What Is Ultra-High Performance Concrete (UHPC)? Mix Design, Admixtures, Mixing, Curing and Testing

Oct. 27, 2026

Concrete Admixture Technical Guide · No. 30

Ultra-high performance concrete (UHPC) is the strongest concrete in everyday use — compressive strength of 120 MPa and above, or roughly 4 to 6 times a normal mix. It gets there through an extremely low water-binder ratio, a densely packed particle system, steel fibres, and a high dose of polycarboxylate superplasticizer (PCE). This guide explains how UHPC differs from ordinary concrete, how it is graded, and how to design, mix, cure and test it.

UHPC vs Ordinary Concrete

The difference is not "more cement". It is a completely different mix, built around a different principle.

Property	Ordinary Concrete	UHPC
Compressive strength	30–60 MPa	120 MPa and above
Water-binder ratio	0.40–0.55	0.14–0.22
Binder content	300–500 kg/m³	800–900 kg/m³
Maximum aggregate size	≤ 20 mm	≤ 1.25 mm (quartz sand)
Steel fibre	None	1–2.5% by volume
PCE dosage	0.1–0.5%	1.2–1.5%
Typical curing	Ambient	Steam curing (or extended moist)

Three things set UHPC apart: an ultra-low water-binder ratio, a densely packed particle skeleton, and steel fibres that give it tensile strength and ductility instead of brittle failure.

How UHPC Is Graded

UHPC has a formal grading system — by use, by curing, and by performance. This is the professional way to specify it.

By use and curing:

Type	Code
Structural UHPC	ST
Non-structural UHPC	NST
Ambient-cured	N
Heat-cured	H

By performance (defined in standards such as T/CECS 10107-2020):

Grade	Flow (spread)
UF1	< 650 mm
UF2	650–750 mm
UF3	≥ 750 mm

Grade	Compressive Strength
UC1	100–120 MPa
UC2	120–150 MPa
UC3	150–180 MPa
UC4	≥ 180 MPa

Grade	Tensile Behaviour
UT1	Tensile ≥ 5 MPa, no strain hardening
UT2	Tensile ≥ 5 MPa, mild strain hardening
UT3	Tensile ≥ 7 MPa, strain hardening
UT4	Tensile ≥ 10 MPa, strong strain hardening

A UHPC is labelled by combining these, for example ST-N-UHPC UF2/UC3/UT3 — a structural, ambient-cured UHPC with flow grade UF2, strength grade UC3 and tensile grade UT3.

What Makes UHPC So Strong

Ordinary concrete fails because of the pores left by excess water. UHPC removes almost all of them:

1.Ultra-low water-binder ratio (0.14–0.22). With almost no free water, there are almost no capillary pores.

2.Dense particle packing. Cement, silica fume, quartz powder and fine quartz sand fill every size gap, so the matrix is nearly void-free.

3.Steel fibres. 1–2.5% by volume of micro steel fibres bridges the micro-cracks and turns a brittle material into a tough, ductile one.

The result is a concrete that is not just stronger, but far more durable — with very low chloride penetration, high freeze-thaw resistance and a long service life.

The Mix Design and Raw Materials

A typical UHPC mix looks nothing like normal concrete. These are indicative ranges (always confirm by trial mix):

Ingredient	Typical Range
Cement (P·II 52.5 or 52.5R)	450–850 kg/m³
Silica fume (SiO₂ > 90%)	80–180 kg/m³
Quartz sand (≤ 1.25 mm)	950–1200 kg/m³
Quartz powder (SiO₂ > 95%)	0–300 kg/m³
Steel fibre (1–2.5% vol)	80–160 kg/m³
Water	120–220 kg/m³
PCE superplasticizer	8–45 kg/m³ (1.2–1.5%)

The raw materials are held to tighter limits than normal concrete:

Material	Key Requirement
Silica fume	SiO₂ > 90%
Quartz powder	SiO₂ > 95%, > 95% finer than 0.16 mm
Quartz sand	Max size ≤ 1.25 mm, low clay
Steel fibre	6–25 mm long, 0.10–0.25 mm dia, tensile ≥ 2000 MPa

The aggregate is fine sand, not stone — and every ingredient is chosen to pack the matrix as densely as possible.

Admixture Selection

UHPC relies on two admixtures, with the PCE doing the heavy lifting.

Admixture	Role	Typical Dose
Polycarboxylate superplasticizer (PCE)	Achieve the low w/b ratio and keep flow	1.2–1.5% of binder
Powder defoamer	Remove air bubbles, densify, improve surface	0.05–0.2%

Some recipes also add a small amount of an expansion agent (to offset shrinkage) or a retarder (to control setting). But the PCE and the defoamer are the two that matter most.

The Role of PCE: The Key Admixture

UHPC is impossible without a strong PCE. The water-binder ratio is so low that the mix would be a dry, unplaceable powder — and only a high-range water reducer can turn it into a flowing, self-levelling paste. The standard requirement is explicit: the water reducer must be a high-performance type with a water reduction rate of at least 30%.

Requirement	Why It Matters for UHPC
Water reduction ≥ 30%	Needed to reach w/b of 0.14–0.22
High dosage (1.2–1.5%)	Disperses a very high powder content
Good compatibility with silica fume	The matrix is cement + silica fume

This is where a high-reduction PCE such as our PC 6010 does the job: it provides the water reduction and the flow that UHPC depends on, at the high dosage UHPC requires. Because the PCE dose is precisely linked to the final strength, a PCE with a stable, known active content matters even more here than in ordinary concrete.

Mixing and Casting

UHPC is hard to mix, and you cannot do it in a normal mixer. The extremely low water content and high powder content demand a forced-action mixer (twin-shaft or planetary) — a gravity mixer will not distribute the fine powder or the fibres.

The mixing is done in three stages:

Stage	What Happens
1. Dry mixing	Cement, silica fume, quartz powder and sand, mixed 1–2 min
2. Wet mixing	Add water and PCE, mix at least 5 min until flow develops
3. Fibre addition	Add steel fibres slowly, then mix at least 2 min more

Two casting rules also matter:

1.Do not rod or poke the concrete — UHPC must not be compacted by hand. Pour it from one side of the mould in one pass.

2.Remove air by tapping or light vibration — for low-flow mixes (below 650 mm), a short 10–15 s vibration may be used, otherwise tap the mould to release bubbles.

Curing: The Other Half of the Strength

UHPC's full strength depends heavily on curing. It has two paths, and the standard steam-curing schedule is specific.

Curing Method	Schedule	Typical Result
Steam curing	90 °C ± 1 °C held for 48 h (heat ≤ 15 °C/h, cool ≤ 45 °C/h)	150–180 MPa
Ambient moist curing	Standard moist curing, tested at 28 d	130–150 MPa

Two rules matter:

1.Steam curing gives the full strength. The heat accelerates the silica fume's pozzolanic reaction, which is what pushes the strength past 150 MPa. The temperature must be raised and lowered slowly.

2.Early moisture is critical. With such a low water-binder ratio and a high silica fume content, UHPC shrinks early — cover the surface with film immediately after casting and keep it wet.

The test age also differs: heat-cured UHPC is typically tested at 7 days, ambient-cured at 28 days.

Testing UHPC

UHPC is checked on mechanical performance, durability and shrinkage.

Mechanical and durability requirements:

Property	Structural (ST)	Non-structural (NST)
Compressive strength	≥ 120 MPa	≥ 100 MPa
Flexural strength	≥ 14 MPa	≥ 10 MPa
Elastic modulus	≥ 40 GPa	≥ 40 GPa
Tensile grade	≥ UT2	≥ UT1
Chloride diffusion	≤ 0.40 × 10⁻¹² m²/s	≤ 0.60 × 10⁻¹² m²/s

Fresh-concrete (workability) requirements:

Property	Requirement
Spread (flow)	≥ 650 mm
Spread loss over time	≤ 100 mm
Spread time	3–10 s

Shrinkage requirements:

Property	Ambient-cured	Heat-cured
Drying shrinkage	≤ 300 × 10⁻⁶	≤ 100 × 10⁻⁶
Early-age autogenous shrinkage	≤ 1000 × 10⁻⁶	—

The compressive strength is the headline number, but the durability tests — especially chloride diffusion — are what justify UHPC's long service life in bridges and marine structures.

FAQ

How much stronger is UHPC than normal concrete?

Roughly 4 to 6 times — UHPC is 120 MPa and above, against 30–60 MPa for ordinary concrete.

Why is the PCE dosage so high in UHPC?

Because the water-binder ratio is so low (0.14–0.22) and the powder content is so high. Only a strong dose of a high-range water reducer can make it flow — the standard requires a water reduction of at least 30%.

Can UHPC be mixed in a normal mixer?

No. It needs a forced-action (twin-shaft or planetary) mixer, and the fibres are added last at low speed.

Does UHPC need steam curing?

Steam curing at about 90 °C gives the full 150–180 MPa. Ambient moist curing works, but the strength is slightly lower.

What admixtures does UHPC need?

Mainly a high-reduction PCE (1.2–1.5%) and a powder defoamer. Some mixes add an expansion agent or retarder.