Setting Time Test of Concrete
The setting of concrete is a gradual process, and therefore its initial and final setting times must be defined by specified measurable criteria. The penetration resistance method determines these times from the resistance offered by the mortar fraction sieved from fresh concrete.
Reference
ASTM C403/C403M – Time of Setting of Concrete Mixtures by Penetration Resistance.
Principle of the Test
A representative sample of fresh concrete is wet-sieved through a 4.75 mm sieve to obtain the mortar fraction. The mortar is placed in a suitable container and stored under controlled laboratory or field conditions. At regular intervals, standard needles of known bearing area are forced vertically into the mortar to a depth of 25 ± 2 mm.
The force required for penetration is measured, and the penetration resistance is calculated as:
Penetration Resistance=Penetration Force/Needle Bearing Area
A plot of penetration resistance versus elapsed time is then used to determine the setting times.
Test Specimen Preparation
For field testing, a representative fresh concrete sample is obtained and three specimens are prepared from each sample.
For laboratory investigations, the number of batches and specimens depends on the purpose of the test, with at least three separate batches required when evaluating compliance with performance requirements.
The time of initial contact between cement and mixing water must be recorded as the zero reference time.
The mortar fraction is obtained by wet-sieving the representative concrete through a 4.75 mm sieve. It is thoroughly remixed and placed in a rigid, watertight, nonabsorptive container to a mortar depth of at least 140 mm. The specimen is consolidated sufficiently to remove air pockets and the surface is levelled. The mortar surface should remain at least 10 mm below the top edge of the container to accommodate bleed water.
The fresh concrete slump, air content, and mortar temperature should also be determined and recorded.
Test Apparatus
The test requires standard penetration needles having bearing areas of:
- 645, 323, 161, 65, 32 and 16 mm²
- Equivalent to 1, 1/2, 1/4, 1/10, 1/20 and 1/40 in²
The loading apparatus must have a minimum capacity of 600 N and measure the penetration force with an accuracy of ±10 N. Each needle has a reference mark located 25 mm from its bearing surface to control penetration depth.
Conditioning of the Specimen
Under laboratory conditions, specimens are normally stored at 20–25°C, unless another temperature is specified. Under field conditions, they are stored under ambient conditions and protected from direct sunlight.
To minimise moisture loss, the specimens should remain covered with damp burlap or a tight-fitting water-impermeable cover except during bleed-water removal and penetration testing. Ambient temperature at the start and completion of the test must be recorded.
Penetration Test Procedure
Before each penetration test, bleed water is carefully removed from the mortar surface. The specimen may be tilted approximately 10° for about 2 minutes to facilitate collection of bleed water.
A suitably sized needle is then selected according to the stiffness of the mortar. The needle is brought into contact with the surface, and a gradually and uniformly applied vertical load causes penetration to:
- 25 ± 2 mm depth
- Within 10 ± 2 seconds
The force required is recorded along with the elapsed time since the initial contact of cement and water.
Successive penetrations must be made in undisturbed areas, with adequate spacing between impressions and from the container wall.
Frequency of Testing
For conventional concrete at 20–25°C, the first penetration test is generally made 3–4 hours after initial contact between cement and water, followed by tests at intervals of 30 minutes to 1 hour.
For accelerated mixtures or higher temperatures, testing may begin after 1–2 hours.
For retarded mixtures or lower temperatures, the first test may be delayed until 4–6 hours.
A minimum of six penetration measurements should be obtained, and testing must continue until the penetration resistance reaches at least 27.6 MPa (4000 psi).
Determination of Initial and Final Setting Time
The penetration resistance values are plotted against elapsed time. The setting times are defined as follows:
| Setting stage | Penetration resistance |
| Initial setting | 3.5 MPa (500 psi) |
| Final setting | 27.6 MPa (4000 psi) |
The corresponding elapsed times are obtained either by:
- Hand-fitting a smooth curve through the test data, or
- Regression analysis using a logarithmic relationship.
For regression analysis, the data may be represented as:
log(PR)=a + b log(t)
or directly as a power function:
PR=ctd
where
- PR is penetration resistance and
- t is elapsed time.
If the regression correlation coefficient, after removal of justified outliers, is less than 0.98, the smooth-curve method should be used instead.
The key setting thresholds are explicitly defined as 500 psi for initial setting and 4000 psi for final setting.
Important Points in Data Interpretation
The test measures the setting behaviour of the mortar sieved from the actual concrete mixture. It is not equivalent to testing a separately prepared mortar intended to simulate the concrete mortar fraction; because the prepared mortar may produce longer initial and final setting times.
Potential outliers can result from:
- Larger particles interfering with penetration;
- Voids within the penetration zone;
- Interference from adjacent needle impressions;
- Failure to maintain the apparatus perpendicular to the surface;
- Errors in load measurement;
- Variations in penetration depth; or
- Variations in the loading rate.
What Should Be Reported?
A complete setting-time test report should include the
- concrete mixture proportions,
- cementitious material details,
- aggregate sizes,
- water–cementitious material ratio, admixtures,
- slump, air content,
- mortar temperature,
- ambient temperature,
- date of testing,
- penetration resistance–time plots, and
- individual and average initial and final setting times.
Conclusion
The penetration resistance method provides a practical way to quantify the rate at which fresh concrete transitions from a plastic material to a progressively stiffening and set material. Because it evaluates mortar obtained directly from the concrete mixture, it is particularly useful for assessing the influence of cementitious materials, water content, admixtures, and temperature on setting behaviour and for verifying compliance with specified time-of-setting requirements.
For professional practice, the critical points are specimen representativeness, proper removal of bleed water, controlled penetration depth and loading rate, adequate spacing of penetration locations, and sufficient data points on both sides of the initial and final setting thresholds.
