ACI 211 6T-2014 Aggregate Suspension Mixture Proportioning Method.pdf

1、1AggregAte SuSpenSion Mixture proportioning MethodIntroductionThis document describes the aggregate suspension mixture proportioning method. The method is suitable for normalweight concrete with workability ranging from zero-slump to self-consolidating. This method may not be suitable for mass concr

2、ete mixture proportioning. It is adapted from a method originally published by Koehler and Fowler (2007).The aggregate suspension mixture proportioning method is based on the representation of concrete as a suspension of aggregates in paste and air, as depicted schematically in Fig. 1. All solid mat

3、erial finer than the No. 200 (75 m) sieve is consid-ered to be part of the powder and, subsequently, the paste.To proportion a concrete mixture, the optimal combi-nation of aggregates for the application is selected based on grading, size, shape, angu-larity, and texture. Next, the total volume of p

4、aste and air required for the selected aggregates is determined. Then, the composition of paste and airnamely the relative amounts of water, each powder material, and airis optimized to achieve the desired concrete rheology and hardened properties. Lastly, trial batches are used to make adjustments.

5、 Although this document discusses concrete rheology, measurements of rheology are not required to perform this method. Guidance on measuring rheology is available in ACI 238.1R.Key features of the method include:a) The aggregates are selected on a combined basis, rather than individually.b) The volu

6、mes of aggregates and of paste and air are selected based on the properties of the combined aggre-gates. Aggregates with desired grading, shape, angularity, and texture for the application will typically result in less volume of paste needed.c) All material finer than the No. 200 (75 m) sieve is con

7、sidered part of the powder content and, thus, part of the paste. This material includes fines from the aggregate and separately added fines, such as ground limestone filler.d) The water-powder ratio (w/p) is considered when adjusting workability and the water-cementitious mate-rials ratio (w/cm) is

8、considered when aiming to achieve desired hardened properties. The difference between w/p and w/cm is attributable to noncementitious fines such as ground limestone filler and other mineral fillers.Calculations should be performed in a computer application. Use of this method results in proportions

9、based on aggregates in saturated surface-dry (SSD) condition. The user should make corrections for aggregate mois-ture content when making trial or production batches.Use of this proportioning method may result in otherwise acceptable but different proportions than those determined in ACI 211.1.Keyw

10、ords: durability; optimal grading; packing density; proportioning; shape-angularity factor; water-powder ratio; workability.Fig. 1Concrete as a suspension of aggregate in paste and air.ACI 211.6T-14TechNote2 AGGREGATE SUSPENSION MIXTURE PROPORTIONING METHOD (ACI 211.6T-14)Definitionsangularitysharpn

11、ess of corners and edges of a particle.packing densityvolume of solid particles divided by total bulk volume.paste volumevolume of water and powder, excluding air.passing abilityease with which concrete can pass among various obstacles and narrow spacing in the form-work without blockage.plastic vis

12、cosityfor Bingham materials, such as most concretes, the difference between shear stress and yield stress divided by shear rate.powdersolid materials finer than approximately the No. 200 (75 mm) sieve, including cement, supplemen-tary cementitious materials (SCMs), mineral fillers, and aggregate fin

13、es.segregation resistance (stability)ability of a material to maintain homogeneous distribution of its various constituents during its flow and setting.shaperelative dimensions of a particle; common descriptors include flatness, elongation, and sphericity.slump flowa measure of workability of self-c

14、onsolidating concrete determined by filling a slump cone with concrete, removing the slump cone, and measuring the horizontal diameter that concrete flows.textureroughness of a particle on a scale smaller than that used for shape and angularity.yield stressa critical shear stress value below which a

15、n ideal plastic or viscoplastic material behaves like a solid (that is, will not flow); once the yield stress is exceeded, a plastic material yields, whereas a viscoplastic material flows like a liquid.NotationDRBD = dry-rodded bulk density, lb/ft3(kg/m3)mcement= mass of cement, lb (kg)mcm= mass of

16、cementitious materials, lb (kg)mfiller= mass of filler, lb (kg)mpowder= mass of powder, lb (kg)mSCM= mass of SCM, lb (kg)pi= volume of aggregate fraction i divided by the total aggregate volumeSG = specific gravitySGcement= specific gravity of cementSGfiller= specific gravity of fillerSGOD= oven-dry

17、 specific gravitySGSCM= specific gravity of supplementary cementitious materialSGSSD= saturated surface-dry specific gravitySGSSD-coarse= saturated surface-dry specific gravity of coarse aggregateSGSSD-fine= saturated surface-dry specific gravity of fine aggregateSGSSD-intermediate= saturated surfac

18、e-dry specific gravity of intermediate aggregateVair= volume percentage of air, %Vcoarse= volume percentage of coarse aggregate, %Vfine= volume percentage of fine aggregate, %Vintermediate= volume percentage of intermediate aggregate, %Vminimum paste+air= minimum volume percentage of paste and air,

19、%Vminimum spacing paste+air= minimum volume percentage of spacing paste and air, %Vpaste= volume percentage of paste, %Vwater= volume percentage of water, %w/c = water-cement ratiow/cm = water-cementitious materials ratiow/p = water-powder ratiorwater= density of water, lb/ft3, kg/m3%coarse-to-total

20、 aggregate= coarse aggregate as a percent of total aggregate volume, %fine-to-total aggregate= fine aggregate as a percent of total aggregate volume, %intermediate-to-total aggregate= intermediate aggregate as a percent of total aggregate volume, %voidscompacted aggregate= percentage voids in compac

21、ted aggregate, %AGGREGATE SUSPENSION MIXTURE PROPORTIONING METHOD (ACI 211.6T-14) 3Design criteriaDetermine all relative design criteria before selecting proportions. Design criteria include performance require-ments for workability, strength, dimensional stability, and durability; and prescriptive

22、requirements such as limits on w/cm and cementitious materials content.MethodologyStep 1: Select the maximum size of aggregateSelect the largest maximum size of aggregate that is practical for the application. As required by ACI 318, the nominal maximum size of aggregate should not exceed:a) One-fif

23、th of the narrowest dimension between sides of forms;b) One-third the depth of slabs; orc) Three-fourths of the minimum clear spacing between individual reinforcing bars, bundles of bars, or preten-sioning strands.Increased maximum size of aggregate typically results in increased packing density of

24、the combined aggre-gate, reduced concrete plastic viscosity, increased concrete slump and slump flow, increased segregation poten-tial, and reduced passing ability.Step 2: Select combined aggregatesSelect the relative amounts of fine, intermediate, and coarse aggregates based on grading, shape, angu

25、larity, and texture. The selection of aggregates should balance each of these factors. For example, adding a poorly shaped aggregate to improve grading could have an overall negative effect on concrete. In most cases, the combination of aggregates resulting in maximum packing density is not optimal

26、for workability. Instead, a slightly finer grading is typically preferred.If the combined aggregates contain less than 5 percent passing the No. 200 (75 m) sieve, this fine material can be considered negligible to the volume of paste and accounted for as part of the combined aggregate. Other-wise, i

27、nclude all aggregate material passing the No. 200 (75 m) sieve as part of the powder.GradingThere is no universally optimal grading for concrete, or even a particular type of concrete, such as self-consolidating concrete (SCC). The best grading for a mixture depends on the application and the aggreg

28、ate. As a starting point, select a blend of fine and coarse aggregate best matching the 0.45 power curve or finer and without an excess or deficiency of material on two consecutive sieves.The 0.45 power curve, which is shown in Fig. 2, is a plot of percent passing on the vertical axis and sieve size

29、s raised to the 0.45 power on the horizontal axis. A straight line is drawn from the minimum aggregate size (No. 200 75 m sieve) to the maximum aggregate size (size with approximately 85 percent of the combined material passing). Gradings finer than the 0.45 power curve are also usually preferred to

30、 coarser gradings because they reduce harshness. Finer grading targets are achieved by reducing the exponent to less than 0.45. Exponents of 0.35 and 0.40 are used to achieve satisfac-tory workability and paste volume.In addition, the sum of material retained on any two consecutive sieves should not

31、 be less than 10 percent or greater than 35 percent, with the exception of the combination of the No. 200 (75 m) sieve and pan. The use of gap gradings, where the amount of material on two consecutive sieves is less than 10 percent, can result in increased packing density and reduced water or admixt

32、ure demand. Such gradings, however, should be used with caution because they may increase segregation potential.Shape, angularity, and textureAggregates that are equidimensional (cubical shaped) and well-rounded (low angularity) result in requiring less water, admixture, paste, and air volume, or co

33、mbination thereof to reach a given workability. Aggregates that are more angular and have rough texture typically result in higher compres-sive strength for a given w/cm. The choice among different aggregate sources varying in shape, angularity, and texture depends on the application and the specifi

34、c materials.Fig. 20.45 power curve for combined aggregate. (The curve passes through the No. 200 75 m sieve.) (1 in. = 25.4 mm.)4 AGGREGATE SUSPENSION MIXTURE PROPORTIONING METHOD (ACI 211.6T-14)Step 3: Determine combined aggregate voids content and shape-angularity factorVoids contentBlend a sample

35、 of aggregates in the relative amounts selected in Step 2. Measure the dry-rodded bulk density (DRBD) and voids content of this combined aggregate in accordance with the rodding procedure in ASTM C29.Calculate the voids content in the compacted, combined aggregate with Eq. (1)( ) ( )( )1% 1 100%comp

36、acted aggregate nwater i ODiiDRBDvoidsp SG= (1)where DRBD is in lb/ft3(kg/m3), rwateris the density of water (62.4 lb/ft31000 kg/m3); piis the volume of aggregate fraction i divided by the total aggregate volume; and (SGOD)iis the oven-dry specific gravity of aggregate fraction i.Shape-angularity fa

37、ctorMake a visual rating of the shape and angularity of each aggregate based on Table 1. Calculate the shape and angularity factor of the combined aggregate as the average of each aggregate, weighted by the volume of each aggregate.Step 4: Calculate paste and air volumeCalculate the minimum total vo

38、lume of paste and air, Vminimum paste+air, with Eq. (2)(100 )(100 % )100100minimum spacing paste air compacted aggregateminimum paste airV voidsV+=(2)where Vminimum spacing paste+airis the minimum volume percentage of spacing paste and air selected from Table 1.The paste volume can be increased abov

39、e the minimum to provide improved workability and robustness with respect to variations in aggregate properties. An increase of 1 to 2 percent is typical.The remaining volume of concrete consists of the combined aggregates selected in Steps 1 to 3.A minimum volume of paste and air is required to fil

40、l the voids between compacted aggregates and to separate aggregates, as depicted in Fig. 1. Separating aggregates allows them to flow past each other with less interag-gregate contact.Step 5: Select maximum w/cm and blend of powders for hardened propertiesSelect the maximum w/cm and minimum percent

41、of SCMs to achieve the desired hardened properties, including both strength and durability. The use of lower w/cm and SCMs are typically beneficial to durability and long-term strength. In the absence of historical test data on the relationship between w/cm and compressive strength for the available

42、 materials, refer to Table 2 to select the maximum w/cm. Note that a lower w/cm may be required to achieve other properties, such as durability.Step 6: Select air content for resistance to freezing and thawingFor non-air-entrained concrete, and concrete with freezing and thawing exposure, select the

43、 required average air content based on Table 3.Table 1Shape-angularity factor and minimum volume of spacing paste and air, %Shape-angularity factor1(Well-shaped, well-rounded) 2 3 45(Poorly shaped, highly angular)DescriptionNatural river/glacial gravels and sandsPartially crushed river/glacial grave

44、lsWell-shaped crushed coarse aggregate or manufactured sand with most corners greater than 90 degreesCrushed coarse aggregate or manu-factured sand with some corners less than or equal to 90 degreesCrushed coarse aggre-gate or manufactured sand with many corners less than or equal to 90 degreesMinim

45、um volume of spacing paste and air, %0 to 8 in. (200 mm) slump2 4 6 8 10SCC 8 12 14 16 18AGGREGATE SUSPENSION MIXTURE PROPORTIONING METHOD (ACI 211.6T-14) 5Step 7: Select w/p and admixture doses for workabilityAdjust both the w/p and admixture doses to achieve the desired workability. Use data from

46、trial batches or past experience to select the w/p. If the powder content consists of only cement and supplementary cementi-tious materials, the w/p is equal to the w/cm.One common practice is to adjust the w/p to achieve a certain slump without mid- or high-range water-reducing admixture (HRWRA), w

47、hich is sometimes referred to as a water slump, then adjust the dose of mid-range water-reducing admixture or HRWRA to the target slump. Alternatively, use a fixed dose of admixture and adjust the w/p, or vary both the w/p and admixture doses simultaneously.When making these adjustments, consider th

48、e rheology of the concrete; decreasing the w/p from an accept-able value for a given application may result in concrete with high viscosity that is described as sticky or cohe-sive, whereas increasing the w/p may be prone to segregation and bleeding.Step 8: Calculate volumes and masses of individual

49、 constituentsCalculate the volumes and masses of individual constituents based on the values determined in previous steps with the equations shown or referenced in Table 4. The volume of paste is determined by subtracting the volume of air (Step 6) from the volume of paste and air (Step 4). Ensure the total volume percentage of all constituents in the concrete mixture equals 100 percent.Calculate the w/cm from the w/p with Eq. (3)/1=fillerpowderwpw cmmm(3)Calculate the w/c from the w/cm with Eq. (4)/1SCMcmw cmwcmm=(4)where mcmis the mass