.12 mm of FV, a LC3-50-based cement system with higher physico-mechanical properties can be developed. The microstructural analysis was also conducted through a scanning electron microscope (SEM), Thermogravimetric Analyzer (TGA), and X-ray diffraction (XRD). The results showed Calcium silicate hydrate (C-S-H) development along with consumption of portlandite (CH) for LC3-50-based cement systems. Sustainability analysis of LC3-based mortar in terms of carbon emissions showed a 33.82% reduction in CO2 emissions as compared to OPC.

Performance evaluation of ternary blended cement concrete partially replacement of natural sand with granite quarry dust

Cementitious composites are the most frequently used man-made material, with a 25 billion tonne manufacturing volume and 5% greenhouse gas emissions. Concrete composites release a lot of CO2 into the environment. Thus, replacing concrete composite raw material is a priority. To reduce this industry's carbon footprint, large-scale reuse of industrial byproducts, including Fly Ash (FA), Silica Fume (SF), and Ground Granulated Blast-Furnace Slag (GGBS) in cementitious composites, is growing. This method addresses the waste management for industry byproducts in two ways. The mechanical strength and durability of cementitious composite products with many ingredients must be recognised. This study's major goal is to evaluate high-strength cementitious composites' mechanical strength and durability. FA (20%, 30%, and 40%), SF (5%, 7.5%, and 10%), and GGBS (10%, 15%, and 20%) binder were used to make high-strength cementitious composites. Waste management has developed into a problem for the environment. The illegal and unethical practices involved in mining natural river sand (NRS) have gotten worse. Therefore, by substituting Granite Quarry Dust (GQD) for fine aggregate, the lack of NRS for a building is prevented. GQD was employed to replace natural river sand at different levels of replacement as the fine aggregate phase in 10%, 20%, and 30%. The fresh cementitious composites properties were evaluated, strength properties such as compressive strength, flexural strength, and split tensile strength were also evaluated and additionally, the durability characteristics such as water sorptivity and the Rapid Chloride Permeability Test (RCPT). We shall evaluate it with normal concrete based on the results.

Resistance of ordinary and low-carbon cements to carbonation: Microstructural and mineralogical alteration

The rising demand for green construction materials has led to tremendous research efforts towards the development of low-carbon cements, although their carbonation resistance is expected to be lower than that of ordinary Portland cement (OPC). This study aims to assess the carbonation resistance of various cements by thoroughly investigating the changes in the microstructure and mineralogy under accelerated carbonation conditions, which have not been comprehensively described in the literature, especially for blended cements. Two types of materials were investigated: cement pastes made from type CEM I and III cements and mortars with the same water/cement ratio of 0.55. Various analytical techniques have been used to examine microstructural and mineralogical alterations as a function of carbonation duration. It was demonstrated that CEM III cement pastes exhibited the fastest carbonation rate, whereas CEM I cement pastes had the largest CO2 uptake owing to carbonation. The mass change of carbonated materials and the carbonation depth were found to be well correlated. Overall, carbonation refines the microstructure, resulting in a significant decrease in water sorptivity, although an increase in the specific surface area and micropore volume was observed, indicating the opening of gel pores due to carbonation, which is more pronounced for CEM III materials. Additionally, this study allows a qualitative assessment of the extent in alteration of C-(A)-S-H gel structure and bound water of CEM I and CEM III materials.

Functional and microstructural alterations in hydrated and freeze–thawed cement-oil shale ash composites

The oil shale industry generates a large amount of solid waste, the finer fraction of which can be utilized in civil engineering projects. However, for environmental, economic or technological reasons, oil shale is blended with other fuels, resulting in significant changes in the chemical composition of the residual ash. In this laboratory work, the fly ash from the combustion of oil shale with and without biomass in an industrial power plant was used as a binder substitute in cement-based materials to assess the potential of reuse of this ash. The hydration and pore structure of blended cementitious material subjected to long-term hydration and freeze–thawing has been characterized with a range of techniques, such as XRD, TGA and N2 physisorption. The results revealed that the ash type influences the phase assemblage related to the content of ettringite and monocarboaluminate, significantly affecting the volume of gel (1–6 nm) pores and small (10–30 nm) capillary pores. These microstructural changes impact the mechanical strength and water sorptivity properties in an opposite way after both long-term hydration and freeze–thawing. The results showed that the incorporation of ash obtained after combustion with biomass possesses higher mesoporosity and delays the hydration of cement, increases the total volume of gel (<6 nm) and small capillary pores (20–30 nm) of the composition, and deteriorates the functional properties after freeze–thawing.

A novel admixture to improve durability of alkali-activated slag by reducing water sorptivity and optimising the process of activation

Alkali-activated slag (AAS) has attracted huge attention worldwide for its low CO2 emission. However, the high water sorptivity of AAS is an obstacle before its practical application, while conventional methods can hardly solve this issue. In this study, the water sorptivity of AAS was decreased using a novel admixture, and the admixture shows a little effect on compressive strength at long ages. In order to clarify causes for its working mechanisms, the reaction process, reaction products and pore structure were investigated. The results suggest that sodium stearate (NaSt) plays an instrumental role in reaction process of AAS. Primarily, Na+ can provide a high alkaline environment, which is conducive for the dissolving of slag and increases compressive strength at the long term. Secondly, C17H35COO− can dramatically limit the movability of ions in the liquid phase due to its long molecular chain and thus, regulates precipitation of coagulation structure, improving the of ordering structure of C(N)-A-S-H and promoting formation of hydrotalcite-like phases (LDHs), from which the pore structure is upgraded by coarsening the pore diameters at the level of harmless and less harmful pores and decreases the pore connectivity.

Novel typology of accelerated carbonation curing: using dry and pre-soaked biochar to tune carbon capture and mechanical properties of cementitious mortar

One of the challenges of promoting accelerated carbonation curing (ACC) of concrete as a carbon sequestration strategy is ensuring that carbonation will not deteriorate mechanical strength. This study examined the mechanical strength, water sorptivity and carbonation efficiency of ten types of mortar containing dry or pre-soaked biochar subjected to internal and/or external carbonation. The results obtained enabled a typology of ACC to be proposed, in which the carbon dioxide absorption of mortar containing various types of CO2-dosed biochar ranged between 0.022% and 0.068% per unit dosage hour. In particular, the mortar containing dry biochar dosed with carbon dioxide was the top candidate for concurrently increasing both compressive strength (54.9 MPa) and carbon dioxide absorption (0.055% per unit dosage hour). Mortar containing pre-soaked biochar dosed with carbon dioxide was identified as a strategy that achieved the highest carbonation efficiency (0.068% per unit dosage hour), but it also reduced compressive strength (45.1 MPa). Collectively, the proposed typology offers a useful overview of the different ways by which biochar can be used to tune ACC in mortar, according to any technical constraints and/or intended functions of the carbonated concrete components.Graphical

Water sorptivity prediction model for concrete with all coarse recycled concrete aggregates

This paper examines the water sorptivity of recycled aggregate concrete (RAC) and shows how sorptivity can be predicted using electrical resistivity as the main predictor. The measurements in 48 RAC specimens show that RAC has higher water sorptivity and lower electrical resistivity than regular concrete. RAC sorptivity and rate of saturation prediction models were developed using multiple linear regression analysis. The prediction models include electrical resistivity, percent volume of coarse recycled concrete aggregates, and air content of residual mortar as explanatory variables. A graphical calculating device based on the sorptivity regression models was also created.

A discussion of “Water sorptivity of unsaturated fractured sandstone: Fractal modeling and neutron radiography experiment”

In August 2019, this journal published the paper “Water sorptivity of unsaturated fractured sandstone: Fractal modeling and neutron radiography experiment”, which reports on the experimental monitoring and analytical calculation of capillary moisture absorption in fractured sandstone. This discussion, considered a post-publication review, raises a number of concerns in relation to this paper. These concern the observed deviation between the visual and numeric results of the moisture front penetrations, the suboptimal character of the power-law equation for the temporal evolutions of the moisture penetrations, and the doubtful physical foundation for the pore fractal dimension and pore size ratio applied. These concerns threaten the validity of the disputed paper's findings and conclusions, and this discussion therefore invites its authors to refute these in their reply.

Effect of CNT-FA hybrid on the mechanical, permeability and microstructure properties of gangue cemented rockfill

Solid waste resource reuse, such as fabricating cemented rockfill material, plays a central role in underground reinforcement projects and construction waste recycling. However, the cement applied in the cemented rockfill material still brings massive CO2 emissions and energy consumption. Hence, we take the 0.009 wt% carbon nanotubes (CNTs) combining fly ash(FA) to replace 20% cement to explore a more sustainable improvement for cemented rockfill material. The results demonstrated that CNTs modified specimens exhibited a 17.6% reinforcement in elastic modulus, while the compressive strength remains almost unchanged. The modified specimen also shows fewer and sparser acoustic emission activities, indicating lower destruction intensity. Furthermore, with the help of CNTs filling the pores, water sorptivity and gas permeability tests showed that the impermeability improved by 8.4%-19.7%. By calculating the fractal dimension of the fracture surface SEM images, the CNTs reinforced specimens show better integrity and less structural damage. Metal intrusion measurements indicated that CNTs minify the ITZ width, split micropores in ITZ to reduce porosity under all equalized diameters significantly, especially at 65–70 μm, and form a network skeleton in the pores at the edge of the ITZ to prevent pores from connecting with microscopic defects in the cement matrix. The findings of this work can enhance the understanding of CNTs in composites fabrication and guide the application of CNTs in construction, transportation and mineral engineering in the future.

Effect of Sodium Stearate on the Microstructure and Hydration Process of Alkali-Activated Material

In response to the high water sorptivity of alkali-activated slag–red mud–steel slag cementitious material (AASRSS), water and aggressive ions are easily transferred to the interior of cementitious materials, which poses a significant threat to their durability. In order to limit the transfer of moisture and aggressive ions to the interior of AASRSS, sodium stearate (NaSt) was utilized in this paper to reduce its water sorptivity. The aim of this study was to elucidate the role of NaSt in the AASRSS system. The changes in the compressive strength and water sorptivity of AASRSS mortar were tested by mixing different amounts of NaSt into the mortar. The changes in the hydration process and microstructure of AASRSS after mixing with NaSt were analyzed by using the test methods of the isothermal calorimetry, resistivity, SEM and MIP. The results showed that NaSt plays an important role in the pore structure characteristics of AASRSS and that the use of NaSt significantly reduces its water sorptivity. The improvement in the water sorptivity was caused by two main mechanisms, namely the optimization of the pore structure (reduction in defects of the microstructure and alteration of pore size distribution) and the introduction of a hydrophobic film on the pore surface. The addition of NaSt did not change the type of AASRSS hydration product, but it inhibited the hydration reaction, leading to a reduction in the hydration product. The combination of the increased porosity and reduced hydration products mainly accounts for the decrease in the compressive strength of AASRSS due to NaSt.

Impact of duration of land abandonment on soil properties

Abstract Abandonment of agricultural fields triggers the ecosystem recovery in the process referred to as secondary succession. The objective of this study was to find the impact of secondary succession during 12 years lasting abandonment of agricultural fields with loamy sand and sandy loam soils on soil properties, namely soil organic carbon content, pH, water and ethanol sorptivity, hydraulic conductivity, water drop penetration time (WDPT), and repellency index (RI). The method of space-for-time substitution was used so that the fields abandoned at different times were treated as a homogeneous chronosequence. The studied soils showed a permanent increase in WDPT and a monotonous decrease in pH and water sorptivity with the duration of field abandonment. The dependence of the other characteristics on the duration of field abandonment was not unambiguous. The ethanol sorptivity decreased between 0 and 8 years of field abandonment, and increased between 8 and 12 years, when it copied a similar course of sand content during abandonment. The hydraulic conductivity halved within the first eight years of field abandonment and then increased statistically insignificantly between 8 and 12 years of abandonment. The repellency index decreased statistically insignificantly between 0 and 8 years of abandonment and then increased between 8 and 12 years.