FP-96 English Version - Eastern Federal Lands Highway Division

Section 552(a) Central-mix plant. Dispense liquid admixtures through a controlledflowmeter. Use dispensers with sufficient capacity to measure, at one time,the full quantity of admixture required for each batch. If more than oneadmixture is used, dispense each with separate equipment.Charge the coarse aggregate, one third of the water, and all air entraining admixtureinto the mixer first, then add remainder of the material.Mix for at least 50 seconds. Begin mixing time after all cement and aggregateare in the drum. Add the remaining water during the first quarter of themixing time. Add 4 seconds to the mixing time if timing starts the instantthe skip reaches its maximum raised position. Transfer time in multipledrummixers is included in mixing time. Mixing time ends when the dischargechute opens.Remove the contents of an individual mixer before a succeeding batch ischarged into the drum.(b) Truck mixer. Do not use mixers with any section of the blades worn 1inch or more below the original manufactured height. Do not use mixers andagitators with accumulated hard concrete or mortar in the mixing drum.Add admixtures to the mix water before or during mixing.Charge the batch into the drum so a portion of the mixing water enters inadvance of the cement.Mix each batch of concrete not less than 70 nor more than 100 revolutionsof the drum or blades at mixing speed. Begin the count of mixing revolutionsas soon as all material, including water, is in the mixer drum.552.08 Delivery. Produce and deliver concrete to permit a continuous placementwith no concrete achieving initial set before the remaining concrete beingplaced adjacent to it. Use methods of delivering, handling, and placing thatwill minimize rehandling of the concrete and prevent any damage to thestructure.Do not place concrete that has developed an initial set. Never re-temper concreteby adding water.377