Cements Mixed

The technology and management of cement mixing and handling is well known the equipment is commonplace and specialized labor is not required. 

Steinholz, n. xylolith (magnesia cement mixed with sawdust or the like). 

Determine the cementing operation time and thus the minimum thickening time. Assume a cement mixing rate of 25 sacks/min. Also assume an annular displacement rate no greater than 90 ft/min while the spacer is moving through the open-hole section and a flowrate of 300 gal/min thereafter. A safety factor of 1.0 hr is to be used. 

Polymer-modified cementitious floor toppings are now widely used instead of separately laid granolithic toppings. The polymers used are normally supplied as milky white dispersions in water and are used to gauge a carefully selected sand/aggregate/cement mix as a whole or partial replacement of the gauging mortar. They must always be mixed in a forced-action mixer. 

Schutt reported that the coke breeze specification and conditions in which the mix is prepared are important factors in determining the optimum operation of the conductive cement mix, whilst further details on the coke breeze asphalt mix composition are given by AndersonConductive concrete mixes, with a polymer binder have also been developed as an anode system specifically for reinforced concrete cathodic protection systems . 

The glass polyalkenoate cement sets rapidly within a few minutes to form a translucent body, which when young behaves like a thermoplastic material. Setting time (37 °C) recorded for cements mixed very thickly for restorative work varied from 2-75 to 4-7 minutes, and for the more thinly mixed luting agents from 4-5 to 6-25 minutes. Properties are summarized in Table 5.15. 

Zinc phosphate cement mixes to a paste which is thin and mobile. Under pressure it flows readily to give a film 24 to 40 pm thick (Table 6.3). This film thickness is adequate to seat restorations, especially as McLean von Fraunhofer (1971) and Dimashkieh, Davies von Fraunhofer (1974) have shown that in practice the gap between tooth and restoration can be as much as 100 pm or more. 

Figure 6.4 Effect of pH on the elution of phosphate from a zinc phosphate cement mixed at two different consistencies (Wilson, Kent Lewis, 1970).

Cement properties are affected by a number of factors. Some are determined by the manufacturer, for example the chemical composition of the cement components. Others are under the clinician s control. These include the powder/liquid ratio of the cement mix and the temperature of the surgery. Increase in either of these variables accelerates the reaction and affects properties. 

The powder/liquid ratio used in the cement mix affects a number of properties. As it is increased, setting time and working time are reduced. Compressive strength increases almost linearly with powder/liquid ratio (Savignac, Fairhurst Ryge, 1965). 

More recently, Stanicioiu, Chinta Hartner (1959) attempted to reinforce the cement with glass fibres, but this was not successful. The most serious study on the reinforcement of dental silicate cement was made by J. Aveston (in Wilson et al., 1972). Silicon carbide whiskers, carbon fibres and alumina powder were introduced into the cement mix. Unfortunately, the glass powder/liquid ratio had to be reduced, and the strength gained by reinforcement was thereby lost. It is clear that dental silicate cement cannot be strengthened by fibre or particulate reinforcement. 

Myers, C. L., Drake, J. T. Brantley, W. A. (1978). A comparison of properties for zinc phosphate cements mixed on room temperature and frozen slabs. Journal of Prosthetic Dentistry, 40, 409-12. 

Norman, R. D., Swartz, M. L., Phillips, R. W. Sears, R. (1970). Properties of cements mixed from liquids with altered water content. Journal of Prosthetic Dentistry, 24, 410-17. 

E. M. Gartner and R. P. Kreh. Cement additives and hydraulic cement mixes containing them. Patent CA 2071080, 1993. 

When anhydrous cement mix is added to water, the silicates react, forming hydrates and calcium hydroxide. Hardened Portland cement contains about 70% cross-linked calcium silicate hydrate and 20% crystalline calcium hydroxide. 

Partial replacement of cement with fly ash improves the workability but reduces the strength up to 28 days. At 90 days the strengths attained are very similar to 100% Portland cement mixes. 

The basic mechanism of plasticizing effect on fresh cement mixes is explained by forming a temporarily stable double layer on cement particles. Since the formation of the double layer is also connected with the surface of particles, the increased demand for AEA, WRA and SP, in silica fume concrete and the decreased demand for AEA in the presence of a WRA or SP can be directly correlated to the specific surface increase of silica fume-cement blends and the dispersing action of WRAs and SPs in achieving a mortar consistency that enables the air-bubble-generating and stabilizing process [147, 149]. Concrete producers are now cognizant of the effect of these factors. Field silica fume concrete with a satisfactory, stable air-void system can therefore be produced consistently. 

T0679 S.M.W. Seiko, Inc., Soil-Cement Mixing Wall... 

T0675 Roy F. Weston, Inc., Transportable Incineration Systems T0677 Rust Federal Services, Inc., VAC TRAX Thermal Desorption T0679 S.M.W. Seiko, Inc., Soil-Cement Mixing Wall... 

The soil-cement mixing wall (SMW) is an in situ technology for the fixation, stabilization, and solidification of soils contaminated with metals and semivolatile organic compounds. SMW can be used to treat soils contaminated with pesticides, polychlorinated biphenyls (PCBs), phenols, and poly aromatic hydrocarbons (PAHs) to depths of up to 100 ft. The technology uses hollow-stem augers to inject solidification/stabilization agents and blend them with the soil. 

Small-scale, tabletop nuclear fusion devices, known as compact accelerator neutron generators, are routinely used as a source of neutron radiation. By design, however, these devices consume more energy than they release. The beam of neutrons generated by these devices can be used to identify the elemental composition of amaterial.The coal industry uses such beams to measure the sulfur content of coal in real time as the coal moves over conveyor belts. The cement industry similarly uses these beams to judge the quality of cement mixes. These fusiongenerated neutrons are also used to identify the elemental composition of nuclear wastes and for the detection and identification of explosives. 

DILUENT. (I) An ingredient used to reduce the concentration of an active material to achieve a desirable and beneficial effect. Examples are combination of diatomaceous earth with nitroglycerin to term the much less shock-sensitive dynamite addition of sand to cement mixes to improve workability with no serious loss of strength addition of an organic liquid having no solvent power to a paint or lacquer to reduce viscosity and achieve suitable application properties. 

Fly ash incorporation improves the fluidity of a Portland cement mix, which improves workability. For solidification/stabilization applications, this increased fluidity may allow a reduced water/cement ratio to be used in the casting operation. 

Jahjah [the prior art reference cited by the USPTO] combines the preformed foam into various cement and concrete mixtures wherein known aggregates may optionally be incorporated. The foam is introduced from a reservoir into a concrete mixer containing the cement mix, and, in our opinion, it would be obvious to a technician having ordinary skill in the art to add the foam gradually to the cement mix while it was being mixed, since, as pointed out by the Examiner, conventional cement mixers operate in this fashion. Further, Jahjah obtains uniform dispersion of the foam and produces a multicellular cementitious product not differentiated in this record from that obtained by appellant. 

Hanor J.S. (1978) Precipitation of beachrock cements Mixing of marine and meteoric waters vs. CO2 degassing. J. Sediment. Petrol. 48,489-501. 

The induction period is shortened by adding prehydrated CjS (013), but additions of lime or CH, including that formed from CjS, are variously reported to be ineffective (013,B67) or to lengthen it, though shortening it with cement (Ull). In cement mixes, additions of pfa or some other finely divided materials accelerate hydration after the first day, apparently by acting as nucleation sites for C-S-H (Section 9.3.3). Additions of reactive silica markedly accelerate hydration (S53). Most of this evidence supports hypothesis 3 and tells against hypothesis 4. Hypothesis 3 does not exclude hypothesis 1, as the breakdown of a protective layer could be associated with formation of a new product. 

The alkali cations in pfa normally occur almost entirely in the glass, and when the latter reacts may be presumed to enter the alkali-rich silicate that appears to be the initial product. When this phase is decomposed by reaction with Ca, they will be distributed, like alkali cations from any other source, between the solution and the solid hydration products, on which they are probably adsorbed (Section 7.3.2). The C-S-H tends to take them up more strongly as its Ca/Si ratio decreases (BI58,G63) consequently, the alkali cations released from the pfa are less effective in raising the OH concentration of the pore solution than are those released from the cement. The method outlined in Section 7.5.2 for calculating the OH concentration in the pore solution of Portland cement mix was extended to cover Portland-pfa cement mixes taking this into account (T37). 

Pretesting is done by using a consistometer (Fig. 15.2), in which the cement mixing slurry cup is placed in a bath of oil. The oil temperature and pressure can be raised or... 

A large bag of cement mix weighs 38y pounds. How many quarter-pound bags of mix can be made from this large bag ... 

Occasional repointing of the mortar joints is normally the only maintenance required. In the dilution zone, where attack of the Portland cement mortar may occur, repointing with a polyester or vinyl ester mortar will usually solve the problem. If voids are detected in the wall, these can be filled by pumping a port-land cement mix or a catalyzed resin into the wall by the technique described for filling voids in a digester lining. The service and maintenance history of these vessels has generally been excellent. 

When the forms are stripped, make sure that all surface laitance and form marks are removed. All the wires must be cut back well below the concrete surface. Check and sound the surface for holidays, honeycombing and stone pockets, breaking surface crusts open to expose any that may be hidden under a thin skin. These (and the wire holes) must all be hand-filled (packed) carefully with a stiff and strong sand/cement mix and packed tightly. Over troweling is not permitted. This brings laitance to the top and creates a weak surface. 

---