| HRM High Reactivity Metakaolin. | (Concrete Engineering) Refined form of an ASTM C618, Class N (natural) pozzolan. A high performance, mineral admixture, similar in performance to silica fume, additionally comparable in cost. Pure white powdered in form will, not effect the natural color or darken concrete as silica fume does. Suitable for high-performance color matching in architectural concrete. Dosage at 5% to 10%, of cement by weight. No bleed water, better finishability, more creamy, cleanup is easier with slightly higher 28 day strengths and 25% - 35% less plasticizer is required than silica fume. |
| Hydrologic Cycle | (Concrete Engineering) The Hydrologic Cycle consists of the evaporation of water from oceans and other bodies of open water; condensation to produce cloud formations; precipitation of rain, snow, sleet or hail upon land surfaces; dissipation of rain or melted solids by direct run-off into lakes and by seepage into the soil. Thereby producing a continuing endless source of water in the sub-grade. |
| Jacking Equipment | (Concrete Engineering) In prestress concrete, the device used to stress the tendons. |
| Jacking Force | (Concrete Engineering) The temporary force exerted by the jacking device which introduces tension into the tendons. Jacking Stress In prestress concrete, the maximum stress occurring in a tendon during stressing. |
| Keene's Cement | (Concrete Engineering) A finely ground high density plaster composed of anhydrous, (calcined or "dead burned") gypsum, the set of which is accelerated by the addition of other materials. |
| Kelly Ball | (Concrete Engineering) A device for determining the consistency of fresh concrete. It is sometimes used as an alternative to the slump test. |
| Magnetite | (Concrete Engineering) An aggregate used in heavy weight concrete, consisting primarily of ferrous metaferrite (Fe304). A black magnetic iron ore with a specific gravity of approximately 5.2 and a Mohs hardness of about 6. |
| Non-agitating Unit | (Concrete Engineering) A truck-mounted unit for transporting ready-mixed concrete short distances, not equipped to provide agitation (slow mixing) during delivery. |
| Ottawa Sand | (Concrete Engineering) A sand used as a standard in testing hydraulic cements by means of mortar test specimens. Sand is produced by processing silica rock particles obtained by hydraulic mining of the orthoquartzite situated in open-pit deposits near Ottawa, Illinois; naturally rounded grains of nearly pure quartz. |
| Peeling | (Concrete Engineering) A process in which thin flakes of matrix or mortar are broken away from concrete surface; caused by adherence of surface mortar-to forms as forms are removed, or to trowel or float in portland cement plaster. |