ISO 679 cement compressive and flexural strength test method

Information on the most widely used ASTM standards within the materials testing industry

Descriptions of the most prominent lSO standards within the materials testing industry

Standards including EN, DIN, JlS, and more

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ISO 679 — Cement — Test Methods — Determination of Strength

ISO 679 determining the compressive strength (and optionally flexural strength) of cement, using a standardized mortar mix rather than testing pure cement paste or concrete. It is the benchmark that allows different cements from different plants and countries to be compared on a level playing field.

Test Principle and test methods:

A standardized mortar mix (1 part cement : 3 parts ISO standard sand : 0.5 water by mass, fixed water-cement ratio = 0.50) is mechanically mixed, compacted into 40 mm × 40 mm × 160 mm prismatic moulds via reference jolting or validated vibration compaction equipment.

Compressive strength test (mandatory): Each fractured half-prism is loaded axially to collapse, calculating compressive stress at maximum breaking force.

If disputes arise, only the reference jolting compaction procedure and ISO reference sand are accepted as authoritative test methods.

Flexural strength test (optional): Three-point bending load breaks the prism into two halves, calculating flexural tensile stress at fracture.

ISO 679 cement compressive and flexural strength test method

Test Specimen Information

Standard prismatic bar 40 mm (square cross-section) × 160 mm length; three specimens cast per single mortar batch.

Raw material mix for one batch (3 prisms): 450±2 g cement, 1350±5 g ISO standard sand, 225±1 g water.

Curing rules:

Pre-demould: Moulds covered and stored in moist cabinet for 20–24 h; delayed demoulding allowed if strength insufficient (max 48 h).

Post-demould: Fully submerged in temperature-controlled water, spaced ≥5 mm apart on grates for full water contact on all faces.

ISO 679 Cement compressive and flexural strength test equipmnet required:

Include environmental control facilities, specimen preparation equipment and Strength testing machines.

1, Environmental control facilities	In the requirment temperature and humidity.
Water curing tank/chamber	UnitedTest Cement Specimens Constant Temperature Water Curing Tank. Immersion water held at (20.0±1.0) °C, inert non-cement-reactive material with support grates.
2, Core specimen preparation equipment	Used to prepare the test specimen, wait for next step strength test.
Planetary mortar mixer	Stainless steel bowl + counter-rotating planetary blade, fixed gap (3±1) mm between blade and bowl wall, two regulated mixing speeds.
Three-unit steel prism moulds	Internal dimensions 160±1 mm × 40.0±0.2 mm × 40.1±0.1 mm; internal surfaces HV ≥200 (recommended HV 400), surface texture N8 or smoother.
Reference jolting compaction apparatus	15.0±0.3 mm free fall height, 60 jolts per compaction cycle, total assembly mass (20.0±0.5) kg, mounted on heavy 600 kg concrete vibration-isolated base.
Validated alternative vibration tables	Electromagnetic sinusoidal vertical vibration, fixed 120-second compaction cycles, fully validated against jolting equipment.
Measuring tools	Balance (±1 g accuracy), precision timer (±1 s), ISO 3310-1 compliant test sieves.
3, Strength testing machines	Recommend UnitedTest Compression/Flexural Testing Machine
Compressive testing machine	Calibrated per ISO 7500-1, load rate (2400±200) N/s, tungsten carbide/hardened steel platens HV ≥600 (40×40 mm contact area) with spherical self-aligning seating.
Cement flexural tester	Max 10 kN capacity, load rate (50±10) N/s; three 10.0±0.5 mm diameter support rollers with 100±0.5 mm span.
Compression/flexural test jig	Supplementary alignment jig if machine spherical seating fails compliance rules.

Key Test Parameters:

Parameter	Specification	Unit
Specimen cross-section side (b)	40.0±0.2	mm
Specimen length	160±1	mm
Flexural support span (l)	100.0±0.5	mm
Compression loading area	40 × 40 = 1600	mm²
W/C ratio of standard mortar	0.50	mass ratio
Reference jolts per mortar layer	60 per layer, two layers total	cycles
Vibration compaction duration	120±1	seconds
Flexural loading rate	50±10	N/s
Compressive loading rate	2400±200	N/s

Standard Test Stipulations & Regulatory Rules

Temperature non-negotiables: All raw materials pre-conditioned to lab ambient temperature before mixing; curing water and moist room temperatures strictly logged daily.

Compaction priority: Reference jolting apparatus is primary; vibration tables only usable after full formal validation per Clause 11.

ISO standard sand control: All commercial standard sand must pass initial qualification, monthly verification, and annual confirmation testing against ISO reference sand (validation criterion D < 5.0%).

Age testing windows (calculated from mortar mixing "zero time"):

24 h ±15 min; 48 h ±30 min; 72 h ±45 min; 7 d ±2 h; 28 d ±8 h minimum.

Result rejection rules: Individual results exceeding mean ±3×standard deviation are discarded; multiple outliers invalidate the full test batch.

Report mandatory content: Standard reference ISO 679, cement identification, sand type, curing temperatures, compaction equipment type, test age, individual and average flexural/compressive strength values, equipment validation records.

Step-by-Step Full ISO 679 Cement Strength Test Procedures (include sample preparaion)

Step 1	Mortar Mixing (mechanical planetary mixer)
Add water and cement to bowl, start low-speed mixing for 30 s. Add ISO standard sand evenly over next 30 s, switch to high speed for another 30 s. Pause mixer for 90 s; scrape adhered mortar from bowl walls to centre in first 30 s of pause. High-speed mix for final 60 s to complete homogeneous mortar.
Step 2	Specimen Compaction (Reference Jolting Method)
Secure oiled three-gang mould + hopper on jolting table. Fill first mortar layer (half-depth), spread evenly, apply 60 jolts compaction. Fill second overfilled layer, level, compact with another 60 jolts. Remove mould, strike off excess mortar with sawing motion using metal straight-edge, label mould.
Step 3	Specimen Conditioning & Curing
Cover mould with impermeable plate, place in moist cabinet undisturbed for 20–24 h. Demould carefully without surface damage; mark specimens with water-resistant ink. Fully submerge prisms in temperature-controlled water tank until scheduled test age.
Step 4	Flexural Strength Test
Place prism horizontally on two support rollers, central loading roller aligned mid-span. Apply load at constant 50±10 N/s until prism fractures into two halves; store halves damp for compression testing. Calculate average flexural strength from three specimens.
Step 5	Compressive Strength Test (Mandatory)
Centre each fractured prism half on compression machine platens (10 mm overhang on ends). Increase load steadily at 2400±200 N/s until collapse; record maximum failure load. Compute compressive strength for all six half-prisms, calculate batch average after removing statistical outliers.
Step 6	Validation Testing (For sand or alternative compaction equipment)
20 paired mortar batches are prepared (reference vs test sand/equipment), 28 d compressive strength compared to calculate deviation factor D; only D < 5.0% qualifies sand or vibration tables as compliant.

Applicable Industry Fields

ISO 679 is the universal quality control standard across the global cement and construction value chain:

Cement manufacturing plants: Batch release inspection, raw material quality screening, new cement formulation R&D.

Construction material laboratories: Third-party conformity testing for cement procurement and project acceptance.

Civil engineering & infrastructure: Roads, bridges, high-rise buildings, dams, tunnels, precast concrete component factories.

Building materials R&D: Development of blended cements, supplementary cementitious materials (fly ash, slag, silica fume), low-carbon green cement.

Academic & industrial research: Long-term cement hydration performance, durability, strength development studies.

Related Test Standard

ASTM C109	Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens)
EN 196-1	Methods of testing cement-Determination of strength
TCVN 6016	Cement. Test methods. Determination of strength
GB/T 17671	Test method of cement mortar strength ( ISO method )
ASTM C349	Standard Test Method for Compressive Strength of Hydraulic-Cement Mortars (Using Portions of Prisms Broken in Flexure)
KS L 5105	Standard Test Method for Compressive Strength of Hydraulic Cement Mortars
EN 1015	Methods of test for mortar for masonry-Determination of flexural and compressive strength of hardened mortar
BS 4551	Mortar. Methods of test for mortar and screed. Chemical analysis and physical testing
AS 2701	Methods of sampling and testing mortar for masonry construction
EN 934	Admixtures for concrete, mortar and grout-Admixtures for grout for prestressing tendons. Definitions, requirements, conformity, marking and labelling

Compression and Flexural Integrated Testing Machine used for both flexural strength tests of concrete specimens and compressive strength tests of building materials such as cement, mortar, and red bricks. It can also perform compressive and flexural strength tests of cement mortar.

According to the ISO 679 cement strength testing method, the molded cement specimens are cured in water, meeting the ISO 679, GB/T 17671-2021 requirements. The water temperature should be 20°C ± 1°C, and the specimens must be cured in still water.

Electronic compression testing machine mainly used for compressive strength tests of cement mortar and concrete blocks, it can also be used for compressive tests of rubber pads, tiles, metal products, components, and other materials.

Cement, brick, ceramic tiles Flexural test fixture is an industrial device used to test the flexural strength of cement mortar, brick, ceramatic products. Composed of the lower/upper fixture base, clamping rollers, and the upper and lower pressing strip of the anti-splitting fixture.

Cement, brick, ceramic tiles compression test fixture is an industrial product used to test the compressive strength of cement mortar, brick, ceramatic products.

Q1: What is the core purpose of ISO 679:2009?

A1: ISO 679:2009 sets a unified global laboratory method to measure the compressive strength (mandatory) and optional flexural strength of standard cement mortar prisms (40 mm × 40 mm × 160 mm). It evaluates the hardening strength development of hydraulic cement and provides standardized data to classify cement strength grades, verify production quality, and support construction engineering design.

Q2: Why is the ISO 679 strength test extremely important for cement materials?

A2:Basis for cement strength classification: All international cement product standards define cement strength classes (32.5, 42.5, 52.5 MPa, etc.) solely based on 28-day compressive strength results from ISO 679 tests.

Guarantees structural safety: Cement acts as the binder in concrete and mortar. If cement fails ISO 679 strength requirements, finished structures (buildings, bridges, dams) will suffer insufficient load-bearing capacity, cracking, deformation or even collapse.

Unifies global testing consistency: Fixed mortar proportion, compaction, curing and loading rules eliminate lab-to-lab deviation, enabling fair quality comparison for cross-border cement trade.

Detects factory production abnormalities: Abnormal strength values signal defects like improper clinker burning, incorrect grinding fineness, unqualified blended materials or unstable raw ores, allowing manufacturers to adjust production timely.

Supports low-carbon cement R&D: The standard provides validation rules for alternative standard sand and vibration compaction equipment, facilitating research on slag, fly ash and other supplementary cementitious materials.

Legal & contractual arbitration standard: In disputes between cement suppliers, construction contractors and inspection bodies, the reference jolting procedure specified in ISO 679 is the authoritative test method accepted worldwide.

Predicts long-term durability: Strength test data at 24 h, 7 d and 28 d reflects cement hydration speed, helping engineers evaluate concrete resistance to weathering, chemical erosion and cyclic loads.

Q3: What fixed mortar mix ratio is required by ISO 679 for test specimens?

A3: The mass ratio is strictly fixed: 1 part cement : 3 parts ISO standard sand : 0.5 part water, creating a water-cement (W/C) ratio of 0.50. One batch for three prisms uses 450±2 g cement, 1350±5 g ISO standard sand, and 225±1 g water. No arbitrary adjustment of proportions is allowed.

Q4: What size are the standard test specimens in ISO 679?

A4: Prismatic bars with a square cross-section of 40 mm × 40 mm and a total length of 160 mm. Three specimens are produced from one single mortar batch. After flexural fracture, each prism splits into two halves, giving six pieces for compressive strength testing.

Q5: What is ISO standard sand, and why does it need regular validation?

A5: ISO standard sand is high-purity siliceous sand with ≥98% silica and fixed particle size distribution. It must be validated against ISO reference sand because inconsistent sand grading, impurities or moisture will change mortar strength and invalidate test results. Validation includes three parts: initial qualification testing for new sand products, monthly routine verification, and annual confirmation testing. The strength deviation factor D must be less than 5.0% to pass validation.

Q6: What water can be used to prepare mortar for ISO 679 testing?

A6: Tap drinking water is acceptable for daily routine tests. Distilled or deionized water must be used for sand validation testing. If there is a quality dispute over cement strength, all tests shall use distilled/deionized water.

Q7: What ages are specified for strength testing in ISO 679?

A7: Tests shall be carried out within strict time windows calculated from the mortar mixing "zero time":

24 h ±15 min

48 h ±30 min

72 h ±45 min

7 d ±2 h

Minimum 28 d ±8 h

The 28-day compressive strength is the core index for cement grade classification.

Q8: Is flexural strength testing mandatory under ISO 679?

A8: No, flexural testing is optional. Compressive strength testing is compulsory. If flexural testing is skipped, the prisms can be broken by other damage-free methods before compressive loading. However, most cement factories and third-party labs still perform flexural tests to comprehensively assess cement tensile ductility.

Q9: What loading rates must be followed for flexural and compressive tests?

A9: Flexural strength test: Constant load increase rate of (50±10) N/s.

Compressive strength test: Constant load increase rate of (2400±200) N/s.

Unstable or incorrect loading speed will cause large deviation in final strength values.

Q10: How to judge whether an individual strength test result should be discarded?

A10: Calculate the mean value and standard deviation of a group of test data. If a single result differs from the mean by more than three times the standard deviation (3s), this outlier shall be discarded. If two or more outliers exist, the entire batch of test data is invalid and the test must be repeated.

Q11: What factors will cause inaccurate ISO 679 test results?

A11: Non-compliant equipment: Worn moulds exceeding dimensional tolerances, uncalibrated compression machines, jolting tables with incorrect drop height;

Unqualified raw materials: Non-validated standard sand, high-impurity water, cement stored with moisture absorption;

Non-standard operation: Incorrect mixing timing, insufficient compaction jolts/vibration time, wrong loading speed;

Improper curing: Temperature fluctuation, specimens stacked together in water tanks without free water contact;

Improper specimen handling: Damage during demoulding or before testing.

Q12: Can I skip the validation test for new vibrating compaction tables?

A12: No. Any alternative compaction equipment (vibrating tables) must complete full validation testing with three different cement grades before formal use. Without valid test reports proving strength deviation D < 5.0%, the equipment cannot be used for ISO 679 compliance testing.

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