How to do construction of concrete foundations - Concrete Pouring step by step

Construction of concrete foundation is divided into number of work activities with specific objectives and completion time for each activity is defined. Each activity for construction of concrete foundations has to be planned, as it requires specific equipments at every stage. Activities for construction of concrete foundations can be divided into following:

• Marking of foundation layout at site.
• Earth excavation up to the required depth by means of machine.
• Earth excavation and levelling of soil by means of hand operated tools.
• Placing of PCC.
• Placement of reinforcement steel
• Erection of concrete form-works for footings.
• Placement of concrete and vibrating and levelling of concrete surface.
• Removal of form work after the concrete has set.
• Curing of concrete for the required number of days.
• Applying finishing coats on concrete surface.
• Site cleanup.
• Back filling of excavation up to the required depth in the number of layers.

Each activity for the construction of foundation requires different skill sets of workmen and different equipment's. For a construction large construction projects, there can be many number of foundations to be casted on a single day. Therefore it is required to plan each and every activity of this construction. The project planner for foundation construction should determine the quantity of works involved in each activity and estimate the quantity of materials to be required. The number of tools and equipment's, workforce and other resources to be utilized for this construction should be well planned in advance. For example the placement of concrete could involve the total number of cubic meters of concrete involved in the activity. The building of forms would normally be measured by the square meter of concrete surface area.

Construction project activities

Construction Project Activities

All the activities for a foundation construction must be properly sequenced and resources required at different times of the activity must be estimated. From this information the possible necessary to complete the construction and the amount of resources required can be known. At this point the planner might not considered factors such as delays due to weather and other unforced circumstances. The construction plan for foundation is affected by following:

• The ability of the contractor to accomplish the project.
• The resulting costs of the project.

The rate of concreting for foundation construction should be estimated to complete the work within the time. The concrete work should not be stopped for more than 30 minutes unless all the concreting has been completed.

Forecasting duration of Construction Project - Scheduling a construction project

Forecasting construction duration in a project can be achieved by many means and depends on the stage of construction planning. Forecasting construction duration informs the project owner to allow the contractor to complete the work within given time. On the other hand, the contractor could prepare realistic and practical detailed schedule at the minimum costs within the limited time frame.

Definitions

Construction duration can be defined as one or a combination of the following:

1) The construction duration arising from critical path in which duration for items of work or activity in sequence cannot be reduced further (Barrie and Paulson, 1992).

2) Duration means the time required to complete a specified task or activity. And, construction duration is the time determined by the owner’s needs to occupy, utilize, or rent the completed space of the project (Callahan et al., 1992).

3) Construction duration is a duration resulting from an examination of one or more methods of carrying out the works on the basis of minimum cost, it is usually estimated in the first instance for normal condition (Pilcher, 1992).

4) Construction duration refers to a given time to execute and complete item(s) of work using all project information and resources within an estimated or predicted cost (Kwaku, 1994).

5) Construction time can be defined as the elapsed period from the commencement of site works to the completion time of building to the client. It is usually specified prior to the commencement of construction (Nkado, 1995).

In this research, construction duration is defined as the time frame given by the owner for the contractor to complete the project under normal work conditions, normal practice of construction, and based on the minimum costs. It starts when the contractor receives the instruction to proceed and ends at the completion of construction works on site. It also includes delays caused by unanticipated circumstances, e.g. alteration of works (changed conditions and change orders), extra works, supply of materials, location, weather, and site work conditions. Major changes that after the scope of work significantly are not included.

Scheduling and Schedulers

Control of construction duration needs a clear systematic plan and commitment on the part of the people involved (McNulty, 1982). The systematic plan is known as schedule. The scheduling is the determination of the timing of activities and follows logically from the planning process (Callahan et al., 1992). It is normally used for controlling construction duration (Callahan et al., 1992). To both the owner and contractor, scheduling plays an important role in financial proposal and budgeting (Peurifoy and Ledbetter, 1985; Kaka and Price, 1991). The schedule is prepared by the scheduler and/or planner. In preparing a schedule, the scheduler or planner may meet or discuss with some people for crucial information, e.g. estimator, manager, superintendent, sub-contractor, architect, engineer, owner, and materials’ suppliers (Callahan et al., 1992). They may need to study the contract, drawings, specification, and perhaps, conduct site reconnaissance. Further, they need to know about manpower and productivity. (Callahan et al., 1992; Pilcher, 1992). Apart from the schedule, it is also necessary to prepare systematic monitoring to provide early warning of restraints as well as imaginative action to overcome them (McNulty, 1982).

Nowadays, computers may assist the scheduler or planner by storing and sorting the information, as well as performing mathematical calculations but they do not provide the intellectual direction (Callahan et al., 1992). Human skill and experience are still necessary, i.e. the scheduler or planner may use experience of similar projects in estimating the construction duration (Pilcher, 1992). The scheduler or planner may use their judgement according to various constraints, e.g. location and access, weather, space and site work conditions, complexity of the project, quality of workmanship, delivery of materials, and economic or marketing conditions (Pilcher, 1992).

Forecasting Construction Duration

Inputs required:

The basic inputs for project scheduling are:

1) contract;

2) drawings;

3) specification;

4) resources (materials, manpower and productivity); and

5) other constraints, e.g. site conditions and weather (Burgess and White, 1979; Fisk, 1982; McNulty, 1982; Peurifoy and Ledbetter, 1985; Ashworth, 1988; Barrie and Paulson, 1992; Callahan et al., 1992; Pilcher, 1992).

The contract may clearly specify the completion date. Therefore, the scheduler or planner may use this time frame to prepare the schedule together with other factor constraints. First, it is usual to prepare the schedule for normal conditions by assuming one or more methods of carrying out the works on the basis of minimum cost (Nkado, 1992; Pilcher, 1992). When it is necessary to shorten the duration for an activity or a project, crashing may be done, e.g. increase manpower and overtime working. This process leads to increase in construction cost (Puerifoy and Ledbetter, 1985; Barrie and Paulson, 1992; Pilcher, 1992).

Drawings contain physical features of the project: 1) function; 2) height; 3) systems (e.g. plumbing, fire fighting, and lighting); and complexity (Ireland, 1985; Ashworth, 1988; Pilcher, 1992; Nkado, 1992). In other words, the information on the drawings is presented in form of dimensions and descriptions (Ashworth, 1988). Materials and installed equipment for the project, as well as the plant and construction equipment can also be known from the drawings (Ashworth, 1988; Peurifoy and Ledbetter, 1992). Meanwhile, the contract may specify the constraints of work, e.g. construction cost, duration, payment, inspection, method or conditions of works, delays, and damages. In addition, the specification may address the quality of materials, workmanship, and method of working (Barrie and Paulson, 1992).

2. Resource scheduling

The scheduler or planner has to allocate the resources, i.e. materials and manpower (or working team) to each activity or task at the proper time they are needed. Thus, the resource schedule deals with levelling and allocation of all necessary resources (Peurifoy and Ledbetter, 1985). The former smoothes out the peaks and valley in resource use within the project duration. The latter determines the shortest project duration consistent with the limited resources.

4. Other judgements

They also have to provide timing for preliminary works, e.g. construction plant, and mobilization (Peurifoy and Ledbetter, 1985). This often includes time for remedial works and site clearing after completing the construction.

Site reconnaissance enables the scheduler or planner to adjust the schedule against various constraints, e.g. location and access, weather, space and site work conditions, complexity of the project, quality of workmanship, delivery of materials, and economic or marketing conditions (Barrie and Paulson, 1992; Pilcher, 1992).

Some Methods for Project Scheduling

There are many forms of schedules, e.g. Gantt or bar chart, Critical Path Method (CPM), and Program Evaluation and Review Technique (PERT). Each has its own advantages, disadvantages, and application areas for which it is most appropriate. They are means of visual presentation of a construction program (Pilcher, 1992), and used for project planning, management, and control (Burgess and White, 1979; Fisk, 1982; McNulty, 1982; Barrie and Pualson, 1992).

Gantt chart simply represents the activity and its duration by a bar. It is sometimes called Bar chart. Gantt or bar chart can include a great deal of anticipated and actual information for; 1) cashflow; 2) manpower and/or manpower by trade; and 3) productivity (Barrie and Paulson, 1992; Callahan et al., 1992).

In CPM scheduling, a construction project is sub-divided into several activities. An activity is a single work step that has a recognizable beginning and finishing or ending (Callahan et al., 1992). In other words, the activity is a time-consuming task. The basis of CPM is network diagram, i.e. which needs nodes and arrows. It deals with four aspects: 1) activities identification; 2) logical sequence,; 3) network construction; and 4) allocation of resources (Barrie and Paulson, 1992). Callahan et al. (1992) divided the development of CPM schedule into six phases:

1) understanding the project;

2) conceptual approach definition;

3) physical creation of the schedule;

4) computerization;

5) refinement; and

6) reproduction.

Further, physical creation of CPM scheduling is divided into eight steps: 

1) select software;

2) divide project into several activities and sub-networks;

3) develop responsibility code;

4) develop information code;

5) develop specific sub-networks;

6) build or plot the logic diagram;

7) numbering the activities; and

8) linking the sub-networks together.

The longest interconnected path of activities through the network called “critical path” becomes the project duration. On the critical path means that the duration for items of work or activity on the sequence cannot be reduced further without paying extra costs (Peurifoy and Ledbetter, 1985; Barrie and Paulson, 1992).

PERT is like CPM scheduling. It uses logical diagram to analyze performance time. It overcomes difficulties associated with duration of activities which could not be estimated reliably. PERT enables the scheduler to estimate the most probable project duration and the probability that the project or any portion of the project will complete at particular time. PERT focuses on events or nodes, called event-oriented. Unlike the CPM, it requires three estimates of duration for each activity: 1) optimistic (high productivity); 2) pessimistic (low productivity); and 3) most likely duration (Peurifoy and Ledbetter, 1985; Barrie and Paulson, 1992; Callahan et al., 1992; Pilcher, 1992).

Factor Affecting Construction Duration

The following are some factors affecting construction duration and its estimate.

1. Size of project

Size of the project can be represented in terms of functional or floor area, i.e. in ft2, or m2. The larger the building size, the more complex the construction, thus needing longer duration to complete (Sadashiv, 1979; Ireland, 1985; Ashworth, 1988; Pilcher, 1992; Nkado, 1992).

2. Function

Function implies type of building and required engineering systems, e.g. plumbing, fire fighting, and lighting (Ashworth, 1988; Pilcher, 1992). It is an important facet in designing of construction project (Ashwoth, 1988). Function of a building implies business target that the building serves. It can be considered as qualitative variables, e.g. office, retail, and other buildings (Nkado, 1992).

3. Height

Height of building, represented by number of floors (or storeys) affects the construction duration (Sadashiv, 1979; Ireland, 1985). The height of building indicates construction technique, major equipment used, and construction sequence (Sadashiv, 1979; Callahan et al., 1992).

4. Complexity

Complexity implies unfamiliarity with work (Pilcher, 1992). The complexity of building impacts the form of construction, i.e. building frame, foundation, and systems (Ireland, 1985; Ashworth, 1988). Complexity can be represented in form of construction equipment, method and sequence (Sadashiv, 1979; Callahan et al., 1992; Chan and Kumaraswamy, 1995).

5. Quality

Quality can be classified by variables or attributes, i.e. appearance, strength, stability, materials used, performance finish. Appearance of the building, e.g. external facing is one aspect of quality (Ashworth, 1988). Sadashiv (1979) considered number of major finishing works in duration forecasting instead of a defined quality index.

6. Location

The location of the building has a significant effect on the construction duration (Chan and Kumaraswamy (1995). It reflects restrictions or easements that exist and availability of services (Burgess and White, 1979). It effects supply of resources, e.g. materials, and equipment (Sadashiv, 1979). Consequently, it also effects the use of major equipment (Sadashiv, 1979), and productivity on site (Callahan et al., 1992).

There are other possible factors affecting the construction duration, e.g. construction planning (Sadashiv, 1979; Ireland, 1985), design-construction interface coordination (Ireland, 1985), dispute per unit of time (Ireland, 1985). Type and/or variation to the contract refers to risk allocation management structure and payment modalities (Burgess and White, 1979; Ireland, 1985; Chan and Kumaraswamy, 1995). By contrast, Walker (1994) concluded that client related factors have more significant affect on speed of construction, or construction duration, than the contract type. Callahan et al. (1992) pointed out that quality of supervision, labour training and motivation, can also be affecting factors. Al Tabtabai et al. (1997) developed the models for expert judgment in forecasting construction project completion. The factors are: 1) performance of management; 2) cash flow situation; 3) material and equipment availability; 4) labour productivity; 5) weather and environment influences; 6) rework, extra work, and work difficulty; 7) percentage of work completed; and 8) trend in schedule variance.

Project Delays and their Causes:

Project duration is normally specified by the owner. The completion and operation of many buildings are restricted as they are seasonal in nature, e.g. a school must open in September, a retail outlet must open for booking in August to meet the Christmas sale season, and an apartment must open in May to reach the spring market (McNulty, 1982). Construction duration affects the financial interest to the owner, e.g. selling price, and on-site management. Then, the contractor is traditionally responsible for the detailed planning and scheduling to ensure the completion of the project within the owner’s time frame. However, the actual construction duration consist of two parts:

1) contract time; and

2) delay.

Delay is the time during which some parts of construction project has been extended or not performed because of unanticipated circumstances (Barrie and Paulson, 1992). When necessary, the contractor may need to allocate an additional budget for corrective actions to maintain the schedule, otherwise, it may cause liquidated damages charges against the contractor for failure to meet the owner’s requirements (Fisk, 1982; McNulty, 1982).

Alteration of working drawing is one of a major factor affecting the construction duration, i.e. it may cause a delay beyond the contract time (Sadashiv, 1979; Chan and Kumaraswamy 1995). Barrie and Paulson (1992) summarized causes of delay into four areas:

1) changed conditions and change orders;

2) extra works;

3) owner or his/her agent; and

4) third party contractors.

However, other possible delays may result from location, weather, site work conditions, labour productivity, sub-contractor, supply and delivery of materials (Burgess and White, 1979; Sadashiv, 1979; Callahan et al., 1992; Chan and Kumaraswamy, 1995).

Relationship between Cost and Time:

There is a relationship between cost and duration (or time). In construction planning and scheduling, alternative duration and costs for activities are always considered. For example, when it is necessary to shorten the duration of activities or project, the cost may increase. This is called “crashing“.

Sadashiv (1979) found that some of the independent variables used in regression model for cost forecasting also have major affects on construction duration, e.g. height, and types of major equipment. However, he used the number of major finishing works in his duration forecasting model instead of the quality index as used in the cost forecasting model.

Ireland (1985) found a relationship between construction time and cost. In his study, the construction time and cost are dependent on some common independent variables:

1) construction planning during design;

2) variation to the contract; and

3) complexity of form of construction.

In addition, number of storey’s, design-construction interface co-ordination, and dispute per unit of time also affect the construction time while architectural quality, and use of nominated sub-contractors affect only the construction cost.

Kaka and Price (1991) found strong relationship between the cost and duration of construction projects that can be used in contractor’s budgeting systems and corporate financial model. Investors of project can utilize the relationship for financial appraisal and budgeting. Estimating of project cost can be used to derive the expected duration and vice versa.

Pre-design Estimating of Project Duration:

Pre-design estimating of construction duration is important. Chan and Kumaraswamy (1995) noted that pre-contract determination of the construction duration is essential for proper cash flow forecasting by both the contractor and the client. It can facilitate optimal resource allocation, financial planning, profitability and efficiency of capital flow within a pre-determined time limit.

Based on the inputs required for scheduling, all the current methods of scheduling seem to be efficiently applied only when the detailed design is completed. Normally, the contractor must complete this planning prior to bidding for the project (Peurifoy and Ledbetter, 1985). Without sufficient information, the schedule can be prepared based on only the best guess, i.e. using experience of similar projects in estimating the construction duration (Pilcher, 1992).

Nkado (1992) established a computerized construction time information system for planning of buildings at the early stage of design. Two key assumptions are:

1) the building team is competent and efficacious in setting up the building process and working within local norms and organization form to bring the project to a successful completion; and

2) the frame of reference for construction times is based on the overall time consistent with the minimum direct cost of construction to the contractor.

Al Tabtabai et al. (1997) developed the multi-regression and neural network models to capture the decision-making procedure of project experts involved in schedule monitoring and prediction. The models were applied to a multi-storey building under construction. They provided the convenient and realistic generation of revised schedules at appropriate junctures during the progress of the project. The accuracy of the models mainly depends on the soundness of the underlying expert decision, i.e. inputs generated from judgment of the experts are not free of bias. However, they concluded that modelling construction experience to use in future projects can help significantly in achieving project objectives.

A model for forecasting the construction duration should be valid in application for a reasonably long period of time without the effects from changes in price level. The price indices may not be applied or included in the model. The model should be slightly affected by change in construction technology in long term application. Today, the construction industry is still labour intensive. Automation which has reduced the labour force in manufacturing industry, has not been matched in the construction industry (Ashworth, 1988). This means construction technology has changed only slightly over time.

Summary

A variety of methods and techniques for construction planning and scheduling exist but they are based mainly on the completed design and details of project, e.g. Gantt chart, CPM, and PERT. Construction schedule is normally prepared by the contractors at the time they submit bids. Without sufficient information, the scheduling and forecasting of construction duration is based on the experience of the planner or scheduler. A number of researches found strong relationship between construction duration and cost. This leads to the possibility to build a model for forecasting the construction duration at pre-design phase. The model may consist of part of variables as they are used in the cost forecasting models. The main variables shall consist of building features, e.g. function, structural system, height, foundation, exterior and interior finishing. Adjustment of the construction duration by means of indices is not necessary.

Low Cost Building Materials For Construction Of Low Cost Buildings

Construction of low cost housing by using the low cost building materials increases the access to buildings by low income group peoples. Low cost housing can be achieved by use of efficiet plannng and project management, low cost materials, economical construction technologies and use of alternate construction methods availabe. The profit gained from use of such methods can decrease the cost of construction and make the low cost housing accessible to all.

Materials for low cost housing

The use of low cost alternate building materials also prevents the rise of construction cost due to use of scarce building materials which eventually increase the cost of the project.

Selection of Materials for Low Cost Housing:

The first step to low cost housing material selection is to select ecofriendly building materials. This also enhanaces the sustainable design principle. The life cycle of a building os pre-building, building and post-building stages. Each stage of building should be such that they help conserve the energy. These three stages indicate flow of building materials through different stages of a building. Pre-building stage mainly consists of manufacture which is subdivided in processing, packing and transport. The building phase mainly consists of construction, operation and maintenance whilst as the last stage would be disposal where the material can be recycled or reused.

1) In Manufacturing of low cost building materials – Pollution prevention:

Manufacturing of building materials should be environment friendly. Efforts should be made to study and revise the technologies for producing good quality, efficient building materials and should improve the waste generation during manufacturing. These results in reduction of pollutants to environment.

2) Recycling of wastes in Manufacturing – The wastes which can be recycled can and used in masonries whilst as wooden wastes can be used in manufacture of plywood or soft boards. (Courtesy-BMTPC)

3) Reducing Energy Consumption and use of Natural materials – The total energy required to produce a material is called embodied energy. The greater a materials embodied energy; it requires a greater usage of non-renewable sources. It is therefore advantageous to use materials or composite materials prepared from the wastages. The natural materials such as stones, wood, lime, sand and bamboo can be used in ample where ever possible. The natural materials impact more sustainability to structures as well as they are friendlier to environment.

4) Use of Local material – The use of local materials reduces the dependence on transportation whose contribution to the building material cost is high for long distance. Use of locally available building materials not only reduces the construction cost but also are suitable for the local environmental conditions.

5) Energy Efficiency – Energy efficiently of a building material can be measured through various factors as its R value, shading coefficient, luminous efficiency or fuel efficiency. Energy efficient materials must reduce the amount of generated energy.

6)Use of non-toxic building materials: Use of toxic building materials can significantly impact the health of construction people and the occupants of the building. Thus it is advisable to use the non-toxic building materials for construction. There are several chemicals including formaldehydes, benzene, ammonia, resins, chemicals in insulations, ply boards which are present in furnishings and building material. The effect on health of these toxic materials must be considered while their selection and they should be used only where-ever required.

Higher air cycling is recommended while installation of materials having volatile organic compound such as several adhesives, paints, sealants, cleaners and so on.

7) Longitivity, durability and maintenance of building material: The use of durable cosntruction materials does not only enhance the life of the building but also reduces the cost of maintenance. The lower maintenance costs naturally save a lot of building operating cost. The materials used in building determine the long term costs of an operating.

8) Recyclability and reusability of building material: A material should be available in form which can be recyclable or reusable. Ex – the plastics waste can be used for recycling and producing newer materials. The scrap from steel can be used to manufacture the rcc bars, binding covers and other miscellaneous steel products in building construction.

9) Biodegrability –A material should be able to decompose naturally when discarded. Natural materials or organic materials would decompose very easily. It is also a very important consideration whether a material decomposes naturally or produces some toxic gases.

COMPOSITES AS BUILDING MATERIALS:

The composite building materials are made of composition of two or more materila which have enhanced property. Natural fiber materials are coming up as excellent substitutes for the prevailing building materials. Fibers likes jute, sisal coconut, ramie, banana are cheap and environmentally suited as they are made from natural fibers. They are also replacing the fiber reinforced plastics.

Composite building materials present immense opportunities to replace traditional materials as timber, steel, aluminum and concrete in buildings. They help in reduction of corrosion and their low weight has been proved useful in many low stress applications. Each type of composite has its own characteristic properties and thus useful for specific purpose.

Jute fiber reinforced polypropylene composites, coir fiber reinforced composites, sisal fiber and wollastonite jute pultruded composites are a few to be named. CBRI has developed MDF composite doors containing coir fiber, cashew nut, shell liquid (CNSL) as natural resin and Para formaldehyde as major constituents.

Many composite building materials are generated from glass fibres and industrial wastes. These materials are used for manufacturing of portable toiles, water storage tanks, outdoor furniture, bath tubs, interior decoration, basin, door, window frames etc. Thus the application of composite building materials in construction vary from cladding to internal furnishings and the owner highly benefits due to their application because of their light weight, resistance to corrosion and availability in different colours. Pultrusion is most cost effective method for producing composite profiles. It is commercially applicable for light weight corrosion free structures, electrical non conductive systems and so many other functions.

The pultruded items are recognized and recommended in the Global markets. Pultrated sections are well established alternative to steel, wood and aluminium in developed countries and catching fast in other parts of the world.