水泥砼垫层的缩缝应怎样处理？
参考答案：
室内地面的砼垫层，应设置纵向缩缝和横向缩缝；纵向缩缝间距不得大于6m，横向缩缝间距不得大于12m。
垫层的纵向缩缝应做平头缝成加肋平头缝。当垫层厚度大于150mm时，可做企口缝，横向缩缝应做假缝。
平头缝和企口缝的缝间不得放置隔离材料，浇筑时应互相紧贴。企口缝的尺寸应符合要求，假缝宽度为5—20mm，深度为垫层厚度的1/3，缝内填水泥砂浆。
Passage Five
| As students return to school this fall, parents will again worry about new illnesses as kids come into contact with flu germs. There are other risks they should worry about—illnesses caused by the common bugs and rodents found in school buildings. Perhaps the even more dangerous pests however are those individuals who prevent school administrators from swiftly addressing these problems. Anti-chemical activists have pushed, and nearly 20 states and local governments have passed, 1 aws to eliminate or drastically reduce the use of pesticides in schools. Yet pesticides are used to control roaches, mice, rats, mosquitoes, and other pests. The public health implications of allowing these things to get out of control should be obvious: increased allergies and illnesses related to insect and rodent bites. Some states have passed a seemingly more reasonable policy that demands that school administrators provide notification 48 to 72 hours before using pesticides. But such laws allow problems to escalate during wailing periods when an urgent response is warranted. Notification paperwork burdens also consume limited financial resources. Journalist Steve Milloy reported that the notification law of Maryland costs the state’s schools $32.000 annually. Parents should fear these laws and the pests they harbor more than the pesticides. Environmental Protection Agency (EPA) pesticide standards are so exceedingly cautious that the risks are tiny when the product is used according to label directions. An analysis done by the University of Texas found that the EPA’s risk estimates overstate pesticide exposure damage at a level hundreds of thousands of times greater than the risk of actual exposure. Meanwhile, many of the pests in schools pose serious risks. Allergies and asthma are a particular concern. According to one study published in Environmental Health Perspectives: "Allergens associated with dust mites and cockroaches are probably important in both onset and worsening of asthma symptoms for children who are chronically exposed to these agents." Cockroach allergies are particularly problematic. Children who suffered from this type of allergy missed more days of school and lost more sleep than children suffering from other allergies. Prudent use of chemicals—not reduced pesticide use—can be a big part of the solution. A study in the Journal of Allergies and Clinical Immunology showed that use of chemical baits and regular cleaning can reduce indoor cockroach allergens to levels below that which causes allergies. If people are truly concerned about public health in schools, it’s time to start looking at priorities. Rather than liberate the pests, they should liberate the schools from silly government regulations and dangerous vermin. |
What is the main idea of the passage
A．New chemicals should be developed to control pests
B．Pesticides should be used frequently to control pests
C．Some policies have ruined the efforts to control pests
D．Schools have ignored the need to control pests