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For Teachers

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For Learners

A

The University of Illinois explains that concrete has two main parts. The binder is cement mixed with water, and the filler is fine sand or coarse gravel, called aggregate. The concrete hardens through a chemical reaction between the cement and the water, called hydration. The university says that concrete does not need to dry out to harden, although many people think so.

B

The university says that the cement needs moisture to harden, so builders keep fresh concrete damp. It gets its early strength in the first 7 days, and many tests measure the strength after 28 days. The university adds that concrete goes on getting stronger for a long time, often for several years.

C

The U.S. Geological Survey estimates that the world made about 4.1 billion tonnes of cement in 2023. It estimates that China made about 2 billion of them. The survey says that most cement goes into concrete, mortar and similar building materials.

D

I think the university explains well why wet concrete should not be left to dry too fast, and it seems that strength is a slow process, not a single moment. The cement figures are estimates, so I do not think they show exactly how much concrete people pour, because the sources say nothing about how much cement goes into each batch.

A detailed technical architectural schematic of concrete composition showing binder cement water and filler coarse aggre

Figure 1: Cement and water hardening around pieces of sand and stone.

Key Scientific Terms

• • Binder: Cement + Water paste
• • Filler: Fine sand / coarse gravel
• • Hydration: Chemical hardening reaction

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____ A. Most cement goes into mortar and similar materials, not into concrete. ____ B. The sources do not specify the amount of cement used per batch. ____ C. Concrete keeps getting stronger for years, so a figure from one year cannot be exact. ____ D. Cement figures fail to account for mortar and other building materials.

____ A. It reaches its maximum density within the first 7 days. ____ B. It achieves full hardness immediately after hydration completes. ____ C. It is a gradual development rather than an immediate result. ____ D. It depends entirely on drying out quickly under high temperatures.