Mix Design Basics - Civil Engineering

1 Mix Design BasicsCIVL 31371 CIVL 31372 Mix Design Goalsadequateworkabilityadequatestrength adequatedurabilityminimum costCost of MaterialsCIVL 31374 Source: November 7, 2011 31375 Mix Design Goalsadequateworkabilityadequatestrength adequatedurabilityminimum costCIVL 31376 Minimizing Cost Cementminimize the void space betweenthe aggregate particlesminimize the surface area ofthe aggregate particlesCIVL 31377 Minimizing Void Space Void content = 48%Void content = 41%CIVL 31378 Minimizing Surface Areasurface area = 11 ft2surface area = 22 ft210"CIVL 31379 Minimizing Surface Areasurface area = ft2/ft3surface area = ft2/ft3 CIVL 313711 Obtaining Adequate Workability mortargravelNeed enough mortar to keep all the gravel particles 313712 Inside Concretemortargravelcement pastesandCIVL 313713 Obtaining Adequate Workability cement pastesandNeed enough cement paste to keep all the sand grains

2 ApartCIVL 313714 Inside Concrete cement pastesandwatercementCIVL 313715 Obtaining Adequate Workability watercementNeed enough mixing water to lubricate all the cement grainsCIVL 313716 Obtaining Adequate Workability watercementAir entrainment adds lubrication without adding additional waterairbubbleCIVL 313719 Figure 7 14 CIVL 313720 4500psicfCIVL 313721 4500psicfCIVL 313722 4500psicf 5700psicrfOverdesign FactorsCIVL 313724 Table 7-12 Overdesign Necessary to Meet Strength RequirementsAOverdesign FactorsCIVL 313725 Required Average Compressive Strength When DataAre Not Available to Establish a Standard DeviationAdapted from ASTM C94 CIVL 313726 Trial Mix DesignCIVL 313727 Mix Design ExampleCIVL 313728 CIVL 313729 Step 1: Select the slumpSource: Design and Control of Concrete Mixtures (PCA, 2003)Equivalent to Table 7 13 CIVL 313730 Step 2: Select the NMAS narrowest dimensionNMAS 5 depth of slabNMAS 3 NMAS clear space CIVL 313731 Step 3: Estimate the water and airSource: Design and Control of Concrete Mixtures (PCA, 2003)Equivalent to Table 7 14 Air ContentCIVL 31373240%CementPaste60%AggregateConcrete Air 7% = Air ContentAssume 7%SmallerNMASAir ContentCIVL 31373330%CementPaste70%AggregateConcrete Air 7% = Air ContentAssume 7%LargerNMASCIVL 313735 Adjust for Aggregate ShapeSource: Design and Control of Concrete Mixtures (PCA, 2003)CIVL 313737 Step 4: Select the w/c ratioSource.

3 Design and Control of Concrete Mixtures (PCA, 2003) crfEquivalent to Table 7 15 Overdesign FactorsCIVL 313738 Required Average Compressive Strength When DataAre Not Available to Establish a Standard DeviationAdapted from ASTM C94 CIVL 313739 Step 4: Select the w/c ratioSource: Design and Control of Concrete Mixtures (PCA, 2003) crfEquivalent to Table 7 15 CIVL 313740 Figure 7 14 CIVL 313741 CIVL 313742 Step 5: Calculate the cement weightWW = w/c ratiowatercementCIVL 313743 Step 6: Estimate coarse aggregateSource: Design and Control of Concrete Mixtures (PCA, 2003) obbEquivalent to Table 7 17 CIVL 313744b/bobboCIVL 313745 Step 6: Estimate coarse aggregate bulkbulkgraveloconcreteVbbV bulkbulkgraveloconcrete gravelWbbV bulkbulkgravelgravel gravelWV dry-roddedunit weight CIVL 313746 Step 7: Estimate fine aggregateEstimated Weight Method(Section 7 )Equivalent to Table 7 18 NMAS(in)Non Air Entrained ConcreteAir Entrained Concrete Estimate of Concrete Unit Mass (lb/ft3)CIVL 313747 CIVL 313748 CIVL 313749 Step 7: Estimate fine aggregatetotalcementgravelsandwaterWW W WW sandtotalcementgravelwaterWW W W W Estimated Weight Method(Section 7 )CIVL 313750 Step 7: Estimate fine aggregatetotalcementgravelsandwaterairVV V VV V sandtotalcementgravelwaterairVV V V V V Absolute Volume Method(Section 7 )CIVL 313751 Step 7.

4 Estimate fine aggregate sandtotalcementgravelwaterairVV V V V V gravelbulkgravelcementwatersandtotalairw W1 WWVVV sandsabulndkwsandGWV Absolute Volume Method(Section 7 )CIVL 313754 Step 8: Adjust for Aggregate Moisture1. Increase Wwaterby an amount equal to the weight of water needed to saturate the fine and coarse Increase Wsandand Wgravelby an amount equal to the moisture contents of the aggregate Decrease Wwaterby the same amount you increased Wsandand Wgravel.