Production Of Paving Blocks Through Labour Based Technology

The production of concrete paving blocks came into existence during post war Europe reconstruction in the late 1940’s for the purpose of revitalizing the ancient technique of producing pavement. This technique grew out of exigencies of reconstruction because of the advantages offered against other construction materials. They then gained fast popularity in many countries as an alternative to concrete and asphalt paving, with about 400 million m² produced and installed yearly. They are precast solid concrete products of various sizes and shapes, produced to interlock with adjacent blocks. The use of paving blocks for road works has proven the ability of low maintenance and high resistance to deterioration from moisture, point loads, abrasive actions, resistant to skid and petrochemicals. The blocks are produced from a combination of Portland cement, coarse and fine aggregate with sufficient water to produce zero-slump concrete, moulded in specialised equipment under vibration and extreme pressure and sometimes admixtures are added to increase certain engineering properties thereby reducing likelihood of efflorescence and decreasing water absorption. Good quality paving blocks are produced from a homogeneous mixture of cement, fine and coarse aggregates, mixed together in the right proportions, to produce a dense material. When water is added to the mixture, its chemical reaction with cement enables it to harden and make the complete mixture easy to handle and transport to the moulding place. Fine aggregate fills up voids between the paste and the coarse aggregates, provides the bulk and the strength of concrete, while the cement binds individual particles together. Moulding paving blocks, requires mixing concrete responding to the desired specifications, then filling moulds with the mixture, vibrating or compacting on the vibration table to remove air bubbles or voids, curing blocks and carefully demoulding, not forgetting to select the right mould, ensuring proper concrete consistency and carefully handling blocks during the curing process. The moulding process requires concrete constituents be mixed in their correct proportions such as cement, gravel, sand and water. The mixture is chosen based on loads to be transmitted, environmental conditions, quality materials and design mix. However, there are technical specifications providing nominal and standard concrete mixes for various construction works based on experience and testing [Mishra, 2017]. The emphasis in labour based technology approach is on employment, training and development, ensuring that cost and quality of the infrastructure are similar to those of equipment based approach. Construction equipment and specialised tools are only used where appropriate and necessary, while employees are treated with dignity and respect and paid fair wages. This approach contributes to poverty alleviation and economic growth, promotes community participation and in-corporates environmental friendly practices relating to the quality of local materials while minimizing waste. It also offers many advantages in developing coun-tries, where scarce resources are sacrificed for developing and maintaining infrastructure, at the same time reducing unemployment [ILO, 2012]. Quality control is a systematic process that ensures products meet specified standards, requirements and client’s expectations. It comprises monitoring and controlling various stages of production or delivery of services to early identify and correct errors or deviations that occur. One of the greatest challenges in moulding paving blocks is to ensure compliance with established specifications and consistency to acceptable quality. Systematic process and set of activities ensures certain predefined quality criteria and standards are met. The quality control of paving blocks is accomplished in three distinct stages that is control before, during and after moulding. Generally certain tests such as workability, cohesiveness and compressive strength tests are conducted. The compressive strength test is done with cubes of 15x15x15 cm or cylinders, while workability is checked by conducting various tests like Slump test, Compacting factor test and Vee-Bee test.