Infrared Thermometer for Concrete: What It Can and Can’t Tell You

Concrete temperatures influence workability, setting pace, finishing quality, and curing effectiveness. Large swings can cause thermal cracking or premature moisture loss if not managed. Surface temp is a practical signal on the job when pours go ahead or pause.

Infrared thermometers offer a quick, noncontact way to monitor surface temperature during placement and curing. They measure surface temp, not the interior mass, which is why readings must be interpreted with context. Use this tool to guide decisions like delaying pours, adjusting mixes, or selecting curing methods, while being aware of emissivity, moisture, and outdoor conditions that can skew results.

What this article will cover

The following sections explain why temperature matters for concrete and how infrared (IR) thermometers help on job sites. We’ll discuss:

Capabilities: How IR thermometers measure surface temp quickly and noncontact.

Limits: Emissivity, reflections, outdoors vs indoors, moisture on surface affecting accuracy.

Accuracy factors: Ambient conditions, spot consistency, interval recording.

Selection & jobsite integration: Choosing the right IR thermometer and using it effectively on site.

When to use an IR thermometer on concrete

IR thermometers are useful at various stages of concrete work. Here’s when and why:

Pre-pour: Check ambient temp, substrate temp to ensure suitable conditions for pouring.

During placement/finishing: Monitor surface temp to maintain workability, prevent thermal cracking, and optimize finishing quality.

Early cure: Track temp during initial curing (first 24-72 hours) to manage hydration heat and moisture loss. Readings answer questions like:

– Is the concrete too hot or cold for placement?

– Are there any temperature variations that could cause issues?

– How should we adjust curing methods based on temp readings?

Back to top ↑

IR thermometers operate by sensing infrared radiation emitted by a surface and converting it to a temperature reading. The result reflects the surface temperature rather than the concrete’s internal mass. This basic principle makes them fast and noninvasive on site.

Several factors influence readings, including emissivity settings, distance-to-spot ratio, angle, surface texture, and moisture or coatings. Common mistakes include measuring through plastic or on shiny surfaces, or when surrounding objects skew the spot. Maintain a consistent procedure to keep readings meaningful and useful for context and trend checks.

Emissivity and why surface properties matter

The infrared thermometer measures temperature by detecting the infrared radiation emitted by a surface. This is known as emissivity, which varies depending on the surface’s condition.

Concrete surfaces can have different emissivities based on their finish – wet, dry, rough, or smooth. For instance, wet concrete has a higher emissivity than dry concrete.

To account for this, you might need to adjust your thermometer’s emissivity setting or use reference patches with known emissivity values.

Line-of-sight, field of view, and spot measurement

The thermometer’s distance to the target surface determines its field of view – the area it measures. This is often referred to as the distance-to-spot ratio.

Aiming, angle, and obstructions can affect which part of the surface is being measured. For example, if you measure at an angle, you might get a reading from both the target spot and its surroundings.

To ensure accurate readings, keep the thermometer perpendicular to the surface, maintain a consistent distance-to-spot ratio, and avoid obstructions like formwork or rebar.

Back to top ↑

IR thermometers are reliable for surface temperature tracking, identifying thermal gradients across a slab, and flagging ambient conditions that affect placement and finishing. They help you gauge when to modulate curing plans or adjust misting and protection strategies. Use them as a situational check, not a sole decision-maker.

Setups matter: keep emissivity around concrete expectations, watch the distance-to-spot ratio, and note surface moisture or roughness. Readings don’t reveal subsurface temps, moisture pockets, or chemistry directly, so couple with other methods when needed. Document ambient conditions to improve interpretation of results.

Detecting cold spots and thermal gradients

Infrared thermometers can help you spot areas where concrete isn’t curing evenly. This could be due to differences in mix, exposure to wind or sun, or other factors.

To map out these ‘cold’ or ‘hot’ spots, take readings across the slab’s surface in a grid pattern. Look for significant temperature variations – more than 5°F (3°C) – which could indicate thermal gradients.

Remember: Concrete cures from the outside in. So, surface temps might not reflect what’s happening deeper down.

Quick verification for placement and finishing decisions

Before you place or finish concrete, use your infrared thermometer to check surface temps. This helps you make timely choices about admixtures, finishing techniques, and temporary protection.

For instance, if the slab’s too cold (< 50°F/10°C), it might need heating before placement. Or, if it’s hot (>77°F/25°C), consider adding retarding admixtures to slow down setting time.

Pro tip: Check temps at multiple points and times of day. Concrete can heat up or cool down quickly depending on weather conditions.

Back to top ↑

IR thermometers only measure surface temperature and apparent temperature influenced by emissivity and surface conditions. They do not read the internal core temperature of the concrete. For core temps, use probes or embedded sensors as prescribed.

Moisture content, saturation, pore water, and porosity are not directly detectable from the surface with an IR device. Strength and curing quality require lab or non-destructive tests. Surface coatings or recent curing can also skew readings, so interpret results with calibration and context.

Why surface temp is not the same as internal temperature or strength

Infrared thermometers measure surface temperature, but concrete’s internal core temp can differ. Here’s why:

Concrete’s massive nature retains heat in its core while radiating surface heat. This difference matters because:

Surface temp doesn’t reflect curing progress or strength. Concrete gains strength internally over time, regardless of surface temp. Embedded sensors or maturity testing can help track this.

Misleading readings: moisture, reflectivity, and transient conditions

IR thermometers can give false assurance due to certain conditions:

Wet sheen or shiny aggregates can make surfaces appear warmer than they are. Recent sun exposure can also skew readings.

Transient conditions like these require confirmation with other tools. Don’t rely solely on IR for moisture detection or critical decisions based on temporary heat gains/losses.

Back to top ↑

Key accuracy factors include surface moisture, texture, emissivity, ambient temperature, distance-to-spot ratio, and the concrete’s composition or curing state. Each factor can shift readings if not controlled. Plan measurements with these in mind to avoid misleading results.

Choose features wisely: set emissivity appropriately for concrete, know your device’s D:S ratio, and use laser guidance or a spot indicator. Prepare the surface by cleaning and drying as needed, and minimize air flow and direct sun that can skew data. Establish a repeatable protocol for height, angle, and spot selection to improve reliability.

Environmental and Setup Considerations

The weather can throw off your readings. Here’s how to deal with it:

Wind: It can cool the surface, so find a sheltered spot or time your reading when wind is minimal.

Sun: Direct sunlight heats up surfaces. Read in shaded areas or after sun has moved on.

Rain: Wet concrete gives false readings. Wait for it to dry naturally, don’t rush with heaters.

Ambient swings: IR thermometers are sensitive to temperature changes. Let your tool acclimate in the new environment before taking readings.

Probe Positioning, Distance, Angle, and Surface Prep

Choose your measurement points wisely:

Select representative locations – center of slabs, near joints, in shaded areas. Avoid edges and corners.

Keep the probe at a consistent distance from the surface. Your tool’s manual will tell you the ideal D:S ratio (Distance to Spot).

Maintain a steady angle. Hold it perpendicular to the surface for best results.

Prepare surfaces:

Clean off dirt, dust, or debris. Use a damp cloth if needed. Let it dry.

If the surface is glossy, matte it down with a bit of talc or powder to reduce reflectivity.

Calibration, Emissivity Checks, and Verification

Regular calibration keeps your tool accurate:

Check the manual for a blackbody reference or use an ice bath (0°C) as an alternative. Adjust zero if needed.

Concrete’s emissivity is usually around 0.95. Leave it at this standard value unless you’re sure it’s different.

Verify your readings:

Use a contact thermometer for comparison on small areas or where IR can’t reach. Keep in mind, they measure differently.

Take multiple readings and average them out to improve reliability. Consistency is key.

Back to top ↑

Look for a decent distance-to-spot ratio, solid accuracy at typical concrete temperatures, and usable emissivity handling with a concrete preset. Fast response times help you monitor changes in real time on the pour floor. A fixed emissivity around concrete expectations is common, but verify with manufacturer instructions.

Pair the IR thermometer with complementary tools like a moisture meter and, if possible, a thermocouple or data-logger for internal temps. A surface thermometer can provide quick cross-checks. Use a practical workflow to decide when to rely on IR data and when to switch to contact probes for critical decisions.

Key features to evaluate

The manufacturer’s spec sheet is your friend. Here’s what matters:

Accuracy tolerance: Look for ±1-2°C or °F at typical concrete temps (0-50°C/32-122°F).

Adjustable emissivity: Must handle 0.9