No_4_1956 — Page 17

MAFOO QUARTERS

BLUE POOL ROAD

Architect and Engineer: S. E Faber

COST ANALYSIS

The final costs of the above develop- ment have been analysed and the figures obtained are thought to be interesting.

The costs given include all items ex cept the cost of land. Fees are included.

The Quarters are built with plain

(1) The steep slope necessitated the though finishes are not elaborate, they concrete bearing walls, the maximum

footings being stepped, and were selected for low upkeep. The height of the walls being eight storeys.

retaining walls provided at each plumbing, for instance, was done with The School, because of the more open

storey against the earth bank. copper piping throughout. planning required, was of conventional (2) The precautions against sub- reinforced concrete frame construction.

sidence are peculiar to the site. The costs have therefore been shown The Quarters and School are built

The individual quarters have one on the side of Biue Pool Road on a formation, although on a flat site even chen and verandah; this is adequate also for the building excluding the site room of 220 sq. ft. and a private kit- site which slopes at an angle of 33 lower costs would have been possible. by Urban Council Standards for a degrees across the site, and at a gra- dient of 1 in 10 along Blue Pool Road. One further factor affects the cost. family of six persons. The total cost The presence of seven air raid tunnels It was decided to plan and design for per flat comes to an average of $9,900, across the site meant that to guard than a minimum first cost, and al- formation.

a minimum maintenance cost rather or just over $9,000 excluding site

against subsidence it was necessary to backfill the tunnels, and to drive piles under the blocks. Diversion of two large surface water channels was also necessary.

a

In comparing the cost with that of a similar building on flat site, several factors should be borne in mind:

CONCRETE.

Costs per cu. ft. of building.

Structure (including windows & doors, etc.) Plumbing (including pumps, etc.) Electric Lighting.

Drainage and wells.

Cost per cu. ft. excluding site formation. Site Formation.

++

Total cost per cu. ft.

+

Quarters

School

$1.218

$1.482

0.165

0.193

0.023

0.069

0.019

0.027

$1.425

$1.771

0.137

0.275

$1.562

$2.046

difficulty was experienced in produc- to produce good concrete even of the The concrete bearing walls were ing a workable mix for the lean con- lean mixes, and the cube tests showed designed in accordance with

with C.P. cretes, and close site supervision was the following results, in lbs. per sq. in. 111.201 for plain cast-in-situ concrete, necessary, with adjustments of grad- The minimum 28 day strengths and the strength of the concrete was ings made to suit the aggregates specified in C.P. 111.201 for plain adjusted in relation to the load, the obtainable. To prove the quality of concrete of these mixes are respectively lower storeys being of 1:2:4 grade, the concrete, a cube crushing machine 2250, 1650, and 1250 lbs. per sq. in. intermediate storeys of 1:3:6, the was installed on the site, and cubes upper storeys being of 1:4:8 grade.

were made daily and tested at 3 days, Owing to the difficulty of getting 7 days and 28 days to check the rate uniform sand supplies, and the short- of growth of strength. age of crushed granite "fines", some It was however found quite feasible

28 days

5220

3 days

7 days

1:2:4 grade

aver.

3320

4050

min.

2800

2800

4000

max.

4400

5200

7000 *

1:3:6 grade

aver.

2940

3440

4500

min.

2000

2400

3400

max.

4500

5800

6800 *

1:4:8 grade

aver.

1550

1780

2370

min.

800

1200

1400

max.

2500

2600

3800

* unbroken.

Even on the most awkward mixes

of 1:4:8 mix, the minimum 28 day strength was well above minimum specified. When a good grading was possible, i.e. when suitable sand was available, the 28 day strength was about double the minimum specified.

It will be observed that the lowest 28 day strength of the 1:3:6 mix was 3400 lbs. per sq. in. as compared with the 3000 lbs. per sq. in. required for "Works" tests for normal reinforced concrete of 1:2:4 mix. This seems to imply that given adequate site control, a considerable saving in cost could be attained without danger by reducing the cement content of the concrete.

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