外文翻译--混凝土配合比的选择（中英文）.doc

安徽工业大学大学 毕业设计（论文）计算书58 CHAPTER 5CODE COMMENTARYbe maintained through the normal compressive strength test requirements provided by 5.6.5.2 — Selection of concrete proportionsR5.2 — Selection of concrete proportionsRecommendations for selecting proportions for concrete aregiven in detail in “Standard Practice for Selecting Pro- portions for Normal, Heavyweight, and Mass Concrete”(ACI 211.1).5.1 (Provides two methods for selecting andadjusting proportions for normalweight concrete: the esti- mated weight and absolute volume methods. Example cal- culations are shown for both methods. Proportioning of heavyweight concrete by the absolute volume method is presented in an appendix.)Recommendations for lightweight concrete are given in“Standard Practice for Selecting Proportions for Struc- tural Lightweight Concrete” (ACI 211.2).5.2 (Provides a method of proportioning and adjusting structural grade con- crete containing lightweight aggregates.)5.2.1 — Proportions of materials for concrete shall beestablished to provide:(a) Workability and consistency to permit concrete to be worked readily into forms and around reinforce- ment under conditions of placement to be employed, without segregation or excessive bleeding;(b) Resistance to special exposures as required byChapter 4;(c) Conformance with strength test requirements of5.6.R5.2.1 — The selected water-cementitious material ratioshould be low enough, or in the case of lightweight concrete the compressive strength high enough to satisfy both the strength criteria (see 5.3 or 5.4) and the special exposure requirements(Chapter 4). The code does not include provisions for espe-cially severe exposures, such as acids or high temperatures, andis not concerned with aesthetic considerations such as surface finishes. These items are beyond the scope of the code and should be covered specifically in the project specifications. Concrete ingredients and proportions are to be selected to meet the minimum requirements stated in the code and the additional requirements of the contract documents.5.2.2 — Where different materials are to be used fordifferent portions of proposed work, each combination shall be evaluated.5.2.3 — Concrete proportions shall be established inaccordance with 5.3 or, alternatively, 5.4, and shall meet applicable requirements of Chapter 4.R5.2.3 — The code emphasizes the use of field experienceor laboratory trial mixtures (see 5.3) as the preferred method for selecting concrete mixture proportions.5.3 — Proportioning on the basis of fieldexperience or trial mixtures, or bothR5.3 — Proportioning on the basis of fieldexperience or trial mixtures, or bothIn selecting a suitable concrete mixture there are three basicsteps. The first is the determination of the sample standard deviation. The second is the determination of the required average compressive strength. The third is the selection of mixture proportions required to produce that average strength, either by conventional trial mixture procedures or by a suitable experience record. Fig. R5.3 is a flow chart out- lining the mixture selection and documentation procedure.Copyright American Concrete InstituteProvided by IHS under license with ACINo reproduction or networking permitted without license from IHSLicensee=Black & Veatch/5910842100Not for Resale, 11/28/2005 18:20:15 MST第 122 页 共 132 页 CHAPTER 5 59COMMENTARYFig. R5.3—Flow chart for selection and documentation of concrete proportionsCopyright American Concrete InstituteProvided by IHS under license with ACINo reproduction or networking permitted without license from IHSLicensee=Black & Veatch/5910842100Not for Resale, 11/28/2005 18:20:15 MSTCODECOMMENTARY60 CHAPTER 5CODE COMMENTARYThe mixture selected should yield an average strength appreciably higher than the specified strength f ′. The degree of mixture over design depends on the variability of the test results.5.3.1 — Sample standard deviationR5.3.1 — Sample standard deviation5.3.1.1 — Where a concrete production facility hastest records, a sample standard deviation, ss , shall be established. Test records from which ss is calculated:(a) Shall represent materials, quality control proce-When a concrete production facility has a suitable record of30 consecutive tests of similar materials and conditions expected, the sample standard deviation, ss, is calculated from those results in accordance with the following formula:dures, and conditions similar to those expected and21 ⁄ 2 changes in materials and proportions within the testrecords shall not have been more restricted than those for proposed work;(b) Shall represent concrete produced to meet awhere:ss=Σ( xi – x ) -----------。