1、 附录 外文翻译 MIX DESIGN & PROPORTIONING （一） MIX DESIGN The concrete mix design (CMD) for QC/QA superstructure concrete must produce a workable concrete mixture having properties that will not exceed the maximum and/or minimum values defined in the special provision. Workability in concrete defines its c
2、apacity to be placed, consolidated, and finished without harmful segregation or bleeding. Workability is affected by aggregate gradation, particle shape, proportioning of aggregate, amount and qualities of cementitious materials, presence of entrained air, amount and quality of high range water redu
3、cer, and consistency of mixture. Consistency of the concrete mixture is its relative mobility and is measured in terms of slump. The higher the slump the more mobile the concrete, affecting the ease with which the concrete will flow during placement. Consistency is not synonymous with workability. T
4、wo different mix designs may have the same slump； however, their workability may be different. Selection of target parameters by the contractor for any mix design must consider the influence of the following: 1. material availability and economics 2. variability of each material throughout period of
5、 usage 3. control capability of production plant 4. ambient conditions expected at the time(s) of concrete placement 5. logistics of concrete production, delivery, and placement 6. variability in testing concrete properties 7.generation of heat in large structural elements and differential in therma
6、l gradient The qualities of the cementitious paste provide a primary influence on the properties of concrete. Proper selection of the cementitious content and water/cementitious ratio is dependent on the experience of the concrete producer and becomes a very important first step in preparing a desig
7、n. For workable concrete, a higher water cementitious ratio is typically required when aggregate becomes more angular and rough textured. The presence of air, certain pozzolans, and aggregate proportioning will work to lower the water cementitious ratio； however the most significant reduction in wat
8、er demand comes through the use of a high range water reducing chemical admixture. Water/cementitious ratio is determined from the net, per unit, quantity of water and total cementitious materials. The net water content excludes water that is absorbed by the aggregates. For a given set of materials
9、and conditions, as water/cementitious ratio increases, strength and unit weight will decrease. Compressive strength is a concrete parameter used in combination with unit weight and air content to evaluate the durability of the superstructure concretes exposure to freeze / thaw action, and exposure t
10、o deicing salts. It is important to note that the designer of the bridge structure does not recognize the benefit of increased compressive strength. The slab still relies on a minimum design compressive strength (fc) of 4000 psi at 28-days. Proportioning of aggregates is defined by the volume of fin
11、e aggregate to the volume of coarse aggregate, as a percent. The lower percentage of fine to total aggregate provides an increase in compressive strength at the expense of workability. The gradation, particle shape and texture of the coarse aggregate along with fineness modulus of the fine aggregate
12、 will determine how low the fine to total aggregate percentage can be for a given workability requirement. （二） MIXING PROPORTIONING Once the cement content, pozzolan content, water/cementitious ratio, and fine to total aggregate percentage are defined for the concretes intended use in the superstruc
13、ture, proportioning of the mix in terms of design batch weights can begin. Specific gravities must be accurately defined for each material being utilized in order to proportion the mix properly by the absolute volume method. Cement is typically accepted as having a specific gravity of 3.15. Pozzolan
14、s will typically vary between 2.22 and 2.77. Pozzolan suppliers should readily be able to provide current values for their material. Approximate specific gravities are identified for each source on the Departments Approved/Prequalified Materials list； however, they should not be considered the most
15、current. Bulk specific gravity, in the saturated surface dry condition, must be used to proportion the fine and coarse aggregate. Accurate testing of one or more samples of fine and coarse aggregate must be accomplished by the Contractor as part of any proportioning for a mix design. Subsequent shif
16、ts in benching at the aggregate source may cause significant shifts in bulk specific gravity and absorption. These are important aggregate properties to monitor as part of concrete quality control. Proportioning concrete by the absolute volume method involves calculating the volume of each ingredien
17、t and its contribution to making one y3 or 27 ft3 of concrete. Volumes are subsequently converted to design weights, which then become the basis for actual production of concrete from the plant. For cementitious materials and water, the weight to volume conversion is accomplished by dividing the wei
18、ght (lbs) by the specific gravity of the material and again dividing by the density of water. Converting from volume to weight is accomplished simply by taking the known volume of the ingredient and multiplying by the specific gravity of the ingredient and again multiplying by the density of water.
19、Volume to weight conversions for aggregates are accomplished by the same series of computations； however, bulk specific gravity (SSD) must be used. The target air content is established at 6.5% by the special provision, which converts to a volume of 1.76 ft3within a cubic yard of concrete. （三） LINEA
20、R EQUATION OF UNIT WEIGHT vs. AIR CONTENT It is known that the unit weight of plastic concrete is inversely proportional to air content. That is to say, as air content increases unit weight decreases. This relationship becomes a very useful tool when evaluating plastic concrete. Unit weight and air
21、content are properties of plastic concrete that can be easily and quickly measured in the field. A unit weight measurement, at a known air content, that deviates excessively from the linear relationship provides information as to the possible deficiencies in the mix and potential effects on properties such as workability, durability, and strength. The linear equation to predict unit weight based on a given air content is presented below in directional form: UW = m (Air) + b Where: m is the slope of line Air is the plastic concrete air content (independent variable, xcoordinate
