Hot Weather Concreting in the UAE and GCC: Limits, Cooling, Curing and Monitoring

For much of the year, concreting in the UAE, Saudi Arabia, Qatar, Kuwait, Bahrain and Oman is hot weather concreting. UAE summer air temperatures reach 45–50 °C, and concrete that is not cooled can exceed 35 °C at placement. On top of that come direct sun, hot aggregate stockpiles, dry desert winds and long truck journeys through city traffic. This guide explains what ACI 305R recommends, the placing limits commonly used in the region, how contractors cool the concrete, and how to cure and monitor it once it is placed.

What is hot weather concreting?

ACI 305R, the ACI guide to hot weather concreting, defines hot weather as any combination of high air temperature, high concrete temperature, low relative humidity, wind speed and solar radiation that impairs the quality of fresh or hardened concrete. It is defined by these conditions, not by a single air temperature.

Under this definition, a windy 35 °C afternoon with low humidity can be harder on a slab than a still, humid 40 °C evening. ACI 305.1 is the companion specification, written in mandatory language so that it can be cited in contract documents. Many Gulf project specifications are based on these documents or on BS/EN practice and add local requirements. The project specification always governs.

What does heat do to concrete?

Heat speeds up hydration and evaporation. As a result, concrete stiffens sooner, needs more water to stay workable, is harder to finish, is more prone to cracking and, if not controlled, reaches lower long-term quality.

• Fresh concrete: faster slump loss, shorter setting time, a higher risk of cold joints between layers, and a temptation to add water on site, which raises the water-cement ratio.
• Early age: plastic shrinkage cracking when surface water evaporates faster than bleed water rises. There is also a higher peak temperature in thick sections, which raises thermal cracking risk (see mass concrete temperature differential).
• Hardened concrete: higher early strength, but often lower later-age strength and higher permeability than the same mix cured at moderate temperature. This matters for durability in the Gulf, where chlorides and sulfates in the ground and in the air are aggressive to concrete and reinforcement.

Keep two mechanisms apart. Plastic shrinkage cracking is a surface problem that appears within hours and is prevented by evaporation control. Thermal cracking in thick elements develops over days or weeks, driven by the core-to-surface temperature difference (ΔT) and restraint. Peaks above about 70 °C also raise the risk of delayed ettringite formation (DEF), which can appear years later once moisture is present. A thermal control plan does not replace evaporation control, and evaporation control does not replace a thermal control plan.

What placing temperature limits are used in the Gulf?

There is no single regional value. Specifications in the region commonly set 32–35 °C for general elements, and mass concrete and some high-performance elements often have much lower limits. When nothing else is specified, ACI 305.1 uses 35 °C. Read the project specification.

Loads that arrive above the limit are normally rejected, not cooled on site. The practical goal is to batch concrete cool enough that it is still within the limit after the journey and a wait at the pump.

How is fresh concrete cooled?

Concrete is cooled by lowering the temperature of its ingredients. A common rule of thumb (ACI 305R): the concrete drops about 0.5 °C for every 4 °C less in the cement, 1.75 °C less in the water, or 0.75 °C less in the aggregate. Aggregate makes up most of the mass, so it is the biggest lever. Ice and liquid nitrogen add extra cooling. Most Gulf batching plants combine several of the methods below.

Why ice works so well: melting ice absorbs 334 kJ/kg, the same heat needed to warm that water by about 80 °C. That is why chilled water alone is rarely enough in a Gulf summer.

For thick elements, mix design is the cheapest cooling. Typical thermal-control blends use 40–50 % Class F fly ash or 65–75 % slag. A screening rule for thick sections is about 15 °C of temperature rise per 100 kg/m³ of equivalent cement, with peak ≈ placing temperature + rise. This is conservative and for screening only; thick rafts, high binder contents, stiff bases or tight ΔT limits need a project-specific thermal model.

On site, shade the pump line and the waiting area where possible, and schedule deliveries so trucks do not queue in the sun. Mist very hot reinforcement, embedments and forms with water before placing, and remove standing water.

When should you pour at night?

Pour at night when daytime conditions make the placing limit or the finishing time hard to meet. In Gulf summers this applies to most slabs and large pours. Night pours avoid solar radiation and peak air temperatures and lower evaporation.

Night work brings its own risks. Plan lighting, supervision and inspection, and in some locations noise and traffic restrictions. Plan out cold joints too: retarders, backup trucks and pumps, and a realistic placement rate are part of the plan, not extras. Above all, curing must be ready before sunrise. A slab finished at 4 a.m. and left uncovered at 7 a.m. can lose surface moisture quickly. Large pours that run past dawn need a plan for the last layers, which will be placed in the hottest conditions.

How should concrete be cured in hot weather?

Start curing as soon as the surface can take it and keep it going without interruption for the specified period. In hot, dry, windy conditions, a few hours without curing can do lasting damage. ACI 308R, the ACI guide to external curing, describes the available methods.

• Before finishing: fog misting, windbreaks, sunshades and evaporation retarders help prevent plastic shrinkage cracking while the surface is still being worked.
• Moist curing: wet hessian (burlap) covered with polythene, ponding or continuous sprinkling. Intermittent wetting that lets the surface dry and re-wet in the sun is poor practice. Where moist curing stops early, protect the surface with curing paper, heat-reflecting sheets or a curing compound.
• Curing compounds: apply a membrane-forming compound at the specified rate as soon as the surface water has gone. Light-coloured (white-pigmented) compounds reflect solar radiation. Check compatibility with any later coatings or toppings.
• Formed surfaces: keep the formwork in place, and wet timber forms if they dry out. Cure the faces as soon as the forms are removed.
• Duration: commonly at least seven days for moist curing. Blends with fly ash or slag may need longer. The specification governs.

Thick elements need a second kind of protection: stopping the surface from cooling too fast relative to the core.

• Cold water on a hot element can hurt. Water curing can steepen the core-to-surface gradient. For mass concrete, forms are usually left in place and water curing is used only if the thermal control plan shows the limits are still met.
• Insulate to keep the surface warm. Blankets and insulated formwork narrow the core-to-surface gap; they do not cool the core. Insulate projecting starter bars too, as they pull heat out of a much wider zone than their own area.
• Cure long enough. Mass concrete needs longer curing than ordinary elements, and longer again with slag or pozzolan.
• Treat stripping as a thermal event. Removing forms from a hot core on a cooler night can cause thermal-shock cracking. After protection comes off, cooling is commonly limited to about 14 °C per 24 h.

What should be monitored during and after the pour?

Record the fresh concrete temperature at delivery, the ambient conditions during placing, and the in-place concrete temperature for the first days. Together these show that the specification was met and when the concrete is strong enough for the next activity.

Fresh temperature at discharge is a routine acceptance check. In-place temperature logging adds three things. First, it shows peak temperatures and differentials in thick elements. Second, it provides the temperature history for strength estimation by the maturity method. Third, it gives a record if cracking or low results are questioned later. Meeting the specified limits does not always settle a crack dispute, so a complete record matters.

For limits, thermal control plans and sensor placement in thick elements, see the guide to mass concrete temperature differential. A typical sensor layout, based on ACI 301 practice:

• One sensor at the centre of the largest section, and one 50 mm from the centre of the nearest exterior surface.
• A backup sensor at each location. A failed core sensor cannot be replaced after the pour.
• One shaded ambient sensor.
• Readings every hour, accuracy of about ±1 °C, and data to the engineer daily.
• More sensors for large pours, usually at corners and edges.

Protection stays until the core has peaked and the gap between the average daily air temperature and the internal temperature is below the ΔT limit. The end point should be set by temperature, not the calendar. If a limit is exceeded, act per the plan and hold further mass pours until the cause is found.

A monitoring plan works best with a simple trigger-action table agreed before the pour:

In hot climates, remember that the maturity method's accuracy for later-age strength can decrease when early temperatures are very high, because the method assumes the same strength at the same maturity regardless of curing temperature. Confirm maturity estimates with other tests before critical steps such as stripping or stressing. Keep standard-cured cylinders or cubes for acceptance, and use field-cured specimens or in-place estimates for construction decisions, as the specification allows.

How SHM360 helps

SHM360-Node devices record in-place concrete temperature on three probe channels plus ambient air, and send the data over LTE without a gateway or on-site pairing. They are rated to operate from −40 °C to +85 °C. They store readings locally and upload them when the signal returns. The SHM360 platform shows live charts, sends threshold alerts, and estimates in-place strength using the ASTM C1074 maturity method after a one-time calibration for each mix design. It also produces PDF reports and CSV exports for the quality record. See concrete temperature and strength monitoring for details.