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SINGAPORE & THE FEDERATION OF MALAYA
Concrete Institute, the Highway Research Board, the Waterways Experimental Station and the laboratories of the Bureau of Reclamation are notable in the field of research. Holland, Sweden and South Africa among others possess Government research laboratories.
The need for scientific methods in construction opera- tions in the field is still to this day a vital problem with the continuing shortage of manpower, particularly in skilled construction workers. The building and civil engineering contractor is therefore paying increasing attention to research and development in his own particu- Jar sphere. As an example of the application of these methods the work of a contractor's central testing and research laboratory will be described.
Approximately thirty engineers, draughtsmen and others are continuously employed in this laboratory.
The aims of the laboratory are the investigation of soils by means of trial borings in connection with building foundations, earthworks, and road and airfield foundations, the quality control of concrete production, the testing of aggregates, cements and other building materials, quality control of asphalt production, and research work in all these branches. The laboratory also provides a technical information service to keep the firm's outside agents and engineers fully informed on all the latest developments in construction technique.
The work of the Laboratory is divided into four main sections. These are (a) soil mechanics (b) concrete (c) building materials (d) asphalt and tarmacadam.
Soil Mechanics.
This science is comparatively new in civil engineering knowledge but it has aroused keen interest since the soil is the natural material on which every structure is carried. Many failures of buildings and earthworks in the past have been caused by lack of a true appreciation of the stresses set up in the soil below the foundations and the effects of drainage and water percolation on the settlement of structures. One of the earliest applications of soil mechanics science was by the Swedish Geo-Technical Commission which investigated a series of major land- slips on the Swedish State Railways in the 1920's. Since this time the name of Professor Terzaghi has become internationally known in the science of foundation engineering, and he has been consulted on soils and founda- tion problems all over the world. Cooling and Skempton have been largely responsible for early developments in soil mechanics in Great Britain in their work at the Building Research Station and elsewhere.
The soil mechanics section of the Central Laboratory is equipped to deal with all soil problems connected with building and engineering foundations, slopes of embank- ments and cuttings, soil drainage, deep excavation, piling and road and airfield pavement design.
Site investigations, which include the sinking of trial boreholes to obtain undisturbed soil samples, have been made for projects in many parts of Great Britain and countries overseas. The boring teams are equipped with special sampling apparatus for soft soils and diamond drills to investigate rock formation.
The soil samples are brought up from the borehole in a cylinder 4" X 18" the ends of which are immediately sealed with paraffin wax and screwed covers. The cylinder is labelled with details of depth etc. and air-freighted to the laboratory with its original moisture content unchanged.
If bedrock is suspected in a trial borehole the diamond drill is brought into use and a rock core at least ten feet long is obtained to confirm that true bedrock and not a large boulder has been struck.
Apparatus is also available for electrical resistivity surveys in cases where its application is suitable. Borings from floating craft have been made in connection with the design of harbour and jetty works in the Persian Gulf, Syria and Cyprus. Site investigations have been made for the foundations of steelworks, shipyards, oil refineries, gasworks, colliery installations, housing estates, roads and airfields.
Undisturbed soil samples from the boreholes are sent to the Central Laboratory where tests are carried out to obtain values for the bearing capacity of the foundation soil, estimates of the settlement of structures and the application of special processes such as cement grouting or chemical consolidation.
In road and airfield construction problems, the required thicknesses of pavings are studied in relation to the type of soil on the site. Methods of compaction by rolling or other means are recommended to suit the sub-grade or borrow pit soils. Special methods of soil stabilisation may be recommended in suitable cases. Investigations are made in the field on the efficiency of various types of road rollers to deal with particular soils by means of the field density and standard compaction tests.
Concrete.
Before the war much research work was done on the proportioning of concrete mixes to give control of strength and workability. Abrams' discovery of the water cement ratio law which states that the strength of a concrete mix is governed solely by the ratio between the weight of cement and weight of water of the mix gave rise to drastic revisions in methods of proportioning. The work of Glanville and his co-workers* at the Building Research Station did much to put these new theories on a practical working basis for the architect or engineer. It is only during the war years and after that these new principles have been widely adopted, however many authorities still cling to the out dated rule-of-thumb proportioning of the "1:2:4" type.
* "The Grading of Aggregates and Workability of Concrete", Road Research Technical Paper No. 5, by Glanville, Collins and Mathews. H.M. Stationery Office 1938.
Modern technique in concrete production requires in the first place information on the designer's compressive strength for the concrete in his structure. With this strength as the ultimate goal, the engineer finds from tables the appropriate water cement ratio. The require- ments for placing the concrete are then considered. Will the concrete be placed in thin heavily re-inforced members or in large mass concrete slabs? Is the concrete to be placed by shovel, bucket or pump? Is vibration or hand tamping to be used to compact the concrete in the form- work? An appropriate workability in the form of a "slump" or "compaction factor" must be adopted to meet these requirements. Knowing the required water cement ratio and workability, the proportions of cement and aggregates are then decided.
In this connection the type of aggregate, i.e. whether rounded gravel or angular crushed rock and the grading of the aggregate particles from coarse to fine has an important bearing on workability. Considerations of segregation of the concrete during transit and placing and honeycombing of the finished surface are also dependent on the grading of the aggregate. The last stage in the process is the design of a balanced production and placing plant to suit the needs of the particular job being investigated. The storage hoppers, batching plant, mixer, pump or transporting conveyor and placing equipment must all be related in size to give the output of concrete required by the building programme.
The greater part of this work is dealt with by the Concrete Section of the Laboratory. Sources of supply of coarse aggregates and sand are investigated and tested for cleanliness, grading and other properties. Cements are tested to check that they comply with standard specifica- tions. Water is analysed to make sure that it does not contain organic or chemical substances deleterious to concrete. Having selected suitable locally obtainable materials the proportions of water, cement, fine and coarse aggregates are then calculated to give the required strength and workability. Trial mixes are prepared and test cubes cast to confirm that these requirements have been fulfilled. The test cubes are stored under water and crushed at seven days and twenty eight days age, in a 200 ton hydraulically operated compression testing machine. In assessing results allowance is made for a greater strength of concrete cubes cast under laboratory conditions than the strength of concrete produced in the field.
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