GIẢI ĐỀ READING CAM 18 TEST 3 PASSAGE 1

📖 IELTS Reading Test

Materials to take us beyond concrete (C18 Test 3)

A Concrete is the second most used substance in the global economy, after water – and one of the world’s biggest single sources of greenhouse gas emissions. The chemical process by which cement, the key ingredient of concrete, is created results in large quantities of carbon dioxide. The UN estimates that there will be 9.8 billion people living on the planet by mid-century. They will need somewhere to live. If concrete is the only answer to the construction of new cities, then carbon emissions will soar, aggravating global warming.

B The problem with replacing concrete is that it is so very good at what it does. Chris Cheeseman, an engineering professor at Imperial College London, says the key thing to consider is the extent to which concrete is used around the world. (Q13) ‘Concrete is not a high-carbon product. Cement is high carbon, but concrete is not. But it is the scale on which it is used that makes it high carbon. The sheer scale of manufacture is so huge, that is the issue.’

C (Q3) Not only are the ingredients of concrete relatively cheap and found in abundance in most places around the globe, the stuff itself has marvellous properties. (Q10) Cheeseman also notes another advantage: concrete and steel have similar thermal expansion properties. According to Cheeseman, all these factors together make concrete hard to beat. ‘Concrete is amazing stuff. Making anything with similar properties is going to be very difficult.’

D A possible alternative to concrete is wood. (Q5) Climate change is driving architects to turn to treated timber as a possible resource. Recent years have seen the emergence of tall buildings constructed almost entirely from timber. (Q2) Vancouver, Vienna and Brumunddal in Norway are all home to constructed tall, wooden buildings.

E Using wood to construct buildings, however, is not straightforward. (Q6) Wood expands as it absorbs moisture from the air and is susceptible to pests. But treating wood can improve its properties. (Q7) An adhesive is used to stick layers of solid-sawn timber together, crosswise, to form building blocks. Construction experts say that wooden buildings can be constructed at a greater (Q8) speed than ones of concrete.

F Stora Enso is Europe’s biggest supplier of cross-laminated timber. (Q11) Markström reports that the company is seeing increasing demand, with climate change concerns the key driver. Finland has been leading the way. (Q4) But even treated wood has its limitations and only when a wider range of construction projects has been proven in practice will it be possible to see wood as a real alternative.

G (Q1) Fly ash and slag from iron ore are possible alternatives to cement in a concrete mix. Fly ash, a byproduct of coal-burning power plants, can be incorporated into concrete mixes. But (Q9) Anna Surgenor notes that although these waste products can save carbon, if they are transported over long distances, the use of alternative materials might not make sense from an overall carbon reduction perspective.

H While these technologies are all promising, they are either unproven or based on materials that are not abundant. (Q12) Felix Preston and Johanna Lehne reached the conclusion that these alternatives are rarely as cost-effective as conventional cement, and they face raw-material shortages.