Microvascular Research

Abstract This paper studied saline soil’s water and salt migration behavior under evaporation conditions by a self-designed experimental device, and the evolution law of the water content, conductivity, and temperature in different heights of saline soil roadbeds was analyzed. The test results show that at an ambient temperature of 18°C, the water-salt migration of saline roadbed is mainly concentrated in the early stage of hydration (≤48 h), which shows a typical phenomenon in which salt in the soil follows the water and the conductivity of soils increases synchronously with the water content. Under the evaporation condition, the decreased rate of water content was accelerated in the sample area near the heat source, resulting in a constant increase in the rate of conductivity and a wider salt aggregation area. Further, a critical subgrade height prediction model is established based on the maximum salt and water migration height in saline soil roadbeds with the help of Hydrus numerical simulation software. The model analysis results show that the migration rate of salts gradually lags behind that of water because the burial depth of groundwater increases under evaporation conditions. When the burial depth of groundwater is <1.5 m, the change of water-salt migration of the roadbed is gradually stabilized, and the height of salt erosion area on saline soil roadbed no longer rises. The research conclusions can guide the design level of the structure of saline soil roadbeds under evaporation conditions.

Abstract This study demonstrates the successful use of eco-friendly recycled glass powders (RGPs) in mortar and concrete as pozzolanic substitute for portland cement. As part of the evaluation, two RGPs were produced by steel and ceramic ball mills, namely, RGP (SB) and RGP (CB), respectively. Also included in the experiment as a reference was a commercial ceramic ball-milled RGP. All three evaluated RGPs were found to be reactive pozzolans based on a series of reactivity test results, including a strength activity index of greater than 80 % on all ages of 7, 28, and 56 days in mortar and concrete. Multiple indicators, such as higher generated heat in pozzolanic reactivity testing by isothermal calorimetry and portlandite consumption, indicated ceramic milling could produce a more reactive glass pozzolan, perhaps from the alumina residue from ceramics milling media. However, the higher reactivity of RGP (CB) did not lead to a greater compressive strength when used in concrete. Furthermore, a color difference was not detected between RGP (SB) and RGP (CB) concrete specimens. This study shows that both steel and ceramic media are viable for RGP production based on pozzolanic reactivity, strength, electrical resistivity, and concrete color. Other factors, such as productivity and cost, should be considered when choosing the proper production method for RGP at the industrial scale.

Abstract To explore the rheological properties and the modification mechanism of graphene/rubber composite-modified asphalt, a dynamic shear rheometer and low-temperature bending rheometer were used to study the high and low-temperature rheological properties of graphene/rubber composite-modified asphalt. Second, the microstructure and chemical structure of the asphalt were characterized by using Fourier transform infrared spectroscopy and optical microscopy, and the component model of asphalt was constructed with molecular dynamics simulation technology to explore the modification mechanism of graphene/rubber composite-modified asphalt. The results show that compared with rubber-modified asphalt, graphene/rubber composite-modified asphalt effectively improves the high-temperature deformation resistance and low-temperature crack resistance of asphalt, but the ability of graphene to improve the low-temperature performance of asphalt is limited at −24°C or even lower temperatures. The addition of graphene promotes the swelling development of rubber, improves the bonding stability between rubber and resin, and enhances the compatibility between rubber and asphalt systems. Graphene can weaken the aggregation behavior of rubber and asphaltene, and the distribution of rubber and asphaltene in asphalt is more uniform, further improving the overall stability of the asphalt system. Graphene promotes the adsorption of lightweight components by rubber, leading to a decrease in the diffusion coefficients of saturated and aromatic components in asphalt systems. This is also an important reason for the improved high-temperature performance of graphene/rubber-modified asphalt.

Abstract Cement-based solidification/stabilization (S/S) techniques have been widely used to produce stable forms of contaminated soils and reduce the mobility of contaminants into the environment. However, information on the long-term performances of S/S under environmental conditions (i.e., variable loading and atmospheric carbon dioxide) remains sparse. In this study, a triaxial test setup was modified to simulate environmental conditions. The permeability and compressive strength of silica sand solidified with portland cement were measured at different stages of four scenarios involving carbonation only, axial strain only, carbonation followed by axial strain, and axial strain followed by carbonation. X-ray computed tomography (CT) was used to characterize the internal structure of the samples. Permeability and compressive strength results indicate that the axial strain accelerated the damage to the S/S specimens and increased their permeability. The deterioration due to the mechanical strain decreased in the presence of carbon dioxide. Consistent changes in microstructure were observed with the CT scan. The results indicate that the influence of stressors on the void size distribution, compressive strength, and permeability is complex and characterized by interactions between the stressors.

Abstract Using one or more fibers in concrete is called “hybridization.” Although single-fiber concrete offers excellent performance, concrete reinforced with hybrid fibers gains speed as the synergy between the fibers results in amplified performance. This experimental work reflects the effects of incorporating 1, 2, and 3 % untreated singular and hybrid fibers on the physical and mechanical properties of lightweight concrete (LC) at 3, 28, and 90 days. Six mixture types were used: control LC, LC containing metalized plastic waste fibers (MPWFs), LC containing date palm fibers (DPFs), LC containing sisal fibers (SFs), LC with MPWFs and DPFs (Hybrid A), and LC with MPWFs and SFs (Hybrid B). In the fresh state, fiber introduction affected all mixes’ workability and wet density, and the reduction in slump and wet density was proportional to the fiber dose. However, in the hardened state, the results indicate that compressive strength (CS) and modulus of elasticity (MOE) decreased for LC containing only plastic or SFs. However, these properties increased slightly over the long term for blends containing 1 % DPF. Excepting mixtures containing MPWFs, fiber introduction improved flexural strength (FS) for all blends containing 1 % and 2 % fibers at 28 and 90 days. The most significant gains in FS were 8 % and 4 % at 28 and 90 days, respectively, for samples containing 1 % DPF. Nevertheless, fiber hybridization improved these mechanical properties and created a positive synergy in long-term bending. At 1 % fiber dosage, CS, MOE, and FS increased respectively by 3.05, 3.10, and 8 % for Hybrid A compared with the control LC. Pull-out testing provides the best means to understand typical failure modes and assess maximum tensile strength. Consequently, microstructural analysis enabled us to examine the bonding quality at the fiber-matrix interface.

Abstract Additive manufacturing (AM), or 3-D printing, encompasses a range of technologies that “print” material layer by layer to create the final part. Though there is significant interest in the AM of concrete in the construction sector, opportunities for the AM of steel still need to be explored. This review focuses on the AM of low-alloy steels, stainless steels, duplex stainless steels (DSSs), precipitation-hardened (PH) stainless steels, and tool steels, highlighting the challenges and opportunities of employing AM technology for construction applications. Fusion-based AM technologies, such as wire arc additive manufacturing (WAAM), laser powder bed fusion (LPBF), and laser-directed energy deposition (LDED), are the core technologies that have been tested in the industry so far. WAAM has seen the most exploration for construction applications because of its higher deposition rate, larger build volume, and lower cost than other AM technologies. The mechanical performance of low-alloy steel, stainless steel, and tool steel shows increased tensile strengths after AM processing compared with wrought counterparts. Although AM is not economical for geometrically simple metal components or geometries, there is potential for AM to fabricate unique structural connections or joints, optimized load-bearing columns, and even entire bridges, as highlighted in this paper. AM’s digital nature (i.e., using computer-aided design (CAD) to create G-code paths for printing) can increase structural efficiency if coupled with topology optimization methods and high-strength alloys. Currently, however, general applications of AM in the industry are limited because of barriers with structural codes and standards not incorporating AM parts and AM technology barriers (i.e., limited build volumes).

Abstract Marble waste and fly ash are industrial waste, and disposal of these wastes is a big challenge for environmental sustainability. In this study, we explore an innovative approach to sustainable construction by utilizing industrial by-products: sintered fly ash aggregate (SFA) and waste marble sand in lightweight aggregate concrete (LWAC). This study used SFA as a coarse aggregate, whereas river sand was partially replaced by waste marble sand (10–50 %). The waste marble sand modified LWAC has been investigated for mechanical and durability properties. The test related to permeability like water absorption, sorptivity, permeability, and drying shrinkage has been performed. Mercury intrusion porosimetry test was performed to validate durability results. The results indicate that 30 % of river sand can be replaced with waste marble sand as it improves the overall performance of LWAC. Our research contributes to global sustainability efforts by providing a method to reduce industrial waste through its incorporation in building materials. This study not only addresses the urgent need for environmental preservation but also offers potential enhancements in the mechanical properties of LWAC, making it a viable and eco-friendly option in the construction industry worldwide.

Abstract Previous literature has provided contradictory results, so we present the current investigation to provide additional information to assess the suitability of using soak calcination as a pretreatment method to increase the performance of calcined zeolite when used as the supplementary cementitious material. In this study, natural clinoptilolite zeolite was calcined for three hours at 200°C, 400°C, 600°C, 800°C, and 1,000°C, and the effects of calcination on different physical and chemical properties were observed using a range of experimental tests. The impacts of calcined zeolite were investigated in the hydrated system with the replacement of portland cement up to 20 % by mass on hydration kinetics (i.e., heat of hydration, setting time, chemical shrinkage, degree of hydration), drying shrinkage, and compressive strength. Results revealed that calcination minorly decreased the crystallinity, particle size, and peak pore size of the zeolite, leading to a slightly increased external specific surface area, whereas it increased the rate of moisture absorption and pH of zeolite particles. In the hydrated cementitious system, calcined zeolite reduced the workability and heat of hydration and retarded the initial setting time. The calcined zeolite particles absorbed a part of the water from the fresh mixture and expanded volumetrically, which led to a negative volume of chemical shrinkage up to the final setting time and increased the drying shrinkage. As the dosages of calcined zeolite increased, the compressive strength substantially decreased because of the lower degree of hydration. Overall, soak calcination pretreatment decreased the reactivity of clinoptilolite zeolite particles and impacted the performance of calcined zeolite in the blended system.

Abstract The current research studies the effectiveness of steel fibrous layers on the performance of self-compacting lightweight reinforced concrete two-way slabs with (length/width) ratio ≈ 1.618 (golden ratio). In this work, steel fibers (SFs) have been added to four slab specimens with volume fractions of 0.4 % and 0.8 %, in one bottom layer and two top and bottom layers, in addition to a reference slab without SFs, the four slabs were tested under uniform load. The results revealed that when using single or dual fibrous layers, the flexural strength of slabs was considerably enlarged (numerically 41.3 % for single bottom layer and 72.4 % for both top and bottom layers when using 0.4 % SF, and 113.7 % for a single bottom layer and 193 % for both top and bottom layers when using 0.8 % SF) as compared with nonfibrous slabs, and the failure mode had altered from flexure mode to shear one as compared with nonfibrous slabs. The effect of these fibrous layers was enlarged with increasing the content of SF. And for the same amount of SF, the influence of SF is greater when it is distributed in one bottom layer (numerically 113.7 %) than when distributed in two layers (numerically 41.3 %).

Abstract Because of extreme global temperatures driven by climate change, the vulnerability of asphalt pavement to heat-induced damage has become a major concern given increasing traffic loads. Traditional asphalt binders oftentimes do not meet the demanding standards for withstanding this condition. As a result, the use of recycled plastics in asphalt road construction has gained popularity because of its potential performance improvement, sustainability, and cost-effectiveness. This study investigates the impact of recycled high-density polyethylene (rHDPE) and recycled polypropylene (rPP) on the high-temperature rheological properties of asphalt binder throughout its service life. A comprehensive evaluation was conducted to assess the rutting resistance, elastic response, deformability, stress sensitivity, and aging susceptibility of modified binders at high temperature. The findings reveal that the addition of rHDPE and rPP to asphalt binders enhances rutting resistance, as evidenced by improved rutting parameters and rutting failure temperatures. The analysis of nonrecoverable creep compliance and percent recovery also showed improvement in elasticity and resistance to permanent deformation of the modified asphalt. Although rHDPE and rPP-modified asphalt did not meet the criteria for elastomeric polymers, a trend toward improved elastic response was observed with aging. Additionally, the result of the aging index showed that though increased stiffness is observed as asphalt-aged, rPP-modified asphalt is more susceptible to short-term aging but exhibits more stable performance during service life compared with the rHDPE-modified asphalt.

Abstract Water absorbing polymer (WAP) is emerging as soil amendment material for various soil infrastructures, such as urban green infrastructure, green roofs, landfill covers, and climate-resilient agriculture, to promote vegetation growth and thereby increase the sustainability of the projects. WAP amended soils experience alternating periods of drying and wetting because of their exposure to different climate conditions. Precise determination of volumetric water content (VWC) in vadose zone is required to establish the soil-water retention curve (SWRC) in WAP amended soils. This study aims to evaluate the accuracy of a capacitance sensor (CS) for the purpose of continuous VWC monitoring in WAP amended soils. A controlled laboratory environment was used for the performance evaluation of CS in three different surface soils (sand, silt loam, and clay loam) with four WAP amendment rates (0 %, 0.1 %, 0.2 %, and 0.4 %). The CS completely underestimates the VWC of WAP amended soils because of the bound water inside the WAP network. Two different calibration equations (i.e., third-order polynomial and linear) were recommended to enhance the precision of VWC measurement in WAP amended soils. The linear calibration method is further extended for obtaining a generalized calibration procedure valid for all soil textures and WAP concentrations. The importance of the proposed calibration procedure for a precise SWRC measurement of WAP amended soils was demonstrated. The results indicated that the error in VWC measurement further influences the saturated water content, field capacity, and permanent wilting point, which are essential parameters to estimate the soil-water storage, and irrigation water requirement.

Abstract The influence of varying contents of supplementary cementitious material, namely silica fume (SF), on the transport properties of ultra-high performance concrete containing polyethylene therephthalate (PET) fibers under a steam curing regime has been investigated in this study. SF was used as a supplementary binder as a partial replacement of the ordinary portland cement (OPC) in different proportions (5, 10, 15, 20, 25, 30, and 35 %), whereas shredded waste plastic PET bottles were used as fiber reinforcements at 1 % of the total mass binder to produce ultra high performance PET reinforced concrete (UHPPRC). The presence of SF between (5 % and 30 %) in UHPPRC increases compressive strength at all ages of 3, 7, and 28 days; the greatest compressive strength achieved was 146.6 MPa by the SF25-UHPPRC mix, but the compressive strength reduced at higher SF contents, in particular for the SF35-UHPPRC. Besides, the SF inclusion improved the transport properties of PET-fiberized concrete. The greatest improvement was seen with SF25-UHPPRC, which showed increases of 75.2 % in porosity, 92.6 % in water permeability, and 95.8 % in rapid chloride permeability relative to the control mix at 28 days. This could indicate that the incorporation of SF and PET fiber increases the possibility of using PET fibers in the production of ultra-high performance PET fiber reinforced concrete with superior engineering and transport properties.

Abstract Peat is formed from organic matter (OM) in wetlands under an anaerobic environment. Peat is considered weak and problematic soil because of high-water retaining capability, high compressibility, and low shear strength. The cement is generally used to stabilize peat, but cement production is energy intensive and contributes 7–8 % of total carbon dioxide to the atmosphere. Nowadays, there is a need to use a potential “greener” alternative that is sustainable in the long term. Therefore, this research assesses the feasibility of rice husk ash (RHA)–based alkali-activated binder (AAB)–stabilized peat with varying fiber content (6–73 %) and OM (21–79 %). The RHA-based AAB was prepared by adding bauxite powder (as alumina source) to RHA in proportion to keep constant silica to alumina ratio (silica/alumina = 3). The samples were prepared using sodium hydroxide (NaOH) of molarities 3, 6, and 9 to activate the binder with percentages 10, 20, and 30 % by weight of dry peat and alkali (A) to binder (B) ratio chosen as 0.5, 0.7, and 0.9. The results illustrate that the factors like pH of pore solution, the molarity of NaOH, binder content, A/B ratio, OM, and curing affect the unconfined compressive strength (UCS) of treated peat. The maximum UCS of 962, 873, and 668 kPa was found at an optimum combination of molarity (6M), binder content (20 %), and A/B ratio (0.7) for sapric, fibric, and hemic peat. It was seen that OM has a negative impact, whereas the curing period positively impacts the UCS of treated peat. Furthermore, the cumulative mass loss of fibric peat (13.6 %) is more than hemic (11.4 %) and sapric (10.6 %) peat. The X-ray diffraction patterns and field emission scanning electron microscopy micrographs confirm the cementitious minerals that fill pore spaces or cavities to form a smooth and dense gel responsible for strength gain.

Abstract The prohibition of river sand mining has drawn the attention of researchers in finding practicable alternatives. In the approach of finding these alternatives, it is essential to ensure minimal or zero impairment to the ecological balance, which can be mainly attained by making use of industrial waste/byproducts. The wastes from the mining industry are the major contributors in causing impairment to the environment, and their influence on the stability of mortars on using as fine aggregates needs to be systematically investigated with the view of long-term performance concerns. Thus, the present study explores the applicability of mine tailings and finding the optimum dosage in cement mortars by investigating the engineering properties and microstructure development with the aid of qualitative and quantitative analysis associated with hydration products. The studies confirm that the increased consumption of portlandite for secondary hydration reactions followed by the additional formation of calcium silicate hydrate (CSH) and calcium aluminum silicate hydrate (CASH) phases in mine tailing-based mortars helped in achieving a quality microstructure. These additional formations of CSH and CASH phases are also confirmed through Fourier transform infrared spectroscopy by identifying the shift of Si-O-Si stretching vibration bands toward a lower wavenumber. The lowering of calcium/silicate atomic ratio and increased formation of mineralogical compounds related to CSH and CASH in x-ray diffraction patterns also confirms the same. Gismondine, chabazite, and hillebrandite are the additional phases formed and found to take part in refining the pore structure. This enhanced performance of mine tailing mortars was also verified with the aid of a modified Andreasen and Andersen particle packing model. The formation of high-quality microstructure is reflected in the hardened properties of optimized cement mortar in the proportion of 20 % for iron ore tailing and 30 % for copper ore tailing.

Abstract The standard spacing factor developed by Powers is typically used to evaluate the quality of the air void system in hardened concrete, but it does not always correlate with durability of the concrete. Several air void spacing equations, which are also applicable when polymeric microspheres are used in place of air entrainment, have been proposed because of the need for a more robust and comprehensive basis to evaluate the quality of the air void system. However, the spacing parameters provided by the various proposed equations, when used as sole measures in predicting the frost resistance of concrete, do not seem to do any better than the standard spacing factor. Dispersion and spatial distribution have been shown to be effective ways of describing air void or microsphere systems in hardened concrete because they have been quantified to establish criteria to assess the frost resistance of concrete. In this paper, dispersion and distribution factors are further elaborated upon to explain how they characterize zones that are protected by air voids or microspheres in the concrete. Criteria to assess the durability of concrete under rapid cycles of freezing and thawing based on the dispersion and distribution factors are linked to the exposure classes defined in the ACI 318 Code and in the recently proposed Unified Durability Guidance in ACI Committee Documents.