Membrane distillation of synthetic urine for use in space structural habitat systems

Viral Sagar; Lauren M. Mekalip; Joan G. Lynam

doi:10.1515/gps-2023-0197

Article Open Access

Membrane distillation of synthetic urine for use in space structural habitat systems

Viral Sagar , Lauren M. Mekalip and Joan G. Lynam

Published/Copyright: February 21, 2024

Published by

Become an author with De Gruyter Brill

Submit Manuscript Author Information

From the journal Green Processing and Synthesis Volume 13 Issue 1

Abstract

Low-energy separation of potable water from urine is an important area of research, particularly if humans hope to transcend their earth-bound origins. The high cost of water in rocket payloads means that it must be recycled and the byproducts of the crew used productively. Direct Contact Membrane Distillation (DCMD) can use low heat sources to separate water from urea, which can then be used as a plasticizer in regolith-based cement to make it more workable. In the present study, traditional cement curing was compared to vacuum curing for regolith-based cement where artificial urine, concentrated using DCMD, was added as a plasticizer. Increases in workability were found for increasing concentrations of urea. Porosity also tended to increase with increasing urea concentration. Surprisingly, Lunar Highlands Simulant regolith-based batches with urea that were cured under vacuum showed higher compressive strengths than those cured traditionally. No literature is available for DCMD use with urine, indicating that this research is novel and could have widespread applications, such as in desert environments or public urinals.

Keywords: moon; sustainable; potable water; cement; plasticizer

1 Introduction

To construct any permanent structures on the moon, astronauts will need to source the building materials locally using lunar soil and transported resources, which increases mission costs and fuel. A locally sourced resource that can be found on the moon is lunar regolith, which can significantly reduce the amount of Ordinary Portland Cement (OPC) needed from Earth. When working with OPC, adding a superplasticizer can decrease the amount of water needed for the cement mixture by 30% or more [1]. One such possible superplasticizer is urea that can be sourced from the astronauts’ urine. Urine is composed primarily of water and urea, urea being a valuable compound that has previously been found to work as a superplasticizer [2]. Our work in this project investigated the extraction of urea from synthetic urine with Direct Contact Membrane Distillation (DCMD), using low-temperature heat sources that would be available on the moon [3,4]. The concentrated urea solution from DCMD was used as a superplasticizer for the lunar regolith-based cement and pure OPC as a control [5]. Different temperature gradients for the DCMD were examined to see how they affect the workability, compressive strength, and porosity of the OPC and the lunar regolith-based cement. The lunar regolith and OPC samples were cured under vacuum pressure to replicate the conditions on the lunar surface and compared to those cured using a traditional limewater or 2% Ca(OH)₂ solution bath [6]. Experimental work explored the effects of replacing water with urea solution to serve as a plasticizer [7,8]. The scientific and technical objectives were to investigate possible enhancements to lunar regolith-based cement with the addition of urea, a sustainable material, and to reduce the amount of water required while curing under vacuum pressure conditions like that on the moon. This project’s focus was to find sustainable processes for deep space applications.

2 Materials and methods

2.1 Materials

2.1.1 Synthetic urine preparation

Synthetic urine component salts were procured as follows: urea (CH₄N₂O) ACS reagent 99.0–100.5% grade and creatinine (C₄H₇N₃O) anhydrous ≥98% from Sigma-Aldrich (St Louis, MO, USA); sodium chloride (NaCl) ACS crystalline grade from Fisher Scientific (Fair Lawn, NJ, USA); potassium chloride (KCl), sodium citrate (Na₃C₆H₅O₇) dihydrate grade, sodium sulfate (Na₂SO₄) anhydrous, ammonium chloride (NH₄Cl), calcium chloride (CaCl₂) dihydrate grade, sodium bicarbonate (NaHCO₃), and magnesium sulfate (MgSO₄) heptahydrate from Flinn Scientific (Batavia, IL, USA). De-ionized (DI) water was made in an Aqua FX (Winter Park, FL, USA) four-stage filtration system equipped with a TDS monitor consisting of sediment filter, carbon filter, and two DI resin filters. Distilled water was made in a 1-L MP-1 Corning Glass Works unit (Corning, NY, USA).

Synthetic urine (see Table 1 for composition) was synthesized in our lab using these components added to 500 mL of DI water in a 1,000 mL Erlenmeyer flask where each chemical was added one by one, swirling until fully dissolved after every addition.

Table 1

Synthetic urine components

Component	Weight in solution (g)
DI water	500
Urea	21
Sodium chloride	5.6
Potassium chloride	3.9
Sodium citrate	2.3
Sodium sulfate	2.2
Ammonium chloride	1.4
Creatinine	0.8
Calcium chloride	0.6
Magnesium sulfate	0.4
Sodium bicarbonate	0.3

Magnetic stirring for 2 min was performed for full dissolution of the above salts. The concentration of these compounds in synthetic urine is slightly higher than that expected in a well-hydrated person [9,10].

2.1.2 OPC

OPC was bought from Lowe’s, commercial grade from Quikrete Portland cement type I/II (no. 1124) complying with American Society for Testing Materials (ASTM) C 150 specifications.

2.1.3 Lunar regolith

Three types of lunar regolith were used in this study, i.e., Lunar Highlands Simulant (LHS-1), Dust Lunar Highlands Simulant (LHS-1D), and Lunar Mare Simulant (LMS-1), as shown in Table 2. These were used to create the 30% lunar regolith with 70% OPC batches. They were procured from the Exolith lab, University of Central Florida (Orlando, FL, USA). LHS-1D is only different from LHS-1 in that LHS-1D’s mean particle size is 7 µm, while LHS-1’s mean particle size is 88 µm.

Table 2

Lunar Regoliths (Exolith Lab, 2020) and Typical OPC composition (Holcim (US) Inc., 2020) in wt% concentrations

Compound	LHS-1	LHS-1D	LMS-1	OPC
SiO₂	51.2	51.2	46.9	19.3
TiO₂	0.6	0.6	3.6	0
Al₂O₃	26.6	26.6	12.4	4.9
FeO	2.7	2.7	8.6	0
Fe₂O₃	0	0	0	3.7
MnO	0.1	0.1	0.2	0
MgO	1.6	1.6	16.8	1.3
CaO	12.8	12.8	7.0	64.5
Na₂O	2.9	2.9	1.7	0
K₂O	0.5	0.5	0.7	0
P₂O₅	0.1	0.1	0.2	0
SO₃	0	0	0	3.4
LOI*	0.4	0.4	0.9	2.49
Insoluble residue	0	0	0	0.41
Total**	99.4	99.4	99.0	100.0

*Loss on ignition.

**Excluding volatiles and trace elements.

2.2 Methods

2.2.1 DCMD

DCMD operates on the principle of a flux due to a vapor pressure difference across a controlled surface area membrane, from a temperature difference. A bench scale test cell DCMD S/N: 24,595 unit from Sterlitech Corporation (Auburn, WA, USA) was implemented for this research study to measure crossflow membrane flux. A membrane made up of laminated flat sheet polytetrafluoroethylene (PTFE) with spacers (Sepa CF Medium Foulant Spacer, PP 145 mm × 97 mm, https://www.sterlitech.com/ptfe-flat-sheet-membrane-laminated-0-45-micron-sepa-5-pk-1121877) having a surface coverage area of 0.014 m², a thickness of 64–127 µm, and a pore size of 0.45 µm was used. A Masterflex L/S Easy-Load II 77,200–50 peristaltic pump system from Cole-Parmer Instrument Company (Vernon Hills, IL, USA) was used to achieve fluid flow across the membrane. The temperature difference between the streams was achieved using a VWR Scientific, model 1130A hot water bath (Radnor, PA, USA) and a PolyScience with Digital Temperature Controller, model 9510 cold water bath (Niles, Illinois, USA). The water vapor from the synthetic urine feed passed through the hydrophobic PTFE membrane and then condensed on the distillate side, running for 2 h (see Figure 1). Distilled water initially filling the cold side was kept constant at 10°C using a recirculating chiller. The feed solution from the hot side was 500 mL of synthetic urine. The feed streams had tubes that ran through the bath. The feed and distillate streams were continuously circulated through their respective sides of the membrane at 0.2 L·min⁻¹ using two peristaltic pumps. The volume of the distillate water was recorded every 10 min to calculate the flux of the water vapor passing through the membrane and condensing. The initial and final conductivity readings tested at two temperatures, 50°C and 80°C, using a flow-through chiller or heater for the cold and hot side streams, were recorded prior to starting DCMD and after 2 h. After the completion of DCMD, the concentrated urea solution and the distillate water solution were labeled and placed in a freezer for concentration analysis using high-performance liquid chromatography (HPLC) and for use in cement mixes (Scheme 1).

Figure 1

(a) Direct contact membrane distillation process flow diagram, (b) experimental concept of DCMD, and (c) an actual bench-scale DCMD unit on which membrane flux was evaluated for this study.

Scheme 1

Overall application conceptualization with Direct Contact Membrane Distillation.

2.2.2 Conductivity

Conductivity was measured using a handheld Ohaus Corporation ST20C-C Pen conductivity meter (Parsippany, NJ, USA) for samples prior to and after DCMD.

2.2.3 Concentration analysis using HPLC

The concentration of urea in the DCMD processed water solution was measured using an HPLC instrument UltiMate WPS-3000 Series from ThermoFisher Scientific (Waltham, MA, USA) equipped with a refractive index detector. The column was Hypersil GOLD (100 mm × 2.1 mm) with particle size 1.9 µm specification column from ThermoFisher Scientific. The column temperature was maintained at 30°C, the injection volume was 1 µL, and the flow rate was 0.6 mL·min⁻¹ of the mobile phase. The mobile phase was composed of 50 mL DI water, 450 mL acetonitrile, and 0.5 mL formic acid. Each measurement was performed in triplicate.

2.2.4 Cement mixing

The cement samples were prepared following the ASTM C192 standards. For each batch of cement, cylindrical plastic mold casings were used; each mold was 5.08 cm (2 inches) in diameter and 10.16 cm (4 inches) in height. For this project, a control of OPC was used, along with three lunar regolith-based cement batches. LHS-1, LHS-1D, and LMS-1 were used to create three 30% lunar regolith, 70% OPC batches. Using partial lunar regolith, as opposed to 100% regolith, was recommended by our NASA collaborators as a first step to see if urea use with regolith-based cement binders was feasible. Each batch was prepared using a KitchenAid KP26M1XPM or 600™ mixer (Benton Harbor, MI, USA). Solutions with differing concentrations of DCMD-processed synthetic urine were prepared to use as superplasticizers required for the cement samples. Solutions for our project consisted of DI water as a control, synthetic urine without DCMD processing, a 50°C DCMD concentrated synthetic urine, with a temperature gradient (ΔT) of 40°C, and an 80°C DCMD concentrated synthetic urine (ΔT of 70°C). These solutions varied in urea concentrations and in the other components of the synthetic urine. The OPC and lunar regolith-based cement were slowly added to the liquid solutions until a consistent mixture formed.

2.2.5 Mini-slump test

The cement mixture was poured into a mini-slump cone (height = 57.0 mm, top internal diameter = 18.8 mm, and bottom internal diameter = 36.8 mm) and over a grid plate to measure the slump area. This simulates a miniature version of the conventional slump test, as a modification of the standard ASTM C143-00 slump cone test [11,12]. The cone was then lifted, and the area that the cement mixture spread was recorded, with this mini-slump area used as a measure of the workability of the cement mixture [13].

2.2.6 Cement setting and curing

The remaining cement mixture after slump testing was poured into cylindrical molds of 5.08 cm diameter and 10.16 cm height and allowed to set for 48 h, as found to be necessary for regolith-based cement. After 48 h, half the cement samples were removed from the molds and placed into a water bath with excess calcium hydroxide to allow for curing at temperature 298 K (25°C) and pressure = 0.1 MPa for 28 days, the standard method for curing this type of sample.

After 48 h, the other half of the cement samples were removed from the molds and placed in an Across International AccuTemp-09s vacuum oven to allow for vacuum conditions curing at temperature = 298 K (25℃) and pressure = 0.001 Pa (0.01 atm) for 28 days without calcium hydroxide.

2.2.7 Compressive strength test

Compressive strength testing took place following the 28-day curing period. A load rate was manually applied until failure of the sample occurred. The failure of a sample was set to 85%, meaning that if a crack or a fracture in the sample caused the stress of the sample to fall below 85% of the load being applied, then the machine would stop and display the resulting strength of each sample. A Test Mark Industries (East Palestine, OH, USA) equipment was used for compression testing following ASTM C 39 standard test protocol. A load was applied at 658.4 kPa·s⁻¹ (300 lbs·s⁻¹), until failure of the specimen occurred.

2.2.8 Porosity

After compression testing, each sample and its fractured pieces were labeled and bagged. Fragmented pieces of cement from each sample were weighed, 5–10 g in size, and then submerged in a DI water bath to ensure complete saturation. After 24 h, the pieces were removed from the water and lightly patted with a paper towel and then reweighed. Next, the pieces were placed into a drying oven set to 105°C to remove all moisture from the pores of the cement. After 24, 48, and 72 h, the pieces were removed from the drying oven and let cool for 1 h, then the mass of each piece was recorded, and it was replaced in the oven. The percentage of water that each piece held while saturated compared to the stabilized 72 h dry mass was considered to be a measure of the material’s porous capacity or its porosity.

3 Results

3.1 DCMD

The water vapor from the synthetic urine feed passed through the PTFE membrane and then condensed on the distillate side. With a constant distillate temperature of 10°C, the temperature gradient (ΔT) of 70°C (80°C–10°C) gave the highest average flux at 43.32 ± 7.31 mL·(min⁻¹·m⁻²). The ΔT of 40°C (50°C–10°C) yielded an average flux of 16.67 ± 3.82 mL·(min⁻¹·m⁻²); 39% of the flux obtained with the 70°C ΔT. The vapor pressures of water at 80, 50, and 10°C are 47.37, 12.34, and 1.23 kPa, respectively. Thus, for a ΔT of 70°C, the difference in water vapor pressure is 46.14 kPa, while for a ΔT of 40°C, it is 11.11 kPa.

3.2 Conductivity

The average starting conductivity of the synthetic urine for the 40°C gradient was 10.83 mS·cm⁻¹, and the final conductivity was 11.52 mS·cm⁻¹, an increase of 6%. As the ΔT increased to 70°C, the conductivity of the feed solution increased, with an initial and average final conductivity of 9.82 and 10.71 mS·cm⁻¹, an increase of 8.3%. The initial conductivity of the distillate water was 0.00 mS·cm⁻¹, while the final conductivities were 0.24 mS·cm⁻¹ for the 40°C ΔT and 0.29 mS·cm⁻¹ for the 70°C ΔT.

3.3 Concentration

The initial urea concentration was 40,000 ppm. The concentrations of urea in the synthetic urine solution on the hot side after DCMD were 62,000 ± 1,000 and 66,000 ± 6,000 ppm for ΔTs of 40 and 70°C, respectively. These results indicate an increase in urea concentration of more than 50%. Distillate water after DCMD showed urea concentrations 5,000 ± 3,000 and 6,500 ± 1,500 ppm for ΔTs of 40 and 70°C, respectively.

3.4 Workability (mini-slump test)

The results for the mini-slump test performed for OPC, LHS-1, LMS-1, and LHS-1D cement batches are shown in Figure 2(a)–(d), respectively. The general trend for slump area for OPC batches was increasing area for increasing concentration of urea. Similarly, for regolith – OPC batches, the trend was increasing slump area as urea concentration increased. The slump area for the OPC control tended to increase with the urea added, with the 70°C gradient giving the highest slump area as shown in Figure 2(a)–(d), portraying the slump of the smaller particle size regolith 30% LHS-1D with 70% OPC showed a smaller slump area indicating that it would be less workable compared with the others.

Figure 2

Slump areas for the OPC and lunar regolith-based batches. (a) OPC, (b) 70% OPC and 30% LHS-1, (c) 70% OPC and 30% LMS-1, (d) 70% OPC and 30% LHS-1D.

3.5 Compressive strength

After curing periods of 28 days, Figure 3(a) shows the results for 28-day compressive strength for the different concentrations of urea using OPC without any regolith along with the curing methods for each. For the 70% OPC and 30% LHS-1 lunar regolith samples that were limewater bath cured, as shown in Figure 3(b), samples with urea tended to have lower compressive strength. However, a different trend is shown for the vacuum-cured samples in Figure 3(b), with an increased compressive strength with urea. For the higher urea concentration samples, vacuum-cured samples had a higher compression strength compared with limewater bath curing. For the 70% OPC and 30% LMS-1 lunar regolith samples with standard curing with urea, as shown in Figure 3(c), the compressive strength declines; except for the 40°C ΔT which shows a slight increase in compressive strength. Vacuum curing in Figure 3(c) showed higher compressive strength for urea-containing samples compared to the no urea control. For the 70% OPC and 30% LHS-1D lunar regolith samples, a limewater bath curing was not attempted as it is less irrelevant to lunar research, workability was low for LHS-1D, and the same composition was tested in LHS-1. Figure 3(d) shows that the compressive strength was similar for DI water and the highest urea concentration.

Figure 3

Compression strength testing results for: (a) OPC, (b) 70% OPC and 30% LHS-1, (c) 70% OPC and 30% LMS-1, and (d) 70% OPC and 30% LHS-1D using various solutions with differing concentrations of urea for limewater bath (except (d)) and vacuum cured samples.

3.6 Porosity

Figure 4(a)–(d) displays the results of the porosity testing. Figure 4(a) shows the results for porosity for different concentrations of urea using OPC along with curing methods for each. For standard curing, OPC porosity appears to have reduced with urea plasticizer addition. Figure 4(a) indicates slightly higher porosity for the vacuum-cured samples with urea compared to limewater bath curing. Figure 4(b) shows the results for porosity for different concentrations of urea for LHS-1, along with the curing methods. Little difference in porosity can be seen, except for vacuum curing for the highest urea concentration, which had a high porosity. Figure 4(c) shows the porosity results for different concentrations of urea for LMS-1 samples. Those LMS-1 samples with urea had higher porosity compared to those without. Figure 4(d) shows the results for porosity for different concentrations of urea for LHS-1D for vacuum curing. Little difference in porosity can be seen for LHS-1D.

Figure 4

Water absorption porosity test results for: (a) OPC, (b) 70% OPC and 30% LHS-1, (c) 70% OPC and 30% LMS-1, and (d) 70% OPC and 30% LHS-1D, using various solutions with differing concentrations of urea for 28-day-cured samples.

4 Discussion

4.1 DCMD

As expected, the flux was higher when a larger ΔT was used in the process. The greater ΔT between the feed and distillate temperatures produces a greater pressure driving force to move water vapor through the membrane. The higher ΔT results in a greater pressure difference for the water vapor traveling through the DCMD membrane [14,15].

4.2 Conductivity

The distillate water conductivity increased minimally as the ΔT increased. The low conductivity indicates that the other components, such as sodium chloride in the synthetic urine, do not substantially pass through the membrane, suggesting that the distillate water could possibly have a use in deep space life support activities.

4.3 Concentration

As the feed temperature increased, the concentration of urea increased for both the feed solution and the distillate water, with the distillate water having a very low concentration of urea.

4.4 Workability (mini-slump test)

The increase in the slump area is interpreted as an increase in the workability of the cement mixture. Likewise, an increase in workability was found when urea was used with the lunar regoliths, LHS-1, LMS-1, and LHS-1D added to OPC. LHS-1D had lower workability than the others, likely due to its lower particle size. Smaller particles have greater surface area, allowing for more surface interactions or “stickiness” [16]. Increased surface interactions tend to decrease slump. Greater workability will be required for cement used in the 3-D printing of structures that are envisioned for lunar human habitats [17,18]. Cement has radiation-blocking properties [19], so this material will be essential in deep space bases.

4.5 Compressive strength

For OPC batches, there is a significant decrease in the compressive strength as the urea concentration increases. Also for OPC batches, the 2% Ca(OH)₂ solution (limewater) bath-cured samples without urea showed greater compressive strength compared to those that were vacuum cured. This could relate to a more uniform structure throughout the sample, with fewer fault lines or anomalies due to the limited limewater water diffusion into the samples to fill fault lines. Similarly, for the 70% OPC and 30% LHS-1 lunar regolith batches in Figure 3(b), there was lower compressive strength with added urea for limewater-cured batches, possibly for the same reason. However, the vacuum-cured samples with added urea had higher compression strength in Figure 3(b) compared to the no urea vacuum-cured control. This finding may relate to improved workability allowing fewer fault lines. In Figure 3(c) for 70% OPC and 30% LMS-1 lunar regolith batches made with urea solution, standard limewater curing shows lower compressive strength with 40°C ΔT as an outlier, possibly due to errors during the pandemic. Again, higher compression strength in Figure 3(c) for vacuum-cured samples with added urea compared to the no urea vacuum-cured control may relate to improved workability allowing fewer fault lines. For the 70% OPC and 30% LHS-1D lunar regolith batches in Figure 3(d), generally as urea concentration increased, the compressive strength increased but the DI water-based batch also showed relatively high compressive strength. The properties of LHS-1D are slightly different from LHS-1 due to LHS-1D’s mean particle size of 7 µm, which gives it some special low microscopic peculiarities typically observed in 1–10 µm range. Further microscopy study of these samples and the interactions of regolith with urea will be an area of investigation to explore in future work.

4.6 Porosity

For standard limewater bath curing, OPC porosity appears to be reduced with urea plasticizer addition. This finding could relate to greater workability for these OPC batches permitting greater compaction of the samples or better diffusion of the Ca(OH)₂ into the smaller pores to fill them. Conversely, larger but fewer pores could exist in the samples with urea, which would be consistent with the lower compression strength found for these samples. Larger pores or increased porosity leads to decreased compression strength [20]. For the higher porosity of the vacuum-cured samples with urea compared to limewater bath curing such phenomena could result from no diffusion of the Ca(OH)₂ into the pores to fill them. Little difference in porosity can be seen for different concentrations of urea for LHS-1, except for vacuum curing for the highest urea concentration, which had a high porosity. The LHS-1 batch composition showed the highest workability, and its samples had a high compression strength. This outcome could relate to greater workability for these batches permitting greater compaction of the samples. For LMS-1 samples, those samples with urea had higher porosity compared to those without which could be due to the higher magnesium oxide (MgO) content of LMS-1, which is 10 times higher than that for LHS-1. MgO is known to be an expansive agent [21,22], explaining the slightly higher porosity for these samples compared to the LHS-1 ones. The greater workability for the urea-containing batches suggests that more expansion was possible in the samples and that expansion into the pores caused them to be finer, resulting in higher compression strength for some of the urea-containing samples. For LHS-1D, little difference in porosity can be seen. The low workability of these samples suggests that less compaction was possible, which could result in higher porosity. Vacuum curing in general causes less air pressure on the sample and no infiltration of calcium into the sample from a limewater bath can occur, so that a high porosity tends to be produced. More work is needed to investigate the mechanisms by which cement cures under vacuum. Future research will investigate cement properties for 100% regolith and the effects of temperature in vacuum curing.

5 Conclusions

Analysis of the data demonstrated that with a higher temperature difference between hot side and cold side of DCMD, a higher flux rate for the water vapor transfer and a higher urea concentration could be achieved. After the DCMD process, valuable water could be obtained along with a concentrated urea solution that could be used for cement and lunar regolith batching to develop sustainable lunar habitats and other inter-planetary habitats. Also, the results of adding various concentrations of urea to cement batches consisting of OPC, LHS-1, LHS-1D, and LMS-1 were analyzed. The workability for the lunar regolith batches was higher than that of the OPC without regolith, based on the slump test results; and an increase in workability was found for batches with urea. The smaller particle size regolith, LHS-1D, had less workability. Generally, porosity increased when urea was in the batch for all the cement batches: OPC alone and the partial lunar regolith batches with LHS-1, LMS-1, and LHS-1D. The compressive strength for limewater-cured OPC-only samples was lower for those that contained urea. The samples’ higher porosity could have contributed to lower compressive strengths. However, with vacuum curing, the partial regolith samples tended to have higher compression strength if urea was a part of the mix. Thus, sourcing urea from human-crewed lunar missions may improve the feasibility of 3D printing regolith-based structures.

Acknowledgments

We thank Dr Narendra Kumar, an alumnus of the Biomass team, Chemical Engineering at Louisiana Tech University for his expert input on HPLC, DCMD, and compression testing. We also thank the undergraduate researchers: Destiny Lee and Joshua Ekechukwu of Chemical Engineering and Damien Gautreaux of Instrumentation and Control Systems Engineering Technology at Louisiana Tech University who helped with performing several of the DCMD runs and compression testing trials. We also thank Dr Henry Cardenas, of Mechanical Engineering, Dr Sven Eklund, of Chemistry Department, Dr Shaurav Alam, and Dr John Matthews, of Civil Engineering, Associate Professors at Louisiana Tech University for their input on cement work and chemistry support. We would also like to thank Luz Marino Calle, PhD, Lead Scientist Corrosion Lab at Kennedy Space Center for her advice.

Funding information: This work was supported by NASA as Award 80NSSC20M0110 LSU LEQSF(2020-24)-LaSPACE GRSA and the Board of Regents of the State of Louisiana Award LEQSF(2020-24)-LaSPACE REA.
Author contributions: Viral Sagar: data curation, formal analysis, investigation, methodology, project administration, software, validation, visualization, writing – original draft, writing – review & editing; Lauren Mekalip: data curation, investigation, methodology, project administration; Joan Lynam: conceptualization, funding acquisition, project administration, resources, supervision, writing – review & editing.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

References

[1] Ran Q, Miao C, Liu J, Wu S, Shen J. Performance and mechanism of a multi-functional superplasticizer for concrete. Mater Trans. 2006;47(6):1599–604.10.2320/matertrans.47.1599Search in Google Scholar

[2] Pilehvar S, Arnhof M, Pamies R, Valentini L, Kjøniksen AL. Utilization of urea as an accessible superplasticizer on the moon for lunar geopolymer mixtures. J Clean Prod. 2020;247:1–9. 10.1016/j.jclepro.2019.119177.Search in Google Scholar

[3] Wan Aisyah Fadilah Wae A, Abdul Latif A, Ooi Boon S. Carnauba wax/halloysite nanotube with improved anti-wetting and permeability of hydrophobic PVDF membrane via DCMD. Membranes. 2021;11(228):228. 10.3390/membranes11030228.Search in Google Scholar PubMed PubMed Central

[4] Mohammad Ameen NA, Ibrahim SS, Alsalhy QF, Figoli A. Highly salinewater desalination using direct contact membrane distillation (DCMD): Experimental and simulation study. Water (Switz). 2020;12(6):1–24. 10.3390/w12061575.Search in Google Scholar

[5] Alessandra C, Alfredo C, Michele A, Enrico D. Low-temperature direct contact membrane distillation for the treatment of aqueous solutions containing urea. Membranes. 2020;10(176):176. 10.3390/membranes10080176.Search in Google Scholar PubMed PubMed Central

[6] Pilehvar S, Arnhof M, Erichsen A, Valentini L, Kjøniksen AL. Investigation of severe lunar environmental conditions on the physical and mechanical properties of lunar regolith geopolymers. J Mater Res Technol. 2021;11:1506–16. 10.1016/j.jmrt.2021.01.124.Search in Google Scholar

[7] Go G-H, Lee J, Chung T, Ryu BH, Jin H, Zhuang L, et al. Controlling soil disturbance of a lunar regolith simulant bed during depressurization in a vacuum chamber. Sci Rep-UK. 2021;11(1):1–8. 10.1038/s41598-021-81317-1.Search in Google Scholar PubMed PubMed Central

[8] Makul N, Vongpradubchai S, Rattanadecho P. An experimental study of microwave drying under low pressure to accelerate the curing of Portland cement pastes using a combined unsymmetrical double-fed microwave and vacuum system. Int J Heat Mass Transf. 2018;127(Part A):179–92. 10.1016/j.ijheatmasstransfer.2018.06.119.Search in Google Scholar

[9] Deneau JD. Inventor. Composition of Human Synthetic Urine. 2013.Search in Google Scholar

[10] Sarigul N, Korkmaz F, Kurultak İ. A new artificial urine protocol to better imitate human urine. Sci Rep-UK. 2019;9(1):1–11. 10.1038/s41598-019-56693-4.Search in Google Scholar PubMed PubMed Central

[11] Bouvet A, Ghorbel E, Bennacer R. The mini-conical slump flow test: Analysis and numerical study. Cem Concr Res. 2010;40(10):1517–23. 10.1016/j.cemconres.2010.06.005.Search in Google Scholar

[12] Tan Z, Bernal SA, Provis JL. Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes. Mater Struct. 2017;50(6):1–12. 10.1617/s11527-017-1103-x.Search in Google Scholar PubMed PubMed Central

[13] Němeček J. Numerical simulation of slump flow test of cement paste composites. Acta Polytech CTU Pro. 2021;30:58–62. 10.14311/APP.2021.30.0058.Search in Google Scholar

[14] Liu Y, Xiao T, Bao C, Zhang J, Yang X. Performance and fouling study of asymmetric PVDF membrane applied in the concentration of organic fertilizer by direct contact membrane distillation (DCMD). Membranes. 2018;8(1):1–13. 10.3390%2Fmembranes8010009.Search in Google Scholar

[15] Plattner J, Kazner C, Naidu G, Vigneswaran S, Wintgens T. Removal of selected pesticides from groundwater by membrane distillation. Environ Sci Pollut R. 2018;25(21):20336–47. 10.1007/s11356-017-8929-1.Search in Google Scholar PubMed

[16] Cepuritis R, Jacobsen S, Smeplass S, Mørtsell E, Wigum BJ, Ng S. Influence of crushed aggregate fines with micro-proportioned particle size distributions on rheology of cement paste. Cem Concr Compos. 2017;80:64–79. 10.1016/j.cemconcomp.2017.02.012.Search in Google Scholar

[17] Toklu YC, Akpinar P. Lunar soils, simulants and lunar construction materials: An overview. Adv Space Res. 2022;70(3):762–79. 10.1016/j.asr.2022.05.017.Search in Google Scholar

[18] Lin A, Goel A, Wong DHA, Yeo C, Chung J, Pang SD, et al. Compressive load-dominated concrete structures for customized 3D-printing fabrication. Autom Constr. 2022;141:1–16. 10.1016/j.autcon.2022.104467.Search in Google Scholar

[19] Radziejowska A, Sagan J, Sobotka A. Technological and organizational problems in the construction of the radiation shielding concrete and suggestions to solve: A case study. Open Eng. 2021;11(1):1114–21. 10.1515/eng-2021-0082.Search in Google Scholar

[20] Sorokin EM, Yakovlev OI, Slyuta EN, Gerasimov MV, Zaitsev MA, Shcherbakov VD, et al. Experimental Model of the Formation of Nanophase Metallic Iron in the Lunar Regolith. Dokl Earth Sci. 2020;492(2):431–3. 10.1134/S1028334X20060203.Search in Google Scholar

[21] Li S, Feng Y, Yang J. Expansion Mechanism and Properties of Magnesium Oxide Expansive Hydraulic Cement for Engineering Applications. Adv Mater Sci Eng. 2021;2021:1–9. 10.1155/2021/5542072.Search in Google Scholar

[22] Mo L, Deng M, Tang M, Al-Tabbaa A. MgO expansive cement and concrete in China: Past, present and future. Cem Concr Res. 2014;57:1–12. 10.1016/j.cemconres.2013.12.007.Search in Google Scholar

Received: 2023-09-28

Accepted: 2024-01-14

Published Online: 2024-02-21

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/gps-2023-0197

Keywords for this article

moon; sustainable; potable water; cement; plasticizer

Creative Commons

BY 4.0