transferred to either an open bed dump truck or an agitator truck for transport to the job site. 

Shrink mixed concrete is concrete that is partially mixed at the central mix plant and then 

completely mixed in a truck mixer on the way to the job site. Dry hatching, with concrete mixed 

and hauled to the construction site in dry form, is seldom, if ever, used. 

1.3 Hot Mix ~s~hal?'~ 

Hot mix asphalt (HMA) paving materials are a mixture of well graded, high quality aggregate 

(which can include reclaimed asphalt pavement w]), and Liquid asphalt cement, which is 

heated and mixed in measured quantities to produce HMA. Aggregate and RAP (if used) 

constitute over 92 percent by weight of the total mixture. Aside from the amount and grade of 

asphalt cement used, mix characteristics are determined by the relative amounts and types of 

aggregate and RAP used. A certain percentage of fine aggregate (less than 74 micrometers [pm] 

in physical diameter) is required for the production of good quality HMA. Hot mix asphalt 

paving materials can be manufactured by: (1) batch mix plants, (2) continuous mix (mix outside 

drum) plants, (3) parallel flow drum mix plants, and (4) counterflow drum mix plants. This order 

of listing generally reflects the chronological order of development and use within the HMA 

industry. An HMA plant can be constructed as a permanent plant, a skid-mounted (easily 

relocated) plant, or a portable plant. All plants can have RAP processing capabilities. Virtually 

all plants being manufactured today have RAP processing capability. A gendzed process 

diagram for hot mix asphalt is included in Appendix A of tIiis document 

1.4 Vermiculite and Perlite ~rocessin~~~' 

Vermiculite - 

Vermiculite is the geological name given to a group of hydrated laminar minerals that are 

aluminum-iron-magnesium silicates and that resemble mica in appearance. The chemical 

formula for vermiculite is (Mg,Ca,K,Fe ) (Si,Al,Fe ) 0 (ON) 4H 0. When subjected to heat, 

vermiculite has the unusual property of exfoliating, or expanding, due to the interlaminar 

generation of steam. Uses of unexpanded vermiculite include muds for oil-well drilling and 

fillers in fire-resistant wallboard. Vermiculite ore is mined using open-pit methods. Beneficidon 

includes screening, flotation, drying in rotary or fluid bed dryers, and expansion by exposure to 

high heat. All mined vermiculite is dried and sized at the mine site prior to exfoliation. A 

generalized process diagram for vermiculite processing is included in Appendix A of this 

document. 

Crude ore from open-pit mines is brought to the mill by truck and is loaded onto outdoor 

stockpiles. Primary processing consists of screening the raw material to remove the waste rock 

greater than 518 inch and returning the raw ore to stockpiles. Blending is accomplished as 

material is removed from stockpiles and conveyed to the mill feed bin. The blended ore is fed to 

the dl, where it is separated into hctions by wet screening and then concentrated by gravity. 

All concentrates are collected, dewatered, and dried in either a fluidized bed or rotary dryer. 

Drying reduces the moisture content of the vermiculite concentrate fkom approximately 15 to 20 

percent to approximately 2 to 6 percent. At most facilities, the dryer products are transported by 

bucket elevators to vibrating screens, where the material is classified. The dryer exhaust 

Nh4MProc TSD 6-14-02 Created on 6/1812002 9:39:00 AM 3