th a wall 2 ft. thick, was found to be about fifteen 1/2-yd.
batches per hour.

_Cracks in Walls and Longitudinal Reinforcement._--Before the concrete
walls were started, the contractor suggested using forms 100 ft. long and
building the walls in sections of that length; it was decided, however, to
limit the length to 50 ft.

The south walls, in sections approximately 50 ft. long, were built first,
starting at Tenth Avenue and extending for about 500 ft. Soon after the
forms were removed, irregular cracks appeared in the walls between the
joints in practically every section. It was thought that these cracks might
be due to the wall being very thin and being held at the back by the
tie-rods; there was also quite a material change in the section of the wall
at each drainage box. Although it was admitted that these cracks would have
no effect on the stability of the wall, it was thought that, for appearance
sake, it would be desirable to prevent or control them, if possible. The
first method suggested was to shorten the sections to 25 ft., which would
give an expansion and contraction joint every 25 ft., it being thought that
sections of this length would not crack between the joints. This, however,
was not considered desirable. An effort was then made to prevent cracks in
a section of wall, about 46 ft. long, on the south side, by using
longitudinal reinforcement. In the lower and upper face walls, 3/4-in.
square twisted steel rods were placed longitudinally about 4 in. in from
the face and about 1 ft. 4 in. apart vertically. The sections of these
walls were finished on April 10th, and May 5th, 1909, respectively. At
present there are no indications of cracks in these sections, and they are
practically the only ones in the south walls which do not show irregular
cracks.

It was decided, however, that, inasmuch as the cracks did not affect the
stability of the walls, the increased cost of thus reinforcing the
remaining walls was not warranted. An effort to control the cracks was made
by placing corrugated-iron diaphragms in the form, dividing each 50-ft.
section into three parts. The diaphragms were 1 ft. wide, and were placed
with the outer edge 1 in. in from the face of the wall, but in the copings
they were omitted. The purpose of these diaphragms was to provide weak
sections in the walls, so that if there was any tendency to crack it would
occur along the line of the diaphragms. Corrugated iron was used for the
diaph