Publications

Regional Seminar Papers 1997

Road construction and maintenance

Rehabilitating and Maintaining Surfaced Roads

A O Bergh, P J Hendricks and I Cassiem, Division of Roads and Transport Technology, CSIR, Pretoria

Introduction

The South African Department of Transport (SADOT) has recently published a series of manuals prepared by the Division of Roads and Transport Technology of the CSIR which are designed to teach student trainees the art of maintaining and upgrading streets using labour-based methods. The manuals were based on a pilot project undertaken in Phuthaditjhaba in the North-Eastern Free State where various maintenance and upgrading techniques were tested as part of a community training program.

This paper will focus on the labour-based upgrading methodologies used in Phuthaditjhaba and fully described in manual 7 of the series. The manual describes techniques that can be used to upgrade existing gravel streets, using the existing structure as a subbase, where traffic volumes are below 500 vehicles per day, with less than 10% of these being heavy trucks.

Generally speaking, the roadworks in townships have been constructed to grade and crossfall and the houses are normally constructed in a straight line. A number of methods can be used to establish the centre line of an existing street, including using:

1. boundary beacons;
2. the fence lines/boundary lines if uniformly constructed, as shown in Figure 1. However, fence lines are not always correct , thus making this method unreliable and inaccurate;
3. the houses, if these are set out in straight lines;
4. the best line that can be established from the electricity poles;
5. the best line that can be established from the existing gravel road, taking into account the fronts of the houses.

Once the centre line has been established, using ranging rods, the edge of the street can established by placing steel pegs at 10m intervals, 400 mm above the existing ground.

In the pilot project, the pegs were placed on the edge of the topside of the crossfall of the street, in order to construct an open drain on the topside of the crossfall. To reduce the earthworks to a minimum, a "rolling grade" was established by tying a white sisal string line to the tops of the steel pegs. This "line" was adjusted by eye by lowering or raising the pegs to give a smooth rolling grade line.

Once the rolling grade line had been established, reference pegs were placed exactly 400 mm below the top of the adjusted steel pegs (rolling grade line). See Figure 2.

For township drainage it is essential that, prior to surfacing the road, the main stormwater spinal drainage is in place. In this case, the outfall main stormwater drainage was in place.

It was decided to use an open drainage system as this obviated the problem of blocked stormwater drains in townships.

Steel templates were placed every 2m, care being taken to place these templates accurately, as the top of the open drainage system on the edge of the road would form a reference line for construction and preparation of the subgrade.

Concrete was cast in alternate bays using light reinforced mesh only on the leg of the side drain closest to the road. Originally, the concrete was mixed by hand as part of the training, but to expedite the work, a small concrete mixer was used on the latter part of the works.

On relatively flat slopes, the levels, as set out above, were checked with a dumpy level to ensure that sufficient fall had been obtained. It is recommended that where very flat slopes are encountered, this check be instituted.

By selecting the appropriate crossfall, which can vary between 2% and approximately 2.8%, the amount of earthworks to be done with hand labour can be determined, using the final concrete level of the drain as reference points along the length of the road.

The top of the finished side drain served as a datum for establishing the levels of the opposite edge, which were obtained by transferring this level with a spirit level and a straight edge. The subgrade was levelled off to the required levels using picks and shovels. Wheelbarrows were used to cart the material to the fill areas. The subgrade/subbase was well compacted by the traffic prior to construction, but a BOMAG 65 pedestrian roller was used to compact the final earthworks and fill areas.

To expedite this work, the surface was well watered the previous day with a garden hose attached to the standpipe at one of the houses. It was also possible to stockpile some of the gravel obtained in the excavation for use at a later stage in the emulsion treated base.

It was most important to ensure that the levels of the subbase were as accurately constructed as possible, since that assisted with the laying of the steel shutters when the emulsion treated base was placed.

There were one or two minor areas which were clayey. These were treated by hand and compacted in situ.

The in situ material was checked by carrying out a dynamic cone penetrometer (DCP) survey of the four streets involved. It was established that the cover corresponding to the in situ California Bearing Rations (CBR's) obtained from the DCPs was generally greater than that required in the old National Road 7,000lb. design curves. It was therefore decided to use a 100 mm thick base as this would be perfectly adequate for the type of traffic anticipated on these lightly trafficked streets.

From an economy point of view, it was necessary to use whatever local materials were available. The local material that was readily available at the time was a decomposed dolerite material.

The streets were also gravelled with decomposed dolerite. Tests were done, not only on the gravel on the streets, but also on gravel from the quarries, with a view to using this material with emulsion.

As the plasticity indices (PIs) of the gravel were all in excess of 10 (to 15), it was necessary to treat the material not only with emulsion, but with lime before application of the emulsion.

The amount of emulsion used was 2% of anionic stable grade emulsion, 1% of cement and 1% lime. The lime, cement and gravel were first mixed dry by hand, after which the diluted emulsion was applied.

The densities obtained in the field were in the order of 97% Mod. AASHTO density, which were obtained with a 65 BOMAG pedestrian roller.

The CBRs of the materials tested in the laboratory varied from 106 at 93.8% compaction to 290 at a compaction of 99.3%.

Each street, with a road width of 3.5m, was split into half-widths of 1.75m.

The reason for this is that when very coarse material is used, it is onerous for labour to screed the material. The concrete side drain formed one continuous level to which the emulsion treated base had to be placed, the level on the other side being controlled by steel shuttering formed of 100x150 mm angle iron.

The emulsion used was anionic stable grade 60% bitumen emulsion, delivered to the site in 210 litre drums. The drums were rolled off the delivery truck onto steel or timber ramps to prevent any breakages and undue breaking of the emulsion in the drum. The drums were rolled backwards and forwards to ensure proper mixing of the emulsion before they were used, as the drums had been stockpiled on site, which causes the bitumen in the emulsion to settle to the bottom of the drum.

The drums were placed on a steel frame such as the one illustrated in Figure 3 and were fitted with a ball valve. The height of the steel frame was high enough to accommodate the measuring cylinders.

The ball valve allowed the control of emulsion into the measuring containers and to ensure a clean and neat operation with minimum wastage.

The quantities of cement and lime required per batch were measured with the measuring containers (see Figure 3). The ETB was mixed by hand and, in the latter part of the project, with a concrete mixer. The aggregate was delivered on site with a large amount of oversize and was then stockpiled as close as possible to the working area. The grading of the material was very coarse and to overcome this problem, coal forks were used from which the alternative tynes had been removed. This enabled the labour units to remove the coarse material, leaving relatively fine material for the work. The gravel was firstly mixed with cement and lime, followed by the diluted emulsion, up to 1:10, i.e. 1 part emulsion to 10 parts of water. The initial proportion of emulsion to water was 1:3 or 1:4. This was then checked to determine whether the water should be increased or reduced. The amount of water in the gravel was also taken into account as this affected the degree of dilution. The amount of liquid that was added to the mix was approximately 1 - 1.5% over the optimum moisture content required for the Mod. AASHTO density which had been obtained from the laboratory tests.

Measuring containers were essential to maintain accurate work for both aggregate and emulsion. The 25 litre cans were fitted with handles which made them user friendly. The 10 litre cans were used to measure the quantities of cement and lime.

The maximum depth of ETB that can be effectively compacted with the BOMAG 65 is 75 mm. As the thickness of the ETB layer was 100 mm, it was therefore necessary to place the ETB in two layers.

The first layer of ETB was placed level with the shuttering and the top of the drain. (i.e. for 100mm base). Steel squeegees were used for levelling the mixed ETB as the rakes tended to cause the mix to segregate, which is not desirable, whereas steel squeegees distribute the material uniformly without segregation.

The second layer of ETB was placed level with the top of the gauges, which had been placed on top of the shuttering and drain. These ensured the uniformity of the constructed level of the final base. The steel screed was used to obtain the final levels of the ETB uniformly between the steel shuttering and the top of the side drain or that of the inside edge of the concrete gutter.

The surface was dampened with a light application of water to prevent it drying out prior to compaction. Normally four to six passes with the BOMAG 65 were required over the uncompacted material.

The emulsion treated base was placed in the box and screeded to the level of the top of the concrete and the top of the steel shuttering. Steel squeegees were used to spread the material ahead of the screed. Once some 8m of length of road had been placed, the pedestrian roller was used for compacting this material.

Once the first layer had been compacted, second layer of ETB was applied, using 25 x 25 mm box sections on top of the concrete and the steel shuttering. This was compacted with the BOMAG pedestrian roller, until the material had been compacted to the level of the concrete and steel shuttering, the box sections having been removed from the concrete and steel shuttering.

Before the second application of ETB was placed, the surface was treated with diluted emulsion in the ratio of 1 to 10, and on completion of the second layer, the surface was again treated with diluted emulsion in the ratio of 1 to 10 emulsion to water.

There are several advantages to using emulsion treated base, apart from the strength that is obtained with the process:

1. As the work is done with hand labour, there is usually an extended period of time which elapses before the road is surfaced. The emulsion treated base is capable of carrying this traffic without surfacing for extended periods.

These streets were open to traffic for up to three to four months before surfacing was applied, without any damage of consequence to the surface.

2. There is no deterioration as far as cracking of the base is concerned.
3. The problems experienced when priming a base and waiting for it to cure and stopping the public from using the uncured primed base are obviated when an ETB is used, even if the surface has to be treated with diluted emulsion after extended periods of being used by traffic.
4. Should the surface be damaged mechanically, the base will not deteriorate and form potholes, as is the case with other unstabilised material or even crusher run material.

The object of this pilot scheme was to establish which surfacing would be the most economical and appropriate to apply by labour-based methods. Four types of surfacing were placed on four different streets, namely :

• a single seal
• a double seal
• a Cape seal, and
• a slurry seal.

In all cases where binder was sprayed on the road, a motorised hand sprayer as shown in Figure 4 was used.

Before any spraying could be done, it was necessary to establish the delivery rate of the spray pump. The rate of application of the binder was then controlled to within 10% using an enlarged manually-operated clock, controlled by the second hand of a wrist watch. The use of emulsion ensured that any errors in the quantities of the residual binder sprayed were reduced by some 35 to 40%.

1. Single seal

Students were instructed in how to use the ALD method for establishing the application rates of both binder and aggregate by using the pan and cylinder method for establishing the ALD and in the use of graphs to establish their prospective application rates for binder and aggregate. A 65% cationic bitumen emulsion and a 9.7mm aggregate were used for this single seal. Generally a maximum of 0.7 litres to 0.8litres of emulsion can be sprayed before the binder tends to flow. For this reason, a tack coat was applied at 0.7litres/m² and the aggregate neatly spread in a single layer by hand from small accurately measured heaps, spotted along the shoulder of the street. The surface was rolled and the balance of the binder sprayed as a penetration spray. Protective screens as shown in Figure 5 were used to ensure a neat edge line of the surface both for tack and penetration sprays. The final result was a sound and uniform surface, with no whip-off of aggregate.

The measuring containers (half drums) were used for spotting the aggregate along the constructed base to ensure accurate application rates of aggregate.

A manually operated clock was used in conjunction with the spray machine to apply the binder at required rates. The discharge rate of the spray machine was determined, the area to be covered with the binder was demarcated and the required time to cover such a section was then calculated. The spray operator had to finish that section in the required time. The chips were then applied by hand using shovels. The BOMAG roller, Figure 6, was used to roll the chips into the binder.

A double seal was constructed as above using a 13mm and a 6.7mm aggregate with cationic emulsion. To ensure minimum whip-off of aggregate the 13mm aggregate was choked with 6.7mm aggregate to obtain a tightly knitted surface before the penetration spray was applied. The 6.7mm aggregate was uniformly applied in a single layer and well rolled before a final fogspray was applied. The quantity of binder required after application of the tack coat was split between the penetration spray and the fogspray. The final result was sound and the seal was found to be suited to labour-based application if well controlled. A double seal is probably the most difficult seal to apply efficiently with hand labour as much of its success depends on experience in the efficient use of rollers.

3. Cape seal

The Cape seal consisted of a 13 mm aggregate applied in a similar manner as in the single seal, using a cationic emulsion as the binder in the tack coat and penetration sprays. A slurry seal was applied which filled all the voids in the 13 mm single seal. This was dragged with a hessian drag and rolled. The final result was sound and uniform and the seal was found to be user-friendly for labour-based work. A Cape seal is a strong, tough seal and could well be used on bus routes and on more heavily trafficked roads.

4. Slurry seal

10mm slurry (wet) was applied, using a medium-graded aggregate and a stable grade anionic emulsion.10 mm steel guide rails were used to ensure consistent application of the 10 mm slurry.

Any high spots on the base were rectified by hand chipping to ensure that the required thickness of slurry was obtained. The final result was sound and uniform and the process was found to be user-friendly for labour-intensive work. Before the slurry was applied, the surface was cleaned and treated with diluted emulsion in the ratio of 1 part of emulsion to 10 of water.

In all cases where binder was sprayed on the road, a motorised hand sprayer was used.

Before any spraying could be done, it was necessary to establish the delivery rate of the spray pump. The rate of application of the binder was then controlled to within 10% using an enlarged manually-operated clock, controlled by the second hand of a wrist watch. By using emulsion, any errors in nett residual binder sprayed were reduced by some 35 to 40%.

A number of participants from the public and private sector contributed financially, either directly or indirectly, to the pilot project and to the production of the manuals. These included:

• The Division of Roads and Transport Technology, CSIR;
• The SADOT Technology Transfer Centre;
• The Phuthaditjhaba Town Council;
• The Free State Roads and Public Works Department;
• Blue Circle Cement;
• A.J. Broom Road Products (Pty.) Ltd.;
• Quickfix Manufacturing;
• The Southern African Bitumen and Tar association (SABITA);
• TOSAS;
• V.I. Instruments.

Their support and encouragement is gratefully acknowledged.

Highway Maintenance Management

The paper emphasises the importance of timely and scrupulous maintenance of highways and discusses some of direct consequences of failure to follow the normal maintenance procedure. The paper analyses typical routine and recurrent maintenance activities and shows how the critical path method can be used to model such projects.

Every construction project has distinct stages which collectively constitute the project cycle. Some of these stages are identification, designing, tendering, construction, commissioning and maintenance. At the identification stage, the field technical personnel collect and study details of prospective projects and come up with projects which are economically viable. Therefore, projects with high benefit/cost ratios are short listed for designs to be produced. The projects then go for tender, when successful contractors enter into contract to execute them. The completed project is finally commissioned for use. At the commissioning stage, the future performance of the project is evaluated and the strategy for maintenance and repair is considered. Each phase of the project cycle is important. If, for example, the construction process has not been properly supervised and sub-standard materials have been used, the project may not last its design life no matter how good the subsequent maintenance strategy. The Overseas Unit of Transport and Road Research Laboratory has (1981) classified the three main functions of highway maintenance as follows:

1. To reduce the rate of deterioration and thus prolong its life.
2. To lower the costs of operating vehicles on the road by providing good running surfaces.

Highway maintenance therefore basically serves to improve the flow of traffic, conserves the assets represented by the roads, promotes the safety and comfort of road users, and preserves the aesthetic appearance of the roads. Failure to carry out regular maintenance of the road results not only in premature deterioration of the facilities, accident rates are also likely to increase drastically.

Maintenance activities consist of routine, recurrent and periodic activities. Routine maintenance activities are those operations that will be required whatever the engineering characteristics of the road or the density of traffic it carries. Routine maintenance activities include grass-cutting, drain clearing, re-cutting ditches, culvert maintenance, bridge maintenance and road signs maintenance. The recurrent activities may be carried out at intervals throughout the year; the frequency depends upon the volume of traffic using the highway. Some typical recurrent activities are pothole patching, surface repairs, edge repairs, sealing cracks and road surface marking. Periodic maintenance activities may include regravelling (for unpaved roads) and surface dressing/resealing (for paved roads). These activities are needed after intervals of several years.

Robinson (1988) has given suitable definitions for some common terms such as upgrading, stage construction and rehabilitation. Upgrading aims at providing additional capacity when a road is nearing the end of its design life or because there has been an unforeseen change in use of the road. Typical examples of upgrading projects are the paving of gravel roads, the provision of strengthening overlays for paved roads and the widening of roads. Stage construction consists of planned improvements to the initial pavement standards of a road at pre-determined stages throughout the project life. Stage construction differs from upgrading in that any later improvements are planned from the onset. Rehabilitation is needed if the road has deteriorated beyond the condition at which overlaying is a satisfactory engineering alternative. This is the normal result where the road has not received sufficient maintenance. Reconstruction to provide a new alignment should be considered as an upgrading project.

Roads will continue to deteriorate with time, even with adequate maintenance, until the design has elapsed, when the need for strengthening overlay or reconstruction becomes necessary. The need for efficient and regular maintenance operations become obvious if the data contained in Table 1 is critically examined:

If the required routine and recurrent maintenance activities are not carried out, drainage will be ineffective and surface defects will worsen, thereby resulting in water penetrating into the pavement structure. For a paved road, the consequences of the neglected maintenance activity will prematurely cause the need for a periodic maintenance which (from Table 1) will cost approximately 24 times more than the normal routine/recurrent maintenance operation. If the periodic maintenance activity is also delayed, a major upgrading activity (overlay) which is about three times more expensive than the periodic maintenance operation, soon becomes necessary. In the case of most developing countries, the problem is twofold: while the maintenance funds are insufficient, the bulk of the funds is diverted and spent instead on new construction. Maintenance operations cannot therefore be stretched to cover all the road networks.

A typical maintenance management procedure may consist of the following process (Robinson 1986, Robinson 1988): (i) inventory, (ii) inspection, (iii) maintenance needs, (iv) costing, (v) priorities, (vi) execution and (vii) monitoring. The inventory process establishes the basic reference for planning and carrying out maintenance and inspections. Since funds are not sufficient to cover all the road networks, it is necessary to establish priorities in order to determine which should be undertaken and which should be deferred.

The road should be inspected during the dry season and also during the wet season. The main purpose of the inspection is to identify the causes of defects so that maintenance operations can be planned to remedy them. The frequency and extent of carriageway and shoulder maintenance are closely related to the nature and volume of traffic on the road. A knowledge of traffic loadings will not only indicate which roads are likely to deteriorate most quickly but will also assist in establishing priorities. Therefore traffic counts should be undertaken to provide an estimate of annual average daily traffic (ADT).

Maintenance activities must be properly planned so that they can be completed on schedule. Critical path method provides one method for modelling projects. The method may be outlined as follows:

1. Determine sequence of operations and activities that may be executed simultaneously, e.g., materials ordered must arrive before repair activities can start.
2. Determine the duration of activities. By using performance standards (Overseas Road Note 1, Table 8) and suitable allocation of resources e.g., labour, equipment etc., the duration of each activity can be determined.
3. `Forward Pass' determines the Earliest Event Times while
4. `Backward Pass' determines the Latest Event Times. (see Figure 1.)
5. The `floats' have been determined and tabulated in Table 1. Float indicates the range within which the start and finish times of an activity may vary without affecting the completion time of the project.

Robinson R. 1988. A view of road maintenance economics policy and management in developing countries. TRRL Research Report 145, Transport and Road Research Laboratory, Crowthorne

Transport and Road Research Laboratory (1983). Maintenance management for District Engineers. Overseas Road Note 1, Transport and Road Research Laboratory, Crowthorne.

Transport and Road Research Laboratory (1985). Maintenance techniques for District Engineers.'(Second Edition). Overseas Road Note 2, Transport and Road Research Laboratory, Crowthorne.

Yanney, B. K. 1990. Techniques for maintenance cost estimation. Paper delivered at a course on Mass Transportation Planning and Management organised by the Nigerian Institute of Transport Technology, N.I.T.T. in Zaria, September, 1990.

1. Total Float = Latest Date - Earliest Date - Job Duration

(event B) (event A) (activity A-B)

2. Free Float = Latest Date - Latest Date - Job Duration

(event B) (event A) (activity A-B)

3. Critical activities have no float while non-critical activities have floats.

Management of Some Selected Labour-based Highway Construction Activities

Eng. B. K. Yanney, Department of Civil Engineering, University Of Zimbabwe, Harare, Zimbabwe

Summary

The is paper discusses some of the ideal conditions which make a labour-based method of construction an acceptable option. A typical highway construction project is analysed in order to determine its component activities and their sequential relationships. The activities are then critically examined; those which may be executed by plant-intensive operations are separated from those which are best executed by labour-based methods under the local conditions. Simple methods of developing and analysing network diagrams are illustrated. Examples of methods of applying labour constants for construction activities are given. The need for using realistic labour constants is emphasised.

Highway construction activities tend to be highly plant-intensive. Plant-intensive methods of construction can be effectively controlled so as to increase the outputs in order to reduce the project construction duration. Plant requirements for a highway project depend upon the size, type and location of the project. While a number of items of sophisticated equipment will be needed for the construction of an urban motorway, or an airport with a rigid pavement, very little equipment will be required for the construction of a secondary or feeder road, which will normally be designed to meet the requirements of low-volume roads in most developing countries. Labour-based methods of construction can still be introduced to reduce further the level of plant requirement. Most developing countries face severe shortages of foreign exchange, which is needed for the importation of construction equipment.

At the same time, unemployment is a major national issue. It is therefore safe to conclude that a possible solution to these problems would be to train some of the rural folk (who constitute over 60% of the population in most cases) to participate in labour-based construction activities. While conserving scarce foreign exchange, the problem of unemployment will also be redressed.

Planning, organising, directing, co-ordinating and controlling are some of the most important management functions. At the planning stage, the project manager literally breaks the project up into minute details in an attempt to identify all the activities that must be executed in order to complete the project. The sequence of operations and the inter-relationships between activities must also be determined. The `directing' function is concerned with training sub-ordinates to carry out assigned tasks, supervising their work and guiding their efforts. Workers must

be motivated individually and as groups to utilise their creative efforts in achieving specified objectives. The manager co-ordinates by ensuring that all facilities and individuals sustain and reinforce each other. This requires an efficient system of communication so that each department and section is aware of its role and the assistance to be expected from others. Control involves a constant review of the programme of work in order to check on actual achievements and to rectify if necessary any deviations by applying the necessary corrective measures.

The manager arranges regular site meetings to be attended by all senior supervisory staff and sectional leaders. At such meetings, the quantity surveyor submits a report on the monthly measurements of work executed. The project accountant also submits the site cost sheet with a summary of how much has been spent by each section on plant, labour, materials and other incidental expenses (e.g. petty cash). Under such circumstances, a meaningful discussion of unsatisfactory progress and over-expenditure will be made at the regular site meetings.

The programme of work is one of the manager's most important tools for controlling the progress of work. It must therefore be prepared with great caution. If possible most of the senior section leaders must be involved in its preparation at the very onset. Scheduling is an important stage in the preparation of a working programme. It is a process of fitting the working plan to a time format indicating the start and finish of each activity. At the scheduling stage of a labour-based construction activity, the manager first provides materials that will be needed (including tools if necessary) and then proceeds to assign labour (e.g. labourers, masons, carpenters, steel-benders etc.) needed to complete the activity within an acceptable duration. The use of realistic labour constants is the key to successful management of labour-based methods of construction. Where labour constants are not available, works study, work measurements etc may be used to provide the required data for a project in a specified location.

The main purpose of a works study is to discover what time and effort can be saved and made available for other works. Such studies enable existing abilities in an organisation to be matched more carefully with the requirements of specified jobs so that faulty relationships between individuals and work can be rectified. Work measurement, another closely related technique, aims at establishing the time for a qualified worker to carry out a specified job at a defined level of performance. Work measurement helps in comparing times for alternative methods, and allocation of labour to jobs in proportion to the work involved so that an appropriate balance of labour is maintained. The procedure for carrying out work measurement may be outlined as follows:

1. Select and define the work to be studied.
2. Record all relevant facts of the present method by means of charts diagrams and models.
3. Examine the facts critically and in sequence.
4. Develop the most effective method of doing the work.
5. Maintain regular routine checks for the procedure under investigation until it can be established as standard practice.

The Project Planning and Control Division of Ghana's State Construction Corporation (SCC) adopted the works study principles outlined above in establishing labour outputs which have now been approved by the Executives and Workers' Union of the corporation. The labour output document, first produced in 1970 and subsequently amended and approved in 1977, forms the basis for assessing acceptable output from each category of worker. It is also used for establishing taskwork and payment of bonus or incentives.

The labour constant is a figure which tells how many work-days are spent per unit of work. For example, Appendix A (Table 1) shows that one labourer will excavate 3.82 cubic metres in medium soil per day of eight hours. The labour constant works out to:

1 work-day = 0.26 work-day per cu. m.

3.82 cu. m.

If, on the other hand, the excavation had been stony soil one labourer would be expected to excavate only 1.91 cu. metres in the same period and the labour constant would be:

1 work-day = 0.52 work-day per cu. m.

1.91 cu. m.

(Please note: The lower the output the higher, the labour constant).

Assume that the base of a culvert or the foundation of a bridge is to be concreted. The following procedure has been found to be effective:

1. Determine the volume of concrete required from the drawings and/or bill of quantities. Check from the specifications of to ascertain the class of concrete. In this case, the recommended mix of proportions by volume is 1:2:4 .
2. Using, table 2 (Appendix A) determine the quantities of materials needed for the concrete works. For example, if 35 cubic metres of concrete (1:2:4 class) will be needed, then 224 bags of cement, 16 cu. metres of fine aggregates (sand) and 32 cubic metres of coarse aggregates will be needed. These quantities may be increased by about 5% to allow for waste.
3. Provide a good concrete mixer and preferably one that can hold one bag of cement and the aggregates. A stand-by mixer may be arranged.
4. Prepare gauge boxes, at least one for sand and two for the coarse aggregates. Each gauge box must be designed such that its volume is equal to the volume of one bag of cement. A gauge box of dimensions 300 mm x 300 mm x 390 mm i.e. volume 0.035 cu. metres will be acceptable.
5. The labour force for the concreting operation may consist of:

• one labourer (loading cement)
• two labourers (loading sand)
• four labourers (loading coarse aggregates)
• one mason (receiving concrete)
• two labourers (transporting concrete)
• one labourer (adding water)
• one concrete mixer operator
• one gang leader

The labour force for the concreting operation adds up then to 13. Table 3 (Appendix A) shows that the average output for this activity (item 2) is 2.7 cubic metres per worker. The expected output per day is 13 x 2.7 = 35 cubic metres. Therefore, the concreting operation can be finished in a day. The concreting operation may then be given out to the selected workers as taskwork (sometimes referred to as "finish and go") i.e. the piece of work is given out to the workers to be completed in a day. The workers are free to go home any time the work is completed. Output can be drastically improved if the concrete mixer and the aggregates are brought as close as possible to the culvert/bridges site. Batching concrete by volume presupposes that the sand is dry. Wet or moist sand can bulk by about 20%. Therefore, if moist sand is used, the volume of sand should be increased by about 20% to allow for bulking. It may be desirable to carry out a sand bulking test to determine the exact value. Quality control measures must be enforced during labour-based concreting operations. Slump tests must be carried out before commencement and during the concreting process to ensure consistency of water/cement ratio. Test cubes must be prepared during the concreting operations. In this example, the gauge box is designed such that the mix proportions by volume are:

• One bag of cement
• Two boxes of sand
• Four boxes of coarse aggregates

The supervisor must ensure that the exact quantities of fine and coarse aggregates are added during each mixing operation. Workers normally easily get carried away by enthusiasm during concrete works under taskwork basis.

Major questions that must be answered before an attempt is made to develop a network diagram for the highway construction project are as follows:

1. What are the activities that must be executed in order to complete the project?
2. How is each activity going to be executed?
3. What resources must be allocated to each activity so that it may be completed within an acceptable duration?
4. What is the most acceptable sequence of operations?

The answer to question (1) calls for a complete breakdown of the project into distinct activities. Some of the most popular activities for a highway construction project consist of:

1. Excavation for culverts and bridges.
2. Formwork.
3. Cutting, bending and fixing reinforcement.
4. Concrete works (culverts and bridges).
5. Earthmoving operations.
6. Pavement construction and surfacing

To answer question (2) one has to examine the availability of local labour and the type of highway design. In the case of the road bridge with cantilever abutments on spread foundations, the excavation, formwork, reinforcement placing, and concrete works may be planned for execution by labour-based methods. Plant-intensive operations in bridge construction may be restricted to piling works, and the launching pre-cast, pre-stressed bridge beams. Earth-moving operations, pavement construction and surfacing may also be executed by plant-intensive methods. Surface dressing, which is very popular with low-cost roads, can be planned for execution by labour-based methods.

Resource allocation is an important phase in the planning strategy. The main resources to be utilised for construction are plant, labour, materials and finance. Plant must be bought or rented for use only when it is absolutely necessary. Indiscriminate use of plant could wipe out the entire profit margin. The same goes for labour. Workers, on recruitment, are the best friends of management. Relations turn sour when the project is about to be completed and lay-offs become imminent. Therefore, if possible, efforts must be made to retain just enough workers to maintain steady progress on the project. Local labour could then be brought in to complete some items of work when the need arises. The sequence of operations must be carefully examined. Although progress can be drastically improved by executing simultaneously as many activities as possible, this strategy must be attempted only when resources are adequate to meet the demand.

The network diagram for the highway construction project has been developed and analysed as shown in Fig.1 (Appendix B). The normal procedure for analysing networks has been followed viz.:

1. The Earliest Event Times have been determined by the `Forward Pass' method while the Latest Event Times have been determined by the `Backward Pass' method.
2. Critical activities are those activities whose Earliest Start Times (EST) and Latest Start Times (LST) are the same or the Earliest Finish Times (EFT) and Latest Finish Times (LFT) are the same.
3. Floats in all the activities have been calculated in Table 1 (Appendix B). Float indicates the range within which the start and finish times of an activity may be delayed without affecting the completion time of the activity.
4. Eight out of the 15 activities are critical. The project manager must therefore strive to ensure that these critical activities receive utmost attention.

1. Labour-based methods of construction should be encouraged. Therefore, large construction corporations must sponsor studies in these areas.
2. The use of realistic labour constants, prior consultation with workers, and motivation are some strategies which promote productivity.
3. It is being argued that labour-based methods suffer from quality deficiencies. Therefore quality measures must be strictly enforced.

The author would like to thank the Managing Director of Ghana's State Construction Corporation for granting permission for the use of the Corporation's Labour Output Document.

Yanney, B. K. 1988. Technique for maintenance cost estimation. Paper delivered at course on Mass transportation planning and management organised by the Nigerian Institute of Transport Technology N.I.T.T. Zaria, Nigeria.

Yanney, B. K. 1989. Project programming. Paper delivered at a workshop organised by Nigerian Institute of Transport Technology N.I.T.T., Zaria, Nigeria.

Source: Labour output document of SCC, Ghana

Appendix B