Concrete Admixtures: The Complete List of Types, Functions and ASTM C494 / EN 934-2 Classes

Concrete admixtures are constituents added to a concrete batch during mixing, in quantities of not more than 5 % by mass of the cement under EN 934-2:2009+A1:2012, to change how the fresh or hardened concrete behaves. Which functions exist, how are they classified and how much goes into a mix?

ACI documents call them chemical admixtures, European practice names each product by its function, such as plasticiser for a water-reducing admixture, and "mineral admixture" is the older ACI and current Indian term for supplementary cementitious materials. "Concrete additive" is a trade umbrella term, not an ACI, ASTM or EN defined term, and admixtures are one of the four families of concrete additives, next to supplementary cementitious materials, fibers and integral pigments.

ACI PRC-212.3-16 sorts chemical admixtures into 12 groups, and ASTM C494/C494M-24 defines eight types, A to G and S, beside EN 934-2 requirement tables and the five types of IS 9103:1999. Water reducers cut mixing water by at least 5 %, high-range water reducers by at least 12 to 40 %, and shrinkage reducers cut drying shrinkage by 30 to 50 % (ACI PRC-212.3-16 Table 1.2). Doses run from 0.2 to 0.6 % by mass of cement for a normal plasticizer (CAA ATS 1) to 7 to 391 mL/100 kg (0.1 to 6.0 fl oz/cwt) for air entrainers, and ACI CODE-318-25 caps water-soluble chloride at 0.06 % by mass of cementitious materials in prestressed concrete.

Each value is traced to its source: standards and codes to their issuing body, product values to the data sheet named with them, prices to the dated source beside them (methodology and fact-checking).

What Is a Concrete Admixture?#

A concrete admixture is a liquid or dispersible powder used as an ingredient in a cementitious mixture to improve its economy or its properties in the plastic state, the hardened state or both, as ACI CT-25 defines a chemical admixture. ACI PRC-212.3-16 (clause 1.1) describes chemical admixtures as primarily water-soluble substances that modify concrete, mortar or grout in the plastic state, the hardened state or both. The same clause states that they are not a substitute for suitable concrete mixture proportions and acceptable construction practices.

How ACI, EN and IS define an admixture#

ACI, CEN and BIS define the admixture in five documents, and each definition stresses a different limit: chemistry, the batch, the dose or the excluded materials.

ACI CT-25 enters "admixture, see chemical admixture" and defines a chemical admixture as "a liquid, or dispersible powder, used as an ingredient in a cementitious mixture to improve its economy and/or properties in the plastic and/or hardened state". The older wording is the one ACI FAQ 720 gives, citing ACI CT-23 and ACI 212.3R-16: "a material other than water, aggregates, cementitious materials, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing".

EN 934-2:2009+A1:2012, clause 3.2.1, defines an admixture for concrete as a material added during the mixing process of concrete in a quantity not more than 5 % by mass of the cement content, to modify the properties of the mix in the fresh and/or hardened state. EN 206-1:2026, clause 3.2.2, keeps the definition short: a constituent added during the mixing process in small quantities to modify the properties of fresh or hardened concrete.

IS 9103:1999, clause 3.1, defines an admixture as a material other than water, aggregates and hydraulic cement, added to the batch immediately before or during mixing to modify one or more properties of concrete in the plastic or hardened state. In the US, ASTM C125/C125M-26b, active, is the terminology standard for concrete and concrete aggregates.

What admixtures are used for in concrete#

The purposes named in ACI PRC-212.3-16 Table 1.2 fall into the six groups listed below.

• Water reduction and flow: at least 5 % less water for water reducers, 5 to 10 % for mid-range water reducers and at least 12 to 40 % for high-range water reducers, which increase slump and flowability.
• Set control: delayed setting for set-retarding admixtures, and stopped or severely retarded hydration for extended set-control admixtures used with wash water, returned concrete and long hauls.
• Early strength: accelerated setting and early strength development.
• Durability: resistance in freezing and thawing, deicer, sulfate and alkali-reactive environments, a lower steel corrosion rate with a later onset of corrosion, and minimized expansion from alkali-silica reaction.
• Shrinkage reduction: drying shrinkage reductions of 30 to 50 %.
• Stability and permeability control: modified rheology of plastic concrete, slump retention, a water-repellent surface with lower absorption, and resistance to water penetration under pressure.

How Do Chemical Admixtures Work?#

Chemical admixtures work through four mechanisms: they disperse cement grains, stabilize air bubbles, change the rate of cement hydration, or act on the pore water, the pores and the embedded steel. The molecules behind each mechanism, from lignosulfonates and polycarboxylates to calcium nitrite and lithium nitrate, are covered under the substances behind admixtures.

Dispersing cement grains and stabilizing air#

Water reducers disperse cement grains: they adsorb on the grains, lower the attraction between particles and break up flocs, which frees entrapped water (CAA ATS 1). Normal water reducers such as lignosulfonates act by electrostatic repulsion, and polycarboxylate ethers (PCE) add steric hindrance from their polyether side chains (CAA ATS 2). At equal water content, CAA ATS 2 gives a slump more than 120 mm (4.7 in) higher than plain concrete for superplasticized mixes.

Air-entraining admixtures do not generate air; they lower the surface tension of the mixing water and stabilize the bubbles formed during mixing (FHWA-HIF-20-085). The surfactant shell around each bubble resists coalescence, so the paste keeps a system of small, separate voids that relieves pressure when pore water freezes.

Speeding up or slowing down hydration#

Accelerators shorten the dormant period of cement hydration, and retarders lengthen it. Inorganic accelerators such as chlorides, nitrates, nitrites, thiocyanates and formates accelerate the hydration of tricalcium silicate (C3S), and triethanolamine accelerates the aluminate (C3A) reaction (FHWA-HIF-18-017).

Retarders adsorb on early hydration products and on calcium hydroxide and C-S-H nuclei, which poisons their growth and lengthens the dormant period (ACI E4-12; FHWA-HIF-18-017). The retarding effect rises with the C3A content of the cement and with delayed addition.

Lowering pore-water tension, blocking pores and protecting steel#

Shrinkage reducers lower the surface tension of the pore fluid, permeability reducers repel water or block the pores, and corrosion inhibitors protect the embedded steel. Shrinkage-reducing admixtures lower the surface tension of the pore fluid by as much as 50 %, which lowers capillary pressure on drying (InTrans, Iowa State University). In ACI PRC-212.3-16 Table 1.2, non-hydrostatic permeability reducers (PRAN), based on fatty acid derivatives, soaps, petroleum derivatives and fine fillers, give a water-repellent surface, and hydrostatic types (PRAH), based on crystalline materials and hydrophilic polymers, resist water under pressure.

Anodic inhibitors such as calcium nitrite stabilize the passive film on reinforcing steel and raise the chloride threshold at which corrosion starts. Admixed inhibitors delay corrosion initiation, and once corrosion has started, no significant reduction of the corrosion rate was found (Elsener, ETH Zurich, 2011).

Types of Concrete Admixtures by Function#

Concrete admixtures are classified by function, and ACI PRC-212.3-16 describes 12 groups: air-entraining, water-reducing, accelerating, set-retarding, extended set-control, workability-retaining, viscosity-modifying, shrinkage-reducing, corrosion-inhibiting, lithium, permeability-reducing and miscellaneous admixtures. Table 1 lists the admixture functions with what each one does, from ACI PRC-212.3-16 Table 1.2, ASTM C494 and EN 934-3, and the main ASTM and EN specifications behind it.

Four ACI groups have no row of their own in Table 1: lithium admixtures sit with alkali-silica reaction, coloring admixtures with concrete pigments, air-detraining admixtures with air entrainers, and workability-retaining admixtures with superplasticizers. ACI PRC-212.3-16 section 16.2 names iron oxide, chromium oxide and titanium dioxide among the coloring materials.

Admixtures that control water demand, setting and early strength#

Water reducers control water demand, retarders and hydration-control admixtures control setting, and accelerators control early strength, in the bands of ACI PRC-212.3-16 Table 1.2. Normal water reducers (ASTM C494 Type A) cut mixing water by at least 5 %, mid-range water reducers by 5 to 10 % without retarding initial set, and high-range water reducers (Types F and G) by at least 12 to 40 %. Their materials run from lignosulfonates and hydroxylated carboxylic acids to melamine and naphthalene condensates and polycarboxylates. High-range water reducers increase slump and flowability, and self-compacting concrete is made with superplasticizers (high-range water reducers).

Set-retarding admixtures delay setting; ASTM C494 names them Type B (retarding) and Type D (water-reducing and retarding), and ACI PRC-212.3-16 Table 1.2 lists the water-reducing form with at least 5 % less water. Extended set-control admixtures, also called hydration-control admixtures, stop or severely retard cement hydration to stabilize wash water, returned concrete and long hauls. Accelerating admixtures (Types C and E) speed up setting and early strength development, with calcium chloride, triethanolamine, sodium thiocyanate, formates, nitrites, calcium nitrate, aluminates and silicates as the listed materials. ASTM C1622/C1622M-24 (published 2024-06-15) covers cold-weather admixture systems for concrete as low as -5.0 °C (23.0 °F) immediately after placement; a cold-weather admixture system is not an ASTM C494 type.

Admixtures that protect durability#

Five admixture groups in ACI PRC-212.3-16 Table 1.2 target durability: air entrainers, shrinkage reducers, corrosion inhibitors, permeability reducers and lithium admixtures. Air-entraining admixtures (ASTM C260/C260M, AASHTO M 154) improve durability in freezing and thawing, deicer, sulfate and alkali-reactive environments. Shrinkage-reducing admixtures reduce drying shrinkage, and reductions of 30 to 50 % can be achieved with polyoxyalkylene alkyl ethers and propylene glycol; the same ACI group holds shrinkage-compensating systems based on calcium sulfoaluminate, calcium aluminate, calcium hydroxide or magnesium oxide.

Corrosion-inhibiting admixtures reduce the rate of steel corrosion and extend the time to its onset, with calcium nitrite and amine carboxylates among the listed materials. ASTM C1582/C1582M-24 (active, updated 2024-09-24) specifies chloride-corrosion-inhibiting admixtures. Lithium nitrate, lithium carbonate, lithium hydroxide and lithium nitrite minimize deleterious expansion from alkali-silica reaction. EN 934-2:2009+A1:2012 tests water-resisting admixtures, the European counterpart of PRAN types, by capillary absorption in Table 9.

Admixtures for stability, density, mortar and specific performance#

Viscosity modifiers control stability, foaming agents control density, mortar admixtures serve masonry mortar, and ASTM C494 Type S covers specific-performance admixtures. Viscosity- and rheology-modifying admixtures, based on polyethylene oxides, cellulose ethers, alginates, natural and synthetic gums and polyacrylamides, modify the rheology of plastic concrete (ACI PRC-212.3-16 Table 1.2). Workability-retaining admixtures keep slump in combination with a normal, mid- or high-range water reducer, with no effect on initial slump, set time or strength gain. EN 934-2:2009+A1:2012 tests viscosity-modifying admixtures in Table 13 and water-retaining admixtures, which reduce bleeding, in Table 4.

Foaming agents for preformed foam in cellular concrete are specified by ASTM C869/C869M-24 and tested by ASTM C796/C796M-25. Masonry mortar admixtures follow ASTM C1384-23 in the US and EN 934-3:2009+A1:2012 in Europe. ASTM C494/C494M-24 Type S is the US type for an admixture whose purpose is neither water reduction nor a change in setting time: the purchaser states the specific performance characteristic, and the manufacturer provides substantiating data on request.

How Do ASTM, EN and IS Classify Admixtures?#

Three specification systems classify concrete admixtures: ASTM C494/C494M-24 with eight types in the US, EN 934-2:2009+A1:2012 with numbered requirement tables in Europe, and IS 9103:1999 with five types in India. Air entrainers, corrosion inhibitors and cold-weather admixture systems have their own US specifications, ASTM C260/C260M-24, C1582/C1582M-24 and C1622/C1622M-24. Table 2 sets the three systems side by side with the requirement that separates each class from its neighbors.

The eight US types, A to G and S#

ASTM C494/C494M-24, active since its store update of 2024-08-06, defines eight admixture types: A, B, C, D, E, F, G and S. Type A is water-reducing, Type B retarding, Type C accelerating, Type D water-reducing and retarding, Type E water-reducing and accelerating, Type F water-reducing, high range, Type G water-reducing, high range, and retarding, and Type S specific performance. Type S already appears in the scope of C494/C494M-19e1, so the count of eight types is not new to the 2024 edition.

ASTM C494/C494M-24 qualifies a product at three levels. Level 1 is initial approval against Table 1, Level 2 is limited retesting, and Level 3 is lot acceptance or uniformity and equivalence testing, for example solids, density and infrared spectrum, when the purchaser specifies it.

The European tables and what each one tests#

EN 934-2:2009+A1:2012 sets one requirement table per function, each tested against a control concrete. Table 3 lists the values of Tables 2 to 9; Tables 10 (set retarding/water reducing), 11.1 and 11.2 (set retarding/superplasticizing), 12 (set accelerating/water reducing) and 13 (viscosity modifying) are not reproduced, because their values are not in the public preview of the standard.

The test methods come from the EN 480 series, for example EN 480-11:2005 for the air-void structure behind the Table 5 spacing factor.

Water-reduction thresholds in three systems#

The water-reduction threshold is 5 % for a normal water reducer and 12 % for a high-range water reducer in ASTM, EN and ACI terms alike. ASTM C494/C494M-17 and -19e1 Table 1 limit the water content of Types A, D and E to at most 95 % of the control mix and of Types F and G to at most 88 %, the same 5 % and 12 % thresholds as ACI PRC-212.3-16. EN 934-2:2009+A1:2012 asks for at least 5 % water reduction in Table 2 and at least 12 % in Table 3.1.

ACI PRC-212.3-16 Table 1.2 extends the high-range band to at least 12 to 40 % and places mid-range water reducers at 5 to 10 %. In UK practice, CAA ATS 1 (industry guidance) links a normal water reducer dose to 8 to 12 % water reduction. IS 9103:1999 lists water-reducing and superplasticizing admixtures as separate types; its Table 1A values are not reproduced, because no verified copy of the table is available.

Specifications outside the eight US types#

Three active ASTM specifications classify admixtures that are not ASTM C494 types: C260/C260M-24, C1582/C1582M-24 and C1622/C1622M-24. ASTM C260/C260M-24 (store update 2025-01-06) covers air-entraining admixtures; its Table 1 limits are not reproduced, because the numeric values were not read in the standard text. ASTM C1582/C1582M-24 covers chloride-corrosion-inhibiting admixtures, and ASTM C1622/C1622M-24 covers cold-weather admixture systems for concrete at -5.0 °C (23.0 °F) and above. ACI PRC-212.3-16 Table 1.2 lists AASHTO M 194 with ASTM C494 and AASHTO M 154 with ASTM C260.

Withdrawn US specifications#

ASTM C1017 for flowing concrete was withdrawn in 2022 without replacement, and ASTM C1141 for shotcrete admixtures followed in 2024. The last editions were C1017/C1017M-13e1 and C1141/C1141M-15. Flowing concrete is now specified with a high-range water reducer as ASTM C494 Type F or G, and admixtures for sprayed concrete in Europe fall under EN 934-5:2007.

How Are Admixtures Dosed?#

Concrete admixtures are dosed on a stated basis, either a volume per 100 kg of cementitious material (mL/100 kg, or fl oz/cwt in the US) or a percentage by mass of cement, as supplied or as solids. A dose without its basis cannot be batched, because the same number means a different quantity on each basis. Table 4 lists the dose bases with ranges from standards, industry guidance and data sheets.

1 fl oz/cwt = 65.2 mL/100 kg; 1 kg/m³ = 1.6856 lb/yd³; 1 L/m³ = 0.2020 gal/yd³. The final dose is set by trial batches with the job materials.

Worked example, calculated from the CAA ATS 1 range, the EN 934-2 ceiling and the conversion factors above. Inputs: cement content 350 kg/m³ (590 lb/yd³); plasticizer dose 0.2 to 0.6 % by mass of cement, as supplied; EN 934-2 ceiling 5 % by mass of cement; liquid dose 65.2 mL/100 kg (1.0 fl oz/cwt).

1. Plasticizer by mass: 350 kg/m³ × 0.2 to 0.6 % = 0.70 to 2.10 kg of admixture per m³ (1.18 to 3.54 lb per yd³).
2. EN 934-2 ceiling: 350 kg/m³ × 5 % = 17.5 kg/m³ (29.5 lb/yd³).
3. Liquid by volume: 3.5 × 65.2 mL = 228 mL per m³ (5.90 cwt × 1.0 fl oz = 5.9 fl oz per yd³).

The same arithmetic for other admixture doses, bases and batch sizes runs in the admixture dosage calculator.

Volume per mass of cementitious material#

Liquid admixtures dosed by volume are stated in milliliters per 100 kg of cementitious material, or fluid ounces per hundredweight (fl oz/cwt) in the US, where 1 fl oz/cwt equals 65.2 mL/100 kg. The basis is the total cementitious material, so a mix with fly ash or slag cement takes its dose on cement plus the supplementary material. Air-entraining admixtures show the span of this basis: two US data sheets give a typical product range of 7 to 391 mL/100 kg (0.1 to 6.0 fl oz/cwt) of cementitious material, as supplied.

Percent by mass of cement, as supplied or as solids#

UK and EU practice doses admixtures as a percentage by mass of cement, as supplied (CAA ATS 1). CAA ATS 1 gives 0.2 to 0.6 % for a normal water-reducing admixture, and CAA ATS 2 gives 0.3 to 1.5 % for PCE superplasticizers and 0.7 to 2.5 % for SNF and SMF superplasticizers, all by mass of cement as supplied.

The EFCA model EPD for plasticizers and superplasticizers covers 0.2 to 1.6 % and 0.4 to 2.0 % by mass of cement, stated for the finished product. A dose stated as solids counts only the active dry material, so it is a smaller number than the as-supplied dose for the same batch. Shrinkage-reducing admixtures are assessed in Europe at doses below 5 % by mass of cement (EOTA EAD 260054-00-0301).

Dose limits set by standards and codes#

Two kinds of limits cap an admixture dose: the EN 934-2 ceiling of 5 % by mass of the cement and code limits on what the admixture brings into the concrete, such as chloride. EN 934-2:2009+A1:2012 writes the ceiling into its definition of an admixture (clause 3.2.1), so the percentage refers to the cement content, not to the mass of concrete.

ACI CODE-318-25 (publication year 2025, 702 pages) limits water-soluble chloride by mass of cementitious materials in Table 19.3.2.1, as reproduced in NRMCA 2PE004-26: 1.00 % for nonprestressed concrete in exposure class C0, 0.30 % in C1, 0.15 % in C2 and 0.06 % for prestressed concrete. Chloride-bearing accelerators count against these limits, and NRMCA TIP 13 equates a 2 % calcium chloride accelerator dose with about 1 % chloride by weight of cement.

Selecting an Admixture by the Problem It Solves#

An admixture is selected from the problem in the mix or on the job, such as excess water demand, a hot-weather haul, an early-strength target or freezing exposure, and the function then points to the standard it must meet. Table 5 maps 15 problems to the admixture function and the specification it is bought against.

A table match is a starting point, not a mix design: the choice and the dose are confirmed in trial batches with the job cement, supplementary cementitious materials, aggregates and temperature. Pigments show the second limit, the dose cap of a specification: ASTM C979/C979M-24 caps the prescribed pigment dose at 10 % by mass of cement.

Can You Use Two or More Admixtures in One Mix?#

Yes: a concrete mix can combine two or more admixtures, such as a water reducer with an air entrainer, but each one is dispensed separately and the combination is proven in trial batches with the job cement and SCMs. Combined admixtures change each other's effects on air, setting and slump, so the order of addition and the dispensing tolerance belong to the plant procedure. Plant dispensing, haul time and slump retention are covered under admixtures in ready-mix concrete.

Batching order and dispensing tolerance#

Admixtures go into the batch separately and in a set order, and ACI E4-12 sets the dispensing tolerance at 3 % of the required volume or the minimum recommended dose per unit of cement, whichever is greater. ACI E4-12 adds accelerators with the mixing water and keeps them apart from the air-entraining admixture. ACI PRC-212.3-16 section 3.7 covers the batching order for adding chemical admixtures to concrete. The NRMCA guide to improving specifications links improper jobsite tempering with water reducers to excessive slump, setting retardation and cement-admixture compatibility problems.

Known interactions between admixture families#

Six interactions between admixture families are documented by ACI, FHWA, CAA, InTrans and HRB sources, listed below.

• SNF and PCE: blends of naphthalene and polycarboxylate superplasticizers may be incompatible (CAA ATS 2).
• PCE and air: polycarboxylate high-range water reducers can give large, widely spaced bubbles and unstable air (FHWA-HIF-17-009).
• Lignosulfonate and air: 7 of 19 lignosulfonate retarders in HRB Bulletin 310 (1962) entrained more than 5 % air without an air-entraining agent.
• Water reducer and retarder: a Type A or D water reducer combined with a separate retarder compounds retardation, and a high-range water reducer plus a retarder can cause excessive retardation (ACI E4-12).
• Shrinkage reducer and air entrainer: the two interact, so InTrans (Iowa State University) calls for trial batches, the air entrainer early and the shrinkage reducer last, a hardened air check and no premixing with other admixtures.
• Accelerator and heat: accelerators can cause very rapid set in hot weather (FHWA-HIF-18-017).

Which Standards Govern Concrete Admixtures?#

Concrete admixtures are governed by product specifications (ASTM C494/C494M-24, C260/C260M-24, EN 934-2:2009+A1:2012, IS 9103:1999), by the concrete standards and codes that call them up (ACI CODE-318-25, EN 206-1:2026) and by guidance such as ACI PRC-212.3-16. ACI PRC-212.3-16 (formerly ACI 212.3R-16, first printing March 2016, 76 pages, 22 chapters) supersedes ACI 212.3R-10. Table 6 lists each document with edition, status and role, and the full set of concrete admixture standards is summarized under concrete admixture standards.

Europe: product standards, concrete standard and CE marking#

Europe specifies admixtures in the EN 934 series, calls them up in EN 206-1:2026 and bases CE marking on the harmonised parts of EN 934. The series runs from EN 934-1:2008 (common requirements) through EN 934-2:2009+A1:2012 (concrete), EN 934-3:2009+A1:2012 (masonry mortar), EN 934-4:2009 (grout for prestressing tendons) and EN 934-5:2007 (sprayed concrete) to EN 934-6:2019 (constancy of performance) and EN 934-7:2024 (shrinkage-reducing admixtures). Parts 2 to 5 are harmonised under Regulation (EU) No 305/2011, and EN 934-7:2024 (published 2024-11-26) is not cited in the Official Journal, so it gives no CE marking basis. The EN 934-2 systematic review ended with a decision to confirm (CEN, 2026-10-21), and the separate revision draft was rejected.

EN 206-1:2026 (CEN approval 2026-01-19, dated March 2026) supersedes EN 206:2013+A2:2021; clause 6.1.5 sets the basic requirements for admixtures, clause 6.2.6 covers their use, and its normative references include EN 934-1, EN 934-2 and EN 934-7. The numeric admixture limits of the 2026 edition are not reproduced, because that clause text is not public. Regulation (EU) 2024/3110 applies from 2026-01-08, and EN 934-2 stays harmonised under Regulation (EU) No 305/2011 until a new standard is cited.

India: the national admixture specification#

IS 9103:1999, Concrete Admixtures: Specification, is India's national admixture standard, active and reaffirmed in 2018 with two amendments (BIS). It covers five types: accelerating, retarding, water-reducing, air-entraining and superplasticizing admixtures, with superplasticizers in normal and retarding forms. The 1999 text is the first revision of a standard first published in 1979. Clause 1.3 requires the chloride content to be declared and expects superplasticizers to be chloride free. The requirement values of Tables 1A and 1B are not reproduced, because no verified copy of the tables is available.

What a data sheet or declaration must show#

A conforming admixture is bought on its declared type and test evidence, not on its trade name. Four documents set what that evidence contains, listed below.

• ASTM C494/C494M-24: the declared type, with Level 1 initial approval, Level 2 retesting or, when the purchaser specifies it, Level 3 uniformity and equivalence tests such as solids, density and infrared spectrum; for Type S, the claimed performance characteristic.
• EN 934-1:2008: the general requirements declared for each product, namely homogeneity, color, infrared spectrum, density, dry material content, pH, total chlorine, water-soluble chloride and alkali content.
• IS 9103:1999, clause 10.2: generic main active constituent, dry material content, relative density, chloride ion content relative to cement mass at the recommended dosage, storage conditions, incompatibilities, effects of under- and overdosage, and expiry date.
• The product safety data sheet: the hazard statements of each formulated admixture.

When Is an Admixture the Wrong Fix?#

An admixture is the wrong fix when the problem lies in the mix proportions or the site practice: ACI PRC-212.3-16 states that chemical admixtures are not a substitute for suitable mixture proportions and acceptable construction practices. Jobsite retempering with water reducers is one such case, which the NRMCA guide ties to excessive slump and setting retardation.

An admixture also leaves the hazard of the mix unchanged: ASTM C494/C494M-24 notes that fresh hydraulic cementitious mixtures are caustic and may cause chemical burns. Each formulated admixture carries its own hazards, which are stated on the product safety data sheet.

Surface-applied products such as curing compounds, sealers and bonding agents are not covered here. Additives interground at the cement mill are a cement product and not covered here.

Is there a code for admixture?#

Yes: ASTM C494/C494M-24 in the US, EN 934-2:2009+A1:2012 in Europe and IS 9103:1999 in India specify admixtures, and ACI CODE-318-25 and EN 206-1:2026 call them up. The codes control what an admixture brings into the concrete, such as water-soluble chloride under ACI CODE-318-25 Table 19.3.2.1, and the product specifications test its effect against a control mix.

What is a Type G concrete admixture?#

A Type G admixture is a water-reducing, high-range and retarding admixture under ASTM C494/C494M-24. Its water content is at most 88 % of the control mix, as for Type F (ASTM C494/C494M-17 and -19e1 Table 1), with retardation added. The European counterpart is the set retarding/superplasticizing admixture of EN 934-2:2009+A1:2012 Tables 11.1 and 11.2.

How many types of chemical admixtures are there?#

ASTM C494/C494M-24 defines 8 types, A to G and S, while ACI PRC-212.3-16 describes 12 functional groups. EN 934-2:2009+A1:2012 counts requirement tables rather than types, from Table 2 to Table 13, and IS 9103:1999 recognizes five types. Air entrainers and corrosion inhibitors sit outside the C494 count, in ASTM C260/C260M-24 and C1582/C1582M-24.

Which is the best admixture for concrete?#

The best admixture is the one whose function solves the mix or job problem, in a product that conforms to the specified type. A superplasticizer answers water demand in a flowing mix and does nothing for freezing exposure. Conformity is read on the declaration, such as the ASTM C494 type and test level or the EN 934-2 table, not on the brand.

Are SCMs and fibers admixtures?#

Not in the ACI sense: ACI CT-25 points the term admixture to chemical admixture, and the older ACI wording excludes cementitious materials and fiber reinforcement by name. The three neighboring terms are listed below.

• Fly ash, slag cement and silica fume are supplementary cementitious materials, called "mineral admixtures" in older ACI and current Indian usage.
• Steel, synthetic, glass and basalt fibers make fiber-reinforced concrete and are specified by ASTM C1116/C1116M-23 and EN 14889-1:2006 and EN 14889-2:2006, not by admixture standards.
• The terms admixture vs additive vs addition differ in ACI, ASTM and EN usage, and EN 206-1:2026 defines an addition as a finely divided inorganic constituent used in concrete to improve certain properties or to achieve special properties.