LongLifeConcreteBridgesEachyear,roadaccidentskillamilli...

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Long Life Concrete Bridges

Each year, road accidents kill a million people and injure millions more．The economic costs are greatest for developing countries．

Earlier this year, the United Nations called for a campaign to improve road safety．

One way to avoid accidents is better driving．Another is better roads and bridges．Engineers in the United States have designed ten new concrete(混凝土) mixtures that they think could make bridges last longer．

Professor Paul Tikalsky leads the experiments by a team at Pennsylvania State University．He says bridges made of concrete now last about twenty-five to thirty-five years．But he says the new mixtures might extend that to seventy-five or even one hundred years．

Concrete is made of stone, sand, water and cement(水泥)．The materials in the cement hold the concrete together．Ancient Romans built with concrete．Yet strengthened concrete bridges did not appear until the late eighteen-hundreds．People keep looking for new ways to improve concrete．Professor Tikalsky says it is one of the most complex of all chemical systems．

The new mixtures designed by his team contain industrial waste products．He says these make the concrete better be able to resist damage from water and salt over time．One of the products is fly ash．This is released into the air as pollution when coal is burned．

Professor Tikalsky says particles(颗粒) of fly ash are almost exactly the same size and chemical structure as Portland cement．This is the most costly material in concrete． So using fly ash to replace some of it would save money．

Over the next two years, engineers will study ten bridges in Pennsylvania．These were built from the different cement mixtures designed by Professor Tikalsky’s team．He says longer-lasting bridges could save the state more than thirty-five-million dollars a year．And he says the materials would be environmentally friendly．

The federal government is paying for part of the research．Engineers anywhere can use the technology．Professor Tikalsky says some of the ideas have already been put to use in China, the Philippines and other countries．

1．What does the underlined word“This”in the seventh paragraph mean?

A．Fly ash． B．Portland cement． C．Sand． D．Chemical．

2．What is the main idea of the passage?

A．The causes of road accidents．

B．The advantages about fly ash．

C．The measures of avoiding road accidents．

D．Latest information about long-life concrete bridges．

3．What can you conclude from the passage?

A．Engineers have to pay a lot of money to use the new bridge technology．

B．Pennsylvania State University is paying all the money for the research．

C．Bridges built with fly ash are cheaper than common bridges．

D．Fly ash is much expensive than Portland cement．