How Do You Schedule and Cure Mass Concrete in Somaliland's Heat Without Cracking?

Mass concrete in Somaliland fails differently from ordinary concrete. The problem is not the sun burning the surface; it is the temperature gap inside the pour. When cement hydrates it releases heat, and in a thick raft, pile cap or water tank wall the core cannot lose that heat while the surface can. In Hargeisa, where daytime air can sit above 35C in the Jilaal dry season and humidity drops to single digits (long-standing climate records for Hargeisa, not a site measurement), that gap grows fast. The practical answer is to schedule the pour for the coolest hours, cool the mix water or use ice, shade everything, and then cure continuously with a wet cover for at least seven days. Design the pour around these steps before you order the first truck.

Why does mass concrete crack in Somaliland's heat?

It cracks because the inside and outside of the pour cool at different rates, and the surface goes into tension. Heat drives the reaction, thickness traps it. A 1 m raft with an ordinary OPC mix can peak several tens of degrees above ambient in its centre within 24 to 48 hours, because hardened concrete is a poor conductor and the core has nowhere to lose heat. Meanwhile the exposed top and sides radiate into the night, especially during the sharp day-night swing in Hargeisa where nights in Jilaal can be 15C to 18C cooler than the afternoon.

The controlling number most engineers use is the core-to-surface temperature difference: keep it under about 20C until the pour cools, and control the rate of cooling after the peak. That is engineering practice, not a Somaliland-specific rule, and it should be confirmed against the project specification. Two checks matter:

• Peak core temperature. Most specifications cap this at 70C so that delayed ettringite formation does not damage the concrete later. Above that, you risk long-term strength loss, not just early cracking.
• Cooling rate. After the peak, the core should cool slowly. A fast drop from a cold night wind on a hot surface pulls the surface into tension.

In Berbera, salt air adds a second problem on top: the concrete must also resist chloride ingress, so any hot-weather measure that increases water content, such as adding water to keep a stiff mix workable, makes corrosion worse. Design the mix, cooling and curing together.

How do you schedule a pour around Somaliland's heat?

You schedule by putting concrete in the ground when the ambient temperature and the sun load are at their lowest, and by finishing before the heat returns. That normally means starting at night or in the very early morning.

Practical working method:

1. Target a night start. Aim to place between roughly 22:00 and 06:00 so the mix arrives cool and the first critical hours of hydration happen in the lowest ambient temperature of the day. In Hargeisa and Burao, in the hot Haud, the difference between a 05:00 pour and an 11:00 pour in June is large; in Berbera the coastal humidity is higher but the sun load is still heavy.
2. Size the pour to the plant. Somaliland batching is usually done either on-site with a small mixer or by a ready-mix supplier in Hargeisa and Berbera. Ask the supplier for the realistic output in cubic metres per hour and the travel time from the plant to the site, including the Berbera port road. A 200 m3 raft that arrives slower than planned will have cold joints and a hot surface by mid-morning.
3. Plan the joints and the limit. Divide very large pours with construction joints or use a lower-heat mix so you are not forced to place more than the plant and crew can handle in one cool window.
4. Stage the crew. For a night pour in a city without continuous street lighting on every access road, arrange site lighting, a lunch and tea rotation, and a clear hand-over between two crews. The most common night-pour failure is a tired crew that slows down at 04:00 and leaves a cold joint.
5. Back up the plant. Have a spare mixer, a spare vibrator, and, for smaller pours, a standby water supply for curing. One generator failure in a remote site near Erigavo can kill a night pour.

Costs vary by region and supplier. For orientation rather than as a quote: ready-mix concrete in Hargeisa has typically been priced in the range of roughly USD 90 to USD 130 per cubic metre delivered, depending on grade and distance, and small-site mixed concrete usually works out cheaper in materials but more expensive in labour and quality control. Treat those as indicative ranges, not fixed prices, and get two written quotes.

How do you keep the concrete cool before and during placement?

You keep it cool by cooling the ingredients, not just the finished mix. Water is the easiest ingredient to chill, and in a dry climate ice also raises the water content without adding extra water to the mix design.

Methods that work in Somaliland practice:

• Ice in the mix water. Replace part of the batch water with crushed ice. As the ice melts it absorbs heat, and it counts as part of the water in the mix design, not extra. On a 1 m3 batch, a realistic replacement is a fraction of the water, not all of it; check with the mix designer.
• Chilled or shaded water tanks. A black plastic tank standing in the sun in Hargeisa can easily reach 40C or more by afternoon. Shade the tank, paint it a light colour, or buy block ice locally for the pour day.
• Shade the aggregate stockpiles. A canvas or shade net over the sand and coarse aggregate stockpile can cut the stockpile temperature by several degrees. Do not let sand sit on dark tarmac or on dark stone.
• Pre-wet the formwork and the sub-base. Wet the formwork and the blinding or sub-base shortly before the pour, but remove standing water. Wetting cools the surface and stops it sucking water out of the mix.
• Shade the pour. A simple shade structure over the placement area, even a tarpaulin on poles, lowers surface temperature and reduces plastic shrinkage while you finish.
• Limit the ambient window. If you cannot cool the mix, do not place mass concrete when ambient is rising quickly. A concrete that arrives at 32C can still be acceptable if it cools quickly into the ground; one that arrives at 38C in a thick section is a problem.

One number to hold: most hot-weather concrete guidance aims to keep the fresh concrete temperature at placement below about 32C to 35C, and every degree you shave off the placement temperature reduces the peak core temperature. That is standard hot-weather practice; apply it to your specification.

What is the correct curing method for a hot, dry site?

You cure by keeping water on the concrete continuously for at least the period stated in the specification, and by starting it immediately after finishing. Hot, dry air pulls moisture out of young concrete faster than the cement can use it, which causes plastic shrinkage cracks and weak surface layers. In Hargeisa's dry season, a concrete surface can lose water quickly enough to craze within hours if no cover is applied.

What works here:

• Wet burlap or hessian, kept wet. Lay hessian or old cloth over the surface immediately after finishing, then wet it. It must stay wet, not damp. In dry heat, this usually means re-wetting two or three times a day and more in the afternoon. Use a watering can or a hose with a fine spray; a hard jet washes cement out.
• Wet sand blanket on flat slabs. A 25 mm to 50 mm layer of clean sand over a slab, kept wet, holds moisture well and is cheap and available in most Somali towns. It protects the surface from sun and wind.
• Plastic sheeting over wet cover. Polyethylene sheet over wet burlap slows evaporation. It is most useful on wind-exposed sites and on water tank walls. Weight the edges so the wind does not tear it off.
• Water tank walls and vertical faces. Leave formwork in place longer where possible, or use a wet wrap. Vertical faces dry faster than slabs because they catch the wind.
• Duration. For ordinary Portland cement mixes, a minimum of 7 days of continuous wet curing is a common requirement; for blended cements, for low water-cement ratio mixes, or where the specification calls it, 10 to 14 days is normal. Confirm the duration in your specification, because short curing is one of the easiest things to skip under time pressure and one of the hardest to prove afterwards.

Labour for curing is a real cost and should be in the bill. One person per site on a small pour, watering twice a day with a water bowser or a drum-fed hose, is a small daily cost compared to the price of a cracked raft. If the site has no water source, price the water delivery into the curing plan before the pour, not after.

How do you monitor and protect the pour after placement?

You monitor by measuring temperature at the core and near the surface, and you protect by controlling cooling, not by stopping it. On a large raft or a thick water tank base, install two or three temperature probes: one at the centre, one about 50 mm from the top surface, and, where possible, one near a formwork face. Read them at least twice a day for the first three days and note the values in the site diary.

Simple monitoring rules that match most specifications:

• Peak core. Keep the maximum core temperature under about 70C.
• Core-to-surface gap. Keep the difference under about 20C. If the gap widens, insulate the surface rather than cool the core.
• Cooling rate. After the peak, aim for a slow, steady drop. Sudden cold night winds in Hargeisa or along the Berbera coast can cool a surface too fast; leave the wet cover and, where needed, a layer of insulation or sand in place.

For smaller pours, such as a 400 mm to 600 mm thick pile cap or a septic tank base, formal monitoring is often not justified, but the same sequence still applies: night pour, cool mix, immediate wet cover, and no early stripping of formwork. Stripping formwork too early on a hot day can shock a warm section and cause thermal cracking on the exposed face.

On a site where the contractor is doing the work and the client or a relative is supervising, the two things to insist on are the pour time and the curing log. A written record of when the pour started, the concrete temperature on arrival, and when curing started and stopped is the evidence that the work was done properly. This is the same gap in verification that shows up across Somaliland sites, where claims are made but not documented.

What to do next

Before your next mass pour, write a one-page pour plan and share it with the batching plant and the crew. It should state the pour date and start time, the target arrival temperature, the ice or chilled water quantity, the shade arrangements, the probe locations, the curing method, and the name of the person responsible for each item. Then visit the plant or talk to the supplier and confirm two things in writing: the realistic output in cubic metres per hour and the earliest delivery time. Finally, buy and deliver the curing materials, hessian or sand and plastic sheeting, and a stock of block ice, to the site at least one day before the pour. If the materials are not on site the night before, the pour is not ready.