Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests.

The co-contamination of metals and organic pollutants, such as Pb and methyl tert-butyl ether (MTBE), in groundwater, has become a common and major phenomenon in many contaminated sites. This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier (PRB) packed with mixed zeolites (clinoptilolite and ZSM-5) using fixed-bed column tests and breakthrough curve modeling. The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite. The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold. The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules (130.6 mg/g versus 45.3 mg/g) due to higher specific surface areas. The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5% of granular clinoptilolite was mixed with 5% ZSM-5 and 90% sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite. This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs.

Addressing the need for standardization of test methods for self-healing concrete: an inter-laboratory study on concrete with macrocapsules.

Development and commercialization of self-healing concrete is hampered due to a lack of standardized test methods. Six inter-laboratory testing programs are being executed by the EU COST action SARCOS, each focusing on test methods for a specific self-healing technique. This paper reports on the comparison of tests for mortar and concrete specimens with polyurethane encapsulated in glass macrocapsules. First, the pre-cracking method was analysed: mortar specimens were cracked in a three-point bending test followed by an active crack width control technique to restrain the crack width up to a predefined value, while the concrete specimens were cracked in a three-point bending setup with a displacement-controlled loading system. Microscopic measurements showed that with the application of the active control technique almost all crack widths were within a narrow predefined range. Conversely, for the concrete specimens the variation on the crack width was higher. After pre-cracking, the self-healing effect was characterized via durability tests: the mortar specimens were tested in a water permeability test and the spread of the healing agent on the crack surfaces was determined, while the concrete specimens were subjected to two capillary water absorption tests, executed with a different type of waterproofing applied on the zone around the crack. The quality of the waterproofing was found to be important, as different results were obtained in each absorption test. For the permeability test, 4 out of 6 labs obtained a comparable flow rate for the reference specimens, yet all 6 labs obtained comparable sealing efficiencies, highlighting the potential for further standardization.

Environmental and health impacts of using food waste as animal feed: a comparative analysis of food waste management options.

The disposal of food waste is a large environmental problem. In the United Kingdom (UK), approximately 15 million tonnes of food are wasted each year, mostly disposed of in landfill, via composting, or anaerobic digestion (AD). European Union (EU) guidelines state that food waste should preferentially be used as animal feed though for most food waste this practice is currently illegal, because of disease control concerns. Interest in the potential diversion of food waste for animal feed is however growing, with a number of East Asian states offering working examples of safe food waste recycling - based on tight regulation and rendering food waste safe through heat treatment. This study investigates the potential benefits of diverting food waste for pig feed in the UK. A hybrid, consequential life cycle assessment (LCA) was conducted to compare the environmental and health impacts of four technologies for food waste processing: two technologies of South Korean style-animal feed production (as a wet pig feed and a dry pig feed) were compared with two widespread UK disposal technologies: AD and composting. Results of 14 mid-point impact categories show that the processing of food waste as a wet pig feed and a dry pig feed have the best and second-best scores, respectively, for 13/14 and 12/14 environmental and health impacts. The low impact of food waste feed stems in large part from its substitution of conventional feed, the production of which has substantial environmental and health impacts. While the re-legalisation of the use of food waste as pig feed could offer environmental and public health benefits, this will require support from policy makers, the public, and the pig industry, as well as investment in separated food waste collection which currently occurs in only a minority of regions.

The UK waste input-output table: Linking waste generation to the UK economy.

In order to achieve a circular economy, there must be a greater understanding of the links between economic activity and waste generation. This study introduces the first version of the UK waste input-output table that could be used to quantify both direct and indirect waste arisings across the supply chain. The proposed waste input-output table features 21 industrial sectors and 34 waste types and is for the 2010 time-period. Using the waste input-output table, the study results quantitatively confirm that sectors with a long supply chain (i.e. manufacturing and services sectors) have higher indirect waste generation rates compared with industrial primary sectors (e.g. mining and quarrying) and sectors with a shorter supply chain (e.g. construction). Results also reveal that the construction, mining and quarrying sectors have the highest waste generation rates, 742 and 694 tonne per £1m of final demand, respectively. Owing to the aggregated format of the first version of the waste input-output, the model does not address the relationship between waste generation and recycling activities. Therefore, an updated version of the waste input-output table is expected be developed considering this issue. Consequently, the expanded model would lead to a better understanding of waste and resource flows in the supply chain.

Strain Monitoring of Concrete Using Carbon Black-Based Smart Coatings.

Given the challenges we face of an ageing infrastructure and insufficient maintenance, there is a critical shift towards preventive and predictive maintenance in construction. Self-sensing cement-based materials have drawn interest in this sector due to their high monitoring performance and durability compared to electronic sensors. While bulk applications have been well-discussed within this field, several challenges exist in their implementation for practical applications, such as poor workability and high manufacturing costs at larger volumes. This paper discusses the development of smart carbon-based cementitious coatings for strain monitoring of concrete substrates under flexural loading. This work presents a physical, electrical, and electromechanical investigation of sensing coatings with varying carbon black (CB) concentrations along with the geometric optimisation of the sensor design. The optimal strain-sensing performance, 55.5 ± 2.7, was obtained for coatings with 2 wt% of conductive filler, 3 mm thickness, and a gauge length of 60 mm. The results demonstrate the potential of applying smart coatings with carbon black addition for concrete strain monitoring.

Microcapsule Triggering Mechanics in Cementitious Materials: A Modelling and Machine Learning Approach.

Self-healing cementitious materials containing microcapsules filled with healing agents can autonomously seal cracks and restore structural integrity. However, optimising the microcapsule mechanical properties to survive concrete mixing whilst still rupturing at the cracked interface to release the healing agent remains challenging. This study develops an integrated numerical modelling and machine learning approach for tailoring acrylate-based microcapsules for triggering within cementitious matrices. Microfluidics is first utilised to produce microcapsules with systematically varied shell thickness, strength, and cement compatibility. The capsules are characterised and simulated using a continuum damage mechanics model that is able to simulate cracking. A parametric study investigates the key microcapsule and interfacial properties governing shell rupture versus matrix failure. The simulation results are used to train an artificial neural network to rapidly predict the triggering behaviour based on capsule properties. The machine learning model produces design curves relating the microcapsule strength, toughness, and interfacial bond to its propensity for fracture. By combining advanced simulations and data science, the framework connects tailored microcapsule properties to their intended performance in complex cementitious environments for more robust self-healing concrete systems.

Relating monolithic and granular leaching from contaminated soil treated with different cementitious binders.

This work employed a clayey, silty, sandy gravel contaminated with a mixture of metals (Cd, Cu, Pb, Ni and Zn) and diesel. The contaminated soil was treated with 5 and 10% dosages of different cementitious binders. The binders include Portland cement, cement-fly ash, cement-slag and lime-slag mixtures. Monolithic leaching from the treated soils was evaluated over a 64-day period alongside granular leachability of 49- and 84-day old samples. Surface wash-off was the predominant leaching mechanism for monolithic samples. In this condition, with data from different binders and curing ages combined, granular leachability as a function of monolithic leaching generally followed degrees 4 and 6 polynomial functions. The only exception was for Cu, which followed the multistage dose-response model. The relationship between both leaching tests varied with the type of metal, curing age/residence time of monolithic samples in the leachant, and binder formulation. The results provide useful design information on the relationship between leachability of metals from monolithic forms of S/S treated soils and the ultimate leachability in the eventual breakdown of the stabilized/solidified soil.

pH-dependent leaching behaviour and other performance properties of cement-treated mixed contaminated soil.

Portland cement has been widely used for stabilisation/solidification (S/S) treatment of contaminated soils. However, there is a dearth of literature on pH-dependent leaching of contaminants from cement-treated soils. This study investigates the leachability of Cu, Pb, Ni, Zn and total petroleum hydrocarbons (TPH) from a mixed contaminated soil. A sandy soil was spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, and treated with ordinary Portland cement (CEM I). Four different binder dosages, 5%, 10%, 15% and 20% (m/m) and different water contents ranging from 13%-19% dry weight were used in order to find a safe operating envelope for the treatment process. The pH-dependent leaching behaviour of the treated soil was monitored over an 84-day period using a 3-point acid neutralisation capacity (ANC) test. The monolithic leaching test was also conducted. Geotechnical properties such as unconfined compressive strength (UCS), hydraulic conductivity and porosity were assessed over time. The treated soils recorded lower leachate concentrations of Ni and Zn compared to the untreated soil at the same pH depending on binder dosage. The binder had problems with Pb stabilisation and TPH leachability was independent of pH and binder dosage. The hydraulic conductivity of the mixes was generally of the order, 10(-8) m/sec, while the porosity ranged from 26%-44%. The results of selected performance properties are compared with regulatory limits and the range of operating variables that lead to acceptable performance described.

Use of superabsorbent polymer in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing.

Conventional subsurface barrier materials for contamination containment deteriorate in aggressive environments and only have a limited exchange/adsorption capacity for heavy metals. This study focused on the potential use of superabsorbent polymer (SAP) in soil-cement subsurface barriers for enhanced heavy metal sorption and self-healing. The SAP adsorption results for lead, copper, zinc and nickel were well fitted by the Langmuir model. The SAP had the highest adsorption capacity for lead at 175 mg/g, and plays a key role in the removal of the heavy metals in an acidic environment. In addition, the incorporation of SAP in soil-cement increased the ductility and had negligible adverse effects on mechanical and permeability properties. When cracks propagate in the matrix, the SAP is exposed to the ingress of water and swells, and this swelling reaction seals the cracks. The SAP-containing soil-cement demonstrated enhanced self-healing performance in terms of the recovery of permeability. The uniform dispersion and the 3D network of the SAP were observed using micro-CT scanning, and good bonding and self-healing mechanism were confirmed by SEM-EDX analysis. The results suggest the significant potential for the SAP-based approach for the development of more resilient subsurface barriers with enhanced heavy metal sorption and self-healing.

Carbon Nanofibers Grown in CaO for Self-Sensing in Mortar.

Intelligent cementitious materials integrated with carbon nanofibers (CNFs) have the potential to be used as sensors in structural health monitoring (SHM). The difficulty in dispersing CNFs in cement-based matrices, however, limits the sensitivity to deformation (gauge factor) and strength. Here, we synthesise CNF by chemical vapour deposition on the surface of calcium oxide (CaO) and, for the first time, investigate this amphiphilic carbon nanomaterial for self-sensing in mortar. SEM, TEM, TGA, Raman and VSM were used to characterise the produced CNF@CaO. In addition, the electrical resistivity of the mortar, containing different concentrations of CNF with and without CaO, was measured using the four-point probe method. Furthermore, the piezoresistive response of the composite was quantified by means of compressive loading. The synthesised CNF was 5-10 µm long with an average diameter of ~160 nm, containing magnetic nanoparticles inside. Thermal decomposition of the CNF@CaO compound indicated that 26% of the material was composed of CNF; after CaO removal, 84% of the material was composed of CNF. The electrical resistivity of the material drops sharply at concentrations of 2% by weight of CNF and this drop is even more pronounced for samples with 1.2% by weight of washed CaO. This indicates a better dispersion of the material when the CaO is removed. The sensitivity to deformation of the sample with 1.2% by weight of CNF@CaO was quantified as a gauge factor (GF) of 1552, while all other samples showed a GF below 100. Its FCR amplitude can vary inversely up to 8% by means of cyclic compressive loading. The method proposed in this study provides versatility for the fabrication of carbon nanofibers on a tailored substrate to promote self-sensing in cementitious materials.

Application of zeolites in permeable reactive barriers (PRBs) for in-situ groundwater remediation: A critical review.

Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation.

High throughput production of microcapsules using microfluidics for self-healing of cementitious materials.

Capsule-based self-healing of cementitious materials is an effective way of healing cracks, significantly extending the life of structures, without imposing changes due to the incorporation of capsules into products during mixing. The methodologies currently being used for the development of capsules with a liquid core as a healing agent yield a wide range of sizes and shell thicknesses for the microcapsules, preventing a detailed assessment and optimisation of the microcapsule size and its effects. Uniquely, microfluidic technology offers precise control over the size and shell thickness through the formation of double emulsions. The drawback is that only small quantities of material can be typically produced. Here, by using paralleled junctions in a microfluidic device, high throughput production of materials was achieved, focusing for the first time on self-healing of cementitious materials. A microfluidic chip was assembled with 4 channels in parallel and selected hydrophobicity for the formation of the double emulsions. A coefficient of variation below 2.5% was observed for the 4 junctions, demonstrating the formation of monodisperse capsules. The control over the size and shell thickness by adjusting the flow rates was demonstrated, yielding capsules with an outer diameter of 615-630 µm and a shell thickness varying between 50 and 127 µm. By using triethanolamine as a surfactant, capsules with an aqueous core were produced. Furthermore, by selecting PEA, an acrylate with low tensile strength, the capsules embedded in the cement paste were successfully triggered to release the healing agent by crack formation. Capsules were successfully produced continuously for 7 h, with inner and outer diameters of 500 ± 31 µm and 656 ± 9 µm at a production rate of ∼13 g h-1 and a yield of around 80%. With these results and considering up to 6 chips in parallel, the production rate could be up to 1.5 kg per day. This demonstrates the huge potential of the microfluidic device with unique features to produce sufficiently large quantities of microcapsules for laboratory-scale assessment of self-healing performance.

Assessing the influence of pore structure formation on heavy metal immobilization through image-based CFD.

Porous media are widely adopted as immobilization sorbents in environmental engineering. The microscale difference in pore structure formation causes significant deflection in a vast landscape. Computational fluid dynamics (CFD) offers a comparative approach to evaluate the individual influence from pore structure formation with strictly controlled surface and volume properties. This paper presents a comprehensive comparison between the performance of cylindrical media and spherical-media in heavy metal immobilization. Digital testing was performed to measure the surface area, specific surface area, density and porosity. Image-based input technique was developed to reconstruct the cylindrical media. It was found that although the surface area, specific surface area and porosity were the same, the spherical media still had an accelerated immobilization rate. Results further showed that the spherical media in floatation arrangement had an immobilization rate of 16% higher than the cylindrical media with the same surface properties. Non-floatation arrangement of the spherical media caused a reduction in immobilization capacity up to 32.8% lower than the cylindrical media. The cylindrical media demonstrated an advantage of being structurally stable under high porosity, the latter of which resulted in an increased immobilization capacity compared with the spherical-media. The results suggest that the cylindrical bio-microstructure is desirable for heavy metal immobilization in a non-flotational environment. The computational approach provides a digital solution to evaluate the immobilization in 3D architected media. The proposed testing methods are feasible for both experimentally obtained images and structures from algorithm-generation.

Lead (Pb) sorption to hydrophobic and hydrophilic zeolites in the presence and absence of MTBE.

The co-contamination of the environment by metals and organic pollutants is a significant concern, and one such example is lead (Pb) and methyl tert-butyl ether (MTBE) due to their historic use as fuel additives. Clinoptilolite is an abundant and efficient zeolite for metal removal, but the potential interference of co-existing organic pollutants on metal removal, such as MTBE, have rarely been discussed. In this study, a combination of batch sorption tests and synchrotron-based X-ray absorption spectroscopic analyses were employed to investigate Pb sorption mechanism(s) onto clinoptilolite in the presence and absence of MTBE. A comparison was made to synthetic ZSM-5 zeolite to gain insights into differences in Pb binding mechanisms between hydrophilic (clinoptilolite) and hydrophobic (ZSM-5) zeolites. Site occupancy and surface precipitation contributed equally to Pb removal by clinoptilolite, while surface precipitation was the main Pb removal mechanism for ZSM-5 followed by site occupancy. Despite the negligible effect of 100 mg/L MTBE on observed Pb removal from solution by both zeolites, a surface-embedded Pb removal mechanism, through the Mg site on clinoptilolite surface, arises when MTBE is present. This study provides an understanding of atomic-level Pb uptake mechanisms on zeolites, with and without co-contaminating MTBE, which aids in their application in water treatment at co-contaminated sites.

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study.

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications.

Development and Application of Novel Sodium Silicate Microcapsule-Based Self-Healing Oil Well Cement.

A majority of well integrity problems originate from cracks of oil well cement. To address the crack issues, bespoke sodium silicate microcapsules were used in this study for introducing autonomous crack healing ability to oil well cement under high-temperature service conditions at 80 °C. Two types of sodium silicate microcapsule, which differed in their polyurea shell properties, were first evaluated on their suitability for use under the high temperature of 80 °C in the wellbore. Both types of microcapsules showed good thermal stability and survivability during mixing. The microcapsules with a more rigid shell were chosen over microcapsule with a more rubbery shell for further tests on the self-healing efficiency since the former had much less negative effect on the oil well cement strength. It was found that oil well cement itself showed very little healing capability when cured at 80 °C, but the addition of the microcapsules significantly promoted its self-healing performance. After healing for 7 days at 80 °C, the microcapsule-containing cement pastes achieved crack depth reduction up to ~58%, sorptivity coefficient reduction up to ~76%, and flexural strength regain up to ~27%. The microstructure analysis further confirmed the stability of microcapsules and their self-healing reactions upon cracking in the high temperature oil well cement system. These results provide a promising perspective for the development of self-healing microcapsule-based oil well cements.

Effect of Natural Graphite Fineness on the Performance and Electrical Conductivity of Cement Paste Mixes for Self-Sensing Structures.

Cementitious composites are the most widely used construction materials; however, their poor durability necessitates frequent monitoring and repairs. The emergence of self-sensing composites could reduce the need for costly and time-consuming structural inspections. Natural graphite, due to its low cost and wide availability, is a promising additive to generate an electrically conductive network which could ultimately lead to a self-sensing mechanism. Despite several studies using natural graphite as a conductive additive, the effect of its fineness on the cementitious composite's performance has not been explored. This study experimentally investigated the effect of three graphite products of varying fineness on the early age, mechanical, and electrical conductivity performance of cement pastes. The fluidity of the graphite-cement paste reduced significantly with increasing graphite fineness, and graphite did not affect the cement hydration. The finer the graphite, the lower the effect on the mechanical performance, as confirmed by compressive strength testing and micro-indentation. Electrical conductivity testing showed that the percolation threshold depended on the graphite fineness and was found at ~20 wt % for the fine and medium graphite, while it increased to 30-40 wt % for the coarse graphite. This is the first study that has investigated holistically the effect of graphite fineness on the performance of cement pastes and will pave the way for using this material as an additive for self-sensing structures.

Organic Contaminant-Triggered Self-Healing Soil Mix Cut-Off Wall Materials Incorporating Oil Sorbents.

Soil mix cut-off walls have been increasingly used for containment of organic contaminants in polluted land. However, the mixed soil is susceptible to deterioration due to aggressive environmental and mechanical stresses, leading to crack-originated damage and requiring costly maintenance. This paper proposed a novel approach to achieve self-healing properties of soil mix cut-off wall materials triggered by the ingress of organic contaminants. Oil sorbent polymers with high absorption and swelling capacities were incorporated in a cementitious grout and mixed with soil using a laboratory-scale auger setup. The self-healing performance results showed that 500 µm-wide cracks could be bridged and blocked by the swollen oil sorbents, and that the permeability was reduced by almost an order of magnitude after the permeation of liquid paraffin. It was shown by micro-CT scan tests that the network formed by the swollen oil sorbents acted as attachments and binder, preventing the cracked mixed soil sample from crumbling, and that the oil sorbents swelled three times in volume and therefore occupied the air space and blocked the cracks in the matrix. These promising results exhibit the potential for the oil sorbents to provide soil mix cut-off walls in organically-contaminated land with self-healing properties and enhanced durability.

GMCs stabilized/solidified Pb/Zn contaminated soil under different curing temperature: Physical and microstructural properties.

Stabilization/Solidification (S/S) has been widely used in soil remediation to both improve physical properties and immobilize extensive contaminants. GGBS (granulated ground blast furnace slag)-MgO-CaO (GMCs) was used to treat Pb/Zn contaminated soil. The physical and microstructural characteristics of stabilized/solidified contaminated soil were investigated in this study. Microstructural analysis showed that the main hydration products of GMC treated contaminated soil were C-S-H and hydrotalcite like gels (Ht), which dominated the physical strength of S/S soil. The unconfined compressive strength (UCS) and the leachability of GMC treated contaminated soil were improved with the increase in GMC proportion (5%-15%), curing time (7 days and 28 days) and temperature (5 °C, 21 °C and 45 °C) due to the enhanced hydration. The compressive strengths of the majority mixes met the US EPA criterion (0.35 MPa). The strength of S/S soils was less affected by the increase of curing temperature after a longer curing period (28 days). According to the XRD and SEM results, both Pb and Zn in S/S contaminated soil could be immobilized by the precipitation and the adsorption on the surface of calcium silicate hydrate (C-S-H). Zn can also be incorporated into the structure of C-S-H and Ht. The addition of Pb/Zn decreased the physical strength in the order of: Pb(5000 mg/kg)>Pb(10000 mg/kg)>Zn/Pb(5000 mg/kg)>Pb(20000 mg/kg).

Feasibility of Using 3D Printed Polyvinyl Alcohol (PVA) for Creating Self-Healing Vascular Tunnels in Cement System.

Pursuing long-term self-healing infrastructures has gained popularity in the construction field. Vascular networks have the potential to achieve long-term self-healing in cementitious infrastructures. To avoid further monitoring of non-cementitious tubes, sacrificial material can be used as a way of creating hollow channels. In this research, we report a new method for fabrication of complex 3D internal hollow tunnels using 3D printing of polyvinyl alcohol (PVA). The behaviour of 3D printed PVA structures in cement pastes was investigated using computed-tomography (CT) combined with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDX). Results showed that (i) 1300 min were needed to fully dissolve 1 g of a 3D printed PVA structure, and different pH solutions did not significantly change the PVA dissolving process compared with a neutral environment; (ii) a low water/cement ratio can minimize early stage cracking resulting from PVA expansion; (iii) and PVA-cement interaction products were mainly calcite and a Ca-polymer compound. In conclusion, controlling the PVA expansion by decreasing the water/cement (w/c) ratio provides a promising approach to achieve 3D hollow channels in cement and, therefore, makes it possible to create complex tunnels within self-healing cementitious materials.