Huge amount of money is invested in the construction of buildings bridges and roads. Economical consideration needs earliest use of the investment and hence present day demand is automation in construction. To meet this challenge lot of research has gone into and a number of techniques are developed. In this article the automation in buildings, dams, bridges and road constructions are briefly discussed.
AUTOMATION IN BUILDING CONSTRUCTION
Digging for Foundation :- Any construction work starts with digging for foundation. Nowadays manual digging for foundation is almost given up in all cities and towns. JCB is used for this purpose which can finish digging work for most of the buildings in a day or two.
Mining, Lifting, Transporting and Placing of Concrete :- Labour oriented method of mixing, lifting, transporting and placing of concrete needs to be changed to mechanization of concreting. Without it speed and economy cannot be achieved in construction.
Batching and mixing plants :- In large projects like dam construction or in ready mixed concrete plants large batching and mixing plants are used. Ready mixed concreting is new concept in which concrete mixing is done in large plants and then transported to needy places in the city. The capacity of such plants varies from 120-150 cubic metre per hour. These concrete production plant comprise of:
- Silos, containers and bins for storage of raw materials.
- Batching arrangement.
- Measuring and recording equipment.
- Mixing equipment.
- Control system.
- Electrical, hydraulic and pneumatic drives.
- Conveying systems like belt/screw conveyors.
Cement is generally stored in silos. The silos are loaded with cement with the help of pneumatic blowers. If bagged cement is used then tree cement is loaded using compressed air loader and a splitter unit. Water is generally stored in tanks located close to the plant. Aggregates are stored in silos. A storage capacity of 1500 m3 is possible. Cement silos are provided with weigh hoppers which use knife edge balance principle. Larger plants use electromechanical system.
For measuring water, a water meter or a water batch is used. The aggregates weighers are generally identical to the cement weighers in the plant. The aggregates and cement are first dry mixed in hoppers using scrappers. Provision is made up to four types of concrete admixtures to be added with required quantity. Free fall or power mixers are used for thorough mixing of concrete. Fully automatic plant control systems with multiple inputs are based in a container or control room.
Transportation and Placing: – Various modes of transporting concrete are truck agitators, truck miners, cranes, buckets, elevators, belt conveyors, concrete pumps, chutes etc. The suitability of method of mechanical transportation varies from job site to job sites. Often combination of various methods is also used. It may be noted that truck agitators, truck miners are useful for horizontal transport, while cranes, buckets, elevators, belt conveyors and pumps are useful for vertical transport. Chutes are useful for dropping concrete in intricate portions.Minibatching plants are suitable for projects like national highways, flyover, mass housing and industrial projects. They have the capacity of 15 to 20 m3 per hour. The plant includes:
- In built weighing system for fine and coarse aggregates.
- Automated loading system for aggregates.
- Cement hopper with weighing system.
- Automatic admixture dozing system.
- Print out system giving details of batching and mixing.
Self-Compacting Concrete (SCC) :- Self compacting concrete (SCC) as the name signifies should be able to compact itself without any additional vibrations or compaction. It was first developed in late 1980s. It is highly flowable within the form work and fills it without any external vibration. This is used to ensure the filling of congested sections. It includes the high number of super plasticizers and cement to increase flowability. Viscosity agents are also added. The mix may incorporate steel or polypropylene fibres also.
The sand can be finer. In Sweden bridges are built with SCC. In Japan two anchor blocks were constructed in Akashi-Kairo bridge. In France SCC is preferred in cities as noise free concreting. Since there is no vibrations in compacting, form works can be reused several time. Use of SCC is becoming popular in precast industries also.
Prefabricated Structural Elements: – Use of prefabricated structural elements increases construction speed and quality of structural element. It saves time because casting of these elements can start much early in factories much before, they are to be put in the building. For building activity requirement of time is only for putting them in the structure. Some of the commonly used prefabricated structural elements are:
- Precast concrete portions: Precast concrete posts and panels of sizes 1000 × 400 × 40 mm
- Precast roofing units: In Pune, universal temple of Ramakrishna was built with suitable elements to form required geometric forms of Shikharas. The technique of using precast elements has saved construction time by at least 6 to 8 months. After erecting shell units the outer surface of roofs and domes are covered with Glass Mosaic Tiles laid in polymer modified tile adhesive, giving excellent aesthetic view and weather proofing.
- Lift slab construction: In these constructions, slabs are cast at ground level one over the other with separators in between. Then slabs are lifted along columns to their positions using cranes or jacks and clamped. This process has been applied on a two storeyed building built at Roorkee by Central Building Research Institute. It is possible to extend the technique to multi-storeyed structures with several floors. In America this has been tried successfully.
Form Works: – Providing form works takes of considerable time in building construction. Convention method of providing wooden form work needs modernization. Steel form works consisting of steel plates, rods and pipes is gradually replacing conventional wooden form work. Steel form work is speedy; give good finished surface and safe too. In the construction of silos and chimneys slip forms are used. The form work is clamped to already built portion of the structure with about 1 to 1.5 m protection. As the upper portion is built, form work is sided up and fixed to newly cast portion. It saves cost of form work and speeds up the construction activity.
Application of Robots for Building Automation: – It is desirable to have robots for building automation to reduce hazards at work sites, improve quality and reduce the cost of construction. However, there are many problems in the development of robots for construction industry such as:
- Large loads.
- Components of variable sizes to be handled.
- Adverse weather conditions such as variable humidity and temperature.
- Dust and dirt.
- Need for three-dimensional movement.
- Each site having different size and shape.
Some of the robotic applications developed are
- For inspection of interiors of pipes and drainage conduits.
- To detects voids around sewers and offshore pipes.
- For excavation for slurry filled foundations.
- Human-machine interface semi-automated earth movers.
- Concrete cutters and crushers to dismantle concrete structures without creating noise and air pollution.
- For plastering : An encouraging result has been achieved in this area. Robots that can plaster 1.0 m2 area with 15 mm plaster in only one minute have been developed. Manually the same work needs 30 minutes. Sri. B. Srinivas Rao, associate professor, Department of Civil Engineering, University College of Engg. Osmania University, Hyderabad reports that for external plastering of 15050 m2 area in 11 storey complex with 15 mm thick 1: 4 plaster total cost with robot plastering worked out Rs. 2,46,988 = 00 whereas it would have cost Rs. 7,09,700 = 00 if conventional method was used. The whole work was completed in 9 days only whereas conventional plastering would have taken 54 days. Lot of research and development is required to develop robots for construction works since nowadays good number of multistorey buildings are coming up.
AUTOMATION IN DAM CONSTRUCTION
Dam construction is highly mechanized. In earthen dam constructions heavy machinery are used for digging, transporting, placing and consolidating required soil. Concreting is also highly mechanized.
AUTOMATION IN BRIDGE CONSTRUCTION
Modern trend in bridge construction is to use precast construction. Superstructure of bridge is cast in parts and erected on the site. Noida bridge connecting Delhi and Noida provides an eight lane link of 552 m across river Yamuna. The superstructure was cast in 13 spans of 42.5 m. Maximum weight of precast segment was 100 tonnes. Erection was done using launching truss hospital flyover in Mumbai is the most elegant and longest elevated road in India.
For this casting yard could be located at 20 km away from the site. To facilitate transportation and erection it was cast in several segments and connected at site.120 m arch foot bridge across river Seonyce in Seoul, South Korea was built in six precast segment and erected at site. Ultra-strength concrete (compressive strength 200 N/mm2) was used for casting segments. In Panval Nadi viaduct precast box girders were erected using launching girders and pushing the girder by jacks.
AUTOMATION IN ROAD CONSTRUCTION
A number of machines are used to mix, transport, place, compact and level the asphalt on super highways. Concreting is also mechanized in this construction.