{
  "spore": "profile",
  "id": "sulfur-concrete",
  "spore_version": "0.2",
  "family": "regolith",
  "name": "Sulfur concrete (waterless lunar concrete)",
  "role": "Construction material that binds regolith with molten sulfur instead of cement and water",
  "category": "regolith",
  "type": "lunar-concrete",
  "summary": "Sulfur concrete is a construction material made from molten elemental sulfur and regolith aggregate, with no cement and no water. In a NASA Marshall hypervelocity test, a 5 cm cube of a 35% sulfur and 65% JSC-1 lunar regolith simulant mix formed a conical crater 12.8 mm in average diameter and 3.1 mm deep after a 1 mm aluminium projectile hit it at 5.85 km/s. The same mix reached 22.0 MPa compressive strength in Table 1 of the 2010 paper, against 17.2 MPa for conventional concrete in that table. The sulfur binder melts at about 119 °C, and 80 cycles to -191 °C cut compressive strength to 20% of the uncycled value.\n",
  "best_for": "Lunar structures where water is scarce and sulfur can be extracted from regolith; the papers also describe acid and salt resistance on Earth",
  "weakest_at": "Thermal cycling and heat: 80 cycles to -191 °C cut compressive strength to 20% of the uncycled value, and the product cannot be used above the melting point of sulfur, about 119 °C",
  "identity": {
    "formula": "Molten elemental sulfur binder with JSC-1 lunar regolith simulant aggregate; a composite, not a single compound",
    "designations": [],
    "source": "toutanji-a",
    "where": "Section 2 (sulfur is a thermoplastic that binds a non-reactive aggregate); Section 2.1 (35% sulfur and 65% JSC-1 by mass)"
  },
  "tags": {
    "environments": [],
    "stresses": [
      "thermal-cycling",
      "micrometeoroids-and-debris",
      "total-radiation-dose"
    ],
    "applications": [
      "structures",
      "radiation-shielding"
    ]
  },
  "properties": [
    {
      "benchmark": "compressive_strength",
      "label": "Compressive strength, waterless concrete (35% sulfur, 65% JSC-1)",
      "value": 22,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "mix": "35% sulfur and 65% JSC-1 lunar regolith simulant by mass",
        "specimen": "50.8 mm (2 in) cube",
        "strength_as_printed": "3191 psi"
      },
      "method": "Compressive strength as printed in Table 1, row B (waterless concrete)",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 2.2 (Results), Table 1, row B",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "compressive_strength",
      "label": "Compressive strength, conventional concrete comparison (water-to-cement about 0.4)",
      "value": 17.2,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "mix": "Group A conventional concrete: coarse and fine aggregate, cement and water, water-to-cement ratio about 0.4",
        "strength_as_printed": "2500 psi"
      },
      "method": "Compressive strength as printed in Table 1, row A, used by the paper as the comparison concrete",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 2.2 (Results), Table 1, row A",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "compressive_strength",
      "label": "Compressive strength, uncycled sulfur concrete (2009 paper)",
      "value": 35,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "mix": "35% purified sulfur and 65% JSC-1 by mass",
        "specimen": "50.8 mm cube",
        "state": "uncycled control specimens, average maximum compressive strength",
        "test_temperature": "not stated for this average in the text"
      },
      "method": "Average maximum compression strength of non-cycled samples as printed in the text",
      "status": "ground",
      "note": "Same mix as the 22.0 MPa value above, reported in the 2009 paper by the same team, so the two values disagree; both are kept as printed.",
      "source": "toutanji-b",
      "where": "Section 1.2 (Results), compression test text",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "compressive_strength",
      "label": "Compressive strength after 80 cycles to -191 °C",
      "value": 7,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "mix": "35% sulfur and 65% JSC-1 lunar regolith simulant by mass",
        "cycling": "80 cycles between liquid nitrogen (about -191 °C) and room temperature (about 21 °C)",
        "specimen": "25.4 mm cube for the severe freeze-thaw test"
      },
      "method": "Average maximum compression strength of cycled samples as printed in the text; the paper says the cycled samples failed at a load five times lower than uncycled",
      "status": "ground",
      "source": "toutanji-b",
      "where": "Section 1.1 (specimen preparation), Section 1.2 (Results), Figure 2 text",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "strength_retention_after_thermal_cycling",
      "label": "Compressive strength of cycled sulfur concrete as a share of uncycled",
      "value": 20,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "mix": "35% sulfur and 65% JSC-1 lunar regolith simulant by mass",
        "cycling": "80 cycles between liquid nitrogen and room temperature"
      },
      "method": "Share as printed in the abstract",
      "status": "ground",
      "source": "toutanji-b",
      "where": "Abstract",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point of the elemental sulfur binder",
      "value": 119,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "elemental sulfur used as the binder",
        "basis": "approximate value as printed (about 119 °C)"
      },
      "method": "Approximate melting point stated in the text",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete), first paragraph",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "stiffening_temperature",
      "label": "Temperature above which molten sulfur stiffens",
      "value": 148,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "elemental sulfur binder"
      },
      "method": "Value stated in the text",
      "status": "ground",
      "note": "Property name is not in the canonical list; see gaps.",
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete), first paragraph",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "max_service_temp",
      "label": "Upper use limit set by the sulfur melting point",
      "value": 119,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "basis": "the paper states the concrete cannot be used where the environment exceeds the melting point of sulfur, about 119 °C as printed"
      },
      "method": "Upper limit taken from the source statement; the paper gives no service test at this temperature",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete), first paragraph",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "mixing_temperature",
      "label": "Mixing and mould temperature for sulfur concrete",
      "value": 130,
      "value_high": 145,
      "bound": "range",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "process": "sulfur and aggregate mixed and heated between 130 and 140 °C; melting pot heated to 145 °C; moulds placed in an oven at 150 °C"
      },
      "method": "Temperatures as printed in the text and the experimental procedure",
      "status": "ground",
      "note": "The paper gives 130 to 140 °C for mixing; 145 °C is the melting-pot setting in the procedure.",
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete), Section 2.1 (Experimental procedure) steps 2 and 6",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "sulfur_content",
      "label": "Sulfur share in typical sulfur concrete",
      "value": 12,
      "value_high": 22,
      "bound": "range",
      "unit": "wt. %",
      "scope": "material",
      "conditions": {
        "basis": "typical commercial sulfur concrete composition as printed; aggregate makes up 78 to 88 wt. %"
      },
      "method": "Range stated in the text",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete), first paragraph",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "density",
      "label": "Density of sulfur JSC-1 concrete used in the radiation calculation",
      "value": 2.241339,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "composition": "Sulfur 35%, JSC-1 simulant 65%; the table lists sulfur 35%, oxygen 28%, silicon 14%, iron 5.3%, carbon 0.0007%",
        "use": "input to the shielding thickness calculation"
      },
      "method": "Density as printed in Table 2; the paper does not say how the density was obtained",
      "status": "calculated",
      "source": "toutanji-a",
      "where": "Section 4.1 (Sulfur concrete mix), Table 2, row Sulfur JSC-1 Concrete",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "radiation_shielding_areal_density",
      "label": "Shielding thickness of sulfur JSC-1 concrete to reach 80 cSv/yr",
      "value": 15,
      "bound": "exact",
      "unit": "g/cm2",
      "scope": "material",
      "conditions": {
        "dose_limit": "ICRP 60 dose equivalent of 80 cSv/yr as the comparison standard",
        "environment": "galactic cosmic radiation, 1977 solar minimum",
        "code": "NASA Langley mathematical code as described in the paper"
      },
      "method": "Value as printed in Table 2, extrapolated from the ICRP 60 curve in Figure 5; the paper says the code is for comparison only",
      "status": "calculated",
      "source": "toutanji-a",
      "where": "Section 4.1, Table 2 and Figure 5",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "required_wall_thickness",
      "label": "Wall thickness of sulfur JSC-1 concrete to reach 80 cSv/yr",
      "value": 6.6924281,
      "bound": "exact",
      "unit": "cm",
      "scope": "material",
      "conditions": {
        "basis": "shield thickness divided by density (Equation 1), same 80 cSv/yr and 1977 solar minimum basis"
      },
      "method": "Calculated in the paper with Equation 1 and printed in Table 2",
      "status": "calculated",
      "source": "toutanji-a",
      "where": "Section 4.1, Equation 1 and Table 2",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "hypervelocity_crater_diameter",
      "label": "Average crater diameter after a 1 mm aluminium impact at 5.85 km/s",
      "value": 12.8,
      "bound": "exact",
      "unit": "mm",
      "scope": "material",
      "conditions": {
        "target": "5 cm cube of 35% sulfur and 65% JSC-1 by mass",
        "projectile": "1 mm diameter aluminium, about 1.4e-03 g",
        "velocity": "5.85 km/s",
        "facility": "MSFC Impact Test Facility, Micro Light Gas Gun"
      },
      "method": "Measured average crater diameter as printed (6.4 mm radius)",
      "status": "ground",
      "note": "The hydrocode simulation in the same paper gives a crater about 15 mm in diameter and 3.5 mm deep, which the authors describe as in good agreement.",
      "source": "toutanji-a",
      "where": "Section 3 (Impact test) and Figure 4 caption",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "hypervelocity_crater_depth",
      "label": "Central crater depth after a 1 mm aluminium impact at 5.85 km/s",
      "value": 3.1,
      "bound": "exact",
      "unit": "mm",
      "scope": "material",
      "conditions": {
        "target": "5 cm cube of 35% sulfur and 65% JSC-1 by mass",
        "projectile": "1 mm diameter aluminium, about 1.4e-03 g",
        "velocity": "5.85 km/s"
      },
      "method": "Measured central depth as printed",
      "status": "ground",
      "source": "toutanji-a",
      "where": "Section 3 (Impact test)",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
        "year": 2010,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "strength_increase_glass_fibre",
      "label": "Strength increase from lunar glass fibre reinforcement",
      "value": 45,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "reinforcement": "glass fibres drawn from JSC-1 simulant, about 1% by mass; short fibres 3 to 20 µm and long fibres 0.50 to 1 mm",
        "mix": "35% sulfur and 65% JSC-1 by mass",
        "test": "four-point bending for flexural strength"
      },
      "method": "Percentage increase as printed in the abstract; the conclusions give up to 40% for the same reinforcement",
      "status": "ground",
      "note": "The abstract says up to 45% for flexural strength; the conclusions say up to 40%. Both are printed in the paper; the abstract value is kept here.",
      "source": "toutanji-b",
      "where": "Abstract; Section 2.2 (Results); Section 3 (Conclusions)",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "strength_increase_silica",
      "label": "Compressive strength increase from adding silica to the binder",
      "value": 26,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "basis": "as much as 26% as printed; the base for the comparison is not stated in the sentence"
      },
      "method": "Value printed in the introduction, which cites Toutanji et al. 2006; that earlier paper could not be opened",
      "status": "ground",
      "source": "toutanji-b",
      "where": "Introduction (Section 1, first column)",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "glass_fibre_content",
      "label": "Lunar glass fibre content in reinforced sulfur concrete",
      "value": 1,
      "bound": "exact",
      "unit": "% by mass",
      "scope": "material",
      "conditions": {
        "fibre_source": "glass fibres drawn from JSC-1 lunar regolith simulant melted at 1450 to 1600 °C"
      },
      "method": "Value printed as about 1% by mass for the reinforced plates",
      "status": "ground",
      "source": "toutanji-b",
      "where": "Section 2.2 (Results), plates paragraph",
      "source_detail": {
        "title": "Performance of Waterless Concrete",
        "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
        "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
        "year": 2009,
        "kind": "paper",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "density",
      "label": "Relative density of precipitated sulfur powder, product 5735",
      "value": 2.05,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "form": "precipitated sulfur powder, product 5735",
        "temperature": "20 °C (68 °F)",
        "basis": "relative density as printed in the SDS"
      },
      "method": "Relative density printed in Section 9 (Physical and Chemical Properties) of the SDS",
      "status": "ground",
      "source": "columbus-sulfur-sds",
      "where": "Section 9 (Physical and Chemical Properties), Relative density",
      "source_detail": {
        "title": "Safety Data Sheet, Sulfur Precipitated, Powder 5735 (Columbus Chemical Industries)",
        "id": "Columbus Chemical Industries SDS, revised 04/28/2023",
        "url": "https://www.columbuschemical.com/MSDS/SDS/Sulfur%20Precipitated,%20Powder%205735.pdf",
        "year": 2023,
        "kind": "datasheet"
      }
    },
    {
      "benchmark": "density",
      "label": "Density of elemental sulfur powder, NIST reference material 8553",
      "value": 2.07,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "form": "powdered elemental sulfur, NIST RM 8553 (IAEA-S-4)",
        "unit_in_source": "g/mL",
        "temperature": "not stated in the SDS"
      },
      "method": "Density printed in Section 9 (Physical and Chemical Properties) of the SDS; the SDS prints the unit as g/mL, which equals g/cm3",
      "status": "ground",
      "source": "nist-srm8553-sds",
      "where": "Section 9 (Physical and Chemical Properties), Density",
      "source_detail": {
        "title": "Safety Data Sheet, NIST Reference Material 8553 (elemental sulfur, IAEA-S-4)",
        "id": "NIST RM 8553 SDS, date of issue 15 February 2022",
        "url": "https://tsapps.nist.gov/srmext/msds/8553-MSDS.pdf",
        "year": 2022,
        "kind": "datasheet",
        "license": "US government publication (NIST)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point of precipitated sulfur powder, product 5735",
      "value": 118,
      "value_high": 120,
      "bound": "range",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "precipitated sulfur powder, product 5735"
      },
      "method": "Range printed in Section 9 (Physical and Chemical Properties) of the Columbus SDS",
      "status": "ground",
      "note": "Kept beside the 119 °C in the NASA papers and the 113 °C in the NIST SDS, because the sources disagree and all values are printed.",
      "source": "columbus-sulfur-sds",
      "where": "Section 9 (Physical and Chemical Properties), Melting point/freezing point",
      "source_detail": {
        "title": "Safety Data Sheet, Sulfur Precipitated, Powder 5735 (Columbus Chemical Industries)",
        "id": "Columbus Chemical Industries SDS, revised 04/28/2023",
        "url": "https://www.columbuschemical.com/MSDS/SDS/Sulfur%20Precipitated,%20Powder%205735.pdf",
        "year": 2023,
        "kind": "datasheet"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point of elemental sulfur powder, NIST reference material 8553",
      "value": 113,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "powdered elemental sulfur, NIST RM 8553 (IAEA-S-4)",
        "unit_in_source": "C (235.4 F)"
      },
      "method": "Melting point/freezing point printed in Section 9 (Physical and Chemical Properties) of the NIST SDS",
      "status": "ground",
      "note": "Sources disagree: the NASA papers give 119 °C and the Columbus SDS gives 118 to 120 °C, so all three are kept as printed.",
      "source": "nist-srm8553-sds",
      "where": "Section 9 (Physical and Chemical Properties), Melting point/freezing point",
      "source_detail": {
        "title": "Safety Data Sheet, NIST Reference Material 8553 (elemental sulfur, IAEA-S-4)",
        "id": "NIST RM 8553 SDS, date of issue 15 February 2022",
        "url": "https://tsapps.nist.gov/srmext/msds/8553-MSDS.pdf",
        "year": 2022,
        "kind": "datasheet",
        "license": "US government publication (NIST)"
      }
    },
    {
      "benchmark": "flash_point",
      "label": "Flash point of elemental sulfur powder, closed cup, NIST reference material 8553",
      "value": 207,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "powdered elemental sulfur, NIST RM 8553 (IAEA-S-4)",
        "test": "closed cup, as printed on the SDS"
      },
      "method": "Flash Point (Closed Cup) printed in Section 9 (Physical and Chemical Properties) of the NIST SDS",
      "status": "ground",
      "source": "nist-srm8553-sds",
      "where": "Section 9 (Physical and Chemical Properties), Flash Point (Closed Cup)",
      "source_detail": {
        "title": "Safety Data Sheet, NIST Reference Material 8553 (elemental sulfur, IAEA-S-4)",
        "id": "NIST RM 8553 SDS, date of issue 15 February 2022",
        "url": "https://tsapps.nist.gov/srmext/msds/8553-MSDS.pdf",
        "year": 2022,
        "kind": "datasheet",
        "license": "US government publication (NIST)"
      }
    },
    {
      "benchmark": "flash_point",
      "label": "Flash point of precipitated sulfur powder, product 5735",
      "value": 204,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "precipitated sulfur powder, product 5735",
        "test": "test method not given on the printed line"
      },
      "method": "Flash point printed in Section 9 (Physical and Chemical Properties) of the Columbus SDS",
      "status": "ground",
      "source": "columbus-sulfur-sds",
      "where": "Section 9 (Physical and Chemical Properties), Flash point",
      "source_detail": {
        "title": "Safety Data Sheet, Sulfur Precipitated, Powder 5735 (Columbus Chemical Industries)",
        "id": "Columbus Chemical Industries SDS, revised 04/28/2023",
        "url": "https://www.columbuschemical.com/MSDS/SDS/Sulfur%20Precipitated,%20Powder%205735.pdf",
        "year": 2023,
        "kind": "datasheet"
      }
    },
    {
      "benchmark": "sublimation_time_1cm",
      "label": "Predicted time to sublimate a 1 cm layer of sulfur concrete with 57% aggregate by volume at about 20 °C",
      "value": 4.4,
      "bound": "exact",
      "unit": "yr",
      "scope": "material",
      "conditions": {
        "aggregate": "57% aggregate by volume, as printed in the summary",
        "temperature": "about 20 °C (68 °F)",
        "environment": "chamber vacuum of 5 × 10–7 torr; the lunar pressure was not used for this value",
        "basis": "Hertz-Knudsen prediction with an evaporation coefficient of 1.0, from weight loss over 60 days"
      },
      "method": "Prediction printed in the summary of sublimation concerns; the report applies it to the stated conditions only",
      "status": "calculated",
      "source": "grugel2008",
      "where": "Section 2.4 (Summary of Sublimation Concerns)",
      "source_detail": {
        "title": "Sulfur 'Concrete' for Lunar Applications: Environmental Considerations",
        "id": "NASA/TM-2008-215250; NTRS 20080022947",
        "url": "https://ntrs.nasa.gov/api/citations/20080022947/downloads/20080022947.pdf",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "sublimation_time_1cm",
      "label": "Predicted time to sublimate a 1 cm layer of sulfur concrete with 69.6% aggregate by volume at about 20 °C",
      "value": 6.5,
      "bound": "exact",
      "unit": "yr",
      "scope": "material",
      "conditions": {
        "aggregate": "69.6% aggregate by volume, as printed in the summary",
        "temperature": "about 20 °C (68 °F)",
        "environment": "chamber vacuum of 5 × 10–7 torr; the lunar pressure was not used for this value",
        "basis": "Hertz-Knudsen prediction with an evaporation coefficient of 1.0, from weight loss over 60 days"
      },
      "method": "Prediction printed in the summary of sublimation concerns; the report applies it to the stated conditions only",
      "status": "calculated",
      "source": "grugel2008",
      "where": "Section 2.4 (Summary of Sublimation Concerns)",
      "source_detail": {
        "title": "Sulfur 'Concrete' for Lunar Applications: Environmental Considerations",
        "id": "NASA/TM-2008-215250; NTRS 20080022947",
        "url": "https://ntrs.nasa.gov/api/citations/20080022947/downloads/20080022947.pdf",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Thermal cycling between liquid nitrogen (about -191 °C) and room temperature (about 21 °C), 80 cycles",
      "headline": "Cycling to -191 °C cut compressive strength to 20% of the uncycled value.",
      "effect": "Cycled specimens failed at about 7 MPa, against about 35 MPa for uncycled specimens. The authors attribute the loss to cracks from debonding between sulfur and aggregate, because the two have very different coefficients of thermal expansion. They say the temperature at which debonding starts is not known.",
      "rating": "severe",
      "conditions": {
        "cycles": "80",
        "cube_size": "25.4 mm",
        "mix": "35% sulfur and 65% JSC-1 by mass",
        "test_temperatures": "about 21 °C and -101 °C"
      },
      "source": "toutanji-b",
      "where": "Abstract; Section 1.1 and Section 1.2; Section 3 (Conclusions)"
    },
    {
      "environment": "Acid and salt exposure",
      "headline": "Sulfur concrete is well established for corrosive acid and salt environments on Earth.",
      "effect": "Both papers describe sulfur concrete as established in corrosive acid and salt environments, with low water permeability, and say it generally has better mechanical properties than Portland cement. Neither paper gives a corrosion rate or a test duration.",
      "rating": "low",
      "conditions": {
        "basis": "qualitative statements in the papers; no test numbers"
      },
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete)"
    },
    {
      "environment": "Temperature above the melting point of sulfur (about 119 °C)",
      "headline": "Above about 119 °C the sulfur binder melts, so the product cannot be used there.",
      "effect": "The paper says the concrete cannot be used in an environment that exceeds the melting point of sulfur. Mixing is done at 130 to 140 °C because sulfur stiffens above 148 °C, so the working range is narrow.",
      "rating": "severe",
      "conditions": {
        "binder": "elemental sulfur"
      },
      "source": "toutanji-a",
      "where": "Section 2 (Sulfur concrete)"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "The NIST SRM 8553 safety data sheet for elemental sulfur (CAS 7704-34-9) classifies the powder as Flammable Solids Category 2 (H228, Flammable solid) and Skin Corrosion/Irritation Category 2 (H315, Causes skin irritation), with signal word WARNING.",
        "ghs": [],
        "source": "nist-srm8553-sds",
        "where": "Section 2 (Hazards Identification), Classification and Hazard Statement(s)"
      },
      {
        "text": "The Columbus Chemical safety data sheet for sulfur precipitated powder, product 5735, gives H228 Flammable solid and H315 Causes skin irritation, with signal word Warning. It also lists combustible dust as a hazard not otherwise classified.",
        "ghs": [],
        "source": "columbus-sulfur-sds",
        "where": "Section 2 (Hazards Identification), GHS classification and hazard statements"
      },
      {
        "text": "The NIST safety data sheet says 'Dust/air mixtures may ignite or explode' and 'May ignite if exposed to shock, friction or heating', and it advises avoiding friction and static electricity.",
        "ghs": [],
        "source": "nist-srm8553-sds",
        "where": "Section 5 (Fire Fighting Measures), Fire and Explosion Hazards"
      },
      {
        "text": "In a fire the product emits toxic fumes, which the Columbus safety data sheet identifies as sulfur dioxide.",
        "ghs": [],
        "source": "columbus-sulfur-sds",
        "where": "Section 5 (Firefighting Measures), Specific hazards arising from the chemical"
      },
      {
        "text": "The NIST safety data sheet, Section 11, says short-term exposure to sulfur dust may irritate the respiratory tract. It also says eye contact may cause eye irritation, while its serious eye damage classification reads 'Not classified'.",
        "ghs": [],
        "source": "nist-srm8553-sds",
        "where": "Section 11 (Toxicological Information), Potential Health Effects and Serious Eye Damage/Irritation"
      }
    ],
    "failure_risks": [
      {
        "mode": "Impact damage to a lunar silo wall from micrometeoroids",
        "trigger": "Hypervelocity impact; the test used a 1 mm aluminium projectile at 5.85 km/s on a 5 cm cube",
        "consequence": "The test crater was 12.8 mm across and 3.1 mm deep, with fractures about 1 cm into the sample. For a 30-foot-tall silo the paper estimates about 1% probability of serious impact damage over 20 years, and about 10% probability of wall penetration if ten such silos form a lunar base.",
        "severity": "moderate",
        "source": "toutanji-a",
        "where": "Section 3 (Impact test), including the 30-foot silo paragraph"
      },
      {
        "mode": "Cracking from thermal cycling",
        "trigger": "80 cycles between liquid nitrogen (about -191 °C) and room temperature",
        "consequence": "Compressive strength fell to 20% of the uncycled value, from about 35 MPa to about 7 MPa.",
        "severity": "high",
        "source": "toutanji-b",
        "where": "Abstract; Section 1.2 (Results)"
      },
      {
        "mode": "Binder melting above the melting point of sulfur",
        "trigger": "Service environment above about 119 °C",
        "consequence": "The sulfur binder melts, so the product cannot be used in that environment.",
        "severity": "high",
        "source": "toutanji-a",
        "where": "Section 2 (Sulfur concrete)"
      }
    ],
    "side_effects": [
      {
        "text": "Heating lunar soil above 1100 °C in a vacuum releases sulfur as SO2 and H2S gases. The paper describes converting these gases to elemental sulfur and water by the Claus process over a catalyst bed at 323 °C.",
        "affects": "Any proposed lunar sulfur extraction plant",
        "source": "toutanji-b",
        "where": "Section 1 (Introduction), sulfur extraction paragraph and Equation (1)"
      }
    ],
    "handling": [
      {
        "text": "Spray the moulds with oil and heat them before pouring. An unheated mould cooled the outside first and left a hollow hole in the specimen.",
        "source": "toutanji-a",
        "where": "Section 2.1 (step 7) and Section 2.2 (Figure 2 text)"
      },
      {
        "text": "Shake the mould so that no air pockets are trapped.",
        "source": "toutanji-a",
        "where": "Section 2.2 (Results)"
      }
    ],
    "mitigations": [
      {
        "text": "The paper recommends a meteoroid threat analysis for any surface base, identifying vulnerable areas and designing structures for the threat.",
        "source": "toutanji-a",
        "where": "Section 3 (Impact test), closing paragraphs"
      }
    ]
  },
  "uses": [
    {
      "application": "structures",
      "device": "Lunar base silo wall (design study)",
      "example": "The paper studies a 30-foot-tall silo structure for a lunar base and estimates its impact risk. It is a design study, not a built structure.",
      "source": "toutanji-a",
      "where": "Section 3 (Impact test)"
    },
    {
      "application": "structures",
      "device": "Construction in corrosive acid and salt environments on Earth",
      "example": "The paper says sulfur concrete is well established on Earth, particularly in corrosive acid and salt environments, and that it contains no cement.",
      "source": "toutanji-b",
      "where": "Section 1 (Introduction)"
    },
    {
      "application": "radiation-shielding",
      "device": "Wall for radiation shielding (modelled, not measured)",
      "example": "The ICRP 60 calculation gives a required wall thickness of 6.6924281 cm for sulfur JSC-1 concrete, against 4.6296296 cm for aluminium and 7.3684211 cm for polyethylene. The paper says the code is for comparison only.",
      "source": "toutanji-a",
      "where": "Section 4.1, Table 2"
    }
  ],
  "supply": [
    {
      "subject": "Sulfur (elemental, on Earth)",
      "producers": [
        {
          "country": "China",
          "share_percent": 22.6,
          "year": 2025
        },
        {
          "country": "United States",
          "share_percent": 9.6,
          "year": 2025
        },
        {
          "country": "Russia",
          "share_percent": 8.9,
          "year": 2025
        },
        {
          "country": "Saudi Arabia",
          "share_percent": 8.6,
          "year": 2025
        },
        {
          "country": "United Arab Emirates",
          "share_percent": 7.5,
          "year": 2025
        },
        {
          "country": "Canada",
          "share_percent": 6,
          "year": 2025
        }
      ],
      "critical_lists": [
        {
          "list": "USGS 2025 List of Critical Minerals (the page read names 60 minerals and does not name sulfur)",
          "listed": false
        }
      ],
      "recycling": "USGS: typically 2.5 million to 5 million tons of spent sulfuric acid is reclaimed each year from petroleum refining and chemical processes.",
      "substitutes": [
        "USGS: substitutes for sulfur at present or anticipated price levels are not satisfactory; some acids may replace sulfuric acid in certain applications, usually at a higher cost."
      ],
      "source": "usgs-mcs2026-sulfur",
      "where": "World Production and Reserves table, 2025 (world total 84,000 thousand t, rounded; shares calculated by Space Mushroom against that total); Recycling; Substitutes"
    },
    {
      "subject": "Sulfur in lunar soil",
      "abundance": "Apollo soil samples, sulfur abundance as printed in Table 1: Apollo 14 706-778 µgS/g; Apollo 15 (printed as Apollo IS) 517-712 µgS/g; Apollo 16 474-794 µgS/g. Sulfur also occurs as troilite (FeS) on the Moon.",
      "producers": [],
      "critical_lists": [],
      "recycling": "Not applicable: the feedstock is lunar soil, and the sources describe no recycling route.",
      "substitutes": [],
      "source": "toutanji-b",
      "where": "Section 1 (Introduction), Table 1 (sulfur abundance in Apollo soil samples)"
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "Performance of Waterless Concrete (ICPIC 2010, 13th International Congress on Polymers in Concrete; Toutanji, Evans, Grugel)",
      "type": "paper",
      "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
      "year": 2010
    },
    {
      "title": "Performance of Waterless Concrete (Concrete Solutions 2009; Toutanji, Grugel)",
      "type": "paper",
      "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
      "year": 2009
    },
    {
      "title": "Mineral Commodity Summaries 2026, Sulfur",
      "type": "report",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-sulfur.pdf",
      "year": 2026
    },
    {
      "title": "Safety Data Sheet, NIST Reference Material 8553 (elemental sulfur, IAEA-S-4)",
      "type": "sds",
      "url": "https://tsapps.nist.gov/srmext/msds/8553-MSDS.pdf",
      "year": 2022
    },
    {
      "title": "Safety Data Sheet, Sulfur Precipitated, Powder 5735 (Columbus Chemical Industries)",
      "type": "sds",
      "url": "https://www.columbuschemical.com/MSDS/SDS/Sulfur%20Precipitated,%20Powder%205735.pdf",
      "year": 2023
    },
    {
      "title": "Sulfur 'Concrete' for Lunar Applications: Environmental Considerations (NASA/TM-2008-215250)",
      "type": "report",
      "url": "https://ntrs.nasa.gov/api/citations/20080022947/downloads/20080022947.pdf",
      "year": 2008
    }
  ],
  "gaps": [
    "No GHS pictogram or hazard data from PubChem was read in this pass, because its compound page showed a browser check. The hazard entries rest on the NIST and Columbus Chemical safety data sheets.",
    "Wikipedia gives 115.21 °C as the sulfur melting point. It differs from the 119 °C in the NASA papers, the 113 °C in the NIST safety data sheet and the 118 to 120 °C in the Columbus safety data sheet. The Wikipedia value is not used; all sourced values are kept as printed.",
    "Coefficient of thermal expansion for sulfur and for JSC-1 simulant was not found in any source we hold, so the cracking mechanism is described only in words.",
    "Vacuum sublimation on the lunar surface: the 2008 NASA report by Grugel measured weight loss over 60 days in a chamber vacuum, and only its sublimation-time predictions are recorded as values. Its measured weight-loss curves and its lunar-temperature curve are plotted, not printed as numbers, so none were read.",
    "Light freeze-thaw results (50 cycles to about -27 °C) appear only in a figure; no values were read from the text.",
    "Strength values for the glass-fibre mixes (Figure 7 of the 2009 paper) appear only as a chart; no absolute values were read.",
    "The two NASA papers disagree on uncycled strength for the same 35% sulfur and 65% JSC-1 mix: 22.0 MPa in Table 1 of the 2010 paper and an average maximum of 35 MPa in the 2009 paper. Both are kept as printed.",
    "Glass-fibre strength gain is 45% in the abstract of the 2009 paper but 40% in its conclusions; both are printed.",
    "The 26% silica strength gain is quoted from an earlier paper, Toutanji et al. 2006, which could not be opened.",
    "Apollo 15 is printed as Apollo IS in the PDF text, which looks like an OCR error; it is recorded here as printed.",
    "EU critical raw materials list status for sulfur was not found in any source we hold.",
    "Long-term durability, service life and measured radiation shielding for sulfur concrete were not found in any source we hold; the radiation values are model outputs.",
    "The paper says only a single hypervelocity impact test has been done on simulated regolith, so impact values rest on one shot.",
    "Properties with names outside the canonical list, used as custom snake_case names: compressive_strength (the canonical list has no compressive strength name), stiffening_temperature, mixing_temperature, sulfur_content, radiation_shielding_areal_density, required_wall_thickness, hypervelocity_crater_diameter, hypervelocity_crater_depth, strength_increase_glass_fibre, strength_increase_silica, glass_fibre_content, strength_retention_after_thermal_cycling, sublimation_time_1cm."
  ],
  "story": {
    "why": "Sulfur concrete is a construction material that uses molten sulfur in place of cement and water. NASA Marshall researchers Toutanji and Grugel explore it for lunar bases because water is very scarce on the Moon. One 2010 paper reports 22.0 MPa for a 35% sulfur and 65% JSC-1 mix, against 17.2 MPa for conventional concrete in its table. Sulfur is present in lunar soil, with 474 to 794 µgS/g in the Apollo 16 samples as printed, and it also occurs as troilite (FeS).",
    "uses": [
      {
        "where": "Lunar base silo wall (design study)",
        "line": "The 2010 paper studies a 30-foot-tall silo for a lunar base and estimates its impact risk with a meteoroid threat analysis. It is a design study, not a built structure."
      },
      {
        "where": "Corrosive environments on Earth",
        "line": "The papers describe sulfur concrete as well established for acid and salt environments, and say it has been used commercially on Earth for that purpose."
      },
      {
        "where": "Radiation shielding (modelled)",
        "line": "The ICRP 60 calculation gives a required wall of 6.6924281 cm for sulfur JSC-1 concrete, against 4.6296296 cm for aluminium and 7.3684211 cm for polyethylene. The paper says the code is for comparison only, not for design."
      }
    ],
    "can_do": [
      {
        "label": "Strength",
        "line": "The 35% sulfur and 65% JSC-1 mix reached 22.0 MPa compressive strength in Table 1 of the 2010 paper. Conventional concrete in the same table reached 17.2 MPa. The 2009 paper reports 35 MPa uncycled for the same mix, so the two papers disagree.",
        "benchmark": "compressive_strength",
        "scope": "material",
        "value": "22.0 MPa"
      },
      {
        "label": "Thermal limit",
        "line": "The paper says the concrete cannot be used above the melting point of sulfur, about 119 °C. Mixing takes place at 130 to 140 °C, and sulfur stiffens above 148 °C.",
        "benchmark": "max_service_temp",
        "scope": "material",
        "value": "119 °C"
      },
      {
        "label": "Impact",
        "line": "A 1 mm aluminium projectile at 5.85 km/s made a crater 12.8 mm across and 3.1 mm deep in a 5 cm test cube. The hydrocode model in the same paper gives about 15 mm across and 3.5 mm deep, which the authors say agrees well with the test.",
        "benchmark": "hypervelocity_crater_diameter",
        "scope": "material",
        "value": "12.8 mm"
      },
      {
        "label": "Radiation",
        "line": "In the ICRP 60 calculation, sulfur JSC-1 concrete reaches the 80 cSv/yr comparison dose at a shield thickness of 15 g/cm2. The paper says a sulfur JSC-1 wall must be thicker than a plain JSC-1 wall for the same protection.",
        "benchmark": "radiation_shielding_areal_density",
        "scope": "material",
        "value": "15 g/cm2"
      },
      {
        "label": "Glass fibre",
        "line": "Adding about 1% lunar glass fibre raised strength of the mix by up to 45% according to the 2009 abstract, and by up to 40% according to its conclusions. The paper calls the fibre data preliminary.",
        "benchmark": "strength_increase_glass_fibre",
        "scope": "material",
        "value": "45 %"
      }
    ],
    "compare": "Sulfur concrete changes the binder, not the aggregate: sulfur replaces cement and water. In Table 1 of the 2010 paper, the 35% sulfur mix reaches 22.0 MPa, above the 17.2 MPa of conventional concrete, and the 2009 paper states that sulfur concrete is generally stronger than hydraulic concrete. Its upper limit is the melting point of sulfur, about 119 °C, and its main weakness is thermal cycling, which cut strength to 20% of the uncycled value after 80 cycles. The sources give no test data beyond these cases, so the comparison rests on a small number of laboratory cubes.",
    "compare_rows": [
      {
        "label": "Compressive strength",
        "benchmark": "compressive_strength",
        "scope": "material"
      },
      {
        "label": "Density",
        "benchmark": "density",
        "scope": "material"
      },
      {
        "label": "Upper temperature limit",
        "benchmark": "max_service_temp",
        "scope": "material"
      }
    ],
    "handling": [
      "Melt the sulfur and mix it with the aggregate at 130 to 140 °C. Sulfur stiffens above 148 °C, so the working range is narrow.",
      "Pour into heated, oiled moulds and shake to remove trapped air.",
      "Keep the finished product below about 119 °C, the melting point of sulfur.",
      "Expect strength loss after thermal cycling; the paper recorded 20% of uncycled strength after 80 cycles to -191 °C."
    ],
    "good_for": [
      "Places with little water. The mix uses sulfur and regolith with no water, and the paper says water is very scarce on the Moon.",
      "Acid and salt environments. The papers describe sulfur concrete as established for these uses on Earth.",
      "Radiation shielding as a comparison. The modelled calculation gives a wall of 6.6924281 cm for the sulfur JSC-1 mix."
    ],
    "watch_out": [
      "Thermal cycling. 80 cycles to -191 °C cut compressive strength to 20% of the uncycled value.",
      "Upper temperature limit. The sulfur binder melts at about 119 °C, and the product cannot be used above that.",
      "Conflicting strength values. The same mix is given as 22.0 MPa in the 2010 paper and 35 MPa uncycled in the 2009 paper.",
      "Thin evidence. The paper says only a single hypervelocity impact test has been done on simulated regolith."
    ],
    "verdict": "Sulfur concrete is a plausible waterless binder for lunar structures. The melting point of sulfur and thermal cycling are the main limits, and the NASA papers give strength, impact and shielding figures from one team and small laboratory cubes, so the values need more tests before design use.",
    "recipe": {
      "line": "Sulfur concrete is made by melting elemental sulfur, mixing it with lunar regolith simulant aggregate and pouring the hot mix into moulds. The sulfur melts at about 119 °C, and the mix is heated to 130 to 140 °C during mixing. Lunar soil heated above 1100 °C in a vacuum releases SO2 and H2S, which the Claus process at 323 °C converts to elemental sulfur and water.",
      "parts": [
        {
          "name": "Elemental sulfur",
          "symbol": "S",
          "role": "Thermoplastic binder. It melts, wets the aggregate and sets on cooling, so it replaces cement and water."
        },
        {
          "name": "JSC-1 lunar regolith simulant",
          "symbol": "not applicable",
          "role": "Aggregate. It stands in for lunar soil; the paper lists oxygen, silicon, iron, aluminium and calcium as its main elements."
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "The NASA papers describe a hot process but give no toxicity data for the finished product. Two safety data sheets for elemental sulfur, from NIST and Columbus Chemical, classify the powder as a flammable solid and a skin irritant. Neither covers the finished concrete.",
        "points": [
          {
            "label": "Hot process",
            "line": "Sulfur melts at about 119 °C and is mixed at 130 to 140 °C, so hot molten sulfur and hot moulds are the main exposures. The sources give no burn data."
          },
          {
            "label": "Gases from soil heating",
            "line": "Heating lunar soil above 1100 °C in a vacuum releases SO2 and H2S gases in the paper's extraction route. The paper gives no exposure limits."
          },
          {
            "label": "Dust",
            "line": "The sources do not discuss dust from the regolith aggregate."
          },
          {
            "label": "Sulfur dust and fire",
            "line": "The NIST safety data sheet says dust and air mixtures may ignite or explode, and the Columbus safety data sheet lists combustible dust as a hazard not otherwise classified."
          }
        ],
        "level": 0,
        "verdict": "Flammable solid and skin irritant per two sulfur SDSs"
      },
      {
        "title": "If the product fails",
        "lead": "These results come from laboratory tests on small cubes, not from structures in service.",
        "points": [
          {
            "label": "Thermal cycling",
            "line": "After 80 cycles between liquid nitrogen (about -191 °C) and room temperature (about 21 °C), cubes lost strength. Uncycled cubes reached about 35 MPa and cycled cubes about 7 MPa, which is 20% of the uncycled value."
          },
          {
            "label": "Impact",
            "line": "A 1 mm aluminium projectile at 5.85 km/s made a crater 12.8 mm across and 3.1 mm deep in a 5 cm cube. The paper estimates about 1% probability of serious impact damage over 20 years for one 30-foot silo."
          },
          {
            "label": "Heat",
            "line": "The product cannot be used where the environment exceeds the melting point of sulfur, about 119 °C."
          }
        ]
      },
      {
        "title": "Handling and storage",
        "points": [
          {
            "label": "Moulds",
            "line": "Spray the moulds with oil and heat them before pouring. An unheated mould cooled the outside first and left a hollow hole."
          },
          {
            "label": "Mixing",
            "line": "Mix and heat the sulfur and aggregate between 130 and 140 °C, because sulfur stiffens above 148 °C and the working range is narrow."
          },
          {
            "label": "Air",
            "line": "Shake the mould so that no air pockets are trapped."
          }
        ]
      }
    ]
  },
  "updated": "2026-11-02",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 26,
    "unreachable": 2,
    "caveats": 3,
    "note": "Read by an AI assistant on 2026-11-01 from two NASA NTRS PDFs (2009 and 2010), a USGS 2026 sulfur summary, a USGS critical-minerals page and a Wikipedia page used for composition and history only. PubChem could not be read. PDF text was extracted with pdftotext. Deepened on 2026-11-02 from the NIST and Columbus Chemical sulfur safety data sheets and the 2008 NASA report by Grugel (NASA/TM-2008-215250); PubChem showed a browser check and was not read in that pass."
  },
  "sources": {
    "toutanji-a": {
      "title": "Performance of Waterless Concrete",
      "id": "NASA NTRS 20100026417; ICPIC 2010, 13th International Congress on Polymers in Concrete (Toutanji, Evans, Grugel)",
      "url": "https://ntrs.nasa.gov/api/citations/20100026417/downloads/20100026417.pdf",
      "year": 2010,
      "kind": "paper",
      "license": "public domain (NASA)"
    },
    "toutanji-b": {
      "title": "Performance of Waterless Concrete",
      "id": "NASA NTRS 20090033079; Concrete Solutions 2009, 3rd International Conference on Concrete Repair (Toutanji, Grugel)",
      "url": "https://ntrs.nasa.gov/api/citations/20090033079/downloads/20090033079.pdf",
      "year": 2009,
      "kind": "paper",
      "license": "public domain (NASA)"
    },
    "usgs-mcs2026-sulfur": {
      "title": "Mineral Commodity Summaries 2026, Sulfur",
      "id": "USGS MCS 2026, February 2026",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-sulfur.pdf",
      "year": 2026,
      "kind": "report",
      "license": "public domain (USGS)"
    },
    "usgs-crit2025": {
      "title": "About the 2025 List of Critical Minerals (USGS)",
      "id": "Final 2025 List of Critical Minerals",
      "url": "https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals",
      "year": 2025,
      "kind": "web",
      "license": "public domain (USGS)"
    },
    "wiki-sulfur-concrete": {
      "title": "Sulfur concrete (Wikipedia), used for composition and history only",
      "id": "Wikipedia article Sulfur concrete",
      "url": "https://en.wikipedia.org/wiki/Sulfur_concrete",
      "year": 2026,
      "kind": "web",
      "license": "CC BY-SA 4.0"
    },
    "nist-srm8553-sds": {
      "title": "Safety Data Sheet, NIST Reference Material 8553 (elemental sulfur, IAEA-S-4)",
      "id": "NIST RM 8553 SDS, date of issue 15 February 2022",
      "url": "https://tsapps.nist.gov/srmext/msds/8553-MSDS.pdf",
      "year": 2022,
      "kind": "datasheet",
      "license": "US government publication (NIST)"
    },
    "columbus-sulfur-sds": {
      "title": "Safety Data Sheet, Sulfur Precipitated, Powder 5735 (Columbus Chemical Industries)",
      "id": "Columbus Chemical Industries SDS, revised 04/28/2023",
      "url": "https://www.columbuschemical.com/MSDS/SDS/Sulfur%20Precipitated,%20Powder%205735.pdf",
      "year": 2023,
      "kind": "datasheet"
    },
    "grugel2008": {
      "title": "Sulfur 'Concrete' for Lunar Applications: Environmental Considerations",
      "id": "NASA/TM-2008-215250; NTRS 20080022947",
      "url": "https://ntrs.nasa.gov/api/citations/20080022947/downloads/20080022947.pdf",
      "year": 2008,
      "kind": "report",
      "license": "public domain (NASA)"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/sulfur-concrete/"
}