Vemaventuri Helps Master 2nd Gen Eurocode 2 with Real-Time Data

Concrete does not gain strength with time. It gains strength through hydration, the reaction between cement and water, and that reaction runs faster when it is warm and slower when it is cold.

Two walls from the same delivery, one poured on a February night in the open and one inside a heated enclosure, have measurably different strength after three days. The calendar says nothing about it. What does describe it is maturity: a calculated value combining time and temperature to estimate the strength currently present in the element.

What changes

The most consequential change here is easy to overlook. Under the first generation, 28 days was effectively fixed as the age at which concrete had to reach its specified strength. The second generation allows the reference compressive strength to be defined at any age between 28 and 91 days.

The reason is sustainability. Cement production is the dominant source of CO₂ in concrete, and the most direct way to reduce it is to use less clinker. Concretes with high proportions of slag, fly ash or limestone reach the same final strength, but they get there more slowly. Judged at 28 days they look weak. Judged at 56 or 91 days they are not. Allowing a later reference age removes a barrier that was pushing designers toward clinker-rich mixes.

Alongside this, time dependent material behaviour was consolidated into Annex B, which is now normative, with clause B.4 covering the development of concrete strength and stiffness with time. The creep and shrinkage models were updated and unified for normal and high strength concrete.

Why this reaches the site

A slower concrete does not only reach its final strength later. It passes every intermediate point later too, including the one that matters on site: the strength required to strike formwork, transfer prestress or load the element.

This is where experience stops helping. A site team knows how their usual C30/37 behaves after two days in April. With a low-clinker mix on a 56-day reference age, that intuition no longer applies, and the safe response is to wait longer than necessary. The environmental gain is real, and the schedule pays for it.

The models in Annex B describe how strength develops. What they cannot supply is the thermal history of the element, because that is not a property of the mix, it is a property of the pour. Nothing in the design office knows it.

Cubes do not close the gap either. A cube stored beside the element, or in a laboratory water bath, is a different size with a different surface to volume ratio and therefore a different thermal history. It confirms that the concrete delivered was compliant. It does not measure the concrete in the wall.

Some cracks have nothing to do with load. They form in the first few days, while the concrete is still hardening, and they go straight through the wall.

Here is how it happens. Hardening produces heat, and the element expands. Then it cools and wants to contract again. Often it cannot, because it sits on a base slab that has already hardened. Anything that cannot contract goes into tension. And young concrete does not take much tension yet. Where it becomes too much, it cracks through.

On a car park wall that is a blemish. On a water-retaining basement or tank it is a defect that has to be injected, and someone pays for it.

What changes

The first generation had no general method for this. Restraint cracking was largely covered by prescribing minimum reinforcement, with specific provisions only in EN 1992-3 for containment structures. You did not assess the risk. You covered it.

The second generation adds Annex D, "Evaluation of early-age and long-term cracking due to restraint" — one of the scope extensions the European Commission's own workshop material lists among the key additions to the code. It provides a method to actually evaluate the risk.

And it is worth looking at how that method is built. Clause D.4 is "Assessment of temperature history", with D.4.2 covering material properties in relation to temperature development. Only then come D.5, stress calculations, and D.6, crack width calculations.

The order is the point. The temperature history is not an input among others. It is the first step, and everything downstream depends on it.

Why this reaches the site

Anyone applying Annex D has to assume a temperature curve. At the desk that is fine. But nobody there knows what actually happened on site.

The real curve depends on wind, on the overnight temperature, on the mix, on the formwork, on an unplanned gap between deliveries, on when the insulation came off. A 1.8 m raft poured on a windy day does not follow a standard curve.

And here is the difference from the other two topics. Carbonation shows up after twenty years. Strength can be tested. Early age cracking happens over about three days — and during those three days you can still intervene. Leave the insulation on longer, strike later, cool the section.

But that only works if you can see what is happening while it happens.

References & Standards

• European Commission, Joint Research Centre (2025) — The Second Generation Eurocodes: key changes and benefits through design examples. EN 1992 session, A. Pérez Caldentey. Online workshop, 3–5 June 2025. 
• Andrade, C. & Izquierdo, D. (2023) — Durability and cover depth provisions in next Eurocode 2: background modelling and calculations. Hormigón y Acero 74(299–300), 19–40. Open access. 
• Menga, A. et al. (2024) — Early-age cracking due to restraint: laboratory and field investigations on the predictive capacity of the simplified method in Annex D of the future EC2. Structural Concrete 25(6), 4300–4323. 
• Kanstad, T., Klausen, A.B.E. & Menga, A. (2023) — Background document to FprEN 1992-1-1 Annex D. CEN/TC250/SC2/WG1/TG7. 
• von Greve-Dierfeld, S. & Gehlen, C. (2016) — Performance-based durability design, carbonation, parts 1–3. Structural Concrete 17(3) 309–328, 17(4) 523–532, 17(5) 718–728. 
• EN 13670:2009. Execution of concrete structures. CEN, Brussels.
• EN 206:2013+A2:2021. Concrete — Specification, performance, production and conformity. CEN, Brussels.