A low-cement castable is a deflocculated castable that replaces most of the calcium aluminate cement of a conventional mix with reactive fines and a dispersant, so it needs about half the mixing water and reaches higher density and strength. Optimized mixes take 3.5 to 4.5 % water against 10 % for a conventional castable, and a 60 % alumina example reached 20.0 MPa (2,900 psi) MOR after 816 °C (1500 °F) against 5.5 MPa (800 psi) (patent WO1996001700A1).
ASTM C401-12(2022) separates the classes by CaO content, not by cement content, within the wider family of refractory materials.
Every value names its standard and edition, the product data sheet or the dated source it comes from; see our methodology and fact-checking process.
The table below sets the defining attributes of the class side by side.
| Attribute | Value |
|---|---|
| Definition | Deflocculated castable below the conventional cement level (ISO 836:2001, term 049) |
| Classes | Low-cement, ultra-low-cement and no-cement (ASTM C401-12(2022); ISO 836:2001 terms 079, 135, 090) |
| Cement content | Under about 10 % by weight in the patent definition (a formulation figure, not a class limit) |
| Mixing water | 3.5 to 4.5 % for optimized mixes; 4 to 8 % for the low-cement family (Jenkins 2011) |
| Dense threshold | Dried bulk density above 1.68 g/cm³ (105 lb/ft³), ASTM C401-12(2022) |
| Key standards | ASTM C401-12(2022); ISO 1927-1:2012 |
What Is a Low-Cement Castable?#
A low-cement castable (LCC) is the class that ASTM C401-12(2022) and ISO 836:2001 (term 079) place between conventional and ultra-low-cement castables by the CaO its cement contributes. The standard covers castables that gain strength by chemical action when tempered with water.
ISO 1927-1:2012 lists castables first among its unshaped product types, so the class belongs to monolithic refractories.
Four Cement Levels: Conventional, LCC, ULCC and NCC#
Four cement levels name every hydraulic or cement-free castable: conventional (medium-cement), low-cement, ultra-low-cement and no-cement, in falling order of CaO.
The Ruh 1994 review gives class ranges of typical CaO of 2.1 to 2.4 % for LCC, 0.5 to 1.0 % for ULCC and 0.1 to 0.2 % for NCC, against 1.8 % for the named product Hicast Extra; these are typical values, not class limits.
The table below compares the four levels by standard term.
| Class | ISO 836:2001 term | ASTM C401-12(2022) class name | Typical CaO (class range, Ruh 1994 review) | Cement content (formulation figure, not a class limit) | Page |
|---|---|---|---|---|---|
| Conventional | 086 medium-cement | regular | n/a | 10 to 30 % (patent WO1996001700A1) | refractory castables |
| Low-cement | 079 | low-cement | 2.1 to 2.4 % | under about 10 % (patent WO1996001700A1) | this page |
| Ultra-low-cement | 135 | ultra-low-cement | 0.5 to 1.0 % | 2.5 % in one lab ULCC (Kalpakli 2008) | this page |
| No-cement | 090 | no-cement | 0.1 to 0.2 % | no hydraulic cement | this page |
Ultra-Low-Cement Castables (ULCC)#
An ultra-low-cement castable keeps a trace of hydraulic bond: a 2008 laboratory ULCC by Kalpakli used 2.5 % calcium aluminate cement and 0.5 % microsilica. Its water fell from 4.80 to 4.32 % as the packing exponent q rose from 0.21 to 0.26, and at q 0.26 it reached 93 MPa (13,490 psi) after 1500 °C (2,732 °F) for 5 h.
No-Cement Castables and Their Three Binder Systems#
No-cement castables bond without hydraulic cement, and three binder systems carry them: hydratable alumina, silica sol and microsilica gel.
- hydratable alumina: 3 % in a test mix gave a cold crushing strength of 1 MPa (145 psi) after 24 h at 20 °C (68 °F) and 8 MPa (1,160 psi) after 110 °C (230 °F)
- colloidal silica binders for no-cement castables: 10 wt % sol at 40 % solids replaced 10 % cement plus 8 % water, gelled by 0.01 to 0.1 wt % fine MgO (Salomao et al., 2025)
- microsilica gel: 5 to 8 % microsilica plus 3 % gel additive, with 0.5 % of a 70 % Al2O3 cement as initiator (Elkem)
The microsilica-gel mix reached up to 10 MPa (1,450 psi) after 24 h and about 45 MPa (6,527 psi) after 110 °C (230 °F).
What Are Low-Cement Castables Made Of?#
A low-cement castable is graded alumina or alumina-silicate aggregate held by a matrix of reactive alumina, a little cement and a dispersant: Hicast Extra analyzes 80 % Al2O3, 13 % SiO2, 1.8 % CaO and 1.5 % Fe2O3 (Morgan Thermal Ceramics data sheet).
The table below lists the material groups of a low-cement mix.
| Material | Role | Value and basis | Page |
|---|---|---|---|
| Tabular alumina | Aggregate in high-alumina LCC and NCC | n/a | tabular alumina |
| Calcined and reactive alumina | Matrix fines | 7 % reactive and 4 % calcined in one lab ULCC (Kalpakli 2008) | calcined and reactive aluminas |
| Calcined bauxite | Aggregate in bauxite NCC mixes | Elkem NCC papers | refractory-grade calcined bauxite |
| Calcium aluminate cement | Hydraulic binder | 1.5 % CaO in the Almatis concepts (90 % Al2O3 with 5 % silica fume; 98 % optimized) | see binders section |
| Hicast Extra chemistry | Typical value of one product (Morgan data sheet) | 80 / 13 / 1.8 / 1.5 % Al2O3 / SiO2 / CaO / Fe2O3 | n/a |
Grains by chemistry are covered under refractory raw materials.
Which Binders and Additives Do LCC, ULCC and NCC Use?#
An LCC binder system is cement at a reduced level plus fines below 45 µm and submicron fillers that take the place of cement and water, set by a dispersant dosed at 0.1 % or less. Almatis puts the mixing water of a conventional castable at 10 %, a dispersed LCC at 4.5 % and an optimized LCC with a dispersing alumina at 3.5 %. One commercial dispersant at 0.23 % kept a microsilica-gel NCC from setting for 48 h at 20 °C (68 °F).
The table below lists the additive families.
| Additive | Role | Dosage and basis | Page |
|---|---|---|---|
| Calcium aluminate cement | Hydraulic bond at reduced level | 5 % CA-14 M in Almatis LCC test mixes; 3 % with 1 % hydratable alumina in ULCC | calcium aluminate cement for refractories |
| Dispersants (polyphosphates, polyacrylates, polycarboxylates) | Cut water | 0.1 % or less (Almatis) | dispersants and deflocculants for castables |
| Dispersing aluminas ADS and ADW | Dispersion and working time | about 1 % (Almatis); 0.5 % each in a lab ULCC | n/a |
| Retarder in ADS types | Set control | B2O3 0.8 to 2.8 % | accelerators and retarders |
| Hydrated lime | Nozzle accelerator for wet shotcrete | 0.01 to 5.0 % of dry weight (patent WO1996001700A1) | n/a |
| Drying fibers | Melt or burn out to open steam paths | see the supplier data sheet | organic fibers and drying agents |
| All families | Overview | n/a | refractory additives and binders |
Microsilica and the Hot-Strength Trade-Off#
Microsilica lowers water demand and packs the matrix, but it reacts with the lime of the cement near 1400 °C (2,552 °F) to form anorthite- and gehlenite-type liquids that cut hot strength.
Kalpakli found a strength gain only below about 6 % microsilica, with strong mullite formation near 1300 °C (2,372 °F). In a UNITECR 2025 conference paper, an NCC reached a hot modulus of rupture about 50 % above a ULCC at 1450 °C (2,642 °F). Microsilica is CAS 69012-64-2; its effects are detailed under microsilica in refractory castables.
Properties: Standard Requirements and Typical Values#
Low-cement castable data split into two kinds: the class threshold every dense castable meets under ASTM C401-12(2022), and typical values that one named product, reference mix or study reached. The threshold is a dried bulk density above 1.68 g/cm³ (105 lb/ft³).
The table below compares the standard requirement with typical values and names the test methods.
| Property | Standard requirement (ASTM C401-12(2022)) | Typical value (product or mix, basis) | ASTM / ISO method |
|---|---|---|---|
| Dried bulk density | above 1.68 g/cm³ (105 lb/ft³) for dense | 2,784 kg/m³ (173.8 lb/ft³), Hicast Extra, Morgan data sheet | C134-95(2023) / ISO 5017:2025; apparent porosity and bulk density |
| Cold crushing strength | n/a | Hicast Extra: 114 MPa dried, 110 after 815 °C, 127 after 1000 °C, 163 after 1600 °C (16,530 / 15,950 / 18,420 / 23,640 psi); optimized LCC 250 MPa after 1500 °C, Almatis | C133-24 / ISO 10059-1:2025; cold crushing strength |
| Modulus of rupture after 816 °C (1500 °F) | n/a | 20.0 MPa (2,900 psi), 60 % alumina LCC, patent example | C133-24 / ISO 5014:2025; modulus of rupture |
| Permanent linear change | 1.5 % or less at the class temperature | -0.1, -0.2, -1.5 % after 815, 1000, 1600 °C, Hicast Extra | C113-14(2025) / ISO 1927-6:2012; permanent linear change |
| Open porosity | n/a | 15 % optimized LCC (3.20 g/cm³, 200 lb/ft³), 17 % LCC with 5 % silica fume (2.95 g/cm³, 184 lb/ft³), after more than 1000 °C (1,832 °F), Almatis | C20-00(2022) / ISO 5017:2025 |
| Maximum service temperature | n/a | 1700 °C (3,092 °F), Hicast Extra; LCC class range 1093 to 1704 °C (2000 to 3100 °F), Ruh 1994 review | n/a |
| Method for CCS and MOR | see the method page | n/a | ASTM C133 cold crushing strength and modulus of rupture |
| All properties | overview | n/a | properties of refractory materials |
Standards: ASTM C401 and ISO 1927 Side by Side#
ASTM C401-12(2022) names the low-, ultra-low- and no-cement classes in the US, ISO 1927-1:2012 classifies castables internationally, and ISO 836:2001 supplies the class terms; their test methods run side by side but are not interchangeable.
Consistency is checked by flow table under ASTM C1445-13(2025) or ISO 1927-4:2012, and an ISO/AWI revision registered on 2026-09-15 is not published. The international side of the classification is set out under ISO 1927 monolithic refractory products.
Methods in one row measure the same property; results are not interchangeable.
| Purpose | ASTM (edition) | ISO / EN (edition) | Note |
|---|---|---|---|
| Classification | ASTM C401 classification of castables, C401-12(2022) | ISO 1927-1:2012, EN ISO 1927-1:2012 | class names only |
| Terms | n/a | ISO 836:2001 | terms 049, 079, 086, 090, 135 |
| Consistency | C1445-13(2025) flow table; C860-15(2025) ball-in-hand; C1446-19(2025) self-flowing | ISO 1927-4:2012 | methods differ |
| CCS and MOR | C133-24 | ISO 10059-1:2025, ISO 5014:2025 (EN ISO versions replaced EN 993-5 and EN 993-6 on 2025-12-09) | n/a |
| Hot MOR | C583-15(2026) | EN 993-7:1998 | n/a |
| Abrasion | C704/C704M-15(2022)e1 | ISO 16282:2007 | n/a |
| Refinery quality control | API Std 936, 5th ed. (March 2024) | n/a | monolithic linings |
Where Are Low-Cement Castables Used?#
Low-cement castables line steel ladles and blast furnace runners, the hearths and skid protection of reheating furnaces, and the nose rings and dams of cement kilns. Almatis reports that the low porosity of the class let castables replace bricks in ladles and runners where conventional castables failed.
| Industry | Zone | Why LCC | Page |
|---|---|---|---|
| Steel ladles | walls and bottoms | low porosity (Almatis) | steel ladle refractory lining |
| Blast furnace | runners | low porosity (Almatis) | blast furnace trough and runner castables |
| Reheating furnaces | walking-beam and pusher hearths, skid pipe protection | strength, abrasion and impact (Hicast Extra data sheet) | reheating furnace refractories |
| Cement and lime kilns | nose rings, retainer rings, dams | strength and abrasion (Hicast Extra data sheet) | refractories for cement and lime kilns |
| Aluminum and foundry | furnace linings | Ruh 1994 review | aluminum melting and holding furnaces |
| Waste-to-energy | grate sidewalls | alkali-resistant high-alumina LCC (Capital Refractories paper) | waste-to-energy boilers and incinerators |
| Whole steel plant | all zones | overview | refractories for iron and steel |
Installing Low-Cement Castables and the First Heat-Up#
A low-cement castable reaches its data-sheet values only when it is mixed with the small water dose its maker states, vibrated or flowed into place within the working time and heated slowly at first, because its dense matrix lets steam out slowly. The Hicast Extra data sheet specifies a paddle mixer, 4 to 6 min of mixing, 5.5 to 6.5 % water and placement within about 20 min.
Casting is one of the refractory installation methods.
The low-cement family takes 4 to 8 % water at 2,243 to 2,883 kg/m³ (140 to 180 lb/ft³), against 8 to 12 % at 2,082 to 2,723 kg/m³ (130 to 170 lb/ft³) for conventional castables (Jenkins 2011).
Producer schedule temperatures are hot-gas temperatures. The maker sets the schedule, the installer writes the plan and the owner approves it; holds and rates are on the page for refractory dry-out and heat-up schedules.
- refractory castable quantity calculator: Hicast Extra needs 2,750 kg (6,063 lb) per m³ of lining
Why Low-Cement Linings Fail and How They Are Inspected#
Low-cement linings fail by explosive spalling at first heat-up, because their low permeability traps steam; in service they lose hot strength where lime-silica liquids form, and slag penetrates open pores. The table below pairs each failure with its check.
| Failure | Cause | Check |
|---|---|---|
| Explosive spalling | low permeability traps steam at first heat-up | dry-out record; refractory failure modes |
| Loss of hot strength and creep | lime-silica liquids in microsilica-bearing mixes | hot MOR to C583-15(2026) |
| Slag penetration | open pores | porosity to C20-00(2022) |
| Low strength | water above the data-sheet range | C133-24 on production samples |
| Wrong consistency | wrong water or mixing | C1445-13(2025) or C860-15(2025) on site; refractory inspection and quality control |
| Abrasion | n/a | C704/C704M-15(2022)e1 |
Health and Safety When Handling Low-Cement Castables#
The two hazards that matter in handling low-cement castables are respirable crystalline silica, limited in US workplaces to 50 µg/m³ (8-h TWA) with a 25 µg/m³ action level under 29 CFR 1910.1053, and the cement binder. The EU limit is 0.1 mg/m³ (respirable fraction) under Directive (EU) 2017/2398, transposition by 2020-01-17.
Separately, the text of REACH Annex XVII entry 47, as amended by Regulation (EC) No 552/2009, limits soluble Cr(VI) in hydrated cement and cement-containing mixtures to 2 mg/kg (0.0002 %) of the total dry weight of the cement; whether a given product falls under the entry is not assessed here.
The table below gives each substance with its instrument and date.
| Topic | Rule or classification | Instrument and date |
|---|---|---|
| Quartz | No Annex VI entry; product-specific, see supplier SDS (ECHA C&L: no majority; not classified 27.5 %, H372 25.2 %, H373 18.8 %, H350 7.7 %) | CLP Regulation (EC) No 1272/2008 Annex VI, ECHA C&L read 2026-10-27 |
| Cristobalite | see the supplier SDS | n/a |
| Respirable crystalline silica, US | PEL 50 µg/m³, action level 25 µg/m³ | 29 CFR 1910.1053 and 1926.1153, effective 2016-06-23 |
| Respirable crystalline silica, EU | 0.1 mg/m³ respirable fraction, 8-h TWA | Directive (EU) 2017/2398 Annex, OJ L 345/87 of 2017-12-27, transposition by 2020-01-17 |
| Prop 65 | "Silica, crystalline (airborne particles of respirable size)", cancer | OEHHA list, listed 1988-10-01 |
| IARC | crystalline silica Group 1; amorphous silica Group 3 | Monograph 100C, 2012; 1997 |
| Calcium aluminate cement (CAS 65997-16-2, EC 266-045-5) | No Annex VI entry; no hazard statement in a majority of notifications, see the product SDS | ECHA C&L read 2026-10-27 |
| Microsilica (CAS 69012-64-2, EC 273-761-1) | No Annex VI entry; not classified by the REACH joint submission (93.44 % of notifications); see supplier SDS | ECHA C&L read 2026-10-27 |
| Boric acid (005-007-00-2) and boron oxide (005-008-00-8) | Repr. 1B H360FD | CLP Annex VI as amended by ATP 20, in application 2025-02-01 |
| Silica overview | exposure control | crystalline silica and cristobalite in refractories |
Grades, Packaging and Sourcing#
Low-cement castables ship as dry bagged mixes, for example 25 kg (55 lb) bags of Hicast Extra, and buyers compare grades on cement class, Al2O3 and CaO with basis, service temperature, water demand and placement method. Five checks turn any data sheet into comparable numbers.
- Confirm the C401 class name.
- Read CaO and Al2O3 with their basis.
- Read each strength with its firing temperature and method edition.
- Note the water range and the placing method.
- Compare the material required per m³.
Buying routes: refractory manufacturers and suppliers.
What Sets the Price of a Low-Cement Castable?#
Industrial low-cement castable is priced per quote, and six factors set that price: class and Al2O3 grade, raw-material origin, quantity and packaging, freight, installation and dry-out, and payment terms. The US BLS producer price index for clay refractories (WPU1352, 1982 = 100) stood at 405.818 in September 2026, a trend, not a price.
| Price factor | What the buyer states |
|---|---|
| Class and Al2O3 grade | LCC, ULCC or NCC; data-sheet reference |
| Raw-material origin | tabular, bauxite, mullite |
| Quantity and packaging | tonnes, bag size |
| Freight | country, Incoterms |
| Installation and dry-out | supply only or installed |
| Payment terms | n/a |
| Price trend | US PPI clay refractories (WPU1352) 405.818, 1982 = 100, September 2026; a trend, not a price |
Low-Cement vs Conventional Castables and Other Alternatives#
A low-cement castable trades a longer, more careful first heat-up for strength that a conventional castable never reaches: after 816 °C (1500 °F), a 60 % alumina LCC reached an MOR of 20.0 MPa (2,900 psi) against 5.5 MPa (800 psi) for the conventional mix (patent WO1996001700A1).
Cold crushing strength was 75.2 against 32.4 MPa (10,900 against 4,700 psi) and water demand is 4 to 8 % against 8 to 12 %, as set out under conventional refractory castables.
An 89 % Al2O3 brick shows 18 % open porosity and the optimized LCC 15 % (Almatis Table 1).
Self-Flow, Gunning, Precast and Brick Alternatives#
Five alternatives replace a cast low-cement lining where access, shape or heat-up time rule it out.
| Alternative | Placement | When it wins | Page |
|---|---|---|---|
| Self-flow castables | no vibration; q about 0.21 in a lab ULCC | access without vibrators | self-flow and pumpable refractory castables |
| Gunning and shotcrete | wet-spray LCC uses 2.27 to 2.55 m³/min (80 to 90 cfm) of air against 7.08 to 19.82 m³/min (250 to 700 cfm) for gunning; rebound up to one third (patent WO1996001700A1) | vertical or overhead repair | gunning mixes and refractory shotcrete |
| Precast shapes | cast and fired off site | short on-site heat-up | precast refractory shapes |
| Refractory brick | laid in courses | no wet placement | refractory bricks; verdict: castable vs refractory brick |
| Refractory cement | trade term for the binder | n/a | refractory cement |
Low-Cement Castable FAQs#
Is a Deflocculated Castable the Same as a Low-Cement Castable?#
A deflocculated castable is the ISO 836:2001 term (049) for a castable with a hydraulic bond, at least 2 % by weight of particles below 1 µm and at least one deflocculating agent, which covers low- and ultra-low-cement castables.
What Is a Medium-Cement Castable?#
Medium-cement castable is the ISO 836:2001 term (086) for the conventional cement level. Patent WO1996001700A1 describes conventional mixes with 10 to 30 % cement by weight, a formulation figure, not a class limit.