2Water/Cement Ratio The number of pounds of water per pound of cement. A low ratio means higher strengths, a high ratio means lower strengths.For NCDOT, the ratio depends on the class of concrete, whether an air agent is used or not, and the shape of the stone - rounded or angular.
3W/C Ratio Cont. Example: How much cement is needed? W/C = 0.500, and Water = 250 poundsHow much cement is needed?250 / = 500 pounds of `````````````````````` cement
4W/C Ratio Cont. Example: W/C = 0.500, and Cement = 600 pounds How much water is needed?0.500 X 600 = 300 pounds of water300 pounds / 8.33 = 36.0 gallons
5Water/Cementitious Problem Cement Used in Mix – 436 poundsFly Ash in Mix – 131 poundsMaximum Water – 36.0 gallonsTotal Water – 33.5 gallonsMetered Water – 27.5 gallonsFree Water in aggregates – 50 poundsDetermine the design w/c ratio and the batched w/c ratio
6SOLUTION: Design W/C Add Cement And Fly Ash: 436 + 131 = 567 pounds Convert Design Water Into Pounds:33.5 X 8.33 = 279 poundsPlug Into Formula W/C = Ratio:279 / 567 = 0.492(carry answer to three places after decimal)
7Batched W/C RatioAdd Cement And Fly Ash:= 567 poundsConvert Metered Water Into Pounds:27.5 X 8.33 = 229 poundsAdd free water = 279 Lbs279 / 567 = 0.492
8W/C Ratio with IceDetermine the W/C ratio if 68 pounds of ice is used to lower the temperature of the concrete.The W/C ratio remains the same because the quantity of total water does not change.
10% Solids And VoidsIn determining mix designs, you must use an aggregate dry rodded unit weight.This weight is determined at the lab.In the procedure for determining this weight, only the coarse aggregate is used.Therefore, there is a % of solids and a % of voids in the container.
11Formula : % Solids & Voids Dry Rodded Unit Weight(Spec. Gravity) X (62.4)The Answer Is Then Multiplied Times 100To get % Voids:Subtract % Solids from 100
12Example: Dry Rodded Unit Weight: 96.6 pcf Specific Gravity Of Agg.: 2.80% Solids = = (2.80 X 62.4)0.533 X 100 = 55%% Voids = = 45%
13Terms I Should Know…. Abrasion Resistance of an Aggregate Durability HydrationPhSaturated Surface DrySet RetarderUnit WeightWater / Cement RatioTHAT IS ENOUGH FOR A MONDAY!!