ISO 679 — Determination of strength

Cement mortar flexural and compressive strength

European laboratories typically apply the same technical requirements through EN 196-1 (2016), which is harmonized with ISO 679.

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Legal notice

The information on this page is a summary prepared by Vector Scientific Testing Devices based on a review of the applicable standard; it does not replace the official standard. For the authoritative, complete text, obtain ISO 679 from ISO or your national standards body through official channels. Vector accepts no liability for direct or indirect loss arising from reliance on this summary.

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1. Purpose and principle

Purpose: Determine flexural and compressive strength of cement mortar at defined cure ages (commonly 2, 7, and 28 days).

Principle: Prepare plastic mortar from cement, CEN reference sand, and water; cast 40 mm × 40 mm × 160 mm prisms. Test flexure first (prism breaks in two), then compression on each half.

Mass proportions:

• Water / cement = 0.50
• Cement / sand = 1 / 3

Batch for one triple mould:

Component	Mass
Cement	450 ± 2 g
CEN standard sand	1350 ± 5 g
Water (distilled/deionized for reference tests)	225 ± 1 g

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2. Laboratory climate

Zone	Temperature	Relative humidity	Notes
Mixing and moulding	20 ± 2 °C	≥ 50 %	Log room T and RH ≥ once per day
Mould storage (first 24 h)	20 ± 1 °C	≥ 90 %	Log cabinet T and RH every 4 h
Water curing tank	20 ± 1 °C	—	Still water; specimens fully submerged, not touching each other or the floor

Materials and apparatus at room temperature before use.

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3. Apparatus — the ISO 679 laboratory set

ISO 679 defines a coordinated set, not a single machine:

Role	Requirement summary	Vector equipment
Mortar mixer	Planetary motion; low/high speeds; clearance 3 ± 1 mm	Cement mortar mixer VTR-1017
Jolting table	20.0 ± 0.5 kg moving mass; 15.0 ± 0.3 mm drop; 60 jolts per run	Jolting table VTR-1024
Triple prism moulds	160.0 × 40.0 × 40.1 mm internal; wall ≥ 10 mm; faces ≥ 200 HV	User-supplied steel moulds per standard
RH cabinet	20 ± 1 °C, ≥ 90 % RH for first 24 h	Curing cabinet VTR-1025S / VTR-1025D
Strength press	Flexure 50 ± 10 N/s; compression 2400 ± 200 N/s on 40 × 40 mm platens	Cement test press VTR-1026S / VTR-1026D

3.1 Mortar mixer

Speed	Blade spin (rpm)	Planetary orbit (rpm)
Low	140 ± 5	62 ± 5
High	285 ± 10	125 ± 10

• ~5 L stainless bowl; matched blade set.
• Blade–bowl clearance 3 ± 1 mm, checked periodically (monthly in EN 196-1 practice).

3.2 Jolting (compacting) table

• Moving mass (table, arms, empty mould, hopper, clamps): 20.0 ± 0.5 kg.
• Lift 15.0 ± 0.3 mm, free drop onto anvil.
• 1 drop per second; 60 jolts per layer in one automatic run.

3.3 Triple gang prism moulds

• Steel (or equivalent hard metal); inner faces ≥ 200 HV (often ≥ 400 HV in practice).
• Internal: 160.0 ± 0.8 × 40.0 ± 0.2 × 40.1 ± 0.1 mm.
• Joints sealed against leakage; light mould release on inner faces.

3.4 Curing cabinet and water tank

• 24 h at ≥ 90 % RH after moulding (extend to 48 h only if demoulding is impossible — document on the record).
• After demoulding, prisms cured horizontally in 20 ± 1 °C water until test age.

3.5 Auxiliary equipment

• Balance: at least 1 g readability for batching cement, sand, and water.
• Straightedge and scraper for strike-off and mixing scrape step.
• Water tank with stable 20 ± 1 °C temperature monitoring.

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4. Mixing procedure (timing ± 1 s)

Time (s)	Action
0–30	Water and cement in bowl; start low speed
30–60	Low speed; add all sand over 30 s
60–90	High speed 30 s
90–180	Stop; scrape to centre in first 15 s; rest 75 s
180–240	High speed 60 s

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5. Moulding and curing

1. Two layers in the clamped mould on the jolting table — 60 jolts per layer (120 total).
2. Strike off flush with a metal straightedge.
3. 24 h in the RH cabinet.
4. Demould; store in the water tank until the test day.

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6. Strength tests

Workflow: mixer → jolting table → curing cabinet → water tank → test press.

6.1 Flexural strength

• Test wet as removed from the tank (no drying).
• Three-point bending, span 100 mm, mid-span loading.
• Rate 50 ± 10 N/s until break.

6.2 Compressive strength

• Test both halves immediately after flexure.
• Load the smooth mould side faces (not the struck top face) against 40.0 × 40.0 mm platens (1600 mm² area).
• Platens ≥ 600 HV; rate 2400 ± 200 N/s; record Fmax.

The Vector cement test press provides flexure and compression fixtures with programmed rates for ISO 679 / EN 196-1 programmes.

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7. Calculation and validity

Rc (MPa) = Fc / 1600

(Fc in N; platen area 1600 mm².)

1. Two compressive values per prism → six per triple mould set.
2. Mean of six.
3. If one result lies outside ± 10 % of that mean, exclude it and report the mean of the remaining five.
4. If more than one result is outside ± 10 %, void the set and repeat from mortar mixing.

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8. Relation to EN 196-1 and procurement

When a tender calls for an “ISO 679 compliant cement strength laboratory”, suppliers must deliver (or verify):

1. Programmable planetary mixer with the speed table above.
2. Jolting table with controlled mass, stroke, and 60-jolt automation.
3. Qualified triple moulds and batching balance.
4. RH cabinet and thermostatic water tank on the climate table.
5. Calibrated press for flexure and compression rates.

Technical detail for European national implementation: EN 196-1 summary.

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9. Practical notes

1. One climate programme across mixer room, cabinet, and tank — hydration errors show up as strength scatter, not press noise alone.
2. Timing ± 1 s on mixing is mandatory; do not shorten scrape or rest steps.
3. Press calibration and loading-rate checks at 50 N/s and 2400 N/s setpoints are part of ISO 679 conformity, not optional add-ons.
4. Vicat and setting-time work often shares the mixing room — see EN 196-3.

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Summary based on ISO 679:2013. Confirm the current edition at ISO.org before contractual or accreditation use.