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 Unites States have designed ten new concrete 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 1800s . 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 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 .
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 .
小题1:Why did the United Nations launch the campaign ?
A．Because the United Nations wanted to reduce road accidents and economic costs
B．Because two million people were killed in the accidents .
C．Because engineers wanted to design ten new concrete mixtures .
D．Because the United Nations made bridges of the new mixtures which could last for about 20 to 35 years .
小题2:What does the underlined word “ this ” in the sixth paragraph refer to ?
A．Fly ash
B．Portland cement
C．Sand
D．Chemical小题3:Which of the following statements is TRUE ?
A．Ten new concrete bridges have already been built in the United States .
B．A new concrete bridge could last 50 more years than an ordinary concrete one .
C．People didn’t know how to build with cement until the late 1800s .
D．Water and salt won’t do any damage to bridges over time .小题4:What does the passage mainly tell us ?
A．The causes of road accidents .
B．The advantages of fly ash
C．The measures of avoiding road accidents
D．Latest information about long-life concrete bridges