Concrete & Asphalt

Concrete –Batching – process of proportioning cement, water, aggregates and additives prior to mixing concrete –Concrete specs usually require 1-3% accuracy –Materials proportioned by weight –Batches made at central plant and loaded on trucks –Either as concrete or to be mixed by driverF6- 8

Concrete –Standard Classification system for mixers Identifies mixer type and capacity # indicates rated capacity of mixer in cubic feet of plastic concrete Satisfactory mixing if volume of mix is less than 10% more than the capacity Letter indicates mixer type – S= construction mixer, E = paving mixer, M = mortar mixer

Concrete –Construction mixers Wheel mounted, trailer mounted, portable plants, stationary plants Mixer capacities from 3.5 cf – 12cy+ –Truck mixers capable of mixing and transporting concrete Ready mix concrete Charge truck with dry materials at plant, add water when it gets to jobsite. –Usually only have 90 minutes to get concrete off truck once mixed Can also carry plastic concrete with agitator on – can carry more concrete than ready mix

Concrete –Paving Mixers – self propelled designed for paving Come with a boom and a bucket so that they can hit all points on roadway –Mix time 1 minute + ¼ minute /.cy All water in before ¼ of mixing time 70 – 100 revolutions after all water All concrete out after 300 revolutions

Concrete –Handling Concrete can not be dropped more than 5 ft Should not be moved using a vibrator Should be placed within 1.5 hours of mixing why

Asphalt Three parts –Aggregates Aggregate provides load carrying Angular gravel –Asphalt or tar called binder –Fines About 1/3 of mix Inert, non plastic material passing #200 sieve Mineral filler

Asphalt –Handling Bituminous Materials Usually hot Working with asphalt above its flashpoint Safety is important Hot surfaces marked

Asphalt –Hot mix asphalt plants F6-10 go thru parts Two types –Batch plant –Drum mix plant – F6-11 Dryer capacity is usually controlling factor