Mass concrete temperature monitoring is the practice of tracking the internal temperature of a large concrete element at more than one depth during curing, so the crew can see both the peak core temperature and the difference between the core and the surface. Those two readings drive the decisions on a mass pour: whether to add or remove insulation, when it is safe to strip forms, and whether the element is at risk of thermal cracking. Monitoring is normally done with embedded sensors that record temperature at the core and near the surface at the same time, and the readings are compared against the limits set in the project thermal control plan.
Closely monitoring concrete temperatures is critical for ensuring proper strength development of concrete structures and concrete sustainability regardless of their application or size. However, when it comes to mass concrete structures, temperature differentials also need to be considered due to the risk of a large difference between the relatively hot internal temperature and cool surface temperature. If a too-large temperature differential occurs, the surface of mass concrete will start cracking, which is detrimental to its durability and the length of its service life.
What Is Mass Concrete?
Mass concrete is not defined by any specific measurements. According to the American Concrete Institute (ACI), mass concrete is “any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking.” Some examples of mass concrete include dams, large bridge piers and columns, mat slabs and foundations.
Learn how to elevate your mass concrete projects here!
It’s important to note that smaller structures may also be categorized as mass concrete depending on several factors, such as type and quantity of cement, volume to surface ratio of the concrete, weather conditions, concrete placing temperatures, degree of restraints to volume changes, and the effect of thermal cracking on function, durability and appearance.
Why Is It Important to Monitor Mass Concrete Temperature?
Mass concrete is usually placed cool to limit its temperature rise. Placing temperatures of 50°F (10°C) and lower are practical and sometimes specified, and the actual limit comes from the project’s thermal studies. If the temperature is too low, the chemical reactions that strengthen the concrete slow down significantly and, at a certain point, come to a complete stop. If the temperature is too high, it will cause the concrete to have high early strength development but consequently gain less strength in the later stages, resulting in lower overall durability of the structure.
How Do Temperature Differentials Affect Mass Concrete?
As concrete hydrates and hardens, it generates heat. When constructing mass concrete structures, significant tensile stresses and strains are likely to develop due to the difference between the structure’s core temperature and surface temperature (this difference is known as the temperature differential). These stresses occur because the volume of the warmer concrete expands while the cooler concrete contracts.
The likelihood of thermal cracking increases as the inner core of the mass concrete continues to heat (hydration) while the outer surface of the concrete cools (heat dissipation). This is exacerbated by extreme cold weather, which quickly cools the outer surface of the concrete, but does not reach the inner core.
Learn more about thermal cracking here!
According to ACI 301-20: Specifications for Concrete Construction, the maximum concrete temperature differential should not exceed 35 °F (19 °C) during curing.
Without monitoring temperature differentials in mass concrete, contractors and project managers could run into serious problems such as cracking, reduced service life, project delays and noncompliance. These problems can make it hard to have a sustainable concrete construction.
Mass concrete temperature limits at a glance:
| What you monitor | Typical limit or target | What happens if you miss it | Basis |
|---|---|---|---|
| Peak core temperature | 160 °F (70 °C) during hydration | High early strength followed by lower long-term strength and durability, plus risk of delayed ettringite formation | ACI 301-20, section 8.1.3(a) |
| Core-to-surface temperature differential | 35 °F (19 °C) during curing | Tensile stress at the surface as the core expands and the face contracts, leading to thermal cracking | ACI 301-20, Specifications for Concrete Construction |
| Concrete placing temperature | 50°F (10°C) and lower are practical and sometimes specified; the project’s thermal studies set the limit | Too cold slows or stops hydration, too hot drives an unfavourable strength curve | ACI 207.1R-05; confirm against your project’s thermal studies |
| Monitoring duration | Until the core temperature is falling and the differential is inside the specified limit with the element approaching ambient | Insulation removed too early can create a thermal shock differential larger than anything seen during peak hydration | Project thermal control plan |
| Cold weather trigger | Air temperature has fallen to, or is expected to fall below, 40 °F (4 °C) during the protection period | Curing slows, and water in the concrete can freeze and expand, cracking and weakening it | ACI 306R-16, Guide to Cold Weather Concreting |
How to Monitor Mass Concrete Temperature
On construction sites, temperature differentials have traditionally been measured with thermocouples or data loggers. Both work, but both mean running wire out of the pour, protecting it through the rest of the build, and collecting data manually before anyone can analyse it. On a mass pour where a decision may be needed within hours, that lag is the problem.
Embedded wireless sensors remove the lag. A dual-temperature sensor is tied to the rebar before the pour with one probe at the core of the element and one near the exposed face, so both readings come from the same device and the differential is calculated for you rather than inferred from two separate instruments.
Giatec offers two options for mass concrete work:
- SmartRock® records temperature at two locations in the element and sends readings to a mobile device over Bluetooth when someone is on site and within range. It suits pours where a crew member is on the deck regularly.
- SmartRock® Long Range is built for elements where nobody wants to walk out to the sensor every few hours, or where the pour is inside a deep foundation, a remote site or a restricted zone. The sensors send their readings over a long-range wireless link, up to 1,000 ft (300 m), to a SmartHub gateway on site (or a Solar SmartHub where there is no power), which uploads them to SmartRock® Web, so the QC lead can check the core-to-surface differential from the trailer or the office instead of the deck.
Both use the maturity method (ASTM C1074) to convert the recorded temperature history into an estimate of in-place strength, alongside the raw temperature readings that drive the thermal control decisions.
Why Are Temperature Differentials in Mass Concrete So Important in Winter?
In ACI 306: Guide to Cold Weather Concreting, cold weather is defined as a period when the air temperature has fallen to, or is expected to fall below, 40°F (4°C) during the protection period.
In addition to slowing down the curing process, cold weather also causes the water in concrete to freeze and expand, cracking and weakening the concrete. In some cases, the concrete may even be rendered useless. However, it can still be successfully poured and placed in winter as long as the right precautions are taken to heat it properly.
Here are a few tips on how to control the temperature of your concrete in cold weather:
- Keep the concrete in a dry and heated area until it’s ready to use.
- Install internal electric heating: This requires using embedded coils and insulated electrical resistors.
- Optimize your concrete mix: Using low-heat cement; aggregate substitutes such as fly ash, limestone, or slag; and a low water-to-cementitious materials ratio are all good ways to optimize your concrete mix for heat retention in cold weather.
- Use insulation: Layering helps maintain the heat that is generated from the concrete. Insulation methods like heating blankets or forms allow you to control temperature differentials between the core and the surface of your slab.
- Remove standing water: Bleed water needs to evaporate or be removed by a squeegee or vacuum.
For more tips on cold weather concreting, see our blog on 7 common mistakes to avoid in cold weather concreting!
Hot Weather Concreting
For mass concrete, ACI 301-20 (section 8.1.3(a)) limits the maximum concrete temperature to 160°F (70°C) during hydration. If the temperature of the concrete during hydration is too high, it will cause the concrete to have high early strength development but consequently gain less strength in the later stage, resulting in lower durability of the structure overall. Furthermore, it has been observed that such temperatures interfere with the formation of ettringite in the initial stage and subsequently its formation in the later stages is promoted; which causes an expansive reaction and subsequent cracking.
Additionally, high temperature issues are of concern, especially in mass concrete pours, where the core temperature can be very high due to the mass effect, while the surface temperature is lower. This causes a temperature gradient between the surface and the core, if this differential in temperature is too large it will cause thermal cracking.
Here are a few ways to control the temperature of mass concrete in hot weather:
- Cool your mass concrete pour before placement: This can be done using chilled water, chipped or shaved ice, or liquid nitrogen.
- Cool the concrete after placement: Use embedded non-corrosive cooling pipes prior to concrete placement. This removes heat by circulating cool water from a nearby source.
The first step to controlling mass concrete temperature in hot weather is accurate data. Dual-temperature monitoring tells the team when the core is approaching its limit and how wide the differential has become, in time to act on it.
Frequently Asked Questions
What is mass concrete temperature monitoring?
It is the practice of recording the internal temperature of a large concrete element at more than one depth while it cures, so the team can track both the peak core temperature and the core-to-surface differential. Those readings are compared against the limits in the project thermal control plan and used to decide on insulation, cooling and form removal. It is normally done with embedded sensors that report temperature at the core and near the surface at the same time.
What is the maximum temperature differential allowed in mass concrete?
ACI 301 sets a maximum concrete temperature differential of 35 °F (19 °C) during curing. That figure is deliberately conservative and is a default rather than a universal answer. On many projects the thermal control plan sets a project-specific limit based on the mix, the element geometry and the restraint conditions, and that limit is the one that governs.
How many sensors does a mass concrete pour need?
The project thermal control plan specifies it. The general principle is that every element with its own thermal behaviour needs its own dual-temperature sensor, with one probe at the hottest point of the element (usually the geometric centre) and one close to the exposed face at the depth set out in the project thermal control plan. Adding a second sensor at a different location in a large mat is common practice, because a single point can miss a hot spot created by a change in section.
**Editor’s Note: This post was updated for accuracy and comprehensiveness in October 2026.
