The mixing was done in batches. Each batch contained three bags of Giant Portland cement and three bags of crusher dust. The time occupied in mixing was 1 1/2 minutes, and it required about five minutes for the complete operation of charging, mixing, injecting the grout, and preparing the machine for the next batch.

As to the success of this method of grouting, Mr. Robert Ridgway, who was Division Engineer in charge of the tunnel section, reported that the filling of the interstices in the stone packing with grout was excellent where the tunnel was in rock. Where the tunnel was in sand, grout was forced up through the ground and was found filling minute crevices in the earth all the way to the surface.

Stopping Leaks and Seams.-Grout has long been employed for filling the seams in rocks and for stopping springs and leaks.

In excavating for the purpose of obtaining suitable foundations for bridge piers, dams, buildings or other important structures, and in sinking shafts and tunnelling, seamy rock and water-bearing strata are frequently encountered. In the case of dams, the seams must all be filled before the foundation courses can safely be started, since otherwise the leakage beneath the dam would tend to float the masonry, and thus endanger the stability of the structure. Hence it is customary to excavate until sound rock is encountered, and then to inject grout under pressure into any seams or faults that may present themselves.

In the case of ordinary foundations, the chief danger from springs or flowing water is the washing away of the cement which is used in the masonry. It is therefore necessary to take care of any incoming water until the fresh mortar or concrete employed in the construction has had time to set. This is ordinarily done by carrying the water away in pipes. Where the pressure is high the pipes are carried up and the water permitted to flow away while the lower courses are being laid. With a low pressure or hydrostatic head, the downward pressure of the water in the pipe may be sufficient when carried up to prevent any flow.

After the masonry has been carried up a sufficient height, the stoppage of the leak is effected by forcing grout into the pipe. When there is no flow from the pipe, the leak can be controlled by filling the pipe with grout, which will then displace the water and on hardening form an effective plug. Where the spring flows from the

pipe, it is necessary to force in the grout under pressure and to maintain the pressure until the cement has hardened, since otherwise. the flow would wash away the grout. Where practicable, it is desirable to apply sufficient pressure to the grout to cause it to flow into the seams or porous strata as well as to fill the pipe and fill the interstices between the pipe and the masonry.

Grout as a Paint.-Grout, when used as a paint, is one of the surface finishes applied to mass concrete. When so employed it should be applied while the wall is still green, since after hardening the grout has a tendency to flake off in patches. Grout is also employed as a dampproofing paint, but when so used it should be applied to the water side of the wall, as it is far more effective in keeping the moisture from entering the wall than it is in preventing the egress of moisture that has already entered the mass. pressure is encountered, however, the layer of grout is too thin to offer effective resistance to the passage of moisture and under such conditions, the wall should either be made impervious in itself or else surrounded by a bituminous shield or mastic of sufficient mass to be able to withstand the pressure.

Where

Surface Finish.-Grout is more effectively employed as a surface finish when it is applied in such a way as to become perfectly incorporated with the mass of the wall. This is ordinarily done by using a wet concrete mixture for filling the forms and causing the grout to flush to the surface by pulling back the coarse aggregate from the face of the wall with a spade or fork. This forms the ordinary finish for beams, retaining walls, and mass constructions. Some waterproof grouts are now on the market which make excellent surface finishes for concrete and which are made in all colors.

Grout for Walks, Etc.-Grout or mortar forms the ordinary wearing surface for sidewalks, curbs, cellar-floors, etc. In such constructions, the foundation consists of a layer, from 3 to 6 inches thick, composed of cement, sand, and 1/2-inch broken stone, while the surface coat consists of cement and sand, which is usually 3/4 of an inch thick. To improve the appearance and wearing properties of this coat, granite chips are also frequently mixed in with the mortar or grout. To be satisfactory for this purpose, the chips must be hard and tough, and should be trowelled in such a way as to

bring the flat portions of their surfaces uppermost, thus providing a good wearing surface, and affording protection to the cement.

Bonding New and Old Concrete.-Grout is generally employed in bonding new concrete to old. The surface of the old concrete is first scrubbed with a steel brush and a stream of water, or a jet of steam, or compressed air to remove all dirt and grease; and where a good bond is desired, it should also be scratched, etched with acid or tooled so as to produce indentations that will serve as a key. After preparing the surface, a grout composed of neat cement is rubbed in with a broom. While this is still soft it is covered with a layer of the regular concrete mixture, and the ordinary work of concreting is commenced.

Grout in the Machine Shop. In setting up the bedplates of engines and stationary machines, lathes, planers, drillpresses, and other heavy tools, it is customary first to block up the framework to the required height with wooden blocks and wedges and then to bed the framework to the floor or piers forming the foundation by pumping in a rich mixture of Portland cement grout. When used for this purpose, the grout should be mixed as thick as practicable. so that on drying, a strong, durable mortar will be formed, which will easily support the weight and vibration of the machinery without crumbling or settling out of level.

Grout as a Paving Filler.-One of the most common uses for grout is as a filler for paving blocks. When used for brick or stone pavements, the blocks are laid dry and the interstices between the stones or bricks are filled by pouring in grout to serve as a cement.

The materials commonly employed for fillers are asphalt, tar and its compounds, cement, grout, and sand. The principal advantages of grout for this purpose are as follows: (1) cheapness; (2) adequate protection to the edges of the blocks; (3) prevents the blocks from loosening; (4) is watertight; (5) is durable; (6) permits the blocks to be laid close together; (7) is easy to keep clean; and (8) wears uniformly..

The disadvantages of grout fillers are: (1) its tendency to crack; (2) to become slippery; (3) affords a poor foothold on grades; (4) is difficult to remove without breaking the blocks; and (5) causes objectionable noise.

These objections apply chiefly to brick pavements. Where

stone is employed the irregularities of the blocks are generally sufficiently pronounced to prevent them from becoming slippery and to enable the horses to obtain a foothold on grades. Stone blocks are also less subject to injury when removed.

Miscellaneous Uses.-In addition to the uses which have thus far been briefly enumerated in this chapter, grout is employed as a protective coating for iron and steel, for surfacing pipes and conduits to decrease their resistance to the flow of water and for many other purposes. The distinction between mortar and grout is but one of degree. While the excess of water contained in grout tends to increase its porosity over that of cement mortar, yet for many purposes its use is not only legitimate but unexcelled.

Grout is not a safe substitute for mortar in laying up masonry or in important constructions under water. It can, however, be forced into cracks and crevices which thick mortar is unable to penetrate, and thus for stopping springs and leaks, filling voids between the lining and roof of tunnels, filling the crevices in foundations for dams and other structures, and for numerous other purposes, grout is extensively employed in engineering works; while its minor uses such as surfacing, painting iron, steel and concrete, filling between paving blocks, dampproofing, and levelling of foundation areas have extended the employment of this material to many kinds of construction, although other considerations both theoretical and practical have tended to circumscribe its use.

CHAPTER XXXII

INSPECTION OF CONCRETE WORK-A SUMMARY OF ESSENTIAL RULES AND PRINCIPLES OF CONSTRUCTION, FOR SECURING GOOD CONCRETE WORK

The Work of the Inspector.-Inspection of the Cement, Sand, and Aggregates.-Proportioning and Mixing.—Inspection of Forms, Reinforcement and Placing Concrete.-Rules for Removing Forms.-Rules for Surface Finish.-Rules for Blocks, Piles, and Castings.

CAREFUL inspection is essential in all concrete work. The best design will come to naught unless it be carried out with the aid of careful and skilful workmanship and the use of good materials. Good construction can be assured only when the work is under the control of competent and conscientious inspectors.

The Work of the Inspector.-The work of the inspector may be divided into the following parts:

1. Inspection of the cement, sand, and aggregate; a. quality;

b. storage.

2. Proportioning, measuring, and mixing of the ingredients.

3. Inspection of forms, arch-centres, column moulds, etc.

4. Placing of the reinforcement.

5. Placing of the concrete.

(a) General rules.
(b) In reinforced work.

(c) In hot weather.
(d) In freezing weather.

6. Bonding new to old work.

7. Removal of the forms.

8. Surface finish.

9. Moulded blocks, piles, ornamental castings, etc.

Inspection of the Cement.-Cements are subjected to laboratory tests to determine their:

(a) Fineness.

(b) Time of set.