【多选题】
混凝土抗冻试验分为___ 。
A. 快冻法
B. 慢冻法
C. 单面冻融法
D. 双面冻融法
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答案
ABC
解析
暂无解析
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【多选题】
关于亚甲蓝MB值的测定,下列说法正确的有___。
A. 称取试样200g,精确至0.1g。
B. 第一次在悬浮液中加入5ml亚甲蓝溶液,以(400±40)r/min转速搅拌至少1min。
C. 若色晕在第4min消失,再加入2ml亚甲蓝溶液。
D. 记录色晕持续5min时所加入的亚甲蓝溶液总体积,精确至1ml。
【多选题】
符合卵石、碎石吸水率的有___。
A. 按四分法缩分至略大于规定的质量,洗净后分为大致相等的两个样品备用;
B. 浸水,水面高出试样5mm,水温控制在23±5℃,24h后取出试样,用湿毛巾将试样表面水分擦干,立即称量,精确至1g;
C. 将试样置于盛水容器中,水面应高出试样5mm,侵泡24h后取出;用湿毛巾擦干表面水分,立即称量,精确至1g;
D. 在(105±5)℃烘干至恒重,待冷却至室温后,称其质量,精确至1g。
【多选题】
符合砂的有机质含量试验结果评定的说法有___
A. 试样上部溶液颜色浅于标准溶液颜色为合格;
B. 若试样溶液与标准溶液颜色接近时,应把试样连同上部溶液一起倒入烧杯中,房子60℃~70℃的水浴中,加热2h~3h,然后与标准溶液比较,若浅于标准色,认为有机质合格;
C. 经过B处理后,若深于标准色,则应配制水泥浆作进一步试验;
D. 进行水泥浆试验时,当原试样制成的水泥砂浆28d强度不低于洗出有机质试样制成的水泥砂浆28d强度的95%时,则认为有机质合格。
【多选题】
关于混凝土凝结时间试验,下列说法正确的是___。
A. 混凝土凝结时间室内试验时,环境温度应为(20±3)℃;
B. 应在5s内均匀地使测针贯入试样(25±2)mm;
C. 各测点的间距应大于测值直径的2倍且不小于15mm;
D. 贯入阻力测试在0.2~28MPa之间应至少进行6次,直至贯入力大于28MPa;
E. 凝结时间测定用针为100 mm2、50 mm2、20mm2。
【多选题】
关于混凝土凝结时间试验叙述正确的是___
A. 贯入阻力仪的测针长为100mm,承压面积为100、20、50mm2三种。。
B. 混凝土拌合物中筛出的砂浆,一次分别装入3个试样筒中,做3个试验。
C. 砂浆试样制备完毕后,应置于20±2℃的环境中或现场同条件下待试。
D. 凝结时间测定从水泥与水接触瞬间开始计时。
【多选题】
下列关于混凝土试件成型养护叙述正确的是___。
A. 试件成型后应立即用不透水的薄膜覆盖表面
B. 采用标准养护的试件,应在温度为20±10℃的环境中静置一昼夜至两昼夜,然后拆模。
C. 拆模后的试件应立即放入温度为20±2℃,相对湿度为95%以上的标准养护室中养护
D. 试件间隔应有10~20mm,表面可通过直接淋水的方式保湿
【多选题】
关于正态分布曲线,下列叙述正确的是___
A. 正态分布曲线在x=u处具有极大值
B. 正态分布曲线对x=u直线呈对称形状
C. 在相同u值下,σ值越大,曲线越平坦,即随机变量的分散性越大
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【多选题】
依据GB/T 50107-2010《混凝土强度检验评定标准》,采用标准差已知法评定时,σ0取值应满足下列哪些规定___。
A. 应由同类混凝土、生产周期不应小于60d且不宜超过90d;
B. 样本容量不少于45组;
C. 3个月后,应重新按上一个检验批的强度数据计算σ0;
D. 当计算出的σ0小于2.5MPa时,σ0取2.5MPa。
【多选题】
钢筋闪光对焊接头的外观质量应符合___要求。
A. 钢筋表面不得有明显的烧伤或裂纹
B. 接头弯折的角度不得大于4°
C. 接头轴线的偏移不得大于0.1d,且不得大于2mm
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【单选题】
Read this pasaage and answer the five questions
That people often experience trouble sleeping in a different bed in unfamiliar surroundings is a phenomenon known as the “first-night” effect. If a person stays in the same room the following night they tend to sleep more soundly. Yuka Sasaki and her colleagues at Brown University set out to investigate the origins of this effect.
Dr. Sasaki knew the first-night effect probably has something to do with how humans evolved. The puzzle was what benefit would be gained from it when performance might be affected the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining alert enough to avoid predators (捕食者). This led her to wonder if people might be doing the same thing. To take a closer look, her team studied 35 healthy people as they slept in the unfamiliar environment of the university’s Department of Psychological Sciences. The participants each slept in the department for two nights and were carefully monitored with techniques that looked at the activity of their brains. Dr. Sasaki found, as expected, the participants slept less well on their first night than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep, the participants’ brains behaved in a similar manner seen in birds and dolphins. On the first night only, the left hemispheres (半球) of their brains did not sleep nearly as deeply as their right hemispheres did.
Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr. Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps (蜂鸣声) of the same tone and irregular beeps of a different tone during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the irregular beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.
Question1:
What did researchers find puzzling about the first-night effect?
A. What role it has played in evolution.
B. To what extent it can trouble people.
C. What circumstances may trigger it.
D. In what way it can be beneficial. .
【单选题】
Question2:
What do we learn about Dr. Yuka Sasaki doing her research?
A. She found birds and dolphins remain alert while asleep.
B. She found birds and dolphins sleep in much the same way.
C. She got some idea from previous studies on birds and dolphins.
D. She conducted studies on birds’ and dolphins’ sleeping patterns.
【单选题】
在产品只计算材料成本,主要适合于___的产品。
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