IELTS Academic Reading Practice Test 40

A The structures built by Roman engineers between the second century BCE and the fall of the western empire have remained the object of admiration and study for almost two thousand years. Among the most remarkable, in many architectural historians' view, are the great concrete monuments of central Italy: the unreinforced dome of the Pantheon in Rome, which still spans 43 metres without cracking; the marine breakwaters of Portus and Caesarea Maritima, partially submerged for two millennia yet still intact; and the surviving sections of the Markets of Trajan, whose vaults continue to support significant loads. By contrast, much modern concrete begins to deteriorate within fifty to a hundred years, particularly when exposed to seawater. The contrast between the longevity of Roman concrete and the comparative fragility of its modern descendants has long puzzled materials scientists.

B The basic ingredients of Roman concrete are known from descriptions left by the Roman architect Vitruvius and from chemical analysis of surviving samples. Roman builders mixed lime, derived from burned limestone, with a particular form of volcanic ash called pozzolana, found in abundance in the Bay of Naples and around Rome itself. To this binder they added pieces of stone or brick as aggregate. The chemistry of the resulting material is similar to that of modern Portland cement, which also relies on a reaction between lime and silica to form calcium silicate hydrate, the principal strength-giving compound. Yet the differences in long-term performance between the two systems are considerable.

C A breakthrough is widely said to have come in 2017, when researchers led by Marie Jackson of the University of Utah examined samples of Roman marine concrete using high-resolution electron microscopy and X-ray spectroscopy. They discovered that the concrete contained microscopic crystals of aluminous tobermorite, a rare mineral that ordinarily forms only at high temperatures in geothermal environments. The presence of tobermorite in the marine samples indicated that the concrete had continued to react chemically with seawater over many centuries, growing additional crystals within its existing pore spaces. Rather than weakening the material, this slow ongoing reaction was strengthening it: tobermorite crystals filled cracks as they formed, sealing the structure against further damage.

D A separate investigation published in 2023 by an international team based at the Massachusetts Institute of Technology and Harvard University identified another key feature of Roman concrete: small white inclusions, known as lime clasts, that had previously been dismissed as evidence of poor mixing. Using scanning electron microscopy, the team showed that the clasts were produced deliberately by a hot-mixing process in which quicklime was combined directly with the volcanic ash and water at high temperature, rather than being slaked into a paste beforehand. When microcracks subsequently developed in the concrete, water entering the cracks dissolved nearby lime clasts and produced a calcium-rich solution that recrystallised inside the cracks, healing them. This self-healing behaviour has now been replicated in laboratory specimens deliberately formulated to mimic the Roman recipe.

E The implications of these findings extend well beyond classical archaeology. Modern infrastructure is one of the largest sources of carbon dioxide emissions worldwide, with the cement industry alone accounting for around eight percent of global emissions, largely because of the high temperatures required to produce Portland cement clinker. A concrete that could heal its own cracks would, in many researchers' view, significantly extend the service life of bridges, tunnels, and harbour walls, reducing both the frequency of replacement and the resulting carbon footprint. Civil engineers have therefore begun experimenting with modified mixes incorporating lime clasts, pozzolanic materials, and reduced amounts of clinker, with promising laboratory results although significant questions about scalability and standardisation generally remain.

F The Roman material is not, however, generally suitable for all modern applications. Roman concrete sets relatively slowly compared with Portland cement and is weaker in pure compression, particularly at early ages, making it less appropriate for tall reinforced-concrete buildings and other structures in which rapid construction and high strength are essential. The Roman builders themselves seem to have understood this and reportedly to have used different recipes for different purposes: a quick-setting, brittle mix for terrestrial walls, a tougher mix for vaults, and a notably durable variant rich in volcanic ash for marine works. The lesson, modern researchers argue, is not to copy Roman concrete wholesale but to adapt the principles of self-healing and chemical durability to formulations appropriate to particular twenty-first-century challenges.

A For more than a century, urban planners have advocated the planting of trees along streets and in public spaces, citing benefits ranging from aesthetic improvement to the cooling of summer streets. In recent decades, however, the case for urban trees has been transformed by a growing body of epidemiological evidence that links tree canopy directly to measurable improvements in human health. What was once largely a matter of civic beautification has become a public health priority, prompting cities from Singapore to Melbourne to set ambitious canopy targets and to integrate tree planting into climate adaptation strategies.

B The most immediate health benefit of urban trees is the moderation of extreme heat. Through transpiration, in which water evaporates from the leaves, a single mature tree can release several hundred litres of water vapour into the air each day, producing a localised cooling effect broadly comparable to that of several domestic air conditioners. The shade cast by a leafy canopy further reduces the surface temperature of streets and walls, with measured differences of up to 12 degrees Celsius between shaded and unshaded asphalt during a midsummer afternoon. Because deaths from heat waves are now generally among the most rapidly growing categories of climate-related mortality, the cooling provided by tree canopy reportedly has direct life-saving potential.

C Trees also affect air quality, although the picture is more nuanced than is sometimes suggested. Leaves and bark typically capture particulate matter from vehicle emissions and industrial activity. A 2014 study in the Journal of Environmental Pollution estimated that the urban tree canopy of the United States removes approximately 17 million tonnes of air pollutants annually, generating health benefits valued at around 6.8 billion US dollars. At the same time, certain species, particularly some oaks, poplars, and willows, reportedly emit biogenic volatile organic compounds that can contribute to the formation of ground-level ozone, complicating the picture in already polluted cities.

D A surprising body of research has documented the relationship between green spaces and mental health. A landmark 2019 study of more than 900,000 people in Denmark, published in the Proceedings of the National Academy of Sciences, found that children raised in neighbourhoods with the least surrounding greenery were 55 percent more likely to develop psychiatric disorders in adulthood than those raised in the greenest areas, even after controlling for socioeconomic factors. Similar associations between proximity to trees and lower rates of depression, anxiety, and stress have been reported in studies in Australia, the United States, and the United Kingdom.

E The cardiovascular benefits of urban trees have also reportedly been documented. A 2008 study in the United States found that the loss of an estimated 100 million ash trees to the emerald ash borer beetle in fifteen states was associated with an additional 21,000 deaths from cardiovascular and respiratory causes during the period of infestation, even after adjusting for demographic differences between affected and unaffected counties. The exact mechanisms generally remain uncertain, but air quality, heat moderation, and psychological wellbeing are likely to play overlapping roles. Whatever the precise pathway, the magnitude of the effect underscores how deeply integrated trees have become with the everyday health of urban populations.

F The distribution of urban tree canopy is, however, generally often deeply unequal. A 2021 analysis of major American cities found that low-income neighbourhoods had between thirty and fifty percent less tree cover than wealthier ones, a pattern frequently overlapping with historic patterns of residential segregation. Similar inequities have been documented in cities in Latin America, southern Europe, and parts of Asia. The neighbourhoods with the least canopy generally tend to be those with the highest exposure to extreme heat and particulate pollution, compounding existing health disparities. Many municipalities have responded by directing tree-planting budgets disproportionately toward historically underserved areas.

G Achieving and maintaining a healthy urban canopy involves significant challenges. Trees in cities reportedly face stresses unknown to their rural counterparts: compacted soils, restricted root zones, atmospheric pollution, frequent vehicle damage, and high temperatures amplified by reflective surfaces. Many newly planted urban trees reportedly die within the first five years, and some studies estimate average lifespans for street trees as low as twenty to thirty years. Innovative urban forestry techniques, including engineered structural soils, deep-pot irrigation, and the careful selection of species suited to local climate and pollution conditions, have improved survival rates considerably, but the per-tree cost remains higher than that of conventional planting.

H The future of urban tree canopy as a health intervention will, in many planners' view, depend on how effectively city governments can integrate planting into broader systems of urban management. Streets, drains, utilities, and buildings have for the most part been designed with little reference to the requirements of trees, and conflicts between roots and infrastructure generally remain a major source of damage and cost. Proponents of an integrated approach argue that tree canopy should be planned alongside transport, water, and waste systems from the outset, rather than added as an afterthought. As evidence of the public health value of urban trees accumulates, the case for treating them as critical green infrastructure, rather than as ornamental amenities, grows steadily stronger.

A Few European territories of comparable size generally contain as much linguistic variation as the British Isles. Speakers of English from Glasgow, Newcastle, Dublin, and Cornwall can be very difficult to understand for those unfamiliar with their accents, despite all being users of the same language. The roots of this diversity, according to many sociolinguists, lie in successive layers of settlement and invasion: Celtic-speaking peoples were displaced and absorbed by the arrival of Romans, Anglo-Saxons, Vikings, and Normans, each of whom left distinctive marks on the local speech. Modern dialects are therefore generally not simply degraded versions of standard English but the product of long, parallel histories.

B The boundary between dialects is rarely sharp. Linguists working in the early twentieth century, including the Yorkshire-born scholar Harold Orton, conducted house-to-house surveys in rural communities and plotted the geographical limits of particular words, sounds, and grammatical forms. The lines connecting points at which a feature changed, known as isoglosses, were often diffuse and overlapping rather than coinciding neatly. Where many isoglosses cluster, however, a meaningful dialect boundary can be drawn. One of the most striking examples is the line running approximately from the River Humber to the River Mersey, which separates northern English varieties, in which the vowel of "bus" rhymes with the vowel of "put", from the southern varieties in which the two words have distinct vowels.

C Scotland offers a particularly complex picture, in part because Scots, a sister language to English descended from the same Northumbrian origins, has long competed with Scottish Standard English in social settings. Speakers may move along a continuum from broad Scots, with its distinctive vocabulary, grammar, and pronunciation, toward an English influenced by but not identical to that of London. Within Scots itself, sharp differences reportedly exist between the urban dialects of Glasgow and Edinburgh, the rural varieties of the north-east, and the insular speech of Orkney and Shetland, which preserves words and grammatical patterns inherited from the Norn language spoken in the islands until the eighteenth century.

D Welsh and Irish, like Scottish Gaelic, are distinct languages rather than dialects of English, but their long contact with English has produced regional varieties of English with characteristic features. Welsh English, spoken across most of Wales, is recognisable for its musical intonation patterns and for grammatical constructions borrowed directly from Welsh, including emphatic forms such as "is it cold, it is" rather than "it is cold". Irish English, often called Hiberno-English, similarly retains grammatical patterns from the Irish language, including the so-called after perfect construction, as in "she is after eating", meaning "she has just eaten".

E Cornish English in the far south-west and Manx English on the Isle of Man reportedly preserve features from the Celtic languages once spoken in those territories. The Devon and Cornwall dialects typically retain unusual second-person plural pronouns, such as "thee" and "ye", in some rural communities, alongside vocabulary inherited from Cornish such as "emmet", meaning ant and used colloquially for a tourist. Manx English contains a smaller but distinctive set of borrowings from Manx Gaelic, particularly in maritime and agricultural vocabulary, although the everyday distinctiveness of the dialect has weakened considerably since the mid-twentieth century.

F Many traditional rural dialects have undergone significant erosion in recent decades. Studies coordinated by the Survey of English Dialects in the 1950s and 1960s recorded vocabulary and pronunciations that were already disappearing under the influence of national radio and television. The subsequent rise of urban general accents, particularly Estuary English in the south-east and Multicultural London English in the capital, has further accelerated change. Some linguists have argued that traditional dialects are being replaced by a smaller number of younger regional varieties, more closely associated with urban centres than with specific villages.

G The social meaning of dialect has shifted alongside the linguistic landscape. For much of the twentieth century, non-standard accents were associated with reduced career prospects, and speakers of regional varieties were sometimes pressured to acquire received pronunciation, the prestige accent of the BBC and of southern English elites. Public attitudes have softened considerably since the 1980s, and contemporary broadcasting deliberately features presenters from across the country. Nevertheless, audit studies in which actors with different accents read identical scripts continue to find that listeners rate northern, Birmingham, and certain Scottish accents lower in perceived intelligence than southern English speakers, suggesting that prejudice has retreated but not disappeared.

H Computational linguists have begun to use large speech datasets to study dialect change with new precision. Acoustic analyses of thousands of recordings have allowed researchers to track the spread of particular vowel mergers across communities and decades, sometimes confirming and sometimes correcting impressions formed from traditional surveys. The same techniques are being applied to digital chat and social media data, providing evidence of how regional vocabulary survives, mutates, or disappears online.

I Whatever the future of particular varieties, the broader phenomenon of dialect diversity in the British Isles is unlikely to vanish soon. Migration into and within the islands continues to introduce new linguistic influences. Younger speakers reportedly blend features in creative ways, generating new forms even as some older ones fade. And the social identities expressed through accent, from local belonging to ethnic affiliation, generally remain matters that speakers care about and are willing to maintain.